Ammonia recovery using a gas-permeable membrane under different operational conditions

Abstract

Ammonia recovery from wastewaters is one of the best forms of ensuring the natural cycle of nitrogen, because it’s low consume of energy compared to other technologies for ammonia production. In the last decades, membrane technology has emerged because is an effective way recovering nitrogen from urban wastewaters, piggery slurry or organic fraction of municipal solid waste. These effluents are rich on ammonia nitrogen, with a high content in range of 0.5 to 5 g N-NH4+/L. This specie is chemical compound that can be dangerous for human healthiness and environmental risks, such as eutrophication. In this work, a laboratory scale study is conducted using a gas-permeable membrane, which is a membrane that allows gas species pass through it, but not aqueous compounds. Two different operational configurations were tested, applying vacuum inside the membrane and acidic trapping solution in closed loop circulation. When vacuum application was performed in gas-permeable membrane, it did not result in a good efficiency, obtaining about 10% of ammonia removal in about 5 hours. However, the use of an acidic trapping solution achieved a TAN recovery >99% in 14 hours of experiment, and a mass transfer constant (Km) of (1.7±0.1) ·10-7 [m/s]. This method was tested too in piggery wastewater, on a working pH of 9, resulting in a TAN recovery of >99% in 16 hours of experiment, and a Km of (8.8±0.5) ·10-7 [m/s]. This research also studied the water passage through the GPM when the trapping solution achieved high ammonia concentrations, diluting the ammonium sulphate, which is not desirable for economic reasons. Tests in laboratory showed that the water passage is proportional to the N concentration in the trapping solution. To sum up, the gas-permeable membrane technology has been proved to be highly efficient to ammonia removal and recovery from pig wastewater due its efficiency and low operational cost