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 inorganic materials work by using their natural electrical ionic charge and reacting with natural alkalinity within the water to actually precipitate themselves, in doing so they attract or react with and subtly change the physical nature of the material being removed this often results in the removal of certain quantities of soluble material, allowing them to become insoluble.

The materials 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 which increases the settlement rates of all solid particles. When used with the DAF process Floacculants ensure that the particles are more amenable to air entrapment and 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(s) against the value or benefit of improved performance.

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For further information or assistance with any aspect of chemical enhancement please use the "contact us" form below.

Latest Chemical Enhancement Project


Glenmorangie Distillery

AD plant design and project management

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

This initial feasibility study resulted in the selection of the Tain distillery to be 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, allowing 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

The consideration of chemical enhancement 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 the associated costs should be considered. Chemical supply companies will often undertake laboratory scale bench tests to check the efficacy of the proposed chemical treatment programme, allowing for 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, this should be addressed by the controlling body or policing standards for the quality of the treated effluent.

Due to the precipitation of iron or aluminium hydroxide, there is typically an increase in the volume of sludge requiring disposal. It is important that you don't solve an effluent treatment problem by creating a solid waste management problem.