Chemical Dosing

Siltbuster’s range of Chemical Dosing Systems provide a controlled quantity of coagulants and flocculants to ensure slow settling solids can be easily removed.

Why use chemical pre-treatment?
Some waste waters have very fine particles, particularly clays, with slow settling velocities which do not settle even in a lamella clarifier at normal flow rates. In these cases chemical dosing is used to aggregate the particles, increasing the particle settling rate and cleaning the water via gravity separation techniques.

 

Typical process

A typical process involves the sequential adding and mixing of chemicals to the waste water. First a coagulant is added and mixed, followed by a flocculant. In a mix tank this would generally happen in separate chambers within the tank whereas Pipe Flocculator have separate dosing ports along the length to allow addition and mixing of different chemicals in sequence. The water is then be cleaned in a lamella clarifier to remove the resulting settleable solids.

This video shows a demonstration of 2-stage chemical dosing with clay waters.

 

How do Coagulants work?
Fine particles in solution often have negative electrical surface charges. These prevent aggregation due to repulsive forces between them, hence the particles remain in solution. Coagulation is a chemical process that involves the neutralisation of these charges. A coagulant is typically a positively charged metal ion, the choice of which depends on the receiving water. When added, the destabilised particles are able to start coming together forming micro floc. Common coagulants are poly aluminium chloride (PAC), aluminium sulphate, ferric iron and ferrous iron.

 

How do Flocculants work?
To further increase the settling rate a flocculant can be used which work through physical processes alone. In most cases a long string organic compound with charged negative sites is used which bind the micro floc together into rapidly settling aggregates known as flocs.

 

Why is flow proportional dosing important?

By controlling the dosing of chemicals in proportion to the flow rate of the water, Siltbuster systems can ensure that excess chemicals are not added saving money and ensuring better quality water as an output. Over dosing of chemicals can affect the pH of the water causing problems to the environment and making the resulting water out of consent.

 

Here to help
In consultation we will help guide you through the options and identify the chemical treatment regime which is most suited to your needs. Our in-house laboratory can test a wide range of chemicals, all we require is a sample of untreated water, your flowrate and the required discharge limits.

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