Impact of paint shop decanter effluents on biological treatability of automotive industry wastewater

A lab-scale Sequencing Batch Reactor (SBR) was implemented to investigate biological treatability and kinetic characteristics of paint shop wastewater (PSW) together with main stream wastewater (MSW) of a bus production factory. Readily biodegradable and slowly biodegradable COD fractions of MWS were determined by respirometric analysis: 4.2% (SS), 10.4% (SH) and 59.3% (XS). Carbon and nitrogen removal performance of the SBR feeding with MSW alone were obtained as 89% and 58%, respectively. When PSW was introduced to MSW, both carbon and nitrogen removal were deteriorated. Model simulation indicated that maximum heterotrophic growth rate decreased from 7.2 to 5.7 day−1, maximum hydrolysis rates were reduced from 6 to 4 day−1 (khS) and 4 to 1 day−1 (khX). Based on the dynamic model simulation for the evaluation of nitrogen removal, a maximum specific nitrifier growth rate was obtained as 0.45 day−1 for MSW feeding alone. When PSW was introduced, nitrification was completely inhibited and following the termination of PSW addition, nitrogen removal performance was recovered in about 100 days, however with a much lower nitrifier growth rate (0.1 day−1), possibly due to accumulation of toxic compounds in the sludge. Obviously, a longer recovery period is required to ensure an active nitrifier community.