Treatment of a combined dairy and domestic wastewater in an up-flow anaerobic sludge blanket [UASB] reactor followed by activated sludge [AS-system]

ABSTRACT

The feasibility of using an Up-flow Anaerobic Sludge Blanket [UASB] reactor followed by activated sludge [AS-system] for the treatment of wastewater discharged from Dairy factory was explored. The UASB reactor was operated at a Hydraulic Retention Time [HRT] of 24 h and Organic Loading Rates [OLR's] ranging from 1.9 to 4.4 kg COD/m[3].d. Despite variation in OLR, the reactor provided a more or less constant effluent quality of 1385 mg/I for COD total, and 576 mg/l for total BOD5, corresponding to removal values of 69 and 79%, respectively. Total suspended solids [TSS] and volatile suspended solids [VSS] removal averaged above 72 and 75%, respectively. Residual phosphorous and oil and grease concentrations were 8.2 mg P/l and 44 mg/l, respectively, corresponding to removal values of 63 and 83%. This high performance could be attributed to the long Sludge Residence Time [SRT =76 d] imposed to the reactor. Total and faecal coliform counts were reduced by a value of 1.07 and 0.9 log10, respectively. The VS/TS ratio of 0.66 of excess sludge revealed its good quality. Net sludge yield coefficient was found to be around 0.2g VSS per g COD total removed per day, corresponding to 20% of the total influent COD. Preliminary results of activated sludge [AS] batch experiments indicated first order removal kinetics between total organic carbon [TOC] and contact time. The TOC removal reached 98.4% within 2.0h. Accordingly, the AS-system was operated at a HRT of 2.0 h. The AS- step achieved a substantial reduction of COD total, BOD5 total, TSS and oil and grease resulting in residual concentrations of only 35.0, 7.0, 14.0 and 2.8 mg/l, respectively. The geometric mean of total and faecal coliform counts was reduced by a value of 1.28 and 1.64 log10, respectively. The results obtained indicated that the use of an integrated system consisting of UASB followed by an AS-system for the treatment of dairy wastewater could achieve over 98.9% of COD total. 99.6% of BOD5 total and 98.9% of oil and grease