自20世纪60年代以来，许多快速砂滤器已被改造成高速过滤器，双介质已取代砂滤器。这种变化造成的一个常见问题是，在常规过滤器清洗实践中，无烟煤介质的损失过大（每年5-10%）。这是因为滤床顶部和洗涤槽顶部之间的空间不足以容纳轻质煤颗粒，尽管它足以容纳快速砂滤床。此外，旧过滤器设计的洗涤槽间距过小，加剧了煤粒的损失。作者评估了现有快速砂层转化为活性炭层后，在不提升混凝土洗涤槽的情况下，颗粒活性炭（GAC）的损失。初步研究结果表明，一个简单的挡板配置可以减少多达70%的介质损失。 包括表格、数字。

Since the 1960s, many rapid sand filters have been modified to become high-rate filters, and dual media have replaced sand. A common problem caused by this change is excessive loss of anthracite coal medium (5-10 percent annually) under regular filter washing practices. This happens because the space between the top of the filter bed and the top of the wash troughs is insufficient for the lightweight coal grains, even though it was adequate for the rapid sand filter beds. Also, rather tight spacing of wash troughs for old filter designs aggravates the loss of coal grains. The authors evaluate the loss of granular activated carbon (GAC) after existing rapid sand beds are converted to GAC beds without raising the concrete wash troughs. Results of the pilot study indicate that a simple baffle configuration can reduce media loss by as much as 70 percent. Includes tables, figures.