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Optimization of VFA production in an atad reactor with respect to aeration rates and removal of phosphorus, incorporating a magnesium ammonium phosphate (map) crystallizer from the atad supernatant Sharma, Abyartha

Abstract

Previous researchers have demonstrated that a mixture of primary and secondary sludge provides increased production of VFA in ATAD. Experiments were carried out at the UBC pilot plant, in two phases, using a 35/65 mixture of primary/secondary sludge, to determine the optimum aeration rate with respect to production/generation of VFA, and to investigate the removal of phosphorus by forced formation of struvite in an upflow crystallizer. The source sludge for the research was obtained from an on-site modified UCT process, and mixed in the correct ratios prior to feeding on an hourly basis to the 125-L tanks. The tanks, were configured in parallel and operated as individual first stage reactors, one of which was the control tank. During the first stage, the control tank was maintained at a constant aeration rate of 50 ml/min (as suggested by EPA). The aeration rate in the test tank was varied from 0 ml/min (nitrogen was supplied) to 100 ml/min, at increments of 25 ml/min. Throughout the entire experimental period, temperatures were in the thermophilic range, between 47°C and 58°C inside the tanks; feed solids were maintained around 1.4% TSS, and ORP was consistent between -300 mV and -450 mV. There was higher production of VFA at lower aeration rates, the highest occurring when 25 ml/min air was supplied. Analysis of nutrients confirmed that there was a high release of stored phosphorus and an increase in ammonia nitrogen. The ratio of VFA: PO₄-P was the highest when 25 ml/min air was supplied.

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