Practical ultimate hydraulic loading of slaughterhouse waste to anaerobic fixed bed and RAUS reactors

Abstract

Two pilot – scale anaerobic processes, namely, Anaerobic Fixed Bed (An FB) and Reversing Anaerobic Up flow System (RAUS), were installed to investigate the effect of increasing hydraulic loading on treatment efficiency. A feasibility study was conducted for the treatment of wastewater of a slaughterhouse (mainly pigs) by both said systems. After being treated by a floatation system, the wastewater containing COD of 200 -1,000 mg/1 with a ph of 7 – 8 was continuously fed in an up flow mode to both processes at 29 – 32℃. The flow rate was gradually increased until apparent failure was detected. It was found that in both processes, the degree COD removal inversely varied with increasing hydraulic loading rates. For the fixed bed reactor, 65% 0f COD and SS removal were achieved respectively when 0.94 kg COD/(m³.d) loading rate or HRT of 11 h. was applied. Severs biomass washout was apparently the main cause of the failure at 2.38 kg COD/(m³.d) loading rate or 3.4 h HRT while COD removal was reduced to only 30%. Nevertheless, higher fiowrate was continued and absolute failure was observed (when COD removal approached zero) when the loading equaled 5.9 kg COD/(m³.d) and HRT was only 0.85 h. Meanwhile, RAUS could retain a high concentration of granular sludge with excellent setting ability. It could remove, respectively, 70% COD and 66% SS at 0.36 kg COD/(m³.d) loading rate or HRT of 21 h. The COD removal efficiency approached zero level at 1.6 kg COD/(m³.d) loading rate or 3.1 h HRT. Here, the biomass washout was apparent, but the SS removal efficiency was still more than 5o%.