Treatment of linear alkyl benzene (LAB) production wastewater in an integrated photocatalysis and biological treatment process

•Treatment of LAB wastewater in a photocatalytic-biological process was studied.•The effect of three independent factors on the photocatalysis process was studied.•A bioreactor with CFID regime was used to degrade the remained COD from the PCR.

The initial biodegradability of the organic matter present in the linear alkyl benzene (LAB) production wastewater estimated as the BOD5/COD was low 0.12. To decrease the time and operational cost necessary for the mineralization of LAB wastewater, an optimum operation condition of the integrated photocatalysis and biological treatment was investigated. An immobilized TiO2 photocatalytic reactor under UVA (365 nm) irradiation and a continuous feeding intermittent discharge (CFID) bioreactor were employed in this study. The effects of initial COD concentration, reaction time and initial pH on COD removal efficiency and BOD5/COD ratio were studied in photocatalytic reactor. The maximum COD removal efficiency and BOD5/COD ratio for the photocatalytic reaction alone were found 37% and 0.45, respectively at initial COD 400 mg/l and pH of 3 after 240 min. The remaining COD concentration after the photocatalytic reaction (after 120 min) was about 280 mg/l with BOD5/COD = 0.4 which was used as feed for the CFID bioreactor. The bioreactor was operated at hydraulic retention time (HRT) 12 h and mixed liquor volatile suspended solid (MLVSS) 5000 mg/l a corresponding to organic loading rate (OLR) and food to microorganism (F/M) ratio of 0.74 g COD/l d and 0.148 d−1, respectively. The integrated system showed a good performance with about 80% total COD removal efficiency. It is concluded that this combination (PCR–CFID) was a good strategy to achieve a high COD removal efficiency in a short period of time and lower cost for such a low biodegradable wastewater.

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