Phosphorus removal at an ASP and Filter Works using Mecana Filter Technology - findings and experiences from CIP P trials
Lynn Smith1, Estela Alvarez Moreta2, Pete Gardner3 and Lewis O’Brien4
1Yorkshire Water, 2Thames Water, 3South West Water, 4Eliquo Hydrok, UK
Big P Conference, 4th and 5th July 2017
Phosphorus removal using Mecana
CIP2 trials to evaluate meeting a target 0.1mg/l total P in final effluent
1) Mecana overview – Eliquo Hydrok
2) Trials carried out• South West Water, Thames Water, Yorkshire Water
• sites and coagulant dosing rates
3) Results and findings
4) Conclusions
5) Recommendations
What is Cloth Media Filtration?
Uses a Deep Pile Fabric:• Filtration not screening, 7µm / 25µm dia
fibres
• Provides a very large surface area
Fabric fitted onto a rigid frame:• Standard (White)
• Microfibre (Blue)
Disc assembly:• Comprises 6no. interlocking segments
• Vertically mounted onto a centre tube
Frame:• Several discs combined
• Each with a Clean in Place (CIP) system
>> Result is a very compact system
How it works
Size Range and Capability
Windermere WwTW
Bespoke concrete12x SF18/90 units4,149 l/s8 mg/l TSSWorld’s largest installation
Deephams WwTW
Horsham WwTW
Stainless steelFerric additionTF2 unit3 l/s0.1 mg/l Total P
Stainless steel2x SF18/90 units80 l/s10 mg/L TSSBackwash 3% max.
Position of Mecana in process stream
Advantages
• High separation efficiency
• High throughput
• Low head loss
• No backwash water tank required
• Continuous flow – no interruption for backwash
• Low space/footprint requirement
• Unaffected by shock loads
• Low CAPEX
• Low OPEX
• Suitable for a variety of applications
Mecana trials for CIP2
Water companyPE (% of flow to Mecana) Type of treatment
Coagulant dosed
Single filtration (microfibre)
South West Water –North Tawton
2,400 (100%)14l/s
Filters and NSAFPoly Aluminium Chloride
Yorkshire Water -Bentley
25,000 (28%) 36l/s
Filters (ADF mode) Ferric sulphate
Yorkshire Water -Staveley
30,000 (35%) 40l/s
Nitrifying ASP Ferric sulphate
Double filtration (standard cloth and microfibre)
Thames Water -Cirencester
30,555 (100%) 269 l/s
Oxidation ditch Ferric sulphate
Coagulant dosing points
Dose to primary tanks (all sites)
Dose to Mecana feed (all sites)
Dose to humus tanks (North Tawton)
North Tawton STW Mecana trial
Filters and NSAF
PE: 2,400
1 x SF6/30 Mecana unit (6 discs)
100% flow
Integral flocculation tank with Mecana unit (partially buried)
Internal floor across disc chamber
North Tawton
Bentley STW Mecana trial
ADF Filter works
PE: 25,000
1 x SF18/90 Mecana unit (18 discs)
28% flow
Flocculation tank
Mecana unit 18/90and microfibre discs
Bentley
Staveley STW Mecana trial
Nitrifying ASP
PE: 30,0001 x Mecana unit 15/75 (15 discs)35% flow
Flocculation tank
Mecana unit
Backwash chamber
Stage 2 dosing point to static mixer
Staveley
Cirencester STW Mecana trialFlocculation tanks Pile cloth filters
(first stage)
Microfibre filters(second stage)
Backwash tank(Backwash sent to PST)
Oxidation ditch
PE: 30,555
2 x SF15/75 Mecana units (30 standard, 30 microfibre discs)
100% flow
Cirencester
14
Tertiary plant set up at Cirencester
Coagulant dosing arrangements
Site1y dose (Fe:Pmolar ratio) 1y Control Mecana feed dose and control
North Tawton2 (Al:P nominal
ratio)Diurnal P load profilewith turbidity trim
Humus feed dose controlled on DiurnalP profile (2:1 ratio).
Mecana feed dose controlled on Mecana feed ortho-P (20:1 nominal ratio) with turbidity trim
Bentley 1.9 Diurnal P load profile 14mgFe/l flow proportional
Staveley 0.6 Diurnal P load profile14mgFe/l flow proportional (caustic needed for alkalinity)
Cirencester 0.4 Diurnal P load profile 12.3 mgFe/l (control using RTC)
Results of Mecana low P trials
1. Final filtered effluent total P results
2. Final filtered effluent iron results
3. Solids generation due to coagulant addition
4. Solids loading onto Mecana – measured vs design
1. Final effluent total P results
Site
Mecana influent Mecana effluent
Ortho P Total P Ortho P Total P
mg/l mg/l mg/l mg/l
North Tawton 0.1 0.53 0.06 0.13 (0.22)
Bentley 0.4 1.1 0.02 0.14 (0.17)
Staveley 1.2 2.0 0.02 0.08 (0.12)
Cirencester 0.5 0.6 0.04 0.09 (0.23)
Target influent totalP (mg/l) 1.0
Target effluent totalP (mg/l) 0.1
Data with periods of failure/non-rep samples excluded (ALL DATA shown in brackets)
Final effluent total P results – all trials
0
0.2
0.4
0.6
0.8
1
1.2
fin
al e
fflu
en
t to
tal P
mg/
l
North Tawton
Bentley
Staveley
Cirencester
target totalPmg/l
North Tawton - Final effluent total P
0
0.2
0.4
0.6
0.8
1
1.2
fin
al e
fflu
en
t to
tal P
mg/
l targettotalPmg/l
Inaccuratedosing of alum
Alum dose to Mecana feed ratio 20:1
Bentley - Final effluent total P
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Fin
al e
fflu
en
t to
tal P
mg/
l
target totalPmg/l
Dose6mg/l
Dose20mg/l
DosingoffFerric dose to Mecana feed 14mg/l
Staveley - Final effluent total P
0
0.2
0.4
0.6
0.8
1
1.2
fin
al e
fflu
en
t to
tal P
mg/
l
target totalPmg/l Biofilm at sampling tap,
unrepresentative samples
Ferric dose to Mecana feed 14mg/l
Cirencester - Final effluent total P
0
0.2
0.4
0.6
0.8
1
1.2
fin
al e
fflu
en
t to
tal P
mg/
l
target totalPmg/l
Ferric dose to Mecana feed 12.3mg/l (RTC system)
Ferric dosing issues
2. Final effluent total iron results from each trial
Site
Mecana influent total iron/alum
Mecana effluent total iron/alum
mg/l mg/l
North Tawton 1.76 (alum) 0.85 (alum)
Bentley 1.9 1.2
Staveley 0.7 0.6
Cirencester 0.42 0.37
Total iron consent mg/l 4.0
Total aluminium consent mg/l 5.0
Final effluent total iron (or alum for North Tawton) results from each trial
0
1
2
3
4
5
6
0
1000
2000
3000
4000
5000
6000
tota
l iro
n, a
lum
iniu
mµ
g/l Staveley
Bentley
Cirencester
North Tawnton
3. Solids generation results from each trial
Site
Ferric dose rate
Mecana feed
TSS concn
TSS onto Mecanafilters
Kg solids
formed/kg ferric
dosed
(mg/l as Fe) mg/l mg/l
Bentley 6 19 38 3.18
Bentley 20 21 72 2.56
Staveley 14 15 41 1.85
Cirencester 12.3 10 24 1.11
Bentley inlet and floc tank solids
20mg/l ferric dose
Staveley inlet and floctank solids
14mg/l ferric dose
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 5 10 15 20 25
kg s
olid
s /
kg f
err
ic d
ose
d
Mecana feed TSS mg/l
Solids generation from ferric addition as function of influent solids
4. Solids loading rates from each trial
Site
Ferric dose rate
Solids loading to standard fibre Mecana
Solids loading to microfibre Mecana
Backwash
frequency
(mg/l as Fe) (g/m2/hr) (g/m2/hr) mins
Bentley 6 - 30 (56 max) 5 to 10
Bentley 20 - 53 (83 max) continuous
Staveley 14 - 56 (83 max) 5 to 10
Cirencester 12.3 140 (228 max) 40 (149 max) 30
Design solids loading to standard fibre Mecana = 400g/m2/hr
Design solids loading to microfibre Mecana = 200g/m2/hr
Can you see the discs?
Conclusions
➢ The data shows that there are a number of challenges to achieving a final effluent concentration of 0.1mg/l total phosphorus.
➢ Good Instrumentation maintenance is crucial., especially if used as part of the control philosophy
➢ Dosing rates may be impacted by seasonal changes, changes in final effluent quality or site performance
➢ A 2 stage Mecana arrangement(standard fibre followed by microfibre) provides a more robust solution to meet low P levels.
➢ Solids generation due to secondary ferric dosing varied from 2 to 3.5 x influent solids.
➢ Observed solids loading rates didn’t reach design loading rates. At Bentley (filter works), at a solids loading rate below design the Mecana unit was already a maximum capacity.
Recommendations from trials
4) Ensure sufficient operational input is allowed to carry out required monitoring and maintenance
1) A solids generation rate should be based on jar tests on primary dosed final effluent and Mecana sizing based on a solids loading rate appropriate to the works
1) Further work is required on the RTC system to optimise the algorithm to meet a low P target
1) Attention is needed in the control and operation of the dosing system and solids loading onto the Mecana unit are key to compliance and opex:
➢ Instrumentation reliability
➢ Control philosophy
➢ Seasonal effects
➢ Upstream process performance
National Collaborative Project Any Questions?
Any
questions
EXTRA SLIDES
Cirencester slides and graphs
Mecana at Cirencester – two stage filtrationStandard pile cloth filter media (two units)/ Microfibre filter media (two units)
Design Solids loading rate: 400g/m2/hrAverage solids loading rate: 140g/m2/hr
Design Solids loading rate: 200g/m2/hr.Average solids loading rate: 40g/m2/hr.
Each unit 15 discs. Surface per disc: 5 m2 Filter surface:75 m2
Cirencester Mecana plant
Ferric tank
Flocculation tanksPile cloth filters(first stage)
Microfibre filters(second stage)
Backwash tank(Backwash sent to PST)Emergency shower
Cirencester. Surface of Mecanas
Standard filter with no maintenance (26/09/2016)
Microfibre filter with no maintenance (24/08/2016)
Cirencester chemical dosing set up
Flow meter and ferric injection point
Instrumentation kioskFerric dosing tank
Cirencester Pumping station & backwash water tank
Feed pump station and inlet/outlet chamber
Backwash water tank
Cirencester Total phosphorus
Cirencester Total phosphorus in detail.
Cirencester Soluble reactive phosphorus
Cirencester Total suspended solids
Cirencester. What can be achieved
Cirencester. What can be achieved
Cirencester operation scenarios
Final effluent With failures Without failures
TP (mg/L) 0.18 0.09
Low P (mg/L) 0.08 0.01
TSS (mg/L) 3.11 2.97
Total Iron (mg/L) 0.54 0.37
Cirencester process flow diagram
Extra slides. CirencesterImpact on the works.• Increased site sludge production due to the additional sludge from tertiary
treatment.(200kg/d).
• All parameters upstream remain without significant changes.
Operation and Maintenance.
• Instrumentation serviced once a month by supplier technician.
• Iron analyser requires DI water refilling every 10 days.
• Mecana filter tanks require cleaning once a week due to sludge building up on the surface and weed growth during warm weather.
• Ferric sulphate tank refilled approximately once every 6 weeks.
Extra slides. Cirencester (2)Operational issues.
• Faulty Mecana filter ultrasonic level sensor and faulty backwash chain.
• Ferric dosing system catch pot flooded.
• Instrumentation problems (ortho P analyser, Iron analyser, RTC).
• Power cuts.
• Ferric sulphate supply.
North Tawton slides and graphs
North Tawton Mecana during constructionNearest section is integral floc tank
North Tawton Mecana during commissioningPrior to internal flooring being fitted
North Tawton Mecana during trial operationSome build up of surface solids
North Tawton MecanaFinished installation
North Tawton data
•Majority of the TP was removed in primary and secondary treatment stages. The Mecana was used as a polishing stage
North Tawton data
•Problems with the primary and/or tertiary dosing from July until Sept – spike in P and SS. •Towards the end of the year, problems with the PO4-analyser and Tertiary SAF unit led to a spikein P and SS.•Relationship between TP and SS. This confirms that a control on turbidity is a good approach and that high SS or NTU is a good indicator of elevated P levels in the effluent.
North Tawton data
•Areas shaded in grey show the main periods during the trial when the actual Mecana feed dose rate (blue) fell significantly short of the calculated dose (red), leading to an increase in final effluent TP (green).
Bentley slides and graphs
Bentley – Mecana feed totalP, SRP, total iron and TSSvalues
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0
5
10
15
20
25
30
35
40
45
50
tota
lP, S
RP,
To
tal i
ron
mg/
l
TSS
mg/
l
TSS
total iron mg/l
soluble reactivephosphate mg/l
total P mg/l
Bentley Mecana effluent results (1)
0
5
10
15
20
25
30
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
TSS
mg/
l
SRP
, TP
mg/
l
TotalP, TSS in Mecana effluent
solublereactivephosphate
totalphosphorus
target totalP
TSS
High iron in Mecanaeffluent
Jar tests to confirm Stage 2 dose
Excessive solids build up in Mecana
Bentley Mecana effluent results (2)
0
5
10
15
20
25
30
0
500
1000
1500
2000
2500
3000
TSS
mg/
l
Tota
l iro
n, s
ol i
ron
ug/
l
TSS, total iron in Mecana effluent
Dissolved iron
total iron
TSS
Bentley jar tests for Stage 2 dosing
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0
1
2
3
4
5
6
7
8
9
0 6 12 20 25 30
ort
ho
P
pH
, Tu
rbid
ity
NTU
, to
tal i
ron
mg/
l
Ferric concn mg/l
Supernatant Turbidity(Hanna)
Supernatant pH
Supernatant Total ironmg/l
Supernatant OrthoPmg/l
Jar tests carried out to establish if Stage 2 dose needed changing
Jar tests at different ferric dose rates
Ferric colouration of supernatant increased up to 15mgl then cleared.
mg/l ferric dose rates5 10 15 20 25 30
Iron (Hachtest kit)
OrthoP(Hach test kit)
Bentley - solids generation at 6mg/l ferric dose
Sampling programme carried out pre and post ferric dosing to determine solids generation from ferric addition
0
50
100
150
200
250
0
10
20
30
40
50
60
Des
ign
so
lids
load
ing
g/m
2/h
r
solid
s lo
adin
g g
/m2
/hr,
flo
w l/
s, T
SS p
re-d
ose
an
d in
flo
c ta
nk
mg
/l
Solids loading onfilter g/m2/hr
Average hourly flow(site data) l/s
TSS at outlet of floctank mg/l
TSS pre ferric dosemg/l
Design solidsloading on filterg/m2/hr
Bentley - Solids generation at 20mg/l ferric dose
0
50
100
150
200
250
0
10
20
30
40
50
60
70
80
90
des
ign
so
lids
load
ing
g/m
2/h
r
solid
s lo
adin
g kg
/m2
/hr,
flo
w l/
s, T
SS p
re-d
ose
an
din
flo
c ta
nks
mg
/l
Solids loadingon filterg/m2/hr
Average hourlyflow (site data)l/s
TSS at outlet offloc tank mg/l
TSS pre ferricdose mg/l
Design solidsloading on filterg/m2/hr
Ferric and caustic dosing
Ferric dosing skid, chemical dosing kiosk, instrumentation kisok and storage tanks
Issues experienced during trials (1)
Seasonal build up of algae on surface
Mecana main unit with microfibre cloth discs, clean surface
Solids build up on surface. Desludgingfrequency, mass balance across unit
Photo of scum on surface at Bentley, not Cirencester
02468101214161820
050
100150200250300350
July
Au
gust
Sep
tem
ber
Oct
ob
er
No
vem
ber
Dec
emb
er
Jan
uar
y
Feb
ruar
y
Mar
ch
turb
idit
y N
TU
b/w
so
lids
mas
s kg
/d
Bentley backwash solids mass removed
Averageb/w solidskg/day
Ave inletturbidityNTU
Bentley - Final effluent totalP results
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
tota
lP m
g/l
targettotalP mg/l
High iron in filtered effluent, reduced ferric dose
jar tests showed higher ferric dose requried - 20mg/l Fe. Reduced effluent iron, and totalP
Mecana solids overload, dosingturned off
Process commissioning/Optimisation
• M&E/ICA commissioning - control modes confirmed, tested and reliable, dosing equipment proven
• Temporary ferric dosing to acclimatise site to ferric• Stage 1 dosing started to target 1mg/l orthoP at final effluent• Stage 2 dosing
– Based on jar tests, may need to be repeated during commissioning– Check need for caustic (pH), checks on filtered iron levels– Be aware of seasonal differences
• Backwash returns– May need to adjust Stage 1 based on ferric returns
• Aim – balancing Stage 1, Stage 2, backwash returns, meeting target interstage orthoP, and FE totalP and iron levels
• NOTE:– optimisation can take weeks to balance– note difference in effluent/ferric reactions between sites
TSS vs TotalP correlation (each site)
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15 20 25 30 35
Tota
lP m
g/l
TSS mg/l
Staveley
Bentley
Cirencester
North Tawton
Linear (Staveley)
Linear (Bentley)
Linear (Cirencester)
Linear (North Tawton)
Final effluent totalP results from each trial
Site
Mecana influent Mecana effluent
OrthoP TotalP TotalP
mg/l mg/l mg/l
North Tawton 0.2 2.4 0.22 (0.12)
Bentley 0.4 1.1 0.17 (0.14)
Staveley 1.2 2.0 0.12 (0.08)
Cirencester 0.5 0.6 0.23 (0.09)
ALL DATA – including periods of failure/non-rep samples (in brackets without failures)
EXTRA HYDROK SLIDES
70
Potential Applications
• TSS Removal (with associated BOD)
• Total P consents
• Pre-filtration for UV-disinfection
• Upgrading lagoon treatment systems
• Storm Sewer overflow rough filtration
• Post-Primary Filtration
• Priority substance removal
• Clean Water Filtration (DWI approval pending)
• Storm Tank Uprating
OPEX
72
Mecana Installations UK
Permanent
Hire/Trial
