水处理厂残留物的处理可能会有问题，而且成本越来越高。在20世纪70年代之前，大多数水厂的残余物被送回供水系统下游的受纳水体，实际上是将去除的物质和混凝剂一起送回水源。自那以后，监管机构决定减少水处理残余物的直接排放。然而，认识到消除排放缺乏科学依据，一些监管机构重新审视了禁止直接向地表水排放的最初政策，并将允许在科学解决具体问题后恢复直接排放。本文介绍了两个关于混凝剂固体排放到地表水（弗吉尼亚州丹河）的实例研究。这两座水厂直接排放的研究方法利用了可用的植物固体排放信息、实验室分析数据、使用河流中人工地层进行的额外现场工作，以及对- 溪流底栖生物群落。包括表格，数字。

The disposal of water treatment plant residuals can be problematic and increasinglyexpensive. Prior to the 1970s, most water plant residuals were returned to receiving water downstream of the water supply, in effect, returning the material removed, plus coagulant, back to the source water. The regulatory community has since elected to curtail the direct discharges of water treatment residuals. However, recognizing that the elimination of discharges lacked a scientific basis, some regulators have revisited the initial policy of banning direct discharges to surface water and will allow direct discharges to resume once specificconcerns are scientifically addressed. This paper presents two example studies concerning coagulant solids discharge to surface water (the Dan River in Virginia). Thestudy approach to direct discharge for these two water plants utilized available plant solids discharge information, laboratory analysis data, additional field work using artificial stratum placed in the river, and field investigations of in-stream benthic communities. Includes table, figures.