Removal of sewage phosphorus by adsorption and mineral precipitation, with recovery as a fertilizing soil amendment

• Published in: Water science and technology Vol. 77; no. 8; pp. 1967 - 1978
• Main Authors: Jowett, Craig, Solntseva, Irina, Wu, Lingling, James, Chris, Glasauer, Susan
• Format: Journal Article
• Language: English
• Published: England IWA Publishing 01.04.2018
• Subjects: Adsorption; Chemical precipitation; Clay; Corn; Effluents; Electrochemistry; Electron microscopy; Fertilization; Fertilizers; Groundwater; Initiatives; Iron; Iron phosphates; Leaching; Mineralization; Minerals; Organic chemistry; Phosphates; Phosphorus; Phosphorus removal; Precipitates; Precipitation; Removal; Sand; Scanning electron microscopy; Sediments; Septic tanks; Sewage; Silicates; Sludge; Soil; Soil amendment; Soil investigations; Surface water; Vivianite; Water resources; X-ray diffraction; Canada; United States > US; Massachusetts
• ISSN: 0273-1223; 1996-9732
• DOI: 10.2166/wst.2018.027

Clear sand adsorbs 15–35% total phosphorus (P) from septic tank effluent, but P is mobilized when low-P effluent is applied. Amorphous P compounds formed by alkali aluminate chemical addition may also be subject to leaching. Crystalline mineralization is the desired end effect that isolates P thoroughly from the water resource. Using new low-energy iron electrochemistry (EC-P process), dissolved ferrous iron reacts with sewage phosphate ions (PO4) and precipitates onto filtration medium as vivianite [Fe3(PO4)2·8H2O], as identified by scanning electron microscopy and X-ray diffraction and predicted from Eh–pH–aHPO42− phase relations. Removal rates of 90–99% in sand, soil and synthetic foam filters are obtained. The precipitation of vivianite demonstrates that P can be immobilized quickly and without intermediary adsorption phases, as with Fe-rich soils. Vitreous silicate material (VSM) or rockwool that traps and precipitates mineral P after EC-P treatment was investigated as a means of P reuse as a fertilizing soil amendment. Comparative soil leaching and growth studies using corn plants demonstrate that the VSM alone reduces P losses from soils, and that VSM which has received EC-P effluent is equivalent to or better than commercial superphosphate fertilizer.