Study of the nitrogen recovery from an internal stream of a municipal wastewater treatment plant using selective membranes

Abstract

This study is focused on the nitrogen removal and recovery from nitrogen rich wastewater streams using selective membranes. With this technology, nitrogen is removed from wastewater by means of the transfer of matter through the membrane and is subsequently recovered with an acid solution, in this case, sulfuric acid, since ammonium sulfate has fertilizing properties. A bibliographic research of the scientific literature has been made where the viability of this system has been evaluated and subsequently a proposal of a system to be implemented in a wastewater treatment plant has been presented. From the bibliographic research it can be concluded that the most used selective membranes are tubular permeable gas membranes made of e-PTFE. Removal and recovery percentages between 63% and 95% are reported. It is observed that optimum pH and temperature conditions are required to obtain higher yields. Both need to be increased, in case of pH increased to 10, and temperature increased to 30ºC. Subsequently, the nitrogen mass balances of a municipal wastewater treatment plant have been studied, and it has been identified the recirculation water after anaerobic digestion as the stream where the membrane recovery treatment could be easily implemented . A system with a tubular permeable gas membrane has been proposed with an expected 90% removal percentage, of which 95% recovery in the form of ammonia sulfate could be achieved. To obtain these yields, it would be necessary to increase the pH up to 10. By means of this nitrogen treatment, it has been possible to improve its function in the wastewater treatment plant, where the percentage of nitrogen released in the form of atmospheric nitrogen has been reduced from 58% to 52%, as well as the CO2 emissions, the energy demand and the sludge production associated to this savings