Chemical Enhancement

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The efficiency of removal of suspended solids, from any of the media, DAF or clarification processes as described separately in this section, is very much dependent on the nature of the material being removed, as well as the hydraulic flow rate and associated ‘disturbance’ caused within the process.

Certain chemicals can therefore be added to enhance the removal process by changing the physical nature of the material being present. Typical groups of chemical additives include the following:

(a) Coagulants

These are typically inorganic materials such as ferric or ferrous based materials (eg ferric chloride or ferric sulphate) or aluminium based materials (eg aluminium sulphate, known as alum, or poly aluminium chloride, known as PAC).

The way in which they work is by using their natural electrical ionic charge and reacting with natural alkalinity within the water to actually precipitate themselves, and in so doing they attract or react with and subtly change the physical nature of the material being removed. In so doing they are often able to result in the removal of certain quantities of soluble material by allowing them to become insoluble.

They can be used to improve the efficiency and solids removal across both sedimentation and flotation processes.

The precipitation of the ferric or aluminium salt does however add to the amount of solids (in addition to the actual ‘target’ solids) that subsequently require disposal as a sludge.

(b) Flocculants

Flocculants are generally long chain polymers based on polyacrylamide or polyacrylate. They work by aiding coalescence of any fine solids and in so doing increasing the settlement rates of all solid particles. When used with the DAF process, they ensure that the particles are more amenable to air entrapment and so again can improve the effectiveness of the process.

It should be noted that, although the advantages of chemical dosing are many and varied, the chemicals themselves can prove expensive. A cost benefit analysis would normally be undertaken to compare the cost of chemical against the value or benefit of improved performance.




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For further assistance with any aspect of chemical enhancement please just call us on 01244 344233 or add your details to the form on the left.

Latest Chemical Enhancement Project

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Glenmorangie Distillery

AD plant design and project management

ARL Consulting were commissioned to evaluate technical and commercial options for effluent treatment at both Glenmorangie whisky distilleries at Tain and Ardbeg on Islay.

This initial feasibility study resulted in the selection of the Tain distillery as being the site for a state of the art anaerobic digestion plant.

ARL Consulting undertook detailed design for the effluent plant and prepared a detailed specification and contract documentation to allow the project to be tendered on the open market.

ARL undertook detailed negotiation with SEPA to determine the required effluent quality to allow discharge of high quality treated effluent to the Dornoch Firth. The AD plant included beneficial use of the methane in a dedicated biogas boiler to allow displacement of heavy fuel oil.

To view the full Glenmorangie Distillery project details please Click Here.

Chemical Enhancement FAQ's

This very much depends upon the quality and nature of the effluent to be treated. Coagulants and/or flocculants can significantly enhance the performance of the settlement or flotation process, but always remember the associated costs. Chemical supply companies will often undertake laboratory scale bench tests to check the efficacy of the proposed chemical treatment programme, and so allow you to make your own cost benefit analysis.


It is important to consider that common inorganic coagulants (usually aluminium or ferric salts) will be introducing certain levels of those aluminium or iron into the final effluent. You need to make sure this is allowed by whoever is controlling or policing the quality of the treated effluent. 

Also, because of the precipitation of iron or aluminium hydroxide, there is usually an increase in the volume of sludge requiring disposal. It is important that you don't solve an effluent treatment problem and then create a solid waste management problem.