Fecal Coliform Removal Research Articles

Rapid and de-centralized model for municipal effluent reclamation using microalgae

Abstract Microalgal bioremediation is currently being venerated for its potential in municipal liquid waste (MLW) treatment. Algae-based water treatment with retention time competitive to the conventional water treatment processes is a challenge. The present study investigated the role of algal biomass concentration to improve treatment efficiency to reduce the time required for water treatment. Eighty percent removal of pollutants (in terms of chemical oxygen demand (COD), ammonia, phosphate and fecal coliforms) was obtained in 12 hours at a biomass concentration of 1 gL−1. Further, continuous treatment of MLW using membrane-assisted photobioreactor was established. The treatment led to >95% removal of ammonia, >75% removal of COD and 100% removal of fecal coliforms within 12 hours. Physiological assessment of the algal culture showed that the cells did not manifest symptoms of stress throughout the reactor cycle, a consequence of continuous availability of the nutrients, maintaining the culture in continuous growth state.

A novel low-cost multi-barrier system for drinking water treatment in rural and suburban areas

Abstract A low-cost multi-barrier drinking water system incorporating geotextile fabric for pre-filtration, silver-coated ceramic granular media (SCCGM) for filtration and disinfection, granular activated carbon (GAC) as an adsorption media and a safe storage compartment for treated water has been developed and tested. The developed system offers a novel concept of point-of-use drinking water treatment in rural and suburban areas of developing countries. The system is primarily aimed at bacterial and aesthetic improvement and has been optimised to produce >99.99% E. coli and fecal coliforms removal. Although particular emphasis was placed on the elimination of bacteria, improvement of the acceptability aspects of water was also given high priority so that users are not motivated to use more appealing but potentially unsafe sources. This paper discusses key system features and contaminant removal performance. A system using SCCGM only was also tested alongside the multi-barrier system. Strengths and weaknesses of the system are also presented. Both the developed and SCCGM-only systems consistently provided >99.99% E. coli and fecal coliforms removal at an optimum flow of 2 L/h. The developed system significantly recorded improvements of aesthetic aspects (turbidity, color, taste and odor). Average turbidity removals were 99.2% and 90.2% by the multi-barrier and SCCGM-only systems respectively.

REMOCIÓN DE TENSOACTIVOS Y COLIFORMES EN AGUAS RESIDUALES DOMÉSTICAS MEDIANTE PROCESOS FENTON

In many developing countries, domestic wastewater is one of the major pollution sources to water bodies, and advanced oxidation processes appear nowadays as a promising solution to this problem. In this work, the conventional Fenton process, and the chelate-modified Fenton process with citric acid, were tested for surfactants and fecal coliforms removal from an effluent of a domestic wastewater treatment plant located in Quito city, Ecuador. The best conditions (agitation requirements, H 2 O 2 concentration and Fe 2+ :H 2 O 2 molar ratio) for the conventional Fenton process were found. These conditions were applied to the chelate-modified Fenton process with citric acid. For this process, two Fe 2+ :citrate molar ratios (1:1 and 1:1.25) were tested at four pH values (2.80, 4.50, 6.00, and 7.84). The best results were achieved with a H 2 O 2 concentration of 56.33 mM, a Fe 2+ :citrate:H 2 O 2 molar ratio of 1:1:9, continuous stirring and a pH value of 6. The application of these conditions allowed a complete removal of fecal coliforms, a 97 % reduction of surfactants and an 89 % decrease in chemical oxygen demand in 15 min of treatment. The resulting treated waters complied with water quality standards for discharge to water bodies according to the Ecuadorian legislation. This work provides valuable data on the effectiveness of these treatments, thus presenting them as potential solutions for the problematic of domestic wastewater treatment.

Evaluation of Occurrence, Concentration, and Removal of Pathogenic Parasites and Fecal Coliforms in Three Waste Stabilization Pond Systems in Tanzania.

In Tanzania, waste stabilization ponds (WSPs) are employed to treat wastewater, and effluents are used for urban agricultural activities. The use of untreated or partially treated wastewater poses risks of disease transmission, including parasitic and bacterial infections, to exposed communities. Little is known about the occurrence, concentration, and removal of parasites and fecal coliform (FC) bacteria in WSPs in Tanzania. This study evaluates the occurrence and concentration of parasites and FCs in wastewater, the efficiency of WSPs in removing parasites and FCs, and the validity of using FCs as an indicator of parasites. This was a cross-sectional study conducted between February and August 2018. Wastewater samples were collected from three WSPs located in the Morogoro, Mwanza, and Iringa regions. APHA methods were used to test physicochemical parameters. The modified Bailenger method and Ziehl–Neelsen stain were used to analyse parasites. Membrane filtration method was used to analyse FCs. Data were analysed using IBM SPSS version 20. Helminth egg removal ranged from 80.8% to 100%. Protozoan (oo)cyst removal ranged from 98.8% to 99.9%. The Mwanza WSP showed the highest FC reduction (3.8 log units (100 mL)−1). Both the parasites and FCs detected in the effluents of assessed WSPs were of higher concentrations than World Health Organization and Tanzania Bureau of Standards limits, except for helminths in the Morogoro WSP and FCs in the Mwanza WSP. FCs were significantly correlated with protozoa (p < 0.01) and predicted protozoa occurrence well (p=0.011). There were correlations between physicochemical parameters, parasites, and FC bacteria in the WSP systems. Inadequate performance of these systems may be due to lack of regular maintenance and/or systems operating beyond their capacity. FC indicators were observed to be a good alternative for protozoa monitoring, but not for helminths. Therefore, during wastewater quality monitoring, helminths should be surveyed independently.

Biological Sand Filter Performance Test Using Multiple Methods for Pathogen Detection: a Longitudinal Field Study in Kenya

Fifty biological sand filters (BSFs) housed in 70-L plastic containers were built and installed in the West Pokot County of Kenya. Half of the BSFs were installed in June 2010; the remainder were installed in June 2012. BSF performance was analyzed during June 2012 and 2015. Performance indicators included the removal of turbidity and fecal and total coliforms. In 2012, 17 of the original 25 BSFs installed were operational, and their performance was evaluated. In 2015, 15 of the BSFs were operational. BSF performance during 2015 showed an average fecal coliform removal of 98.9%. The most common reasons provided to explain why the BSF installed was no longer in use included the family moved and the BSF was too heavy to carry, and the effluent pipe broke. Relative affluence was observed using the Progress out of Poverty Index (PPI)™. With an increase in elevation, we noted a decrease in PPI. The average PPI for homesteads with operation BSFs was 10 points higher than homes where the BSFs were in disrepair. An assay to estimate Escherichia coli presence and concentration was modified, and the results were compared with more traditional field enumeration methods. The field assay used a five-compartment bag to quantify the most probable number (MPN) of E. coli to provide a low-tech option to field workers in developing country to test the viability of drinking water sources. We used a Hach medium, varying from that prescribed by Aquagenx. Results from using the modified method compared well with the more traditional field assay.

Upflow anaerobic sludge blanket reactor and biofilter in polyethylene as an alternative of decentralized wastewater treatment in municipality of Rio Rufino – SC

Basic sanitation services are essential for promoting public health and for mitigating environmental damage. Thus, the objective of this work was to evaluate a wastewater treatment system consisting of anaerobic sludge blanket reactor and biofilter, as an alternative for the decentralized wastewater treatment in the municipality of Rio Rufino - Santa Catarina. The system was evaluated for its efficiency of removal of fecal coliforms, biochemical oxygen demand, chemical oxygen demand, soluble chemical oxygen demand, phosphorus, Total Kjhedal Nitrogen, nitrite, nitrate, sedimentable solids and maintenance of the hydrogen potential in the effluent. The treated effluent had its parameters compared to the standards established by Resolution 430/2011 of the Conselho Nacional do Meio Ambiente and Law 14.675 / 2009 of the State of Santa Catarina. It was also performed the estimate of the daily biochemical oxygen demand load, originated by the population of the municipality, and its respective impact. The effluent treated by the proposed system, when properly installed, follows what was established by the legislation, which implies in reducing the impacts caused by the municipality. In this way, the system can be an interesting alternative when it comes to decentralized wastewater treatment.

Contrasting Water Quality Treatments Result in Structural and Functional Changes to Wetland Plant-Associated Microbial Communities in Lab-Scale Mesocosms.

The impact of contrasting water quality treatments on wetland plant-associated microbial communities was investigated in this study using 12 lab-scale wetland mesocosms (subsurface flow design) planted with reed canary grass (Phalaris arundinacea) or water speedwell (Veronica anagallis-aquatica) over a 13-week period. Mesocosms received water collected from two sites along the Grand River (Ontario, Canada) designated as having either high or poor water quality according to Grand River Conservation Authority classifications. All mesocosms were established using sediment collected from the high water quality site and received water from this source pre-treatment. Resulting changes to microbial community structure were assessed using PCR-denaturing gel gradient electrophoresis (DGGE) on microbial 16S rDNA sequences extracted from rhizoplane, rhizosphere, and water samples before and after exposure to water quality treatments. Functional community changes were determined using Biolog™ EcoPlates which assess community-level carbon source utilization profiles. Wetland mesocosm removal of inorganic nutrients (N, P) and fecal coliforms was also determined, and compared among treatments. Treatment-specific effects were assessed using a repeated measures restricted maximum likelihood (REML) analysis. Structural and functional characteristics of rhizoplane microbial communities were significantly influenced by the interaction between plant species and water treatment (P = 0.04, P = 0.01). Plant species-specific effects were observed for rhizosphere structural diversity (P = 0.01) and wetland water community metabolic diversity (P = 0.03). The effect of water treatment alone was significant for structural diversity measurements in wetland water communities (P = 0.03). The effect of plant species, water quality treatment, and the interaction between the two is dependent on the microhabitat type (rhizoplane, rhizosphere, or water). Rhizoplane communities appear to be more sensitive to water quality-specific environmental changes and may be a good candidate for microbial community-based monitoring of wetland ecosystems.

Assessment of roughing and slow sand filter modified with slag and clinker ash for removal of microorganisms from secondary effluent

ABSTRACT Slow sand filtration has been used for decades for the removal of pathogens from water. A combination of roughing and slow sand filters has been evaluated for the removal of pathogen indicators from secondary effluent. The filter system was modified with the addition of slag and coal clinker ash. The filter system reached up to 100% removal of faecal coliforms, faecal streptococci, Escherichia coli and total coliforms after 17 weeks of treatment. Log reductions ranged between 0.0–4.1, 1.33–2.0, 1.34–2.37 and 1.4–4.5 for E. coli, faecal streptococci, faecal coliforms and total coliforms respectively. There was no strong correlation between pH and the bacterial counts as correlation coefficients were −0.15, 0.15, 0.38 and −0.07 in respect to E. coli, faecal coliforms, faecal streptococci and total coliforms. The correlation coefficients for temperature were −0.18, −0.14, 0.10, and −0.39 for E. coli, faecal coliforms, faecal streptococci and total coliforms respectively, suggesting that temperature did not influence the bacterial removal efficiency. For turbidity, the correlation coefficients were 0.64, 0.70, 0.68 and −0.06 respectively, for E. coli, faecal coliforms, faecal streptococci and total coliforms. Only total coliforms had no correlation with turbidity. There was a significant difference between effluent from holding tank and slow sand filter as p values of 0.008, 0.0006, 0.00000, and 0.00008 were observed for faecal coliforms, faecal streptococci, E. coli and total coliforms counts, respectively. The results obtained indicate that the combination of roughing and slow sand filters can successfully reduce microorganisms from secondary wastewater.

Assessing local materials for the treatment of wastewater in open drains.

In the present study, three low-cost filter aggregate materials were tested and compared for organic matter and fecal coliform (FC) removal at the laboratory scale. Setups were subjected to synthetic wastewater at two hydraulic loading rates (HLR), i.e. 4 cm/day and 40 cm/day. The hydraulic retention time (HRT) at the two HLRs varied from 4 days to 12 h, respectively. The result obtained shows that the biochemical oxygen demand (BOD5) removal efficiency of aggregate materials decreased with the increase in HLR. Both at high and low HLR, the terracotta aggregate material exhibited maximum BOD5 loading removal and without significant difference for the case of FC removal efficiency for all the three aggregate materials. At higher HLR, cell debris and biofilm loss from the aggregate material contributed to the chemical oxygen demand (COD) levels in the treated water. The terracotta aggregate material provided best organic matter removal at both HLRs. The study demonstrates the potential of incorporating inexpensive and readily available local materials into decentralized, frugal green infrastructure interventions capable of lowering the quantum of harmful biological contaminants in open storm water channels in rapidly urbanizing cities of developing countries, and that the terracotta aggregate material provided best organic removal at both HLRs.

Influence of design and operational parameters on the pathogens reduction in constructed wetland under the climate change scenario

Under the climate change scenario, constructed wetlands (CWs) as an engineered system for treating domestic wastewater will face different challenges. Some of them are: (a) the increase of pathogens concentration in wastewater due to the rise of global temperature; (b) higher precipitation that can cause an increase of pathogens due to runoff; (c) the reuse of treated wastewater related to the water scarcity. These problems can affect the capacity of CWs for removal pathogens. In this context, the objective of this review is to provide an overview of the influence of design and operational parameters on pathogens reduction in CWs. To accomplish with this purpose, the published information (> 30 studies) about the reduction of pathogens and the operational and design parameters in different CWs configurations and were gathered. With this data, statistical analyses were performed considering the most relevant variables which significantly influence the removal of pathogens in CWs. For this, principal component analyses (PCA) were achieved for determining, separately, the correlation of operational parameters with fecal coliform (FC) and total coliform (TC) removal. The results of PCA showed that FC and TC were correlated positively with mass removal rates of chemical oxygen demand (COD) and biological oxygen Demand (BOD5), total suspended solids (TSS) removal and the size of support medium. This study is the first approach that analyzes together the design and operational parameters which influence the pathogen removal in CWs. For this reason, these parameters and the increase on microorganism concentrations due to the climate change have to be considered for the future design of CWs.

Antibiotic resistant bacteria removal of subsurface flow constructed wetlands from hospital wastewater

Eight horizontal subsurface flow pilot scale artificial wetlands were constructed to evaluate their effectiveness in the removal of antibiotic-resistant bacteria from hospital wastewater. A total of 40 composite samples were collected from the inlet and outlet of wetlands, transported and processed for enumeration of indicator organisms, bacteriological identification and susceptibility testing following standard procedure. The treatment wetlands achieved 7.1 logs10 and 5.1 logs10 removal of total and fecal coliforms. Among the total samples, 159 bacterial isolates were detected, of these 45 (28.3%) were from hospital wastewater and 114 (71.7%) from the outlets of wetlands. The most frequently isolated bacteria from hospital wastewater samples were found to be Staphylococcus sp 12 (26.6%) followed by E.coli 11(24.4%), Klebsiella sp 9(20%) and Shigella sp 5(11.1%). Similarly, the overall isolates in treated wastewater samples were E.coli 45(39.5%), Staphylococcus (35.1%) and Klebsiella sp 35 (30.7%). Among bacterial isolates from hospital wastewater, 100% of Salmonella isolates were found to be resistant to ampicillin and 75% to doxycycline, erythromycin, ceftazidime, cefoxitin, and chloramphenicol. E.coli was also found to be 81.8% resistant to ampicillin and 72.7% to cotrimoxazole and amoxicillin-clavulanic acid. Significantly (P < 0.005) higher removal (80.8% to 93.2%) of antibiotic-resistant bacteria was recorded in vegetated wetlands. In contrary, no significant difference between the vegetated and non-vegetated wetlands was observed in the removal of indicator and pathogenic bacteria. Constructed wetlands could help to solve the problem of the cost-effective disposal of hospital wastewater and be promoted in a strategy to reduce water pollution in low-income countries like Ethiopia.

A small-scale low-cost water treatment system for removal of selected heavy metals, bacteria and particles

Abstract Two low-cost sand filtration systems incorporating granular activated carbon (GAC) and non-woven geotextile respectively were assessed for Point-of-Use water treatment. Laboratory scale models were evaluated in respect of selected heavy metals, bacterial and particulate removal when exposed to surface water for five months. System 1 (ISSF-1) incorporated GAC and system 2 (ISSF-2) incorporated non-woven geotextile. Filter-mats were placed on the filter surfaces of both systems. Flow rates ranged between 8 and 15 L/h for longer water contact with the GAC and bio-layer. On average, E.coli removals were 96% and 94%, while fecal coliform removals were 96% and 95%, by ISSF-1 and ISSF-2 respectively. Average TSS removals were 98% and 92%, while turbidity removals were 97% and 91%, by ISSF-1 and ISSF-2 respectively. Average metal removals were: Arsenic (21%), Cadmium (82%), Lead (36%), Iron (65%) and Manganese (94%) by ISSF-1, Arsenic (17%), Cadmium (&amp;lt;LoD), Lead (&amp;lt;LoD), Iron (92%) and Manganese (98%) by ISSF-2. Both models consistently met turbidity guideline (5 NTU) and can remove significant amounts of particles. Both systems can treat the poor-quality water used to provide relatively safe water and could be improved further for heavy metal removal. However, to guarantee continued safe-water supply, supplementary treatment by chlorination is recommended.

Investigation of nutrients and faecal coliforms removal in wastewater using a hydroponic system

Fresh water resources are diminishing rapidly through increased inadequately treated or untreated wastewater disposal in water bodies. Disposal of untreated wastewater in freshwater bodies threatens the environment, aquatic and human life. The primary objective of this study was to investigate the removal of contaminants using a simple cost effective hydroponic system in the treatment of raw wastewater to allowable discharge limits. After macrophytes were planted and water circulated in the hydroponic system the influent and effluent samples were collected at various time intervals between 24 and 244 h for the period of 3 months at varying concentrations. Ammonia, nitrite, nitrate and total phosphorus were measured using spectrophotometric methods and membrane filtration technique was used for faecal coliform counts. The removal of ammonia, nitrite, nitrate, total phosphorus and faecal coliforms reached 87%, 96%, 99%, 87% and 92% respectively. The paired t-test indicated the removal of these contaminants to be statistically significant (0.019 ≥ p ≥ 0.001). Irrespective of the change in wastewater composition the system efficiently treated water to allowable discharge limits. The system proved to be a cheaper method of wastewater treatment and its applications may offer an alternative to the problems of wastewater treatment in areas where modern systems are either unavailable or cost ineffective.

Comparison of Reed and Water Lettuce in Constructed Wetlands for Wastewater Treatment.

In the present study two designs, vertical and horizontal systems, were used and two different plant species, Water Lettuce (Pistia stratiotes) and Reed plant (Phragmites karka), compared for their removal efficiency. The vertical system appeared to be more stable and efficient for almost all the parameters. The vertical system, planted with Water Lettuce, showed percentage removal efficiency for BOD, phosphate and chloride as 82, 95.4, and 51, respectively, whereas turbidity and total suspended solids removal efficiencies were almost the same. However, fecal coliform removal by the Water Lettuce was 98.8% for both designs (vertical and horizontal), showing the ability of the plant to uptake nutrients and release toxins for pathogen disinfection. It appears that the vertical system could be the better option, planted with Water Lettuce, or with both plants in a co-culture environment.

Solar drying of wastewater sludge: a case study in Marrakesh, Morocco

ABSTRACTThis paper presents a site-specific study of solar drying of wastewater sludge in the region of Marrakesh in Morocco. During the course of the experiments, drying pans (DP) and solar greenhouse drying processes were studied in summer and winter seasons. To simulate the DP process, representative samples were dried in plastic cylindrical plates in ambient conditions, near an Open Greenhouse Sludge Dryer (OGSD) designed and constructed as a tunnel plant. Results showed that the dry solids' (DS) concentration of 80% was reached in only 32 h in summer and 57 h in winter by DP process. The OGSD reached the same concentration in 45 and 65 h in summer and winter, respectively. The important influence of wind speed had a greater effect than the temperature on drying rate. The sludge water evaporation caused a large volume reduction during DP and OGSD processes in both seasons. The removal of total and fecal coliforms during summer experiment was noticeably better in the OGSD, even for Clostridium perfringens. Based on the obtained results, the solar greenhouse drying was practical and beneficial to wastewater sludge management and can be recommended as an alternative to DP in arid climate zones generally, and in Marrakesh particularly.

Detailing the start-up and microalgal growth performance of a full-scale photobioreactor operated with bioindustrial wastewater

In this study, a full-scale enclosed microalgal air-lift photobioreactor (PBR) module was operated using both defined and industrial wastewater (WW) media. In the effort to establish full-scale operation: a WW ultrafiltration system, two algal productions, and a harvesting microfiltration system were tested. Bioindustrial WW medium was treated with ultrafiltration and was demonstrated to be a viable microalgal growth medium at large scale; however, further treatment is needed for the removal of fecal coliform to meet drinking water standards. The fresh water mesophilic algae Chlorella sorokiniana was successfully grown on bioindustrial WW medium at suboptimal temperatures (<25°C) and natural lighting with peak specific growth rate (SGR) of 0.48day−1, consistent with lab-scale results from literature. Optical densities (OD) of the algae at 665, 680, and 735nm were found to be viable proxies for cell number of C. sorokiniana grown outdoors with daily fluctuations, despite inherent differences in chlorophyll sensitivity at each absorbance wavelength. However, OD measurements at different reactor locations shown to diverge at the onset of growth. Greenhouse temperature and solar insolation were measured, where it was observed that the SGR did not considerably improve from higher solar irradiance during periods of lower temperatures. Finally, the viability of harvested cells after microfiltration was also examined, with a negative exponential correlation between cell death and the volume of remaining filter condensate (R2=0.9247).

Long-term assessment at field scale of Floating Treatment Wetlands for improvement of water quality and provision of ecosystem services in a eutrophic urban pond.

Pollution of urban water bodies requires stringent control measures and the development of low-cost and highly efficient alternative technologies. In contrast to Constructed Wetlands, Floating Treatment Wetlands (FTWs) have the advantage of not requiring large surface of land since they operate in situ. However, there is limited information about their long-term evaluation while operating at field scale. The aim of this work was to assess the performance of FTWs using a combination of Pontederia sagittata and Cyperus papyrus for the improvement of the water quality and provision of ecosystem services of a eutrophic urban pond. The FTWs were built with low-cost material easy to acquire and to ensemble. Two FTWs (17.5m2 and 33m2) located in Pond 1 within a complex of 4 urban artificial ponds were evaluated for two years. They promoted an increase in the dissolved oxygen (D.O.) within a range of 15 to 67%, a removal of fecal coliforms in the range of 9 to 86% and a nitrate removal in the range of 9 to 76%. The plant productivity reached a maximum of 363gdmm-2d-1 in the FTW1 and 536gdmm-2d-1 in the FTW2 during the period March-June 2016. The TKN and the TP content in the plant were in the range of 18.3 to 28.1 and of 0.05 to 0.196gkg-1 dry matter, respectively. In conclusion, the tested FTWs have proved to be a very beneficial low-cost technology for the improvement of water quality and provision of ecosystem services.

Influences of low-energy input microwave and ultrasonic pretreatments on single-stage and temperature-phased anaerobic digestion (TPAD) of municipal wastewater sludge

The effect of low energy-input (2.5 kJ/g total solids) microwave (MW) irradiation and ultrasonication (US) on single-stage mesophilic anaerobic digestion (AD) and temperature-phased AD (TPAD) treating wastewater sludge was assessed. The goal was to achieve a higher net energy along with improved digestate for agricultural applications. At sludge retention times (SRT) of 20 and 14 days, TPAD achieved significantly (39–45%) higher methane production, pathogen destruction (4-log) and digester volume reductions compared to single-stage AD (controls). The higher methane yields resulted in higher net energies for TPAD (4.7–5.1 kJ/g volatile solids or VS) compared to controls (3.3–3.7 kJ/g VS). Although improvements in organic removals and methane yields were observed after MW and US, the energy input for pretreatments were not compensated by the increased methane production, and therefore were concluded to be infeasible for industrial applications for single-stage and TPAD. All TPADs provided the highest pathogenic removal, and met the Class A biosolids fecal coliform requirements, while MW pretreatment achieved the highest fecal coliform removal for single-stage AD with digestates classified as Class B. Digesters incorporating thermal pretreatment (MW and MW + TPAD) yielded the highest amount of extra heat (4.2–5.8 kJ/g VS) that could be utilized within/outside of the facility.

Disinfection effect of a continuous-flow ultrasound/ultraviolet baffled reactor at a pilot scale

An ultrasound/ultraviolet (US/UV) baffled reactor was developed to fill the gap in ultraviolet (UV) disinfection associated with disinfection efficiency. According to the previously selected operational condition, a continuous-flow US/UV baffled reactor was continuously operated in a wastewater treatment plant at a pilot scale for nearly three months, and the disinfection influent and effluent were analyzed, including fecal coliforms, Escherichia coli, and fecal streptococci. The US/UV baffled reactor could guarantee a high effluent disinfection performance in terms of fecal coliforms removal even with the fluctuation of the secondary effluent. All the disinfected effluents satisfied the requirement of the “Pollutants Discharge Standard of Municipal Wastewater Treatment Plant in China” (fecal coliforms below 1000CFU/L for class 1A), and 87% of the tested fecal coliforms concentration in the disinfected effluent was below 100CFU/L, nearly eliminating all fecal coliforms. Further analysis of the E. coli and fecal streptococci showed the broad disinfection ability and high disinfection efficiency of the US/UV baffled reactor. The flexibility of the specific energy consumption for the disinfection system depends on the water quality.

Optimized Design of a Hybrid Biological Sewage Treatment System for Domestic Wastewater Supply

This study is aimed at evaluating alternative designs of waste stabilization ponds (WSPs) and constructed wetlands (CWs) for Kaputiei Housing Estate consisting of 2000 low cost housing units in Kenya. The entire analysis was carried out by simulating the effectiveness and purification efficiencies of WSPs and CWs in terms of Biological Oxygen Demand (BOD) reduction and faecal coliform (FC) removal under different scenarios of water treatment systems that included Re-sizing of the initial sewage treatment system, optimizing the design of the initial system and design of hybrid system for the estate. The graphic comparison of the simulated parameters under different scenarios showed that a hybrid design that combines both the WSPs and CWS provides an effluent BOD of 20 mg/l and 195 FC per 100 ml that meets the standard effluent discharge that is acceptable for unrestricted crop irrigation and thus will be reused in the housing estate for kitchen gardening and agroforestry.