Open access publications in the SLU publication database

Abstract

Safe reuse of plant nutrients from human excreta increases the sustainability of society and promotes health, both by decreasing disease transmission and by increasing agricultural production. This thesis examined ammonia sanitisation as a treatment method to produce a hygienically safe fertiliser from source-separated urine and faeces. Salmonella spp. and E. coli O157:H7 were inactivated to a high degree even at low NH3 concentrations and temperatures. It was possible to model Salmonella spp. inactivation using these two parameters. Salmonella spp. inactivation is suggested to be verified by determining inactivation of faecal coliforms. Between NH3 concentrations 20 and 60 mM, a sharp decrease in inactivation was observed at 24 ºC or below for Enterococcus spp., bacteriophages and Ascaris eggs, with insignificant inactivation of the latter during 6 months. Urine contains sufficiently high total ammonia concentration and pH for selfsanitisation. Keeping the urine as concentrated as possible proved critical in achieving NH3 concentrations that inactivated Ascaris eggs. Sun exposure increased urine temperature and NH3 and shortened treatment time, and is feasible when urine containers are small. Urea treatment of faeces increased pH and total ammonia concentrations, both contributing to formation of NH3. The final value and stability of the pH achieved depended on initial pH and other material properties, but increased with increasing urea addition. At high pH caused by ash addition, urea was not degraded. When urea was added alone, it could not be confirmed that it was fully degraded. Organism inactivation was always faster in urea-treated faeces compared with untreated faeces. Urea treatment substantially shortened treatment time compared with storage, especially at the higher temperatures studied (24 and 34 ºC). Sanitation systems that collect urine and faeces separate and sanitise them by ammonia permit a high degree of hygienically safe plant nutrient reuse.