Dissolved Oxygen Control System At Wastewater Plant Reduces Costs For Electrical Power, Sludge Removal, And Chemicals
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•Dissolved Oxygen Control System At Wastewater Plant Reduces Costs For Electrical Power, Sludge Removal, And Chemicals
By Mark J. Howarth, Superintendent and Timothy J. O’Dell, Assistant Superintendent, Water Pollution Control Plant, The Township of Morris, NJ
The two wastewater plants in The Township of Morris, New Jersey have experienced significant savings in electricity costs, sludge removal, and chemical usage. Savings result from installation of an effective system to control dissolved oxygen levels in the plants’ aerated digestion tanks. Regulated DO levels optimize the rate of tank aeration and reduce pumping requirements. They also provide a uniform and stable environment for the microorganisms that process the wastewater, which reduces sludge production and chemical usage.
Processing wastewater
Wastewater comes into the Butterworth plant from portions of The Township of Morris, Morris Plains, and Randolph. A smaller plant, called Woodland, treats wastewater from another part of the township. Routinely the Butterworth plant can treat 2.2 million gallons per day, but can accommodate up to 10 million gpd during storm surges.
Pretreatment facilities at Butterworth remove grit, rags, and debris. Raw sewage pumps then send the wastewater to anaerobic and anoxic tanks to reduce the wastewater’s biological oxygen demand. These tanks also convert phosphorus to a readily removable form. Only desirable facultative bacteria, those that can survive with or without oxygen, survive passage through this stage.
Next the wastewater moves to the aerobic stage, arranged in three trains of four tanks each. The plant uses only two trains at a time while the third train undergoes maintenance and refurbishment. Each train contains 947 fine-bubble ceramic air diffusers that aerate the wastewater to attain proper bacterial action. Early in this stage more air is necessary to satisfy the dissolved oxygen content required. The first tank, for example, has 316 air diffusers while the last tank in the train has only 180. This stage reduces biological oxygen demand of the wastewater.
The wastewater then moves to clarifiers to decrease suspended solids. The clarified effluent flows through gravity sand filters, an ultraviolet disinfection stage, and a post-aeration unit before final discharge to the river. The plant recirculates part of the flow to biologically break down nitrates and nitrites into harmless nitrogen, and to remove phosphorus. Thickened sludge is trucked away for disposal.
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•Dissolved Oxygen Control System At Wastewater Plant Reduces Costs For Electrical Power, Sludge Removal, And Chemicals
SOURCE: ABB Measurement & Analytics