Using fertilizers as draw solutes in forward osmosis (FO) can accomplish wastewater reuse with elimination of recycling draw solute. In this study, three commercial fast-release all-purpose solid fertilizers (F1, F2 and F3) were examined as draw solutes in a submerged FO system for water extraction from either deionized (DI) water or the treated wastewater. Systematic optimizations were conducted to enhance water extraction performance, including operation modes, initial draw concentrations and in-situ chemical fouling control. In the mode of the active layer facing the feed (AL-F or FO), a maximum of 324 mL water was harvested using 1-M F1, which provided 41% of the water need for fertilizer dilution for irrigation. Among the three fertilizers, F1 containing a lower urea content was the most favored because of a higher water extraction and a lower reverse solute flux (RSF) of major nutrients. Using the treated wastewater as a feed solution resulted in a comparable water extraction performance (317 mL) to that of DI water in 72 h and a maximum water flux of 4.2 LMH. Phosphorus accumulation on the feed side was mainly due to the FO membrane solute rejection while total nitrogen and potassium accumulation was mainly due to RSF from the draw solute. Reducing recirculation intensity from 100 to 10 mL min(-1) did not obviously decrease water flux but significantly reduced the energy consumption from 1.86 to 0.02 kWh m(-3). These results have demonstrated the feasibility of using commercial solid fertilizers as draw solutes for extracting reusable water from wastewater, and challenges such as reverse solute flux will need to be further addressed.

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Recovery of nutrients, water, and energy from high-strength sidestream centrate offers benefits such as reusable resource, minimized discharge and cost-savings in mainstream treatment. Herein, a microbial electrolysis cell-forward osmosis (MEC-FO) hybrid system has been investigated for integrated nutrient-energy-water (NEW) recovery with emphasis on quantified mass balance and energy evaluation. In a closed-loop mode, the hybrid system achieved recovery of 54.2 ± 1.9 % of water (70.4 ± 2.4 mL), 99.7 ± 13.0 % of net ammonium nitrogen (8.99 ± 0.75 mmol, with extended N 2 stripping), and 79.5 ± 0.5 % of phosphorus (as struvite, 0.16 ± 0.01 mmol). Ammonium loss primarily from reverse solute flux was fully compensated by the reclaimed ammonium under 6-h extended N 2 stripping to achieve self-sustained FO process. The generated hydrogen gas could potentially cover up to 28.7 ± 1.5 % of total energy input, rendering a specific energy consumption rate of 1.73 ± 0.08 kWh m-3 treated centrate, 0.57 ± 0.04 kWh kg-1 COD, 1.10 ± 0.05 kWh kg-1 removed NH 4 +-N, 1.17 ± 0.06 kWh kg-1 recovered NH 4 +-N, or 5.75 ± 0.54 kWh kg-1 struvite. Recycling of excess Mg 2+ reduced its dosage to 0.08 kg Mg 2+ /kg struvite. These results have demonstrated the successful synergy between MEC and FO to achieve multi-resource recovery, and encouraged further investigation to address the challenges such as enhanced hydrogen production, reducing nutrient loss, and optimizing MEC-FO coordination towards an energy-efficient NEW recovery process.

Direct electrochemical reduction provides a novel strategy for selenium removal from complex wastewaters. While electrochemical Se­(IV) reduction is thermodynamically favorable, anion structure reorganization hinders process kinetics and the phase of reduced Se(0) determines process performance. This study evaluates the thermodynamic and kinetic performance of Se­(IV) removal via direct electrochemical reduction (SeDER) and proposes moderate heating to promote efficient and continuous process operation. We find that SeDER is a robust process that can handle 0.001–10 mM Se­(IV) in a weakly acidic solution (pH 4–7). Se­(IV) can be electrochemically removed from the aqueous phase through either a four- or six-electron pathway, with the former generating Se(0) directly attached to the electrode surface and the latter producing Se­(-II) that is subsequently converted to Se(0). The four-electron pathway is a surface-limited process below 70 °C and terminates when the cathode is fully covered with the insulative amorphous Se(0). We demonstrate that raising the solution temperature to 80 °C deposits Se(0) in a conductive crystalline form and enables continuous reduction on the electrode surface. In a simple batch process design, we observe Se­(IV) removal rates of up to 89 mg h–1 m–2 of electrode surface area, up to 10% Faradaic efficiency, and up to 95% removal, although we observe moderate trade-offs between these metrics depending on the electron pathway and the initial concentration of Se­(IV). Our results suggest value in future work to enhance Faradaic efficiency via better reactor and electrode design, investigate parasitic reactions among competing ions, and select cost-effective electrodes for an economically competitive SeDER process.

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