Post-Treatment of Anaerobically Digested Solid Waste in Long Term Space Missions

Post-treatment of anaerobically digested residue produced during long term space missions was investigated. Solid waste was anaerobically digested by employing the SEBAC system. One of the goals of post-treatment step is to convert ammonia in the residue to nitrates via biological nitrification processes. It was found that anaerobically digested residue contained nitrifying microorganisms which could be activated by aeration. Without supplying any external nitrifying inoculum, nitrification was initiated within 2 days by continuously blowing air at 15 ml/min. The maximum rate was 0.78 mg /g dry weight /day. However, denitrification process occurred soon after nitrification and ∼ 50% of nitrate was denitrified. A modified system in which aeration was carried out by holding air within the reactor at a pressure of ∼ 10 psi yielded a higher initial specific nitrification rate of 1.7 mg/g dry weight/day. Moreover, nitrification was initiated within a day. Incorporation of an aerobic curing stage in space would increase ESM for a SEBAC system from 1671 kg to 1818 kg, including oxygen consumption and the crew time for this aerobic operation.