Free Fe3+/Fe2+ improved the biomass resource recovery and organic matter removal in Rhodobacter sphaeroides purification of sewage

The enhancement in biomass production and organic matter removal of Rhodobacter sphaeroides (R. sphaeroides) through iron ions in soybean protein wastewater treatment was investigated. Different dosages of ferric ions were introduced in the reactors under light-anaerobic conditions. Free ferric and ferrous ions in wastewater were formed and their concentrations were the optimal for the growth of R. sphaeroides when the total Fe dosage was 20mg/L. At the optimal dosage, biomass production (4000mg/L) and protease activity improved by 50% and 48% when compared to the controls, respectively. The organic matter and protein removal reached above 90% and hydraulic retention time was shortened from 96 to 72h. A mechanism analysis indicated that iron ions can effectively improve the adenosine triphosphate production, which may furthermore encourage the synthesis of protease and the cellular material.