Browse Publications Technical Papers 2001-01-2208
2001-07-09

Bioprocessing to Recover Crop Nutrients from Advanced Life Support (ALS) Solid Wastes: Improving Rapid Biological Processing of ALS Inedible Crop Residues 2001-01-2208

The overall objective of a NASA Research Announcement funded project at Kennedy Space Center (KSC) is to determine the optimal Advanced Life Support (ALS) solid waste bioprocessing system with the limited goal of nutrient recycling as part of a potential hybrid biological-physical chemical (PC) system. Bioprocess research towards this objective has focused on comparing two bioreactor technologies: (1) continuous stirred tank reactor (CSTR)-suspension culture and (2) continuous flow fixed-film bioreactor (FFB)-which utilizes biofilms to remove organic constituents from crop residue leachate solutions. For optimizing the CSTR we studied the effects of solids loading rate (160, 240, and 320 grams dry weight [gdw] day−1) and stirrer speed (45, 90, 180, and 360 rpm) on the vertical distribution (5 depths) of dissolved oxygen (> 90% oxygen in aeration gas) and total suspended solids in a CSTR operated at an hydraulic retention time (HRT) of 1.25 days. The only significant stratification of dissolved oxygen (DO) and solids occurred at the slowest stirring rate, 45 rpm. At all solid loading rates the vertical distribution of solids were fairly similar for the 90, 180 and 360 rpm speeds. At the 180 rpm stirrer speed and the 320 gdw day−1 loading rate the DO fell below 2 ppm, so lower stirring speeds were not tested at this loading rate. Mixing due to aeration had a significant effect on the vertical distribution of DO and solids. For the FFB, two different designs have been employed: (1) a trickling bed bioreactor – which experienced severe foaming problems, and (2) a continuous flow, suspended-bed, floating-bead biofilm attachment matrix with aeration provided by recirculation of bioreactor liquid contents through an oxygenation cone. In early engineering tests, the suspended-bed, floating bead FFB has been run at HRTs of 24, 6, and 4 hours, with ~92% removal of soluble carbohydrates and low foam, but biofouling of all surfaces has been a problem.

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