pH Effects on Factors Influencing Nutrient Removal and Recovery from Synthetic Animal Waste Via Chemical and Electrochemical Techniques

It has been estimated that there may be as much as 2 billion tons of animal wastes produced in the United States annually. Application of excreta to soil brings benefits such as improved soil tilth, increased water-holding capacity, and some plant nutrients. Concentrated forms of excreta increase the eutrophication problems which has caused a lot of harm to the aquatic life and to water supply for industrial and domestic uses [1]. This eutrophication is due to the presence of phosphorus (P) and nitrogen (N), which are essential nutrients for plant cultivation and the human diet. Therefore, it is desirable that P and N are decreased from these waste streams before discharged to soil and the environment.

In a prior study, the efficacy of electrochemical method was examined with key operating parameters affecting struvite deposition identified as temperature, turbulence, applied potential and competing ion (Ca²⁺) concentration [2]. In addition, a thermodynamic simulation was developed to further investigate the impact of Ca²⁺ in animal waste on the technology’s performance [3]. High phosphorus recovery (83%) and low specific energy consumption (0.43kWh/kg P recovered) were discovered at optimum conditions in these previous studies. However, the effect of multi-factors interactions on electrochemical nutrients reduction is unknown. In this new study, the efficiency of nutrient (P and N) removal and struvite quality from animal waste will be assessed based on multivariate analyses including flow conditions, temperature, Mg²⁺:Ca²⁺ ratio, N:P ratio and the cathodic potential. In addition, the effect of initial solution pH will be evaluated to delineate the difference between chemical and electrochemical driving forces. Initial results from this study indicates that under certain process conditions, a high initial pH results in significant solid dissolution under electrochemical control and decreases the overall nutrient recovery. This suggests chemical driving forces are more significant than electrochemical driving forces for nutrient recovery under certain conditions. These results along with solid characterization analyses and solution speciation will be discussed at the conference.

References

[1] Animal waste “ Environmental Encylopedia” https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/animal-waste

[2] Z. Belarbi and J. P. Trembly, “Electrochemical Processing to Capture Phosphorus from Simulated Concentrated Animal Feeding Operations Waste,” J. Electrochem. Soc., vol. 165, no. 13, pp. E685–E693, Jan. 2018, doi: 10.1149/2.0891813jes.

[3] Z. Belarbi, D. A. Daramola and J. P. Trembly, “Bench-Scale Demonstration and Thermodynamic Simulations of Electrochemical Nutrient Reduction in Wastewater via Recovery as Struvite,” J. Electrochem. Soc., vol. 167, no. 4, Nov. 2020, doi: 10.1149/1945-7111/abc58f.