# IB mud index measurement

To correctly design a settling tank, it is necessary to know the Hazen speed of the liquid to be treated. The Hazen velocity or ascension velocity is determined by measuring the mud index.

This is very easy to do. You’ll need:

• a 1 liter Imhoff cone (glass ideally, but a plastic test tube type equivalent is sufficient)
• at least one liter of liquid to be treated (optional, but common for large plants)
• optional: the coagulants and flocculants that will be used (at the planned dosages),
• A watch or timer
• TSS measuring equipment

• Mix the liquid to be analyzed correctly
• Pour 1 L into the test tube
• Start the timer, wait 30 minutes
• Read the result: volume reached by the sludge (for example 440 ml/L).

This is the value that is decisive for the calculation of the Hazen speed.

## Protocol for TSS measurement

• Dry the filters in a dry oven for a few minutes
• Note the mass of the dry filter (in grams)
• Install this filter in your vacuum filtration unit
• Thoroughly blend the liter of water you used to measure the volume of mud
• Fill the bottle of your vacuum filtration unit and note the volume that will be filtered (between 250 ml and 1000 ml, depending on your equipment)
• Close the package
• Turn on the suction pump and filter the volume of the filter unit
• Once the whole batch has been filtered, dry the filter and the sediment that has settled on it at 105°C
• Measure the final size of the dry filter

## Calculation of the mud index

It is the adjusted volume Vc divided by the TSS concentration.

## Equipment for eliminating TSS

To remove TSS, lamella clarifiers are ideal. They are compact and easy to operate.

## Determination of Hazen speed

Please fill out the form below to determine your Hazen speed for the water you have to treat.

The important measure here is the corrected volume (Vc). For large volumes of water, Hazen velocities (or upward velocities) are low. Since the surface area of a lamella clarifier is generally 10 times larger than that of a conventional clarifier, this type of equipment is of course more than recommended for waters with poor settling capacity.

Of course, if all the mud is floating, settling is not the answer. Use a floater instead!

### Why choose a lamella clarifier

With the Hazen speed, you can determine the pool area. For example, with 100 m3/h of flow to be treated from an effluent with a corrected volume of 440 ml/L, we have :

• A speed of 1.1 m3/m²/h (or m/h) for a classic clarifier. With 100 m3/h, it is necessary 100 / 1.1 = 91 m² of decantation surface, that is to say 91 m² of ground surface
• A speed of 0.44 m/h for a lamella clarifier. With 100 m3/h, 100 / 0.44 = 228 m² of lamella clarifier surface, but as the lamellae surface is on average 10 m² / m² of floor space, the size of the basin will actually be 228 / 10 = 22.8 m² of floor space

A lamella clarifier is 4 times more compact than a conventional clarifier in this case. And the larger the corrected volume, the more this value increases.

With your Hazen speed, you can find the right lamella clarifier on the 1h2o3 lamellar clarifiers presentation page.