Primary sludge fermentation using a pilot-scale mainstream fermenter to enhance biological phosphorus removal

Research was undertaken to assess the feasibility of using a mainstream primary sludge fermenter to produce simple carbon compounds to enhance biological phosphorus removal from wastewater. A mainstream fermenter, which consisted of a complete mix tank followed by a thickener with solids recycle, was constructed and incorporated into the biological nutrient removal process train of the UBC Pilot Wastewater Treatment Plant. The mainstream fermenter was operated for a period of one year to investigate the influence of hydraulic retention time (HRT) and environmental factors on process operation and short chain carbon production. The mainstream fermenter was operated at HRTs of 2.2, 3.2 and 4.3 hours. The HRT of the mainstream fermenter was observed to influence the production of volatile fatty acid (VFA); an increase in HRT resulted in an increase in net production of VFA. Individual acid formation in the mainstream fermenter was found not to be influenced by fermenter HRT. The performance of the mainstream fermenter operating at an HRT of 4.3 hours was equal to that of a side-stream static fermenter or a complete mix fermenter but below that of a side-stream separate complete mix/thickener fermenter. The quantity of simple carbon compounds produced in the mainstream fermenter while operating at an HRT of 4.3 hours combined with that found in the influent sewage were sufficient to stimulate good biological phosphorus removal at the UBC Pilot Wastewater Treatment Plant. Fermenter HRT had little affect on the quantity of soluble COD produced in the mainstream fermenter nor the portion of soluble COD that existed in the form of VFA. There was little change in the concentration of soluble COD between the mainstream fermenter influent and effluent suggesting hydrolysis of particulate organic matter did not readily occur in the mainstream fermenter. Nevertheless, the VFA fraction of soluble COD was significantly higher in the mainstream fermenter effluent than the raw influent indicating there was a conversion of soluble COD to VFA in the mainstream fermenter. The configuration of the mainstream fermenter did not allow for accurate control of solids retention time (SRT). However, a stable biomass inventory was quickly achieved and maintained without purposeful wasting. The steady-state level of biomass was dependent upon the length of HRT; longer HRTs resulted in lower biomass concentrations. Seasonal variations did not significantly affect the operation of the mainstream fermenter.Applied Science, Faculty ofCivil Engineering, Department ofGraduat