(439i) Electrochemical K-Struvite Precipitation: Investigating the Role of pH and Water Chemistry

A resilient food production system heavily relies on macronutrients such as phosphorus (P), nitrogen (N), and potassium (K) as essential fertilizers. Animal wastewaters contain significant amounts of NPK as they pass through the feed of farm animals into their manure. Simultaneous water treatment and recovery of these nutrients in the form of valuable materials are attracting growing interest in the water treatment arena. While electrochemical phosphate recovery processes are mainly focused on coprecipitation of phosphorus with nitrogen (as struvite) or calcium (as calcium phosphate), few studies investigated potassium recovery opportunities as an alternative by-product.

Here, we focused on understanding the possibility of producing another type of fertilizer in potassium magnesium phosphate (KMgPO4·xH2O, K-struvite) by investigating the role of important parameters such as pH and competing ions within an electrochemical reactor. A single-cell batch electrochemical system with sacrificial magnesium anode and stainless steel cathode was used to perform the bench-scale experiments. pH was varied with potassium and phosphate concentrations held constant in synthetic water that contained other background salts. Other key parameters, such as magnesium electrode voltage, were constant for all experiments. Scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) were used to characterize the morphology and purity of the recovered precipitates. Further investigation using x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) was performed to understand the precipitates' nature better. This talk includes a discussion of electrochemistry, water analyses, and precipitate characterization results.