Pilot-scale phosphate recovery from wastewater to create a fertiliser product: An integrated assessment of adsorbent performance and quality

Eutrophication and the predicted limited future availability of rock phosphate has triggered the increased development of phosphorus (P) recovery technologies, however, for remote regions, recovery solutions are still limited. Here, we report on a novel pilot-scale technology (FILTRAFLOTM-P reactor) to recover phosphate (PO43−) from wastewater effluent through a filtration/adsorption process in a rural setting. This unit employs enhanced gravitational filtration through adsorption media (here, a novel KOH deacetylated crab carapace based chitosan-calcite material (CCM)) with continuous self-backwashing. Trials were designed to assess how the FILTRAFLOTM-P unit would operate under ‘real’ conditions (both at low and high PO43− levels), and to ascertain the effectiveness of the adsorbent to recover phosphate from final effluent. High removal was achieved at low phosphate concentrations, bringing the residual effluent PO43− level below 1 mg/L (EU limit for sensitive water bodies), while phosphate was efficiently harvested (at more than 50%) at higher PO43− levels. Surface microprecipitation and inner-sphere complexation were postulated as the main PO43− adsorption mechanisms through XRD, XPS and EDX elemental mapping. Further, a quality assessment of the P-enriched CCM (which could be used as a potential soil amendment) was undertaken to consider elemental composition, microbiological assessment and quantification of organic micropollutants. Quality analysis indicated ∼2.5% P2O5 present, trace levels (well below legislative limits) of heavy metals and extremely low levels of organic pollutants (e.g., PCBs, pharmaceuticals). No detectable levels of target bacterial pathogens were observed. Pot trials showed that ryegrass cultivated with the addition of the CCM adsorbent achieved higher plant dry matter and P concentration when compared to unfertilised controls, with a slow-release kinetic pattern. This study showed that CCM used with the FILTRAFLOTM-P pilot reactor has high potential to recover phosphate from effluents and encourage resource recovery via bio-based management of waste.