The Environmental Protection Agency is seeking tighter standards for airborne emissions of mercury from new and existing sewage-sludge incineration units. Such units often are located at wastewater-treatment facilities.

The proposal, announced on Sept. 30, would cut mercury emissions by 75%, EPA says. The agency plan would require many wastewater-treatment facilities to install controls such as high-efficiency scrubbers and fabric filters. The proposal would not apply to incinerators at commercial, industrial and institutional facilities.

The proposed rule would take effect in 2015. EPA estimates complying with the requirements would cost $105 million per year for all currently operating units. The agency says it expects to issue a final rule in 2011.