Nutrient recovery from human urine by struvite crystallization with ammonia adsorption on zeolite and wollastonite

Urine-separation toilets are a possible route for achieving maximum recover y and recycling of urine nutrients not contaminated by hazardous compounds such as heavy metals. However, the direct use of human urine as agricultura l fertiliser is problematic and controversial with regard to hygiene, stora ge, transport and spreading. In this paper, simple methods for capturing th e nutrients in urine by transformation into solid mineral form are presente d. On the addition of small amounts of MgO to synthetic or natural human ur ine most of the phosphorous and significant amounts of the potassium and ni trogen were precipitated, with crystalline struvite [Mg(K,NH4)(PO4) . 6H(2) O] as a major component together with montgomeryite, newberyite, brucite an d epsonite. Nitrogen recovery could be improved by adsorption. Clinoptiloli te, wollastonite and a natural zeolite all showed excellent adsorbent prope rties in contact with ammoniacal solutions. In combination with struvite cr ystallisation 65-80% of the nitrogen was recovered as crystalline or adsorb ed ammonium. (C) 2000 Elsevier Science Ltd. All rights reserved.