Alum Treatment of Stormwater Runoff -An Innovative BMP for Urban Runoff Problems

摘要

Alum treatment of Stormwater runoff was begun in 1986 as part of a lake restoration project at Lake Ella in Tallahassee, Florida in 1986. Our system provides treatment of Stormwater runoff entering the lake by injecting liquid alum into major stormsewer lines on a flow-weighted basis during rain events. When added to runoff, alum forms non-toxic precipitates of Al(OH)_3 and AIPO_4 which combine with phosphorus, suspended solids and heavy metals, causing them to be rapidly removed from the treated water. The alum Stormwater treatment system resulted in immediate and substantial improvements to water quality in Lake Ella which led to implementation of similar systems on other urban lakes. There are currently 23 alum Stormwater treatment systems either operational or under construction in Florida, and one experimental system in Seattle, Washington. Alum treatment of Stormwater runoff has consistently achieved a 90% reduction in total phosphorus, 50-70% reduction in total nitrogen, 50-90% reduction in heavy metals, and >99% reduction in fecal coliform. Ultimate water quality improvements in the receiving water body have been related to the percentage of total inputs treated by the system. Heavy metal and phosphorus associations with alum floc have been shown to be extremely stable over a wide range of pH and redox conditions. In general, alum treatment of runoff is substantially less expensive than traditional treatment methods and often requires no additional land purchase. Recent designs have incorporated automatic floc collection and removal systems with disposal to drying beds or sanitary sewer.