The start-up of anaerobic sequencing batch reactors at 20 degrees C and 25degrees C for the treatment of slaughterhouse wastewater

The objective of this research was to evaluate the feasibility, the stabili ty and the efficiency of a start-up at 20 degreesC and 25 degreesC of anaer obic sequencing batch reactors (ASBRs) treating slaughterhouse wastewater. Influent chemical oxygen demand (COD) and suspended solids concentrations a veraged 7500 and 1700mgdm(-3), respectively. Reactor start-up was completed in 168 and 136 days at 20 degreesC, and 25 degreesC, respectively. The sta rt-up process was stable at both temperatures, except for a short period at 20 degreesC, when effluent volatile fatty acid (VFA) concentrations increa sed fi om an average of 40 to 400mgdm(-3). Effluent quality varied througho ut start-up, but in the last 25 days of the experiment, as the ASBRs were o perated under organic loading rates of 2.25 +/- 0.21 and 2.86 +/- 0.24kgm(- 3) d(-1) at 20 degreesC and 25 OC, respectively, total COD was reduced by 9 0.3% +/- 1.3%. Methanogenesis was not a limiting factor during start-up. At 20 degreesC, the limiting factor was the acidification of the soluble orga nics and, to a smaller extent, the reduction of propionic, isobutyric and i sovaleric acids into lower VFAs. At 25 degreesC, the limiting factor was th e hydrolysis of particulate organics. To minimize biomass loss during the s tart-up period, the organic loading rate should be increased only when 75 - 80% of the COD fed has been transformed into methane within the design hydr aulic retention time. (C) 2001 Society of Chemical Industry.