Effect of F/M Ratio on the Performance of Sequencing Batch Reactor for Dairy Wastewater Treatment

Abstract

Indian economy has huge contribution of dairy industry. About one fourth of nation’s income is contributed by dairy. Milk processing involves various operations starting from receiving point to disposal end. This whole process demands fresh water leading to wastewater generation and this quantity is highest amongst all industries. Dairy wastewater is composed of organic matter, nutrients, suspended & dissolved solids and high COD, BOD. So it becomes necessary to remove the pollution load before its disposal. Some advanced treatments like SBR, gas stripping, surface filtration show better results and are effective than conventional treatments. In this study, SBR process was used to treat dairy wastewater. SBR process has flexibility, minimal footprint and it conducts all operations like equalization, primary clarification, biological treatment and secondary settling in a single reactor. Time phased Fill and draw type lab scale SBR model was operated with 12 liter total volume and 10 liter working volume. Before loading dairy wastewater to the reactor, loading of sewage was done for acclimatization of microorganisms. Dairy wastewater was collected from equalization tank of an Effluent Treatment Plant of dairy industry. It was analysed for various parameters for 15 days to know the variations in characteristics. For the treatment of dairy wastewater reactor was operated under varying MLSS from 6000 to 8000 mg/L thereby under varying F/M ratio and named as phase 1, phase 2, and phase 3 with 20% Volume Exchange Ratio. Total cycle time provided was 6 hour in which fill was instantaneous, aeration for 5 hour 30 minutes, settling for 25 minutes and 5 minute decant. By keeping all the remaining parameters constant, only F/M ratio was varied. Maximum removal efficiencies for parameters like COD, BOD, TDS, and TSS were determined for each phase. For phase 1, 2 and 3 maximum removal efficiencies were achieved at F/M 0.16, 0.14 and 0.13 per day respectively. But among all three phases, 3rd phase gave maximum removal efficiency at F/M 0.13. Hence it was concluded that SBR performs better at higher MLSS concentration or at lower F/M ratio in order to achieve disposal standards.