Treatment and recovery of phosphate from submerged anaerobic membrane bioreactor effluent using thermally treated biowaste and powder activated carbon.

This study presents a novel treatment system using a submerged anaerobic membrane bioreactor (SAnMBR) followed by adsorption onto thermally treated biowaste, and ending with a final treatment using powdered activated carbon (PAC). Despite limited phosphate and ammonium ion removal during SAnMBR operation, thermally treated eggshell (EGSL) and seagrass (SG) received SAnMBR effluent and enhanced phosphate recovery, achieving removal rates of 71.8-99.9% and 60.5-78.0%, respectively. The SAnMBR achieved an 85% COD removal, which was slightly reduced further by biowaste treatment. However, significant further reductions in COD to 20.2 ± 5.2 mg/L for EGSL effluent and 57.0 ± 13.3 mg/L for SG effluent were achieved with PAC. Phytotoxicity tests showed the SAnMBR effluent after PAC treatment notably improved seed growth compared to untreated wastewater. In addition, volatile organic compounds (VOCs) were significantly reduced in the system, including common wastewater contaminants such as dimethyl disulfide, dimethyl trisulfide, phenol, p-cresol, nonanal, and decanal. Fractionation analysis of the solid fraction, post-adsorption from both synthetic and domestic wastewater, indicated that for SG, 77.3%-94% of the total phosphorus (TP) was inorganically bound, while for EGSL, it ranged from 94% to 95.3%. This study represents the first attempt at a proof-of-concept for simultaneous treatment of domestic wastewater and phosphorus recovery using this integrated system.

Recovery of phosphate from dewatered anaerobic sludge and wastewater by thermally treated P.oceanica residues and its potential application as a fertilizer.

A process for the valorization of seagrass residues has been developed, aiming to investigate its potential as a phosphate adsorbent and the production of added-value products, which can be assessed in agricultural applications. Posidonia oceanica residues were thermally treated (500 °C, 1 h) and were tested as an adsorbent of phosphate from real wastewater. Chemical leaching experiments of phosphate from dewatered anaerobic sludge (DWAS) were conducted, evaluating sonication and inorganic acids (sulfuric acid (SA), thermal-sulfuric acid (TSA), and nitric acid (NA)) as extraction methods. Τhe extraction efficiency of each method tested demonstrated that the most suitable acid medium to leach out phosphate were SA and TSA processes with 84.9 and 93.2% removal efficiency, respectively. Moreover, the saturation capacity of thermally treated P. oceanica was assessed, and the results confirmed the high phosphate adsorption capacity (179.1 mg g-1). Adsorption batch experiments with real wastes (anaerobic effluent wastewater and leached solution from DWAS), demonstrated that thermally treated seagrass could have a high adsorption efficiency and selectivity towards phosphate. After phosphate adsorption, the solid residues were mixed with compost in different ratio and then tested as fertilizer substitutes on plant growth. The solid residue after adsorption produced from anaerobic effluent or synthetic solutions imposed a positive effect on plant growth with germination index (GI) values 96.7-111.14%, for all types of seeds tested (Solanum Lycopersicum, Lepidium sativum, and Sinapis alba), while the solid residue after adsorption produced from DWAS leached solution negatively affected the germination of plants, probably due to potentially refractory compounds contained in DWAS.