Chemically enhanced primary treatment (CEPT) is a process that uses coagulant and/or flocculant chemicals to remove suspended solids, organic carbon, and nutrients from wastewater. Although it is not a new technology, it has received much attention in recent years due to its increased treatment capacity and related benefits compared to the conventional primary treatment process. CEPT involves both physical and chemical processes. Alum and iron salts are the commonly used coagulants in CEPT. Several types of anionic, cationic, and uncharged polymers are used as flocculants, where poly aluminum chloride (PACL) and polyacrylamide (PAM) are the widely used ones. Some of the coagulants and flocculants used may have inhibitory and/or toxicity effects on downstream treatment and recovery processes. There has been an increasing amount of work on the treatment of wastewaters from various sources using CEPT. These wastewaters can range from municipal/domestic wastewater, combined sewer overflow, landfill leachate, cattle manure digestate to wastewaters from textile industry, pulp and paper mill, slaughterhouse, milk processing plant, tannery and others. In recent cases, CEPT is employed to enhance carbon redirection for recovery and substantially reduce the organic load to secondary treatment processes. CEPTs can remove between 43.1–95.6% of COD, 70.0–99.5% suspended solids, and 40.0–99.3% of phosphate depending on the characteristics of wastewater treated and type of coagulants and/or flocculants used. This article reviews the application, chemicals used so far, removal efficiencies, challenges, and environmental impacts of CEPT.

The increased interest in biomass energy provides incentive for the development of efficient and high throughput digesters such as anaerobic membrane bioreactors (AnMBRs) to stabilize waste activated sludge (WAS). This paper presents the results of a pilot and short term filtration study that was conducted to assess the performance of AnMBRs when treating WAS at a 15 day hydraulic retention time (HRT) and 30 day sludge retention time (SRT) in comparison to two conventional digesters running at 15 (BSR-15) and 30 days (BSR-30) HRT/SRT. At steady state, the AnMBR digester showed a slightly higher volatile solids (VS) destruction of 48% in comparison to 44% and 35.3% for BSR-30 and BSR-15, respectively. The corresponding values of specific methane production were 0.32, 0.28 and 0.21 m(3) CH(4)/kg of VS fed. Stable membrane operation at an average flux of 40+/-3.6 LM(-2 )H(-1) (LMH) was observed when the digester was fed with a polymer-dosed thickened waste activated sludge (TWAS) and digester total suspended solids (TSS) concentrations were less than 15 gL(-1). Above this solids concentration a flux decline to 24.1+/-2.0 LM(-2) H(-1) was observed. Short term filtration tests conducted using sludge fractions of a 9.7 and 17.1 gL(-1) TSS sludge indicated 84 and 70% decline in filtration performance to be associated with the supernatant fraction of the sludge. At a higher sludge concentration, the introduction of unique fouling control strategy to tubular membranes, a relaxed mode of operation (i.e. 5 minutes permeation and 1 minute relaxation by) significantly increased the flux from 23.8+/-1.1 to 37.8+/-2.3 LMH for a neutral membrane and from 25.7+/-1.1 to 44.9+/-2.9 LMH for a negatively charged membrane. The study clearly indicates that it is technically feasible to employ AnMBRs to achieve a substantial reduction in digester volumes.

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This study investigated the impact of Solid Retention Time (SRT) (40 to 100 days) and Hydraulic Retention Time (HRT) (2.5 to 8.5 hours) on the treatment of municipal wastewater in pilot and bench scale AnMBRs. The results revealed good permeate quality with respect to concentrations of COD (<40 mg/L) and BOD5 (<10 mg/L) was achieved under all conditions. Over the range of values tested SRT and HRTdid not significantly influence COD and BOD5 removal efficiencies. Extended SRTs resulted in reduced sludge production and enhanced methane production. Oversaturation of dissolved methane in permeate appears to have been responsible for a consistent lack of COD mass balance closure in all tests. After calibration of biokinetic coefficients, PetWin 4 (EnviroSim Canada) was found to effectively simulate the concentrations of particulate COD, readily biodegradable COD and acetic acid over a range of SRTs and HRTs. The calibrated saturation coefficients for hydrolysis and aceticlastic methanogenesis processes were comparable to those reported in literature. The saturation coefficient of fermentation was significantly lower than those reported in literature. The simulated methane mass flows were consistently higher than the measured values which was consistent with the lack of COD mass balance closure and was attributed to reduction of sulfate and oversaturation of the permeate with respect to Henry's Law.