Assessing the potential of purple phototrophic microbial community for nitrogen recycling from ammonia-rich medium and anaerobic digestate.

Purple phototrophic bacteria (PPB) community, enriched from municipal wastewater, was characterized to assess their growth, tolerance, composition and potential for resource recovery from NH4+-rich medium. Batch experiments were conducted in tissue culture flasks and glass bottles under anaerobic conditions with infra-red lights. PPBs showed remarkable tolerance to high concentrations of NH4+-N and acetate. Below 1.5 g/L, growth was unaffected by NH4+-N with optical density at 590 nm (OD590) reaching 2.6-2.9, while they could tolerate 4.5 g/L NH4+-N. Similarly, PPB growth was unaffected at acetate concentrations below 4 g/L and they could tolerate >20 g/L acetate. Taxonomic characterization showed that the community comprised of 37-52% PPBs (with 15-20% proteins) under different conditions, with Rhodobacter sp. over Rhodopseudomonas sp. dominating at higher NH4+-N concentrations. PPBs showed growth and removal rates in anaerobic digestate and accumulated 26% proteins. These results indicated the potential of PPBs in resource recovery from NH4+-rich wastewater.