Biological nutrient removal from meat processing wastewater using a sequencing batch reactor

Meat processing effluents are rich in nutrients (nitrogen: 75-200 mg L⁻¹ and phosphorus: 20-40 mg L⁻¹) and COD (800-2,000 mg L⁻¹) after primary treatment. A laboratory scale sequencing batch reactor (SBR) was operated for the treatment of a beef processing effluent from slaughtering and boning operations. An effective SBR cycle was found for removal of COD, nitrogen and phosphorus at 22°C. The solid retention time was 15 days while the hydraulic retention time (HRT) was 2.5 days. The total nitrogen in the wastewater was reduced to less than 10 mg L⁻¹, while the total phosphorus decreased to less than 1.0 mg L⁻¹. The residual effluent soluble COD was found to be non-biodegradable as reflected by no further soluble COD removal following prolonged aeration. Removal of biodegradable soluble COD, ammonia nitrogen and soluble phosphate phosphorus of greater than 99% was achieved in the SBR. Good prediction of ammonia and nitrate nitrogen removal was obtained using IWA Activated Sludge Model. The operating cycle is shown to be appropriate to achieve simultaneous removal of COD and nutrients from the meat processing wastewater. Alkalinity and pH have an inverse relationship during the initial anaerobic and aerobic stages due to production and stripping of CO₂. Use of a low level of DO in the final aerobic stage ensured complete ammonia removal and enhanced denitrification.