Plant Tour

Raw wastewater (sewage) flows by gravity sewer pipelines, from parts of 10 different municipalities, into the Main Pump Station, where the volume of water is continuously measured by a flow meter. An automated Fine Screen removes non-biodegradable debris. Four submersible pumps, each capable of pumping 5 MGD, then pump the wastewater uphill for grit and grease removal.

The Grit and Grease Removal Unit is a physical process that allows the heaviest material (mainly grit) to settle to the bottom of the tank. Diffused air is pumped into the tank, which causes any floatable material (mainly grease) to float up on one side of the tank. The combination of diffused air and rapid velocity keeps all other bio-degradable waste material in suspension for further treatment. Both the grit and the grease are automatically removed from the tank, de-watered, and transferred to a dumpster for disposal.

Wastewater then flows to the Equalization Basins, where it is stored for a period of time to equalize the normal daily flow fluctuations. Diffused air is pumped in to keep the wastewater fresh and keep solids in suspension. The wastewater flows out from here at a constant rate to the Oxidation Ditch. The Basins also provide over 1.5 million gallons of storage capacity for excessively high flows during wet weather.

The Oxidation Ditch is a modified version of the activated sludge process, similar to extended aeration. Its tanks are arranged in three, aerated, complete-mix, concentric rings that are designed to reduce Suspended Solids and BOD levels up to 95% and Total Nitrogen and Phosphorus removals up to 80%. Oxidation of ammonia is accomplished in excess of 95%.

In the Oxidation Ditch, various microorganisms metabolize (feed on), and biologically flocculate (clump together) the organic pollutants. This biological processing of the waste organics results in a build-up of a microbial mass (activated sludge) in the system, the amount of which is maintained at the optimum level to achieve the desired treatment. The system has a long detention time (over 12 hours) and passes the microorganisms rapidly through alternating aerobic and anoxic (no free oxygen) zones, thus achieving biological nutrient (nitrogen and phosphorus) removal.

After aeration in the Oxidation Ditch, the wastewater/activated sludge mixture (called mixed liquor) moves downstream to the Final Clarifier Tank. The activated sludge portion of the mixture is allowed to settle by gravity in the circular tank with a detention time of about 4 hours. Ferrous chloride and polymer are added to aid flocculation and settling, and to achieve phosphorus removal. Settled activated sludge is returned by pumps to the Oxidation Ditch to maintain the continuous cycle of activated sludge in the system.

The clarified effluent flows from the Final Clarifier Tank to the Ultraviolet Disinfection System for its final treatment. Here, the effluent is exposed to high-intensity ultraviolet light for the destruction of any remaining pathogenic (disease-causing) organisms. The flow is then metered and receives final aeration by flowing down a Cascade. The effluent is then discharged to the Neshaminy Creek.

The Facility’s Laboratory analyses the influent, effluent, and unit processes daily, to ensure the required quality of treatment.

The processing of the residual solids (sludge) consists of thickening, digestion, de-watering, and drying. The processing of solids results in a final product called BioSolids, which is recycled for beneficial uses.

Excess amounts of activated sludge are continually generated in the Oxidation Ditch by the growth of the microbial mass and the accumulation of solids. To maintain a constant optimum concentration of activated sludge, this excess sludge must be removed (called “wasting”). This “waste” activated sludge is pumped to the Dissolved Air Flotation Thickener. This process blends the sludge with pressurized, air-saturated water. This causes water to separate out of the sludge and the sludge to float to the surface and thicken. The Flotation Thickener will concentrate the thin (½ % solids) waste activated sludge up to about 6% thickened sludge, thereby removing much of the water prior to further processing.

This thickened sludge is pumped to the Anaerobic Digestors. Digestion is a biological process that reduces the amount of organic (volatile) solids in the sludge, stabilizes the organic content, and reduces odors. The sludge is mixed and heated to maintain the proper environment for the anaerobic bacterial activity. This process takes about 30 days. A byproduct of the process is methane gas, which is used for fuel to heat the sludge, making the process self-sustaining. Digested sludge, which is removed from the bottom of the Digesters, is a black, homogenous liquid having a solids concentration of 2%-4%. At this point, the quantity of total solids that were fed to the digestion process has been reduced by as much as 50% through the decomposition of the volatile solids into methane, carbon dioxide, and water.

Digested sludge is then pumped to a Centrifuge, which de-waters the liquid sludge into a cake-like material. Sludge is first conditioned with a coagulant polymer, then passes through the centrifuge, a cylinder-shaped bowl which spins at about 3500 revolutions per minute (RPM). In a very short time, the high gravitational forces in the centrifuge will separate out about 75% of the remaining water in the sludge. The g-forces in the centrifuge bowl are over 2500 times that of normal gravity. The remaining sludge cake material, at a solids concentration of 20-25%, is then conveyed to an intermediate storage hopper prior to the drying process.

Dewatered solids are fed to a BioSolids Dehydrator (dryer). Solids are heated to about 210 degrees F° to evaporate all of the remaining water content. This is a batch process that takes about 3 hours for each batch to complete. Hot oil (450 F°) is circulated within the drying chamber to raise the temperature of the solids. The resulting granular material, now called BioSolids, has a dry solids content of about 90%. For purposes of land application, the BioSolids meet all Class “A” standards under EPA Regulations-Part 503, and also meet Pennsylvania DEP standards as “Exceptional Quality”. Under these regulations, the material may now be distributed as a soil conditioner and fertilizer.

Dried BioSolids are stored in a 155 Ton capacity Storage Silo, prior to distribution to land application customers. BioSolids are produced by CNBTJSA under the name C'n'B Green. Information about obtaining and using C'n'B Green may be obtained from the Authority office.