Nutrient Recovery by Bio-Electroconcentration is Limited by Wastewater Conductivity

Abstract

Removal and recovery of nutrients from waste streams is essential to avoid depletion of finite resources and further disruption of the nutrient cycles. Bioelectrochemical systems (BESs) are gaining interest because of their ability to recover nutrients through ion migration across membranes at a low energy demand. This work assesses the feasibility of the concept of nutrient bio-electroconcentration from domestic wastewater, which is a widely available source of nutrients in ionic form, collected via sewer networks and easily accessible at centralized wastewater treatment plants. Here, we demonstrate the limits of a three-chamber BES for the recovery of nutrients from domestic wastewater. Because of low ionic conductivity, the measured current densities did not exceed 2 A m–2, with corresponding limited nutrient ion recoveries. Moreover, in a 3D electrode, forcing higher current densities through potentiostatic control leads to higher Ohmic losses, resulting in anode potential profiles and runaway currents and potentials, with consequent unwanted water oxidation and disintegration of the graphite electrode. At the current density of 1.9 A m–2, N removal efficiency of 48.1% was obtained at the anode. However, calcium and magnesium salts precipitated on the anion-exchange membrane, putatively lowering its permselectivity and allowing for migration of cations through it. This phenomenon resulted in low N and K recovery efficiencies (12.0 and 11.5%, respectively), whereas P was not recovered because of precipitation of salts in the concentrate chamber.

Self-Powered Bioelectrochemical Nutrient Recovery for Fertilizer Generation from Human Urine

“…Unlike other ions, phosphate appeared to be down-concentrated in the product, possibly as a reflection of its higher charge (at pH 8.8, HPO 4 2− is the prevalent species) and consequently larger hydration sphere. Precipitation of phosphate could also have occurred in the concentrate chamber, as previously described [35]. The analysis shows that heavy metals, including Cd, Cr, Cu, Pb, and Zn, are below detection limits, indicating that they are not upconcentrated from the source-separated urine.…”

Concentration Dependencies of Diffusion Permeability of Anion-Exchange Membranes in Sodium Hydrogen Carbonate, Monosodium Phosphate, and Potassium Hydrogen Tartrate Solutions

“…The development of such technologies is constrained by several challenges. The first of them is related to fouling and destruction of ion-exchange membranes during their long-term operation [11][12][13][14].…”

Urine in Bioelectrochemical Systems: An Overall Review

“…This energy demand is quite high compared with electroconcentration cells using bioanodes (8.6 MJ kg N À 1 ). [118] More recently and based on the same concept, [119] reported the use of a bio-electroconcentration cell similar to their previous work reported by Ledezma et al (2017) [20] but using an air-breathing cathode. Unlike previously, in this work, real human urine was used to feed the system.…”