Soluble Reactive Phosphorus Removal Research Articles

Variation in extracellular enzyme activities and their influence on the performance of surface-flow constructed wetland microcosms (CWMs)

Eight constructed wetland microcosm (CWM) units have been designed using three macrophytes for domestic wastewater treatment. The main aim of this study is to evaluate enzyme activities with respect to time and soil depth and their correlation with removal efficiency of pollutants within different CWM units. The findings of this study show that the activity of enzymes and pollutants removal efficiency vary to a great extent on the soil depth, time of the sampling and type of pollutants. The correlation between removal of soluble reactive phosphorus and total phosphorus was significant with phosphatase activity in most of the CWM units. Activity of urease and NH4+-N removal was positively correlated with significant positive correlation in CWM units planted with Phragmites karka, and Pistia stratiotes (Ph + Pi) and Typha latifolia, Phragmites karka and Pistia stratiotes (T + Ph + Pi). Urease activity was found to be both positively and negatively correlated with respect to removal of NO3−-N and NO2−-N in different CWM units. Dehydrogenase activity showed negative correlation with respect to biological oxygen demand (BOD) removal except in CWM units with Ph + Pi and T + Ph + Pi. Similarly, a moderate positive and negative correlation exists between fluorescein diacetate hydrolysis and BOD removal. Removal of BOD and microbial biomass carbon (MBC) was negatively correlated with each other in most of the CWM units. With respect to vertical variation, the top layer of CWM units expressed significantly higher activity of extracellular enzymes and were significantly different from the deeper layer. CWM units exhibited significant variations in enzyme activity with respect to time.

Approaches for phosphorus removal with calcium hydroxide and floating macrophytes in a mesocosm experiment: impacts on plankton structure

Cultural eutrophication has promoted the application of several mitigation strategies in the last 50 years. In this study we tested the combined effects of two techniques: calcium hydroxide [(Ca(OH)2), lime] and a free-floating macrophyte (Salvinia rotundifolia Willd) to examine the soluble reactive phosphorus removal capability and the effects on plankton (phytoplankton and zooplankton) structure in a in situ lake mesocosms experiment. The experiment lasted 10 days (n = 12, 500 l each) with a control and three treatments (lime (CH), plants (FM), and the combination of both (CH + FM)). Samples of several physical and chemical variables (including nutrients) and phytoplankton were taken at the beginning, 2 days after, 4 days, and 10 days (end of the experiment). Zooplankton was sampled at the beginning and at the end. The highest depletion effect of soluble reactive phosphorus (SRP) was observed in presence of lime. Phytoplankton biovolume was highly and negatively affected in lime treatments (CH and CH + FM). Zooplankton changed from Rotifera to Cladocera and Copepoda in presence of macrophytes. We conclude that lime + plants reduces more effectively SRP, phytoplankton biovolume and promotes herbivorous zooplankton development; becoming by this way, in a suitable mitigation strategy to be explored in future field manipulation studies.

Nitrogen and phosphorus removal and Typha domingensis tolerance in a floating treatment wetland

The aim of this work was to study the efficiency of microcosms-scale floating treatment wetlands (FTWs) in the N and P removal from a synthetic runoff effluent and to evaluate the effluent tolerance of Typha domingensis. Each FTW consisted of a raft constructed with a plastic net where T. domingensis plants were installed. In order to evaluate the plant role, reactors with FTWs and without FTWs (controls) were used. P and N additions were carried out as follows: 5 mg L−1 P (P5 and P5-control); 10 mg L−1 N (N10 and N10-control); 5 mg L−1 P + 10 mg L−1 N (P5N10 and P5N10-control). Also, a biological control (B-control) without contaminant addition was used. The removal of soluble reactive phosphorus and total phosphorus were significantly higher in the FTWs than in the controls. Ammonium and nitrate concentrations were not significantly different between FTWs and controls at the end of the experiment. However, nitrate concentrations showed significant differences between FTWs and controls during the experiment. N and P were mainly accumulated in plant tissues and not in the sediment. Plants tolerated the effluent conditions and showed a positive growth rate. The use of FTWs is a promising strategy for the sustainable treatment of water bodies affected by runoff waters.

Experimental study and simulation of phosphorus purification effects of bioretention systems on urban surface runoff.

Excessive phosphorus (P) contributes to eutrophication by degrading water quality and limiting human use of water resources. Identifying economic and convenient methods to control soluble reactive phosphorus (SRP) pollution in urban runoff is the key point of rainwater management strategies. Through three series of different tests involving influencing factors, continuous operation and intermittent operation, this study explored the purification effects of bioretention tanks under different experimental conditions, it included nine intermittent tests, single field continuous test with three groups of different fillers (Fly ash mixed with sand, Blast furnace slag, and Soil), and eight intermittent tests with single filler (Blast furnace slag mixed with sand). Among the three filler combinations studied, the filler with fly ash mixed with sand achieved the best pollution reduction efficiency. The setting of the submerged zone exerted minimal influence on the P removal of the three filler combinations. An extension of the dry period slightly promoted the P purification effect. The combination of fly ash mixed with sand demonstrated a positive purification effect on SRP during short- or long-term simulated rainfall duration. Blast furnace slag also presented a positive purification effect in the short term, although its continuous purification effect on SRP was poor in the long term. The purification abilities of soil in the short and long terms were weak. Under intermittent operations across different seasons, SRP removal was unstable, and effluent concentration processes were different. The purification effect of the bioretention system on SRP was predicted through partial least squares regression (PLS) modeling analysis. The event mean concentration removal of SRP was positively related to the adsorption capacity of filler and rainfall interval time and negatively related to submerged zones, influent concentration and volume.

Scaling Dissolved Nutrient Removal in River Networks: A Comparative Modeling Investigation

AbstractAlong the river network, water, sediment, and nutrients are transported, cycled, and altered by coupled hydrological and biogeochemical processes. Our current understanding of the rates and processes controlling the cycling and removal of dissolved inorganic nutrients in river networks is limited due to a lack of empirical measurements in large, (nonwadeable), rivers. The goal of this paper was to develop a coupled hydrological and biogeochemical process model to simulate nutrient uptake at the network scale during summer base flow conditions. The model was parameterized with literature values from headwater streams, and empirical measurements made in 15 rivers with varying hydrological, biological, and topographic characteristics, to simulate nutrient uptake at the network scale. We applied the coupled model to 15 catchments describing patterns in uptake for three different solutes to determine the role of rivers in network‐scale nutrient cycling. Model simulation results, constrained by empirical data, suggested that rivers contributed proportionally more to nutrient removal than headwater streams given the fraction of their length represented in a network. In addition, variability of nutrient removal patterns among catchments was varied among solutes, and as expected, was influenced by nutrient concentration and discharge. Net ammonium uptake was not significantly correlated with any environmental descriptor. In contrast, net daily nitrate removal was linked to suspended chlorophyll a (an indicator of primary producers) and land use characteristics. Finally, suspended sediment characteristics and agricultural land use were correlated with net daily removal of soluble reactive phosphorus, likely reflecting abiotic sorption dynamics. Rivers are understudied relative to streams, and our model suggests that rivers can contribute more to network‐scale nutrient removal than would be expected based upon their representative fraction of network channel length.

Phosphorus Removal in Constructed Stormwater Wetland Mesocosms Amended with Water Treatment Residuals.

Constructed stormwater wetlands (CSWs) reduce stormwater volume and improve water quality. One quality improvement is the removal of soluble reactive phosphorus (SRP). There has been limited study on SRP fate and transport or on the mechanisms to improve SRP removal due to the difficulty in quantifying the complex, spatially heterogeneous removal processes in two-dimensional flow. The present research analyzed the ability of wetland soil (Control) and wetland soil amended with 2%, 5%, and 8% (by mass) of aluminum-based water treatment residuals (AlWTRs) to remove SRP in surface-flow vegetated CSW mesocosms. Batch adsorption experiments showed increasing SRP sorption capacity with increased AlWTR content (590-850 mg/kg soil) compared to the Control (385 mg/kg soil); however, AlWTR-amended flowing mesocosms removed only 6.0-8.8 mg/kg SRP compared to 9.3 mg/kg SRP for the Control. The lack of increased SRP removal in AlWTR-amended mesocosms was attributed to flow dynamics (only 20% of the surface outflow was quantified as subsurface flow). These results suggest the extent of infiltration versus surface flow is key to soil amendments improving SRP removal in a CSW.

Phosphorus Speciation and Treatment Using Enhanced Phosphorus Removal Bioretention

This field research investigated the water quality performance of a traditional bioretention cell retrofitted with 5% (by mass) water treatment residual (WTR) for enhanced phosphorus removal. Results indicate that WTR incorporation into the bioretention media does not negatively influence the infiltration mechanism of the bioretention system. Total suspended solids (TSS), total phosphorus (TP), and particulate phosphorus (PP) concentrations in runoff inflow were significantly reduced compared to outflow due to filtration of particulate matter. TP concentrations were significantly reduced by the bioretention cell; before WTR retrofit TP export occurred. Although net removal of soluble reactive phosphorus (SRP) and dissolved organic phosphorus (DOP) from incoming runoff was not found, leaching of dissolved phosphorus (DP) was prevented not only from incoming runoff, but also from the media and captured PP. Near constant outflow SRP and DOP concentrations suggest an equilibrium adsorption treatment mechanism. Both event mean concentrations and mass loads were reduced for TSS and all P species. Pollutant mass removals were higher than the event mean concentration removals due to the attenuation of volume by the bioretention media.

STELLA software as a tool for modelling phosphorus removal in a constructed wetland employing dewatered alum sludge as main substrate

A dynamic simulation model was developed for the removal of soluble reactive phosphorus (SRP) from the vertical flow constructed wetlands (VFCW) using a dynamic software program called STELLA (structural thinking, experiential learning laboratory with animation) 9.1.3 to aid in simulating the environmental nature and succession of relationship between interdependent components and processes in the VFCW system. In particular, the VFCW employed dewatered alum sludge as its main substrate to enhance phosphorus (P) immobilization. Although computer modelling of P in treatment wetland has been well studied especially in recent years, there is still a need to develop simple and realistic models that can be used for investigating the dynamics of SRP in VFCWs. The state variables included in the model are dissolved phosphorus (DISP), plant phosphorus (PLAP), detritus phosphorus (DETP), plant biomass (PLBI) and adsorbed phosphorus (ADSP). The major P transformation processes considered in this study were adsorption, plant and microbial uptake and decomposition. The forcing functions which were considered in the model are temperature, radiation, volume of wastewater, P concentration, contact time, flow rate and the adsorbent (i.e., alum sludge). The model results revealed that up to 72% of the SRP can be removed through adsorption process whereas the uptake by plants is about 20% and the remaining processes such as microbial P utilization and decomposition, accounted for 7% SRP removal based on the mass balance calculations. The results obtained indicate that the model can be used to simulate outflow SRP concentration, and it can also be used to estimate the amount of P removed by individual processes in the VFCW using alum-sludge as a substrate.

Nutrient transport within three vegetative treatment areas receiving silage bunker runoff

Silage bunker runoff can be a very polluting substance and is increasingly being treated by vegetative treatment areas (VTAs), but little information exists regarding nutrient removal performance of systems receiving this wastewater. Nutrient transport through the shallow subsurface of three VTAs (i.e. one VTA at Farm WNY and two VTAs at Farm CNY) in glaciated soils containing a restrictive layer (i.e., fragipan) was assessed using a mass balance approach. At Farm WNY, the mass removal of ammonium was 63%, nitrate was 0%, and soluble reactive phosphorus (SRP) was 39%. At Farm CNY, the mass removal of ammonium was 79% in the West VTA, but nitrate and SRP increased by 200% and 533%, respectively. Mass removal of ammonium was 67% in the East VTA at Farm CNY; nitrate removal was 86% and SRP removal was 88%. The East VTA received a much higher nutrient loading, which was attributed to a malfunctioning low-flow collection apparatus within the settling basin. Results demonstrate that nutrient reduction mechanisms other than vegetative uptake can be significant within VTAs. Even though increases in nitrate mass were observed, concentrations in 1.65m deep wells indicated that groundwater impairment from leaching of nitrate was not likely. These results offer one of the first evaluations of VTAs treating silage bunker runoff, and highlight the importance of capturing concentrated low flows in VTA systems.

Comparison of phosphorus removal between vertical subsurface flow constructed wetlands with different substrates

AbstractPhosphorus removal by constructed wetlands is a key strategy in diffuse pollution control. Phosphorus retention by experimental unplanted vertical‐flow constructed wetlands depends on substrate, influent quality and hydraulic residence time (HRT). The maximal phosphorus adsorption capacities of shale, gravel, ironstone and hornblende were 619.7, 89.05, 324.9 and 153.1 mg/kg, respectively, when the grain size ranged between 0.5 and 1.0 mm. Phosphorus adsorption capacities of shale, ironstone and hornblende were best explained by Langmuir adsorption isotherms. In comparison, Freundlich adsorption isotherms fitted gravel well. In separate column experiments with eutrophic Jin River water, shale showed better soluble reactive phosphorus (SRP) and total phosphorus (TP) retention performances than gravel, ironstone and hornblende. When the HRT was 2.2 days, the mean SRP removal rates were 96.7, 21.1, 33.6 and 33.0% for shale, gravel, ironstone and hornblende, respectively. Findings indicate that both SRP and TP removal rates increased when the HRT was prolonged.

Growth and Contaminant Removal Effect of Several Plants in Constructed Wetlands

The aim of the present study is to probe the relation between plant growth and its decontamination effect in constructed wetlands. Four species were studied in the small-scale mono-cultured constructed wetlands, which were fed with domestic wastewater. Plant growth indexes were correlated with contaminant removal performance of the constructed wetlands. Wetlands planted with Cyperus flabelliformis Rottb. showed the highest growth indexes such as shoot growth, biomass, root activity, root biomass increment, and the highest contaminant removal rates, whereas wetlands planted with Vetiveria zizanioides L. Nash had the lowest growth indexes and the lowest removal rates. Above-ground biomass and total biomass were significantly correlated with ammonia nitrogen removal, and below-ground biomass with soluble reactive phosphorus removal. Photosynthetic rate had higher correlation with nitrogen removal in these species. Root activity and root biomass increment was more correlated with 5 d biochemical oxygen demand removal. Chemical oxygen demand removal had lower correlations with plant growth indexes. All four species had higher removal rates in summer and autumn. The results suggest that the effect of plant growth on contaminant removal in constructed wetlands were different specifically in plants and contaminants.

Influence of suspended clay on phosphorus uptake by periphyton

We investigated the effect of suspended clay upon the phosphorus uptake rate exhibited by lotic periphyton communities. Suspended inorganic clays and periphyton are common to aquatic environments, and both can strongly influence physical and chemical water conditions. We used replicated artificial stream channels to test the prediction that suspended clay particles would affect the uptake of soluble reactive phosphorus (SRP) by periphyton. Commercially available kaolinite and bentonite clays were characterized for their aqueous suspension behavior and affinities for SRP. Periphyton was grown in a recirculating stream system and subjected to simultaneous suspended clay and SRP additions. SRP removal from solution, both in the presence and absence of suspended clays, was used to quantify SRP uptake parameters by periphyton. Clay type and concentrations of 20, 80, and 200 mg l−1 had no significant effect upon SRP uptake rate exhibited by periphyton during three 90-min experiments. Less than 1% of SRP removal was attributable to the suspended clay load or artificial stream construction materials, based on clay isotherm data and material sorption studies, indicating that 99% of SRP removal was attributable to biotic uptake. Removal of SRP (as KH2PO4) was described by a first-order equation with rate constants ranging between 0.02 and 0.14 min−1. Our results suggest that high turbidity conditions caused by suspended mineral clays have little immediate effect upon SRP removal from the water column by periphyton.

Assessment of the nutrient removal performance in integrated constructed wetlands with the self-organizing map

The self-organizing map (SOM) model was applied to predict outflow nutrient concentrations for integrated constructed wetlands (ICWs) treating farmyard runoff. The SOM showed that the outflow ammonia-nitrogen concentrations were strongly correlated with water temperature and salt concentrations, indicating that ammonia-nitrogen removal is effective at low salt concentrations and comparatively high temperatures in ICWs. Soluble reactive phosphorus removal was predominantly affected by salt and dissolved oxygen concentrations. In addition, pH and temperature were weakly correlated with soluble reactive phosphorus removal, suggesting that soluble reactive phosphorus was easily removed within ICWs, if salt concentrations were low, and dissolved oxygen, temperature and pH values were high. The SOM model performed very well in predicting the nutrient concentrations with water quality variables such as temperature, conductivity and dissolved oxygen, which can be measured cost-effectively. The results indicate that the SOM model was an appropriate approach to monitor wastewater treatment processes in ICWs.

Laboratory investigation of the phosphorus removal (SRP and TP) from eutrophic lake water treated with aluminium

Mechanisms involved in phosphorus (P) removal from eutrophic lake water with aluminium (Al) were assessed by jar tests. For this purpose, eutrophic lake water enriched with soluble reactive phosphorus (SRP), algae or sediments in order to mimic the various conditions found in shallow eutrophic lakes was studied. Total phosphorus (TP) removal was reached after floc settling, the maximal TP removal efficiency (90–95%) was obtained for an Al concentration ranging from 2 to 5 mg L −1, depending on the organic matter (OM) origin (algae or sediments). Algae appeared to limit macro-floc formation (those able to settle). In contrast, in the presence of sediments, macro-floc formation was favoured at low Al dose (2–3 mg L −1 Al). High SRP removal was obtained with the lowest Al dose (1 mg L −1 Al) and remained greater than 60% for an SRP concentration up to 350 μg L −1. SRP removal was not influenced by the OM origin. The experimental data and literature were used to suggest a hypothetical model for floc formation and P removal with Al under the conditions observed in treated lakes.

Sewage-effluent phosphorus: A greater risk to river eutrophication than agricultural phosphorus?

Phosphorus (P) concentrations from water quality monitoring at 54 UK river sites across seven major lowland catchment systems are examined in relation to eutrophication risk and to the relative importance of point and diffuse sources. The over-riding evidence indicates that point (effluent) rather than diffuse (agricultural) sources of phosphorus provide the most significant risk for river eutrophication, even in rural areas with high agricultural phosphorus losses. Traditionally, the relative importance of point and diffuse sources has been assessed from annual P flux budgets, which are often dominated by diffuse inputs in storm runoff from intensively managed agricultural land. However, the ecological risk associated with nuisance algal growth in rivers is largely linked to soluble reactive phosphorus (SRP) concentrations during times of ecological sensitivity (spring/summer low-flow periods), when biological activity is at its highest. The relationships between SRP and total phosphorus (TP; total dissolved P + suspended particulate P) concentrations within UK rivers are evaluated in relation to flow and boron (B; a tracer of sewage effluent). SRP is the dominant P fraction (average 67% of TP) in all of the rivers monitored, with higher percentages at low flows. In most of the rivers the highest SRP concentrations occur under low-flow conditions and SRP concentrations are diluted as flows increase, which is indicative of point, rather than diffuse, sources. Strong positive correlations between SRP and B (also TP and B) across all the 54 river monitoring sites also confirm the primary importance of point source controls of phosphorus concentrations in these rivers, particularly during spring and summer low flows, which are times of greatest eutrophication risk. Particulate phosphorus (PP) may form a significant proportion of the phosphorus load to rivers, particularly during winter storm events, but this is of questionable relevance for river eutrophication. Although some of the agriculturally derived PP is retained as sediment on the river bed, in most cases this bed sediment showed potential for removal of SRP from the overlying river water during spring and summer low flows. Thus, bed sediments may well be helping to reduce SRP concentrations within the river at times of eutrophication risk. These findings have important implications for targeting environmental management controls for phosphorus more efficiently, in relation to the European Union Water Framework Directive requirements to maintain/improve the ecological quality of impacted lowland rivers. For the UK rivers examined here, our results demonstrate that an important starting point for reducing phosphorus concentrations to the levels approaching those required for ecological improvement, is to obtain better control over point source inputs, particularly small point sources discharging to ecologically sensitive rural/agricultural tributaries.

Phosphorus concentrations in the River Dun, the Kennet and Avon Canal and the River Kennet, southern England

Variations in phosphorus (P) concentrations in an agriculturally impacted river draining a Chalk aquifer and an associated canal in the west of the Thames Basin, southern England are examined and linked to agricultural and sewage sources and within river/canal process controls. The study area comprises the River Dun, the adjacent River Kennet and the Kennet and Avon (K&A) Canal. Large seasonal variations are observed for soluble reactive phosphorus (SRP) and dissolved silicon (Si) with low concentrations in the spring and summer times when biological activity is high. The K&A Canal shows the largest SRP and Si concentration declines. This reflects high biological activity coupled with higher temperatures and higher water residence times. The extent of SRP removal is examined in relation to organic (uptake/release with phytoplankton growth/decay) and, to a lesser extent, inorganic (SRP coprecipitation with calcite) mechanisms. Boron (B) is used as a tracer of sewage sources. Agricultural inputs of both dissolved and particulate P (PP) can be important particularly under conditions where the catchment is wet and near surface/overland flow is important: sewage treatment works effluent and septic tank discharges to groundwater also probably provide a major component of the SRP occurring within the water column. The canal, and to a lesser extent the river, acts as sink for P in sewage effluent sources due to the high biological activity especially during the spring and summer. The aquifer probably acts as a major sink for agricultural and septic tank inputs of P.

Effect of organic components and aeration regimes on the efficiency of a multi-soil-layering system for domestic wastewater treatment

Multi-soil-layering (MSL) system can be applied to wastewater treatment. The component of an MSL system can be varied as a function of site-specific availability of materials. This study investigates the comparative efficiency of five MSL systems as a function of alternative organic materials (Japanese sawdust, Thai sawdust, rice straw, kenaf, and corncob). The MSL systems were set up in 15 × 50 × 100 cm boxes consisting of “soil mixture blocks” alternated with a zeolite layer. The February–May 1999 results indicated that all the MSL systems under a non-aeration regime effectively reduced the biochemical oxygen demand (BOD5) and removed soluble reactive phosphorus (SRP) with percentages ranging from 88.0–99.8 and 92.5–100, respectively. From January to September 2000 when an on-off aeration regime was adopted, the MSL treatments comprising rice straw, kenaf, and corncob continued to effectively reduce BOD5 and remove SRP. On the other hand, the efficiency of Japanese sawdust and Thai sawdust MSL treatments in reducing BOD5 and removing SRP gradually decreased. Fine particles and slowly decomposable characteristics of Thai sawdust and Japanese sawdust induced compaction and subsequent clogging. Therefore, rice straw, kenaf, and corncob were found to be more appropriate than Thai sawdust and Japanese sawdust for use as components of the MSL systems. Aeration at a rate of 64,000 L m−3 d−1 for 1 week enhanced BOD5 reduction and SRP removal, especially, when clogging was observed. However, aeration at this rate reduced the TN removal efficiency of the MSL system due to the inhibition of denitrification, excessive nitrification as well as the discharge of stored NH4 +-N.

Effect of intermittent aeration regulation of a multi-soil-layering system on domestic wastewater treatment in Thailand

This study investigated the effect of aeration of a multi-soil-layering (MSL) system on domestic wastewater treatment. The MSL system was constructed in a 100×200×150 cm concrete tank. Clayey soil was mixed with sawdust and iron scraps at a ratio of 75:10:15, respectively, based on dry weight. The soil mixture was filled into the tank as blocks, thus forming a brick-like layer pattern. The void spaces between the soil blocks were filled with zeolite. Combined toilet and cafeteria wastewater, which was pre-treated by using settlement tanks, was discharged periodically to the MSL system. The loading rate of wastewater varied from 100 to 600 l m −2 d −1. Aeration was applied to the MSL system at rates of 0, 4000 and 20,000 l m −3 d −1. The results revealed that the aeration assists the removal efficiency of biochemical oxygen demand (BOD 5), chemical oxygen demand (COD) and soluble reactive phosphorus (SRP). When the MSL system was aerated at a rate of 4000 l m −3 d −1 for 1 week, BOD 5, COD and SRP removal efficiencies reached 87.4, 53.2 and 80.3%, respectively. However, at this aeration rate, the efficiency of total nitrogen (TN) removal declined to −26.7%. Aeration at a rate of 20,000 l m −3 d −1 for 3 days was more effective for enhancing BOD 5, COD, TN and SRP removals than aeration at the rate of 4000 l m −3 d −1. The removal percentages of BOD 5, COD, TN and SRP at values of 92.2, 73.3, 15.0 and 74.7, respectively, were recorded. Two months of non-aeration decreased the COD removal efficiency to <27%, whereas the BOD 5, TN and SRP removals were at high levels of 82.1, 65.3 and 83.0%, respectively. This suggested that COD removal needed more intensive aeration than the other parameters. Aeration at a rate of 20,000 l m −3 d −1 alternated with 2 months of non-aeration is appropriate for operating the tested MSL system in Thailand.

Control of the eutrophication of the reservoir of Esch-sur-Sûre (Luxembourg): evaluation of the phosphorus removal by predams

The phosphorus retention capacity was established for two predams having the same water supply and the same seasonality but with contrasting hydraulic retention times and phosphorus loads. The annual retention of total phosphorus of the shallow Misere predam amounted to about 60%, whereas the deeper Bavigne predam retained about 82%; for soluble reactive phosphorus (SRP) the annual retention rates were 4 and 54%, respectively. The different behaviour of the predams is probably due to their different flow regimes and morphology. The highest retention rates were observed during summer, when up to 90% of SRP could be retained in the Bavigne predam. The comparison of the measured removal rates of SRP with those calculated on the basis of the model proposed by Benndorf & Putz (Wat. Res. 1987 21: 829–838) shows a rather good agreement for the thermally stratified Bavigne predam. For the shallow Misere predam, the model adequately predicts the annual trends of SRP removal, but a great discrepancy is observed for the absolute values. This is probably due to the phytoplankton composition and to the release of phosphorus from the sediments in the summer period.

Performance of a Single-Cell Aerated Waste Stabilisation Pond Treating Domestic Wastewater: A Three-Year Study

An aerated waste stabilisation pond treating domestic effluent (15,000 inhabitant-equivalents) after primary treatment was investigated from January 1994 to December 1996 for hydraulic regime, performance in nutrient removal, decrease in oxygen demand and microbial pollution. The pond has a complete mixed hydraulic regime with virtually no short-circuiting or stratification. During the studied period, the pond provided satisfactory primary and secondary treatments meeting most of the time the European requirements for COD, BOD 5 and Total Suspended Solids. COD and BOD 5 removal rates varied from 44 to 70% and from 69 to 81 %, respectively. Decrease in germ density always reached more than 93 %. Ammonium and soluble reactive phosphorus removal rates were most of the time lower than 40%. The lack of a significant nutrient removal rate was notably linked to the low phytoplankton development and to the globally low level of nitrification in the pond due to anoxic conditions. Moreover, a dense population of the large and efficient grazer Daphnia magna counteracted the ammonium and the soluble reactive phosphorus removal through feeding and remineralization of a significant part of the nitrogen and phosphorus assimilated by algae and bacteria. The benefits of an intensive harvesting of the zooplankton are discussed in relation to waste water treatment performance and to the potential commercial value of the harvested biomass.