Concentrated Wastewater Treatment Using a Ferric Iron-dosed Anaerobic Upflow Sludge Blanket Reactor for Recovery of Phosphorus and Ammonium

Abstract

This study evaluated the performance of a novel, ferric iron-dosed anaerobic bioreactor to recover two separate nutrient products from concentrated wastewaters -- phosphorus as vivianite (Fe3(PO4)2×8H2O) and an ammonium-containing effluent with low organics. A bench-scale upflow anaerobic sludge blanket (UASB) reactor fed with a synthetic wastewater (458.0 mg/L total organic carbon, 282.7 mg/L ammonium, and 84.4 mg/L phosphate) was dosed with a ferric chloride solution at an org. C/Fe3+ molar ratio ~17.5 to facilitate organic carbon oxidation coupled to iron reduction. The reactor design allowed natural settling of vivianite to its cone-shaped bottom for collection. The UASB reactor was operated under two hydraulic retention times (HRT, 7 and 10 hours) and the results showed that an increase in HRT from 7 hours to 10 hours resulted in a higher removal efficiency of TOC (54% to 58%) and a higher removal (loss) of ammonia (16% to 38%). The change in HRT did not affect phosphate removal (79%). The total suspended solids (TSS) were 0.3, 20.5, and 172.8 gTSS/L at three heights of the bioreactor from top to bottom. Nitrite was below detection limit (0.01 mg/L) in both the influent and the effluent. Average total iron concentration in the influent was 14.93 mg/L including 0.14 mg/L Fe2+ and 14.79 mg/L Fe3+. The effluent had an average total Fe concentration of 1.90 mg/L including 1.26 mg/L Fe2+ and 0.64 mg/L Fe3+. Analysis of the microbial composition within the reactor was performed using quantitative polymerase chain reaction (qPCR), and results indicated the presence of Feammox bacteria (Acidimicrobiaceae A6) and iron-reducing bacteria (Geobacter). Further characterization of the biomass was completed with x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy equipped with energy dispersive x-ray spectroscopy (SEM-EDS). These results revealed oxygen (O), iron (Fe), carbon (C), and phosphorus (P) as the major elements present in the sludge sample obtained from the bottom of the reactor. X-ray diffractometry (XRD) revealed vivianite formation in the bottom sludge material. The process outlined by this research has the potential of recovering nutrients from concentrated wastewaters as a standalone system or as an add-on to biogas producing systems. The separate products of vivianite and ammonium-containing effluent low in organics offer flexibility in applying these as fertilizers at ratios best suited for the applied soils.