ANSI AWWA B100-16 pdf free download – Granular Filter Material
High-specifc gravity (high-density) flter media consisting of garnet, ilmenite, hematite, magnetite, or associated minerals of those ores are used by some utilities in an attempt to remove more suspended solids at higher fltration rates. Tese small, high-density media remain as a layer under the silica sand as a result of particle size and specifc gravity diferences in the same way that silica sand remains separated from overlaid anthracite in a dual-media flter. Some intermixing usually occurs at the inter- face between the layers. Te term garnet refers to several diferent minerals (mostly almandite and andra- dite) that are silicates of iron, aluminum, and calcium mixtures. However, garnet could also be grossularite, spessartite, and uvarovite, the latter being a chromium mineral. Ilmenite is an iron titanium mineral that invariably is associated with hematite and magnetite, both iron oxides. Properties of granular activated carbon when used as a flter medium are described in ANSI/AWWA B604, Standard for Granular Activated Carbon. Testing require- ments for granular activated carbon vary from those for anthracite, silica and garnet. Refer to ANSI/AWWA B604, Standard for Granular Activated Carbon. Properties of media used in precoat flters (such as diatomaceous earth) can be found in ANSI/AWWA B101, Precoat Filter Media. Synthetic media and membrane flters are not included in this standard. Sand or anthracite flter media used in a wide range of bed depths and particle sizes have produced satisfactory results. Selection of the bed depth, particle size, and particle density of each media layer to be used in any particular flter is the responsibility of the designer and should be done with careful consideration of raw water conditions, plant pretreatment facilities, and flter backwash system design.
Filter-Media Support. If the openings in the underdrain system are larger than the flter media, a system of supporting material is required to prevent the flter media from entering and blocking the underdrain system and to help distribute backwash water evenly. Tis can be achieved by layers of gravel installed over the underdrain system or by use of proprietary media support systems provided by underdrain system manufacturers. When using gravel, the size and depth of the gravel layers must be selected to achieve the objectives of minimizing media loss through the underdrains, aid in evenly distributing backwash water, and minimizing displacement of the gravel by the rising backwash water and/or air scour supply. Guidance for selecting appropriate support gravel size and layer depths, along with examples, is included in appendix D. Te use of air scour must also be considered in the proper selection of underdrain and media support systems. Te user of this standard is urged to carefully consider several factors in determining the appropriate underdrain and flter-media support system for a particular application, including water quality, flter operating and backwash rates, whether air scour is provided, and type of treatment practiced at the facility (softening, biological fltration, etc.). Information and guidance to assist the user in proper selection of flter underdrains and media support systems are available in several of the references included in appendix A. In addition, advice and guidance can be solicited from underdrain system manufacturers and qualifed consulting engineers.