Evaluation of an anaerobic/aerobic system for carbon and nitrogen removal in slaughterhouse wastewater

In this work the performance of an anaerobic UASB reactor coupled with an a ctivated sludge reactor for carbon and nitrogen removal in slaughterhouse w astewater is investigated. Periods with and without recirculation of aerobi c effluent over 165 days are analysed. Working with a recirculation ratio o f 2, removal efficiencies up to 90% and 65% are obtained for DQO and total nitrogen (TN), respectively. Higher recirculation ratios caused severe wash out of active biomass in both reactors due to the high hydraulic loading ra tes applied. Denitrification in the UASB reactor was complete, with no nitr ite accumulation and mainly to nitrogen gas. Significant decreases in COD r emoval efficiencies in the UASB reactor were observed at recirculation rati o of 2. Sudden decreases in total nitrogen efficiencies were related to inh ibition process of nitrifying microorganisms, especially at high recirculat ion ratios.