Restart of anaerobic filters treating low-strength wastewater.

The anaerobic filter (AF) technology offers an alternative method for the direct treatment of low-strength wastewater and the study was undertaken to access AF-biomass reactivation after prolonged nonfeeding periods, an important characteristic making the process suitable for handling variable or intermittent pollution loads. Four upflow AF (three 12.5-L and one 3.9-L, each with different packing), which had treated municipal-type wastewaters (natural, amended or synthetic) for 34 months at 25 or 16 degrees C and varying hydraulic loads and had remained inactive for 24 months, were used. All units were fed synthetic wastewater [mean chemical oxygen demand (COD) 323 mg/L, total suspended solids (TSS) 47 mg/L] and operated at 27 degrees C for 2.5 months (phase 1); and following a 6-month idle period, the smaller filter treated municipal wastewater (mean COD and TSS 820 and 448 mg/L) at 16 degrees C for an additional 2.5 months (phase 2). The larger units operated at a 2.0-d hydraulic retention time and the smaller at 1.0-0.33-d in phase 1 and 2.0 or 1.0-d in phase 2. Reactivation was quick and yielded efficient treatment. Restart was affected by the AF history and packing morphology, the types of wastewater previously handled, and the duration of the nonfeeding period.

Municipal-wastewater treatment using upflow-anaerobic filters.

Three 12.5-L upflow-anaerobic filters (AF), with ceramic-saddle, plastic-ring, and crushed-stone packing, were used to evaluate the sustained treatment of municipal wastewater. The reactors were initially fed dogfood-fortified wastewater and then raw municipal wastewater, and operated at 25.4 degrees C (32 months) and 15.5 degrees C (2 months). During 23 months, the AF units treated municipal wastewater (mean chemical oxygen demand [COD] 442 mg/L and total suspended solids [TSS] 247 mg/L), the hydraulic retention time (HRT) ranged from 3.1 to 0.30 d (empty bed), and the organic loading rate ranged from 0.115 to 1.82 kg COD/m3d. At the higher temperature and an HRT (void volume) of 1.0 d, COD and TSS removals ranged from 74 to 79% and 95 to 96%, respectively; however, efficiencies declined substantially at HRT values less than 0.4 d. Reactor performance, under the same hydraulic and organic loadings, deteriorated with time and was adversely affected by lower temperature.

Organic and nitrogen removal in a two-stage rotating biological contactor treating municipal wastewater.

A laboratory scale rotating biological contactor (RBC) predenitrification system incorporating anoxic and aerobic units was evaluated for the treatment of settled high-strength municipal wastewater. The system was operated under four recycle ratios (1, 2, 3 and 4) and loading rates of 38-182 gCOD/m(2)d and 0.22-14 gOxid-N/m(2)d on the anoxic unit and 3.4-18 gCOD/m(2)d and 0.24-1.8 gNH(4)-N/m(2)d on the aerobic. The average removal efficiency in terms of chemical oxygen demand (COD), biochemical oxygen demand (BOD(5)), total suspended solids (TSS) and total nitrogen (Total-N) was 82%, 86%, 63% and 54%; settling of the RBC effluent increased COD and TSS removal to 94% and 97%. An increase in hydraulic loading resulting from higher recirculation, had limited negative effect on organic removal but improved nitrogen removal, and in terms of Total-N removal efficiency increased up to a ratio of 3 and then decreased.

Anaerobic treatment of low-strength wastewater in a biofilm reactor.

A 3.9-L (70-cm high) upflow anaerobic filter (AF) packed with corrugated plastic rings was employed to evaluate the direct treatment of low-strength wastewater over a long period of operation (32 months at 25.4 degrees C and 2 months at 15.5 degrees C). The AF was fed four complex synthetic-type wastewaters with a low-solids content [chemical oxygen demand (COD) 325-403 mg L(-1), soluble COD (SCOD) 86-339 mg L(-1) and total suspended solids (TSS) 65-156 mg L(-1)] at organic loading rates (OLR) ranging from 0.02 to 0.91 kg COD m(-3) d(-1). Operation with filtered municipal wastewater supplemented with a sugar-nutrient based substrate (OLR 0.27-0.91 kg COD m(-3) d(-1)) yielded removal efficiencies in the range of 72-80% for COD and 80-92% for TSS, and use of a completely synthetic substrate resulted in improved effluent quality. Under these test conditions, removal of organic matter and solids occurred within the first 40cm of column height and accumulation within the reactor was not substantial or affected by the length of operation.

Low-strength wastewater treatment using an anaerobic baffled reactor.

A 14.7-L, three-chamber anaerobic baffled reactor (ABR) was used to evaluate the treatment of low-strength synthetic wastewater (chemical oxygen demand [COD] of 300 to 400 mg/L) and assess process reactivation after a prolonged period of inactivity. The reactor was inoculated with anaerobic seed and start-up was immediate. At 26 degrees C and hydraulic retention times (HRTs) of 24 and 12 hours, COD removal averaged 87.2 and 91.0%, respectively, and biogas yield for methane (CH4) was 0.184 and 0.102 m3 CH4/kg COD removed, respectively. The ABR was reactivated after two years without feeding. Response was prompt and removal averaged 85.3% even during the initial 10-day period. Lowering temperature to 16 degrees C did not impair removal efficiency at HRTs of 24 and 12 hours. However, biogas release decreased by 30% and apparent COD conversion to methane dropped by 24 and 31%, respectively. At the end of the study, biomass was mostly in the bottom of the reactor and had moved from the first to the second chamber, while organic stabilization was occurring essentially in the first two chambers (56.1 and 22.4%, respectively, in terms of COD).