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199170 https://hdl.handle.net/2286/R.2.N.199170 http://rightsstatements.org/vocab/InC/1.0/ All Rights Reserved 2024 172 pages Doctoral Dissertation Academic theses Text eng Alsanea, Anwar Rittmann, Bruce Delgado, Anca Zhou, Chen Arizona State University Partial requirement for: Ph.D., Arizona State University, 2024 Field of study: Civil, Environmental and Sustainable Engineering Phosphate production, the main component of fertilizers, generates a byproduct phosphogypsum (PG; CaSO4•H2O). In this work, I present a sustainable biotechnological method to recover elemental sulfur (S0) from PG using membrane biofilm reactors (MBfRs) with the first step of sulfate reduction to soluble sulfide in the hydrogen (H2)-based MBfR and second step as soluble-sulfide oxidation to elemental sulfur (S0) in the oxygen (O2)-based MBfR. I evaluated the H2-MBfR to reduce sulfate leached from phosphogypsum water (PG water). In-depth alkalinity, precipitation, and mass balance analysis revealed that inorganic precipitation, mainly calcium sulfate, competed with sulfate reduction to soluble sulfide especially when H2 delivery was lower due to CO2 accumulation in the fibers’ lumen. The H2-MBfR is a feasible biotechnology to reduce sulfate from PG water to soluble sulfide and its long-term operation success for sulfur recovery requires calcium removal and ensuring hydrogen availability by venting CO2 when delivered through the fibers. I removed calcium from PG water via cation-exchange and re-evaluated the H2-MBfR. A high sulfate reduction flux was achieved, double the flux achieved when calcium was present but soluble sulfide concentrations remained low. Shallow metagenomic analysis of the collected biofilm sample revealed several bacteria genera competing for H2 and SO42-. A careful control of H2 is needed to minimize the growth of competing bacteria and a pH control method is needed to promote dissimilatory sulfate reduction pathway to increase soluble sulfide in the effluent. I optimized the O2-MBfR to partially oxidize sulfide into S0 using a synthetic high-sulfide wastewater. I found that the ratio of O2-delivery capacity to the O2 surface loading for partial oxidation of sulfide to S0 1.5 gO2/gO2 to simultaneously achieve high degrees sulfide oxidation and S0 recovery. To be able to control S0 recovery in the O2-MBfR, I tested a biofilm management method, hydraulic-flow reversal, in which I applied a reverse recirculation to gently shear off the retained S0. All the retained S0 was released but performance declined to 70%. Further development of the frequency of hydraulic-induced detachment is needed to determine its best application and its effects on the biofilm and S0 formation. Environmental engineering The Recovery of Elemental Sulfur from High Sulfate Phosphogypsum Water using Membrane Biofilm Reactors