Saline wastewater treatment with purple phototrophic bacteria

Biological removal of organics, nitrogen and from saline wastewaters is adversely impacted by high salinity, which can be a major concern for treatment of industrial or domestic saline wastewater. In anaerobic treatment systems, sulfidogensis, especially when treating sulfate-rich saline wastewaters (e.g. seawater has 930 mgSO₄-S L⁻¹, or 2800 mg L⁻¹ as SO₄²⁻) can cause additional biological, operational, and safety issues, due to H₂S toxicity. Here, the use of anaerobic purple phototrophic bacteria (PPB) is tested as mediator to treat high salinity domestic wastewater (NaCl), and marine wastewater (Red Sea Salt – high sulfate, potassium, etc.) in a continuous anaerobic infra-red photo bioreactor, operated over 372d. Saline adapted PPB simultaneously removed COD, nitrogen and phosphorus with biomass yields of 0.8 gCOD gCOD⁻¹. Batch activity tests found a broad optimum peak for saline adapted PPB between 30 and 70 mS cm⁻¹, and 50% reduced activity at 140 mS cm⁻¹ (3.5x seawater). For marine wastewater, high sulfate influent concentrations (770 mgSO₄-S L⁻¹) did not result in substantial H₂S production (<1.6 mgS L⁻¹) over 80 d. When irradiation was removed, sulfide rapidly rose to >90 mgS L⁻¹ and the process failed. The results indicate rapid adaptation to high-salt conditions (both NaCl and marine), and the capacity for PPB to form a combined wastewater treatment/resource recovery process, particularly for salty industrial wastewater.