Modified biochars present an economic challenge to phosphate management in wastewater treatment plants

Abstract In order to reduce phosphorus (P) discharge into aqueous systems, wastewater treatment plants usually precipitate sludge water with iron or aluminum salts and produce slow–release P fertilizer (struvite). Continued tightening of P discharge limits require additional equipment and larger doses of these salts which increase wastewater treatment cost. Many research teams are involved in P recovery and theoretical knowledge is rapidly increasing. However, most new proposals are only economically viable with the support of public funds. Novel and technically undemanding concepts are designed and techno–economically assessed on a pilot scale. The cheapest biochar derived from fermentation residues that are pyrolyzed by waste heat, was used as sorbent. Multiple austerity measures have been designed to modify the sorbent by ferric (Fe3+) and calcium (Ca2+) chemisorption. It is firstly reported that over 2.5 kg of P per 100 kg of modified biochar from the 80 mg P L–1 environment can be obtained, whereas the P forms are more readily available to plant nutrition than struvite. Provided that a majority of used reactants are recovered from waste, or their price is irrelevant (subsequently used for their original purpose), there are indications that the newly proposed technology is one of the few environmentally friendly measures that can swiftly become widespread in the wastewater industry for economic reasons.