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Reuse of sewage biosolids in Victoria, Australia, typically involves mesophilic anaerobic digestion followed by air-drying and long-term storage to ensure removal of ova of soil-transmitted helminths (STH) such as Ascaris lumbricoides. Long-term storage degrades the biosolids' agronomic quality due to the loss of key plant nutrients and takes up large areas of storage space. The impact of varying biosolids holding times and other processes on STH using Ascaris as the reference STH pathogen was examined in this study using a quantitative risk analysis approach. Risk modelling of the potential human health impacts from the presence of Ascaris ova in biosolids was undertaken for discrete holding periods of 1, 2 and 3 years. Modelling showed that to meet the WHO 1 µDALY·person-1·year-1 disease burdens guideline for limiting exposure category, a biosolids storage period of 1.24 years or 2.1 years would be required, depending on the data source of ova shedding rates per worm (Bangladesh or Nigeria, respectively). The soil exposure and salad/root vegetable consumption models included a number of variables with moderate to high degrees of uncertainty. Monte Carlo simulation was used to assess the effect of uncertainty in model input variables and to assist in highlighting areas for further research. [ABSTRACT FROM AUTHOR]

To estimate the expectable enhanced biological phosphorus removal value of a wastewater, the concentration of volatile fatty acids (VFAs) and the biochemical acidogenic potential (BAP) are generally determined on grab samples of wastewater, as these variables are prone to rapid change after sampling. However, such sampling technique do not take into account the variations of these parameters during the day. This work has evaluated the changes of VFAs and BAP occurring during sampling and storage in an automatic sampler over 24 h. The consequences of waterfall oxygen input during sampling, and changes during storage (fermentation and sulfatereducing process) were studied. The results for two wastewaters showed that the sampling technique used for daily flow proportional composite samples provided a correct estimation of VFAs, and underestimated BAP by up to 25%. For hourly-average composite samples of wastewaters, significant modifications of the concentrations of these two parameters were recorded around the daily average values. [ABSTRACT FROM AUTHOR]

Within the last 15 years 34 waste stabilization pond systems have been built in Central America in the countries of El Salvador (6 systems), Honduras (12 systems), Guatemala (9 systems), and Nicaragua (8 systems); these systems were built for municipalities with populations ranging from 5,000 to 80,000 persons. There are 14 additional systemsin the final design phase or under construction in the region, including the first designs for large cities: a 162 hectare facultative system for Managua, Nicaragua (population (1,000,000); and a 168 hectare system for San Pedro Sula, Honduras (population (640,000). Monitoring data from Honduras and Nicaragua show that treatment efficiency isgenerally comparable to tropical pond systems cited in the literature in other parts of the world, although fecal coliform removal has not been as good as theoretically predicted and the desludging of facultative ponds has been a significant operational cost. While waste stabilization ponds are generally considered the technology of choice for municipal wastewater treatment within Central America, there are, nevertheless, problem areas that need to be addressed if waste stabilization pond use is to have continued acceptance and long-term sustainability. These areas of concern at the regional level are: i) design guidelines using parameters from data developed in Central America; ii) effluent guidelines that are realistic for pond effluents for reuse or surface water discharge; iii) monitoring programs focusing specifically on pathogen removal; iv) cost-effective grit removal and sludge removal from facultative ponds; v) improving designs for pathogen removal; vi) the need for centralized (El Salvador and Nicaragua) versus decentralized (Guatemala and Honduras) mechanisms for financing and operation and maintenance; vii) the development of comparative cost data for construction, operation and maintenance, pond desludging, and microbiological monitoring; and viii) the development of trainingpr [ABSTRACT FROM AUTHOR]

A broad overview of mechanisms of disinfection of waste stabilization ponds (WSPs) is based on a review of the literature on indicator micro-organisms in ponds, including our own recent experiments. There is appreciable evidence that sunlight is the single most important factor in WSP disinfection. Much of the uncertainty in the literature regarding pond disinfection may reflect the interaction of sunlight with other factors, including dissolved oxygen (DO) and pH, which fluctuate diurnally within WSPs owing to algal metabolism. Our experiments with WSP effluent (conducted in small, stirred reactors with well-controlled physico-chemical conditions) showed that different faecal indicators are inactivated by different components of the solar spectrum, and the rates of sunlight inactivation have differing dependencies on physico-chemical conditions. For example, F-specific DNA phage wasinactivated only by solar UV-B (300-320 nm) at a rate unaffected by other factors, whereas enterococci and F-specific RNA phage were inactivated by a wide range of wavelengths (300-550 nm) by (DO-dependent)photo-oxidation. Sunlight inactivation of faecal coliforms was particularly complicated: at pHs < 8.5 only solar UV-B (300-320 nm) caused(slow) inactivation, but at higher pHs, the inactivation rate increased and a wider range of wavelengths (300-550 nm) contributed - suggesting photo-oxidative damage to membranes which sensitises faecal coliforms to high external pH. Our findings on the different influences of physico-chemical conditions for different indicators suggest difficulties in interpreting microbiological quality of WSP effluent in terms of a single indicator micro-organism. However, clearly disinfection in WSPs may be enhanced by increasing sunlight exposure, for example with shallower ponds or increased residence times. [ABSTRACT FROM AUTHOR]

The wastewater stabilisation ponds system of the city of Boujaad wasconstructed and put into operation in 1992. The two main objectives of this plant are the prevention of pollution of water resources and the environment by means of wastewater discharges as well as the saving of fresh water by means of reuse of treated wastewater for irrigation purposes. Within the period of March 1997 to March 1998 a comprehensive analysis campaign of both the raw and the treated wastewater at a number of different sampling points has been carried out in orderto evaluate the treatment efficiency of this wastewater treatment plant.The results of these investigations showed an average raw wastewater flow of 1600 m3/d, which is well below the design flowof 2500 m3/d, With respect to the physico-chemical treated wastewater quality and in comparison with the French treated wastewater standards (1980) these results indicated that 90 % of the wastewater samples showed BOD5-figures below the quoted French standard, whereas 83 % of the samples showed COD-figures above the corresponding French treated wastewater standard. With average treated wastewater suspended solids contents of 56 mg/l the suspended solids removal ratehas been determined as being in the range of 65 %. If compared to the anticipated Moroccan wastewater standards for direct wastewater discharge into receiving water bodies as stipulated in the Moroccan Standards Project the obtained wastewater analysis results showed COD- and BOD5 values below these foreseen Moroccan wastewater discharge standards. The analysis results of SS, TKN and total phosphorus (Ptot) showed figures slightly above these Moroccan standards. In view of the microbiological wastewater characteristics the treated effluents of the Boujaad WSP respond to the WHO directive with respect to wastewater to be used for restricted irrigation (category B). Taking into consideration the CEC directive for wastewater generate [ABSTRACT FROM AUTHOR]

Respirometric tests have been undertaken on sediments in aerated lagoons and waste stabilization ponds to quantify their oxygen demand and to determine the main factors governing the process. Factors such as seasonal variations, temperature, substrate, sediment layer thickness, density of macro-invertebrates and suspended sediments were investigated. The results showed that temperature and substrate concentration are the main factors that influence sediment oxygen demand; followed by spatial heterogeneity and resuspension of sediments, whereas the density of macro-invertebrates could have an effect in summer (hotseason). Sediment layer thickness had no effect. A model of sedimentoxygen demand is developed for the two main factors (temperature andsubstrate) with an r2 of 0.98. [ABSTRACT FROM AUTHOR]

The sludge layer in a primary, facultative wastewater stabilization pond in Texcoco, Mexico was studied. Five sludge cores were taken in the pond, near the entrance, middle, exit, and at the midpoint about 5 m from each side. Each core was stratified into four subsamples andanalyzed. Temperature, pH, ORP, and %VS decreased with depth (age) in the sludge layer, whereas ammonia and TS concentrations increased. The concentrations of fecal coliforms and viable helminth eggs also decreased with depth in the sludge layer, but significant concentrations of both organisms were still present in the oldest sludge, which is estimated to be over seven years old (average). From a sludge depthsurvey it was found that the majority of the sludge accumulated nearthe inlet of the pond. The average net sludge accumulation rate was estimated to be 24 mm/yr. [ABSTRACT FROM AUTHOR]

The Altiplano, located at 15 deg. -20 deg. S, has an altitude of about 4000 m above sea level which determines extreme climatic conditions that may affect the performance of stabilization ponds: strong solar radiation due to a thin atmosphere of rarefied, clean, dry air; lowmean temperatures of water and air; strong differences in temperature between day and night; low oxygen pressure. The oxygen pressure at 4000 m altitude is only 60% of that at sea level. However, lower water temperatures increase oxygen solubility in water compensating for the effect of altitude in the actual concentration of dissolved oxygenin water. Lack of oxygen is not a crucial limiting factor for sewagetreatment at high altitudes. Anaerobic ponds are effective in the Altiplano, in spite of the low water temperatures (7-9 deg. C). Design criteria for WSP at different altitudes in Bolivia are presented. An important conclusion with social connotations is that the communitiesof the Altiplano will need to construct waste stabilization ponds which are 3-5 times larger (and more expensive) than those of the 'Los Llanos'. [ABSTRACT FROM AUTHOR]

A kinetic model has been developed to predict changes with time of different parameters (COD, nitrogen, phosphorus, phytoplankton and alkalinity) in urban wastewater stored in deep (13.5 m) stabilization ponds in southeastern Spain. The effect of thermal stratification on the behaviour of the pond is represented in the model by means of two interconnected reactors, one above the other, representing the hypolimnion and the epilimnion respectively, separated by a moving thermocline. The values predicted by the model closely matched the experimental results. [ABSTRACT FROM AUTHOR]

The Bertrix wastewater treatment plant was designed and built for experimental purposes, especially for comparing aerated lagoons and stabilization ponds in a temperate climate. This plant was designed for a capacity of 7500 inhab. eq, and aerated lagoons were dimensioned toeliminate 50% of the organic load. The remaining load has to be degraded in the series of stabilization ponds. In this paper we shall present the plant in more detail and the results of a 3-year study, i.e., 79 rounds of samples for each of the five ponds under study, placing emphasis on the performances of aerated lagoons and stabilization ponds. Principal components analysis (of inflow and outflow) of aerated lagoons and stabilization ponds will be presented and commented on.The most important factors are the hydraulic loading and the concentrations. Seasonal variations appear only in the basins' temperatures.The fates of nitrogen compounds are quite different from those of organic compounds, confirming that a high efficiency of nitrogen removal is difficult to achieve, especially for short residence times (lessthan eight days). A few other conclusions of our study are given below: The ponds' hydrodynamics has been studied and a mathematical model is now available If there is no stratification in the ponds, a thermal model can be proposed where the mean absolute difference is 0.7 deg. C+/-0.2. In the system under study, the contribution of algal biomass to the system is very small. [ABSTRACT FROM AUTHOR]

A tracer test was performed in a 3,000 m3 and 1 m deep maturation pond located in the south of France. A retention time distribution was determined on the basis of tracer study. Tracer distribution into the pond was also monitored. Physico-chemical parameters and faecal coliform contents were measured at pond inlet and outlet and at 4 points in the pond. During the same period, two 20 m3 and 1 m deep pilot pools were set close to the pond and filled with inlet water. A die-off constant was calculated after the variations offeacal coliform contents observed in the pilot pools. The objective was to verify whether faecal coliform removal can be predicted from observed retention time distribution, assuming a first-order faecal coliform decay with a die-off constant determined in pilot pools. A very good prediction was achieved despite some uncertainties in the experimental data mainly due to pond operation and climatic conditions. [ABSTRACT FROM AUTHOR]

A 3-modular units facultative waste stabilisation pond was experimentally studied for performance and efficiency, in relation to its original design. The system was located at La Esmeralda, Melipilla a small town of the central region in Chile. It was found that treated water did not comply with treatment requirements due to overloading, flowdynamics, wrong assumptions regarding hydraulic mixing behaviour, and an overestimation of systems kinetics. The overloading in terms of flow led to a retention time which was 62% of original design. Furthermore, bad mixing further decreased the designed residence time to only 18%. The effluent did not meet the WHO faecal coliforms guidelinesfor unrestricted irrigation. The modelling work on the batch faecal coliforms and coliphage removal concluded that the effective decay rates were 1.359x1.087(T-20 deg. C) day-1 for coliforms, and 0.439x1.044(T-20 deg. C) day-1 for coliphages. The data was also well fitted by a model that incorporated solar radiation. However, model discrimination indicated that the dependence on temperature gave a better and more sensitive fit with the observed data. As theoriginal design considered a lower faecal coliforms decay ratio, namely 0.7 day-1, the failure of the system had to relate more to mixing than overloading. Operational seasonal data (flow and retention time) and physical, chemical and microbiological parameters, and tracer studies are included. Some solutions for improving the La Esmeralda SWP performance are also discussed. [ABSTRACT FROM AUTHOR]

In laboratory-scale batch experiments, duckweed (Limna gibba)-based and algae-based wastewater containers have been monitored over 15 days in two experiments with different initial total nitrogen concentrations of 50 (experiment 1) and 100 mg-N/L (experiment 2). Clear differences in environmental conditions were observed. High dissolved oxygen (DO) concentrations were observed in the algae-based ,compared to duckweed-based, containers. In the algae-based containers the DO rangewas between 2.1 to 6.6 mg/L and 1.2 to 4.3 mg/L in experiment 1 and 2, respectively, whereas in the duckweed-based containers DO ranged between 1.1 to 3 mg/l and 0.5 to 2.1 mg/L. Higher pH values were measured in algae-based due to algal photosynthetic activity compared to duckweed-based containers where the duckweed mat prevented sunlight penetration and hence algal development. In algae-based containers, thepH range was 7.9 to 8.6 and 8.1 to 8.4 in experiments 1 and 2, respectively, and 7.3 to 7.5 and 7 to 7.6 in the duckweed-based containers. Depending on initial nitrogen concentrations, duckweed-based containers removed between 42%-62% of total nitrogen and between 56%-95% ofKjeldahl nitrogen from the wastewater, while algae-based containers removed between 45%-48% and 48%-58% of total nitrogen and Kjeldahl nitrogen, respectively. Nitrogen loss, probably due to denitrification and ammonia volatilisation, represents 40% of the total nitrogen content of algae-based and duckweed-based containers. However, in duckweed-based containers only 28% of N-loss was observed in containers withhigher initial N-content. This study demonstrates that there were differences in environmental conditions in algae-based and duckweed-based containers, which have caused differences in nitrogen transformation mechanisms. [ABSTRACT FROM AUTHOR]

Heavy metals, zinc (Zn), copper (Cu) and lead (Pb) removal in two wastewater treatment units were compared. One of the systems consisted of a train of Waste Stabilisation Ponds (WSP) including one anaerobic, three facultative in series and two maturation ponds, also in series. The other system, called High Rate Ponds (HRP) consisted of one anaerobic, one High Rate Algal Pond (HRAP) and two maturation ponds in series. The two treatment systems were located on the same site and received the same wastewater. Data collected from the two treatment systems, for a period of three consecutive months (May, June and July, 1995) show that the content of the three elements in the crude wastewater of the city of Ouarzazate varied from 210 to 340 mg/l for Zn; 35to 55 for Cu and 30 to 25 for Pb. The removal rate for the three elements reached 91, 92 and 71% respectively for Zn, Cu and Pb in the WSP train. The corresponding values in the HRP train were, respectively89, 88 and 51%. However, since the two trains were not receiving thesame flow, the use of specific removal rate expressed as mg removed m-2 d-1 showed that the HRAP was 1.3, 10 and 2 times more efficient respectively for Zn, Cu and Pb removal than the three facultative ponds in series of the WSP. Also, the collected data showed that the content of the sediment of the anaerobic pond was high for all the three elements. However, the recorded concentrations 613, 99 and 78 mg/kg, respectively for Zn, Cu and Pb did not exceed the EEC recommended limits. [ABSTRACT FROM AUTHOR]

The waste stabilization pond (WSP) systems are useful for the treatment of wastewater. Despite a good knowledge of these systems, the dynamics of phosphorus elimination in these systems are not well known, especially concerning the forms of phosphorus in the sediment. Phosphorus dynamics were studied with data collected from the three stabilization ponds of the Meze (France) system. A conceptual model based ontheoretical considerations was developed, and applied to each pond. The percentage of observed variation described by these models rangedbetween 46.2% and 74.1%. The results showed that the principal variables affecting orthophosphate in WSP systems were phosphorus input and particulate phosphorus. When the model was applied to high rate algal pond (HRAP) data, the role of photosynthesis on pH increase and P precipitation was clear. Sediments sampled in the three facultative ponds were characterised with a fractionation scheme, currently used for sediments of natural aquatic ecosystems. Inorganic phosphorus accounted for 92-94% of total sediment phosphorus, with 57-59% bound to iron hydroxides and 33-37% bound to calcium. Surprisingly, organic phosphorus represented only between 6 and 8%. Polyphosphate was detected. Phosphorus concentration was greatest in the sediment from the third pond, where an aerobic layer at the sediment surface prevented phosphorus release. [ABSTRACT FROM AUTHOR]

Waste stabilization ponds (WSP) are one of the most appropriate wastewater treatment methods to reduce nematode and faecal coliforms. However, there is still a risk of contamination of crops and soil irrigated with this kind of effluent. The purpose of this work was to examine the fate of microorganisms (faecal coliforms, F+, and somatic coliphages and helminth eggs), from WSP effluent used for irrigation of a vineyard orchard, under onsurface (ODI) and subsurface drip (SDI) systems. The field is located near the City of Arad (Israel). The soil and water samples were taken during the irrigation periodsof two consecutive years (1997 and1998). During the first year the vineyard was irrigated with a low quality effluent from WSP (sedimentation and maturation ponds only) and during the second year a high quality effluent (sedimentation, anaerobic, and a series of aerobic ponds and a final reservoir) was used. The results showed a substantial elimination of microorganisms in the soil, decreasing negative impacts, and minimising environmental and health risks. [ABSTRACT FROM AUTHOR]

Most wastewater treatment programs in Morocco are directed towards reuse of the effluent in irrigation. A ten-year running of an experimental two-stabilization-pond system in Marrakech showed that despite retention times around 50 days, the quality of the effluent corresponded to a restrictive irrigation reuse (B category according to the WHOguidelines). This quality can be achieved even with BOD loading reaching 780-1000 kg BOD / had in one anoxic stabilization pond with a depth of 2.3 m and a retention time of 9.5 days. This primary anoxic pond did not show signs of organic matter over-loading with an active algae population, a pH all the time higher than 7 and a nematode egg concentration lower than 1 egg/L. The performance of such a system in terms of organic matter removal can be evaluated using a linear relation of the same type as the one proposed by Mac Gary and Pescod but with lower removal efficiency. However, nitrogen levels were still high with a concentration above FAO irrigation standards and can lead togroundwater quality degradation. We proposed an integrated approach to stabilization pond design that can be based on the required effluent quality to protect both public health (WHO guidelines) and the receiving environment. Groundwater vulnerability maps should be drawn and evaluated for nitrogen and other pollutant tolerance before any wastewater treatment system design. Models for nitrogen removal in stabilization ponds should be combined with those already in use for organic matter and pathogenic organisms removal to allow design of systemsthat are aesthetically attractive, sanitarily safe and harmless to the receiving environment. [ABSTRACT FROM AUTHOR]

Nitrogen removal from wastewater from rubber factories using attached-growth waste stabilization ponds (AGWSP) was evaluated. Usually, wastewaters generated from rubber factories such as concentrated latex factories and rubber sheet factories contain a high amount of nitrogen originating from natural rubber and ammonia compounds added in the production processes. From an investigation of 3 rubber factories, atSongkhla, Thailand, average concentrations of TKN, NH3-N and Org-N in raw factory wastewater were found to be 889, 578 and 311mg/l respectively. Two series of laboratory waste treatment ponds, waste stabilization ponds (WSP) and attached-growth waste stabilization ponds were investigated to compare the efficiency of nitrogen removal from wastewater from a concentrated latex factory. The wastewater fed to the experimental units was collected from the effluent of the anaerobic treatment pond at the factory. The experiments were conducted with hydraulic retention times (HRT) of 40 and 20 days. Another experiment run with an HRT of 40 days together with 50% recirculating of effluent was also conducted. Finally, an experiment run at an HRT of 4 days was carried out in order to observe the effect of shock loading. The results revealed that TKN, NH3-N and BOD5 removal efficiencies in AGWSP were higher than in control ponds (WSP). Increased removal efficiencies were achieved which resulted from an increase in biomass on media in the pond water. (C) 1999 Published by Elsevier Science Ltd on behalf of die IAWQ. All rights reserved. [ABSTRACT FROM AUTHOR]

The Danish International Development Assistance agency has funded a project in Bhutan which includes a water supply component in six urban centres, a sewerage component in the two largest cities plus associated institutional development. The project includes the implementation of an extensive water-borne sewerage system and associated wastewater treatment. The treatment process adopted was waste stabilisation pond technology due to the low associated construction, operations and maintenance costs and low requirements for technical skills hence contributing to financial and O&M sustainability of the project, as well as meeting the water quality requirements for the receiving waters. Since essentially all available land is utilised in the country, the locations of the treatment plants are adjacent to rivers which are fast flowing, leading to a risk of severe erosion conditions during the monsoon season. In order to protect the treatment plant structure,river training was necessary. The high elevation of the country alsohas consequences for the design and operation of the plants. The wastewater treatment process includes a train of anaerobic, secondary facultative and maturation ponds, lined with a high density polyethylene liner. This paper describes the project as implemented, focusing onthe wastewater treatment plants and the hurdles required to be overcome to ensure sustainable operation of the waste stabilisation pond treatment plants, in particular overall design of the system, the re-design required due to the loss of land occasioned by the intense monsoon rains in the south of the country prior to construction of river training works, the training required for the local staff from the operations and maintenance authorities and the financial aspects of theproject. Thc project is discussed within a broader framework of Danish development aid in the country which covers the health, environment and the public health infrastructure sectors. Lessons learnt from the p [ABSTRACT FROM AUTHOR]

Performance of baffles in waste stabilization ponds (WSP) comprisinglaboratory-scale ponds with different number of baffles was evaluated. This study was aimed at promoting waste stabilization ponds practice for wastewater treatment in tropical countries by reducing the land area requirement through the use of baffles which increased the biofilm and biomass concentrations. The experiments started with the tracer study to find out the hydraulic characteristics of each pond. It was shown that the dispersion number decreased with increasing flow length and number of baffles, which indicates more plug flow conditions. The deviation of actual HRT from theoretical HRT was computed and the flow pattern suggested the existence of an optimum spacing of baffles in baffled waste stabilization pond (BWSP) units. The investigations by feeding with synthetic wastewater further revealed that more than 65% TN and 90% NH3-N removal were achieved at HRT of 5 days in 6-baffled pond which corresponds to the specific area of 35.20 m2/m3. TN and NH3-N removal was increasing with number of baffles in the BWSP units. COD removal increased with higher number of baffles with its maximum removal efficiency at 6 baffles. The computed COD removal encompassed first-order reactions of both suspended and biofilm biomass was higher than that without the biofilm biomass activity and agreed well with the observed data. Compared with normal WSP, BWSP gave higher TN, NH3-N and COD removal. The effluent SS concentrations from 6 baffled-pond were less than 20 mg/l at HRT of 3 days. [ABSTRACT FROM AUTHOR]