Bioprocessing to Recover Crop Nutrients from ALS Solid Wastes: A Two-Stage Solid-Liquid Separation System for Removal of Particulates from Bioreactor ‘Broth’ 2001-01-2205

The effluent, or ‘broth’ output of bioreactors fed Advanced Life Support (ALS) solid wastes contains suspended particulate material composed of undigested waste residues and microbial cells. ALS crop scientists have required the removal of particulates from these solutions before they can be used to recycle soluble crop nutrients, also contained in the effluents, to hydroponic crop growing systems. A two-stage filtration system was designed and evaluated with different membrane filtration elements. The first stage, prefiltration, was designed to remove large particles (μm to mm range). The key study factors for prefiltration were: (1) filter bag pore size – 50 vs. 5 vs. 0.5 μm- and (2) rinse solution - none, de-ionized water, and simulated graywater). Between 22 to 30% of the liquid was retained by the pre-filters and retained solids, indicating the necessity of introducing a rinsing step to better recover soluble crop nutrients. Between 66 and 70% of total solids (TS) were removed by the pre-filter. Filtrates contained very small particulates. Filter bag pore size had no effect on recovery of major crop nutrients, e.g. K, Ca, Mg. Rinsing of the filter and retained solids resulted in a significant increase in mineral recovery including K: 24 – 32%, Ca: 33 – 48%, and Mg: 24 – 40%. The key study factors for membrane filtration were: (1) filter type (pore size) – microfiltration (0.2 μm) vs. ultrafiltration (500,000 nominal molecular weight cutoff) and (2) flow-rates – 150 vs. 450 mL min⁻¹. Membrane filter type and flow rate had no influence on recovery of permeate, 93–96%, and little effect on recovery of crop nutrients, 95 – 103% for K, Ca, and Mg-no trends). Filtration time for the microfilter at the 450 mL min⁻¹ flow rate was the best (i.e., shortest) measured, 12 hrs to reach a pressure cutoff of 10 psi.