During storage of urine, urea is biologically decomposed to ammonia, which can be lost through volatilization and in turn causes significant unpleasant smell. In response, lactic acid fermentation of urine is a cost-effective technique to decrease nitrogen volatilization and reduce odour emissions. Fresh urine (pH = 5.2–5.3 and NH₄⁺-N = 1.2–1.3 g L⁻¹) was lacto-fermented for 36 days in closed glass jars with a lactic acid bacterial inoculum from sauerkraut juice and compared to untreated, stored urine. In the lacto-fermented urine, the pH was reduced to 3.8–4.7 and the ammonium content by 22–30%, while the pH of the untreated urine rose to 6.1 and its ammonium content increased by 32% due to urea hydrolysis. The concentration of lactic acid bacteria in lacto-fermented urine was 7.3 CFU ml⁻¹, suggesting that urine is a suitable growth medium for lactic acid bacteria. The odour of the stored urine was subjectively perceived by four people to be twice as strong as that of lacto-fermented samples. Lacto-fermented urine induced increased radish germination compared to stored urine (74–86% versus 2–31%). Adding a lactic acid bacterial inoculum to one week old urine in the storage tanks in a urine-diverting dry toilet reduced the pH from 8.9 to 7.7 after one month, while the ammonium content increased by 35%, probably due to the high initial pH of the urine. Given that the hydrolyzed stale urine has a high buffering capacity, the lactic acid bacterial inoculum should be added to the urine storage tank of a UDDT before urine starts to accumulate there to increase the efficiency of the lactic acid fermentation.

Resource oriented sanitation has emerged as a need to improve the efficacy of excreta treatment schemes, reduce the environmental pollution from their disposal and improve soil fertility. In urine diverting dry toilets, the storage alone is inefficient for faeces treatment due to poor hygienization, incomplete decomposition, as well as high losses of organic matter and nutrients. The purpose of this study was to assess the effect of stored faeces and bio-waste treated via lactic acid fermentation and supplemented by urine charged biochar on the growth and yield of corn as well as on the soil quality in a two year field experiment. Lacto-fermentation of faeces and bio-waste was performed under microaerobic conditions in earth pits covered with plastic foil, by the addition of microbial innoculum and molasses. The fertilizer was compared to an unfertilized control, a lacto-fermented mix (faeces, bio-waste, molasses and microbial innoculum) without biochar, stored faeces, cattle manure, urine and mineral fertilizer. In addition, during the second year, a vermi-composted lacto-fermented mix and biochar was applied as well. Differences of means among the treatments concerning corn growth parameters, yield and soil quality were evaluated using the Dunnet test of multiple comparisons. The lacto-fermented mix supplemented by biochar significantly improved plant height (p < 0.05 and confidence interval CI with both negative values) compared to all fertilizers during the first production year and compared to the control, stored faeces and vermicompost during the second year. This fertilizer also achieved a significantly higher corn yield compared to all other fertilizers during first and second production year, except for the lacto-fermented mix without biochar and the mineral fertilizer, which showed no significant yield difference (p > 0.05, CI with both positive and negative values). The bulk density was reduced during both years while the soil potassium content increased only during the first production year.