OPERATION AND MAINTENANCE LESSONS FROM AN ACTIVATED CARBON FILTER SECONDARY TREATMENT SYSTEM

Granular activated carbon adsorption/filtration has served as the secondary treatment process at the City of Niagara Falls, New York wastewater treatment facility for over 15 years. Physical and chemical treatment processes were selected over more traditional biological methods due to the nature and quantity of industrial wastewater produced at the time of facility design in the 1970's. Operational experience with this unique and evolving system has led to a variety of maintenance practices, structural changes and operational procedures aimed at improving performance and reliability while controlling costs.The original plate and pier type of underdrain structure failed after less than one year in service, and was replaced with a plastic modular block underdrain system, above which 14 inches of layered gravel supports 8 feet of activated carbon. Carbon transport and filter backwashing procedures were developed to reduce the extent of gravel layer disruption. Air scour piping was modified on each filter to cushion the initial pulse of compressed air during full backwashes. An abbreviated backwash procedure was developed to recover filter headloss, and produces significantly less backwash water to treat. An automated backwash control system has enabled greater uniformity in operations. The use of chemical oxidants to control unavoidable anaerobic growths in the underdrains is an important considerationThe condition of the underdrain system is inspected annually, coincident with the annual carbon regeneration campaign. The structural condition of the modules is checked, as well as the support gravel and concrete containment. An eventual project to remove, clean and relayer the gravel (in a new configuration) in each filter is anticipated.