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Relative agronomic efficiency (RAE) of phosphorus (P) in nutrient-rich residues with different chemical characteristics must be known in order to optimize their use as fertilizers, to avoid underfertilization of crops or eutrophication of surface waters due to overfertilization. In this study, we determined the chemical characteristics and RAE of manures (cattle, pig, fox) and sewage sludges subjected to different treatments (anaerobic digestion, composting, lime stabilization, thermal hydrolyzation, pyrolyzation, hydrothermal carbonization (HTC)) by growing barley (Hordeum vulgare, var. Elmeri) to maturity in three independent growth trials. All manures had high RAE (up to 189% in pig slurry), while RAE was only 6-17% for digested and composted sewage sludges when precipitation with Fe used for P removal from wastewater. Pyrolyzation and HTC further depressed RAE to 1-6%. Alternative wastewater treatment processes are therefore needed to increase P recycling potential. For cattle and pig manures and anaerobically digested or composted sewage sludges, molar ratio of (Fe + Al)/P, varying from 0.08 to 2.69, was the best predictor of RAE (R 2  = 0.99), with negative correlations with grain yield. Sources in which calcium was more influential for P solubility (fox manure and lime-stabilized sewage sludge) and pyrolyzed and HTC-treated residues did not follow this trend. Conventional extraction methods (2% formic acid, 2% citric acid, neutral ammonium citrate, water and 0.5 M NaHCO 3 ) either underestimated or overestimated RAE of P-rich organic residues, depending on their chemical characteristics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Electro-concentration enables treatment and nutrient recovery from source-separated urine, and is a potential technology for on-site treatment using a 3 compartment configuration that has anode, cathode and middle concentrate compartments. There is a particular focus on driving concentration towards the precipitation threshold in the concentrate compartment to generate solid ammonium salts, including ammonium bicarbonate. To evaluate controlling mechanisms and the feasibility of achieving high concentrations, a dynamic mechanistic model was developed and validated using experiments with synthetic urine. It was identified that high concentrations are prevented by increased back diffusion (diffusion from the middle chamber to the anolyte and catholyte) due to large concentration gradients, and the preferential migration of protons or hydroxide ions due to a loss of buffering capacity in the anolyte and catholyte (due to pH extremes). Model-based sensitivity analysis also identified that electrolyte ion concentrations (including buffer capacity) were the main controlling mechanisms, rather than membrane or electrolyte current transfer capacity. To attain high concentrations, operation should be done using a) a high current density (however there is a maximum efficient current density); b) feed at short hydraulic retention time to ensure sufficient buffer capacity; and c) a feed high in ammonium and carbonate, not diluted, and not contaminated with other salts, such as pure ureolysed urine. Taking into account electron supply and bio-anodic buffer limitations, model testing shows at least double the aqueous concentrations observed in the experiments may be achieved by optimising simple process and operational parameters such as flow rate, current density and feed solution composition. Removal of total ammonium nitrogen (TAN) and total carbonate carbon (TCC) was between 43-57% and 39-53%, respectively. Balancing the sometimes conflicting process goals of high concentrations and removal percentage will need to be considered in further application. Future experimental work should be directed towards developing electrodes capable of higher current densities. In addition it would be desirable to use ion exchange membranes with higher resistance to water fluxes and which limit back diffusion. Future modelling work should describe osmotic and electro-osmotic water fluxes as a function of the concentration gradient across the membranes and ionic fluxes, respectively. More generalised wastewater physico-chemistry speciation models should identify best methods where relatively simple Davies activity corrections do not apply., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

This work presents and explores a novel methodology for the removal and recovery of ammonia from wastewater based upon two mechanisms: electrochemical oxidation and a previously unreported electrochemically-assisted surface transfer mechanism. Recovery of ammonia is enabled by placing a porous cathodic electrode at the wastewater-air interface. In this configuration, the cathode creates local alkalinity and an electric field that draws ammonium ions towards the wastewater-air interface, resulting in near-linear reductions of dissolved ammonium irrespective of concentration. This approach leads to significant ammonia recovery without the need for ion-exchange membranes. In addition, anodic reactions that simultaneously occur at depth in the wastewater induce ammonia oxidation in accordance with proven mechanisms. The floating electrode approach offers improved ammonia removal efficiency in comparison to electrooxidation. Trials conducted on synthetic wastewater (900 mg NH 4 + -N l -1 ) and filtered anaerobic centrate (560 mg NH 4 + -N l -1 ) demonstrated ammonia concentration decreases up to 216 mg l -1 hr -1 and 110 mg l -1 hr -1 , respectively, under the application of 5 mA cm -2 current density. The technology would be best used to treat municipal and industrial wastewaters possessing high ammonia concentration, including anaerobic digester centrate and urine, and offers potential to assist in removing ammonia from environmental waters.