Ammonia Recovery from Digestate Using Gas-Permeable Membranes: A Pilot-Scale Study

Abstract

The reduction and recovery of nitrogen (N) from anaerobically digested manure (digestate) is desirable to mitigate N-related emissions, mainly ammonia and nitrate, derived from digestate land application in nutrient-saturated zones. This work reports the results of a gas-permeable membrane (GPM) pilot-scale plant to recover ammonia from digestate in the framework of the EU project Ammonia Trapping. The total ammonia nitrogen (TAN) concentration in digestate was reduced by 34.2% on average (range 9.4–57.4%). The recovery of TAN in the trapping solution in the form of a (NH4)2SO4 solution averaged 55.3% of the removed TAN, with a TAN recovery rate of 16.2 g N m−2 d−1 (range between 14.5 and 21.0 g N m−2 d−1). The TAN concentration in the trapping solution achieved a value of up to 35,000 mg N L−1. The frequent change of the trapping solution has been proven as an efficient strategy to improve the overall performance of the GPM technology.

Keywords

• anaerobic digestion
• digestate
• gas-permeable membranes
• ammonia recovery