Three-segmented counterflow pilot-scale electrodialysis for ammonia and potassium treatment in liquid anaerobic digestate: A trade-off among advanced ion removal, nutrients concentration limitation, and energy consumption
Han Xiao, Fanghui Pan, Fei Huang, Zhu HongGuang, Qi Wu
Abstract
In this paper, a three-segmented counterflow (COUN) electrodialysis (ED) for ammonia ( NH 4 + -N) and potassium (K + ) treatment in liquid anaerobic digestate (LAD) was proposed to break the high-concentration limit of nutrient recovery without sacrificing the ion removal performance and energy efficiency. The effects of the COUN operation mode on ED performance were studied based on pilot-scale experiments. The results indicate that the COUN mode improves the distribution of concentration difference (Δ c ). Hence, the ion fluxes of NH 4 + -N and K + have increased by 51.0% and 25.3%, respectively. A highly concentrated product ( NH 4 + -N at 10428 ± 225 mg/L and K + at 7500 ± 156 mg/L) can be obtained, and the concentration multiples of NH 4 + -N and K + have increased by 14.1% and 9.8%, respectively, with slight effects on their removal rates. The current efficiency for NH 4 + -N and K + was increased by 38.1% and 14.5%, reaching 54.7 ± 3.5% and 12.4 ± 0.5%, respectively, and the final energy consumption of 3.8 ± 0.2 kWh/kg-N) has reduced by 31.8%. The non-ideal transport mechanisms associated with the Δ c (back-diffusion and water osmosis) have been taken into consideration. The COUN mode is a new exploration of the ED operating patterns to alleviate the detrimental effect of high Δ c . It will provide a reference for designing and operating large-scale engineering projects for nutrient recovery by ED process and a trade-off among advanced ion removal, high-concentration limitation, and energy consumption.