Armfield Engineering Education
WATER TREATMENT PROCESSES
W4 Filterability Index Unit - Issue 8
The Armfield Filterability Index Unit enables a water quality test to be made on a suspension to be filtered through sand or similar granular media. It can therefore be used in routine control at waterworks, or at a sewage treatment works which employs tertiary filtration.
ORDERING SPECIFICATION
• Equipment consists of a metal framework supporting a 1.5 litre vessel connected by transparent tubing to a 60mm high filter unit
• A needle valve controls the flow which is observed on a variable area flowmeter. Flow meter range: 20-280ml/min
• A 0.5m water manometer measures head loss across the filter
• Test filter cell diameter: 38mm.
Demonstration Capabilities
> measurement of filterability of a given suspension
performance of a standard water quality test
> procedure for filtration
> basic principles of filter operation for student study
Description
The use of deep beds of porous granular media to filter liquids to improve their clarity is widespread in municipal and industrial practice. Predominant is the filtration of drinking water and industrial water, although the filtration of sewage as a tertiary stage of treatment is increasing. Other liquids are filtered through granular media in the processing of beverages and food products for example.
A simple measure of whether the liquid is filterable is useful to enable assessment of filtration as an appropriate process, if so what type of pre-treatment and filter media are required. Although the normal methods of chemical and physical analysis such as suspended solids content, turbidity, colour etc. may, with experience, indicate whether a suspension is filterable, they give no direct measure of this property.
A number of measures of filterability have been proposed, using woven micromesh, lint pads or membrane filters, which have application where these materials represent, or are identical to, the filter media to be used. However none of them is representative of porous granular filter media, such as sand, consequently they are not applicable to deep bed filtration.
The W4 Filterability Index Unit utilises a bed of granular material, normally sand, which can be chosen by the investigator to suit his own purposes. The measurements taken with this apparatus enable a filterability number to be calculated which has significance in deep bed filter performance.
It must be stressed that the W4 Filterability Index Unit is not intended for filter design purposes. That requires pilot filter column equipment such as the W5 Deep Bed Filter Column. However preliminary assessment of pre-treatment processes, and possible filter media with the W4 Filterability Index Unit will reduce the amount of testing required with pilot filter columns.
A particular application of the W4 Filterability Index Unit is in the process control of existing deep bed filter operation. The effects of changing pre-treatment dosing (for example poly-electrolyte dose) can be rapidly tested before making changes on the operating plant.
The unit can also be used to determine the changes in filterability of a flocculating suspension subject to different degrees of prior flocculation and to measure the improvement in tertiary sewage filtration when poly-electrolytes are added to fine suspensions from humus tanks. In conjunction with the well-known waterworks jar test, the settling characteristics and the filterability characteristics of flocs can be assessed.
The equipment comprises a filter unit which contains a small plug of sand about 30mm thick, through which the suspension flows downwards from a 1 litre vessel containing the sample under test.
Flow is controlled by a needle valve and observed on a variable area meter. Head loss is measured directly by a water manometer. The filter unit can be readily demounted to change the sand. This unit and all tubing connections are transparent so that the operation can be observed and air bubbles avoided. Metal fittings are corrosion resistant.
Technical Details
Test filter cell diameter: 38mm
Height of filter: 60mm maximum
Variable area meter range: 20-280m/min
Water manometer length: 0.5m
Recommended Accessories/instruments
(not supplied by Armfield)
1 litre Measuring cylinder
Thermometer
Stop clock
Triple beam top loading balance:
capacity: 2610g; sensitivity: 0.1g; tare: 225g
100ml Measuring cylinder
Requirements
Services
Laboratory drain or 1 litre receiving vessel
Shipping specification
Volume 0.3m3
Gross weight: 40kg
Overall dimensions
Height: 0.97m
Width: 0.45m
Depth: 0.25m
|
 |
|---|