Wednesday, 16 March 2022 08:31

FOSPHORUS

The new paradigm in wastewater treatment proclaims that wastewater treatment plants (WWTPs) should evolve to water resource recovery facilities where material and energetic resources should be recovered from wastewater. Among all the potential resources to be recovered, phosphorus (P) arises as a perfect candidate since P has a vital role in life activities, is a limited and non-renewable resource with an expected growing demand and with P discharge limits that are expected to become more stringent in the future. If P entering the WWTP could be recovered, 15-20 % of the global P demand could be covered. P can be recovered as struvite or as vivianite depending on whether enhanced biological phosphorus removal (EBPR) has been already integrated in the WWTP.
When EBPR is integrated, P-recovery as struvite from the digestate seems the best option. Struvite (MgNH4PO4·6H2O) is a slow-release rate fertiliser that also provides nitrogen and magnesium and has been reported to be a good option for agricultural uses. However, WWTPs with EBPR frequently show unstable performance. FOSPHORUS will study an alternative method for improving EBPR process stability: the side- stream EBPR (S2EBPR), which implies the integration of an side-stream sludge fermenter (SSSF) for VFA production. FOSPHORUS will study with long-term experiments the effect of RAS diversion, SRT and HRT in SSSF, mixing conditions in the performance yield to overcome the existing knowledge gaps in S2EBPR process fundamental mechanisms. Struvite crystallization may not be the optimal solution for P recovery in all scenarios due to the low recovery yield and low ratio between the struvite sales price to production costs in a WWTP. Vivianite (Fe3(PO4)·8 H2O) is an alternative to struvite in systems where EBPR is not implemented. Vivianite is ubiquitous, has an attractive economic value because of its high P content, easy accessibility and slow release and has been employed both in the chemical industry and in agricultural industries as a slow-release fertilizer. FOSPHORUS will study the key parameters (the molar Fe/P ratio, the pH and its separation from sludge).
The main objective of FOSPHORUS is the development, experimental validation and in-silico assessment of the techno-economic and environmental feasibility of two different alternatives for P recovery from urban wastewaters: struvite production and vivianite-based Precovery.
For this aim, FOSPHORUS includes an exhaustive experimental assessment of the opportunities for P recovery implementing the innovative configuration S2EBPR in an already existing and fully monitored pilot plant. The final choice between these struvite and vivianite is not straightforward and this is where FOSPHORUS will take a big step forward. Our aim is to bring together our previous background and the experimental knowledge gained during FOSPHORUS into a final Decision Support System tool that will allow WWTP managers to select the best option for implementing P-recovery in their facilities by providing a thorough analysis based on:

Performance: C/N/P mass balances, N- and P-recovery yields, potential C redirection to biogas production

Environmental parameters: mass and energy recovery, decrease of GHG emissions: CO2, CH4, N2O, carbon footprint of the plant, biogas production

Economics: P-recovery implementation costs, benefits from avoiding chemical precipitation and struvite/vivianite revenues, preventing
undesired precipitation in pipes.

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