Frequently Asked Questions


DAF Clarification

How much mixing time is required?

This will be determined by the raw water quality and the level of solids (TSS) that need to be removed/reduced. Flotation jar tests and pilot tests can establish what the design criteria should be. It is normally designed for 12 to 15 minutes.

How high of a loading rate can I get?

This will be determined by the raw water quality and the level of solids (TSS) that need to be removed/reduced. Flotation jar tests cannot be used to determine this design criteria, only pilot tests can establish what the design criteria should be. It is normally designed for 12 gpm/ft2 (30 m/hr).

What recycle rate will I require and where does it come from?

This will be determined by the raw water quality and the level of solids that need to be removed/reduced. Flotation jar tests and pilot tests can establish what the design criteria should be. It is normally designed for 10%, but the system will allow a range of 5% to 15%. Water is pumped from the effluent launder to a saturator where air is added to saturate the water solution. The saturated water releases bubbles in the reaction zone when nozzles reduce the pressure to atmospheric and millions of microbubbles are formed.

What TSS removal rate can I get?

With the correct chemical feed, mixing time and energy, and loading and recycle rates, the effluent TSS should be below 10 mg/L. This can be confirmed by flotation jar tests and pilot tests.

What BOD removal can I get?

With the correct chemical feed, mixing time and energy, and loading and recycle rates, the effluent TSS should be below 5 mg/L. This can be confirmed by flotation jar tests and pilot tests.

What P removal can I get?

With the correct feed rate of either aluminum- or iron-based coagulant to precipitate the soluble phosphorus, adequate mixing time and energy, and loading and recycle rates, the effluent should be below 0.05 mg/L of P. This can be confirmed by flotation jar tests or pilot tests.

What turbidity removal can I get?

With the correct feed, mixing time and energy and loading te recycle rates, the effluent should be below 1mg/L. This can be confirmed by flotation jar tests or pilot tests.

How much chemical will I use?

This will vary from location to location and will need to be confirmed by flotation jar testing or pilot testing.

How often do I need to complete maintenance?
General Maintenance Change lubricant in flocculator & rapid mix drives 1 person/quarterly
Lubricate motors 1 person/6 months
Lubricate skimmer drives 1 person/6 months
Calibrate turbimeters 1 person/monthly
Change oil in compressors (2) 1 person/quarterly
Change air filter compressors (2) 1 person/quarterly
Change airline filters 1 person/6 months
Recycle Pumps Adjust packing 1 person/quarterly
Change packing 1 person/yearly
Rebuild/service pump (bearings, wear rings etc.) 2 people/unk. frequency
Saturator Packing Inspect 1 person/yearly
Sludge Scraper Replace stainless steel cable 2 people/unk. frequency
Touch-up-paint skimmer supports 2 people/yearly
Replace skimmer pulleys 2 people/unk. frequency
Inspect nozzles 2 people/6 months
What is the energy usage?

After design is completed, we supply a spreadsheet with energy requirements for the rapid mix drives, flocculators, skimmer, recycle pumps, air compressor, and control panel. The spreadsheet contains a file to input cost/kilowatt hour so that the total annual cost can be calculated.

How is sludge removed and what concentration can I achieve?

Mechanical reciprocating skimmers remove solids from the top of the flotation cell periodically, depending on the incoming solids load and chemical feed concentration. Typically, they operate every 30 to 35 minutes and scrape off solids of 2% to 5% concentration into the sludge hopper. Another option is hydraulic de-sludging which occurs by closing the effluent valve and allowing the water level to rise in the flotation cell so that the solids flow off the tank into the sludge hopper. Once completed, the effluent valve opens again and the water drops to normal levels. This results in solids content of 0.5%.

How does the cost compare to other clarification processes?

When considering cost, both the capital cost and the operational cost of downstream equipment (e.g. filter operator and sludge dewatering equipment) must be considered. If evaluating the total cost, the Leopold® Clari-DAF® is usually a low cost alternative.

Is the Leopold® Clari-VAC® floating sludge collector suitable for any wastewater treatment plant solids removal?

The system will only work in rectangular tank systems that have had primary solids removal prior to the secondary biological process. The solids should be low density biological solids removed in the final clarifier.

Can the Leopold® Clari-Vac® floating sludge collector system work in cold climates?

The system will work in wastewater treatment plants that require continuous solids removal where the secondary clarifier will not accumulate ice or freeze over the surface.

What maintenance is required?
Equipment Frequency
  As Req'd Weekly Monthly Quarterly Semi-Annual Annual
Hydraulic System
Check fluidizing vanes for wear           X
Check end wipers for wear           X
Check seals on bucket/wedge valve           X
Lubricate operator nuts       X    
Reprime siphon pipes   X        
Skimming System
Clean surface of tipping weir X          
Clean underside of tipping weir X          
Skimmer mechanism check tightness of bolts           X
Trip arm/supports check tightness of bolts           X
Guidance System
Guide wheel - no lubrication necessary            
Check wheels for wear         X  
Spring-loaded wheel assembly attached to beam - check tightness of bolts           X
Drive System
  As Req'd Weekly Monthly Quarterly Semi-Annual Annual
Drive Cable
Check cable tension in new cable (up to 6 months)   X        
Check tightness of wire rope clips (on new cable up to 2 months)     X      
Check cable tension       X    
Check cable for wear/fraying       X    
Check corrosion of wire rope clips       X    
Lubricate thrust bearings     X      
Sheaves
Check sheave wear         X  
Check split taper bushing setscrew tightness         X  
Reducer
Oil level check X          
Change oil     Every 2500 hours      
Check mounting bolts for tightness     Every 4 months      
  As Req'd Weekly Monthly Quarterly Semi-Annual Annual
Pillow Block Bearings
Lubricate         X  
Check set screw tightness           X
Check mounting bolts for tightness           X
Check bearing alignment         X  
Check for damaged seals         X  
Check bearing temperature         X  
Check for bearing noise         X  
Chain & Sprockets
Lubricate       X    
Check setscrews & bushing cap screws for looseness         X  
Check chain tension         X  
Check for chain stretch           X
Check sprocket teeth         X  
Check sprocket alignment         X  
What are the power requirements of the Leopold® Clari-Vac® floating sludge collector?

The unit is pulled by cable with a ½ hp motor and the control panel requires a 120 V power supply.


Media Filtration

My filter takes too long to ripen, what can I do to shorten the ripening time?

Allow the filter to sit idle for a period of time from 30 minutes to 24 hours. This allows the media to compact and particles to re-agglomerate. Another method is to add a coagulant such as polymer or alum to the influent or to the end of the backwash. This allows the media to have a charge and re-agglomerate loose particles. Finally, a short low-rate backwash can be added after the final high-rate backwash. This helps to settle and compact the bed quicker.

When I first start my filters, there is a high initial turbidity spike coming from the filters. How can I stop this?

Some of the things listed in the first question can also be applied to a high initial spike, such as allowing the filter to sit idle, adding a coagulant to the influent or backwash water, and using a low-rate backwash after the final high-rate backwash.

I need to select a media configuration for a potable water treatment filter. What media should I use?

A pilot study can be conducted to determine the optimal media configuration. When conducting this study be sure the l/d ratio is similar for all of the configurations. If a pilot study cannot be performed, the most widely used media configuration is 12 in. (300 mm) of 0.45 to 0.55 mm effective size silica sand with a uniformity coefficient of <1.4 under 18 in. (450 mm) of 0.95 to 1.05 mm effective size anthracite coal with a uniformity coefficient of <1.4.

How do I select the media configuration for a wastewater filter?

Generally a smaller media such as dual media of sand and anthracite is used where the influent is clean (<15 mg/L TSS) and the effluent needs to be clean ( <2 mg/L TSS). Where the influent is greater than 15 mg/L (up to 60 mg/L or more), deep bed mono-media would be used. In this case the effluent quality could be as high as 5 mg/L TSS or more.

Can we use granular activated carbon with your equipment?

Yes, we have many installations that are either granular activated carbon (GAC) contactors or GAC filter/contactors where sand is placed below the GAC to provide filtration. We have designed the materials to be compatible with GAC.