The objective of this work was to determine how some wastewater acids could be used to prevent the decomposition of urea into ammonia during storage. The effect of storing human urine with olive oil mill wastewaters (OOMW) or water bubbled with CO2 (BW), was studied. Moreover, the application of two levels of urine dissolved in water OOMW, has been studied in relation to the properties of two soils (loam and silty-clay loam). Our data provide evidence that human urine dissolved in OOMW significantly reduced the release of ammonium-N. Moreover, OOMW and CO2 significantly lowered the pH. A dosage higher 10% OOMW dissolved in fresh urine in volume could inhibit the hydrolysis of the urea for more than 6 months. Moreover, urine-N dissolved in OOMW significantly reduced the emission of nitrates from soils for 3 months, increasing K and P values. The application of urine with BW raised the soil pH and lowered the EC, but had no effect on nutrient contents. Thus, urine dissolved in OOMW and applied to soils could act as NPK-fertilizer. However, the impact of fertilization with human urine–OOMW–CO2 requires further investigation with respect to crop production and pollution.
Keywords: carbon dioxide, nitrogen conservation, olive oil wastes, organic wastes recycling, urine