The influence of organic loading and anoxic/oxic times on the removal of carbon, nitrogen and phosphorus from a wastewater treated in a sequencing batch reactor

Abstract

In this study, 10 L sequencing batch reactors (SBRs) were operated at a 12-h cycle length (four alternating anoxic/oxic conditions) to assess the biological nutrient removal potential of a domestic wastewater treated at the Huay Kwang plant, Bangkok, Thailand. The wastewater was found to be carbon-limited (chemical oxygen demand (COD) to total Kjeldahl nitrogen (TKN) (i.e., COD:TKN) ratio of 6.4:1). This ratio was insufficient to support good phosphorus removal. Glucose was therefore added to increase the COD:TKN ratio ultimately to 10:1 and the COD, TKN and total phosphorus (TP) removals at this ratio were all in excess of 95%. An alternative carbon source from a local fruit canning industry was then added at the same COD:TKN ratio; and, in order to increase the throughput of the waste treated, the cycle length was simultaneously shortened to 8 h keeping approximately the same anoxic/oxic fractions. The COD removal remained high (> 95%), however the TKN and TP removals were substantially reduced (79% and 66%, respectively), indicating that the shortened cycle length was sub-optimum. The last phase of the research involved changing the anoxic/oxic fractions of the cycle time to maximize performance. It was found that for the conditions studied in this research, the performance improved in proportion to the increase in the first anoxic fraction, being most stable at the highest anoxic fraction of the cycle length (0.33).

Keywords:

• Wastewater treatment
• organic loading
• anoxic/oxic time
• phosphorus removal
• sequencing batch reactor

Acknowledgments

The authors would like to thank S. Chernchaivachirakul and A. Zummapetcharat for providing the background information for this study. We also wish to thank the staff at the Sanitary Engineering Laboratory, Mahidol University, Bangkok, Thailand for their excellent technical assistance.