Use these questions to review a proposal and compare its scope with your wastewater duty. Expand any question for the reason to ask, the information to request and the Watterson arrangement.
The questions cover a separate air dissolving tube (ADT), a microbubble generator pump and the air cavitation method. Here, “air cavitation method” means air injected into the suction of an ordinary centrifugal pump. Watterson uses the separate ADT arrangement; our details are labelled below.
Three terms first
TSS means total suspended solids. A/S ratio is the air mass required per unit mass of solids. Recycle flow is the clarified water returned through the pressurised air-dissolving system.
1. What is it sized for?
Why it matters
Both water flow and the solids entering the DAF affect the duty.
What to ask
Ask for daily volume, operating hours, controlled feed flow, incoming TSS, chemical-treatment solids, A/S ratio and calculated recycle flow.
Watterson arrangement
We use daily volume divided by DAF operating hours, laboratory TSS plus calculated chemical solids, and a calculated recycle requirement.
Look for
A stated design duty and its assumptions, rather than only a nominal flow rating.
2. How did you size it for my wastewater?
Why it matters
The upstream chemistry prepares contaminants for separation.
What to ask
Which wastewater sample was tested? What chemicals, doses and operating pH were selected? Were chemical solids included in the sizing?
Watterson arrangement
We normally run a jar test before finalising the design, then recalculate chemical solids, recycle flow and tank requirements.
Look for
A clear connection between test results and the proposed design inputs.
3. What operating pressure and air supply does the system need?
Why it matters
The pressure and air-supply requirements need to be stated for the proposed bubble-generation arrangement.
What to ask
What is the design operating pressure, and is it gauge or absolute? Does the system need an external compressed-air supply? If so, what pressure and flow are required at the connection?
Watterson arrangement
Our separate ADT starts at about 5 bar gauge, and we normally require at least 5.5 bar gauge compressed-air supply pressure at the DAF connection.
Look for
Pressure stated with its reference, air-supply requirements and suitable pressure indication for operating checks.
4. What type of recirculation pump is used?
Why it matters
The pump supplies the recycle flow and pressure; service and replacement arrangements also matter.
What to ask
What are the pump duty, type, service requirements and replacement-parts arrangements? How is recycle flow checked?
Watterson arrangement
An end-suction centrifugal pump meets our duty. We normally estimate recycle flow from the pump curve and operating pressure; a flow meter can be quoted on request.
Look for
A documented duty and clear provision for operating and service checks.
5. Is chemical dosing included?
Why it matters
Chemical pretreatment and DAF separation are separate parts of the treatment train.
What to ask
Does the quote include chemical-dosing equipment, pH adjustment, coagulation and flocculation tanks, and their controls?
Watterson arrangement
Chemical-dosing equipment is quoted separately for each project. Coagulation and flocculation take place in separate upstream tanks.
Look for
A package boundary that lists what is included and what is quoted separately.
6. How does the skimmer work, and what happens to the float?
Why it matters
The separated sludge needs collection, transfer, thickening and dewatering.
What to ask
How is skimmer timing set? What controls the transfer pump? Where does the sludge go after the hopper?
Watterson arrangement
A timer controls intermittent scraper operation. A sludge-level-controlled pump transfers hopper sludge to the thickener. The transfer pump is included; thickening and dewatering equipment are quoted separately.
Look for
The complete sludge route, including equipment outside the DAF package.
7. How are the flotation bubbles generated and controlled?
Why it matters
The air-entry point alone does not establish how much air dissolves or what bubbles reach the flotation zone.
What to ask
Is the proposal based on a separate ADT, a microbubble generator pump or the air cavitation method? For an ADT, how are water level and excess-air venting controlled? For either pump-based arrangement, how is air intake controlled, and is the pump suitable for the air–water mixture? How can an operator sample the white water, and what operating evidence supports flotation performance?
Watterson arrangement
Our separate ADT receives water through a spiral spray fitting above the packed vertical section. Air enters the top air space. A proximity switch controls the vent valve, a needle valve sets vent rate, and a sampling port allows a white-water check.
Look for
Controls appropriate to the proposed arrangement, a white-water check procedure and supporting operating evidence. Air injection into an ordinary pump should not be assumed to perform like a purpose-built microbubble generator pump.
8. What is it made of, and can I get inside to clean it?
Why it matters
Construction, cleaning access and removable parts affect maintenance arrangements.
What to ask
What are the tank, plate, frame, chain and sprocket materials? How are the plates drained, cleaned and removed?
Watterson arrangement
The tank is usually SS304, with FRP available on request. SS304 plates are fixed as standard; a removable plate pack on an SS304 frame is optional on request. The skimmer uses PTFE chain and engineered-plastic sprockets. Operators drain the flotation compartment and hose the plates down.
Look for
Materials and maintenance access described in the equipment proposal.
9. How will I know it is working properly?
Why it matters
Operators need to distinguish air-system problems from chemical-treatment problems.
What to ask
Which pressure, air-flow and level instruments are included? Is recycle flow measured or estimated? What checks come before changing the chemicals?
Watterson arrangement
Normal instruments include ADT pressure and water level, air flow and pressure, recycle-pump pressure indication and sludge-level switches. Check the recycle and air system first, then dosing and pH with a jar test if those checks are normal.
Look for
An instrument list and an operating check sequence. A recycle flow meter is optional in our normal scope.
10. Does the flotation zone have plates?
Why it matters
The plate arrangement has its own geometry, flow path, cleaning access and separation-area assumptions.
What to ask
What are the plate angle, perpendicular clear gap, bottom clearance and removal arrangement? How is projected plate area credited in sizing?
Watterson arrangement
Our current arrangement is 55° from horizontal, with 40 mm minimum perpendicular gap and 50 mm preferred, and at least 0.3 m bottom clearance. Plates are fixed as standard; a removable pack is optional on request. The worked example labels the nested pack and combined-area credit as assumptions.
Look for
A layout that distinguishes pack fit, physical water volume and justified separation-area credit.
For the arithmetic behind the design inputs, read the illustrative sizing guide.