Sidestream treatment for improved BNR process performance

摘要

The removal of nutrients from the wastewaters through biological processes is a costeffective and environmentally sound alternative to chemical treatment. The primary driverfor the success of the biological nutrient removal (BNR) processes is the availability ofsuitable carbon sources in the influent wastewater. Unfortunately, in the UK thewastewaters considered being weak for the BNR carbon limited processes and hencemany methods have been examined in the past for the enhancement of BNR.In this project an internal carbon source was proposed and examined. The carbon wasproduced from the disintegration of activated sludge by a mechanical process, which wasexplored and its impact on the BNR carbon limited processes was evaluated. Theequipment used in this study for mechanical sludge disintegration was a deflaker, whichwas able to cause significant increase in chemical oxygen demand and volatile fatty acids(VFA) in the soluble phase of sludge. Laboratory scale tests revealed that this carbonsource can improve the phosphorus release and denitrification process and hence thephosphorus and nitrogen removal.These results led us to investigate the carbon source produced from disintegration in pilotscale and two BNR reactors were used for this purpose. The mechanical disintegration of5.8% of return activated sludge was able to increase the concentration of VFA in theinfluent wastewater by 2.5-7 mg l-1 and successfully replace the equivalent amount ofacetic acid, which is normally considered to be the best carbon source for biologicalphosphorus removal. The performance of the test reactor in terms of nitrogen, suspendedsolids and chemical oxygen demand was also unaffected. In addition, the sludgedisintegration affected the bacteria growth yield, which combined with the longer sludgeage by 6 days compared to the control reactor caused a 20-26% reduction in sludgeproduction. In order to examine whether this process could be used by the water utilities acost analysis took place, which revealed that the operational cost of the specificdisintegration process and under the conditions examined in this study outweighs thesavings from the produced carbon source and reduced amount of sludge.