Evaluation of agricultural reuse practices and relevant guidelines for the alba rancho WWTP (primary and secondary facultative ponds) in Cochabamba, Bolivia.

Many cities in developing countries are experiencing high population growth, which is generating chaotic and unplanned development, reducing land areas available for agriculture, and polluting surface and groundwater. Consequently, the reuse of untreated or partially treated wastewater for agricultural irrigation is increasing in arid and semi-arid regions in developing countries. Cochabamba city in Bolivia also has a high population growth. The climatic characteristics and the lack of clean water sources in this city are forcing the agriculture sector to use treated and untreated wastewater for irrigation. We investigated the effluent quality of the Alba Rancho Wastewater Treatment Plant (WWTP) in Cochabamba, Bolivia, and the existing effluent reuse practices for irrigation of fodder crops in the surrounding agricultural land (La Mayca area). The plant uses primary and secondary facultative ponds, and does not achieve the required effluent quality (according to Bolivian environmental law) for effluent BOD, COD, TDS and faecal coliforms. This paper also includes a brief comparison of guidelines for wastewater reuse in agriculture from several developing and developed countries, comparing the parameters measured as pollution indicators. It appears that for developed countries, the main concern is the health risk that reuse can cause to the farmers and consumers. For developing countries on the other hand, pollution reduction is currently the major aim in their guidelines and standards.     

Feasibility of a constructed wetland and wastewater stabilisation pond system as a sewage reclamation system for agricultural reuse in a decentralised rural area.

The performance of a constructed wetland (CW) and wastewater stabilisation pond (WSP) system for sewage reclamation and paddy rice irrigation in a decentralised rural area was examined using a feasibility study. The CW was satisfactory for sewage treatment, with good removal efficiency even in the winter period, but the effluent concentration was relatively high in the winter period owing to the high influent concentration. The CW effluent was further treated in a WSP and the WSP effluent was considered safe for crop irrigation with respect to sewage-borne pathogens. Reclaimed water irrigation did not adversely affect the yield of rice; on the contrary, it resulted in an approximately 50% greater yield than in controls. The chemical characteristics of the soil did not change significantly during the experimental period of irrigation with reclaimed water. In the winter, CW effluent could be stored and treated in a WSP until the spring; the water could then be discharged or reused for supplemental irrigation during the typical Korean spring drought. Overall, sewage treatment and agronomic reuse using a CW-WSP system could be a practical integrated sewage management measure for protecting receiving water bodies and overcoming water shortages in decentralised rural areas.     

Reuse potential analysis on WWTP effluent of industrial parks in Taiwan.

This study examined the reuse potential of the effluents discharged from several unified wastewater treatment plants (WWTPs) of industrial parks in Taiwan, with designed capacity exceeding 10,000 CMD. Parameters were selected based on the relevant reuse purposes. The "potential recycling percentage", R of the WWTP effluent was defined as the maximal percentage of pure water extractable by the "ideal reverse osmosis module" while the RO retentate still met local effluent standards and required no treatment. The analytical results demonstrated that the WWTP effluents had potential for recycling. A pilot plant was installed in one of the WWTPs. The treatment process included a sand filter, an ultrafiltration unit (UF) and a reverse osmosis module (RO). Results of this study demonstrated that the production quantity and quality are stable and appropriate for various purposes, including both industrial and domestic applications.     

Changes in waste stabilisation pond performance resulting from the retrofit of activated sludge treatment upstream: part II--Management and operating issues.

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.     

Sustainability of Natural and Mechanized Aerated Ponds for Domestic and Municipal Wastewater Treatment in Palestine

Abstract

More than half of the current wastewater treatment facilities constructed in Palestine are waste stabilization ponds (WSP) and have several problems in their operation. This article evaluates three selected case studies on the various pond systems including WSP, algae- and duckweed-based ponds (ABP and DBP, respectively) and one mechanically aerated lagoon (AL) system. The effects of various design and operating parameters on the pond system' performance, with special emphasis on nitrogen removal, are discussed. The effluent quality of WSP and AL complies only with BOD limits, but not with microbiological limits prescribed for agricultural purposes, as determined by national standards. ABP and DBP achieved nitrogen removal only under high surface area demand (5-7 m2capita-1). Suitable plans for modifying existing aerated lagoons or for upgrading natural lagoons are suggested in order to comply with microbiological standards for effluent use in restricted irrigation. Finally, the suggested sustainability criteria for the evaluated pond systems may help the decision makers, as well as their designers and donor countries, to better select and design low-cost treatment options for sustainable wastewater management in developing countries.     

Waste stabilization ponds and rock filters: solutions for small communities.

In temperate climates facultative ponds and rock filters (either unaerated or, if ammonia removal is required, aerated) are a low-cost but high-performance treatment system for small rural communities. Effluent quality is suitable for surface water discharge or, in summer, for restricted crop irrigation. In tropical climates anaerobic and facultative ponds and either unaerated rock filters or, if ammonia reduction is required, subsurface horizontal-flow or vertical-flow constructed wetland, can be used if the effluents are discharged to surface waters. However, if the treated wastewater is to be used for crop irrigation, then a 3-log unit pathogen reduction by treatment in anaerobic, facultative and single maturation ponds is required for both restricted and unrestricted irrigation, provided that, in the case of unrestricted irrigation, there are in place post-treatment health-protection control measures that together provide a further 4-log unit pathogen reduction.     

Simple wastewater treatment (UASB reactor, shallow polishing ponds, coarse rock filter) allowing compliance with different reuse criteria.

UASB reactors followed by polishing ponds comprise simple and economic wastewater treatment systems, capable of reaching very high removal efficiencies of pathogenic organisms, leading to the potential use of the effluent for unrestricted irrigation. However, for other types of reuse (urban and industrial), ponds are limited in the sense of producing effluents with high suspended solids (algae) concentrations. The work investigates a system with coarse rock filters for polishing the pond effluent. The overall performance of the system is analyzed, together with the potential for different types of reuse. The excellent results obtained (mean effluent concentrations: BOD: 27 mg/L; SS: 26 mg/L; E. coli: 450 MPN/100 mL) indicate the possibility of unrestricted use of the effluent for agriculture and restricted urban and industrial uses, according to WHO and USEPA.     

Reuse of treated wastewater and sewage sludge for fertilization and irrigation

The objective of the present work was to assess the short-term potential of treated wastewater and sewage sludge for ornamental lawn fertilization and irrigation. A field experiment was performed and the following treatments were considered: sewage sludge application + irrigation with public water; sewage sludge application + irrigation with treated wastewater; irrigation with public water; irrigation with treated wastewater (TW). Irrigation with treated wastewater showed a positive effect on lawn installation through higher growth of grass (1,667 cm) and higher dry matter yield (18,147 g m(-2)). These results represent a significant increase in the grass yield compared with public water irrigation. The grass height (2,606 cm) and dry matter yield (23,177 g m(-2)) increased even more, when sewage sludge produced in the wastewater treatment plant (WWTP) was applied to soil, which proves once more its benefits as an organic fertilizer. At the end of the experiment, an increase of some soil parameters (pH, electrical conductivity, organic matter, Ca2+, Na+, K+, Mg2+ and NH4+) was observed, indicating that treated wastewater irrigation can cause a soil sodization. This short-term study indicated that use of treated wastewater and sewage sludge for ornamental lawn fertilization and irrigation is an environmentally sustainable option for re-use of the WWTP by-products.     

Comparison of nutrient cycling in a surface-flow constructed wetland and in a facultative pond treating secondary effluent.

There is a growing interest in the possibilities offered by combinations of waste stabilisation ponds (WSP) and constructed wetlands (CW). The purpose of our study was to compare treatment performances and nutrient cycling in a surface-flow wetland (SFW) and in a WSP treating secondary effluent. In the period between 2000 and 2003, a pilot SFW and a pilot WSP were constructed at the outlet of the wastewater treatment plant and their performance monitored while both were active under the same conditions. The SFW was planted with Phragmites australis and Eichhornia crassipes, while in the WSP development of algae was spontaneous. Performance efficiency was monitored by means of evaluation of physical and chemical parameters in water, by measurement of plant productivity and by analysis of N and P contents in biomass. The SFW with macrophytes proved more efficient in decreasing the suspended solids (64.6%), settleable solids (91.8%), organic N (59.3%), total N (38%), COD (67.2%) and BOD5 (72.1%) than the WSP. The WSP with algae was more efficient in treatment of ammonia nitrogen (48.9%) and ortho-phosphate (43.9%). The results of this study provide data that are of help in optimising combinations of SFW and WSP.     

Nitrogen speciation in wastewater treatment plant influents and effluents-the US and Polish case studies.

The fate of N species, particularly dissolved organic nitrogen (DON), through process trains of a wastewater treatment plant (WWTP) was investigated. In this study, three fully nitrifying plants in Illinois, USA and biological nutrient removal (BNR) plants in northern Poland were sampled for N characterization in the primary and secondary effluents as a function of the particle size distribution. The correlations between dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations were examined. The key findings are that DON becomes significant portion (about 20%) of the effluent N, reaching up to 50% of effluent total N in one of the Polish plants. The DON constituted 56-95% of total ON (TON) in the secondary effluents, whereas in the Polish plants the DON contribution was substantially lower (19-62%) and in one case (Gdansk WWTP) colloidal ON was the dominating fraction (62% of TON). The DOC to DON ratio in the US plants is significantly lower than that in the receiving waters indicating potential for deterioration of receiving water quality. In Polish plants, the influent and effluent C:N ratios are similar, but not in the US plants.     

Performance of very shallow ponds treating effluents from UASB reactors.

Polishing ponds are units conceived for the post-treatment of the effluents from anaerobic reactors, are designed as maturation ponds, and aim at a further removal of organic matter and a high removal of pathogenic organisms. The paper investigates the performance of four very shallow (H = 0.40 m) polishing ponds in series, with very low detention times (1.4-2.5 days in each pond), treating anaerobic effluent from the city of Belo Horizonte, Brazil. The system was able to achieve excellent results in terms of BOD and E. coli removal, and good results in terms of ammonia removal, allowing compliance with European standards for urban wastewater and WHO guidelines for unrestricted irrigation. The paper presents the values of BOD and E. coli removal coefficients, which were much higher than those found in conventional pond systems. No statistically significant difference was found in the effluent E. coli concentrations from a pond with low depth and low detention time, and another pond in parallel, with double the depth and approximately double the detention time. The results endorse the applicability of the system composed by UASB reactors followed by very shallow ponds in series, with low detention times.     

SHARON process evaluated for improved wastewater treatment plant nitrogen effluent quality.

New stricter nitrogen effluent standards and increasing influent loads require existing wastewater treatment plans (WWTPs) to extend or optimize. At WWTPs with limited aeration capacity, limited denitrification capacity or shortage of aerobic sludge age, implementation of SHARON to improve nitrogen effluent quality can be a solution. SHARON is a compact, sustainable and cost-effective biological process for treatment of nitrogen-rich rejection waters. At WWTP Rotterdam-Dokhaven and WWTP Utrecht a SHARON has been in operation for several years. For both WWTPs the effect of SHARON on the nitrogen effluent quality has been evaluated. WWTP Rotterdam-Dokhaven has limited aeration capacity. By implementation of SHARON, the ammonia load of the effluent was reduced by 50%. WWTP Utrecht had limited denitrification capacity. The implementation of SHARON improved the effluent nitrate load by 40%. The overall TN removal efficiency increased from 65% to over 75% and strict nitrogen effluents standards (TN = 10 mg N/l) could be reached. Through modelling and supported by full scale practice it has been shown that by implementation of SHARON in combination with enhanced influent pre-treatment, the aerobic sludge age can be extended to maintain total nitrogen removal at lower temperatures.     

Wastewater irrigation of salad crops: further evidence for the evaluation of the WHO guidelines.

This paper presents the results of an experiment on salad crop irrigation with waste stabilisation pond effluents, conducted in Southeast Brazil. Over about 18 months several trials were carried out using different effluent qualities to irrigate lettuce, kale, arugula, spinach, and green pepper. Equations for predicting the bacterial quality of irrigated crops (E.coli per gram) based on the irrigation water quality (E.coli per 100 mL) were derived for low and high growing crops. The quantitative microbial risk analysis (QMRA) technique, using pathogen-ingestion scenarios based on these field data and on official statistics of vegetables consumption in Brazil, was used to estimate infection risks arising from the consumption of wastewater irrigated crops. It is inferred that irrigation with effluents complying with the WHO guidelines for unrestricted irrigation should result in salad crops acceptable for consumption.     

Nitrification in bulk water and biofilms of algae wastewater stabilization ponds.

Nitrogen removal in wastewater stabilization ponds is poorly understood and effluent monitoring data show a wide range of differences in ammonium. For effluent discharge into the environment, low levels of nitrogen are recommended. Nitrification is limiting in facultative wastewater stabilization ponds. The reason why nitrification is considered to be limiting is attributed to low growth rate and wash out of the nitrifiers. Therefore to maintain a population, attached growth is required. The aim of this research is to study the relative contribution of bulk water and biofilms with respect to nitrification. The hypothesis is that nitrification can be enhanced in stabilization ponds by increasing the surface area for nitrifier attachment. In order to achieve this, transparent pond reactors representing water columns in algae WSP have been used. To discriminate between bulk and biofilm activity, 5-day batch activity tests were carried out with bulk water and biofilm sampled. The observed value for Rnitrbulk was 2.7 x 10(-1) mg-N L(-1) d(-1) and for Rbiofilm was 1,495 mg-N m(-2) d(-1). During the 5 days of experiment with the biofilm, ammonia reduction was rapid on the first day. Therefore, a short-term biofilm activity test was performed to confirm this rapid decrease. Results revealed a nitrification rate, Rbiofilm, of 2,125 mg-N m(-2) d(-1) for the first 5 hours of the test, which is higher than the 1,495 mg-N m(-2) d(-1), observed on the first day of the 7-day biofilm activity test. Rbiofilm and Rnitrbulk values obtained in the batch activity tests were used as parameters in a mass balance model equation. The model was calibrated by adjusting the fraction of the pond volume and biofilm area that is active (i.e. aerobic). When assuming a depth of 0.08 m active upper layer, the model could describe well the measured effluent values for the pond reactors. The calibrated model was validated by predicting effluent Kjeldahl nitrogen of algae ponds in Palestine and Colombia. The model equation predicted well the effluent concentrations of ponds in Palestine.     

Experience in non-conventional wastewater treatment techniques used in the Czech Republic.

Among the most common non-conventional wastewater treatment techniques used in the Czech Republic are waste stabilisation ponds (WSP), subsurface horizontal flow constructed wetlands (CW) and vertical flow groundfilters (GF). These extensive systems can be advantageously used for treatment of waters coming from sewerages where the ballast weighting commonly makes more than half of dry-weather flow. The monitoring was focused at 14 different extensive systems. Organics removal efficiencies were favourable (CW-82%; GF-88%); in the case of WSP only 57% due to the algal bloom. Total nitrogen removal efficiencies were 43 and 47% for WSP and GF; in the case of CW only 32% due to often occurring anaerobic conditions in filter beds. Total phosphorus removal efficiencies were 37, 35 and 22% for WSP, GF and CW, respectively. Often occurring problems are the ice-blockage of surface aerators at WSP during wintertimes, the pond duckweed-cover or the algal bloom at WSP during summers; a gradual colmatage of filter systems; and the oxygen deficiency in beds of subsurface horizontal flow constructed wetlands. Czech legal regulations do not allow treated wastewater disposal into underground waters. There is only an exception for individual family houses. Up to now, knowledge gained by monitoring of a village (which uses the infiltration upon a permission issued according to earlier legal regulations) have not shown an unacceptable groundwater quality deterioration into the infiltration areas.     

Effluent treatment by multi-media filtration, microfiltration and ultrafiltration: results of a pilot investigation at WWTP Hoek van Holland.

Upgrading of wastewater treatment plant (WWTP) effluent as a part of the Dutch governmental policy to close the water cycle has increasing interest now. The Water Board Hoogheemraadschap van Delfland together with the project team of Witteveen + Bos Consulting Engineers, Delft University of Technology and Rossmark water treatment investigated the reuse possibilities of WWTP effluent in the region of Delfland. Therefore pilot research was carried out at WWTP Hoek van Holland applying different filtration techniques: multi-media filtration, micro- and ultrafiltration. The results show stable process performances of the different filtration techniques when proper pre-treatment was applied. For microfiltration the filtration characteristics were strongly influenced by particles which were not retained in the multi-media filter. For ultrafiltration the filtration characteristics were strongly influenced by organic components < 0.2 microm. The upgraded WWTP effluent could not be used directly as process water or for agriculture purposes, due to high concentrations of COD and salts in the WWTP effluent and filtrates. However WWTP effluent or floc filtrate could be applied directly as water for the washing of sea-sand.     

Membrane bioreactor application in wastewater re-use from the effluent of Bali primary WWTP, northern Taiwan.

Two MBR pilot systems were constructed and tested in the Bali Primary WWTP. The pilot study shows that two MBR systems, i.e. the Green-MenBio system (MBR-1) and the Bio-MF system (MBR-2), can both fulfill the requirement of wastewater reclamation standard. The MBR-2 system is more economical compared with MBR-1 system. The cost of US dollars 0.10-0.16/m3 is estimated to reclaim the effluent of primary WWTP in Taiwan. The Bali Primary WWTP has the capacity of 1,320,000 cmd which is the biggest in Taiwan. The domestic wastewater of partial Taipei City and Taipei County are collected and transported to the Bali Primary WWTP. The effluent of the Bali Primary WWTP is then discharged into the ocean through two 3.8 m marine outfalls. The AO processes are installed in both MBR systems. More than 90% of the NH3-N can be removed through the AO and membrane processes. The outflow of the MBR systems (without RO) can reach the quality of COD <30 mg/l, BOD <10 mg/l, SS <5 mg/l, NH3-N <3 mg/L. The outflow of the MBR system is proposed to transport 40 km south to the Taoyuan County where four new industrial parks are to be constructed. Part of the reclaimed water is to be used on irrigation and another portion is to be sent to the industries after RO treatment.     

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.     

Plant-wide (BSM2) evaluation of reject water treatment with a SHARON-Anammox process.

In wastewater treatment plants (WWTPs) equipped with sludge digestion and dewatering systems, the reject water originating from these facilities contributes significantly to the nitrogen load of the activated sludge tanks, to which it is typically recycled. In this paper, the impact of reject water streams on the performance of a WWTP is assessed in a simulation study, using the Benchmark Simulation Model no. 2 (BSM2), that includes the processes describing sludge treatment and in this way allows for plant-wide evaluation. Comparison of performance of a WWTP without reject water with a WWTP where reject water is recycled to the primary clarifier, i.e. the BSM2 plant, shows that the ammonium load of the influent to the primary clarifier is 28% higher in the case of reject water recycling. This results in violation of the effluent total nitrogen limit. In order to relieve the main wastewater treatment plant, reject water treatment with a combined SHARON-Anammox process seems a promising option. The simulation results indicate that significant improvements of the effluent quality of the main wastewater treatment plant can be realized. An economic evaluation of the different scenarios is performed using an Operating Cost Index (OCI).     

Pathogen removal efficiency from UASB + BF effluent using conventional and UV post-treatment systems.

The aim of this study was to verify the efficiency of removal of microorganisms in effluents of a Wastewater Treatment Plant (WWTP) comprising an association of a UASB reactor followed by three submerged aerated biofilters (BAF) and one tertiary filter. The WWTP designed to treat domestic wastewater from a population of 1,000 inhabitants showed high removal efficiency for organic matter and suspended solids. Helminth eggs were also efficiently removed from the tertiary effluent and were found in the sludge from the UASB reactor; however, removal of bacteria in this system was very low. To enhance the efficiency of the system, the effluent from tertiary filters was submitted to UV disinfection in a real scale reactor. Our results showed that UV irradiation was very effective at lowering the concentrations of E. coli, thermotolerant coliforms and coliphages to acceptable levels for agricultural reuse. Salmonella spp. and helminth eggs were seeded into the tertiary effluent before passing through the UV reactor. Salmonella was not found in the final effluent, but helminth eggs were not completely inactivated by UV irradiation and viable eggs were detected after 28 d of incubation.