Recovery of nutrient nitrogen from municipal wastewater residuals by gas membrane separation

There are relatively high amounts of ammonia returned to the headworks of a municipal wastewater plant that are extracted from the dewatering process. This ammonia load contributes to a significant oxygen demand in the secondary treatment, requiring greater air blower energy costs. This goal of this research was to evaluate the feasibility of the recovery of an ammonium sulfate product from belt press filtrate. The objectives of this research were to: (1) analyze wastewater treatment average monthly data flows and constituents with respect to ammonia nitrification, (2) the evaluate the technical performance of a two sage gas-separation membrane for recovering ammonia separation, and (3) evaluate the economic feasibility of wastewater plants operating ammonium sulfate production. Results showed that, for the years 2012–2013, the Bustamante Wastewater Treatment Plant had a monthly average of 1197 lb/day of ammonia (as N), which required an average energy cost of $60,868per year. The ammonia separation process was observed to operate optimally at a pH of 9.8 in the belt press filtrate influent, which maximizes the ammonia speciation without causing calcium carbonate precipitation. At a filtrate feed flowrate of 2.0 gpm in the pilot system, 68% of the ammonia was removed, producing approximately 11 lb/day of ammonium sulfate. Scale-up to treat the average 0.18 million gallons per day (mgd) of belt press filtrate would have an estimated annual energy cost savings of $23,900 and ammonium sulfate revenue of $15,135 per month for a total net financial benefit of $205,500 per year. With an estimated total capital cost of $1,680,280 the simple payback period was estimated to be 8 years. Future work should evaluate more efficient particle pretreatment to minimize fouling of the gas-separation membranes