Fundamentals of Sludge Fermentation for Enhanced Biological Phosphorus Removal

Abstract

Most enhanced biological phosphorus removal (EBPR) plants do not have sufficient influent carbon in the form of either short-chain volatile fatty acids (SCVFA) or readily biodegradable COD (rbCOD) that could be converted into VFA in the anaerobic zone. This requires an external source of rbCOD or the generation of either rbCOD or VFA on site. Fermentation of the primary sludge or some of the mixed liquor is then required to augment the available soluble carbon to ensure reliable phosphorus removal. This paper describes the background and fundamentals of fermentation for ensuring an adequate supply of VFA.

Sidestream RAS Fermentation for Stable Bio-P Combined with Short Cut Nitrogen Removal in an A/B Process

“…Barnard (1985) discovered that mixed liquor fermentation was taking place in a "dead zone" within the MLE process, and adding sufficient VFA to the post-anoxic zone which resulted in phosphorus release of over 30mg/L as P (J. L. Barnard and Kobylinski, 2014). This discovery along with other observations of phosphorus removal occurring at plants not specifically designed for BPR were able to achieve this through turning off mixers or air at the beginning of plug-flow processes, and determine that mixed liquor or RAS fermentation could facilitate EBPR (J. L. Barnard and Kobylinski, 2014). Another example of mixed liquor fermentation from Clark and Neethling (2009) showed by switching off a mixer in one of two anaerobic zones, fermentation in the reactor occurred and was able to send enough SCVFAs to achieve phosphorus removal from 8mg/L to 0.5mg/L.…”