Invited Speaker
Dr. Qian Wang
Department of Environmental Science and Engineering, Guangdong Technion – Israel Institute of Technology, China;Department of Civil and Environmental Engineering, Technion, Israel
Speech Title: Chemical Mapping of Phosphorus (P) in Sewage Sludge throughout Wastewater Treatment Plants for Efficient P Recovery
Abstract: Phosphorus (P) is a necessary element for all living organisms. However, phosphate rock, the primary source of P, is finite and will be depleted in a century. This makes it urgent to recover P from secondary sources, e.g., wastewater treatment plants (WWTPs). To provide insights into efficient P recovery from WWTPs, this study mapped the P speciation in the sludge throughout three WWTPs in Denmark, i.e., Ejby Mølle, Billund, and Esbjerg WWTPs. Our recently validated sequential P extraction protocol, which can quantify vivianite Fe3(PO4)2·8H2O, was combined with a suite of analytical techniques such as optical microscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), powder X-ray diffraction (PXRD), and nuclear magnetic resonance (NMR). At Ejby Mølle WWTP, which used Fe-dosing chemical P removal and enhance biological P removal (EBPR), the primary sludge comprised of comparable inorganic orthophosphate (ortho-P, 53% of total P) and organophosphate (organic-P, 45%). The secondary sludge contained abundant polyphosphate (poly-P, 44%) formed by poly-P accumulating organisms during EBPR. However, the biogenic P (poly-P and organic-P) was degraded after anaerobic digestion, making inorganic ortho-P the dominated P in the downstream sludge (93-95%) with a bit organic-P. Fe-P, i.e., vivianite-P and Fe(III)-P, was the main inorganic ortho-P in all sludge samples, and it increased from 46% to 71% of total P by anaerobic digestion. Vivianite, a promising P recovery product which can be recovered from sludge by magnetic separation, was observed in the sludge after anaerobic digestion at high quantity with PXRD reflections (10-11 mg-P/g, 37-39% of total P). It was also found in all other sludge samples by microscopy and chemical extraction but not detected by PXRD. The PXRD amorphous properties of these vivianite particles may cause their overlook in sludge in previous studies. Similar trends of P variation were observed throughout Billund and Esbjerg WWTPs; but Al-P (P sorbed to amorphous Al hydroxides) was a P mineral phase as dominant as Fe-P (both 38%) in the downstream sludge at Esbjerg WWTP, which co-dosed Al and Fe.
