A review of technologies for closing the P loop in agriculture runoff: contributing to the transition towards a circular economy

Phosphorus (P) scarcity and the environmental hazards posed by P discharges have triggered the development of technologies for P sequestration and removal from waste streams. Agriculture runoff usually has P concentrations high enough to contribute to eutrophication and harmful algal blooms, but they are still too low for successful P removal with conventional technologies commonly applied in wastewater treatment. For this reason, realistic approaches to remove P from agricultural waste streams mainly include natural assimilation and constructed wetlands. Although these technologies have been implemented for some time, P removal is not always achieved to the needed extent and sometimes sufficient surface areas required are unattainable. Phosphorus sorbing materials, especially materials rich in calcium, have emerged to increase the removal potential of runoff treatment wetlands and at the same time sequester P for potential subsequent reuse. This paper analyses the current strategies and technologies for P removal and reuse from agriculture surface runoff streams taking a circular economy approach. It particularly addresses the current state of calcium rich materials commonly used for P removal that have also shown positive results as fertilizers or soil.This work has been possible thanks to the European funding programme “Iniciativa de Empleo Juvenil” and the Spanish Ministry of Science and Innovation (project reference: PEJ2018-005586-A).Peer ReviewedPostprint (published version

Process optimization of the polyhydroxybutyrate production in the cyanobacteria Synechocystis sp. and Synechococcus sp.

The effect of four parameters (acetate, NaCl, inorganic carbon and days in darkness) affecting the polyhydroxybutyrate (PHB) production were tested and optimized for Synechococcus sp. and Synechocystis sp. using a Box-Behnken design. The optimal conditions for Synechocystis sp. were found to be 1.2 g L-1 of acetate, 4 gC L-1 of NaHCO3, 18 g L-1 of NaCl and 0 days in darkness. For Synechococcus sp., equal acetate concentration and days in darkness, and lower inorganic carbon and NaCl concentrations than those for Synechocystis sp. were needed (0.05 g L-1 inorganic carbon and 9 g L-1 NaCl). Optimal conditions were scaled up to 3 L photobioreactors. Using Synechocystis sp., 5.6 %dcw of PHB was obtained whether adding or not acetate. In opposition, a maximum of 26.1 %dcw by using acetate was reached with Synechococcus sp. These results provide an easy method to optimize the cultivation conditions to enhance PHB production with cyanobacteria.Authors would like to acknowledge the Spanish Ministry of Science, Innovation and Universities (MCIU), the Research National Agency (AEI), and the European Regional Development Fund (FEDER) for funding this study [AL4BIO, RTI2018-099495-B-C21]. Estel Rueda wants to thank the Spanish Ministry of Education, Culture and Sport [FPU18/04941] for her grant. Beatriz Altamira-Algarra thanks the Agency for Management of University and Research (AGAUR) for her grant [FIAGAUR_2021].Peer ReviewedPostprint (author's final draft

Process conditions affect properties and outcomes of polyhydroxyalkanoate accumulation in municipal activated sludge

The developments of mixed culture polyhydroxyalkanoate production has been directed to maximize the biomass PHA content with limited attention to polymer quality. Direct comparison of PHA accumulation literature is challenging, and even regularly contradicting in reported results, due to underlying differences that are not well expressed. A study was undertaken to systematically compare the commonly reported process conditions for PHA accumulation by full-scale municipal activated sludge. A biomass acclimation step combined with a pulse-wise feeding strategy resulted in maximum average PHA contents and product yields. pH control and active nitrification did not result in observable effects on the PHA productivity. Under these conditions a high molecular weight polymer (1536 ± 221 kDa) can be produced. Polymer extraction recoveries were influenced by the PHA molecular weight. A standard protocol for an activated sludge PHA accumulation test including downstream processing and standardized extraction has been developed and is available as supplementary material

Process conditions affect properties and outcomes of polyhydroxyalkanoate accumulation in municipal activated sludge

The developments of mixed culture polyhydroxyalkanoate production has been directed to maximize the biomass PHA content with limited attention to polymer quality. Direct comparison of PHA accumulation literature is challenging, and even regularly contradicting in reported results, due to underlying differences that are not well expressed. A study was undertaken to systematically compare the commonly reported process conditions for PHA accumulation by full-scale municipal activated sludge. A biomass acclimation step combined with a pulse-wise feeding strategy resulted in maximum average PHA contents and product yields. pH control and active nitrification did not result in observable effects on the PHA productivity. Under these conditions a high molecular weight polymer (1536 ± 221 kDa) can be produced. Polymer extraction recoveries were influenced by the PHA molecular weight. A standard protocol for an activated sludge PHA accumulation test including downstream processing and standardized extraction has been developed and is available as supplementary material.BT/Environmental Biotechnolog