Insights into liquid digestate treatment through batch electrocoagulation-flocculation system

Abstract

This study aims to evaluate the performance of the electrocoagulation-flocculation (ECF) process for treating liquid digestate generated via anaerobic digestion (AD). For this purpose, ECF in batch system was studied as a treatment for turbidity reduction and total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) decrease by using as process factors electrode distance and applied voltage onto the electrodes, as well as the ECF time. The Response Surface Method approach through a 23 full-factorial experimental design showed a non-linear influence of the factors on the dependent variables considered in this study. The maximum turbidity reduction (about 92%) was obtained at an ECF time of 90 min, 12V applied voltage and 2 cm electrode distance (reduction of 35.5% TN, 50.7% TP, 67.8% TOC). For lower energy consumption, for example at 9V, 3 cm between electrodes and 60 min reaction time, turbidity reduction and TP significantly decreased to 57% and 38.1% respectively, while the reduction rates for the other monitored parameters, 31.9% TN and 65.2% TOC, were only slightly lower than those obtained in the more energy demanding ECF process which yielded the highest turbidity reduction. When considering the application of ECF at a larger scale, a more promising option would be lower applied voltage and shorter reaction times, combined with other contaminant removal technologies, such as microalgae cultivation for nutrient reclamation.