Aerobic treatment of dairy wastewater with sequencing batch reactors

Single-stage and two-stage aerobic treatment systems were tested and compared in the laboratory for treating dairy wastewater to remove solids and oxidize ammonia for later nitrogen removal through denitrification. Treating the dairy waster of 20,000 mg/L COD and 540 mg/L NH3-N at five hydraulic retention times (HRTs) varying from 1 to 5 days, the single-stage sequencing batch reactor (SBR) system achieved 68.9% to 85% VS removal from the liquid. A longer HRT resulted in a cleaner liquid effluent with lower solids (TS and VS) contents. It was found that the 5-day HRT was necessary to achieve complete oxidation of ammonia to nitrate. The treatment efficiencies of the two-stage SBR system at 2.5-day HRT (2-day for the first-stage and 0.5-day for the second-stage) were equal to or better than those of the single-stage SBR system at 5-day HRT. This means that the treatment volume of a two-stage system can be 50% less than the volume of a single-stage system. The results also showed that the sequencing batch reactor (SBR) performed better than the completely mixed biofilm reactor (CMBR) in terms of solids and COD removals. Field-testing of a pilot-scale two-stage SBR system confirmed the laboratory research findings and concluded that a single-stage system is good for solids removal but a two-stage system is recommended if ammonia oxidation is also desired.