Impact of Iron Salt Dosage to Sewers on Downstream Anaerobic Sludge Digesters: Sulfide Control and Methane Production

The addition of iron salts to sewers for sulfide control has a significant impact on downstream wastewater-treatment performance, in which iron ions can be resolubilized from iron sulfide precipitates in aeration tanks to precipitate phosphate, thus enhancing phosphorus removal from the wastewater. In this study, the impact of iron salt dosage to sewers on the performance of anaerobic sludge digesters was investigated at bench scale. Anaerobic digesters were fed with mixed primary sludge, activated sludge, and sludge that contained ferric phosphate precipitates, formed by aerating iron sulfide- and phosphate-containing wastewater with activated sludge. In anaerobic conditions, ferric ions were released from ferric phosphate precipitates and utilized for a third time to precipitate sulfide that formed during sludge digestion, which ultimately resulted in complete control of H2S emissions from digesters. The results indicate that iron salt addition to sewers at typical dosing rates (e.g., 5-20 mg Fe L-1) would provide an excessive quantity of iron salts for sulfide control in sludge digesters. Methane production and other digestion processes were not negatively impacted by iron addition to the wastewater. DOI: 10.1061/(ASCE)EE.1943-7870.0000650. (C) 2013 American Society of Civil Engineers.