Enhanced synergistic denitrification and chemical precipitation in a modified BAF process by using Fe2+

A modified BAF system configuring synergistic denitrification and chemical phosphorus precipitation: Examination on pollutants removal and clogging development

“…In phases I to III, the average NO x À -N removal efficiencies in the pre-denitrification tank with the following sedimentation tank were 62.75%, 89.54%, and 93.31%, respectively. These results corresponded well with the authors' previous finding that denitrification rate was accelerated when dosing Fe 2+ (Wang et al, 2014). A predominantly microbial Fe 2+ -dependent nitrate reduction process with high rate is believed to be responsible for such enhanced denitrification (Straub et al, 1996;Nielsen and Nielsen, 1998).…”

“…6), though the SS loading here was lower than in phase II. In phase II, Fe 2+ dosed sludge floc was found more compacted and had relatively smooth surface in the authors' previous study (Wang et al, 2014), which shall be due to the presence of condensed and less hydrated EPS. The effect of dosing Fe 2+ in this study displayed by the smaller size of SS particles in the BAF influent and the less EPS content in the solids entrapped in the filter media (see Supplementary data Fig.…”

“…Besides SS loading, clogging development in a filter layer also depends on the characteristics, such as density and adhesivity, of the SS particles (Boller and Kavanaugh, 1995). Since there was no chemical precipitation in the pre-denitrification tank in phase I, sludge flocs formed there was found featured by less compacted structure and relatively rough surface in the authors' previous study (Wang et al, 2014), which is attributed to the presence of more hydrated EPS matrix (Liss et al, 2002). As a result, the SS particles in the BAF influent would be lower in density and higher in EPS content, leading to a higher EPS content in the solids entrapped in the filter layer (Supplementary data Fig.…”

“…First, the hydrolysis of the dosed Fe 2+ in the pre-denitrification tank consumes alkalinity in wastewater stream, which might lower pH and in turn affect ammonia oxidation in BAF. Second, the higher SS content in the pre-denitrification effluent (Wang et al, 2014), resulting from the formation of compact and smaller-sized sludge flocs after adding Fe 2+ , may increase SS loading to the BAF column and lead to easier clogging in the filter layer, and hence result to more frequent backwashing. In order to fully examine the overall performance of a whole BAF system employing the proposed synergistic pre-nitrification and chemical phosphorus precipitation process and provide further information for engineering modification work, a laboratory study using a continuously running BAF setup to treat real domestic wastewater was carried out.…”

“…Because solids removal in BAF is achieved mainly through filtration, and SS in BAF influent is usually required below 100 mg/L (Canler and Perret, 1994). To costeffectively meet the demand of denitrification, pre-treatment of phosphorus, and utilizing organic matters as the carbon source for denitrification, as well as removal of SS in the influent loaded into BAF, a process employing simultaneous chemical precipitation in pre-denitrification was proposed in the authors' previous study (Wang et al, 2014). The performance of dosing Fe 3+ or Fe 2+ on affecting denitrification, precipitating phosphorus, and SS removal in a denitrification/flocculation tank was investigated in laboratory experiments.…”