Fate of micronutrients and heavy metals in digestate processing using vibrating reversed osmosis as resource recovery technology

Abstract

This study aims to evaluate the full-scale performance of vibrating membrane filtration (VSEP) technology in resource recovery from the liquid fraction of digestates, while reducing macronutrient concentrations down to dischargeable water. Although increasing attention is paid to mass flow assessment of macronutrients, to date little is known about the fate of micronutrients and heavy metals upon digestate processing. In this research, process streams were characterized and mass balances for micronutrients and heavy metals were performed throughout a complete digestate processing train. The VSEP system operated with reversed osmosis membranes and followed by a lagoon was capable of producing dischargeable water according to Flemish regulatory standards. Concentrates produced by one VSEP filtration of the liquid fraction of digestate and dried thick fractions resulting from solid-liquid separation were rich in macro- and micronutrients, while heavy metal concentrations did not exceed regulatory standards. Hence, these products showed high potential for reuse in agriculture.