The fat, oil and grease (FOG) in raw sewage tend to build-up and restrict flow inside a pipe. This is particularly pronounced in many domestic and industrial sewer networks and treatment plants around the world. Although there are methods to remove FOG from pipes and pump stations, this is an additional cost to operating the network and plants. A few years ago, the Rosedale Waste Water Treatment Plant (WWTP) was experiencing problems associated with FOG clogging in pipes.
Rosedale WWTP operates a gravity belt thickener (GBT) which is primarily used for thickening sludge from primary sedimentation tanks. Previously, FOG was an ongoing issue in the treatment process as it would buildup layers inside the GBT discharge pipe and restrict flow to the digester feed tank. Maintenance and cleaning of blocked pipe was required to maintain flow through the solid processing units at the plant. The plant also experienced pump failures due to blocked conveying lines.
To minimize FOG build-up in GBT discharge and downstream pipes, digested sludge from an anaerobic digester was recycled back and mixed with thickened primary sludge to address the issue. The novel process has been implemented at minimal cost.