Treatment of farm dairy effluent with hybrid upflow multilayer bioreactor and activated sludge module

Abstract

Biological removal of nitrogen and carbon from farm dairy effluent (FDE) was studied with two laboratory-scale systems following nitrification and denitrification processes. Each system consisted of an upflow multilayer bioreactor (UMBR) as a pre-denitrification unit, an aeration tank (AT) as nitrification unit and a secondary clarifier. The optimization of two operational variables, total hydraulic retention time (HRT) and internal recycle (IR) rate with both real-FDE and a synthetic-wastewater were investigated. First, HRTs of 2, 3, 4 and 5 days were tested with synthetic-wastewater at uniform IR rate. The HRT of 4 days proved optimum with high efficiencies for nitrification (>90%), denitrification (>90%) and total chemical oxygen demand (COD) removal ( approximately 90%). The lowest efficiency was recorded at 2 days HRT with 7% nitrification efficiency. This was followed by experimentation with IR rates of 200%, 300% and 400% on both real-FDE and synthetic-wastewater at optimized HRT. The increase in IR to 300% improved the denitrification potential and overall performance with continuous high nitrification efficiency and COD removal whereas IR of 400% retarded the process. The application of combined UMBR and activated sludge system showed good potential for biological removal of nitrogen from FDE.