Why is having a wastewater treatment plant beneficial for York?
Anytime water enters the sanitary sewer system, via wash water, the sink, toilet, or bath it is considered wastewater. A wastewater treatment plant removes a variety of contaminants from water to make it usable again. The York, Pennsylvania Wastewater Treatment Plant is a 26 million gallon per day (mgd) facility and discharges into the Codorus Creek.
In 2011 a new computer system was put into service after one year in development. This system uses hardware and software from GE. The programming was done by a local firm, Multi-Dimensional Integration, Inc. The computer system utilizes redundant PLCs connected through a fiber optic network to five workstations. All major processes are monitored by system, with many of them able to be controlled by it.
In addition, security and logging was improved. Every time a change is made, an operator must log into the system using their username and password. This information can then be retrieved and reviewed.
The Operations Manager and General Manager are also able to access the system via a Virtual Private Network (VPN). This has proven to be useful in making necessary process changes during recent construction projects.
Wastewater Laboratory & Maintenance
The regional York Wastewater Treatment Plant laboratory is DEP accredited, and capable of analyzing a great number of samples with an efficient turnaround time. Staff consist of a Lab Supervisor, a DEP designated Quality Assurance Officer/Chemist, and two additional Chemists. Three members of the staff are DEP certified class A wastewater operators, and DEP certified Laboratory Supervisors. More than 50,000 tests are conducted each year.
The BIOLOGICAL NUTRIENT REMOVAL (Secondary Treatment) process at the York plant is delicate and fragile. With the help of some automated instrumentation, the lab personnel may provide operational personnel with valuable data in a reduced period of time from sample collection, to evaluate the efficiency of plant operation.
The lab also performs tests on samples collected by our Municipal Industrial Pre-Treatment Program (MIPP). These samples are tested for a wide variety of parameters and used to monitor industries for compliance with federal, state, and local regulations.
Maintenance at the York facility is organized through use of a software program. This program schedules equipment preventive maintenance. It also allows the Process Control Manager to input repair work orders for malfunctioning equipment. The software also tracks parts inventory, and is capable of printing out purchase orders when spare parts inventory run below a given set point. Since using this program, preventive maintenance has improved, while unscheduled major maintenance on equipment has decreased.
Most of the maintenance at York is performed by a crew of six and the maintenance supervisor. They are capable of repairing and servicing a variety of equipment.
Becoming An Operator
The City of York wastewater treatment plant emphasize sustainability and resource recovery, turning ordinary sewage into useful products. We biologically extract methane gas to generate electrical power and heat for processes and buildings. We biologically remove pollution, nitrogen and phosphorus from the water primarily by manipulating oxygen levels in the plant, as opposed to adding chemicals or using expensive membrane technologies. All of our biosolids are stabilized, conditioned and applied to Pennsylvania farmland as a soil conditioner and fertilizer, which is recycling on a grand scale. We extract and pelletize phosphorus in the form of a clean, marketable fertilizer product. We disinfect our treated water prior to stream release using ultraviolet disinfection, which is much more friendly to stream biology than chemical disinfection. We reuse some of our treated effluent as in-plant process and spray water.
Examples of ways that the wastewater treatment plant utilizes sustainability include:
- Biological nutrient removal to naturally treat the wastewater while minimizing chemicals
- Anaerobic digestion to extract methane gas
- Microturbine generators to produce electric power from the methane and get peak load rebates from energy utilities
- Fertilizer plant to produce a clean pelletized fertilizer for resale
- Agricultural utilization of biosolids to recycle nutrients and save landfill space
- Recovery of nutrients at the Ostara Nutrient Recovery Facility
Wastewater Treatment Plant Process
The first step in treating the wastewater entering the treatment plant is to remove RAGS (things like paper towels) and GRIT (sand and gravel).
This is a two step process. First, the rags and other large material are removed using BAR SCREENS. The Bar Screens have narrow slits that capture this material, while letting the wastewater pass through to the next stage of treatment. The debris is removed in this stage of treatment so it will not interfere with the other stages further downstream.
The CYCLONE DEGRITTERS remove sand and grit from the wastewater. This prevents wear and tear on pumps and piping within the rest of the treatment facility.
The PRIMARY TREATMENT process consists of a series of tanks that allows the separation of heavy solids (fecal matter) and floating solids (greases and oils) from the wastewater. The PRIMARY CLARIFIERS are sized to permit enough detention time so that large solid material settles to the bottom of the tanks. These solids are then continually scraped from the bottom and transferred to the ANAEROBIC DIGESTERS for further treatment.
Greases and oils are collected from the surface of these tanks and are also conveyed to the anaerobic digesters.
In SECONDARY TREATMENT the majority of pollutants are removed. This treatment phase utilizes MICRO-ORGANISMS to remove the food and nutrients(pollutants) that are found in wastewater.
As the wastewater enters this particular phase of treatment, the micro-organisms are introduced. Then an anoxic or low DISSOLVED OXYGEN zone follows. Next, this liquor is aerated so the dissolved oxygen can be increased to allow NITRIFICATION and BIOLOGICAL PHOSPHATE reduction to occur.
The York facility, through a patented process and tank design, is able to have these micro-organisms metabolize the organic matter and convert ammonia to nitrates. The process also allows the micro-organisms to uptake ortho-phosphates into their cells.
After the aeration stages, the MIXED LIQUOR (micro-organisms and wastewater) enter the SECONDARY CLARIFIERS. Here the velocity of the wastewater is slowed to allow for the biomass to clump together and settle to the bottom while allowing the clean water to flow over the tank weirs. Large pumps return the micro-organisms from the bottom of these secondaries and return them to the beginning of the secondary treatment phase to start the cycle all over again.
During secondary treatment the micro-organisms reproduce in great numbers. To keep the system in check a portion of these critters removed through a wasting process. This sludge is thickened in our DISSOLVED AIR FLOATATION THICKENER and this thickened material is sent to the anaerobic digesters.
In 1990, the York W.W.T.P. installed 5 shallow bed sand filters which removed any remaining particulate matter after secondary treatment. These filters were capable of treating a maximum peak flow of 42 mgd. Effluent leaving the Sand Filters typically had suspended solids concentrations of less than 5 mg/l.
In 2000, the sand filters were modified with a more efficient under drain and backwash system. The maximum peak flow through these units is now 55 mgd. Cost of this renovation was $3,000,000 less than adding additional filters to handle the new peak flows.
The plant management is evaluating the performance of a larger sand particle size in order to increase the hydraulic capacity of each of the five filters. Sand filter No. 5 went back into service in late January 2007 with this new media type.
An ULTRAVIOLET light system is used to disinfect the effluent that leaves the sand filter process. In 2001 the existing system was upgraded to the Trojan UV3000PlusTM . Unlike our previous Trojan Technologies system, the 3000Plus series utilizes a low pressure-high intensity lamp. This enabled the York facility to reduce the number of lamps needed for disinfection from 1728 to 768. The UV light inhibits any bacteria from replicating, thus making them harmless. This system has proven to be much safer than Chlorine, while being more cost effective. No toxic chemical needs to be added in the disinfection process. In addition, the 3000 series also has automatic wipers so operators do not have to spend time cleaning the lamps, thus saving on labor costs.
Final Effluent Aeration
The final stage of treating the EFFLUENT(or treated wastewater) is to increase its dissolved oxygen content. This is accomplished by allowing the water to run down over a series of steps and blocks. This agitation is enough to bring the dissolved oxygen content of the water back up to better than 7 mg/l. This insures that plenty of oxygen will be available to fish and other aquatic life.
Muskie Caught at Final Effluent Discharge Point!
For years people in the York area had the impression that the Codorus Creek was “dead”. It had been the discharge point for industries and residents since York was founded in the early 1700’s. Nothing could survive in that water.
Then in 1972 the Clean Water Act was passed and changes began to occur. The discharge of pollutants were no longer permitted into this stream. This facility, along with several other WWTPs, discharging into the Codorus Creek was upgraded. These modifications did little to change people’s minds about the Codorus.
Our last upgrade in 1990 allowed us to clean wastewater to such an extent that our permitted pollutants discharged to this stream were very low. After this construction was completed and the “new” facility went online, one of our computer system consultants began fishing at our final effluent discharge point. Much to everyone’s surprise, he caught several small mouth bass. This continued over the next several months until one day nothing was biting. Then the “BIG FISH” hit. Above is a photograph of the 24-inch Muskie. This proved to many skeptics that the Codorus Creek was no longer dead.
The solids that are removed from the Primary Treatment and Secondary Treatment processes are sent to one of three ANAEROBIC DIGESTERS(a biological step that occurs in the absence of oxygen). During this digestion, bacteria convert any remaining organic matter(food) into METHANE GAS, carbon dioxide, and water. After a detention time of 20 to 30 days at 98 degrees F., the sludge is considered stabilized and is ready for dewatering.
The methane gas is captured and used to produce electricity in our Co-generation facility. The sludge is dewatered and disposed of on farmer’s fields by an outside contractor.
Stabilized sludge from the anaerobic digesters is conveyed to holding tanks to await dewatering. The sludge is then dewatered using two Bird centrifuges. Dewatered sludge(BIOSOLIDS), averaging 18 percent total solids, is then sent into the sludge bin where it is stored until our contractor removes it. The sludge cake is then used as a fertilizer on permitted crop land in Pennsylvania and Maryland or used as a soil conditioner for remediating depleted strip mines.
On October 11, 2011 the City of York Wastewater Treatment Plant retired its 23-year old co-generation facility which was powered by internal combustion engines. Since the start-up of this facility in 1988 more than 57 million kilowatt hours have been generated.
In its place eight 200 kW Capstone® microturbines were brought online. Three microturbines will use methane gas produced by our anaerobic digesters to generate electricity. Heat will also be recovered from their exhaust gas to warm the digesters year-round and heat buildings during cooler months. The other five units will use utility gas as fuel to produce additional electricity based on the facility’s demand.
The Capstone® microturbines are much more energy efficient, producing the 30 percent more electricity than the older system. In addition this new technology produces far less air pollution.