DIAGNOSIS AND RESTORATION OF DIMINISHED FORCE MAIN CAPACITY

摘要

A reduction in hydraulic capacity recently developed in a wastewater transmissionrnline linking the City of Niagara Falls wastewater treatment plant with its largestrnpumping station. The flow limitation reduced first flush capture from the combinedrncollection system and occasionally resulted in manhole surcharging up to street level.rnInternal inspections were performed using cameras on umbilicals, a self-containedrncamera carrying vehicle, and by manned confined space entry. Two engineeringrnstudies were supplemented with efforts by the plant staff. Several diagnostic andrncorrective actions were pursued, involving physical, chemical and biologicalrnmeasures. An air injection system installed at the pumping station during a recentrnrehabilitation project was discovered to be the root cause. In addition to it抯 intendedrnfunction of reducing pump hydraulic noise, the injection system also led to force mainrnpipewall growths and intermittent air binding. Changes to the injection system and thernpump controls reduced the quantity of air entering the force main, reversing bothrneffects and gradually restoring the lost capacity. Only small seasonal variations havernbeen observed since then.