Introduction:

The Graver Reactivator® is a high rate, solids contact, sludge recirculation type clarifier which, in minimum time and space and using a minimum amount of chemicals, produces an effluent of the highest quality. It is used principally for clarification, lime softening, silica reduction, or organics reduction of water and wastewaters containing suspended solids, color and organic impurities. As such, it provides a means for chemical addition and mixing, flocculation and upflow clarification in a single unit.

In operation, raw water, chemicals, and a large quantity of recirculated precipitates are thoroughly mixed in a draft tube (mixing section). These are maintained in intimate contact for a prolonged period under the detention hood (flocculation zone). The contact between the water treatment chemicals and the performed precipitates causes additional precipitation, and the recirculated floc rapidly grows to an exceptionally large size and high density. In addition, the large volume of recirculated precipitates provides an adsorptive surface which maximizes the reduction of color and organics.

Principles of Operation:

Untreated water enters the unit through an above grade inlet pipe (1) which introduces the water to the draft tube (2) via a tangential nozzle immediately above the sludge recirculation impeller (3). The draft tube and impeller configuration is essentially a low-lift pump. The impeller is driven by a variable speed drive (4) which permits setting the optimum speed to draw recirculated sludge into the lower draft tube and thoroughly mix it with inlet water and treatment chemicals. To insure complete reaction and minimum chemical consumption, over 80% of the flow beneath the detention hood (5) is recycled through the draft tube. The impeller is located at the bottom of the draft tube so that it recirculates properly aged sludge from the floor of the unit and mixes it with incoming raw water and coagulant chemicals. The recycle rate is set to recirculate a flow of water and sludge at 5-15 times the influent rate depending upon the application. Raw water and chemicals are introduced above the eye of the impeller to prevent polymer shearing and are flash mixed with the recirculated sludge.

After leaving the upper draft tube, the water and recirculated sludge flows downward beneath the detention hood (flocculation zone), where a portion of the stream flows into the settling zone and rises to the effluent collector, while the remaining portion of the stream flows back to the lower draft tube for continued recirculation. The flocculation zone is sized to allow the preformed floc particles to grow to a setteable size before entering the settling zone. (6) Each unit is designed to incorporate the ideal retention time in the flocculation zone for the specific application.

In the settling zone, any suspended particles not already settled in the vicinity of the draft tube and detention hood are allowed to settle in the quiescent region at the bottom of the unit. The streamlined laminar flow achieved by the increase in settling area allows any light floc particles to settle to the bottom in this quiescent zone.

The sludge scraper rake arms (7) continuously move the precipitates which settle to the floor of the clarifier to the central sludge pit (8) where they are concentrated with the aid of thickening pickets and blown off to waste. (9) This system is of double importance as it prevents any sludge, even light particles, from comimg close to the effluent collectors and quickly removes settled particles which could be re-suspended by flow surges. The separation zone for the floc is located at the lower periphery of the detention hood, typically ten or more feet below the surface of the unit.

The scraper arms are equipped with angled blades which sweep the entire bottom of the unit on each revolution. The arms are driven from a central shaft attached to a low RPM drive assembly. (10) Thickening pickets (11) attached to the scraper shaft extend into the sludge pit, therby further thickening the settled floc. The thickening of the sludge permits a relatively high density sludge to be removed from the clarifier, with resultant savings in blowdown waste.

The Reactivator employs a radial pipe launder (12) collection system using submerged orifices. The system is designed to provide uniform collection of clear water over the entire surface area of the unit, minimizing horizontal travel and "short-circuiting" of flow.

Advantages Of The Graver Reactivator:

The design features of the Reactivator provide the three zones necessary for proper clarification:

• Rapid mix zone, where raw water, recirculated precipitates and flash reagents are rapidly mixed together.
• Slow mix zone, where gentle mixing permits floc formation, brings thefloc into intimate contact with the suspended impurities, and provides sufficient time for chemical reactions to go to completion.
• Clarification or settling zone, where the upward flow (rise rate) is reduced to a low value to permit the precipitates to settle out.

Standard Features:

• Clear water zone extending over 8-10 feet below the surface
• Positive sludge removal through full coverage sludge scraper arms
• Radial pipe effluent collectors with submerged orifices
• Access bridge with walkway to mid span drive platform
• Above grade influent pipe
• Steel units include a minimum wall thickness
• Sample valves and sink at grade level
• Variable speed recirculator drive with efficient, high capacity turbine impeller
• High torque, constant speed scraper

Available Options:

• Floc Barrier tube settles for increased throughput
• Scum baffle & oil skimmer designs
• Circular stairway or ladder access to drive platform
• Scraper drive torque overload protection
• Concrete shell design
• Above grade false bottom design (on smaller units)
• Field erection of shell and internals
• Automatic chemical feed & desludging controls
• Alternate materials of construction and coating
• Chemical feed equipment
• External sludge thickener
• Sludge pumps and filter press
• Gravity or pressure filters for effluent polishing
• Full cover for fume control
• "Smart" state of the art control system
• Pilot size units for on-site testing.

Experience:

Graver has hundreds of Reactivator installations worldwide and more than half a century of experience serving many industries. Our capabilities span the entire spectrum of water and wastewater treatment equipment. In addition to Reactivator clarifiers we offer lamella inclined plate type clarifiers, pressure and gravity filters, sludge thickeners, oil/water coalescers, ion exchange equipment, deaerating heaters, zeolote softeners, hot process systems, reverse osmosis systems, and other equipment packages to meet the water and waste water needs of today's industries. We are an organization of engineers and chemists, with specialities in virtiually all engineering disiplines and technologies.

Typical Aplications:

Graver's installations include a wide range of applications as noted below. These installations encompass pre-engineered units ranging from 10 feet to 70 feet in diameter as well as custom designed units of up to 200 feet or more including three 185 feet diameter units at the Yuma desalting plant in Arizona.

• Clarification
• Softening
• Silica removal
• Phosphate removal
• Color and organics removal
• Trace metal removal
• Boiler make-up pretreatment
• Potable water treatment
• Waste water treatment and recycle
• Reverse Osmosis Pretreatment
• Demineralizer pretreatment
• Cooling tower make up & blow down
• Cooling tower side stream treament
• Secondary treatment of municipal effluent

Suggested Specification