Improving Water Quality and Biosolids

Since 1969, the Industrial Waste Program has required many industries to pretreat wastewater before discharging it into the sewer. The result has been a continuous improvement in water quality and biosolids.

Biosolids are nutrient-rich organic solids produced by wastewater treatment processes. King County biosolids are used to enrich soil for agriculture, forestry, and landscaping. The county's goal is to produce the most contaminant-free biosolids practically achievable.

Wastewater pretreatment removes wastes including heavy metals. The partnership between KCIW and county industry has contributed to a decline in heavy metals in wastewater received at King County's West Point and South Treatment Plants as indicated by the low levels of these metals in their biosolids.

The graph shows more than two decades of improvements in the pretreatment of the county's industrial wastewater. The quality of both treatment plants' biosolids remains well below the U.S. Environmental Protection Agency's exceptional quality standards (federal rule 40 CFR Part 503) for heavy metals (external link).

The recent years' levels of metals on the graph show the continuous overall effectiveness of industrial wastewater pretreatment.