Waste Stabilization Pond Effluent Research Articles

Optical characteristics of waste stabilization ponds: recommendations for monitoring

The optical character of waste stabilization ponds (WSPs) is of concern for several reasons. Algal photosynthesis, which produces oxygen for waste oxidation in WSPs, is influenced by attenuation of sunlight in ponds. Disinfection in WSPs is influenced by optical characteristics because solar UV exposure usually dominates inactivation. The optical nature of WSPs effluent also affects assimilation by receiving waters. Despite the importance of light behaviour in WSPs, few studies have been made of their optical characteristics. We discuss simple optical measures suitable for routine monitoring of WSPs (including at sites remote from laboratories): optical density of filtrates - an index of dissolved coloured organic (humic) matter, visual clarity - to provide an estimate of the beam attenuation coefficient (a fundamental quantity needed for optical modelling) colour (hue) - as an indicator of general WSP 'condition' and irradiance attenuation quantifying depth of light penetration. The value of optical characterisation of WSPs is illustrated with reference to optical data for WSPs in NZ (including high-rate algal ponds) treating dairy cattle wastewater versus domestic sewage. We encourage increased research on optical characteristics of WSPs and the incorporation of optical measures in monitoring and modelling of WSP performance.

Design of water hyacinth ponds for removing algal particles from waste stabilization ponds

In this study it was demonstrated that when water hyacinth ponds (WHPs) are used for polishing the effluent from waste stabilization ponds (WSPs), suspended solids (mostly algal particles) are efficiently separated, which also resulted in the reduction of insoluble forms of COD and nutrients. The high pH of the WSPs effluent was easily adjusted to 6-7 as it passed through the WHPs. However, the use of water hyacinth rapidly reduced dissolved oxygen at the first cell to less than three mg/L or very frequently to a level of anaerobic state. Reduction of suspended solids at the WHPs mainly depends on the detention time and pH. An empirical separation model incorporating the detention time and pH dependence was developed.

Use of coupled dynamic roughing filters and subsurface horizontal flow constructed wetland system as appropriate technology for upgrading waste stabilisation ponds effluents in Tanzania

As a part of a comprehensive evaluation of post-treatment techniques for upgrading waste stabilization pond (WSP) effluents, coupled dynamic roughing filters (DyRF) and subsurface horizontal flow constructed wetland system (HSSFCW) system was evaluated in Tanzania. Coupled DyRF and HSSFCW were considered as cheaper and yet effective and appropriate alternative technology for upgrading WSP effluents in tropical environments like Tanzania. The main objective of the study was to determine the performance treatment of coupled DyRF and HSSFCW for upgrading WSP effluents with respect to organic compounds (TSS and BOD 5) and pathogen (FC). A pilot of coupled DyRF and HSSFCW was constructed at the outlet of the Maturation WSP at the University of Dar es Salaam, Tanzania. The study was carried out in a 2.2 m × 0.7 m × 0.7 m deep DyRF as a first stage, using three different fractions of gravel ranging from 8 mm to 32 mm, from the top to the bottom respectively. In the second stage, a HSSFCW planted with Phragmites Mauritianus with 0.6-m wide, 1.75-m long and 0.6-m deep was used. The DyRF–HSSFCW system achieved TSS load reduction by 89.35%, which is 15.97 g TSS/m 2/day, while BOD 5 load reduction by 84.47% which is 9.29 g BOD 5/m 2/day was achieved. The FC mean removal rate of 99.99% was also achieved. By achieving mean effluent TSS (12.63 ± 4.12 mg/l), BOD 5 (14.12 ± 3.84 mg/l), and mean effluent FC concentrations of 790 FC/100 ml it was concluded that application of coupled DyRF and HSSFCW in the tropics can be considered technically one of the most appropriate technology for upgrading WSP effluents.

Sunlight inactivation of fecal indicator bacteria and bacteriophages from waste stabilization pond effluent in fresh and saline waters.

Sunlight inactivation in fresh (river) water of fecal coliforms, enterococci, Escherichia coli, somatic coliphages, and F-RNA phages from waste stabilization pond (WSP) effluent was compared. Ten experiments were conducted outdoors in 300-liter chambers, held at 14C (mean river water temperature). Sunlight inactivation (k(S)) rates, as a function of cumulative global solar radiation (insolation), were all more than 10 times higher than the corresponding dark inactivation (k(D)) rates in enclosed (control) chambers. The overall k(S) ranking (from greatest to least inactivation) was as follows: enterococci > fecal coliforms greater-than-or-equal E. coli > somatic coliphages > F-RNA phages. In winter, fecal coliform and enterococci inactivation rates were similar but, in summer, enterococci were inactivated far more rapidly. In four experiments that included freshwater-raw sewage mixtures, enterococci survived longer than fecal coliforms (a pattern opposite to that observed with the WSP effluent), but there was little difference in phage inactivation between effluents. In two experiments which included simulated estuarine water and seawater, sunlight inactivation of all of the indicators increased with increasing salinity. Inactivation rates in freshwater, as seen under different optical filters, decreased with the increase in the spectral cutoff (50% light transmission) wavelength. The enterococci and F-RNA phages were inactivated by a wide range of wavelengths, suggesting photooxidative damage. Inactivation of fecal coliforms and somatic coliphages was mainly by shorter (UV-B) wavelengths, a result consistent with photobiological damage. Fecal coliform repair mechanisms appear to be activated in WSPs, and the surviving cells exhibit greater sunlight resistance in natural waters than those from raw sewage. In contrast, enterococci appear to suffer photooxidative damage in WSPs, rendering them susceptible to further photooxidative damage after discharge. This suggests that they are unsuitable as indicators of WSP effluent discharges to natural waters. Although somatic coliphages are more sunlight resistant than the other indicators in seawater, F-RNA phages are the most resistant in freshwater, where they may thus better represent enteric virus survival.

Microbiological quality of a waste stabilization pond effluent used for restricted irrigation in Valle Del Cauca, Colombia

This paper discusses the applicability of effluent reuse in agriculture after treatment in a series of anaerobic, facultative and maturation ponds. The WSP system is located in Ginebra municipality, a small town in southwest Colombia. The total HRT is 12 days. Several samples of the final effluent were taken over a 55 day period and were analysed for E. coli, Streptococcus spp. and helminth eggs. Some additional grab samples were taken to determine the presence of pathogenic bacteria such as Salmonella spp. and Shigella spp. The results showed that the system was able to remove 4 log units of E. coli, 1 log unit of Streptococcus spp. and 100% of helminth eggs. Meanwhile, Salmonella spp. were detected in the effluent of the facultative pond whilst Shigella spp. were not detected in any sample. The main species of helminth eggs encountered were Taenia spp., Ascaris spp., Trichuris spp., Hymenolepis nana, H. diminuta and Enterobius vermicularis. Removal efficiencies were satisfactory despite the relatively short HRT. Nevertheless, WHO guidelines were slightly surpassed in the case of E. coli for unrestricted irrigation. The helminth egg value was always below the maximum WHO limit. Hence, this effluent can be safely used for restricted irrigation provided that field workers are protected from direct contact with wastewater given the presence of Salmonella spp. in the facultative pond effluent.

Control and separation of algae particles from WSP effluent by using floating aquatic plant root mats

In this paper, the potential uses of water hyacinth and its root mats for separating algae particles in the effluent from waste stabilization ponds (WSPs) were discussed. Pilot-scale integrated processes consisting of WSPs and multiple WHPs (water hyacinth ponds) were operated in order to extract effects of the root mats on the reduction of algae concentrations. Root mats in the bottom of WHPs separated significant amount of the algae cells through attachment as the effluent from WSPs passed through them. Attachment of the algae particles to the surface of live roots was found to be similar to adsorption phenomena but it lasted even at saturation, probably due to the continuous reproduction of active attachment sites by detachment and growth of the roots. Additionally, this paper discusses attachment mechanisms and other issues concerning design and polishing of the WSPs effluent by WHPs.

Analysis of socioeconomic and environmental impacts of waste stabilization pond and unrestricted wastewater irrigation: interface with maintenance.

The effluent from the waste stabilization ponds (WSPs) of the University of Nigeria, Nsukka Campus, is used for irrigation by poor rural farmers. There has been fear that the poorly maintained WSPs and the reuse practices are contributing to environmental degradation and health hazards. In this study the environmental and socioeconomic impacts of the WSPs and reuse were evaluated based on data collected from questionnaires and the literature. The engineering and agricultural properties of soil in the irrigated and nonirrigated areas were compared. Comparison of the health status of the farmers and nonfarmers, of consumers of crops irrigated with wastewater and nonconsumers was performed using Student's t test and the z-score test. The occurrences of diarrhea, typhoid fever, and malaria among the various groups were used as indices. Analyses show that the health status of the farmers and consumers is poorer than those of nonfarmers and nonconsumers at the 5% level of significance. Vegetable cultivation using WSP effluent is a means of sustenance to the farmers and provides an affordable means of satisfying their nutritional deficiencies. However, the poorly maintained WSPs create odor and mosquito nuisances, trap and destroy livestock, and flood nearby compounds with waste debris. At both 1% and 5% levels of significance, communities around the ponds (< 300 m) suffer malaria more frequently than those who live far away (> or = 300 m). Cost-benefit analysis argues in favor of improvement of WSP management and irrigation reuse of wastewater. Dredging of the ponds, training workers and farmers, and adopting appropriate maintenance and monitoring strategies will greatly enhance the socioeconomic status of the urban poor farmers.

Attenuation of microorganisms in the soil during drip irrigation with waste stabilization pond effluent

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 periods of 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.

Towards a mechanistic understanding of pond disinfection

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 was inactivated 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 &amp;lt; 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.

Roles of water hyacinths and their roots for reducing algal concentration in the effluent from waste stabilization ponds

This paper deals with use of water hyacinth and its root mats for controlling algal concentrations in the effluent from waste stabilization ponds (WSPs). Pilot-scale integrated processes coupled WSPs with multiple WHPs (water hyacinth ponds) were operated in order to determine the effects of the plant and root mats on reduction of algal concentrations on a quantitative basis. As flows from WSPs passed through the WHPs, root mats in the bottom as well as leaves and stems on the water surface of WHPs separated and controlled significant amount of algal cells by various mechanisms such as attachment, settling, respiration and suppression of algal growth. Attachment of algal particles to the plant roots was very similar to adsorption processes; i.e. there is a maximum capacity in a given weight of roots. However, effluent algal concentrations did not increase at saturation probably because of the sloughing-off of attached particles as a clump from the roots and generation of new attachment sites due to the growth of roots. Additionally, this paper discusses attachment forces and other issues concerning polishing of the WSPs effluent by WHPs.

Potential for reuse of waste stabilization pond effluent for irrigated agriculture

Potential for reuse of waste stabilization pond effluent for irrigated agriculture

Treatment of anoxic pond effluent using crossflow microfiltration

The treatment of anoxic waste stabilization pond effluent was investigated using crossflow microfiltration in conjunction with dynamic membranes. The primary membrane used throughout the study was made of woven polyester, while the dynamic membrane was formed of manganese dioxide (MnO 2). Effluent from a lab-scale anoxic waste stabilization pond was treated with and without the addition of slug doses of polyaluminum silicate sulphate (PASS) as a coagulant. Removal of suspended solids, turbidity, COD and E. coli was found to be affected by feed turbidity and the addition of PASS. On the other hand, removal of Streptococcus faecalis and algal species was found to be 100% and was not affected by feed turbidity. This was attributed to their size which could be more than the pore size of the dynamic membrane. Addition of slug doses of PASS were found to have a positive effect on the permeate flux and quality, which was attributed to the influence of crossflow velocity on the agglomerated particles.

Real-time quality monitoring by remote sensing of contaminated water-bodies: Waste stabilization pond effluent

The hypothesis of obtaining real-time water quality information was verified by monitoring a wastewater treatment facility consisting of a series of stabilization ponds, differing in quality and an adjacent reservoir. The changes in reflectance of the wastewater were the result of quality variations as expressed primarily by the suspended solids content, along the course of treatment. The variations in the wastewater quality along the treatment course, as well as in the reservoir at the end of the system are comparable with those in natural high quality water bodies. The importance of the proposed method is that it can promote better decision making with regards to heavily contaminated water bodies.

Evaluation of the WHO nematode egg guidelines for restricted and unrestricted irrigation

Epidemiological studies were conducted in Mexico to assess the health risks associated with restricted crop irrigation using raw and treated wastewaters. Experimental studies were done in northeast Brazil and Leeds, in which Ascaris lumbricoides contamination of lettuces spray-irrigated with raw wastewater and waste stabilization pond effluents containing different helminthological qualities was determined (Brazil); and Ascaridia galli infection was monitored in immunosuppressed chickens fed lettuces spray-irrigated with water containing different A. galli egg numbers (Leeds). The results indicate that the WHO guideline quality of ≤ 1 egg per litre protects crop consumers, but not necessarily fieldworkers and their families especially children. This is particularly the case when wastewater treatment systems are not stable, when recontamination of the partially treated wastewater with small quantities of raw wastewater may occur, and when wild vegetables are harvested and consumed. In such cases a stricter guideline quality of ≤ 0.5 egg per litre may be required.

Evaluation of the WHO nematode egg guidelines for restricted and unrestricted irrigation

Epidemiological studies were conducted in Mexico to assess the health risks associated with restricted crop irrigation using raw and treated wastewaters. Experimental studies were done in northeast Brazil and Leeds, in which Ascaris lumbricoides contamination of lettuces spray-irrigated with raw wastewater and waste stabilization pond effluents containing different helminthological qualities was determined (Brazil); and Ascaridia galli infection was monitored in immunosuppressed chickens fed lettuces spray-irrigated with water containing different A. galli egg numbers (Leeds). The results indicate that the WHO guideline quality of ≤ 1 egg per litre protects crop consumers, but not necessarily fieldworkers and their families especially children. This is particularly the case when wastewater treatment systems are not stable, when recontamination of the partially treated wastewater with small quantities of raw wastewater may occur, and when wild vegetables are harvested and consumed. In such cases a stricter guideline quality of ≤ 0.5 egg per litre may be required.

The bacterial quality of salad crops drip and furrow irrigated with waste stabilization pond effluent: an evaluation of the who guidelines

Field- and glasshouse-grown lettuces and radishes were drip- and furrow-irrigated with waste stabilization pond effluent and with trickling filter effluent diluted with clean water. Crop contamination levels varied considerably. Under dry weather conditions they were at worst of the orders of 103 and 104E. coli per 100 g (fresh weight) for radishes and lettuces, respectively; salmonellae were always absent. The bacterial quality of experimental lettuces was similar to those of lettuces on sale in local markets. When rainfall occurred E. coli numbers increased and salmonellae were isolated from lettuce surfaces. These results are interpreted as partially, substantiating the current World Health Organization bacteriological guideline for unrestricted wastewater reuse, but suggest the need for further assessment on the variation in crop contamination caused by climatic conditions.

Upgrading waste stabilization pond effluent by rock filters

Pilot-scale rock filters were constructed at the outlet of a large waste stabilization pond facility in Jordan. Their viability in upgrading the ponds' effluent was studied over a period of eleven months. This was done through studying the efficiency of four different types of locally available inexpensive materials placed in six filters and configured in three trains. The efficiency of each filter and the three combinations was evaluated. Results show that the filters can reduce the ponds' effluent content of TSS and BOD5 by 60%, TFCC by a maximum of 94% and T-P by 46%. This was achieved with a loading of 0.033-0.044 kgTSS/m3.d at an average temperature of 25 °C. Of the four media, the wadi gravel medium (3-23 cm) performed best. It was concluded that rock filters constitute a promising upgrading technique for pond effluent.

The bacterial quality of salad crops drip and furrow irrigated with waste stabilization pond effluent: An evaluation of the who guidelines

Field- and glasshouse-grown lettuces and radishes were drip- and furrow-irrigated with waste stabilization pond effluent and with trickling filter effluent diluted with clean water. Crop contamination levels varied considerably. Under dry weather conditions they were at worst of the orders of 103 and 104E. coli per 100 g (fresh weight) for radishes and lettuces, respectively; salmonellae were always absent. The bacterial quality of experimental lettuces was similar to those of lettuces on sale in local markets. When rainfall occurred E. coli numbers increased and salmonellae were isolated from lettuce surfaces. These results are interpreted as partially substantiating the current World Health Organization bacteriological guideline for unrestricted wastewater reuse, but suggest the need for further assessment on the variation in crop contamination caused by climatic conditions.

Upgrading waste stabilization pond effluent by rock filters

Pilot-scale rock filters were constructed at the outlet of a large waste stabilization pond facility in Jordan. Their viability in upgrading the ponds' effluent was studied over a period of eleven months. This was done through studying the efficiency of four different types of locally available inexpensive materials placed in six filters and configured in three trains. The efficiency of each filter and the three combinations was evaluated. Results show that the filters can reduce the ponds' effluent content of TSS and BOD5 by 60%, TFCC by a maximum of 94% and T-P by 46%. This was achieved with a loading of 0.033–0.044 kgTSS/m3.d at an average temperature of 25 °C. Of the four media, the wadi gravel medium (3–23 cm) performed best. It was concluded that rock filters constitute a promising upgrading technique for pond effluent.

Enumeration of salmonellae in wastewater by the MPN technique

Abstract A comparative study of the use of double and single strength RV enrichment media for the enumeration of salmonellae by the MPN method was carried out. Of 53 samples of raw municipal wastewater and waste stabilization pond effluents examined 83% yielded higher numbers of positive tubes when the various volumes of the samples utilized for the estimations were inoculated into single strength RV enrichment medium than when inoculated into double strength medium. Extending the incubation period of the XLD agar plates from 24h to 48h at 37°C increased the number of confirmed positive tubes by 1–9% with a mean value of 3%. The effect of the strength of the enrichment medium used on the MPN values is discussed.