Public Works Department
Treatment Plant Process
The headworks is on line May 1 through October 31. It is an open facility which is not designed for winter conditions. The headworks consist of two (2) Parkson 15mm automatically self-cleaning, mechanical screens and two (2) Smith and Loveless Pista Grit degritter units. One is designed for 20 million gallons per day (MGD) and one is for 12 MGD, for a total of 32 MGD capacity. The screens catch material that is larger than 3/8 inches, which is deposited into the screenings conveyor press. The press reduces the volume and water content by pressing or mashing the material. The pressed screenings are collected in a dumpster, mixed with lime and taken to the central landfill for disposal.
The grit chambers remove any grit that may be contained in the raw wastewater. The grit moving across the bottom of the chamber is hydraulically scoured as the propeller blade of the Pista unit moves over the grit. This causes the hydraulic currents to lift up the organic material which continues through the treatment process. The remaining inorganic material or grit passes from the removal chamber through an opening in the transition plate and drops into a grit storage hopper until it is pumped to the Pista grit concentrator. From there the grit goes by a grit screw conveyor to a dumpster for removal to the central landfill. Excess water is removed in the grit screw conveyor.
Primary Influent Building
The effluent from the headworks enters the Primary Influent Building through an influent vault. All processed flows returning to the head of the plant re-enter the influent vault. The raw wastewater goes through a second set of grit chambers and manually cleaned bar screens. The wastewater continues through a set of dimminutors.
A dimminutor is essentially a circular bar screen placed in the influent channel. It is traversed by a rotating rake that serves as a cutter to engage and shred the accumulated debris, thus, screening and shredding are accomplished in one operation. Shredded solids are returned to the sewage flow, eliminating equipment and labor for separate handling, shredding and disposal.
After the dimminutors, the influent is pumped to the equalization wet well. The equalization system consists of 6 holding cells or basins with a total capacity of 2.8 million gallons. Four blowers maintain air to the diffuser system to aid in keeping the wastewater fresh and 3 variable speed pumps with a pumping capacity of 16 MGD each to pump the wastewater to downstream treatment units. The equalization basins are operated to approximate a constant flow to downstream processes in a given day. The variable speed pumps are adjusted as required. The flow at which they are set is dependent on the equalization basin water level and expected influent flow. Peak flows are from approximately 9 AM to 6 PM.
Primary Settling Tanks
Flow from the equalization basin is directed to primary treatment through a flow splitting chamber. The primary units include the following tanks:
Three 90 foot diameter clarifiers with a side water depth of 10 feet and a volume of 71,200 cubic feet each or 532,576 gallons.
Two 40 foot diameter clarigesters with a side-weighted depth of 8 feet and volume of 10,700 cubic feet each or 80,036 gallons.
All five units may be operated during the summer and have a total surface area of 21,600 square feet and a total volume of 235,100 cubic feet or 1,758,548 gallons.
Untreated wastewater from the equalization basins contains materials which will either settle to the bottom or float to the water surface readily when the wastewater velocity is allowed to become very slow. Solids which settle to the bottom of the settling tanks are scraped into the middle sump. Solids are pumped from the sump to the gravity thickeners. An arm moves over the surface of the tank to collect any floating materials or grease. These are deposited into a scum pit.
Primary solids are pumped to three 22 foot diameter gravity thickeners by 6 pumps controlled by timers. The timers are set manually to maintain a 1 foot sludge blanket in the primary settling tanks. During normal summer operations, each pump is on 2 minutes and off 13 minutes. Each thickener has a surface area of 380 square feet and a side water depth of 10 feet. Solids are held in these units for several hours to thicken. The thickened solids (sludge) is pumped from the thickeners to the Bio-Solids Process.
Secondary Influent Pumps
Three secondary influent pumps convey primary effluent to a flow-splitting chamber which divides the flow into 3 pure oxygen tanks. The 3 variable speed secondary influent pumps are rated at 16 MGD.
Pure Oxygen Aeration Tanks (Oasis)
Each of the 3 pure oxygen aeration tanks is divided into 3 different compartments. Oxygen is applied to the second compartment in each tank and passes through the 3 compartments prior to release. Surface turbines in each compartment provide for dissolution of the oxygen into the wastewater. A flow splitting chamber at the end of the oxygenation units divides flows to the 3 secondary clarifiers. The amount of flow which goes to each clarifier is controlled by gates which are manually opened and closed after visual inspection of the water depth in the corresponding clarifier.
The VPSA oxygen system has production capacities of 15 tons per day based on its original certification testing. Liquid oxygen evaporation capacity is available for augmenting the system. The Oxygen Dissolution System (aerators) have a rated capacity of 25,400 lbs/day. Each oxygenation train has a volume of 0.35 mg.
Secondary Settling Units (Final Clarifiers)
Flow from the splitter chamber of the oxygenation units flows to the final clarifiers. These clarifiers are square with a surface area of 5,700 square feet and a volume of 74,900 cubic feet per clarifier or 560,252 gallons.
The return sludge (sludge needed to maintain a concentrated population of micro-organisms in the oxygenation tanks for the treatment of wastewater) is drawn off hydraulically with suction tubes which are located across the bottom of each tank and which rotate with the scraper blades. The scraper blades extend mechanically into the corners. Each clarifier has 8 suction tubes, 4 of which are fully open and 4 are slightly open, during normal operation.
Sludge is wasted from a pit at the bottom of each tank and pumped to the dissolved air flotation thickener units.
Dissolved Air Flotation Thickening (DAFs)
Three waste-activated sludge (WAS) pumps, each dedicated to a specific final clarifier, pump the sludge from the clarifier to the DAF units. During summer months, all 3 pumps are operated continuously. During the winter months the pumps are operated 4 to 5 hours per day intermittently to maintain the desired wasting rate. Each pump is rated at 150 gallons per minute (gpm) at 25 psi.
The DAF system consists of two 352 square foot tanks, blowers and a polymer feed system. The DAF centrate is returned to the head of the plant. Polymer is added to the sludge to aid in dewatering. The thickened sludge is then pumped to the Bio-Solids Process.
Chlorine is added to the effluent from the final clarifiers in the chlorine contact tank. Sulfur dioxide is added in the last channel of the northern chlorine contact tank for dechlorination, before being pumped into the ocean. The total volume of the chlorine contact tanks and the 700 foot length of 42 inch diameter piping between the tanks is 377,400 gallons.
The final effluent is pumped through the ocean outfall by 3 constant speed pumps. The pumps are rated at a 16 mgd capacity.
The Ocean City outfall system includes an outfall pumping station (with the effluent pumps above) located at the Wastewater Treatment Plant approximately 700 feet of ductile iron pipe from the Wastewater Treatment Plant to the beach area, an air release valve vault just short of the beach and 4,600 feet of pre-stressed concrete cylinder pipe discharging to a diffuser section which is in water approximately 30 feet deep.
The 1,000 foot long diffuser section has (49) 4 inch risers which extend approximately 7 feet above the center line of the pipe, ending in 4 inch by 4 inch tees that are intended to discharge effluent parallel to the beach. The effluent is diluted to 1 part effluent to 200 parts water.
Bio-Solids (Sludge) Disposal
Bio-solids (sludge) is not a waste to the Town of Ocean City anymore. It is a beneficial waste water product. Bio-solids from the Ocean City Wastewater Treatment Plant are currently being applied to agricultural land. The town produces a class "A" Bio-Solids. An envessel pasturization process is utilized.
Land application of treated sludge is recycling in its simplest form. Sludge is applied to the land by surface application. In surface application, the material is spread on land at prescribed rates and then plowed under the soil. The land application process rejuvenates the soil. Many farmers in Maryland and Delaware have improved their fields with sludge and enjoy a significantly higher crop yield.
The U.S. Environmental Protection Agency (EPA), U.S. Department of Agriculture, and U.S. Food and Drug Administration (FDA) all sanction beneficial land application of sludge. Land application is closely monitored and regulated in Maryland by the Maryland Department of the Environment (MDE) to ensure proper application, sludge quality, and protection of ground and surface water. Extensive scientific research has established the environmental safety and agricultural value of recycled high quality sludge. This beneficial use of sludge increases the soils water-holding capability, thereby reducing runoff and soil erosion. Land application of sludge returns organic resources to natures cycle, adding plant nutrients to the soil and improving soil structure and fertility.
Sludge contains three primary crop nutrients -- nitrogen, phosphorous and a trace of potassium. It also contains lime and several nutrients that crops need in smaller amounts-- sulfur, magnesium, manganese, iron, calcium, copper and zinc. These nutrients are not found in most commonly used commercial fertilizers.
Sludge is applied only in amounts required to meet the nitrogen need of the crop to be grown. It contains organic nitrogen that is released slowly throughout the growing season and enables the growing crop to use nitrogen as needed. Therefore, nitrogen is not released into ground or surface water and ultimately into the Chesapeake Bay. Soil replenished with sludge yields quality crops, and, unlike chemical fertilizers, sludge actually improves soil structure, preserving and improving precious topsoil long after application.
The Wastewater DepartmentsLaboratory Services analyzes samples collected at the Ocean City Wastewater Treatment Plant to meet the National Pollution Discharge Elimination System (NPDES) permit requirements. These tests include BOD5, Suspended Solids and Fecal Coliform. They are done on a daily basis -- even weekends. Analyses are also done throughout the plant for operation monitoring of the treatment process for variables such as Mixed Liquor Suspended Solids (MLSS), Mixed Liquor Volatile Suspended Solids (MLVSS), Percent Solids, Total Dissolved Solids (TDS), ammonia nitrogen, nitrite and nitrate nitrogen. Besides the tests performed for the wastewater treatment plant, Laboratory Services also does testing for the Ocean City Water Department and, on request, for the Worcester County Department of Water and Wastewater Services and various other municipalities.