Phosphorus recovery alternatives for sludge from chemical phosphorus removal processes – Technology comparison and system limitations

Several approaches have recently been proposed in the literature for P recovery after metal precipitation, but a robust comparison of these approaches in a techno-economic framework is still lacking. Five phosphorus recovery methods using sewage sludge or sludge ash as feed material were compared based on their specific operational recovery cost by scaling the processes to unified size and operational conditions. The selected technologies were (1) wet leaching + struvite precipitation, (2) magnetic vivianite separation, (3) sludge melt gasification, (4) the thermochemical sodium sulfate process, and (5) white phosphorus recovery. The analyses were based on the literature values in addition to a plant-wide model used to estimate chemical consumption and phosphorus and metal-related sludge properties. The technologies were assessed by operational cost, end-product quality, recovery efficiency, and technology maturity. The choice of the recovery process is dependent on the precipitant used in the wastewater treatment processes. Technologies using sewage sludge ash, (4) and (5), had the highest recovery efficiency, technical maturity, and product quality, but they require mono-incineration. Technology (3) had better recovery efficiency than (1), but the end-product had much lower P content. Technology (2) had the lowest recovery efficiency among all the compared technologies, however, it produced an end-product with the second highest P content. The operational costs were calculated for energy and chemical costs for same scale and operational conditions. The specific recovery cost ranges from 6 to 38 €/kgP_recovered.