Effect of Alkali and Membrane Area on the Simultaneous Recovery of Nitrogen and Phosphorous from Digestate by Membrane Technology and Chemical Precipitation

Nutrient recovery from the agri-food sector waste is an increasingly recognized option within the framework of the bioeconomy. Membrane technologies and chemical precipitation are among the best valued options for their economic and practical feasibility. In this study, the combination of gas-permeable membrane (GPM) technology for the recovery of nitrogen (N) and the chemical precipitation for phosphorous (P) recovery from anaerobically digested swine manure is evaluated. This work studies the effect of the membrane area and the addition of alkali on N and P recovery efficiencies. Specifically, two different membrane area ratios (180 and 100 g of N per m(2) of membrane) with and without the addition of alkali were studied. High nutrient recovery efficiencies, of 77% for N and 80% for P, were obtained after 10 days of experiment with a ratio of 180 g N per m(2) of GPM and the addition of NaOH (1.5 N), along with the precipitant agent (MgCl2) for P precipitation. Hence, a combined configuration was proposed to perform an effective simultaneous recovery of N and P with the minimum amount of membrane needed in a short time.

Automated summary

Nutrient recovery from agri-food waste through membrane technologies and chemical precipitation is an economically and practically feasible option.