Bio Cos 03 En

UNIV.-PROF. DIPL.-ING. DR. TECHN. KURT INGERLE A-6091 Götzens, Josef-Abentung-Weg 37, Austria

Telefon +43 / (0)5234 / 33471, Telefax +43 / (0)512 / 507-2911

BIOCOS ® Wastewater Treatment

Plants

September 2003

C O N T E N T S

1. DEVELOPMENT OF THE BIOCOS-STRATEGY 1 1.1. Activated sludge system 1 1.2. Biocos strategy 2

2. PHYSICAL AND BIOCHEMICAL PROCESSES IN THE SU-REACTOR 5 2.1. General 5 2.2. The settling behaviour of the activated sludge 5 2.3. Floc filter 6 2.4. The endogenous denitrification in the SU- reactor 6

3. COMPARISON BETWEEN BIOCOS AND THE ACTIVATED SLUDGE PROCESS 9 3.1. General 9 3.2. Denitrification 9 3.3. Suspended solids (SS) in the reactors 10 3.4. Reactor size 10 3.5. Space requirements 12 3.6. Biomass 12 3.7. Energy consumption and connected load 12 3.8. Comparison between the hydraulic load in the SU reactors and secondary clarifiers 13 3.9. Effluent quality for municipal wastewater 13 3.10. Floating sludge 13 3.11. Economics 14

4. LARGE BIOCOS WASTEWATER TREATMENT PLANTS 15 4.1. Description 15 4.2. Characteristic design values of the reactors 18 4.3. Operational equipment of the Biocos-plant 18 4.4. Modular design 19 4.5. Preliminary design 20 4.6. Specifications for an SU-reactor unit (10 x 15 x 6 m) 21 4.7. S-siphon design 22

5. DESIGN AND SIMULATION OF FOUR-PHASE BIOCOS PLANTS (CONTINUOUS FLOW) 23 5.1. Design 23 5.2. Simple nitrogen simulation 28

6. LITERATURE 34

7. ANNEX 35 7.1. Sedimentation tests performed 35 7.2. Endogenous denitrification in the SU reactor of the Biocos plant in Längenfeld 38 7.3. Drafts of an SU-reactor 43 7.4. 7.5. Activated sludge plants constructed or planned (Ingerle) 50 7.6. Enlargement of the WWTP Vienna with the Biocos-strategy (variant, not realized) 51 7.7. Documentation and optimization of a BIOCOS-plant for approx. 10.000 PE (in German) 55

K. Ingerle, Biocos wastewater treatment plants 1

1. DEVELOPMENT OF THE BIOCOS-STRATEGY

1.1. Activated sludge system The activated sludge system represents the basis of the Biocos-strategy. The conven-tional strategy is shortly described in order to have a better understanding of the devel-opment of the Biocos-system. The activated sludge system is currently the method world wide used for purification of municipal waste water. The method has become dominating, especially at large treat-ment plants. The activated sludge system for nitrogen removal basically assembles an aeration tank, a secondary clarifier and a return-sludge pumping station (RS). In the activated sludge tank an anoxic for denitrification and an aerated compartment for removal of organic substances and nitrification is needed. The anoxic zone requires up to 50 % of the total volume of the aeration tank. The secondary clarifier usually provides the separation of sludge and supernatant water as a exclusively physical process. Purpose of the RS-pumping station is the recycle of sludge moved from the aeration tank to the secondary clarifier back into the anoxic section of the aeration tank for denitrification. Simultane-ously nitrate generated in the activated sludge tank is fed back into the anoxic section via the secondary clarifier. The denitrification is located before the nitrification and is called “pre denitrification”. For this type of denitrification the required organic matter is covered by the influent waste water. The clarifier is operated at a low sludge blanket level and therefore low sludge mass. Degradation processes in the clarifier are not relevant and must not be considered in the plant design. The clarifier volume required for sedimentation is designed for storm water flow. In case of a combined sewer system the ratio between dry weather and rain weather flow is in the range of 1:4 and consequently the degree of utilisation is 25 % most of the time. This fact is economically dissatisfying and can cause troubles with frost during winter season. Other disadvantages are current and short circuit effects in the secondary clarifier. Mixed liquor from the aerated reactor is continuously fed to the clarifier, the supernatant water discharged and the return sludge recycled and these complex flow pattern can influence the sedimentation process and lead to the wash out of sludge articles. Reduced treatment efficiency is the consequence. Finally an addi-tional cost intensive construction is required – the pumping station for the return sludge cycle. Figure 1: Activated sludge treatment (pre denitrification)

anoxic aerobic

aeration tank

Q Q

clarifier

pumping station QRS (nitrate)

Q+QRS

2 K. Ingerle, Biocos wastewater treatment plants

1.2. Biocos strategy

(German Handbook: Abwassertechnik und Gewässerschutz, Band 2, C.F. Mül-ler publishing-firm, 2001; Biocos-Kläranlagen)

The Biocos-strategy (biological combined system), developed and patented by K. Ingerle, represents an advancement of the conventional activated sludge system. Main differences concern the sludge-water-separation and the sludge recycle. The develop-ment of the Biocos-strategy was based on the intention to avoid disadvantages of the secondary clarification and the sludge recycle. Wastewater is fed to an aerated reactor (B-reactor) and from there to a sedimentation and circulation reactor (SU-reactor). Several operation cycles are conducted every day with a recycle period (sludge recycle phase "S") and a stirring period when the settled sludge in the SU-reactor is mixed with the supernatant water (mixing phase "U"). After-wards the sludge in the SU-reactor settles (settling phase "V") and finally supernatant water is withdrawn (discharge phase "A"). The B-reactor and the SU-reactor are hydrau-lically connected near the bottom in order to grant efficient sludge recycling. Due to the cycles in the SU-reactors a large amount of sludge is present in the B-reactor. Besides that an additional large and bio-chemically active sludge volume is present in the SU-reactor. This enables an endogenous denitrification, a biological phosphorus removal, additional reduction of COD and the development of a floc filter ensuring solid free effluent quality. An operation cycle of the Biocos-strategy is usually divided into 4 phases (S,U,V and A). Therefore this system is addressed as the 4-phase Biocos-strategy. Biocos-WWTPs for municipal wastewater are adjusted to 10 to 14 operation cycles a day in most cases. During the S-phase (sludge recycle) well thickened sludge is pumped from the bottom of the SU-reactor to the B-reactor. At the same time the displaced content of the B-reactor flows via the connection near the bottom to the SU-reactor. Since both reactors are hydraulically connected with nearly the same water level, only a small amount of energy is required. A siphon operated with pressed air is an proved facility for sludge recycling. During the U-phase (mixing phase) the sludge in the SU-reactor is stirred for a few min-utes until a homogeneous content of this reactor is achieved. At the end of the U-phase the sludge concentration in the B-reactor is significantly higher than in the SU-reactor. The high biomass content in the B-reactor promotes the biochemical processes whereas a low suspended solids concentration in the SU-reactor accelerates the sedi-mentation process (see chapter 6.6). During the V-phase (settling phase) the sludge settles after a short period of subsiding turbulence and starting flocculation in the SU-reactor. A horizontal sludge blanket de-velops and settles at a nearly constant velocity (approx. vs =2,0 m/h). The slowly settling sludge body operates like a floc filter which filtrates also small particles out of the super-natant water and guarantees a solid free effluent quality. This effect reduces not only the COD-concentration but also is a precondition for disinfection measures (e.g. UV-treatment) if required.


During the A-phase (discharge phase) supernatant water is withdrawn from the SU-reactor while the sludge blanket continues settling. The content of the B-reactor flows to the SU-reactor via a connection near the bottom entering the layer of settling sludge. Discharge facilities are locates at the opposite side of the SU-Reactor in order to avoid a short circuit from the influent to the effluent flow. During each of the 4 operation periods relevant biochemical processes occur in the SU-reactor. As long as nitrate or nitrite is available endogenous denitrification is the main process. The biomass itself is the main carbon source for denitrification. A smaller part of the carbon supply is taken from the soluble fraction (hardly degradable organic matter) causing a decrease of the COD effluent concentration. After a complete reduc-tion of the oxidised nitrogen an advanced biological P-elimination is promoted. Following the 4-phase Biocos-strategy (S-, U-, V- and A-phase) the S- and the U-phase are performed consecutively. Both phase require separate facilities. This leads to a higher sludge concentration in the B-reactor than in the SU-reactor. In chapter 2 each phase was described. Figure 2: 4-phase strategy

With the 4-phase Biocos strategy potential floating sludge built in the SU-reactor is mingled with the sludge during the U-phase. Based on experience this can be done without problems. The high energy density at the circulation (U-phase) guaranties that there is no sludge deposition in the SU-reactor. The total energy required for a Biocos-system is fully attributed to the stirring process of one SU-reactor. If the influent flow of a WWTP is equal to the effluent flow than a continuous flow strat-egy has been applied. Since supernatant water can be discharged from the SU-reactor during the A- (discharge) phase, each B-reactor has to be assigned to at least 2 SU-reactors. In this case at any time the influent flow fed to the B-reactor displaces the su-pernatant water via the open effluent valves of one SU-reactor. Considering two SU-reactors the phase intervals have to fit following condition: S + U + V = A (4-phase cy-cle).


Figure 3: Floor plan

Figure 4: 4 phases of a Biocos operation cycle

During the S-, U- and V-phase neither influent nor effluent flow occurs in the SU-reactor. For about one hour during the V-phase the sludge settles without any hydraulic distur-bances. In the following A-phase the SU-reactor is subjected to flow equal to the treat-ment plant inflow. The flow in the SU-reactor is controlled by the effluent valve. An almost constant water-level is achieved by a fixed weir (see Fig 5) or a water level regulated gate valve. The S-phase is operated using pressured air (air pressured siphon). Less air is available for the B-reactor during that time. During the very short U-phase is the aeration in the B-reactor turned off. The pressured air is fully used for the operation of the U-phase. Figure 5: Section of the discharge equipment

The Biocos strategy has been developed on basis of numeral planned and carried out smaller and larger activated sludge systems (see Chapter 7.5). The Biocos strategy is not a „single reactor system” such as the SBR system. With the Biocos system are more reactors (mostly three) used to maintain the free flow through the system. The cycles performed in the SU-reactors include a aeration phase, without which single reactor systems do not get by. The Biocos system is, as already mention, an advanced activated sludge system.


2. Physical and biochemical processes in the SU-reactor 2.1. General In order to optimise physical and biochemical processes in the SU-reactors, the follow-ing questions had to be clarified:

• What settling velocity of the sludge surface vs can be expected?

• What maximum comparative sludge volume (VSVmax) can not be exceeded, for still having the necessary settling characteristics of the sludge?

• What is the mean dry matter of compressed sludge (SSE,m), during the S-phase in the SU-reactor being returned into the the B-reactor for calculation purposes?

• What is the optimum return sludge volume (VR)?

• What is the minimum comparative sludge volume (VSVmin) not to be below, in or-der to keep the floc filter’s effects?

• What endogenous capacity for denitrification is to be expected in the SU-reactors? 2.2. The settling behaviour of the activated sludge The first four questions from chapter 2.1 are related to the settling behaviour of acti-vated sludge. Investigations using activated sludge from 5 different treatment plants and thorough review of pre-existing literature lead to the following results (details see Annex 7.1):

• For a wanted settling velocity of vs = 2.0 m/h the formula vs = 650 / VSV with VSV � 350 ml/l can be used (from ATV-M210).

• Considering a factor of safety to the following shall be complied to:

VSVmax = SSSU,max * SVI � 350 ml/l. The resulting settling velocity of the sludge level is then in the range from vS = ~1,8 m/h to 2,0 m/h.

• At the end of settling after approx. 2.5 h (one cycle) the mean dry matter of the compressed sludge, returned from the SU-reactor to the B-reactor, can be calcu-lated by SSE,m = 1.000 / SVI in g/l. The height of the compressed sludge zone is given by HE = H*SS0/SSE,m = H*SS0/(1.000/SVI) = H*VSV / 1.000.

• The total sludge present in the SU-reactor (after U-phase) shall be returned to the B-reactor during the S-phase: VR = FSU*HE = VSU*VSV / 1000 = 0.35 * VSU (with VSV = 350 ml/l, approx. one third of the volume of the SU-reactor)

Because SSSU,max occurs at maximum hydraulic loading Qmax , VR represent this maxi-mum loading case. At lower flow to the treatment plant VR is kept constant, as shown later on. This leads to a wanted increase of SSB in the B-reactor and a decrease of SSSU in the SU-reactor.


2.3. Floc filter The floc filter built new in the SU-reactor during each cycle assures a solid free effluent quality. It also reduces the COD and benefits the denitrification. Tests have shown that the effects of the floc filter decreases when the sludge concen-trations decreases. A comparative sludge volume VSV lower than 200 ml/l shall be avoided. This non-favourable conditions can occur at low flow to the treatment plant. A return of clear water from the SU-reactor to the B-reactor can act corrective. A reduction of VR is possible 2.4. The endogenous denitrification in the SU- reactor In the sedimentation- and recycle tanks (SU-tanks) of BIOCOS treatment plants bio-chemical processes take place – mainly endogenous denitrification and biological phos-phorus reduction. After a mixing phase of about 20 minutes during the remaining cycle period (total cycle time about 160 minutes) the settling activated sludge in the SU-tank generates a filter layer where endogenous denitrification occurs. This endogenous denitrification is significant for the Biocos strategy. Thorough investi-gation were carried out on this issue during the last years. The denitrification is carried out by various micro organisms as alternative to the aerobic metabolism under anoxic conditions. It occurs under pH conditions from 6.5 – 8.5 with-out restraint. At increasing temperature the denitrification increases as well. In case of release of organic substance due to die back of micro organisms or from internally stored cell-matter, the denitrification process is called endogenous denitrification. Exact specifications about denitrification can be given from the Längenfeld Biocos-treatment plant (10.000 PE), which is operating since 1998. The swell of temperature for nitrification is, according to Austrian Standards for waste water emission, 8 °C and for nitrogen removal 12 °C. In case of a temperature drop be-low 11 °C in the waste water in the Längenfeld treatment plant the B-reactor is aerated continuously (O2-concentration between 2.0 und 3.0 mg/l) causing continuous aerobe conditions (full operation). In the B-reactor maximum nitrification is aimed. Denitrification within the Biocos system is only in the SU-reactors possible. This type of operation is typical for the first half of the year (details see Annex 7.2) Data about the endogenous denitrification capacity during a 3 years’ period at the BIOCOS-treatment plant Längenfeld (10.000 PE) have been analysed. Half a year in 2001, 2002 and in 2003 the activated sludge tanks (B-reactors) have been operated under continuously aerobic conditions. Hence all the denitrification activity has been ex-clusively performed in the SU-tanks. The nitrogen balance leads to following minimum endogenous denitrification rate at a water temperature of 8.5 °C and an aerobic sludge retention time of > 7 days: DNSU = 0.5 g NO3-N/kg SS.h.


Table 1: Nitrogen balance for Ntot in kg/d, average values in the 1st semester

period Nges,in kg/d

BOD5,in kg/d

Ntot,S kg/d

Ntot,effl kg/d

Ntot,SU kg/d

Qin m³/d

1. semester 2001 77.1 439 18.8 32.3 26.0 1353

1. semester 2002 77.6 432 18.6 22.0 37.0 1386

1. semester 2003 85.3 444 19.0 27.5 38.8 1446

Table 2: Endogenous denitrification in SU-reactor DNend in g NO3-N/kg SS.d, aver-age values in the 1st semester

period Ntot,SU kg/d

SSSU g/l

SSB g/l

DNend g/kg SS.d

T °C

SVI mg/l

tSS, aerob d

pH

1. semester 2001 26.0 2.8 2.4 13.9 8.4 192 7.4 7.2

1. semester 2002 37.0 4.6 4.2 12.1 8.1 119 13.2 7.6

1. semester 2003 38.8 3.4 3.0 17.1 9.0 115 9.2 8.0

From the annual report 2001 following yearly mean values for 2001 are obtained, show-ing the excellent clarification performance of Biocos systems: Table 3: Average values 2001

Q = 1308 m³/d

BOD5,in = 410 kg/d = 310 mg/l

CODin = 747 kg/d = 565 mg/l

Ptot,in = 9.15 kg/d = 7.0 mg/l

BOD5,effl = 8.84 kg/d = 6.8 mg/l < 20 mg/l

CODeffl = 46.62 kg/d = 35.6 mg/l < 75 mg/l

Ptot,effl = 0.86 kg/d = 0.66 mg/l < 1 mg/l

Temperature waste water Teffl = 10 °C At a temperature of waste water > 8 °C is the NH4-Neffl < 5 mg/l and at > 12 °C is the elimination of Ntot > 70 % to be maintained. This requirement applied in 2nd semester of 2001 (mean values for the 2nd semester 2001). Table 4: Average values for the 2nd semester of 2001

Teffl = 11.6 °C

NH4-Neffl = 0.7 mg/l < 5,0 mg/l

Ntot,in = 72.5 kg/d

Ntot,effl = 7.,6 kg/d

Elimination of Ntot = (55.4 – 7.6) : 55.4 = 0.86 = 86 % > 70 %


Further investigations from Wett, Gluderer and Rauch approved the good characteristics for denitrification of settling sludge. The report is published in gfw-Wasser-Abwasser 138 (1997):

„Parallel denitrification-tests were conducted in a settling tank and a com-pletely stirred tank reactor. The denitrification processes ran at equal average rates considering the limiting influence of the carbon source. Thus the mixing effect due to the settling flux of the activated sludge and the water displace-ment ensures the contact between biomass, nitrate and - if available - sub-strate. Additional stirring energy causes no measurable increase of the deni-trification rates. Time controlled strategies, that are single-tank-technologies, seem to be most convenient for the technical application of simultaneous sedimentation and denitrification. Experiments at the pilot plant in Strass demonstrated, that the amount of nitrogen, which was nitrified during the aeration phase, was completely denitrified during the settling- and drawing offphase without caus-ing floating sludge.“

Values for endogenous denitrification presented in table 5 are taken from [8]: Table 5: Endogenous denitrification

mg NO3-N / g SS.h Literature from [8]

2.9 Carruci et al. (1996)

0.2 – 0.5 Henze (1991)

0.1 – 0.8 Kujawa et al (1997)

0.2 – 0,5 STOWA (1992)

0.2 – 0.6 Kujawa et al (1999)

0.6 ± 0.32 Kujawa et al (1999)


3. COMPARISON BETWEEN BIOCOS AND THE ACTIVATED SLUDGE PROCESS

3.1. General As mentioned above, the main difference between the Biocos process and the activated sludge treatment method relates to the cyclical mode of operation of the SU reactors in the case of the Biocos system. As a result of the physical and biochemical processes in the SU reactors (see section 2), Biocos offers advantages in the following respects:

Denitrification

Suspended solids in the reactors

Reactor size

Space requirements

Biomass

Energy consumption and connected load

Hydraulic load in the SU reactors

Effluent quality

Floating sludge

Economics

3.2. Denitrification In the Biocos process endogenous denitrification continues for as long as there is ni-trite and nitrate in the SU reactors. The denitrification process downstream from the B reactor offers a high level of nitrogen elimination regardless of the BOD5 concentration in the influent flow. The slowly settling layer of activated sludge (sludge blanket) is suffi-cient for this purpose. No energy is required for stirring, and nitrate recirculation is un-necessary. In the case of large-scale Biocos plants with primary treatment serving combined sewer systems, endogenous denitrification plays a key role. The large SU reactors required for such plants are sufficient to ensure the necessary denitrification even at low tempera-tures. The B reactor need only be designed for the removal of organic material and nitri-fication (aerobic milieu, see section 5.1). As a result of the continuous process of endogenous denitrification, high annual nitro-gen elimination rates are achieved with positive effects in terms of reduced power con-sumption and the quality of the effluent. In the activated sludge process denitrification is restricted to the aeration tank. This pre-denitrification stage requires a correspondingly large anoxic volume (up to 50% of the volume of the aeration tank). A power supply is needed for stirring the anoxic zone and for the return flow of liquor containing nitrate. Care must also be taken to ensure adequate organic mass in the anoxic zone for denitrification to take place.


Nitrogen elimination through pre-denitrification is limited because of the need for nitrate recycling. At low temperatures, the whole aeration tank is often operated in an aerobic state without denitrification. Annual nitrogen elimination is then correspondingly low. 3.3. Suspended solids (SS) in the reactors Hydraulic design is based on maximum plant flow Qmax. In the case of a combined sys-tem, that means storm water conditions. For the biochemical design, mean dry weather flow Q24 is used. With the Biocos process, storm water conditions produce the lowest SS concentrations in the B reactor and the highest in the SU reactors. Given a constant volume of return sludge in the S phase (VR), optimum SS concentrations automatically develop in the B reactor and in the SU reactors at lower plant flows. For SVI=120 ml/g, the calculations are as follows (see section 5.1):

• Average SS concentrations under storm water conditions: 4.15 g/l in the B reactor and 2.75 g/l in the SU reactors.

• Average SS concentrations at dry weather flow: 5.70 g/l in the B reactor and 2.50 g/l in the SU reactors.

Thanks to the larger volume of the SU reactors (2.000 m³) compared with the B reactor (650 m³), SS concentrations in the SU reactors decline less at low hydraulic loads, whereas the SS concentrations in the B reactor increase significantly. The high SS concentrations in the B reactor at dry weather flow explain the low volume requirement of the B reactor. The activated sludge process does not produce such high SS concentrations at dry weather flow as the Biocos process and therefore requires a higher aerobic volume in the aeration tank (see section 5.1: SSBB = 4.0 g/l). 3.4. Reactor size The Biocos process, with its endogenous denitrification and high SS concentrations at dry weather flow, enables the B reactor to be designed for a very small volume. That also has advantages for stirring the reactor content (small number of stirrers and lower power consumption). The size of the SU reactors has a significant effect on the following three processes:

• denitrification

• maintaining a high SSB,m in the B reactor

• hydraulic capacity


The size of the SU reactors depends on their design (example from section 5.1):

Variant A: The design focus is on maximum denitrification (N elimination > 90%) and very high hydraulic capacity. SSB,m is easily maintained. High N elimination is achieved with (calculation from section 5.1):

hKW = 0.25; SSB,m = 4.15 g/l Vtot. = approx. 2.600 m³ N elimination 91 % HW = (1-0.33-0.25) x 6.0 = 2.52 m > 0.6 m (residual supernatant water)

Variant B: The design focus is on maintaining a high SSB,m in the B reactor. This is achieved with (calculation from section 5.1):

hKW = 0.33, SSB,m = 4.15 g/l Vtot. = 600 + 2 x 800 = approx. 2.200 m³ N elimination 75 % HW = (1-0.33-0.33) x 6.0 = 2.04 m > 0.6 m

This design offers adequate N elimination without the need for denitrification in the B reactor. Reserve hydraulic capacity is very high. This variant should be selected in the normal case as it satisfies all 3 requirements of the SU reactors. Variant C: The design focus is on maintaining the necessary hydraulic capacity. The SU reac-tors are smaller: FSU = Qmax x Z : hKW = 200 x 1.2 : 0.57 = 430 m³

hKW = 1.0-0.33-0.1 = 0.57, SSB,m = 3.00 g/l Vtot. = 1.040 + 2 x 430 = approx. 1.900 m³ N elimination approx. 70 % HW = 0.10 x 6.0 = 0.60 m = 0.6 m

The B reactor can only hold approx. SSB,m = 3.0 g/l. The aerobic volume must ac-cordingly be increased from 600 m³ to 600 x 4.15 : 3.0 = 830 m³. Since denitrifica-tion in the SU reactors alone is now no longer sufficient, the B reactor must have an anoxic zone of approx. 210 m³. Although this design requires the smallest vol-ume, it should not be selected as it has no hydraulic and biochemical reserves.

For the activated sludge process the following volumes apply (see section 5.1, N elimination 70 %): Vtot. = VBB + VNK = 1.330 + 1.070 = 2.400 m³ Table 6: Comparative volumes of the Biocos and activated sludge processes in m³ Process B reactor or

aeration tank SU reactors or

clarifier Vtot. [m³]

Biocos process (B) Biocos process (C) Activated sludge process

600 1.040 1.330

2 x 800 = 1,600 2 x 430 = 860

1.070

2.200 1.900 2.400


The aeration tank for the activated sludge process is more than twice as big as the B reactor in variant B of the Biocos process. Total volume for the activated sludge process is approx. 10 % higher than in variant B of the Biocos process and approx. 25 % higher than in variant C. 3.5. Space requirements Space requirements are low with the Biocos process as the rectangular B reactor and the SU reactors can be designed for a compact configuration. The lower total volume in the Biocos process also has a positive effect on space requirements. In comparison, the activated sludge process is a space-intensive solution, especially if individual circular tanks are to be used for secondary clarification, as is very often the case today. 3.6. Biomass A high biologically active biomass content has a very positive effect on the treatment processes and acts as a buffer for peak toxic loads. With the Biocos process (variant B) approx. 30 % (6.980 kg SS : 5.320 kg SS) more biologically active biomass is available than with the activated sludge process (for calcu-lations, see section 5.1). 3.7. Energy consumption and connected load The Biocos process requires considerably less energy than the activated sludge treat-ment method. The high degree of denitrification in the Biocos process means a lower oxygen requirement in the B reactor. Nor does the B reactor have anoxic zones, requir-ing constant agitation. Also, less energy is necessary for the return sludge flow. In the case of large-scale Biocos treatment plants, energy savings of approx. 30 % can be ex-pected for the biological stage (see section 7.5). In addition to lower energy consumption, the connected load is also smaller in the case of the Biocos process. That is due to the lower energy requirements on the one hand and to that fact that compressed air is used for the return sludge flow (S phase) and for stirring (U phase) on the other. The compressed air is taken from the system used to aerate the B reactors when there is excess capacity there. The secondary clarifiers re-quired for the activated sludge process also operate with scrapers, which are superflu-ous in the SU reactors.


3.8. Comparison between the hydraulic load in the SU reactors and

secondary clarifiers After the U phase of the Biocos process, the sludge in the SU reactor is left to settle undisturbed for about one hour so that an approx. 2.0 m deep supernatant zone can form (V phase). Supernatant water is then withdrawn (A phase), and a corresponding volume of mixed liquor flows from the B reactor to the SU reactor. This does not nega-tively affect the supernatant water zone and supernatant discharge because the mixed liquor flows into the sludge blanket at low velocity and a relatively high SS concentration and is held there. This means there is only through flow in the SU reactor corresponding to the influent flow in the A phase. The secondary clarifier employed in the activated sludge process, on the other hand, is continuously subjected to significant hydraulic loading. As a result of the discharge and return sludge flows, the inflow in the tank is twice as high as the outflow. The large volume of mixed liquors entering the secondary clarifier from the aeration tank and si-multaneous return sludge flow make it difficult to separate the supernatant water from the sludge and can cause sludge flocs to be washed out. Problematical flows occur in particular in rectangular secondary clarifiers, and for that reason there is now a growing tendency to employ a circular design. The disadvantage in that case, however, is that the tanks have to be individually spaced out and cannot be combined to form a compact layout as rectangular clarifiers can. That makes space re-quirements correspondingly high. 3.9. Effluent quality for municipal wastewater The Biocos process produces very low effluent concentrations. As a result of the con-stantly renewed sludge blanket, the effluent is almost solid-free. COD concentrations are below 40 mg/l. In the normal case over 90 % nitrogen elimination can be expected. In spite of biological phosphorus elimination, phosphorus precipitation is required in or-der to achieve phosphorus concentrations of less than 1.0 mg/l (see sections 2.4 and 7.7). Continuous sedimentation in the activated sludge process creates a density-driven current to the bottom of the tank in the influent activated sludge. A homogeneous sludge body cannot therefore form, and there is no sludge blanket effect. As a result, the efflu-ent can contain very fine particles of poor settle ability. 3.10. Floating sludge Any floating sludge that forms in the SU reactor in the Biocos process is reintegrated in the sludge body in the U phase and does not need to be removed. Floating sludge in the secondary clarifier in the activated sludge process, on the other hand, is removed and returned to the aeration tank or pumped to the sludge treatment point.


3.11. Economics A combination of many factors – flow through the plant under hydraulic head, low energy consumption for stirring the contents of the B reactor and for sludge return flows from the SU reactors to the B reactor, high rates of N elimination, small size of the reactors, low connected load, simple and proven mechanical engineering, and highly reliable con-trols – makes Biocos wastewater treatment plants highly attractive in terms of econom-ics, including low initial and running costs. The many Biocos plants now operating in Germany, Austria and other countries are a reflection of the advantages deriving from the physical and biochemical processes in the SU reactors compared with the activated sludge process (see section 7.8). With the activated sludge process, the return sludge flow from the secondary clarifier to the aeration tank requires the use of scrapers, which are an expensive and mainte-nance-intensive item. The fact that scrapers are not employed in the Biocos process also contributes to the lower costs of the Biocos system. The compressed air equipment employed in the SU reactors for the Biocos process is a highly cost-effective and reliable solution. It also helps to keep the connected load for Biocos plants as low as possible. In addition, Biocos treatment plants require very little space, an extremely important fac-tor in the urban environment. The Biocos process is a particularly attractive solution for large-scale wastewater treatment plants operating with a combined system. The large SU reactors re-quired in such cases always achieve very high levels of denitrification. None of the volume of the B reactor is needed for denitrification. Even at very low tem-peratures, when nitrification alone occurs in conventional aeration plants, Biocos treatment plants achieve high rates of nitrogen elimination through denitrification in the SU reactors.


4. LARGE BIOCOS WASTEWATER TREATMENT PLANTS 4.1. Description The description of a design example for a large WWTP of 1.0 million PE should deepen the understanding of the Biocos-strategy. The municipal wastewater from a combined sewer system of a large city is assumed to be fed to a Biocos-plant after pre-clarification. The P-elimination is mainly achieved by precipitation. The Biocos-plant consists out of 10 lines, each line comprises one B-reactor and two SU-reactors. Wastewater is fed to a generously designed middle channel where a almost horizontal water table occurs because of only small energy head losses. To prevent settling of suspended solids the middle channel is intermittently aerated and stirred. The wastewater from the middle channel is led via valves and weirs to the B-reactors of the 10 Biocos lines. The B-reactors are designed as oxidation ditches and equipped with fine-bubble aeration stirrers. During V-, A- and S-phases the B-reactors are aerated and nitrification and aerobic organic degradation is promoted. During the S- and U-phases aeration can be interrupted aiming on pre- or simultaneous denitrification. After the effluent valve is opened supernatant water is discharged from the SU-reactor during the A-phase. In the same time biologically treated wastewater-sludge mixed liq-uor flows through apertures near the bottom from the B- to the SU-reactors. Relatively high energy head losses within the discharge facilities are adapted in order to achieve a constant line-discharge. The return flow of the sludge which has been displaced from the B- to the SU-reactor during the A-phase happens discontinuously during the S-phase. After a thickening period of about 2.5 hours well thickened activated sludge is recycled to the B-reactor by siphons. The siphons are run by pressed air which is avail-able from the aeration system. The stirring equipment is also run by pressed air and mixes the content of the SU-reactor (U-phase) including floating sludge. During the U-phase the aeration system is still interrupted and pressed air is provided for stirring. Af-terwards the pre-settling phase (V-phase) starts. A short flocculation period of about 0.1 h precedes the actual sedimentation of the sludge blanket with the constant settling ve-locity vs. According to ATV M210 the settling velocity is calculated by following equation: vs = 650 : (SVI x SSSU). At the beginning of the discharge period (A-phase) the sludge blanket should have set-tled at least 50 cm and this clarification zone should stay stable while discharging. The settling sludge body serves as a flocculation filter adsorbing suspended and floating solids and improving the effluent water quality. In the Su-reactor permanent endogenous denitrification takes place as long as NO3 is available. The rates of endogenous denitri-fication reach values of at least 50 % of the pre-denitrification rates.


Figure 6: Exposition of the S-, U-, V- and A-phase


Figure 7: Biocos strategy for 10 lines and for 1,0 million PE

Supernatant water discharged from the SU-reactors is fed to the effluent channel and further on to the receiving water. The Biocos-lines are operated in parallel phases. This concept results in a simple con-trol system and a clear survey of the operator. Waste-sludge withdrawal is performed automatically at the beginning of the S-phase. If necessary state of the art devices for floating sludge separation should be installed in the B-reactors but not in the SU-reactors. The amount VR of thickened sludge which should be recycled from the SU-reactor to the B-reactor during dry weather flow determines the mean suspended solids concentra-tion and consequently the volume of the B-reactor. When the influent flow exceeds the dry weather flow QDW the amount of recycled sludge VR is automatically switched to storm weather conditions. Obviously the total sludge mass in the system needs to be considered. Computer calculations and full-scale experiments at a 10.000 PE Biocos-plant have shown that at a constant amount of recycled sludge VR variations of suspended solids concentrations in B- and SU-reactors due to influent flow variations is relatively small because of the large total sludge mass SMtot.


4.2. Characteristic design values of the reactors

Experiences from full-scale applications indicate the optimum range of two design pa-rameters:

• Depth H of the reactors of large Biocos-plants should not undershoot 5.0 m. Pref-erable is a depth of 6.0 m.

• Width BSU of the SU-reactors should be in the range between 12.0 and 14.0 m in order to optimise the required energy input for stirring.

Further design parameters of the SU-reactor have to agree with the hydraulic and of the B-reactor with the biochemical design calculations. 4.3. Operational equipment of the Biocos-plant

To avoid sedimentation in the middle channel aeration devices for short term operation should be installed. Additionally 10 plain slide valves are required in order to close each Biocos line separately (B / H = 1.0 / 0.7 m). Exact distribution of the wastewater is man-aged by 1.0 m wide weirs, which can also be closed for maintenance. The B-reactors are constructed as state of the art oxidation ditches. A stirring device to induce the cycling current with a velocity of v = 0.5 m/s and a fine-bubble aeration is installed. The oxygen input is controlled by oxygen probes. In case of flotation sludge occurrence an approved separator is suggested. Continuous hydraulic connections be-tween the B- and the SU-reactor are ensured by apertures without valves. Supernatant water is withdrawn from the SU-reactor (A-phase) by discharge devices with gravity driven balls. The devices are installed every meter and have been approved during the last 5 years at several treatment plants. At maximum hydraulic load the en-ergy head losses within the discharge devices are about 25 cm causing an exact distri-bution of the effluent flow (line-discharge). The discharged water is fed to a generously designed pressure pipe with very low hydraulic head losses. An automatic plain slide valve at the end of the pipe keeps the water level in the SU-reactor always constant. The return sludge flow from the SU- to the B-reactor (S-phase) is performed by com-pressed-air siphons (S-siphons). The stirring of the SU-reactor is also driven by compressed-air. The aeration in the B-reactor is still interrupted during this phase (U-phase). Lines of coarse-bubble aerators are installed at the bottom of the reactor in distances of about 10.0 m. Vertical internal cycle currents are induced to mix the content of the SU-reactor including flotation sludge with a low energy input. This kind of stirring device is also applied for aerated sand- and grease traps. The S-siphon and the line-aerators are operated at lower air-pressure than the aerator in the B-reactor. Therefore the air-supply for the aerators in the B-reactors need not be closed during the S- and the U-phase. The SU-reactors can be divided by concrete walls each 20.0 to 30.0 m in order to avoid disturbances by wind and eventual transverse flows.


Figure 8: Hydraulic longitudinal section

The compressed air demand depends exclusively on the aeration of the B-reactors. When the aeration is interrupted the provided compressed-air is sufficient for the opera-tion of the S- and the U-phase. Each Biocos line employs 5 electronic valves to direct the air-flow either to the aeration, to the S-siphon or the U-siphon which are located near the middle channel.

The control system operates the phases of all 10 lines in parallel in order to maintain a uniform state of the plant. 4.4. Modular design A large-scale Biocos wastewater treatment plant is composed of a number of reactors on a modular basis as follows:

• A Biocos treatment plant comprises several identical Biocos lines (preferably an even number).

• Each Biocos line comprises several Biocos assemblies.

• Every Biocos assembly has two SU reactor units and a B reactor. The B reactor

is normally designed as an oxidation ditch.


Figure 9: Modular system

• All SU reactor units (10 x 15 x 6 m) have the same specifications and dimen-sions (see diagrams in section 7.3). Sets of three Biocos assemblies can be built without connecting walls to reduce construction costs.

• Influence of phase length within a cycle:

- A longer S phase reduces the capacity requirement of the S siphons. - A longer S and U phase means higher N elimination.

4.5. Preliminary design A Biocos assembly (10 x 15 x 6 m) can be designed for a maximum hydraulic load of qmax = FSU x H : 3.5 = 150 x 6.0 : 3.5 = 250 m3/h. In the design of a Biocos plant for a max. hydraulic load Qmax expressed in m3/h, we first calculate the required number of Biocos assemblies K (K = Qmax : 250). The next step is to determine the necessary number n of Biocos lines. The quotient m = K : n gives the number of Biocos assemblies per line. The width of the B reactor can be calculated approximately using the equation FB = B x 10 = 0.002 x S0 x surplus sludge x sludge age x SVI : (H x n x m). Preliminary design parameters Biological load: S0 = d x PE With primary treatment: surplus sludge = 0.8 kg SS/kg BOD5; SVI = 120 ml/g; d = 0.04 kg BOD5/PE Without primary treatment: surplus sludge = 1.0 kg SS/kg BOD5; SVI = 100 ml/g; d = 0.06 kg BOD5/PE Extended treatment: sludge age = 17 d (10°C); sludge age = 8 d (20°C) Without extended treatment: sludge age = 8.5 d (10°C); sludge age = 5 d (20°C) The SU reactor units should be adjusted to max. hydraulic load Qmax (e.g. 9.60 x 15.00 x 6.00).

Biocos assembly

Oxidation ditch design

SU1 SU2

15.0 15.0

B 10


4.6. Specifications for an SU-reactor unit (10 x 15 x 6 m)

6 PVC S-siphons with 9 DN 100 orifices are supplied in lengths of up to 5.0 m and as-sembled on site (socket connections). The horizontal line is placed under the top layer of steel reinforcement and secured to prevent floating. Prior to concreting it is filled with water and the orifices closed. The vertical line is also positioned prior to concreting the walls (see section 7.1). 2 PE line aerators are supplied in 5.0 m sections, assembled on site and affixed to the bottom of the reactor using a total of 2 x 2 x 18 screws. Supernatant recycling (2 PE siphons DN 150) operates only as required in the A phase. 15 PE spherical valves (DN 150) are supplied with DN 150 sockets and installed on site. The DN 150 sockets must be concreted in place accurately. All SU compressed-air lines (stainless steel) are located on the walkways between the SU reactors and the B reactor. Together with the main aeration line, a total of 4 com-pressed-air lines per walkway must be laid:

• one for aeration in the B reactor • one for the S siphons • one for the line aerators • one for supernatant recycling.

In the case of Biocos lines for up to 30.000 PE, 2“ or 3/4“ solenoid valves can be used to operate the S siphons, line aerators and supernatant recycling for each SU reactor individually. To ensure reliable operation with larger Biocos treatment plants, each Bio-cos line must be fitted with 4 large electric valves for the S siphons and line aerators, and 2 small ones for supernatant recycling. Expansion joints must be provided to cope with variations in temperature. The diameter of the SU stainless lines on a walkway (siphons, line aerators, supernatant recycling) depends on the number of Biocos assemblies per Biocos line:

• 2 DN 70 and 1 DN 20 : up to 6 Biocos assemblies • 2 DN 150 – DN 70 and 1 DN 40 – DN 20 : 8 Biocos assemblies • 2 DN 200 – DN 70 and 1 DN 50 – DN 20: 10 Biocos assemblies • 2 DN 250 – DN 70 and 1 DN 60 – DN 20: 14 Biocos assemblies • 2 DN 300 – DN 70 and 1 DN 70 – DN 20: 20 Biocos assemblies

The equipment in the SU reactors operates at a lower pressure than the aerators in the B reactor. The main line for the aerators therefore does not need to be valved off when compressed air is required for the SU reactors. Each Biocos line must also be fitted with two electric plain slide valves. The effective area of flow depends on the number of Biocos lines n: FN ≥ Qmax : n [m2] ... (Qmax in m3/s)


The SU reactor controls can be combined with the main plant controls (pumps, screens, grit chamber, primary treatment equipment where provided, aeration for the B reactor, sludge treatment, volumetric measuring, etc). Alternatively they can be de-signed as a separate system linked only to the compressor controls. The compressors must be operated to ensure that, regardless of oxygen requirements in the B reactor, there is enough compressed air in the S and U phases for the S siphons and line aera-tors. Also, a small volume of air must always be available for supernatant recycling in the case of low influent flows. Separate compressors should be provided for that pur-pose. Where a wastewater treatment plant comprises several Biocos lines, they are operated in parallel. That means the control system is always very simple even in the case of large-scale Biocos plants. 4.7. S-siphon design In the horizontal suction line there are two sources of hydraulic head losses ∆H:

• Head losses at the 9 DN 100 orifices: ∆HE • Head losses in the horizontal line starting with DN 100 and widening up to

DN 250 : ∆HL The effective area of the DN 100 intake apertures is FN = 0.67 x 0.0079 = 0.0053 m2. The intake volume Qi = FN x vi = FN x 4.43 x √ ∆Hi in m3/s depends on total losses ∆Hi = ∆HE + ∆HL. In order to achieve a constant line intake per S siphon, the spacing between the 9 ori-fices is varied. At the first intake aperture, a velocity of flow of 1.0 m/s for a flow rate of Q1 = 5.3 l/s is desirable (∆HE,1 = 5 cm). The horizontal line starts with DN 100 and is subsequently widened to keep ∆HL losses down to about 0.5 cm/m. At the ninth intake aperture, total losses amount to ∆H = 0.05 + 13.0 x 0.5 = 11.5 cm (QE,9 = 8.0 l/s). The flow rate for an S siphon can then be approxi-mated as Qs = 9 x (5.3 + 9.0) : 2 = 64 l/s.


5. DESIGN AND SIMULATION OF FOUR-PHASE BIOCOS PLANTS

(continuous flow) 5.1. Design Figure 10 shows the phases and the suspended solid concentrations SS in the individ-ual reactors of a Biocos treatment plant. The aeration factor ζB expresses the duration of aerobic conditions in a half cycle Z. At low temperatures (T ≤ 12 °C) it is preferable to operate the B reactor for nitrification only (ζB = 1.0). Even in this load case, the anoxic conditions in the SU reactors ensure substantial nitrogen elimination. At higher temperatures, additional denitrification is pos-sible in the B reactor, leading to almost complete nitrogen elimination. The B reactor can be designed in the same way as an aeration tank for the acti-vated sludge process (e.g. ATV A131). Complete nitrification will be achieved. The calculations are based on the following presuppositions:

• Influent flow Q is constant and steady. • The surplus activated sludge is removed at such a rate that the sludge mass

in the system (MStot.) remains constant. • All return sludge flows are brief operations. The same applies to stirring (S=0,

U=0). In the A phases, a volume of sludge dependent on influent flow Q is transferred from the B reactor the SU reactors, and in the following S phases is returned to the B reactor. As a simplification, it is assumed that the return sludge flow at the end of the A phases is a momentary operation. The length of the A phases is equivalent to half the cycle time Z. This sludge mass SMp alternating between the B reactor and the two SU reactors is of eminent importance for the operation of Biocos wastewater treatment plants. It is de-pendent on influent flow Q, cycle time Z and the mean suspended solid concentration in the B reactor SSB,m. The return sludge flow (VR) required for Qmax is also kept constant in the case of smaller influent flows. Biocos plants adapt automatically to changing influent flow conditions. Smaller influent flows lead to a pronounced increase in sus-pended solids in the B reactor, whereas the decrease in the SU reactors is rela-tively slight. The design calculations are also based on the following ideas and assumptions:

• The sludge in the SU reactor at the end of the U phase expressed as SSSU,min is completely absorbed in the thickening zone (hE = HE : H) and thickens in approx. 2.5 hours to an average of SSE,m = VSV : 1.000.

• The volume of sludge entering the SU reactor from the B reactor in the A phase expressed as SSB,m is equal to the volume of the discharged supernatant water (hKW). This sludge thickens in the SU reactor for an average of approx. 80 : 2 = 40 minutes, but this thickening can be discounted. With this assumption one is always on the safe side when selecting SSE,m.


• The calculations for the size of the SU reactors are based on Qmax. At the end of the A phase there are three zones in the SU reactor:

hE = VSV : 1.000 with SSE,m (hE = HE : H ... depth of thickening zone)

hKW with SSB,m (hKW = HKW : H ... depth of supernatant discharge = depth of replacement content from the B reactor)

hW = 1 – hE - HKW with SS = 0 (hW = HW : H ... depth of remaining supernatant water zone)

• The volume of sludge returned to the B reactor in the S phase VR = hS x H x FSU should not exceed the volume of the thickening zone: hS ≤ hE.

• It is advisable to select hS = hE. After the S phase we then have (hE + hKW) x SSB,m = SSSU,min. With the assumed parameters VSV = 330 ml/l, SVI = 120 ml/g, SSSU,min = 330 : SVI and SSB,m = 500 : SVI, we have hKW = 0.33.

• If the hydraulic load in the SU reactors is increased beyond hKW=0.33 , SSB,m must be reduced accordingly. With an absolutely essential residual depth of supernatant water in the SU reactor hW = 0.10 m (HW = 0.10 x H = 0.60 m; H = 6.0 m), we have hKW + hE = 0.90 and SSB,m = SSSU,min : (hE + hKW) = 2.75 : 0.90 = 3.06 g/l (reduc-tion from 4.15 to 3.06 g/l).

As an aid to understanding the calculation method employed, an example follows for the design of a wastewater treatment plant for 10,000 PE (for one Biocos assembly de-signed as variant A as explained in section 1.4). The situation with regard to suspended solids is illustrated in Figure 11. Figure 10: Suspended solid concentrations


BIOCOS-WASTE WATER TREATMENT PLANT: EXAMPLE A (10.000 PE, one Bio-cos-assembly) Primary treatment: ......yes....... yes/no Combined sewer: ......yes....... yes/no Parameters of the treatment plant: • Qd = 1.600 m³/d

• Qmax = 200 m³/h (Qd * 1,75 / 14)

• Q24 = 66,6 m³/h

• Q48 = 33,3 m³/h

• S0 = 10.000 PE x 0,04 kg/PE = 400 kg BOD5/d

• Qe = 1,00 kg SS/kg BOD5

• tSS,aerobic = 9,3 d (e.g. age sludge age according to ATV A131)

• ζB = 1,00 (aeration factor)

• TKN = 110 kg N/d

• SVI = 120 ml/g; T = 10 °C; H = 6,0 m

• VSV = 330 ml/l

• Z = 1,2 h (half cycle)

Parameters for design with Qmax: • SSSU,min = VSV : SVI = 2,75 g/l

• SSE,m = 1000 : SVI = 8,30 g/l

• SSB,m = 500 : SVI = 4,15 g/l

• hKW = 0,25; HKW = hKW x H = 1,50 m

• vs = 650 : (SVI x SSSU,min) = 2,0 m/h

• SSB,m,24 = 5,7 g/l (estimated with 1,40 x SSB,m)

Parameters for design with Q24: • VR,24 = VR; SMges,24 = SMges; SSE,m,24 = SSE,m

• DNsim = 1,0*T/10 = 1,0 gNO3-N/kg SS.h

• DNend = 0,5*T/10 = 0,5 gNO3-N/kg SS.h

Design with Qmax:

• VSU = FSU x H = Qmax x Z : hKW = 1000 m³

• VB = S0 x Qe x tSS,aerobic : (ζB x SSB,m,24) = 650 m³


• SMP = SSB,m x Qmax x Z = 996 kg SS

• ∆SSB = SMP : VB = 1,53 g/l

• ∆SSSU = SMP : VSU = 1,00 g/l

• SSB,min = SSB,m – ∆SSB : 2 = 3,39 g/l

• SMtot = SMP + SSB,min x VB + 2 x SSSU,min x VSU = 8700 kg SS

• VR = SMP : (SSE,m – SSB,m) = const. = 240 m³ (recirculation sludge volume)

Design with Q24:

• SSB,m,24 = VR x SSE,m : (Q24 x Z + VR) = 5,7 g/l

Verifying of the estimated SSB,m,24

• SMP,24 = SSB,m,24 x Q24 x Z = 455 kg SS

• ∆SSB,24 = SMP,24 : VB = 0,70 g/l

• ∆SSSU,24 = SMP,24 : VSU = 0,46 g/l

• SSSU,min,24 = [SMtot – SMP,24 – (SSB,m,24 – ∆SSB,24 : 2) x VB] : (2 x VSU) = 2,38 g/l

• SSSU,m,24 = SSSU,min,24 + ∆SSSU,24 : 4 = 2,50 g/l

Design with Q48:


• SMP,48 = SSB,m,48 x Q48 x Z = 284 kg SS

• ∆SSB,48 = SMP,48 : VB = 0,44 g/l

• ∆SSSU,48 = SMP,48 : VSU = 0,28 g/l

• SSSU,min,48 = [SMtot – SMP,48 – (SSB,m,48 – ∆SSB,48 : 2) x VB] : (2 x VSU) = 1,97 g/l


Design with Q=0:

SSE,m – SSB,m,0 = 0; SSB,m,0 = SSE,m = 8,30 g/l

SSSU,m,0 = (SMtot – SSB,m,0 x VB) : (2 x VSU) = 1,65 g/l

N-elimination for Q24:

• TKN = 110,0 kg SS

Nsludge = 0,35*TKN = 40,0 kg SS

NSU = 2 x VSU x SSSU,m,24 x DNend x 24 = 60,0 kg SS

NB = VB x SSB,m,24 x (1- ζB ) x DNsim x 24 = 0,0 kg SS

Neffl = TKN – Nsludge – NSU – NB = 10,0 kg SS

N-elimination = 100 x (TKN – Neffl) / TKN = 91 %


In comparison between the Biocos-strategy and the activated sludge strategy the vol-ume of the aeration tank and the secundary clarifier of the activated sludge strategy will be estimated (in conformity with ATV A131).

VB,aerob = S0 * Qe * tSS,aerobic / SSB = 930 m³ (SSB = 4,0 g/l). VDN / VBB = 0,3; VDN / (VDU+VB,aerobic) = 0.3; VDN = 0.3 * 930 / 0.7 = 400 m³; VBB = 930 + 400 = 1.330 m³ qA=qsv:(SSBB*SVI)=450:(4,0*120)=0.94 m/h FNK=Qmax:qA=200:0.94=215 m²; VNK = FNK x HNK = 215 x 5.0 = 1.070 m³

The volume of the aeraton tank VBB of the activated sludge strategy is approx. 100% higher than the B-reactor of the Biocos-strategy (VB = 650 m³).

Comparison of the biomass: Biocos-strategy / activated sludge strategy = 1,64 / 1,00. The biomass of the Biocos-strategy is in the load hKW=0,25 (variant A) about 66% higher than in the activated sludge strategy. Figure 11: Suspended solid concentrations for the example A (10.000 PE)


5.2. Simple nitrogen simulation (Simple Nitrogen Simulation = SNS)

For Biocos wastewater treatment plants, simple dynamic simulations for ammonium and nitrate can be performed. In most cases, there is no need to simulate other parameters for the following reasons:

• As long as the B reactor is designed in accordance with ATV-A131, experience shows that – thanks to the sludge blanket and endogenous denitrification in the SU reactors – the COD concentration in the effluent is mostly around 30 mg/l and cor-responds to inert dissolved COD. Dynamic simulation of this parameter is therefore superfluous.

• In large-scale wastewater treatment plants, it is standard practice to employ phos-phorus precipitation to obtain P concentrations in the final effluent of less than 1 mg/l. This again makes simulation unnecessary.

• As a result of the large masses of sludge in the B reactor and the SU reactors, only minor fluctuations in suspended solids occur. As an approximation, it is possi-ble to work with reasonable accuracy with average values for the expected SS concentrations. Thus, dynamic simulation for suspended solids is not absolutely essential, either.

• It can also be assumed that surplus activated sludge is removed at such a rate that the sludge mass in the plant remains constant. Therefore surplus sludge pro-duction is not simulated.

• The aeration systems are designed with the reserves needed to ensure that enough oxygen is always available. This makes oxygen simulation superfluous.

• The retention period of the activated sludge in the SU reactors corresponds ap-proximately to 2 half cycles (approx. 2.4 hours). This means that redissolution processes can be discounted.

• The sludge in the system is so old that no nitrifying and denitrifying bacteria are washed out. Micro-organism growth, therefore, is not simulated.

• The organic matter required for endogenous denitrification in the SU reactors is present in the form of the bacterial mass. Thus there is no need to calculate COD and BOD5 concentrations in the Biocos process.

Nitrogen simulation is performed with nitrification and denitrification rates derived from laboratory tests and data from operating Biocos treatment plants and can be veri-fied with the help of ATV A131. In large-scale Biocos treatment plants, nitrification occurs exclusively in the B reactor. At lower temperatures the B reactor is constantly maintained in an aerobic state. As long as the B reactor is designed pursuant to ATV A131 it can be assumed that complete nitrification will be achieved with NH4-N effluent concentrations below 1.0 mg/l. Ammo-nium is nevertheless included in the simulation. The simulation is performed with the help of daily load curves for influent flow and the ammonium loads entering the system. The influent volumes allocated to 20 half cycles (1.2 hours each) amount to Vi=ζQ,i*Qd , using dry weather flow for the calculations (QTW in m³/d). It is also assumed that 65 % of


TKN enters the B reactor as NH4 (Ain,i = ζA,i*TKN*0.65). The remaining nitrogen (approx. 35 % of TKN) is removed with the sludge. For suspended solids in the B and SU reactors, the averages are taken that apply at dry weather flow. These values can be used to calculate denitrification capacity per cycle (DNB and DNSU). Denitrification of the sludge in the upper reactor zone that settles following the U phase can be discounted. It is a safe assumption that the nitrogen concentration in the effluent corresponds to the concentration present at the beginning of the sedimentation phase. For calculation of the nitrogen returned to the B reactor in the S phase, an average value is assumed, taking into account the fact that only denitrification occurs in the SU reactors. The SS and N concentrations in the SU reactor are shown in Figure 12. Total simulation can be performed if required, using Activated Sludge Model no. 1 (ASM 1) adapted for Biocos treatment plants. Figure 12: SS- und N-concentrations in the SU-reactor for the example A


Biocos wastewater treatment plant: Example A page 1

4-phase strategySNS (Simple Nitrogen Simulation)

Population equivalent 10.000 PEPrimary treatment yes (yes/no)Combined sewer: yes (yes/no) (Qmax = QRW = 200 m³/h)

Input: Calculation for dry weather

Comparative sludge volume VSV = 330 ml/lDry weather flow Qd = 1600 m³/dTotal nitrogen TKN = 110 kg/d (11 g/PE)

Volume B-reactor VB = 650 m³

Volume SU-reactor VSU = 1000 m³ (1 reactor)

Volume return activated sludge VR = 240 m³ (approx. 0,25*VSU)

Reactor depht H = 6.0 m

Suspended solid B-reactor SSB,m,24 = 5.7 kg/m³

Suspended solid SU-reactor SSSU,m,24 = 2.5 kg/m³

Nitrification in B-reactor NR = 1,6*T/10 = 1.60 g/kg.h (8 ≤ T ≤ 20 °C)

Denitrification endogenous DNend = 0,5*T/10 = 0.50 g/kg.h (8 ≤ T ≤ 20 °C)

Denitrification simultaneous DNsim = 1,0*T/10 = 1.00 g/kg.h (8 ≤ T ≤ 20 °C)

Aeration factor ζB = 1.00Half cycle Z = 1.2 [h]

Initial values: NB,0 = 10 g/l AB,0 = 0 g/l

NSU,0 = 10 g/l AB,-1 = 0 g/l

NSU,-1 = 10 g/l ASU,0 = 0 g/l

ASU,-1 = 0 g/lTime-variaton curve per day:

hour �Qi [%] �Ai [%] Std �Qi [%] �Ai [%]

1.2 2.2 2.1 13.2 5.7 6.4

2.4 2.3 2.1 14.4 6.3 8.1

3.6 2.4 2.2 15.6 5.9 7.5

4.8 2.6 2.3 16.8 5.4 6.5

6.0 3.1 2.7 18.0 6.4 6.9

7.2 4.0 3.4 19.2 6.7 7.0

8.4 5.4 4.5 20.4 6.9 6.6

9.6 6.2 5.1 21.6 6.5 6.1

10.8 6.3 5.6 22.8 5.7 5.3

12.0 5.7 5.6 24.0 4.3 4.0

total 100.0 100.0


Calculation (elimination of nitrogen): page 2

vs = 650 / VSV = 1.97 m/h

A = VB*SSB,m,24*ζB*Z*NR = 7114 g/Z

DNB = VB*SSB,m,24*(1-ζB)*Z*DNsim = 0 g/Z

DNSU = VSU*SSSU,m,24*2*Z*DNend = 3000 g/Z

a = 3,3*SSSU,m,24*DNend*(2*Z-0,25*H / vs) = 6.76 g/m³

Vi = ζQ,i * Qd

Azu,i = ζA,i * TKN * 0.65

Before the S-phase

Formula 1: AB,S,i = [2*Azu,i - 2*A + AB,i-1*(2*VB-Vi)] / (2*VB+Vi) if < 0 then 0

if AB,S,i = 0 then Ni = Azu,i + AB,i-1 * (2*VB-Vi) / 2

if AB,S,i > 0 then Ni = A

Formula 2: NB,S,i = [2*Ni - 2*DNB + NB,i-1*(2*VB-Vi)] / (2*VB + Vi) if < 0 then 0

Formula 3: ASU,S,i = [ASU,i-2 * VSU + (AB,S,i + AB,i-1)*Vi/2 - ASU,i-2*Vi] / VSU if < 0 then 0

Formula 4: NSU,S,i = [NSU,i-2*VSU + (NB,S,i + NB,i-1)*Vi / 2 - NSU,i-2*Vi - DNSU] / VSU if < 0 then 0

After the S-phase

NSU,i-2 - a = if < 0 then 0

Formula 5: AB,i = [AB,S,i * VB - AB,S,i *VR / 2 + ASU,i-2*VR)] / (VB + VR/2) if < 0 then 0

Formula 6: NB,i = [NB,S,i * VB - NB,S,i*VR / 2 - (NSU,i-2 - a)*VR)] / (VB + VR/2) if < 0 then 0

Formula 7: ASU,i = [ASU,S,i * VSU + (AB,S,i + AB,i)*VR / 2 - ASU,i-2*VR)] / VSU if < 0 then 0

Formula 8: NSU,i = [NSU,S,i * VSU + (NB,S,i + NB,i)*VR / 2 - (NSU,i-2 - a)*VR)] / VSU if < 0 then 0

After day 5:

Atot = Σ ASU,i * Vi = 0.0 kg/d Ael = (TKN - Atot) / TKN = 100 %Ntot = Σ NSU,i * Vi = 10.6 kg/d Nel = (TKN - Ntot) / TKN = 90 %

32 K

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Figure 13: Ammonium- and Nitrate- simulation

page 4

time-variation curve day 5

0

2

4

6

8

10

12

14

16

0 4 8 12 16 20 24

time [h]

con

cen

trat

ion

NB,i

NSU,i

[NO3-N g/m³]

NO3-N in B-reactor

Neffl day 5

0

200

400

600

800

1000

1200

0 4 8 12 16 20 24

time [h]

NS

U,i

* V

i

ASU,i*Vi

NSU,i*Vi

[NO3-N g/Zyklus]

NO3-N in SU-reactor

Effluent from the SU-reactor

NO3-N

NH4-N


6. LITERATURE [1] Worksheet of the German Association for Water, Wastewater and Waste: ATV-A

131 and ATV-M 210 (in German) [2] Tyrolean Government – Urban water management: Reports 2001 and 2002,

WWTP Längenfeld (in German) [3] Ingerle, K.: Biocos-strategy, wastewater technologies and water protection, vol-

ume 2, C. F. Müller-publishing house, Dr. W. Wagner, 2001 (in German) [4] Wett, B.; Ingerle K.: Feedforward aeration control of a Biocos-WWTP. Water Sci-

ence & Technology 43/3, pp. 85-91, 2001 [5] Ingerle, K: Large Biocos wastewater treatment plants, Korrespondenz Abwasser,

2001 (48) (German Association for Water, Wastewater and Waste) [5] Ingerle, K: Biocos treatment plants, description and design, Korrespondenz Ab-

wasser, 1999 (46) (German Association for Water, Wastewater and Waste) [6] Ingerle K.: Biocos-strategy, wastewater treatment plants Längenfeld and Pielenho-

fen, gwf-Abwasser Spezial, 139, Heft 14, 1998 (in German) [7] Wett, B.; Gluderer, D.; Rauch, W.: Denitrification of settling sludge. gwf-

Wasser/Abwasser 138/7, S 345-350, 1997 (in German) [8] Kujawa, K.; Klapwijk, B.: A methode to estimate denitrification potential for predeni-

trification systems using NUR batch test. Wat. Res. Vol. 33, No. 10, 1999


7. ANNEX 7.1. Sedimentation tests performed A 4.0 m high Plexiglas tube (DN 200 mm) was filled with activated sludge from the Zirl water treatment plant (45,000 PE; SVI=140 ml/g; SS=2.4g/l; VSV=340mg/l; 10°C) and settlement of the sludge blanket level measured. Settlement in a DN 200 mm tube cor-responds approximately to settlement in a large reactor. After a sedimentation period of 150 minutes, sludge samples were taken from the thick-ening zone (HE = 134 cm) at 25 cm intervals and the solids measured. The 150 minutes represent standard cycle time for the Biocos process and are thus equal to the sludge settlement period in the SU reactors. Figure 14: Sediment test in a DN 200 Plexiglas tube

In the first 60 minutes the sludge blanket level settled at a constant rate of vs = 1.85 m/h. During this period the suspended solids in the sinking sludge body remained un-changed in the upper 1.9 m. The measured rate of settlement is in good agreement with the ATV design value vs = 650 / VSV = 650 / 340 = 1.9 m/h. After one hour’s settlement, the limit of the settlement process is reached. This phase is followed by thickening in the whole of the sludge body with a much slower rate of settlement in sludge blanket level. After 150 minutes, a thickening zone of 134 cm has built up. This is approximately equivalent to the result of the equation HE = H * VSV / 1000 = 400 * 340 / 1000 = 136 cm. Analysis of the solids in the thickening zone after 150 minutes showed an almost linear increase from top to bottom (SSo = 4.5 g/l; SSu = 9.5 g/l; SSE,m = 7.0 g/l). The measured results were compared with the results of the equation for bottom sludge in ATV A131 (SSBS = 1000 * tE

0.33 / SVI). For tE = 2.5 hours and SVI = 140 ml/l, the equation produces SSBS = 9.7 g/l. That is in good agreement with the test result of SSu = 9.5 g/l. In the S phase of the Biocos process, the sludge formed after approx. 2.5 hours is ex-tracted from the bottom of the SU reactor to a depth of 0.25*H to 0.33*H and pumped back into the B reactor. It is therefore safe to assume mean suspended solids SSE,m for this return sludge volume of SSm = SSBS = 1000 / SVI in g/l. At tE = 1 hour, the ATV equation is SSBS=1000/SVI=1000/140=7.1 g/l, while in the test SSE,m = 7.0 g/l.


The sludge mass SMS = VR * SSE,m returned to the B reactor in the S phase is therefore calculated with the equation SSE,m = 1000 / SVI. The return sludge volume VR is so large that almost the whole sludge mass in the SU reactor at the end of the U phase is recycled in every cycle, thus avoiding redissolution problems. The retention period of the activated sludge in the SU reactor is little more than 2.5 hours. Two laws can be formulated to describe settlement behavior of the activated sludge: • Settling velocity of the sludge blanket level: vs = const. with SS0 = const.

• Thickening rate of the sludge: SSE,m = SS0 + c * t + d * t² [g/l]

(e.g. SS = 1000 * tE0.33 / SVI pursuant to ATV A131 for SSE,m with half the thicken-

ing time: at t = 1 h... tE = 0.5h and at t = 2h... tE = 1.0h)

During the settling period a constant volume of sludge per unit of time enters the thick-ening zone from the settling zone. During the thickening period the sludge mass in the thickening zone remains constant. Figure 15: Settling and thickening

Similar tests were performed on activated sludge from other wastewater treatment plants: • Innsbruck: activated sludge process 400.000 PE SVI=140 • Strass: two-stage biological process 160.000 PE SVI=47 • Zirl: activated sludge process 45.000 PE SVI=110 • Längenfeld: Biocos process 10.000 PE SVI=125 • Model plant: Biocos process 30 PE SVI=110 For Biocos treatment plants, VSVmax ≤ 350 ml/l should not be exceeded. SBR plants should not be designed for VSV > 400 ml/l as settling velocity is otherwise very low. From the results of the tests and study of the available literature, the following conclu-sions can be drawn:

For the desired settling velocities of vs = 2.0 m/h, the ATV-M210 equation vs = 650 / VSV with VSV � 350 ml/l applies.


• The following figure should not be exceeded with a safety factor included: VSVmax = SSSU,max * SVI � 350 ml/l. That produces a sludge blanket level settling velocity of vS = approx. 1.8 - 2.0 m/h.

• At the end of the settlement period of approx. 2.5 hours (cycle time), average total solids in the thickened mud returned from the SU reactor to the B reactor is ob-tained as SSE,m = 1.000 / SVI in g/l. The depth of the thickening zone is then de-rived from HE =H*SS0/SSE,m = H*SS0/(1000/SVI) = H*VSV / 1.000.

In the S phase, all the sludge in the SU reactor at the end of the U phase should be returned to the B reactor: VR = FSU * HE = VSU * VSV / 1000 = 0.35 * VSU (at VSV = 350 ml/l, approximately one third of the content of the SU reactor).

As SSSU,max occurs at maximum hydraulic load Qmax , VR corresponds to this maximum load case. At lower influent flows, VR remains constant, as will be shown later. This has the positive effect of an increase in SSB in the B reactor and a decrease in SSSU in the SU reactor. Figure 16: Settling velocities vs as an expression of VSV


7.2. Endogenous denitrification in the SU reactor of the Biocos plant in Längenfeld

Very accurate data can also be provided with regard to denitrification at the Biocos wastewater treatment plant in Längenfeld, which was commissioned in 1998. In the first halves of 2001 and 2002 the aeration tank (B reactor) was continuously operated under aerobic conditions so that denitrification occurred exclusively in the SU reactors and was endogenous. The Längenfeld plant is designed for 10.000 PE (600 kg BOD5/d). The weekly averages varied in 2002 between 290 and 572 kg BOD5/d (tourism), with a peak day of 759 kg BOD5/d. Maximum hydraulic load was 1.936 m³/d (separate system). The influent wastewater flows via a screen, grit chamber and primary treatment stage to the twin-line Biocos plant. Sludge treatment involves primary thickening, heated anaero-bic sludge digestion, secondary thickening, sludge storage and a plate-and-frame filter press. The sludge treatment process water is stored in a tank and added to the influent flow at night. The prescribed phosphorus limit value of 1.0 mg/l is achieved by adding a precipitant. The Längenfeld plant is completely covered and has the following reactor sizes: VB = 402.4 m³; VSU = 166.6 m³; two lines. The Austrian Wastewater Emissions Code stipulates a temperature threshold of 8 °C for nitrification and 12 °C for nitrogen elimination. When wastewater temperature in the Längenfeld plant falls below 11 °C, the B reactor is operated under continuous aeration (O2 content between 2.0 and 3.0 mg/l) and aerobic conditions are always maintained (full operation), with maximum possible nitrification as the goal in the B reactor. In that case denitrification in the Biocos stage is only possible in the SU reactors. This is the operating mode for the first half of each year. At wastewater temperatures above 11 °C, denitrification is also performed in the B reactor so as to achieve the required level of nitrogen reduction. Figure 18 shows the Q, COD and BOD5 values and the temperature curve for the Längenfeld wastewater treatment plant. In the first half of every year the temperature falls below 11 °C. Full operation is accordingly maintained from the 1st to the 26th week. Figure 19 lists the nitrogen values. All the data are taken from the annual reports pub-lished by the Water Resources Management Office of the Tyrolean Regional Govern-ment [1]. For the Längenfeld plant, the degree of endogenous denitrification in the SU reactors is easily determined. At full operation, denitrification occurs only in the SU reactors. As the plant is always in full operation in the first half of the year, a reliable average figure can be quoted for endogenous denitrification during this period. The fact that denitrifica-tion in the SU reactors is an endogenous process can be seen from the lower COD value of the substrate of < 40 mg/l. The following figure illustrates the nitrogen balance in kg/d: Figure 17: Nitrogen balance in kg/d

total treatment plant

Ntot, S Ntot, effluent

Ntot, SU

Ntot, in


The daily nitrogen load in the influent Ntot.,in can be divided into three flows:

Ntot,S: nitrogen in the digested and pressed sludge Ntot, effluent: nitrogen in the final effluent Ntot,SU: endogenously denitrified nitrogen in the SU reactor

For the analysis it was assumed that the minimal COD concentrations in the substrate in the aerobically operated B reactor mean that no simultaneous denitrification takes place (complete mixing in the B reactor and high oxygen concentrations > 2 mg/l). Any anoxic or anaerobic ammoniac oxidation in the SU reactors was included with denitrification (Ntot.,SU), because the two processes cannot be clearly separated. Mean BOD5 load in 2001 was 410 kg/d and mean Ntot.,in load was 75 kg/d. This influent load compares with a pressed sludge yield of 298.000 : 365 = approx. 816 kg/d with 39 % SS. The result for the digested sludge including the precipitant is therefore 816 x 0.39 : 410 = 0.78 kg SS / kg BOD5. The results of the analyses indicate a maximum of 0.055 kg Ntot.,S / kg SS and a mean value of 0.040 kg Ntot.,S / kg SS. For the first half of 2001 this gives a maximum of Ntot.,S = BOD5,in x 0.78 x 0.055 kg / d = 18.8 kg / d (corresponding to 100 x 18.8 : 77.1 = 24.4 %). The calculations were based on the highest measured result for nitrogen from a large number of sludge samples analyzed so as to have a good margin of safety for en-dogenous denitrification. In the first half of 2001 and 2002, endogenous denitrification in the SU reactors was de-termined as follows:

Table 7: Nitrogen balance for Ntot. in kg/d, six-month averages

Period Ntot, in kg/d

BOD5, in kg/d

Ntot,S kg/d

Ntot,effluent kg/d

Ntot,SU kg/d

Qin m³/d

1. semester 2001 77.1 439 18.8 32.3 26.0 1353 1. semester 2002 77.6 432 18.6 22.0 37.0 1386 1. semester 2003 85.3 444 19.0 27.5 38.8 1446

Table 8: Endogenous denitrification in the SU reactors DNend in g NO3-N/kg SS.d, six-month averages

Period Ntot,SU

kg/d SSSU

g/l SSB g/l

DNend g/kg SS.d

T °C

SVI mg/l

sludge age

tSS, aerob d

pH

1. semester 2001 26.0 2.8 2.4 13.9 8.4 192 7.4 7.2 1. semester 2002 37.0 4.6 4.2 12.1 8.1 119 13.2 7.6 1. semester 2003 38.8 3.4 3.0 17.1 9.0 115 9.2 8.0 As SS is measured at the end of the U phase, sludge return in the course of a cycle leads to an increase in average SS in the SU reactors and a corresponding decrease in the B reactor (SSB and SSSU therefore differ).


Figure 18: Annual report 2001: BOD5-, COD and wastewater temperature of the influent and effluent flow from the WWTP Längenfeld [2]

COD- and BOD5 – concentrations of the influent flow

COD- and BOD5 – concentrations of the final effluent flow

COD- values BOD5- values

COD- values BOD5- values

COD- values

full operation BOD5- values

Annual report 2001 WWTP Längenfeld

week

week

Tyrolean Government – urban water management


Figure 19: Annual report 2001: Nges; NH4-N; NO3-N of the influent and effluent

flow from the waste water treatment plant Längenfeld [2]

N- concentrations of the influent flow

N- concentrations of the final effluent flow

Annual report 2001 WWTP Längenfeld

Ntot- values

week

NH4-N - values

Ntot- values NO3-N - values NH4-N - values

week

Tyrolean Government – urban water management


The endogenous denitrification in the SU-reactors DNend can be calculated with DNend = Ntot,SU : (4 x VSU x SSSU) and the aerobic sludge age with tSS,aerob = 2 x VB x SSB : (0,66 x BOD5,in x Qe). Qe = 0,9 kg SS / kg BOD5. With sufficient safety in operation the endogenous denitrification in the SU-reactor of the BIOCOS-strategy can be settled by a temperature from 8,5 °C and an aerobic sludge age by 8 days with DNend = 12,0 g NO3-N / kg SS.d = 0,5 g NO3-N / kg SS.h. Apparently there are specialized micro organisms in the SU-reactor to work under this conditions.


7.3. Drafts of an SU-reactor Figure 20: Floor plan (H=6.0m)

spherical valves

stir

rin

g (

line

aera

ter)

SU

-rea

cto

r

S-s

iph

on

DN

250

sup

ern

atan

t re

cycl

ing

B-reactor


Figure 21: Supply of pressured air, one Biocos-line � 30.000 PE

stainless steel box

stainless steel box

main aeration line for B-reactor

axle

S-s

iph

on

DN

250

stir

rin

g (

aera

tio

n li

ne)

sup

ern

atan

t re

cycl

ing

su

per

nat

ant

recy

clin

g

spigot 2“

solenoid valve 2“

stirring

S-siphon DN250 effluent channel

sph

eric

al v

alve


Figure 22: Supply of compressed air, one Biocos-line � 30.000 PE

main aeration line for B-reactor S-siphon DN250

stirring

sup

ern

atan

t re

cycl

ing

effluent channel

stirring

S-siphon DN250

main aeration line for B-reactor

stirring

S-siphon

sup

ern

atan

t re

cycl

ing

sph

eric

al v

alve

sup

ern

atan

t re

cycl

ing

stir

rin

g

S-s

iph

on

DN

250

axle


Figure 23: S-siphon

sockets DN100

S-siphon Flow rate: approx. 60 l/s Pressed air: 8 l/s; 0,6 bar Length SU-reactor: 15,00 m Minimum water level: 6,00 m Material: PVC


Figure 24: Stirring

STIRRING

Aeration line at the middle wall: variant with polyethylene-pillar

Aeration line at the exterior wall: variant with stainless steel-pillar

stainless steel-pillar

For the stirring you can use another aeration lines too.


Figure 25: Final effluent discharge (ball valve)

FINAL EFFLUENT DISCHARGE

hole diameter

min. water level

spherical diameter

DN100, spherical 80 mm, hole 60 mm




�


7.5. Activated sludge plants constructed or planned (Ingerle) The following is an excerpt from our list of reference plants: • Planning works and submission for approvals:

(Detail design and site supervision: Ingenieurgemeinschaft Lässer Feizlmayr ILF, Innsbruck) - Tannery process water in Istanbul (Aydinli plant: approx. 2 million PE) - Plant for Strass i. Zillertal: municipal wastewater (220,000 PE) - Water treatment plant in Radfeld: municipal wastewater (60,000 PE) - Längenfeld plant: municipal wastewater (10,000 PE)

• General planning and site supervision:

- Brewery process water (Kaltenhausen plant, approx. 30,000 PE) - Hotel wastewater plant in the Dominican Republic (5,000 PE) - Upgrade to Längenfeld plant (10,000 PE)

• Chairman of the international steering committee for an upgrade to the water

treatment plant in Innsbruck: municipal wastewater (400,000 PE) • Consulting services on behalf of the Tyrolean Regional Government for the design

of numerous wastewater treatment plants (10,000 - 120,000 PE)


7.6. Enlargement of the WWTP Vienna with the Biocos-strategy (variant, not realized)

Figure 26: Floor plan (20 BIOCOS-lines)

influent flow en

larg

emen

t ar

ea

sludge pumping station

final effluent flow

enlargement area

com

pre

ssed

air

st

atio

n

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Figure 27: Floor plan of one Biocos-line

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BIOCOS-WWTP: Vienna (18 lines, dimension for 1 line) Primary treatment: ......yes....... yes/no Combined sewer: ......yes....... yes/no Parameters of the treatment plant: • Qmax = 2600 m³/h

• Q24 = 1127 m³/h

• Q48 = 564 m³/h

• S0 = ........... PE x ............ kg/PE = 7060 kg BOD5/d

• Qe = 0,95 kg SS/kg BOD5

• tSS,aerob = 8,0 d (e.g. age sludge age according to ATV A131)

• ζB = 1,00 (aeration factor)

• TKN = 1180 kg N/d

• SVI = 100 ml/g; T = 10 °C; H = 6,0 m

• VSV = 330 ml/l

• Z = 1,2 h (half cycle)

Parameters for design with Qmax: • SSSU,min = VSV : SVI = 3,30 g/l

• SSE,m = 1000 : SVI = 10,0 g/l

• SSB,m = 500 : SVI = 5,0 g/l

• hKW = 0,30; HKW = hKW x H = 1,80 m

• vs = 650 : (SVI x SSSU,min) = 2,0 m/h

• SSB,m,24 = 7,0 g/l (estimated with 1,40 x SSB,m)

Parameters for design with Q24: • VR,24 = VR; SMges,24 = SMges; SSE,m,24 = SSE,m

• DNsim = 1,0 x T : 10 = 1,0 gNO3-N/kg SS.h

• DNend = 0,5 x T : 10 = 0,5 gNO3-N/kg SS.h

Design with Qmax:

• VSU = FSU x H = Qmax x Z : hKW = 10.400 m³

• VB = S0 x Qe x tSS,aerob : (ζB x SSB,m,24) = 7.665 m³

• SMP = SSB,m x Qmax x Z = 15600 kg SS

• ∆SSB = SMP : VB = 2,04 g/l

(SU-reactot 2 x 15,8 + 11,6 + 6,0 = 49,20m < 54,60m) 20 lines possible


• ∆SSSU = SMP : VSU = 1,50 g/l

• SSB,min = SSB,m – ∆SSB : 2 = 3,98 g/l

• SMges = SMP + SSB,min x VB + 2 x SSSU,min x VSU = 114.750 kg SS

• VR = SMP : (SSE,m – SSB,m) = const. = 3.120 m³ (recirculation sludge volume)

Design with Q24:


Verifying of the estimated SSB,m,24

• SMP,24 = SSB,m,24 x Q24 x Z = 9.467 kg SS

• ∆SSB,24 = SMP,24 : VB = 1,24 g/l

• ∆SSSU,24 = SMP,24 : VSU = 0,91 g/l

• SSSU,min,24 = [SMges – SMP,24 – (SSB,m,24 – ∆SSB,24 : 2) x VB] : (2 x VSU) = 2,71 g/l


Design with Q48


• SMP,48 = SSB,m,48 x Q48 x Z = 5.560 kg SS

• ∆SSB,48 = SMP,48 : VB = 0,73 g/l

• ∆SSSU,48 = SMP,48 : VSU = 0,53 g/l

• SSSU,min,48 = [SMges – SMP,48 – (SSB,m,48 – ∆SSB,48 : 2) x VB] : (2 x VSU) = 2,36 g/l


Bemessung für Q=0:

SSE,m – SSB,m,0 = 0; SSB,m,0 = SSE,m = 10,0 g/l

SSSU,m,0 = (SMges – SSB,m,0 x VB) : (2 x VSU) = 1,83 g/l

N-Elimination für Q24:

• TKN = 1.180 kg SS

Nsludge = 0,35*TKN = 410 kg SS

NSU = 2 x VSU x SSSU,m,24 x DNend x 24 = 750 kg SS

NB = VB x SSB,m,24 x (1- ζB ) x DNsim x 24 = 0 kg SS

Neffl = TKN – Nsludge – NSU – NB = 20 kg SS

N-elimination = 100 x (TKN – Nab) / TKN = 98 %

The reduction of energy in the secondary treatment between the activated sludge strategy and the BIOCOS-strategy is: 62,5 – 42,2 = 20,3 million kWh/a (e.g. 33%).


7.7. Documentation and optimization of a BIOCOS-plant for approx.

10.000 PE (in German) Results (see page 58 resp. page 22 of the following German report): The full operation could be simulated by a pilot operation (where the dry weather flow with full organic load was clarified with only one BIOCOS-line). Since the fully functional operation the analysis of the final effluent flow values from the WWTP Petershausen looks better than the required values.





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