Study of a gas-permeable membrane contactor for ammonia recovery from manure

Abstract

Ammoniacal nitrogen present in livestock manure represents a valuable resource that can be recovered to generate fertilizers by using gas-permeable hydrophobic membranes, which have gained increasing interest for their efficiency and low cost. In this study, the use of an ammonia-permeable hollow fibre membrane (active surface area of 0.50 m2) to recover the nitrogen present in a synthetic solution and filtered manure was analysed. Its principle of operation is based on the ammonia (NH3) mass transfer from the feed to an acid extract solution or trapping solution (in this study, using diluted H2SO4 75%) due to the difference in concentrations of ammonia, enhanced by the control of pH. For experiments with 2L of synthetic feed at pH values above 9, more than 98% of ammonia (1.8 g N/L) was recovered in 8 hours at 25°C (equal volumes of feed and trapping solution). The manure experiments were performed after pre-treating the manure by centrifugating and filtrating it in order to determine the nitrogen recovery under different conditions. The pH set for the manure experiments was determined from the synthetic feed experiments where duplicates were executed testing a pH range value for the feed from 6 to 12. Volume ratios of 1:1 and 1:10 were analysed and recoveries of more than 99% were obtained with a trapping volume 10 times lower than the feed solution (pre-treated manure) under the conditions mentioned above. From the current project, the use of a lab-scale hollow-fiber ammonia gas permeable membrane contactor has been proved to be highly efficient to recover ammonia from a high loaded nitrogen wastewater such as pre-treated manure.