A Complete Treatment of Slaughterhouse Wastewater Combined with Sludge Stabilization Using Two Stage High Rate UASB Process

Abstract

The main objectives of the present investigations were to assess the feasibility of two stage high rate UASB-reactors for complete treatment of slaughterhouse wastewater which contains approximately 55 % insoluble coarse suspended COD. The study presented in this paper addresses the maximum loading rates (hydraulic and organic) the extent of sludge stabilization (i.e. conversion into methane) and the length of the sludge stabilization period (i.e. digestion time). The experiments were performed in two stage high rate anaerobic sludge UASB-reactors. The wastewater treatment experiments were performed at an operational temperature of 18 °C, while the sludge stabilization experiments were performed at a process temperature of 30 °C. Two different types of anaerobic sludge were used in this experiment: flocculent sludge for the first stage and granular for the second stage of the system. The first stage of the reactor system consists of 2 reactors which are used alternately. In the second stage, one reactor is in operation permanently. The results of the present study indicate that the system can satisfactorily handle organic space loads up to 15 kg COD m−3.day−1 at a liquid retention time of 4 h and 1.5 h. for the first and second stage of the system, respectively. For the whole system a treatment efficiency up to 90 % on CODtotal basis, 95 % on CODcoarse suspended solids basis, 80 % on CODcolloidal basis and 80% on CODsoluble basis was achieved. The maximum extent of sludge stabilization (i.e. conversion into methane) at 30 °C was approximately 50 % for the accumulated coarse suspended solids and colloidal fractions in the reactors of the first stage of the system. The length of the sludge stabilization period (i.e. digestion time) was 14 days.