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The goal of this study was to determine the removal efficiencies of chromium, copper, lead, nickel, and zinc from raw wastewater by chemically enhanced primary treatment (CEPT) and to attain a total suspended solids removal goal of 80%. Operating parameters and chemical doses were optimized by bench-scale tests. Locally obtained raw wastewater samples were spiked with heavy metal solutions to obtain representative concentrations of metals in wastewater. Jar tests were conducted to compare the metals removal efficiencies of the chemical treatment options using ferric chloride, alum, and anionic polymer. The results obtained were compared with those from other studies. It was concluded that CEPT using ferric chloride and anionic polymer is more effective than CEPT using alum for metals removal. The CEPT dosing of 40 mg/L ferric chloride and 0.5 mg/L polymer enhanced heavy metals removal efficiencies by over 200% for chromium, copper, zinc, and nickel and 475% for lead, compared with traditional primary treatment. Efficient metals capture during CEPT can result in increased allowable headworks loadings or lower metal levels in the outfall. Water Environ. Res., 80, 472 (2008). IntroductionThe presence of heavy metals in the influent to municipal wastewater treatment plants can adversely affect the performance of biological treatment processes and quality of the effluent and influence decisions regarding the reuse and land application of biosolids. These negative effects can result in limits on the allowable headworks metals loadings. Preventing heavy metals from reaching downstream processes and the receiving waters can be accomplished by removing the heavy metals using chemically enhanced primary treatment (CEPT) and can result in increased allowable headworks metals loadings or lower metal levels in the outfall.Chemical precipitation by coagulation and flocculation by trivalent metal salts is a century old and proven technology.

Although small, rural water supplies may present elevated microbial risks to consumers in some settings, characterizing exposures through representative point-of-consumption sampling is logistically challenging. In order to evaluate the usefulness of consumer self-reported data in predicting measured water quality and risk factors for contamination, we compared matched consumer interview data with point-of-survey, household water quality and pressure data for 910 households served by 14 small water systems in rural Alabama. Participating households completed one survey that included detailed feedback on two key areas of water service conditions: delivery conditions (intermittent service and low water pressure) and general aesthetic characteristics (taste, odor and color), providing five condition values. Microbial water samples were taken at the point-of-use (from kitchen faucets) and as-delivered from the distribution network (from outside flame-sterilized taps, if available), where pressure was also measured. Water samples were analyzed for free and total chlorine, pH, turbidity, and presence of total coliforms and Escherichia coli. Of the 910 households surveyed, 35% of participants reported experiencing low water pressure, 15% reported intermittent service, and almost 20% reported aesthetic problems (taste, odor or color). Consumer-reported low pressure was associated with lower gauge-measured pressure at taps. While total coliforms (TC) were detected in 17% of outside tap samples and 12% of samples from kitchen faucets, no reported water service conditions or aesthetic characteristics were associated with presence of TC. We conclude that consumer-reported data were of limited utility in predicting potential microbial risks associated with small water supplies in this setting, although consumer feedback on low pressure—a risk factor for contamination—may be relatively reliable and therefore useful in future monitoring efforts.

Weathered crystalline bedrock aquifers sustain water supplies across the tropics, including East Africa. Although well yields are commonly <1 L s −1 , more intensive abstraction occurs and provides vital urban and agricultural water supplies. The hydrogeological conditions that sustain such high abstraction from crystalline bedrock aquifers remain, however, poorly characterised. Five sites of intensive groundwater abstraction (multiple boreholes yielding several L s −1 or more) were investigated in Uganda and Tanzania. Analysis of aquifer properties data indicates that the sites have transmissivities of 10-1,000 m 2 day −1 , which is higher than generally observed in deeply weathered crystalline bedrock aquifers. At four of the five sites, weathered bedrock (saprolite) is overlain by younger superficial sediments, which provide additional storage and raise the water table within the underlying aquifer. Residence-time indicators suggest that: (1) abstracted water derives, in part, from modern recharge (within the last 10-60 years); and (2) intensive abstraction is sustained by recharge occurring over several decades. This range of encountered residence times indicates a degree of resilience to contemporary climate variability (e.g. short-term droughts), although the long-term sustainability of intensive abstractions remains uncertain. Evidence from one site in Tanzania (Makutapora) highlights the value of multi-decadal groundwater-level records in establishing the long-term viability of intensive groundwater abstraction, and demonstrates the influence of intra-decadal climate variability in determining the magnitude and frequency of recharge.

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