Multi-stage EGSB/MBR treatment of soft drink industry wastewater

Abstract

A multi-stage anaerobic/aerobic membrane bioreactor (MBR) was used to evaluate the treatment of soft drink industry wastewater (SDIW). The SDIW was classified as medium to high strength wastewater with pollutants of caustic soda, pH of between 6.1 and 11.8, sucrose, CODt between 2242 and 11,717mg/L and BOD of up to 1150mg/L. The anaerobic expanded granular sludge bed (EGSB) pre-treatment, was maintained between 35 and 37°C, at hydraulic retention times (HRT) between 12 and 60h and upflow velocities (Vup) between 0.59 and 1.1m/h. CODt treatment efficiency (TE) up to 93% was achieved at a HRT of 12h, Vup of 0.85m/h and organic loading rate (OLR) of 11COD/m3d. The EGSB produced biogas up to 70% methane and up to 41% nitrogen. The MBR was operated with feeds of 12–50L/d; DO between 2 and 3.7mg/L in the aerobic zone, and overall HRT of 3.3–14h and membrane flux of between 3.4 and 17L/m2h. The MBR post-treatment removed up to 87% CODt at a feed flowrate of 34L/d, an OLR of 2.3 and 3.1kgCOD/m3d for anoxic and aerobic zones, respectively, and a corresponding HRT of approximately 0.41h for both zones. A membrane flux of 12–15L/m2h was achieved at a TMP of 60–100kPa. The integrated EGSB/MBR treatment was able to achieve CODt TE up to 95%. The MBR reduced CODt in the permeate to consistently below 253mg/L with all the macro-nutrients (NH4+, NO3− and PO43−) below the discharged standards. The MBR did not decrease all the macro-nutrients to within the drinking water standards for reuse.