A comprehensive laboratory assessment of the effects of sewer-dosed iron salts on wastewater treatment processes

The effect of iron-dosing in the sewer system, on wastewater treatment processes, was investigated using laboratory-scale wastewater systems comprising sewers, wastewater treatment reactors, sludge thickeners, and anaerobic sludge digesters. Two systems, fed with real domestic wastewater, were operated for over a year. The experimental system received ferric chloride (FeCl₃) dosing at 10 mgFe L⁻¹ in the sewer reactor whereas the control system received none. Wastewater, sludge and biogas were extensively sampled, and analysed for relevant parameters. The FeCl₃-dosed experimental system displayed a decreased sulfide concentration (by 4.3 ± 0.5 mgS L⁻¹) in sewer effluent, decreased phosphate concentration (by 4.7 ± 0.5 mgP L⁻¹) in biological treatment reactor effluent, and decreased hydrogen sulfide concentration in biogas (911.5 ± 189.9 ppm to 130.0 ± 5.9 ppm), as compared with the control system. The biological nitrogen removal performance of the treatment reactor, and biogas production in the anaerobic digester were not affected by FeCl₃-dosing. Furthermore, the dewaterability of the anaerobically digested sludge was enhanced by 17.7 ± 1.0%. These findings demonstrate that iron-dosing to sewers can achieve multiple benefits including sulfide removal in sewers, phosphorus removal during wastewater treatment, and hydrogen sulfide (H₂S) removal during biogas generation. Therefore, an integrated approach should be taken when considering iron salts usage in an urban wastewater system. © 2018 Elsevier Ltd