Dairy milking wastewater treatment using a lab-scale sequencing batch reactor (SBR)

Use of a sequencing batch reactor (SBR) to treat dairy milking wastewater was investigated in this project. Characterization work showed that the milking wastewater properties varied a great deal with the milk content in the wastewater, possibly due to bulk milk wastage. Average biochemical oxygen demand (BOD) and soluble chemical oxygen demand (COD) levels of the milking wastewater were 1608 and 1010 mg L ^-1, respectively. Most of the phosphorus was soluble, and almost all the suspended solids were volatile. Good linear relationships among BOD, soluble COD, and total COD were observed for the milking wastewater used. The SBR was operated in fixed 8 h cycles, each consisting of 1 h anaerobic, 3 h aerobic, 2 h anoxic, 1 h aerobic, 50 min settle, 10 min decant, and idle with an HRT of 5.3 days and an SRT of 40 days. In organic loading tests, it was found that the optimal loading rate for the SBR studied was around 0.125 kg COD kg ^-1 MLSS d ^-1 (MLSS = mixed liquor suspended solids), at which a COD removal efficiency greater than 99%) and an effluent with COD and BOD concentrations less than 55 and 25 mg L ^-1, respectively, was obtained. The average removal efficiencies for total Kjeldahl nitrogen (TKN), ammonium nitrogen (NH ₄ ⁺-N), total phosphorus (TP), dissolved phosphorus (DP), total solids (TS), and total suspended solids (TSS) were 96.7%), 92.4%, 95.9%, 94.0%), 78.5%, and96.6%), respectively. The reactor sludge settleability was good, with a sludge volume index (SVI) always under 100 mL g ^-1 during all the test periods.