Pumice is a granular filter media that  is a suitable alternative solution to sand for the treatment of potable water, sewage and industrial effluents.  The typical use of pumice for each of the various applications is shown in the table below.

Water Treatment and Waste Water Treatment Applications

Process / Water Type	Ground Water	Surface Water	Sewage	Industrial Effluents
Clarification	Ballast	Ballast	-	Ballast
Filtration	Media	Media	Media	Media
Aerobic Treatment	-	-	Ballast	Ballast
Anaerobic Treatment	-	-	Biomass support	Biomass support
Sludge Treatment			Sludge Conditioning	Sludge Conditioning

Applications – Process Descriptions

1. Clarification

When added to the raw water, pumice increases the density of the flocs that result from the coagulation process and accelerates sedimentation.  Coagulation occurs when the raw water, either surface or bore hole, reacts with the chemical primary coagulant and the flocs then attach themselves to the pumice particles giving a ballast effect.  Settlement occurs under gravity and the clarified water is recovered from the upper part of the clarifier with the sludges being removed from the bottom.  This process is suited to potable water, sewage and industrial effluent treatment.

2. Filtration

Pumice is a versatile filtration media used in the treatment of water, sewage and industrial effluents.  It is used in mono, dual and multi media applications in both pressure and rapid gravity installations.

Being of a low bulk density, pumice provides a valid and cost effective alternative to anthracite in dual or multi media media filters.  A dual media filter traditionally consists of an upper layer of pumice above a layer of fine sand.  Pumice traps most of the large floc particles whilst the finer sand in the lower layer removes the remaining impurities with small particle sizes.  The voidage of pumice has an average value of 0.51 which allows for an increased retention of suspended solids in the filter bed and a lower headloss.

Being light in weight, pumice also is able to reduce the operating costs of the filtration plant, be it a rapid gravity or pressure filter installation due to the significantly lower (typically 30% lower) backwash water consumption requirements.

Advantages include:

• Savings in energy and water during filter backwash

• Lower bulk density

• Reduced capital cost

3. Aerobic Treatment

Pumice, in addition to its ability to assist clarification, is an essential addition in the Sequencing Batch Reactor (SBR) process where inadequate time has been allowed for phase separation to take place.  The addition of pumice just prior to the settlement stage enhances the settlement of the sludge allowing the plant to perform as initially designed.

4. Anaerobic Treatment

Where effluents are highly polluted with organic pollutants, the treatment that is finding increasing application is anaerobic treatment or methanisation where the pollutants are treated in the absence of air and methane is generated.  Pumice acts as a biomass support in this process, typically employed in the treatment of wastes from breweries, sugar processing, paper manufacturing, daries etc.  The concentration of biomass is significantly increased, growing in ideal conditions on the porous surface of the pumice and resulting in reduced retention times and higher methane gas generation.

Advantages include: For anaerobic biomass within methanisation reactors, eg. CPB-concentrated proteins from sugar beet, pumice offers:

• Large surface area

• Favourable surface conditions for bacterial growth

• Increased concentration of biomass

• Reduced retention time

• Increased methane generation

 

5. Sludge Treatment

Sludges derived from the biological treatment of sewage or industrial effluents require further treatment processes to allow their safe disposal.  These processes include de-watering where, by the addition of pumice into the mixer prior to the de-watering stage, a superior filter cake is produced.  This cake does not blind the cloth, allows greater filter runs with improved filtrate quality and produces a cake that can be used for agricultural or horticultural purposes.

 

Physical Characteristics

Grades	1/2	No.3	No.4	No.8
Applications	Ballast	Inert Support	Filter Media	Filter Media
Typical Properties
Size - mm	0.1 – 0.3	0.2 - 0.5	0.3 – 1.4	1.2 – 3.0
Silica Content – SiO2 %	70.9	71.75	71.75	71.75
Bulk Density – kg/cu.m	550	470	450	410
True Density – kg/cu.m	2400	2400	2400	2400
Moisture Content	Dry	Dry	Dry	Dry
Hardness – Mohs	6	6	6	6

Certification
Pumice, as supplied by Techfil (Europe) Limited, is approved by the Drinking Water Inspectorate for potable water applications and complies with BS EN 12906:1999 “Products used for the treatment of water intended for human consumption – Pumice”.

Further Information and Technical Support

For further information and case studies please contact us at: info@techfil.co.uk