ENGINEERING INFORMATION BULLETIN
DISSOLVED AIR FLOTATION AT
SAFETY-KLEEN SYSTEM, INC.
Buffalo, New York Facility
The facility= s operations include the removal of water from used oil and treatment of non-hazardous oily wastewater. The facility currently processes about 25 million gallons of used oil and wastewater per year. Most of the oil processed by the facility is sent to Safety-Kleen= s oil re-refineries in Breslau, Ontario and East Chicago, Indiana. Pre-treated wastewater from the process is discharged to the Buffalo Sewer Authority sanitary sewer.
The facility operates 24 hours per day and 7 days a week. The average volume of wastewater treated is 40,000 gallons daily. The POTW permit allows 147,000 gallons per day discharge from the facility.
This project was to install a new Dissolved Air Floatation Unit (DAF) to add to the facility= s wastewater treatment capability and to meet the new US EPA= s CWT pretreatment standards.
The DAF unit includes the following sub-systems: flotation tank, contact chamber, skimming removal system, effluent discharge, re-circulation system air dissolving pipe. The specifications for each sub-system is described as follows:
A. Flotation Tank:
The unit consists of a flotation rank constructed of corrosion resistance coated carbon steel or 304 stainless steel plate and reinforced with corrosion resistance coated carbon steel or 304 stainless steel tubular vertical wall structural supports and horizontal cross member supports. The unit is supported on a stainless steel base consisting of horizontal beams across the width of the unit and a continuous beam structure down both sides of the length of the unit. The base is constructed to allow for easy cleaning around and under the unit.
B. Contact Chamber:
Influent wastewater enters the DAF unit through a flanged influent header into the contact chamber. The recycle stream is injected into the header nozzle prior to entry into the unit, and the recycle stream mixes with the influent. The contract chamber serves as an internal weir which provides even distribution and mixing of the process flow across the width of the unit. The contact chamber has a separate drain for removal of heavy solids which settle in the chamber.
C. Skimmings (Float) Removal System:
The unit is equipped with a chain and flight top skimmings removal system driven by a low speed, gear motor assembly. The top skimmer system shall consist of double strands of 304 stainless steel double pitch roller chain, guided by UHMW shoes on stainless steel angle. The chain supports adjustable, reinforced SBR skimmer blades retained on 304 stainless steel or fiberglass angle plates with stainless steel fasteners. The skimmer blades are spaced approximately every 5 ft. along the chainlength.
The chain system operates on single duty, carbon steel sprockets mounted on 303 stainless steel shafts turning in adjustable bearing supports. The system is driven by a variable speed drive (VFD) with TEFC motor through a chain and sprocket system. An adjustable torque limiter with automatic re-engagement shall be installed to protect the equipment in case of overload. Adjustable timer controls are installed to provide for intermittent skimmer operation which allows for flexibility in the removal of skimmings from the unit. Sprocket guards are provided for all four skimmer chain sprockets.
D. Effluent end, the bottoms trough is segregated from the effluent flow by a vertical baffle. A second vertical baffle directs the clarified effluent up into the header box and through and adjustable weir system. The weirs shall be adjustable and allow for up to 5" of vertical travel to determine the optimum liquid level in the unit, and they are designed to provide minimum fluctuation of the tank liquid level with the variation of influent flow. Clarified effluent overflowing the weirs collects in an internal trough and is discharged through a flanged nozzle.
E. Recirculation System:
Clarified wastewater from the discharge is recycled through the unit by a centrifugal pump designed to operate at pressures in excess of 85 psi. The pump features a cast iron casing, stainless steel shaft and bronze impeller, mechanical seals and a 460 V/3 ph/60 Hz/TEFC motor. Air is supplied into the recycle stream via an eductor loop from the discharge of the pump to the pump intake, drawing in ambient air and forcing it into solution with the recycle stream under pressure from the pump. Compressed air is added through this system via plant air. All recirculation piping is Sch80 PVC.
F. Air Dissolving Pipe (ADP):
A 304 stainless steel air dissolving pipe rated for 125 psi is equipped with an automatic pressure safety relief valve. Liquid level in the ADP is automatically maintained by an air release valve with an in-line equalizer. Discharge pressure from the recycle pump and the ADP is controlled by a diaphragm control valve with a EPDM diaphragm and a position indicator and a series of secondary whitewater injection points through stainless steel ball valves.
G. liquid filled pressure gauge was provided for monitoring recycle pressurization performance. The ADP was equipped with a 3/4" bottom drain valve and a 4" x 6" removable handway for inspection and servicing. The recirculation pump and ADP tank was mounted to the flotation tank.
