RESUMEN
Attenuation of sunlight in wastewater treatment ponds reduces the depth of the water exposed to disinfecting irradiances. Shallow pond depth with paddlewheel rotation increases exposure of pathogens to sunlight in high rate algal ponds. Generation of thin films, using pond walls as inclined planes, may increase inactivation of pathogens by increasing sunlight exposure. The performance of a laboratory based model system incorporating an inclined plane (IP) was evaluated. F-RNA bacteriophage, in tap water or wastewater, was exposed to sunlight only on the IP with the bulk water incubated in the dark. MS2 inactivation was significantly higher when the IP was present (P < 0.05) with a 63% increase observed. Prolonged exposure increased MS2 die-off irrespective of IP presence. Versatility of the IP was also demonstrated with faster inactivation observed in both optically clear tap water and wastewaters. IPs of different surface areas produced similar inactivation rates when operated at similar hydraulic loading rates regardless of slope length.
Asunto(s)
Desinfección/métodos , Estanques , Luz Solar , Aguas Residuales , Purificación del Agua/métodos , Bacteriófagos/efectos de la radiación , Estanques/microbiología , Estanques/virología , Aguas Residuales/microbiología , Aguas Residuales/virologíaRESUMEN
Over the last 20 years, there has been a growing requirement by governments around the world for organisations to adopt more sustainable practices. Wastewater treatment is no exception, with many currently used systems requiring large capital investment, land area and power consumption. High rate algal ponds offer a sustainable, efficient and lower cost option to the systems currently in use. They are shallow, mixed lagoon based systems, which aim to maximise wastewater treatment by creating optimal conditions for algal growth and oxygen production-the key processes which remove nitrogen and organic waste in HRAP systems. This design means they can treat wastewater to an acceptable quality within a fifth of time of other lagoon systems while using 50% less surface area. This smaller land requirement decreases both the construction costs and evaporative water losses, making larger volumes of treated water available for beneficial reuse. They are ideal for rural, peri-urban and remote communities as they require minimum power and little on-site management. This review will address the history of and current trends in high rate algal pond development and application; a comparison of their performance with other systems when treating various wastewaters; and discuss their potential for production of added-value products. Finally, the review will consider areas requiring further research.
Asunto(s)
Microalgas , Estanques , Eliminación de Residuos Líquidos/métodos , Aguas Residuales , Biomasa , Costos y Análisis de Costo , Eucariontes , Nitrógeno/metabolismo , Oxígeno/metabolismo , Factores de Tiempo , Eliminación de Residuos Líquidos/economía , Purificación del Agua/economía , Purificación del Agua/métodosRESUMEN
This study investigated the volume of wastewater retained on the surface of three different varieties of lettuce, Iceberg, Cos, and Oak leaf, following submersion in wastewater of different microbial qualities (10, 102, 103, and 104 E. coli MPN/100 mL) as a surrogate method for estimation of contamination of spray-irrigated lettuce. Uniquely, Escherichia coli was enumerated, after submersion, on both the outer and inner leaves and in a composite sample of lettuce. E. coli were enumerated using two techniques. Firstly, from samples of leaves - the direct method. Secondly, using an indirect method, where the E. coli concentrations were estimated from the volume of wastewater retained by the lettuce and the E. coli concentration of the wastewater. The results showed that different varieties of lettuce retained significantly different volumes of wastewater (p < 0.01). No statistical differences (p > 0.01) were detected between E. coli counts obtained from different parts of lettuce, nor between the direct and indirect enumeration methods. Statistically significant linear relationships were derived relating the E. coli concentration of the wastewater in which the lettuces were submerged to the subsequent E. coli count on each variety the lettuce.
Asunto(s)
Escherichia coli/aislamiento & purificación , Microbiología de Alimentos/métodos , Lactuca/microbiología , Aguas Residuales/microbiología , Recuento de Colonia Microbiana , Lactuca/genética , Lactuca/crecimiento & desarrollo , Hojas de la Planta/microbiologíaRESUMEN
This study assessed the contamination of Escherichia coli, in lettuce grown with treated domestic wastewater in four different irrigation configurations: open spray, spray under plastic sheet cover, open drip and drip under plastic sheet cover. Samples of lettuce from each irrigation configuration and irrigating wastewater were collected during the growing season. No E. coli was detected in lettuce from drip irrigated beds. All lettuce samples from spray beds were positive for E. coli, however, no statistical difference (p > 0.05) was detected between lettuces grown in open spray or covered spray beds. The results from the field experiment were also compared to a laboratory experiment which used submersion of lettuce in wastewater of known E. coli concentration as a surrogate method to assess contamination following irrigation. The microbial quality of spray bed lettuces was not significantly different from submersed lettuce when irrigated with wastewater containing 1,299.7 E. coli MPN/100 mL (p > 0.05). This study is significant since it is the first to validate that the microbial contamination of lettuce irrigated with wastewater in the field is comparable with a laboratory technique frequently applied in the quantitative microbial risk assessment of the consumption of wastewater irrigated salad crops.
Asunto(s)
Escherichia coli/crecimiento & desarrollo , Lactuca/microbiología , Verduras/microbiología , Aguas Residuales/microbiología , Riego Agrícola , Lactuca/crecimiento & desarrollo , Medición de Riesgo , Verduras/crecimiento & desarrollo , Aguas Residuales/análisis , Microbiología del AguaRESUMEN
AIMS: High rate algal ponds (HRAPs) have been suggested as replacements for waste stabilization ponds (WSPs) in Community Wastewater Management Systems (CWMS) used in rural South Australian (SA) towns. Treated effluent from CWMS is reused for irrigation. To manage the risk of human exposure to pathogens, the disinfection performance of HRAPs was validated using the common indicators Escherichia coli and F-RNA bacteriophage; aerobic spore-forming bacteria (ASFB) were used as indicators for protozoa. METHODS AND RESULTS: Using standard culture methods, the removal of the indicator organisms F-RNA bacteriophage, E. coli and ASFB by a HRAP at Kingston-on-Murray, SA, was measured. The mean log10 reduction values achieved for the F-RNA bacteriophage was 1·59 ± 0·82 log10 PFU 100 ml(-1) and for E. coli it was 2·13 ± 0·55 log10 E. coli MPN 100 ml(-1) . ASFB numbers in the treated pond effluent often exceeded those of the influent. CONCLUSIONS: The results show that HRAPs are able to remove viral and bacterial indicators to levels acceptable for subsurface irrigation of nonfood crops. Additionally, it was concluded that alternate environmental sources and the potential for regrowth made ASFB unsuitable indicators for pathogenic protozoa in natural pond systems. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows HRAPs would be suitable replacements for WSPs in CWMS schemes in regard to pathogen disinfection. Such demonstration of the treatment efficacy of HRAPs, together with their smaller land area requirements relative to WSPs, should facilitate their wider adoption in rural and remote communities.
Asunto(s)
Bacterias/crecimiento & desarrollo , Chlorophyta/fisiología , Estanques/microbiología , Aguas Residuales/microbiología , Purificación del Agua/métodos , Australia , Bacterias/aislamiento & purificación , Viabilidad Microbiana , Estanques/química , Eliminación de Residuos Líquidos/métodosRESUMEN
The interference of ammonia with the chlorination process is a problem for many reclaimed water treatment plant operators. This paper presents the findings from a series of pilot experiments that investigated the efficacy of high flow rate nitrifying trickling filters (NTFs) for the removal of low concentrations of ammonia (0.5-3.0 mg N L(-1)) from reclaimed wastewater. Results showed that nitrification was impeded by a combination of high organic carbon loads and aquatic snails, which consumed much of the active biomass. With adequate snail control, nitrification rates (0.3-1.1 g NH(4)-N m(-2) d(-1)) equivalent to that of traditional wastewater NTFs were achieved, despite operating under comparably low ammonia feed concentrations and high hydraulic flow rates.
Asunto(s)
Amoníaco/aislamiento & purificación , Eliminación de Residuos Líquidos/métodos , Animales , Biodegradación Ambiental , Biomasa , Carbono/análisis , Carbono/aislamiento & purificación , Filtración/métodos , Nitratos/aislamiento & purificación , Nitritos/aislamiento & purificación , Compuestos Orgánicos/aislamiento & purificación , Proyectos Piloto , Caracoles , Purificación del Agua/métodosRESUMEN
Waste stabilisation ponds (WSP) are efficient, cost-effective methods of treating wastewater in rural and remote communities in Australia. It is recognised that sunlight plays a significant role in their disinfection, however, due to the poor penetration of light in turbid waters it has been hypothesised that other mechanisms may also contribute to disinfection in WSPs. To date, studies have reported various and conflicting results with regards to the relative contributions of UVA, UVB, PAR and environmental factors including pH, DO and photo-sensitisers on micro-organism disinfection. Initially we investigated the role of these environmental factors on the solar disinfection of enterococci in buffered distilled water to control for potential confounding factors within the wastewater. Die-off rate constants were measured, in sterile buffered distilled water at varying pH and dissolved oxygen concentrations, for enterococci irradiated with UVA and UVB. Enterococci were found to be predominantly inactivated by UVB (p<0.001), however, UVA was also observed to increase inactivation rates relative to the dark control (p<0.001). DO and pH were found to have no effect on inactivation rate when enterococci were irradiated with UVB (p>0.05), however, when irradiated with UVA, both DO and pH were observed to further increase inactivation rates (p<0.01).
Asunto(s)
Enterococcus/metabolismo , Luz Solar , Microbiología del Agua , Contaminantes del Agua/aislamiento & purificación , Purificación del Agua/métodos , Sustancias Húmicas , Concentración de Iones de Hidrógeno , Luz , Nefelometría y Turbidimetría , Oxígeno/química , Oxígeno/metabolismo , Fármacos Fotosensibilizantes/farmacología , Rayos Ultravioleta , Eliminación de Residuos Líquidos/métodos , Agua/químicaRESUMEN
This study compared the nitrification potential of two separate Waste Stabilisation Ponds (WSPs) operating under differing physical and chemical conditions. In order to probe the nitrification potential of each system, the oxidation of ammonium and also the intermediate product nitrite was assessed using both in situ and laboratory micro-scale incubations. The role of sediment in determining the nitrification potential of the two WSPs was also investigated. Results from laboratory microcosm incubations revealed a competent and strikingly similar nitrification potential for both WSPs in spite of their differing nitrogen and organic loadings, and also suggested a significant role for sediment in WSP nitrogen cycling. Results from in situ field experiments identified biomass uptake to be the dominant nitrogen removal mechanism in natural pond environments. Other aspects of WSP nitrogen cycling are also discussed.
Asunto(s)
Nitritos/química , Eliminación de Residuos Líquidos/métodos , Biomasa , Reactores Biológicos , Diseño de Equipo , Sedimentos Geológicos , Cinética , Miniaturización , Oxidación-Reducción , Compuestos de Amonio Cuaternario/química , Eliminación de Residuos/métodos , Purificación del Agua/métodosRESUMEN
The spatial and temporal variation of physical, chemical, and biological parameters was determined, in summer and winter, at nine sites in a large (112 ha) waste stabilisation pond (WSP) at the Bolivar Wastewater Treatment Plant. Each site was extensively sampled over the course of one day, with the nine sites sampled over successive days at exactly the same times of day, progressing in the direction of bulk flow through the pond. Analyses of covariance were used to test the independent impact of site and climate on the way in which the mean values and stratification gradient of the physical, chemical, and biological parameters varied diurnally at each site. In both winter and summer studies there was a very strong correlation at all sites between changes in temperature, pH and dissolved oxygen (DO). Mean pond temperatures were higher in summer than winter, and thermal stratification was more common in summer. In summer, during the day at each site, concentrations of chlorophyll-a, DO, suspended solids and pH increased with higher solar radiation levels. This relationship was less evident in winter. There was no systematic depth or temporal variation identified in either the summer or winter study for the broad range of chemical parameters measured. Mean values for these parameters, and to a lesser extent their stratification gradients, increased by varying extents throughout the day at the different sites in both summer and winter, irrespective of changes in climate when the different sites were sampled. Sites nearer the inlet to the WSP recorded lower NH4N and higher NO2N and NO3N concentrations than the rest of the WSP. This was indicative of nitrification. Somewhat surprisingly, high DO concentrations were also recorded at these sites near the inlets. Computational fluid dynamics (CFD) modelling, incorporating the predominant wind conditions, offers a rationale for these observations. Recirculation was evident, which may increase the residence time for the slow growing autotrophic nitrifying bacteria and recirculate oxygen rich water around these sites - conditions which would enhance nitrification. Understanding the effect of these variations, overlaid by the influence of hydraulic and temporal scenarios, assists in developing a mechanistic understanding of pond operation.
Asunto(s)
Clima , Modelos Teóricos , Estaciones del Año , Eliminación de Residuos Líquidos/estadística & datos numéricos , Microbiología del Agua , Agua/química , Análisis de Varianza , Clorofila/análisis , Clorofila A , Concentración de Iones de Hidrógeno , Compuestos de Nitrógeno/análisis , Oxígeno/análisis , Australia del Sur , Temperatura , Eliminación de Residuos Líquidos/métodos , Movimientos del AguaRESUMEN
An experimental pilot plant was operated over a five month period to assess the relative treatment performances of: a duckweed (DW) pond; a rock filter (RF); and an open pond (OP); for the upgrading of final WSP effluent prior to reuse applications. Each pilot treatment system consisted of three identical ponds arranged in three parallel series, each fed a continuous flow of wastewater from the local Bolivar treatment plant. Light penetration profiling for the DW and OP systems revealed some 55% greater light attenuation capacity for DW ponds compared to the OP system. Results showed a significantly elevated performance capacity for the RF treatment with respect to BOD5, SS, turbidity and NH4-N removal, but equal treatment performances for algal (chlorophyll) removal. No significant performance differences were evident between the DW and OP treatments for any of the monitored parameters. Soluble reactive phosphorus, faecal coliform and E. coli removals were similar for all pilot treatment systems. Rock filters not only demonstrated an enhanced performance capacity in terms of removal of loaded parameters, but also showed greater reliability of performance and produced a consistently higher quality final effluent. Rock filters demonstrated greater potential over both DW and OP systems for the upgrading of WSP effluent prior to reuse application.
Asunto(s)
Araceae/metabolismo , Reactores Biológicos , Eliminación de Residuos Líquidos/métodos , Purificación del Agua/métodos , Bacterias/metabolismo , Clorofila/metabolismo , Clorofila A , Filtración , Nefelometría y Turbidimetría , Nitrógeno/metabolismo , Fósforo/metabolismo , Proyectos PilotoRESUMEN
Bolivar Wastewater Treatment Plant (WWTP) was originally commissioned with trickling filter secondary treatment, followed by waste stabilisation pond (WSP) treatment and marine discharge. In 1999, a dissolved air flotation/filtration (DAFF) plant was commissioned to treat a portion of the WSP effluent for horticultural reuse. In 2001, the trickling filters were replaced with activated sludge treatment. A shift in WSP ecology became evident soon after this time, characterised by a statistically significant reduction in algal counts in the pond effluent, and increased variability in algal counts and occasional population crashes in the ponds. While the photosynthetic capacity of the WSPs has been reduced, the concomitant reduction in organic loading has meant that the WSPs have not become overloaded. As a result of the improvement in water quality leaving the ponds, significant cost savings and improved product water quality have been realised in the subsequent DAFF treatment stage. A number of operating issues have arisen from the change, however, including the re-emergence of a midge fly nuisance at the site. Control of midge flies using chemical spraying has negated the cost savings realised in the DAFF treatment stage. While biomanipulation of the WSP may provide a less aggressive method of midge control, this case demonstrates the difficulty of predicting in advance all ramifications of a retrospective process change.
Asunto(s)
Conservación de los Recursos Naturales , Aguas del Alcantarillado/microbiología , Eliminación de Residuos Líquidos/métodos , Purificación del Agua/métodos , Agricultura , Animales , Biodegradación Ambiental , Ceratopogonidae/fisiología , Arquitectura y Construcción de Instituciones de Salud , Fertilizantes , Filtración , Oxígeno/química , Oxígeno/metabolismo , Aguas del Alcantarillado/química , Eliminación de Residuos Líquidos/economía , Administración de Residuos , Purificación del Agua/economíaRESUMEN
This paper describes changes in effluent quality occurring before and after an upgrade to the Bolivar Wastewater Treatment Plant in South Australia. Trickling filters (TF) were replaced with an activated sludge (AS) plant, prior to tertiary treatment using waste stabilisation ponds (WSPs). The water quality in the WSPs following the upgrade was significantly improved. Reductions in total and soluble BOD, COD, TKN, suspended solids and organic nitrogen were recorded and the predominant form of inorganic nitrogen changed from NH(4)-N to NO(2)/NO(3)-N. The reduction in ammonium and potentially toxic free ammonia removed a control upon the growth of zooplankton, which may have contributed to decreases in algal biomass in the final ponds and consequently lower dissolved oxygen. Additionally, changes in inorganic nitrogen speciation contributed to a slightly elevated pH which reduced numbers of faecal coliforms in WSPs. The AS pretreated influent recorded significantly lower inorganic molar N:P ratio (10-4:1) compared to those fed with TF effluent (17-13:1). Algae within the WSPs may now be nitrogen limited, a condition which may favour the growth of nitrogen-fixing cyanobacteria. The decrease in algal biomass and in dissolved oxygen levels may enhance sedimentary denitrification, further driving the system towards nitrogen limitation.
Asunto(s)
Aguas del Alcantarillado/microbiología , Eliminación de Residuos Líquidos/métodos , Purificación del Agua/métodos , Amoníaco/aislamiento & purificación , Animales , Biodegradación Ambiental , Biomasa , Enterobacteriaceae/aislamiento & purificación , Eucariontes/metabolismo , Heces/microbiología , Concentración de Iones de Hidrógeno , Nitritos/química , Nitritos/metabolismo , Nitrógeno/aislamiento & purificación , Oxígeno/química , Oxígeno/metabolismo , Aguas del Alcantarillado/química , Factores de Tiempo , Eliminación de Residuos Líquidos/economía , Purificación del Agua/economía , Zooplancton/aislamiento & purificaciónRESUMEN
As part of a study examining the efficacy of high-rate algal pond treatment of high-strength abattoir wastewater, the impact of pond configuration and loading rate on nitrification was determined. The extent of nitrification in all ponds was consistent with mass balance estimates of oxygen demand and availability. Deeper ponds were more stable nitrifying systems, with shallow ponds displaying greater variation in response to changes in nitrogen loading. In a separate experiment the pond system was modified by covering a part of an in-series HRAP to exclude light, providing conditions suitable for denitrification. Specific denitrification rates were often within the range typical for endogenous carbon sources, with mass balance calculations indicating removals of up to 95%.
Asunto(s)
Mataderos , Eucariontes/crecimiento & desarrollo , Nitratos/metabolismo , Eliminación de Residuos Líquidos/métodos , Purificación del Agua/métodos , Amoníaco/aislamiento & purificación , Biodegradación Ambiental , Residuos Industriales , Nitratos/química , Nitrógeno/aislamiento & purificación , Oxígeno/química , Oxígeno/metabolismo , Australia del Sur , Factores de TiempoRESUMEN
A thermal profiling study was undertaken at four depths at each of nine sites, and at the inlets and outlets of a large waste stabilisation pond (WSP). Results were collected simultaneously using a network of 42 thermistors and dataloggers. Profiles at each site were categorised as either "stratified" or "unstratified", and persistence analysis was used to determine the frequency and persistence of stratification events at each of the nine sites. Stratification was found to persist most strongly at the site furthest upwind in the WSP, with respect to prevailing wind during the study, leading to the conclusion that stratification induced short-circuiting will be greatest in this region of the WSP. A computational fluid dynamics (CFD) model was constructed of the WSP, including an energy balance to predict the bulk stratification gradient in the pond. Environmental conditions and WSP inlet temperature during one day in June 2001 were used as boundary conditions. The pond thermal profiles measured during the profiling study, together with outlet temperature during the day, were used to validate the CFD model results. The model predicted mean pond temperature with a high degree of accuracy (r2 = 0.92). However it was evident that even modest winds (> or = 1.5 m/s) partially broke down stratification, leading to poor prediction of the gradient by the CFD model, which did not directly account for the impact of wind shear stress on mixing in the WSP.
Asunto(s)
Eliminación de Residuos Líquidos/métodos , Movimientos del Agua , Modelos Biológicos , Temperatura , Factores de Tiempo , VientoRESUMEN
AIMS: To determine the persistence of the faecal indicator organism Escherichia coli in recreational coastal water and sediment using laboratory-based microcosms and validation with in situ measurements. METHODS AND RESULTS: Intact sediment cores were taken from three distinct coastal sites. Overlying estuarine water was inoculated with known concentrations of E. coli and decay rates from both overlying water and sediment were determined following enumeration by the membrane filtration method at fixed time intervals over a 28-day period. It was demonstrated that E. coli may persist in coastal sediment for >28 days when incubated at 10 degrees C. Escherichia coli survival was found to have an inverse relationship with temperature in both water and sediment. In general the decay rate for E. coli was greater in water than in sediment. Small particle size and high organic carbon content were found to enhance E. coli survival in coastal sediments in the microcosms. CONCLUSIONS: Results of this microcosm study demonstrated the more prolonged survival of E. coli in coastal sediments compared with overlying water, which may imply an increased risk of exposure because of the possible resuspension of pathogenic micro-organisms during natural turbulence or human recreational activity. SIGNIFICANCE AND IMPACT OF THE STUDY: A more accurate estimate of exposure risk has been described which may subsequently be used in a quantitative microbial risk assessment for recreational coastal waters.
Asunto(s)
Escherichia coli/aislamiento & purificación , Sedimentos Geológicos/microbiología , Microbiología del Agua , Técnicas Bacteriológicas/métodos , Carbono/análisis , Recuento de Colonia Microbiana , Ecosistema , Exposición a Riesgos Ambientales , Heces/microbiología , Océanos y Mares , Tamaño de la Partícula , Recreación , Temperatura , Contaminación del AguaRESUMEN
This paper reports the results of work to allow a more accurate enumeration, and gravimetric determination, of the relative proportions of algae and bacteria within the floccular matrix present in a High Rate Algal Pond (HRAP). Methodology involving a combination of physical and chemical treatments was used and the resulting material was separated using density gradient centrifugation. The "fractions" were analysed using microscopical image analysis. Each "fraction" was categorised as containing bacteria only, algae only or an association of bacteria and algae, the relative proportions of which were then determined by image analysis to enable a "true" gravimetric determination of the algal and bacterial components of HRAP biomass for the first time. The biomass from HRAPs operated both outdoors and in a glasshouse was examined over complete operational seasons to investigate environmental effects as well as possible effects of variation in COD loading rate and retention time on cell biovolumes and cell quotients. In this study, the accurate assessment of both algal and bacterial biomass, determined as cell volume or dry matter, in addition to measurement of carbon and nitrogen has enabled the calculation of cell quotients. This allows a direct comparison between these values obtained from a nutrient-rich system and those published values obtained from systems with various nutrient status. Conversion factors obtained may also be of value for deriving inputs for computer models for the design and operation of high rate algal ponds.
Asunto(s)
Bacterias , Eucariontes , Eliminación de Residuos Líquidos/métodos , Biodegradación Ambiental , Biomasa , Monitoreo del Ambiente , Floculación , Microscopía , Dinámica Poblacional , Abastecimiento de AguaRESUMEN
As part of a study examining the efficacy of high-rate algal pond treatment of high-strength abattoir wastewater, the oxygen dynamics of a pilot scale system were characterised. The relationship between photosynthesis and irradiance was investigated using online data collected throughout a year of operation under varying conditions of climate and wastewater quality. Changes in climate were reflected in changes in the net rate of photosynthesis in deep ponds, consistent with adaptation of algal populations to changing light intensity, whilst the response of shallow ponds was more varied. The use of online monitoring and the calculation in real time of photosynthetic rates should allow for improved design and management of full scale treatment systems and further the understanding of factors driving biological reactions within these systems.
Asunto(s)
Mataderos , Eucariontes/fisiología , Oxígeno/metabolismo , Fotosíntesis , Eliminación de Residuos Líquidos/métodos , Animales , Automatización , Monitoreo del Ambiente , Contaminantes del Agua/análisisRESUMEN
The effect of light/dark (L:D) cycle times on the recovery from photoinhibition of green micro-alga Chlorella vulgaris (CCAP211/11c) and the cyanobacterium Synechococcus (CCAP1479/5) was investigated using an irradiated, temperature controlled oxygen electrode. The onset of photoinhibition in both organisms occurred at irradiances > 300 micromol m(-2)s(-1) at temperatures >15 degrees C. Light/dark cycle times were controlled independently using a relay timer and shutter placed between the quartz iodide light source and the oxygen electrode chamber. Oxygen evolution decreased rapidly when cells were continuously irradiated at 300, 500 and 750 micromol m(-2)s(-1). However, Chlorella cells irradiated at 300, 500 and 750 micromol m(-2)s(-1)on a L:D cycle of 60s:20s, 30s:60s and 60s: 120s respectively, maintained a constant rate of oxygen evolution over a 24 h incubation period. Exposure time to a given incident irradiance rather than the total light dose received appeared to determine the effect of light/dark cycle times on photosynthesis. A relationship was established between L:D ratio required to maintain constant oxygen production and incident photon flux density. The results suggest that the adverse effects of high irradiances on algae near the surface of a stratified waste stabilisation pond might be ameliorated by controlled mixing of algal cells through the depth of the pond.
Asunto(s)
Chlorella/fisiología , Cianobacterias/fisiología , Fotoperiodo , Fotosíntesis/fisiología , Reactores Biológicos , Temperatura , Eliminación de Residuos Líquidos , Abastecimiento de AguaRESUMEN
Over the past fifty years, considerable research in waste stabilization pond operation has led to the development of a number of models used to describe the hydraulic regime and predict treatment efficiency. Models range in complexity from plug or completely mixed simplifications to computational fluid dynamics (CFD) models which are able to predict flow hydraulics at a local level. Information about the exit age of pond effluent can be used to estimate pollutant decay. However, a mechanistic approach to understanding pond operation highlights the importance of knowing both the time and spatial history of pond effluent. A CFD model of a large pond system was constructed to demonstrate various hydraulic scenarios under different boundary conditions. Two scenarios were compared to visually demonstrate the effects of differing hydraulic conditions. Typical mechanistic models were applied to each condition to quantify biological differences. This simple example indicates that integrating biological and localised flow models will lead to a more holistic understanding of pond operation and treatment efficiency.
Asunto(s)
Modelos Teóricos , Eliminación de Residuos Líquidos/métodos , Movimientos del Agua , Reactores Biológicos , Control de CalidadRESUMEN
Algae play several key roles in waste stabilisation ponds. A model has been developed to predict algal concentration in waste stabilisation ponds, in which the relationship between photosynthesis and underwater light availability is central. One equation was selected from several alternative expressions that describe this relationship. The selected equation consisted of four photosynthetic parameters. A field sampling programme was designed to investigate the relationships between the photosynthetic parameters and the pond environment. Although initial regression analyses were unsuccessful, distinct diurnal variations were revealed in two key photosynthetic parameters, related to an inverse variation in chlorophyll a concentration. This led to the derivation of a dynamic feedback hypothesis which challenges the classic assumption in algal modelling of constant photosynthetic parameters.