Waste Water Treatment
Wastewater Facilities - Summary of Treatment Plant Process
The pretreatment process is provided to remove any coarse solids which may damage the equipment within the wastewater treatment plant. Wastewater flows through the swing gate at the influent end of the treatment plant, which directs the flow through one of two channels. The wastewater then flows through the coarse bar racks which are mechanically cleaned. Following the coarse bar racks, the flow passes through the mechanically cleaned fine screens where smaller sized solids are collected. The wastewater which is discharged from the fine bar screens then flows through the grit chambers. The removal of the settled grit from the bottom of the chamber is achieved by flights, plows and buckets attached to arms on an endless chain, which rotates and moves the grit to the upstream end of the chamber. The grit which is scraped backward (against the flow) is deposited on an auger type lifting device called a grit screw. As the grit screw rotates, the grit is lifted up an incline and washed by the flow entering the chamber. Currently, the grit and screenings collected are placed into containers and, are landfilled.
The primary treatment process is employed to remove the settleable solids and floating scum from the sewage. This is achieved by the physical process of sedimentation and flotation, so as not to overburden the follow up biological processes. The wastewater enters the primary settling tanks upon leaving the grit chambers. Here the velocity of the flow is reduced to allow the suspended solids which were too tiny to be screened to settle. In the primary settling tanks, scrapers are pulled upstream along the tank floor by traveling bridges, pushing the settled solids to the cross collector located at the inlet end of the tank. The scrapers are then lifted and the skimming blades lowered to the surface of the tank where they serve to push floating solids, grease and oil to a scum collector at the outlet end of the tank. A scum trough is located at the downstream end of the primary settling tanks.
Secondary treatment is a wastewater process used to convert dissolved or suspended materials into a form more readily separated from the water being treated. The secondary treatment process at the Joint Meeting was designed to be able to be operated either as a conventional or step aeration process. The plant is operated as a conventional aeration process with a single feed point. The wastewater from the primary settling tanks flows by gravity to the five main sewage pumps, where it is pumped to a higher elevation for the beginning of the activated sludge process and flows by gravity through the secondary process. The aeration tanks are the first step in the secondary treatment process where the mixture of wastewater, return activated sludge and oxygen is brought together utilizing mechanical aerators. The wastewater which is discharged from the aeration tanks enters the final settling tanks. Here the mixed liquor solids are allowed to separate from the liquid, leaving the solids to settle to the bottom and form return sludge. When the proper operating levels of the mixed liquor solids are reached in the aeration tanks, the removal of suspended solids above this amount is done by wasting to the sludge handling facilities.
Disinfection is accomplished by the use of sodium hypochlorite. The final effluent which is carried over the effluent weirs of the four final settling tanks flows into the post-chlorination chamber. From this chamber, the effluent flows through a two chambered chlorine contact tank. Here the flow is detained in order to accomplish the disinfection process. Following disinfection, sodium bisulfite is added to remove any residual chlorine. The disinfection and de-chlorination of the wastewater is the final phase of treatment before it is discharged into the Arthur Kill.
Sludge handling deals with the solids that are removed by various plant units, such as raw sludge from the primary settling tanks, scum, and waste activated sludge and from the secondary biological process. Removal of the suspended solids that are above the amount required for the proper operating levels in the aeration tanks is controlled by wasting of mixed liquor from either the aerated channel or the return activated sludge piping. The mixed liquor to be wasted from the aerated tank effluent channel goes to the waste activated sludge dilution wet well and then pumped to the thickeners. The return activated sludge is pumped direct to the thickeners from the return activated sludge piping. From the thickeners the sludge goes through grit removal and a mechanical bar rack to the splitter box. The splitter box distributes the flow evenly to the four sludge thickener tanks. At this point the thickener underflow, flows to the thickened sludge pumps which pump the sludge to the gravity belt thickeners. The thickened sludge is pumped to the digester as feed sludge. The thickener overflow from the sludge thickeners flows by gravity to the influent end of the primary settling tanks.
Each of the digesters employs floating gas holding covers to collect and store the gas which is generated in the digestion process. This gas is consumed in three ways. First, the gas is returned to the digester in order to aid in the digestion process by mixing the tank contents using gas lift pumps. Secondly, the gas is consumed as fuel for boilers heating the sludge and various buildings and in the cogeneration engines for the production of electricity and heat. Finally, excess gas could be consumed by the waste gas burner or other source requiring this type of fuel.
The sludge within the digesters is removed and stored in one of the two sludge storage tanks. The storage tanks utilize floating covers to minimize odors and retain any released digester gas. A second waste gas burner is currently being utilized at the storage tanks to burn the digester gas.
Biosolids Handling Facility
The sludge from the sludge storage tanks is pumped to the Biosolids Handling Facility. The sludge is pumped to two of three high solids centrifuges, where the solid concentration is raised to 25% total solids. Lime can be added for lime stabilization of the sludge, increasing the percent total solids to 30%. The sludge is then pumped into trucks and to be used as soil conditioner or sent to composting facilities without lime and land applied as soil conditioner.
Wastewater Facilities Design
The following are the design loadings utilized by Elson T. Killam Associates during the design of the facilities. Originally designed as a 75 million gallons per day facility, the plant was subsequently rated for an average hydraulic flow of 85 million gallons per day with a design peak flow of 120 million gallons per day. BOD and suspended solids removals were anticipated to average 90% and 95% respectively.
The wastewater treatment facilities for the Joint Meeting were designed to conform to the following permitted operating parameters of the NJDEP. References should be made to the operating reports which reflect the actual operating parameters of the plant.
Virtual Plant Tour
In order to view Joint Meeting's Virtual Plant tour, you must have either Adobe Acrobat Reader or Microsoft PowerPoint. Please note that Adobe Acrobat Reader is available free for download by clicking here.
- Virtual Plant Tour.pdf (Adobe Acrobat Reader)