Apparent diffusion coefficients in sewer force main biofilms treated with iron salts

Abatement of sulfides in sewer force mains using salts of ferrous or ferric iron is a commonly applied practice. Addition of iron salts has been focused on primarily from a precipitation point of view, with a focus on efficiency. Possible influences on the biofilm matrix due to accumulation of ferrous sulfide have not been investigated for biofilms grown under conditions experienced within sewer force mains. Diffusion through biofilms under different flow regimes was measured in situ in force mains conveying fresh municipal wastewater. One force main served as an untreated control whereas the two other force mains were treated with ferrous or ferric iron, respectively. A biofilm model was constructed and fitted to experimental data to derive the apparent diffusion coefficients. It was found that addition of ferrous and ferric iron decreased the apparent diffusion coefficient of the biofilms, compared to an untreated control, with ferric iron exhibiting the most pronounced decrease.