| dc.description.abstract | Sustainable food production requires replenishment of plant nutrients from agricultural soils. One way to achieve this, is to return plant nutrients from the food produced and consumed. Urine by far comprises of the largest proportion of plant nutrients (nitrogen (N), phosphate (P), and potassium (K) in household waste. To reduce bulkiness and therefore, transport concentrated nutrient content, easier to apply and improve food production, the water content in the urine should be decreased. To achieve this without compromising the nutrient content, requires stabilization followed by drying. In this work, urine was stabilized by alkalization and thereafter, dried to evaporate out the water. Solar combined with passive drying and ventilation were utilized to dry the urine.
In this research, the urine was stabilized during collection in urinals by using wood ash and lime (alkalization). Wood ash and white hydrated lime (calcium hydroxide) at doses of 100 g/L and 15 g/L, respectively, were used to stabilize freshly collected urine during collection in 20 L jerry can containers to achieve a pH greater than 11 after shaking. The human urine treated by wood ash and lime was dried in a laboratory-scale solar dryer (concentrator). The temperature, humidity, solar irradiation, weather conditions (sunny and cloudy), and air velocity were monitored. With temperatures inside the solar concentrator were typically higher than those outside the dryer and the opposite being true for humidity, a rapid increase in drying rate was found to occur between 2 and 4 pm, peaking at the latter time. In studying the thermodynamics of the drying of ash-stabilized and lime-stabilized urine, a thermos-gravimetric analyzer was used. Ten different mathematical drying models were compared based on their correlation coefficient, root mean square error, and reduced chi-square to estimate the drying curve. Drying models were fitted to experimental data by means of statistical parameters in the models for the drying air temperature of 50 °C at an airflow rate of 1.0 ms−1. During empirical modelling for the thermo-gravimetric drying of ash-stabilized and lime-stabilized urine samples, the two-term model best predicted the drying for ash stabilized urine while the page model best predicted the drying for lime stabilized urine. The Nitrogen recovery with wood ash substrate about 19 ± 1 % is higher the N recovery using lime which is about 1± 0.5% on average. For the Phosphorus recovery, the recovery using lime substrate about 71 ±0.5 % being higher the that for wood ash of on average 12 ± 3% and also the Potassium recovery of on average 45 ± 3% using lime being higher than 25 ± 4% while using wood ash | en_US |
