An analysis of cascade‐aerated facultative waste stabilisation ponds in the United Kingdom

This paper examines the performance of cascade‐aerated facultative ponds in a waste stabilisation pond (WSP) installation in the United Kingdom. The pond system is privately owned and treats wastewater from a conference centre with a population equivalent between 20 and 40. A snapshot analysis investigates the removal efficiency of BOD, COD, SS, FC and nutrients. Further, the oxygen supply through ‘flow form’ cascades is examined, and the DO concentrations, surface loads and retention times are discussed. The results show a very high removal of BOD, COD and SS; and nutrient removal is satisfactory. An unusual finding is that the FC removal efficiency is almost two log units better than for a common maturation pond. This is possibly attributable to the high cascade flow, where wastewater is exposed to the damaging effects of sunlight (photo‐oxidation).     

Optimisation of hydraulic performance to maximise faecal coliform removal in maturation ponds

The present study was conducted with the aim of improving faecal coliform (FC) and faecal streptococcus (FS) removal efficiencies in tertiary maturation stages of a sewage treatment plant in Southern England, where climatic conditions are sub-optimal. The research used intensive field assessments (bacteriological, general quality and hydraulic) to identify the parameters that affect the bacteriological quality of the effluent from three parallel maturation ponds (North, Central and South) of similar geometry and dimensions. An engineering intervention was carried out to convert the South pond to three channels to increase the L/W ratio from 9:1 to 79:1. Hydraulic tracer studies in the South pond with Rhodamine WT showed that the dispersion number 'd' was reduced from 0.37 (dispersed flow) to 0.074 by this intervention under similar flow conditions (4.5l/s). Hydraulic retention time was thus increased by 5h, delay in jet flow short-circuiting was increased from 2.5 to 17.5h thus increasing the exposure times for all elements. As a result of the intervention FC removal increased substantially. Maximum channel-lagoon efficiency of 99.84% was obtained at 4.5l/s and 19 degrees C, when exposure to sunlight was 17 h in summer. It is concluded that the channel configuration produces a higher hydraulic efficiency than conventional maturation ponds. It is therefore recommended as a viable engineering solution which permits a low-cost upgrading of plant performance, requiring no additional land, and with minimal maintenance costs.     

Upgrading a facultative pond by implanting water hyacinth

Water hyacinth was implanted in one of two existing facultative ponds and both units were operated in parallel under comparable conditions. The ponds were fed with mainly domestic wastewater after pretreatment in anaerobic ponds and operated at a BOD₅-loading of about 48 kg (ha d)⁻¹ and a detention time of 12 days. This paper covers a period of 4 months, from the implantation of the water hyacinths until no further systematic change in the treatment efficiency of the water hyacinth pond was observed. The median effluent concentrations of the facultative pond for SS, COD, TKN and TP were 55, 95, 6.4 and 1.4 mg l⁻¹, respectively. The values for the water hyacinth pond were 12, 26, 2.5 and 0.4 mg l⁻¹, respectively. The average DO effluent concentration of the water hyacinth pond was 1.2 mg l⁻¹, but this still increased slightly as compared to the influent. The study demonstrates that the implantation of water hyacinth is an appropriate option for upgrading facultative ponds. In many cases where more stringent effluent standards are imposed the method may be a suitable alternative to technical treatment processes.     

Nitrogenous compounds in facultative oxidation pond sediments

The protein content of sludge samples from facultative oxidation ponds was measured and was found to have even distribution in the pond floor. Proteolytic activity which degrades protein to intermediate compounds, was found to be slightly higher near the pond inlet region. It was also shown that proteolytic activity increased with increasing depth of overlying pond liquor.Ammonia content of, and ammonification by pond sludge appeared to be independent of locality. Urea and urease activity were restricted to the regions close to the pond inlet region.     

Reuse of urban wastewater treated by a combined stabilisation pond system in Benslimane (Morocco)

The aim of this paper is to study the performance of a combined waste stabilisation pond after three years of functioning and the reuse of treated wastewater for irrigating potatoes and lettuce culture. The combined ponds showed good functioning conditions and excellent performances either for organic load (90%), faecal coliform (6 log units) or helminth eggs (100%) and produced a high and perennial effluent quality. The effluent could be used for non-restrictive irrigation, with a clear improvement of culture production and hygienic quality for both fruits and soil.     

NATURAL SEWAGE TREATMENT IN THE UK: SELECTION GUIDELINES

The design of septic tanks, constructed wetlands, waste-stabilisation ponds and rock filters is detailed, and their applicability in the UK is discussed. Septic tanks are a suitable primary treatment system for villages with a population of less than 500. Constructed wetlands, which are secondary or tertiary treatment units, have the disadvantage that their plants do not play any significant role in their performance, except for nitrogen removal. Secondary facultative waste-stabilisation ponds, with pre-treatment in septic tanks and post-treatment in rock filters, provide primary, secondary and tertiary treatment and can produce high-quality effluents. The costs of these processes for small rural communities in the UK are compared.     

Performance of the Burwarton Estate Waste Stabilization Ponds

The Burwarton Estate waste stabilization ponds, near Bridgnorth, Shropshire, serve a population of 150. There are three ponds in series: a facultative pond, and two equal maturation ponds, followed by two parallel and alternately used constructed wetland ditches. This paper describes the design of the ponds and reports upon their performance during the first two years of operation.     

Seasonal and diurnal variations of temperature, pH and dissolved oxygen in advanced integrated wastewater pond system treating tannery effluent

Seasonal and diurnal fluctuations of pH, dissolved oxygen (DO) and temperature were investigated in a pilot-scale advanced integrated wastewater pond system (AIWPS) treating tannery effluent. The AIWPS was comprised of advanced facultative pond (AFP), secondary facultative pond (SFP) and maturation pond (MP) all arranged in series. The variations of pH, DO and temperature in the SFP and MP followed the diurnal cycle of sunlight intensity. Algal photosynthesis being dependent on sunlight radiation, its activity reached climax at early afternoons with DO saturation in the SFP and MP in excess of over 300% and pH in the range of 8.6-9.4. The SFP and MP were thermally stratified with gradients of 3-5 degrees C/m, especially, during the time of peak photosynthesis. The thermal gradient in the AFP was moderated by convective internal currents set in motion as a result of water temperature differences between the influent wastewater and contents of the reactor. In conclusion, the AFP possessed remarkable ability to attenuate process variability with better removal efficiencies than SFP and MP. Hence its use as a lead treatment unit, in a train of ponds treating tannery wastewaters, should always be considered.     

Photodegradation of three stormwater biocides

Photodegradation of carbendazim, diuron and terbutryn was investigated at controlled laboratory conditions under UV light and under natural sunlight. Demineralized water and two different waters from stormwater retention ponds were used. An observed decline in biocide concentration was related to the accumulated light energy during the degradation time. Diuron and terbutryn were degradable under UV light following 1^st order degradation kinetics, while no significant decrease of carbendazim was observed throughout the duration of experiments. Photodegradation of diuron and terbutryn was slightly faster in demineralized water compared with pond water. The outdoors experiments showed limited degradation of the compounds for the duration of the test (8–17 days). The results emphasize the importance of water type, the wavelength and energy of the light when investigating pollutant’s photo fate. Also, this study indicates that photodegradation is not a major process contributing to the removal of carbendazim, diuron and terbutryn in stormwater retention ponds.     

Nitrification in modified sewerage stabilisation ponds prior to discharge into the Ugandan side of Lake Victoria

Large volumes of wastewater in the Ugandan capital Kampala have seriously polluted Lake Victoria, from which the city draws its freshwater. Untreated effluent drains directly into this lake. In tropical temperatures, oxidation ponds are used for wastewater treatment, especially for organic matter. This technology should be the focus of work to improve its efficacy, and thus to secure the sustainability of the lake and its freshwater fish which are marketed worldwide. A pilot scale plant was set up comprising an anaerobic tank, a facultative pond and four fibre‐glass maturation tanks. The total nitrification rates in the tanks T₁–T₄ were 5.5, 7.5, 10.1 and 6.4 (±0.4) mg‐N/l/day, respectively. For more efficient wastewater treatment stabilisation pond systems, a modification similar to that in T₃ should be considered. T₃ was constructed with biofilm attachment surfaces in a manner which allowed effluent to be channelled round them, contrary to direct T₁ flow which is currently in use.     

Sludge accumulation, characteristics, and pathogen inactivation in four primary waste stabilization ponds in central Mexico

To support the development of safe and feasible sludge management strategies, the accumulation rates of sludge and its characteristics were studied in four primary wastewater stabilization ponds (WSPs) in central Mexico (three facultative and one anaerobic). The accumulation rates and distribution of sludge were determined by measuring the thickness of the sludge layer at 8-40 locations throughout each pond. The average, per capita sludge accumulation rates ranged from 0.021 to 0.036m(3)/person/yr. In the anaerobic pond the sludge distribution was uniform throughout the pond, whereas in the three facultative ponds most of the sludge accumulated directly in front of the inlet. To measure the horizontal and vertical variation in the sludge characteristics, sludge cores were collected from 3 to 7 locations in three of the ponds. Each core was divided into 4 sub-samples in which various physical, chemical, and microbiological parameters were measured. In addition, the inactivation of several pathogen indicator organisms was studied in a batch of sludge for 7 months. Based on the microbiological results, it is concluded that reasonable estimates of the inactivation of fecal coliform bacteria, fecal enterococci, F+ coliphage, somatic coliphage, and Ascaris eggs in WSP sludge in central Mexico can be made using first-order rate constants of 0.1, 0.1, 0.01, 0.001, and 0.001d(-1), respectively. From the observed changes in the concentrations of total solids and the volatile to fixed solids ratio, empirical equations were developed to describe anaerobic degradation and compression, which are the two most important processes affecting the volume of sludge after its deposition.     

Comparison of model approaches for predicting coliform removal in waste stabilization ponds

This paper compares the two most frequently used approaches for the prediction of faecal coliforms in the effluent (FC_e) of waste stabilization ponds (WSPs): the continuous stirred reactor (CSTR) model and the dispersed flow (DF) model. On the basis of theoretical and practical analysis, it is concluded that, under most conditions usually found in practice, the DF model can be expected to predict unrealistically low FC_e. This trend is more pronounced the more the flow conditions in the pond(s) approach plug flow, and the higher the average retention time per pond. Model differences in FC_e prediction typically deviate from one another by up to 1–2 log units. This can lead to the design of substantially different pond sizes, with footprint differences between the two models of 30–50% not being exceptional. Consequently, on the basis of usually applied model parameters, for the time being it appears safer to use the CSTR model for FC_e prediction in WSP systems.     

Cyanobacteria diversity and toxicity in a wastewater treatment plant (Portugal)

Cyanobacteria are common in eutrophic natural waters. Being favoured by warm, stable and nutrient-enriched waters they may constitute an important part of the phytoplankton community in Wastewater Treatment Plants (WWTP). The phytoplankton communities of two ponds (facultative and maturation) of the WWTP of Esmoriz (North Portugal) were studied, with particular importance given to cyanobacteria. Mouse bioassays were performed with cyanobacteria samples during some of the blooms and ELISA assays specific for hepatotoxic microcystins were carried out. During the study period (January-July 1999) cyanobacteria were frequently dominant in the ponds ranging from 15.2 to 99.8% of the total phytoplankton density. The main species were Planktothrix mougeotii, Microcystis aeruginosa and Pseudanabaena mucicola. Mouse bioassays were performed during Oscillatoria bloom period but the results were negative, in spite of the high cyanobacteria biomass. ELISA assays were performed for both ponds but only in the maturation pond positive values were found. Microcystin concentrations (as MCYST-LR equivalents) varied from 2.3 to 56.0 micrograms/l on the margin of the pond and between 1.7 and 4.6 micrograms/l in the outflow of this pond. These values indicate that WWTP may be a source of contamination of water bodies with cyanobacteria toxins.     

Distribution of indicator bacteria in Canyon Lake, California

The spatial and temporal distributions of indicator bacteria in a small, multiple-use source drinking water reservoir in Southern California, USA were quantified over the period August 2001-July 2002. High levels of total and fecal coliform bacteria were present in Canyon Lake (annual geometric mean concentrations+/-SEM of 3.93+/-0.02 and 3.02+/-0.03 log cfu/100mL, respectively), while comparatively low levels of enterococci and E. coli were found (1.16+/-0.02 log cfu/100mL and 0.30+/-0.03 log MPN/100mL, respectively). As a result, these different indicator bacteria yielded quite divergent indices of water quality, with 72.1% of all surface samples (n=294) exceeding the USEPA single-sample limit of 400 cfu/100mL fecal coliform bacteria, while none (0%) of the samples exceeded the single-sample limit for E. coli (n=194). Regression analyses found a positive correlation between total and fecal coliform bacteria (R=0.50, significant at p<0.001) and between enterococci and E. coli (R=0.51, significant at p<0.001), but no correlation or inverse correlations were found between coliform concentrations and enterococci and E. coli levels. External sources responsible for the high total and fecal coliform bacteria were not identified, although laboratory studies demonstrated growth of the coliform bacteria in lake water samples. Enterococci and E. coli were not observed to grow, however. Bacteria concentrations varied relatively little laterally across the lake, although strong vertical gradients in fecal coliform and enterococcus bacteria concentrations were present during summer stratification, with concentrations about 10x higher above the thermocline when compared with surface concentrations. In contrast, total bacteria, total virus and total coliform bacteria levels were unchanged with depth. Seasonal trends in bacteria concentrations were also present. This study shows that the choice of indicator bacteria and sampling depth can both strongly affect the apparent microbial water quality of a lake or reservoir.     

Removal of organic matter in stormwater ponds: a plug-flow model generalisation from waste stabilisation ponds to shallow rivers

ABSTRACT

This study investigates the effect of flow conditions on the organic matter concentration, removal efficiency, and reaction kinetics in a stormwater pond in Fortaleza, Brazil. As a result of unauthorized sewage discharges, BOD and COD concentrations were similar to those of combined sewer systems. The concentrations remained roughly the same during the rainy season, which was attributed to sewage network overflow. Removal efficiencies ranged from 70–90%, similar to primary facultative ponds. Fitting different hydraulic models to the field data, it was possible to obtain BOD and COD removal rates that could be described as functions of the Reynolds number. The best fit was achieved considering the plug-flow assumption, and a general BOD model including data reported in the literature for waste stabilisation ponds, stormwater ponds and shallow rivers was derived. Lastly, simulations with this general model were performed to assess the impact of remediation measures on the studied pond.     

Septage disposal in waste recycling ponds

Experiments were carried out to investigate the feasibility of septic tank sludge (septage) disposal into pilot-scale waste recycling ponds for the production of algae and fish. A septage loading of 100 kg COD ha⁻¹ day⁻¹ to four 4-m² single-stage ponds resulted in the production of algal biomass and dissolved oxygen in the pond water, suitable for Tilapia growth. Some microbiological investigations of this waste recycling scheme were undertaken using ten earth ponds (each with the dimensions of 20 × 10 × 1.3 m: length × width × depth). It was found that the densities of coliform bacteria and bacteriophages in the pond water and sediment tended to increase with increased septage loadings and loading periods. The ponds fed with septage at the loading of 100 kg COD ha⁻¹ day⁻¹ were found to contain higher densities of these microorganisms than those of the control pond without septage feeding. The possible public health impact resulting from this practice was assessed.     

Effect of tapering on the performance of waste stabilization ponds

A model for wastewater degradation in a tapered waste stabilization pond was derived as a modified Bessel function by materials balance approach. Based on hypothetical data, the tapered model gave lower faecal bacteria removal than the conventional (rectangular) model for various values of dispersion number, die-off rate coefficient, average width and shape factors. The above results were corroborated by data collected from two laboratory ponds operated in parallel; one having a tapered and the other a rectangular surface area. The latter gave slightly higher hydraulic efficiency and BOD5 removal. Besides, faecal bacteria removal was significantly lower in the tapered pond than in the rectangular pond at 0.10 level of significance. Calculated faecal bacteria reduction using the tapered model was in good agreement with measured data with coefficient of correlation and standard error of 0.904 and 0.014, respectively. Effects of tapering on ponds with respect to construction cost, operational and maintenance ease and accuracy of estimated design parameters are also discussed.     

Comparison of ammonia volatilisation rates in algae and duckweed-based waste stabilisation ponds treating domestic wastewater

Quantification of ammonia volatilisation from wastewater stabilisation ponds is important in order to understand its significance for overall nitrogen removal in these widely applied low-cost treatment systems. Ammonia volatilisation rates were measured in pilot plant facilities consisting of one line of four algae-based ponds in series and a parallel line of four ponds with a floating mat of duckweed (Lemna gibba). Ammonia volatilisation was assessed during a period of one and a half years. The method applied is accurate, convenient and is proposed for analysis of a wide range of gasses emitted from stabilisation ponds and possibly other aquatic systems. The ammonia volatilisation rates in algae-based ponds (ABPs) were higher than in duckweed-based ponds (DBPs). This can be explained by the lower values of NH(3) in DBPs due to shading and lower pH values, since the volatilisation rate highly correlated with free ammonia concentration (NH(3)) in pond water. The duckweed cover appeared not to provide a physical barrier for volatilisation of unionised ammonia, because whenever NH(3) concentrations were equal in ABP and DBP also the volatilisation rates were equal. Volatilisation was in the range of 7.2-37.4 mg-Nm(-2)d(-1) and 6.4 -31.5 mg-Nm(-2)d(-1) in the ABPs and DBPs, respectively. Average influent and effluent ammonium nitrogen measurements showed that the ammonia volatilisation during the study period in any system did not exceed 1.5% of total ammonium nitrogen removal. Therefore this study confirmed results from simultaneous experimental work in our laboratory indicating that nitrification/denitrification, rather than ammonia volatilisation, is the most important mechanism for N removal in ABPs and DBPs.     

Survival in maturation ponds of coliform bacteria with transferable drug resistance

The behaviour of drug-resistant coliform bacteriasin a series of sewage maturation ponds was investigated. The average reduction through the ponds of coliforms resistant to ampicillin, chloramphenicol, kanamycin, streptomycin or tetracycline was 6.83 per cent lower than that of drug-sensitive bacteria. This difference was mainly due to coliforms with transferable resistance (R⁺ coliforms) which increased from 0.86 per cent to 2.45 per cent through the ponds. The spectrum of transferable resistance of coliforms in the effluent did not differ notably from that of coliforms in the influent. The average incidence of Escherichia coli I among R⁺ coliforms decreased from 66.08 per cent to 62.09 per cent. This indicates that low-level transfer of R factors may occur in ponds. Possible mechanisms and the epidemiological significance of the increased survival of R⁺ coliforms in maturation ponds are discussed.     

Effects of baffles on the performance of model waste stabilization ponds

The performance of three baffled laboratory-scale facultative stabilization ponds were compared with that of an unbaffled control pond. The hydraulic characteristics of the ponds were estimated from the results of tracer tests.The biochemical oxygen demand (BOD₅) removals achieved with the control pond and with the ponds having 3, 6 and 9 baffles were 79, 81, 86 and 89% respectively and the chemical oxygen demand (COD) removals were 81, 84, 84.2 and 84.2%. The reductions in total solids (TS) were respectively 43, 46, 51 and 64%. Dispersion indices of 0.161, 0.126, 0.112 and 0.096 were obtained for the control, 3, 6 and 9 baffle ponds respectively, which indicated a trend of decreasing dispersion index with increasing number of baffles.