Removal of Urea and Ammonia from Wastewater

Abstract

Compounds like urea and ammonia form one of the major constituents of wastewater. Urea is a principal outcome of protein degradation in mammals and is abundant in sewage wastewater. Urea is also widely used as fertilizer in agriculture. The production of 1300 tons of urea per day results in a wastewater output of 650 tons per day. The discharged wastewater comprises 0.5–2 wt% urea, which contributes to water pollution and algal growth, leading to eutrophication. Ammonia is produced by the hydrolysis of urea, which is very hazardous and toxic to aquatic organisms. Ammonia and urea leach from breeding farms, agricultural runoffs, and many other industrial processes. These can be treated and recovered from wastewater for fertilizer and energy production, reducing the risk of water pollution. There are various technologies for the removal of urea and ammonia, some of which are widely used while others are relatively new. Physicochemical, electrochemical, as well as non-electrochemical methods can be utilized to remove urea and ammonia. Electrochemical and non-electrochemical methods can remove urea. Non-electrochemical treatment methods for urea removal are hydrolysis, enzymatic decomposition, biological degradation, decomposition by strong oxidizing agents, and degradation by catalysts. Electro-oxidation and bio-electro-oxidation are electrochemical methods to remove urea. Urea in urine can be utilized to produce energy through direct urine fuel cells and microbial fuel cells. There are various physicochemical methods for the removal of ammonia. Some of the methods, like air stripping, struvite precipitation, and ion exchange, are very common. Microwave radiation and ozone microbubbles are relatively new and costly. Membrane-based processes like reverse osmosis are gaining interest. The chapter focuses on various wastewater treatment methods for urea and ammonia removal. The chapter also aims to describe methods of using urea-containing urine waste streams for their potential application in space to produce energy.