Recovery of N and P from human urine by freezing, struvite precipitation and adsorption to zeolite and active carbon

The majority of the nutrients in domestic waste originate from human urine. This study deals with methods for recovery of N and P from urine. Results from a freezing-thawing method (FTM) together with struvite recovery and nitrogen adsorption on zeolite and active carbon (AC) are presented. Various amounts of MgO, zeolite and AC were added to samples of 100 ml urine. After 3 days the supernatants were analysed for pH, total-N, total-P and acute toxicity for Daphnia magna. One set of samples was frozen and then thawed and the supernatants collected were tested as before. The FTM method concentrated 60% of the nutrients in 40% of the initial volume and significantly improved the N reduction and D. magna survival. The P recovery was 95–100%, mainly as struvite. No significant effect of AC was found. Zeolite improved the P recovery and in some combinations of MgO also the N recovery.