Anatomy of the organic carbon in an industrial wastewater: Implications of particle size distribution, respirometry and process modelling

This study evaluated the fate of chemical oxygen demand (COD) fractions of an organized industrial district effluent treated with pilot membrane bioreactor (MBR) system. A series of respirometric analyses were performed on raw wastewater together with 450 nm, 100 kDa and 1 kDa filtered samples obtained from particle size distribution (PSD) experiments. The PSD analysis revealed that more than 300 mg/L of the influent COD accumulated in the lowest size range (<2 nm), accounting for 49–52 % of the total COD. The bulk (64 %) of the influent COD consisted of soluble hydrolysable COD (S_H1). The hydrolysis rates for S_H1 (0.80–1.28 1/day) were slightly below the levels suggested for domestic wastewaters, indicating the presence of inhibitory compounds in industrial wastewaters. The COD removal efficiency of MBR pilot was found as 85 %; however, 43 % of effluent COD (106 mg/L) still included rapidly hydrolysable organics in the size bracket of 5–30 nm. In this respect, the COD fractions for activated sludge process models used for MBR applications require a new-insight to correctly reflect organic matter balances in the treatment system.