Chemical Oxidation of Leachate

Process Type: Chemical

Description:

Chemical Oxidation Processes

We quote the EA (UK) form their BAT Guidance on leachate treatment as follows;

"Chemical oxidation processes are potential treatment options for the removal of specific organic and inorganic pollutants from landfill leachates, but are unlikely to provide full treatment of the wide range of contaminants present in typical samples.

Oxidation involves the loss of one or more electrons from the element being oxidised the electron acceptor being another element, including an oxygen molecule, or a chemical species containing oxygen, such as hydrogen peroxide, ozone, or some other electron acceptor.

In practice, the application of such processes will be restricted by cost, by the rate of reaction possible (oxidation rates for some organic compounds may be too slow), and by the availability of alternative treatment processes for specific contaminants.

In a complex wastewater such as leachate, the amount of chemical oxidant required in practice, is generally greater than the theoretical mass calculated from first principles. This results from a number of reasons, including incomplete oxidant consumption, and lack of specificity of the desired process oxidant also being consumed by other chemical reactions. Oxidation reactions are often pH- dependent, and control of pH-values may be an important consideration.

For treatment of landfill leachates, a limited range of oxidants have found successful application to date, primarily ozone or hydrogen peroxide. Use of others has been limited by concerns about formation of toxic reaction by-products for example, chlorine and chlorine compounds giving rise to trihalomethanes, or other halogenated compounds.

Nevertheless, in specific situations, chemical oxidation processes can provide particular benefits for example, at elevated pH-values, cyanide can be oxidised to carbon dioxide and nitrogen using sodium hypochlorite (e.g. see Patterson, 1985). It is likely, therefore, that chemical oxidation processes will find only occasional application in leachate treatment, and then to deal with individual and site-specific circumstances. Ozonation and use of hydrogen peroxide will probably account for most applications.

For all reagent-based chemical oxidation processes, the storage and handling of potentially hazardous chemicals must be addressed and considered, and appropriate standards of design and care applied. If extreme conditions are required within a treatment reactor, then high standards of control and containment become even more important safety considerations.

Because of their nature, advanced chemical oxidation processes continue to be developed experimentally. Examples include wet air oxidation, and electrochemical oxidation systems. At the time of drafting, these have not been successfully applied to leachate treatment, but over coming decades it is possible that novel processes may be developed and need to be considered."

Advantages:

Must be considered case by case.

Can be useful to address some problems of leachate odour for example.

Disadvantages:

Vary, however, usually these treatments are specific to certain contaminants, leaving others present untreated.

Where best used:

Non-EU Directive complaint landfills, old landfills, and to avoid some problems which may occur to non EU Directive/Waste Regulations compliant landfills during operation.

Costs comments:

Can be fairly low capital and running cost, but these processes are often just pre-treatment or pre-conditioning before sewage works treatment or similar, and not sufficient on their own to enable discharge off-site. , thus costs overall will include the further treatment needed for leachate disposal from the landfill.