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.

Evaluation of Different Capture Solutions for Ammonia Recovery in Suspended Gas Permeable Membrane Systems

“…Comparing the values obtained with those reported in the literature, the NH 3 capture efficiencies for sulfuric, phosphoric, and nitric acid obtained in this study were similar to those attained by other authors [40,45], and the differences may be attributed to the fact that the capture system was not the same. Riaño et al [50], using a submerged GPM system with a sulfuric acid capture solution, reported capture efficiencies of up to 79.7%; Zhang et al [45], using a CapAmm system, obtained NH 3 capture efficiencies of 75% for phosphoric acid and 73% for sulfuric acid; and Reig et al [40], using hollow fiber liquid-liquid membrane contactors (HF-LLMC) combined with ion exchange, attained NH 3 capture efficiencies of 74% and 85% with nitric and phosphoric acid, respectively.…”

Fertiliser Effect of Ammonia Recovered from Anaerobically Digested Orange Peel Using Gas-Permeable Membranes

“…Digestate samples from the vessels and acidic solution samples from the acid tank were collected daily to monitor pH and total ammonia nitrogen (TAN). In addition, initial and final samples from the digestate were taken to determine total solid (TS), volatile solid Experimental set-up of the gas-permeable membrane system, consisting of 1 a wastewater vessel, 2 a tubular membrane submerged in the wastewater, 3 a tank containing the acidic trapping solution, 4 a peristaltic pump that continuously recirculated the acidic solution through the tubular membrane, 5 an air pump to supply air to wastewater, and 6 an airflow meter to control the supplied airflow rate.…”

“…For that, air stripping can present high requirements of energy and chemicals compared with the GPM technology. This technology has been successfully proved to recover NH 3 from digestate at pilot scale [3]. Now, the Life Green Ammonia aims at scaling results to the livestock sector market by means of commercial models.…”

“…In this sense, the recovery of N from wastewater could partially offset the demand for nitrogen-based fertilisers [2]. The effluents produced after anaerobic digestion of agro-industrial waste (digestate) are an important source of N. At the same time, decreasing the N content from anaerobic digestate can reduce the environmental risks associated with its use as fertiliser in nitrate-vulnerable zones [3]. The current technologies for N recovery include precipitation by struvite, ultrafiltration/ion exchange, ultrafiltration/reverse osmosis, or acid absorption following separation by gas stripping or gas-permeable membrane (GPM) technology [2,4].…”

“…Figure 1.Experimental set-up of the gas-permeable membrane system, consisting of 1 a wastewater vessel, 2 a tubular membrane submerged in the wastewater,3 a tank containing the acidic trapping solution,4 a peristaltic pump that continuously recirculated the acidic solution through the tubular membrane,5 an air pump to supply air to wastewater, and6 an airflow meter to control the supplied airflow rate.…”