Alternating pulse approach for electrochemical production of struvite as an option for phosphorous recovery from wastewater

Abstract

Water pollution is a concern, as sewage water contains phosphates that come from different sources, generating eutrophication in bodies of water. There is also an overexploitation of phosphorous, which has a huge relevance due to its use in agriculture. Traditionally, different physical or chemical treatments have been used to remove pollutants from water, some of which use a sustainable management approach focusing on nutrient recovery, rethinking wastewater treatment as resource recovery. Recent developments have used chemical precipitation as an alternative, by adding different metals to yield a slow-release fertilizer. There is considerable literature on struvite production with magnesium added or obtained by electrochemical methods; the latest methods offer the advantage of providing the magnesium from a sacrificial magnesium electrode in a system with low energy consumption, avoiding the addition of chemicals. Although this may be a good alternative, passivation occurs in the anode, causing loss of efficiency in the system. Considering all these factors, this paper examines the influence of different variables such as the concentration of nutrients, distance between electrodes, current density, and frequency of electrical pulses in the efficiency of the system to remove P-PO₄³⁻ and N-NH⁴⁺ for the production of struvite. On the whole, the results show that the current influences the promotion of Mg²⁺ release and prevents its excess at 53 mA, and that the optimal frequency of 0.0005 Hz is important to avoid passivation and increase the removal of nutrients from water.