Integrated Decentralized Treatment for Improved N and K Recovery from Urine

Abstract

Urine has been recognized as the main contributor of nitrogen (N), phosphorus (P), and potassium (K) at wastewater treatment plants, yet it makes up less than 1% of the volume. This study aimed to assess a novel decentralized approach of recovering N, P, and K from urine as separate fertilizer products. Previous work by the authors showed integrating struvite precipitation for P recovery, ammonia stripping–acid absorption for N recovery, and evaporation for K recovery was effective at recovering >80% N, P, and K from urine. However, improvements to the N and K treatment processes were still needed to produce urine-derived fertilizer products of similar nutrient composition and concentration as commercial fertilizers on the market. Two technologies, ammonia stripping–acid absorption and ion exchange, were evaluated for N removal and recovery as ammonium sulfate. Both treatments removed 70% of N but implementing ammonia stripping–acid absorption resulted in a higher concentration N product. Distillation was evaluated for K recovery as potash and nonpotable water recovery. The process was able to recover approximately 100% of K and over 50% of water in urine. Distillation of effluent from the ammonium stripping process resulted in a higher concentration of K in the potash product compared to effluent from the ion exchange process.