Electrochemical phosphorus leaching from digested anaerobic sludge and subsequent nutrient recovery

Phosphorus Recovery from Whole Digestate through Electrochemical Leaching and Precipitation

“…The treatment plant centrifuges the whole digestate and disposes of the dewatered solid sludge cake in landfill. Further details on the chemical properties of the whole digestate can be found in Tables S1 and S2 and in our previous study …”

“…With the use of proper technologies, approximately 90% of P that enters a municipal wastewater treatment plant (WWTP) is removed and incorporated into wastewater sludge, which can be a promising source for P recovery . Whole digestate, a slurry produced from anaerobic digestion of wastewater sludge, is typically enriched with inorganic orthophosphate (IP) in both aqueous and solid phases. − Direct land applications of digestate can be subject to restrictions due to the concerns over high concentrations of ammonium and salinity, recalcitrant compounds, and heavy metals. , To maximize P recovery from whole digestate, various treatments including strong acid and base, complexing agents, ozonation, ultrasonication, thermal, and electrochemical treatment have been applied to leach P out of the solid phase. − Electrochemical treatment, which relies on water electrolysis to mobilize solid P, is of particular interest with potential benefits such as reduced handling of corrosive chemicals, flexible operation, and relatively low environmental impact.…”

“…For example, a two-chamber electrochemical system using AEM extracted 71% of the P from the secondary sludge as PO 4 3– –P in its anolyte . However, the migration efficiency of PO 4 3– –P through AEM is typically low (<5%) due to the competition from other anions. , The extracted P can be recovered by being converted into solid products via precipitation, which involves the addition of metal and basic solution to form various precipitates such as calcium phosphate (CaP), iron phosphate (FeP), or magnesium ammonium phosphate (struvite). ,, The recovered P-rich products can be used in industrial processes for fertilizer production or as agricultural fertilizer. However, the direct use as fertilizer is still restricted by high heavy metal contents such as Cu, Ni, Cd, and Pb as observed in some case studies. ,− To date, the electrochemical recovery of PO 4 3– –P from whole digestate is still energy- and chemical-intensive and less economically competitive compared to phosphate rock mining. , …”

“…EMP has been studied to treat various liquid waste streams containing 7.8–789 mg PO 4 3– –P L –1 and achieved adequate PO 4 3– –P precipitation (40–90%) with energy consumption of 26.4–4399 kW h kg –1 P, but its application to solid waste streams has yet to be explored. − In addition, PO 4 3– –P is typically in excess in liquid streams and external metal ions such as Ca 2+ , Fe 3+ , and Mg 2+ still need to be added to facilitate high PO 4 3– –P precipitation efficiency. − Considering that the anodic leaching of whole digestate releases these native metal ions with PO 4 3– –P, we proposed a two-chamber electrochemical phosphorus recovery cell (EPRC) that creates two different pH environments for simultaneous P leaching (anode) and EMP (cathode) in real whole digestate. In contrast to electrochemical P recovery studies of solid waste streams that relied on PO 4 3– –P migration across the AEM, the proposed EPRC enables chemical-free EMP by harnessing the native metals naturally present in whole digestate. , To our knowledge, this is the first endeavor to integrate EMP into the recovery of P from solid waste stream without the need for chemical inputs. The specific objectives of this study were to: (1) demonstrate the feasibility of the EPRC for simultaneous P leaching and EMP; (2) evaluate the effects of current density on the P recovery performance, P mass distribution, and product quality; and (3) assess the P solids harvesting strategy during a long-term operation.…”

REDOX physical-chemical method boosted phospholytic bacteria technology for enhanced phosphorus solubilization

“…As for the scale application, the challenges may be located at the distribution of the anode and cathode pair in the practical soil, the anti-corrosion of the electrode materials by the salt and bacteria and the cost control of the integrated electro-bacteria system. Overally, it is very promising to have the introduction of electrochemical technology into the phosphorus-solubilizing bacteria system, which is of great benefits for the transformation of phosphorus elements and plant growth ( Rodríguez and Fraga, 1999 ; Acevedo et al, 2014 ; Wang and He, 2022 ).…”