Enhancement of struvite generation and anti-fouling in an electro-AnMBR with Mg anode-MF membrane module.

Severe membrane fouling and the inability to remove/recover nitrogen and phosphorus are bottlenecks of anaerobic membrane bioreactors (AnMBRs) for large-scale application in wastewater treatment. Herein, an electrochemical AnMBR with a Mg anode-membrane module (electro-AnMBR) was built and showed good performance in terms of membrane fouling mitigation and nutrient recovery during sewage treatment. Compared with the traditional AnMBR, membrane fouling in the electro-AnMBR was reduced by up to 30%. The application of an electric field decreased the zeta potential, viscosity, and EPS concentration of the sludge-water liquor in the electro-AnMBR, which could improve the cake layer structure and thus enhance water permeability. Meanwhile, 26% of NH4+ and 48% of PO43- co-precipitated with Mg2+ generating from the sacrificial Mg anode and were recovered as struvite deposited onto cathode in the electro-AnMBR. Hydrogen evolution provided a relatively alkaline pH environment, resulting in struvite electrodeposition on the graphic cathode, which partly separated the formed struvite from the sludge with a purity of 77%. In the electro-AnMBR, the electrochemical reactions provided alkalinity and effectively inhibited anaerobic acidification. The applied voltage of 0.6 V reduced the relative abundance of methanosaeta, but increased that of methanosarcina, which is also beneficial for the membrane anti-fouling.

Enhanced struvite generation and separation by magnesium anode electrolysis coupled with cathode electrodeposition.

Adding magnesium ions (Mg2+) to produce struvite is an important method to recover nitrogen and phosphorus from wastewater. Both the Mg2+ source and subsequent separation of struvite are key factors for the utilization of struvite. In this study, we developed an efficient method to recover nutrient salts from wastewater using sacrificial Mg anodes to generate struvite, with its simultaneous separation through cathode electrodeposition. The anode-released Mg2+ reacted with NH4+-N and PO43--P in bulk solution to form struvite, which was more intense on the cathode surface due to the relatively higher pH environment from hydrogen evolution, resulting in most of the struvite being deposited on the cathode surface and simultaneously separated out of the bulk solution. Using a cathode with a higher solution-cathode interface area and relatively low current density facilitated struvite deposition. Results showed that under optimal electrolysis condition (5.76 A/m2, pH 8.5, 180 min, and 1.2:1.0 Mg:P), 91% of the undissolved substances as the phosphate precipitation were deposited on the graphite cathode surface, and the proportion of struvite in the deposition reached 41.52%. This study provides a novel electrochemical method for struvite synthesis and separation for the recovery of nitrogen and phosphorus from wastewater.

Antifouling potential and microbial characterization of an electrochemical anaerobic membrane bioreactor utilizing membrane cathode and iron anode.

Serious membrane fouling limits the application of anaerobic membrane bioreactors (AnMBRs) in sewage treatment. Herein, a novel electrochemical AnMBR (eAnMBR) was established by integrating electrocoagulation and a conductive membrane into an AnMBR. Compared with the traditional AnMBR, TP average removal rate increased by 24.97% and the membrane service cycle extended by 109.68% in the eAnMBR. Low extracellular polymeric substance concentration and large floc size were found in the mixed liquid of the eAnMBR due to the combined effect of coagulation and electric field, which induced a porous and hydrophilic cake layer, resulting in excellent water permeation capabilities. Additionally, the conductive membrane cathode effectively suppressed membrane fouling by the electrostatic repulsion and gas scouring. In the eAnMBR, the presence of an electric field and iron ions enriched the diversity of the microbial community, which may improve the adaptation of biochemical systems to environmental changes.