Calculating credits for iron enhanced sand filter
Contents
Volume credits
Volume credits are not applicable to iron enhanced sand filters. Some volume credit may be given for evapotranspiration and evapotranspiration below underdrains for certain BMPs.
TSS credits
TSS credits are provided for filtration practices.
Phosphorus
The primary advantage of iron-enhanced filtration is that it removes dissolved constituents including phosphate, color and some metals by chemically binding. {{alert|Dry or wet pre-treatment is Required prior to media filter treatment for all filters, unless influent is relatively free of solids (pre-treatment volume equivalent to at least 25% of the computed Vwq is Recommended).|alert-danger]] Iron-enhanced sand filters can be used as a retrofit to existing BMPs or in new construction. If the iron-filtration bed remains oxygenated, iron will be retained in the bed. Iron-filtration beds that are persistently deoxygenated risk iron loss or migration and clogging.
Total phosphorus reduction
Annual total phosphorus (TP) reductions were divided into two components: particulate phosphorus (PP) and dissolved phosphorus (DP). Each of the three filtering systems was assumed to provide zero DP reduction without the incorporation of iron in the filter media. It was also assumed that of TP, 55 percent is PP and 45 percent is DP. Using these assumptions the TP removal can be described by
\(R_{TP} = 0.55R_[[:Template:PP]] + 0.45R_{DP}\)
where:
- R is the removal efficiency for each of the phosphorus constituents.
The removal efficiency for RPP is based on the annual TP reductions provided by each of the filtering BMPs without the inclusion of iron in the filter media. It was assumed that all removal of phosphorus in these systems is provided through the removal of particulate phosphorus. Therefore, the RTP reductions can be converted to RPP using the above equation by setting RDP to 0.
Total phosphorus reduction
Annual total phosphorus (TP) reductions were divided into two components: particulate phosphorus (PP) and dissolved phosphorus (DP). Each of the three filtering systems was assumed to provide zero DP reduction without the incorporation of iron in the filter media. It was also assumed that of TP, 55 percent is PP and 45 percent is DP. Using these assumptions the TP removal can be described by
\(R_{TP} = 0.55R_[[:Template:PP]] + 0.45R_{DP}\)
where:
- R is the removal efficiency for each of the phosphorus constituents.
The removal efficiency for RPP is based on the annual TP reductions provided by each of the filtering BMPs without the inclusion of iron in the filter media. It was assumed that all removal of phosphorus in these systems is provided through the removal of particulate phosphorus. Therefore, the RTP reductions can be converted to RPP using the above equation by setting RDP to 0.