Anaerobic co-digestion of abattoir and textile industry wastewater in a UASB reactor

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Ondari, James Maati
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Textile industry effluents are carcinogenic and highly recalcitrant hence difficult to degrade especially through biological methods. Abattoir effluents are classified under high-strength wastewaters because of their characteristic high organic load hence highly biodegradable. Anaerobic co-digestion is the concept of degrading two effluent streams with complementary characteristics in order to improve the substrate removal rate. The feasibility of co-digesting abattoir and textile wastewater in a UASB reactor was evaluated at mesophilic and ambient temperature conditions. Preliminary experiments were conducted in 500 ml batch reactors to evaluate the optimum abattoir to textile synthetic wastewater ratio. The effect of COD, TVFA, alkalinity and pH on biogas yield was examined at both ambient and mesophilic temperatures. Anaerobic co-digestion of abattoir to textile wastewater in the ratio determined in the batch process was carried out in a 3 L UASB reactor by a continuous process. The continuous biodegradation process was executed at three different HRTs (22, 18 and 14 hrs) over a 60 day operation period. UASB reactor efficiency was achieved at organic loads ranging from 3.0 – 10.8 gCOD L-1 day-1. Continuous mode experiments were carried out at influent flow rates which corresponded to HRTs ranging between 1 to 8 days in order to evaluate the steady state operating parameters for the co-digestion process. The abattoir to textile effluent ratio was found to be 60:40 respectively. The COD, TVFA, alkalinity and pH and biogas yield followed a similar pattern over time at both mesophilic and ambient temperature conditions. Experimental data adequately fit the Grau first order kinetic model and average COD removal efficiencies of 85% and BOD5 of around 96% were achieved. The average biogas yield remained essentially constant, around 0.19 L/g CODremoved. The co-digested mixture was found to be biodegradable judging from the BOD:COD ratio of 0.53. TCOD removal efficiency decreased from 93% to 16% as HRT decreased from 8 days to 1 day. The kinetics of a UASB reactor co-digesting the mixture of synthetic abattoir and textile wastewater was evaluated in this study using Grau second order multicomponent substrate removal kinetic model. The Grau second order kinetic model, whose kinetic coefficient (ks) was 0.389, was found to be suitable for predicting the performance of a lab-scale UASB reactor.
M. Tech. (Civil Engineering, Faculty of Engineering and Technology), Vaal University of Technolog
Textile industry effluents, Biological degradation, High-strength wastewater, Anaerobic co-digestion, UASB reactor