Anaerobic treatment of slaughterhouse waste using a granular sludge UASB reactor.

This study was carried out to assess the feasibility of the upflow granular anaerobic sludge blanket (UASB) process for one-stage anaerobic treatment of unsettled slaughterhouse wastewater, which contains approximately 50% insoluble coarse suspended COD. The experiments used continuous feeding (24 h day) during the working days combined with weekend feed interruptions at 30°C and 20°C. An organic space load up to 11 and 7 kg CODm−3 day−1 was satisfactorily accommodated at process temperatures of 30°C and 20°C, respectively, with a treatment efficiency up to 55% on CODtotal basis and 85% on CODfiltered basis. The system was less effective in the removal of the coarse Suspended Solids than the removal of the colloidal and soluble fractions. The data indicate that a proper application of a one-stage granular UASB system treating unsettled wastewater, such as slaughterhouse waste, strongly depends on the processes involved in the removal of the colloidal and soluble fraction from the waste and on its conversion into methane. Under the optimal loading conditions of 11 kg COD m−3 day−1 (30°C) and 7 kg COD m−3 day−1 (20°C) the conversion of removed colloidal and soluble materials into methane was up to 87% and 82%. However, the system still performed very satisfactorily in the removal of the colloidal and soluble pollutants up to loading rates of 15 and 9 kg COD m−3 day−1 at 30°C and 20°C, respectively, although the conversion of the removed organic matter into methane dropped dramatically, rendering the application of the process under these conditions unattractive, if not impossible.