journa l homepage: www.e lsev ier .com/ locate /eco leng
ilot-scale study on preserving eutrophic landscape pond waterith a combined recycling purification system
hen Xuechua,∗, Huang Xiaochenb, He Shengbinga, Yu Xiaojuana, Sun Mengjiea,ang Xiaodongc, Kong Hainana
School of Environmental Science and Engineering, Shanghai Jiao Tong University, Dong Chuan Road 800, Shanghai 200240, PR ChinaShanghai East Sea Marine Engineering Survey & Design Institute, Shanghai 200137, PR ChinaWhenzhou Water Supply Company, Wenzhou 325000, PR China
r t i c l e i n f o
rticle history:eceived 15 April 2013eceived in revised form 16 July 2013ccepted 20 September 2013vailable online 31 October 2013
eywords:utrophicationandscape pondecycling purification system
a b s t r a c t
Landscape ponds are vulnerable to eutrophication due to continuous pollutant load from surface run-offand excessive fish feeding. A combined recycling purification system consisting of an aquatic plant filter,bio-zeolite filter, bio-ceramic filter, gravel bed filter, and in situ algal control facility was built to solve thisproblem. The advantage of this system is its ability to preserve landscape pond water quality and controlalgal biomass without periodically refreshing water. A pilot-scale experiment was conducted within anartificial landscape pond. The results suggested that the system performed well in pollutant removal; theremoval efficiencies for SS, TN, NH4
+-N, NO3−-N, NO2
−-N, and PO43−-P were all above 50% at hydraulic
loading rate of 1.2 m/d. The aquatic plant filter performed the best for SS, NH4+-N and phosphorus removal.
The bio-ceramic filter accounted for the primary COD removal. The gravel bed filter built for denitrophi-−
lgal control cation eliminated 60.6% of TN load and 62.0% of NO3 -N load. When the purification system was stopped,
the pond water quality deteriorated rapidly in six days. When the system resumed operation, COD, TP, TNimmediately declined in the landscape area. Additionally, the purification system showed high efficiencyin algal removal. To further understand the algal reduction mechanism, floating plants and the aeratorwere removed. In response, an increase of Chl-a was observed, suggesting that in situ treatment was animportant supplement to the purification system.
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. Introduction
Landscape ponds or lakes, which are usually located in the cen-ral area of urban communities, possess crucial ecosystem serviceunctions. Landscape ponds not only perfect the living conditionf humankind but also benefit the survival of endemic organismsBiggs et al., 2005). Due to continuous accumulation of pollutants,rimarily from surface run-off and excessive fish feeding, the nutri-nt level of pond water will gradually increase. As a result, theandscape ponds usually suffer from eutrophication, and certainmounts of those nutrients will even cause algal blooms.
A common solution to this type of water problem is periodiceplacement of pond water with fresh water. From an ecologicaloint of view, however, such a simple approach exerts a positive
mpact on the ecosystem by significantly reducing endemic plank-on population. Nevertheless, this approach threatens the wateruality of water bodies that receive the discharged water. Given
hese concerns, building a treatment system that can purify andecycle the pond water is the best choice. Currently, the majorityf recycling purification systems usually consists of bio-film unitsChang et al., 2010) or constructed wetlands (Li et al., 2009a), andhese systems are primarily utilized in the field of aquiculture andesigned to remove COD, NH4
+-N, NO2−-N, to ensure the healthy
rowth of aqua-cultural species (Lin et al., 2005, 2010; Sindilariut al., 2009; Konnerup et al., 2011). In contrast to aquaculture pondater, landscape pond water is often micro-polluted, with much
ower pollutant concentration. Although the pollutant concentra-ion in a landscape pond is low, algal blooms may occur due toufficient supply of nutrients and light. When designing recyclingurification systems, multiple objectives should be collectivelyonsidered:
) Removal of nutrients with low concentrations) Control of algal biomass
) Compatibility of introduced system with targeted pond
However, our recent study suggested that a low light condi-ion with sufficient DO accelerates the death rate of algae due to
ignificant respiration consumption of algal biomass. At residenceime of 5 d with treatment of light-shading plus aeration, algaliomass could be reduced by more than 65% with simultaneousater quality improvement. Light-shading plus aeration can be an
ptional measure to improve algal removal in a recycling purifica-ion system (Chen et al., 2009a, 2009b). In this article, we reportednovel recycling purification system that not only preserved land-
cape pond water but also controlled algal biomass. The main ideaehind our design is coupling ecological treatment system withiological treatment system. The entire system consisted of fournits: aquatic plant filter, bio-zeolite filter, bio-ceramic filter, andravel bed filter. Floating plants were introduced into the landscapeond to shade the water surface with their large leaves (Pinto et al.,006; Yeh et al., 2010), and a micro-bubble aerator was installed
n pond to aerate and mix the water. A pilot-scale experiment wasonducted to test and verify such combinations and evaluate itserformance and removal mechanisms.
. Material and methods
.1. Landscape pond and purification system
The landscape pond, totaling 4 m2, was wrapped in a woodentructure, waterproofed with high-density polyethylene fabric,ivided into two functional areas: landscape and recycling purifi-ation system (Fig. 1). The landscape area was the main part ofhe pond. The landscape area measured approximately 40 cm deepnd occupied approximately 3.5 m2, with a total water volume of.4 m3. The relative ratio of water volumes between the “landscapeond” and the “purification system” under normal running situa-ion is 1.4 m3:0.288 m3. The bottom was filled with 5 cm height ofeo-lite and gravel. Approximately 40 goldfish ranging from 8 to0 cm long were raised as ornament fish, with Bellamya Aeruginosas benthic organisms. To enrich the diversity of landscape, somemergent plants, such as Pontederia cordata and Cyperus Alterni-olius, were planted in the landscape area.
The combined recycling purification system was situated in theecond area; each unit consisted of a 0.3 m × 0.4 m × 0.6 m open-outhed PVC box. The first unit was aquatic plant filter, filled with
0 cm of gravels and 5 Myriophyllum Verticillatum. It was expectedhat when water passed through the aquatic plant filter, large sus-ended particles, such as redundant fish baits, could be capturedy the root system of aquatic plants and then precipitate (Li et al.,009; Song et al., 2009). The overall depth of water for this unit wasontrolled below 0.55 m. The second unit consisted of a bio-zeolitelter designed to absorb NH4
+-N (Albuquerque et al., 2009; Dant al., 2011; Lee and Scholz, 2007; Ou et al., 2006; Tuncsiper, 2009)nd capture SS by contact precipitation. The second unit was filledith 5–8 cm diameter natural zeolite and covered with Hydrocotyle
ulgaris. The overall depth of water in this unit should not exceed.5 m. The third unit consisted of a bio-ceramic filter to provide anerobic condition for micro-organism growth and allow for CODemoval and nitrification through contact with the surface of theeramic (Sang et al., 2003). An aeration device was installed at theottom, and P. cordata was planted on its surface. The water level
n this unit was controlled below 0.45 m. The last unit consisted ofgravel bed filter, filled with 1–2 cm diameter gravel. Calamus waslanted on its surface. The water level was maintained under 0.4 m.hese four units were connected to form an entire system.
.2. System operation
Fish baits were the main source of pollution in this landscapeond. During the experiments, approximately 10–12 g fish baits
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ering 61 (2013) 383–389
ere added into the water each day. The polluted landscape pondater was pumped into the combined recycling purification sys-
em, flowed through the aquatic plant filter, bio-zeolite filter,io-ceramic filter and gravel bed filter, and returned to the land-cape pond by gravity. The results of our preliminary study indicatehat the main hydraulic loading rate of the purification system wasept at 1.2 m/d with a hydraulic retention time approximately 6 h.ue to natural vaporization, the water level would slowly reduceuring the experiment period. When the water level decreased to
ower than 35 cm, tap water was added to maintain the water levelt approximately 40 cm.
The experiments were conducted in three stages. Stage 1 lastedrom late February to early April 2010. During this period, theurification system continually operated for 55 days. Stage 2 waserformed in late April, followed by stage 3 through late May. Stageonly lasted for 6 days, and the purification system was out of
peration for the balance of time. Stage 3 lasted for 40 days; at theeginning of stage 3, the purification system was restarted, and sixymphaea tetragonas and a micro-bubble aerator were introduced
nto the landscape area.
.3. Water sample and analysis
Grab water samples were taken from water in landscape areand the influent and effluent of each unit (Fig. 1). The samplingypically was performed at approximately 9–10 a.m. The samplesere analyzed for SS, TP, TN, COD and chlorophyll a, while filtered
amples were analyzed for NH4+-N, NO3
−-N, NO2−-N, and PO4
3−-. All analytical measurements were taken according to Standardethods (APHA et al., 1995). To evaluate the performance of the
urification system, several variables, including pollutant load, pol-utant removal, removal efficiency, and removal of loading, werealculated according to methods reported in previous studies (Lint al., 2005; Juang et al., 2008).
The specific decreasing rate of algal biomass could be calculateds Eq. (1) (Reynolds, 2006):
t = Rr − Rg (1)
ere Rr denotes the specific alga growth rate within pond water, Rg
enotes the specific reduction rate in the purification system, andt denotes the specific rate of algal biomass decrease.
. Results and discussion
.1. Removal capacity of purification system and its units
A steady state was achieved after 25 days of operation, and theemoval efficiency in the four units remained almost constant forhe following 30 days. The concentrations of pollutants in influentnd effluents were averaged, and the values of pollutant load, pol-utant removal, removal efficiency, and removal of pollutant load
ere calculated to confirm the removal performance of differentnits. The removal performance of the purification system and eachreatment unit are summarized in Table 1. In general, the purifica-ion system performed well for pollutant removal, and the removalfficiencies of SS, TN, NH4
+-N, NO3−-N, NO2
−-N, and PO43−-P all
xceeded 50% at a hydraulic loading rate of 1.2 m/d. To purify lakeater or pond water, natural systems such as marsh wetlands could
nly obtain similar removal efficiencies with much lower hydraulicoading rates, such as 0.2 m/d (De Ceballos et al., 2001; Coveneyt al., 2002). On the other hand, constructed wetland systems and
ravel contact oxidation treatment systems reportedly treat micro-olluted water at a hydraulic loading rate reaching 1.2 m/d, butheir performance in nutrient removal was limited, especially forN and NO3
−-N (Dan et al., 2011; Konnerup et al., 2011; Juang et al.,
008; Ou et al., 2006). Thus, the relative high hydraulic loading ratend high nitrogen removal efficiency are two main advantages ofhis purification system.
.2. Removal of SS and COD
According to the average values summarized in Table 1, allreatment units, except the bio-ceramic filter, showed SS removal.s anticipated, the aquatic plant filter, which was designed toapture large suspended particles with its root, appeared to behe major remover in the three units. The aquatic plant filteraptured 38.0% of SS load, with an average removal efficiencyf 28.3%. The other two filter units removed lower percent-ges of SS, but removal efficiency remained relatively high. Anfficient SS filtration by the aquatic plant filter was crucialo prevent clogging; no clogging occurred in our later experi-
ent.The bio-ceramic filter accounted for the main removal of COD.
he bio-ceramic filter could remove 50.9% of COD load with aean removal efficiency of 23.3%. This result suggested forma-
ion of a suitable condition for aerobic biodegradation. The secondajor pathway for COD removal was the aquatic plant filter.pproximately 21.8% of COD load was eliminated, and the aver-ge removal efficiency was approximately 8.5%. COD removal byquatic plant filter might relate to its high SS removal capac-ty because influent SS primarily consisted of organic matters,
specially fish baits. This possibility could be proved by a highorrelation of COD and SS removal within aquatic plants (Pear-on’s R = 0.756, P < 0.01). Comparatively, bio-zeolite filter and graveled filter showed a low COD removal capacity because these
oNNm
able 1emoval performance of the whole purification system and each treatment unit at stage
wo units tended to form anaerobic conditions that inhibit CODiodegradation.
.3. Removal of nutrients
According to Table 1, the gravel bed filter had the best nitro-en removal performance in the experiment. Approximately 60.6%f TN load and 62.0% of NO3
− load were eliminated by the graveled filter, suggesting that denitrification was successfully achieved.pproximately 29.9% of NH4
+-N load was removed, and the meanemoval efficiency of 23.5%, indicating that emergent plant assimi-ation performed well. As suggested by previous research, a graveled filter with no aeration could form a proper oxidation–reductionondition for denitrification (Kadlec and Knight, 1996; Lee et al.,009). However, such filters are usually inefficient due to a lack ofarbon sources (Headley et al., 2005; Saeed and Sun, 2012). Consid-ring this problem, our purification system filled the gravel bedlter with small grain-size gravel and placed this filter in the lastnit. Small particles that escaped the former units were primarilyaptured by the gravel bed filter. Those particles containing algaend tiny remnant bait are fairly good carbon sources for oxidation-eduction processes. Additionally, the gravel bed filter was plantedith Calamus, and this emergent plant effectively produced carbon
ources and assimilated NH4+-N (Trang et al., 1993; Saeed and Sun,
012).The aquatic plant filter exhibited an appreciable nitrogen
emoval capacity. Approximately 31.5% of TN load and 23.8%
f NO3-N load were eliminated by the aquatic plant filter.otably, the aquatic plant filter was the most efficient at NH4
+-removal, removing approximately 41.3% of NH4
+-N load, with aean removal efficiency of 24.6%. Three mechanisms explain the
itrogen removal in the aquatic plant filter, including assimila-ion of dissolved nitrogen (Li et al., 2009a, 2009b; Ou et al., 2006),enitrification of nitrate (Yeh et al., 2010), and sedimentation ofarticulate nitrogen (Jorgensen et al., 1995). Table 1 indicates thathe removal of NO3-N accounted for 50.3% of the total removal ofitrogen and 38.7% of NH4
+-N. Comparatively, removal of NO2−-N
as relatively small; only 1.1% of total nitrogen was removed. A fur-her calculation showed that no less than 9.9% of TN was removedy sedimentation, suggesting that sedimentation was not the mainathway. We deduced that denitrification might not be significant
n the aquatic plant filter due to the short retention time of 2 h.revious studies on natural treatment systems indicate that deni-rification usually requires a relatively long retention time, such as
day. Given a short retention time of only 2 h, we deduced thatenitrification was not the driving force in the aquatic plant filterDe Ceballos et al., 2001; Tuncsiper, 2007; White, 1995).
The bio-zeolite filter, which was designed to absorb NH4+-N,
emoved 18.2% of NH4+-N load, with an average removal efficiency
f 11.2%. The bio-zeolite filter removal of NH4+-N was not signifi-
ant as expected. This result might be attributed to the low NH4+-N
oncentration in influent, which would limit the adsorption abilityf bio-zeolite. The bio-zeolite filter showed a high removal capac-ty of TN and NO3-N, eliminating approximately 29.9% of TN loadnd 29.8% of NO3-N load. Denitrification could occur when theeolite offered large surface for attached-growth of denitribacte-ia, and organic matters captured by the filter could be the mainarbon sources (Cooper et al., 1996; Saeed and Sun, 2012). H. vul-aris assimilation could also contribute to nitrogen removal (Dant al., 2011; Lee and Scholz, 2007; Ou et al., 2006; Tuncsiper, 2009)n this experiment.
The bio-ceramic oxidation filter effectively removed influentH4
+-N, but did not contribute to TN removal. The effluent TNnd NO3
−-N increased by 18.4% and 18.3%, respectively, follow-ng treatment by the bio-ceramic oxidation filter. The increase ofN and NO3
−-N related to the biodegradation of particulate organicatter in bio-ceramic filter, and the nitrogen within the particulate
rganic matter generally released during the hydrolysis process.Particulate phosphorus was the main component of TP; notice
hat PO43-P only accounted for 27.1% of TP in the influent,
nd we assumed that most phosphorus was removed through
Tb
r
ndscape land.
edimentation and filtration (Li et al., 2009a; Ou et al., 2006). Thisssumption was confirmed by a high positive correlation of TPnd SS removal within different units (Pearson’s R = 0.649, P < 0.01).quatic plant filter was the majority of phosphorus in the first unit,nd approximately 58.4% of TP load and 68.4% of PO4
3−-P load wereemoved by the first unit. After the aquatic plant filter treatment,he effluent PO4
3−-P was lower than 0.01 mg/L and approached theetection limit, so we did not present the PO4
3−-P removal capacityf the other units in Table 1. After purification system treatment,ffluent phosphorus was as low as 0.032 mg/L.
.4. Restoration of pond water quality with purification system
Following steady system operation for more than 30 days, theater quality in landscape area was good, as indicated by COD as
ow as 30 mg/L, TP 0.067 mg/L, and TN 0.51 mg/L. Then, we stoppedhe system and observed the variation in pond water quality. Asuggested by Fig. 3, the water quality deteriorated rapidly in theollowing six days. On the sixth day, COD reached 99 mg/L, TP.13 mg/L, and TN 2.6 mg/L. The water color turned light brown,nd the transparency plummeted lower than 20 cm. Then, weperated the purification system to restore the water quality. Aubstantial decline of COD, TP, TN in landscape area occurred imme-iately after the purification system was restarted. On the 29th day,OD decreased to 47 mg/L, and TP and TN reached 0.036 mg/L and.31 mg/L, respectively—even lower than the end of stage one. Theond water turned transparent, and the bottom of the pond wasasily observed.
The profiles of influent and effluent concentrations of major pol-utants within the purification system are shown in Figs. 2 and 3.fter the system was restarted, a steady reduction of COD wasbserved, and removal efficiency remained above 18%. On the 12thay, influent COD gradually decreased from 90.0 mg/L to 65.0 mg/L.otably, no decrease in removal efficiency was observed despite
he decrease in influent COD. Instead, COD removal efficiency grad-ally increased from 21.1% to 43.7% during the following 11 days.
his phenomenon could be explained by biofilm growth in theio-ceramic filter, which enhanced COD removal.
The TN variation trend was similar to COD. A continuous TNeduction was observed during the experiment, indicating that the
X. Chen et al. / Ecological Engine
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Fig. 3. Variation of water quality in landscape area.
ystem performed well in denitrification. In response, influent TN
radually decreased from 1.5 to 0.6 mg/L, and effluent TN decreasedrom 1.2 to 0.1 mg/L. The TN removal efficiency gradually increasedrom 17.3% to 81.8% at the end of experiment (stage 3). The increasen removal efficiency might be primarily attributed to the growth
iimc
Fig. 4. Removal of pollutants
ering 61 (2013) 383–389 387
f denitrifying bacteria in the gravel bed filter (Lu et al., 2009).otably, such TN removal efficiency was much higher than thealue obtained at the steady state condition (stage 1). A possiblexplanation would be the influence of temperature on denitrifica-ion. The first experiment (stage 1) was conducted in early spring,hereas the second experiment (stage 3) started in mid April, when
he water temperature was much higher.The phosphorous (TP) concentration ranged from 0.064 mg/L to
.04 mg/L in influent and 0.028 mg/L to 0.04 mg/L in effluent (Fig. 3).he system maintained reduction efficiencies from 30% to 43.8%uring the experiment. Effluent TP did not obviously decrease, andhe removal efficiency appeared to be relatively stable comparedo COD and TN (Figs. 4 and 5).
.5. Control of algal biomass
After the system was halted, a significant increase of algaliomass was observed. Within six days, Chl-a in the landscape area
ncreased exponentially from 15.9 �g/L to 57.2 �g/L, with a specificlgal growth rate between 0.19 d−1 to 0.24 d−1. Then, the purifi-ation system was restarted. N. tetragonas floating plants were
ntroduced to the landscape pond, and a micro-bubble aerator wasnstalled to aerate and mix the water. At the beginning, approxi-
ately 23% of water surface was covered by floating plants, andoverage rate at the end was approximately 40%. We introduced
by purification system.
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Fig. 5. Removal of Chl.
his in situ treatment because our previous studies suggested thatight-shading plus aeration could efficiently inhibit algae growthChen et al., 2009a, 2009b).
A substantial decline of algal biomass in the landscape areaccurred immediately after the purification system was restarted.hl-a in pond water exponentially decreased from 63.1 �g/L to2.1 �g/L in 17 days, with a specific deceasing rate between.07 d−1 and 0.12 d−1. Additionally, the purification system showedChl-a removal of approximately 40–50%. At the beginning of thexperiment, the influent Chl-a was approximately 60.4 �g/L, andhe effluent Chl-a was reduced to 35.1 �g/L with a removal effi-iency of 41.9%. Since then, the removal efficiency remained almosthe same, but a significant decline in influent Chl-a was observed.his outcome suggested an effective algal biomass reduction by theurification system.
However, another explanation contributed to the reduction oflgal biomass in the pond water. Because the algal biomass wasnfluenced by both reduction process and growth process. Althoughhe purification system removal efficiency reached as high as 50%,nly 40% of total water quantity went through the purification sys-em each day. Therefore, the maximal specific reduction rate oflgal biomass within the purification system was approximately.20 d−1. The specific algal growth rate stayed between 0.19 d−1
nd 0.24 d−1, as previously suggested. The specific rate of decreaseithin the pond, calculated according to equation Eq. (1), was noore than 0.04 d−1. However, this value was much lower than our
bservations during the purification period, indicating that anotherechanism might also regulate algal biomass.To further understand the algal reduction mechanism, we
emoved the floating plants and the aeration aerator. The purifi-ation system still worked well, but an increase of Chl-a in theandscape area was observed in the following days. When thexperiment ended on the 39th day, the value was approximately3.4 �g/L—nearly two times greater than the in situ treatmentalue. Floating plants and aeration clearly acted as important sup-lements to the purification system and improved algal controlerformance.
. Conclusion
The purification system performed well in pollutant removal,+ − −
nd the removal efficiencies of SS, TN, NH4 -N, NO3 -N, NO2 -
, and PO43−-P were all above 50%, with a hydraulic loading
ate of 1.2 m/d. The aquatic plant filter appeared to mostfficiently remove SS and captured approximately 38.0% of SS load.
J
ering 61 (2013) 383–389
he bio-ceramic filter removed most COD and accounted for 50.9%f COD load. The gravel bed filter that was built for denitrifica-ion eliminated 60.6% of TN load and 62.0% of NO3
− load. Theio-ceramic filter made no contributions to TN removal, and theffluent TN and NO3
− increased by 18.4% and 18.3%, respectively.quatic plant filter appeared to be the best at NH4
+-N removal andemoved approximately 41.3% of the NH4
+-N load. Additionally,he aquatic plant filter was located in the main pool of phosphorusnd removed approximately 58.4% of TP load and 68.4% of PO4
3−-Poad.
When the purification system was halted, the pond water qual-ty rapidly deteriorated in six days. When the purification system
as restarted, COD, TP, TN in the landscape area immediately andubstantially declined. The purification system exhibited a steadyeduction of COD, and removal efficiency increased from 21.1% to3.7% during 11 days. The system performed well in denitrification,nd the TN removal efficiency increased from 17.3% to as high as1.8% at the end of experiment. TP reduction efficiencies from 30%o 43.8% were maintained.
Floating plants and a micro-bubble aerator were added tomprove the algal control performance. Chl-a in landscape areaxponentially decreased from 63.1 �g/L to 12.1 �g/L over 17 days.he purification system demonstrated the ability to remove algae,ith a Chl-a removal efficiency of approximately 40–50%. Theoating plants and the aeration aerator were removed to furthernderstand the reduction mechanism. In response, an increasef Chl-a was observed, suggesting that in situ treatment was anmportant purification system supplement.
cknowledgements
The present work was supported by the National Scienceoundation of China under Grant No. 41001361, the Programor Wenzhou Sci & Tech bureau Foundation under Grant No.20080024, the Program for New Century Excellent Talents in Uni-ersity under Grant No. NCET-11-0320.
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