Phosphorus Recovery from Decentralized Wastewater by a Novel Siderite-Calcite Integrated Electrochemical Process: Efficacy, Mechanism, and Optimization

Electrochemical enhancement of sulfite-induced phosphate release from iron phosphate with concurrent micropollutant degradation in water.

The recovery of phosphorus (P) from high-strength acidic waste streams with high salinity and organic loads is challenging. Here, we addressed this challenge with a recently developed electrochemical approach and compared it with the chemical precipitation method via NaOH dosing. The electrochemical process recovers nearly 90% of P (∼820 mg/L) from cheese wastewater in 48 h at 300 mA with an energy consumption of 64.7 kWh/kg of P. With chemical precipitation, >86% of P was removed by NaOH dosing with a normalized cost of 1.34–1.80 euros/kg of P. The increase in wastewater pH caused by NaOH dosing triggered the formation of calcium phosphate sludge instead of condensed solids. However, by electrochemical precipitation, the formed calcium phosphate is attached to the electrode, allowing the subsequent collection of solids from the electrode after treatment. The collected solids are characterized as amorphous calcium phosphate (ACP) at 200 mA or a precipitation pH of ≥9. Otherwise, they are a mixture of ACP and hydroxyapatite. The products have sufficient P content (≤14%), of which up to 85% was released within 30 min in 2% citric acid and a tiny amount of heavy metals compared to phosphate rocks. This study paves the way for applying electrochemical removal and recovery of phosphorus from acidic P-rich wastewater and offers a sustainable substitute for mined phosphorus.

Photo-electrochemical oxidation of hypophosphite and phosphorous recovery by UV/Fe2+/peroxydisulfate with electrochemical process

To separate and concentrate NH4+ and PO4 3– from the synthetic wastewater to the concentrated solution through a novel electrochemical reactor with circulated anode and cathode using the difference of the concentration between electrode chamber and middle chamber.In recent years, the research on electrochemical processes have been focused on phosphate and ammonium removal and recovery. Among the wide range of possibilities with regards to electrochemical processes, capacitive deionization (CDI) saves the most energy while at the same time does not have continuity and selectivity. In this study, a new electrochemical reactor with electrolyte cyclic flowing in the electrode chambers was constructed to separate and concentrate phosphate and ammonium continuously and selectively from wastewater, based on the principle of CDI. At the concentration ratio of NaCl solution between the electrode chambers and the middle chamber (r) of 25 to 1, phosphate and ammonium in concentration level of domestic wastewater can be removed and recovered continuously and selectively as struvite. Long-term operation also indicated the ability to continuously repeat the reaction and verified sustained stability. Further, the selective recovery at the certain r could also be available to similar technologies for recovering other kinds of substances.

Electrochemical crystallization for phosphate recovery from an electronic industry wastewater effluent using sacrificial iron anodes

Land application of manure can be a sustainable supply chain practice that improves soil quality by recycling important nutrients contained in animal waste. Yet, runoff of phosphorus and nitrogen nutrients contained in the animal waste has contributed to significant watershed eutrophication. Recovery of the dissolved nutrient species as a condensed solid fertilizer product would increase sustainability of the agricultural supply chain, while reducing watershed pollution. This study was conducted to evaluate the recovery of phosphorus (primarily) as struvite using an electrochemical process while varying temperature, applied cathodic potential, turbulence and Ca2+ concentration. High phosphorus recovery with high current efficiency and low specific energy consumption was possible at 20 °C, −1.1 V vs Ag/AgCl at the cathode, and a Reynolds number of 9150 in the absence of Ca2+ when the Mg:N:P ratio was 1.37:1:1. Further, a thermodynamic model of the waste solution indicated an increase in Ca2+ concentration, which impedes struvite recovery, can be negated by increasing dissolved Mg2+ concentration and operating at a pH below NH3 volatilization.

Electrochemical phosphorus precipitation (EPP) from wastewater is a promising emerging technology for recovering valuable nutrients. While there are significant advantages of EPP compared to traditional phosphorus recovery, large gaps in reported performance exist between EPP methods and between EPP and industrial methods. Herein we discuss Figures of Merit (FOM) to normalize and report EPP performance at low-to-intermediate technology readiness levels (TRLs). The appropriate use of FOM in electrochemical engineering enables better comparison between technologies, enhanced understanding of electrochemical and mass transport phenomena, and faster scale-up and adoption of nascent technologies.¬ FOM specific to EPP are discussed along with important considerations and adaptations from traditional electrochemical engineering FOM. Importantly, this FOM approach may be adapted for many different electrochemical processes and technologies, aiding in the push toward and adoption of electrification in chemical processing.

This study reported two-phase electrochemical processes, including struvite electrochemical precipitation and ammonia electrooxidation, for the treatment of supernatant from the hydrolysis sludge. The results showed that in phase I, the removal efficiencies of 92.3% PO43--P and 50.1% NH4+-N could be achieved in electrochemical precipitation with magnesium sacrificial anode at pH9.0 and 40mA after 120-min electrolysis, and slightly increased to 95.1% and 57.3%, respectively, when current further increased to 120mA, while the energy consumption (ECS, from 0.6 to 6.7kWhm-3) and specific energy consumption [SECS, from 2.7 to 29.9Whg (PO43--P)-1] sharply increased. In phase II, the residual NH4+-N is further indirectly electrooxidized to nitrogen with modified Ti anode (Ti/SnO2-Sb-Pd). With the generation of active chloride, about 83.2% NH4+-N was removed with the molar ratio of Cl/N 5:1 at 50mA after 120-min treatment, and slightly increased to 92.2%, when current increased to 125mA, while SECS significantly increased [from 0.027 to 0.117kWhg (NH4+-N)-1]. The results indicated that current were the crucial factors; meanwhile, lower current and longer reaction time may be the optimal options in electrochemical process with higher efficiency and lower energy consumption. Finally, the integrated process was conducted at the optimal conditions (pH = 9.0, I= 40mA in phase I; Cl/N = 5, I= 50mA in phase II) with the supernatant of the alkaline hydrolysis sludge. Removal of ammonia nitrogen (79.3%) and removal of phosphorus (94.3%) were achieved, confirming the feasibility of practical application for the simultaneous phosphorus recovery and ammonia removal.

Electrochemical Process for Phosphorus Recovery from Water Treatment Plants

Phosphorus (P) is a nonrenewable macronutrient, indispensable for plant growth. There is a critical need to reassess current use of P, recover it from “waste” and reuse it in various applications. This is the basis of preserving P as a valuable resource. It would significantly contribute to resolving the issue of environmental degradation as well as resource scarcity while ensuring global food security.