Utilization of liquid human wastes and introduction into the material cycling in biological life-support systems

The possibilities of step-by-step utilization of liquid human wastes in biological life-support systems on long-functioning space stations have been considered in this work. Utilization involves "wet" urine incineration with hydrogen peroxide at normal pressure and 90 - 95°C temperature, urease-enzymic decomposition of urine and biological desalination in the higher plant link. The soybean flour was used as a source of urease. Growing soya plants as a component of the higher plant link would give a steady source of urease to the system. To decompose urea (9-15g) contained in 1l of incinerated urine we used 0.5 - 1 g of soy flour. The duration of hydrolysis of daily urea excreted by a human is 70 - 95 hours. It is supposed that ammonia excreted in the reaction of urea decomposition will be processed by nitrifying bacteria. The concentration of total nitrogen in urine after urea hydrolysis and removal of ammonia formed during the reaction constituted 0.6 - 1.2 g/l. Further biological desalination was carried out in the higher plant link, for that the edible salt-accumulating halophytes Salicornia europaea were used. To grow this plant under the aqueous culture conditions, the urine was additionally mineralized at 180 °C after incineration and decomposition of urea. The process of additional mineralization was related to the necessity of removal of organic materials and nitrogen residues, which higher concentration under the aqueous culture conditions has negative effect on plants. The volume of the nutrient solution for growing 6 plants of Salicornia europaea was 1.5 l (daily norm of urine excreted by human), the planting area was 0.032 m2. By the end of vegetation the productivity and mineral composition of Salicornia europaea plants were analyzed. The productivity of plants grown on liquid human wastes (the experiment) practically was not different from the productivity of plants grown on the mineral solution with sodium chloride (checkout). In experimental plants the content of potassium increased on 30% and the sodium content decreased on 30% as compared to the check plants. As a result the NaCl content constituted 23% of dry plant mass. The variant making the additional mineralization of urine at 180 °C avoidable has been considered in this work as well. For this purpose the technology of substrate growing of Salicornia europaea plants and intermittent introduction of urine during vegetation after "wet" incineration and urease-enzymatic decomposition of urea has been introduced.