Anaerobic treatment of slaughterhouse waste using a flocculant sludge UASB reactor

Abstract

This study was carried out to assess the feasibility of using the upflow anaerobic sludge blanket (UASB) process for the one-step anaerobic treatment of slaughterhouse waste, which contains approximately 50% insoluble suspended COD. Batch experiments, as well as continuous experiments, were conducted. The continuous experiments were carried out in a 30 m 3 UASB pilot-plant with digested sewage sludge from the municipal sewage treatment plant of Ede, The Netherlands (Ede-2 sludge), used as seed. Initially the UASB pilot-plant was operated at a temperature of 30°C, but, 20 weeks after the start up, the temperature was reduced to 20°C, because application of the process at this lower temperature might be quite attractive for economic reasons. The process can be started up at an organic space load of 1 kg COD m −3 day −1 (sludge load, 0·11 kg COD kg −1 VSS day −1) and at a liquid detention time of 35 h at a process temperature of 30°C. Once started up, the system can satisfactorily handle organic space loads up to 3·5 kg COD m −3 day −1 at a liquid detention time of 8 h at temperatures as low as 20°C. A treatment efficiency up to 70% on a COD tot basis, 90% on a COD sol basis and 95% on a BOD 5 sol basis was smoothly approached. Temporary shock loads up to 7 kg COD m −3 day −1 during the daytime at a liquid detention time of 5 h can well be accommodated provided such a shock load is followed by a period of underloading, e.g. at night. The methane yield amounted to 0·28 Nm 3 per kilogram of COD removed; the methane content of the biogas from the wastewater varied between 65 and 75%.