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Phosphorus recovery from a membrane enhanced biological phosphorus removal (MEBPR) process Yue, Chaoyang


Phosphorus is an essential yet limited element for sustaining life of human beings. Municipal wastewater contains rich phosphorus, which is not sufficiently recovered or recycled. This dissertation developed a system that could recover phosphorus from wastewater as struvite fertilizer (MgNH₄PO₄•6H₂O). Such a system included three major components — a membrane enhanced biological phosphorus removal (MEBPR) process, a side-stream unit to extract PO₄³⁻ and NH₄⁺ from wasted solids, and a struvite crystallizer. This dissertation focused on optimizing the first two steps through pilot- and bench-scale studies, respectively. The MEBPR process was tested at increasing solids retention time (SRT) to increase total phosphorus (TP) concentration in mixed liquor (ML). The operation at SRT = 60 days proved to be technically feasible and achieved comparable phosphorus removal (95−96 %) and organic carbon removal (91−92 %) to that observed during operation at the control SRT (25 days). The 60-day SRT operation also removed 14 % more nitrogen, wasted 17 % less dry solids, more than doubled the TP concentration of aerobic zone ML, but did not increase membrane fouling rates. Cost analyses showed that the energy requirements were 0.94 and 2.1 kWh/m³ of permeate for SRT = 25 and 60 days, both within the reported range for full-scale membrane bioreactors. To solve foaming problem in the MEBPR process, foam was characterized as an alternative resource for phosphorus recovery. Methods were assessed to extract phosphorus from ML and foam. With suitable conditions, microwave-based hydrogen peroxide advanced oxidation process (MW-H₂O₂ AOP) could extract > 90 % of TP as PO₄-P from foam, and anaerobic P-release could extract up to 60 % from ML. Anaerobic digestion could extract 44−46 % of TP under digestion pHs, 64−65 % with pH ≤ 5.5, and generate sufficient NH₄⁺ that matched the quantities of PO₄³⁻ extracted. Finally, a system was proposed that included an MEBRP process operating at SRT = 60 days, and an anaerobic digester to extract both PO₄³⁻ and NH₄⁺. This system could recover about 60 % of the incoming phosphorus in the influent. To recover more phosphorus, MW-H₂O₂ AOP could be used after anaerobic digestion, whenever justified.

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