How Chemical Waste is Treated
Chemical waste can be treated through four different methods; chemical, physical, thermal, and biological. Different methods of treatment are selected based on the chemical waste involved.
Many organisations produce some form of hazardous waste on a daily basis, be it chemical cleaners, pesticides or solvents, paint or construction materials, or even just printer ink. Learn more about best practices to both limit and manage chemical waste here.
While reducing the amount of chemical waste an organisation produces and recycling wherever possible are the most desirable options, sometimes it isn’t possible. In these cases, it’s vital that hazardous waste disposal is carried out correctly, to avoid causing damage to human health and/or the environment. It is also a criminal offence to dispose of hazardous waste inappropriately. Chemical waste which is not managed correctly may contaminate our water streams, seriously impacting both human and aquatic life. You can read more about the effects of chemical waste on water streams here.
Chemical Treatment Methods
Chemical treatment involves a chemical process that transforms hazardous waste into less dangerous substances that can be extracted from a solution.
These methods include the ion exchange reaction, whereby the charges of atoms or groups of atoms are exchanged between two chemical substances, allowing them to bond together.
Chemical precipitation is another method, which uses a chemical reaction to form separable particulate matter in solutions, either by changing the substance into an insoluble form, or by changing the properties of the solution to diminish the solubility of the contaminant. The effectiveness of this process can be increased by using coagulants and flocculants.
The oxidation and reduction (a.k.a. redox) reaction involves the oxidation number of chemicals changing, to facilitate their removal and or render the chemicals benign; this is the same process as the rusting of metals or browning of fruit.
Neutralisation is where the pH of a corrosive chemical solution is altered by adding acids to alkaline solutions, and vice-versa.
Often, chemical treatment is combined with physical treatment methods to achieve optimum results, for example, using coagulants along with physical flocculation techniques to expedite the formation of solid clumps for removal by dewatering techniques .
Physical Treatment Methods
Physical treatments include filtering operations, like passing contaminated wastewater over activated carbon or resin to remove pollutants (adsorption / resin adsorption).
Other treatments may involve using gravity to separate materials from solutions by causing them to sink (sedimentation) or float to the surface (floatation).
Phase change systems remove volatile substances from liquid waste by passing air and steam over them; and evaporation is used to treat metal plating, coolants or paint solvents.
Finally, solidification is a physical process that captures waste in either asphalt, concrete or plastic, producing a solid mass of material that resists leaching. Waste can also be mixed with fly ash, lime and water, to create a solid mass, similar to cement.
Thermal Treatment Methods
The most common form of thermal treatment is high temperature incineration, which is increasingly becoming the preferred option for treating hazardous waste, despite surrounding controversy. This is because it’s well-suited to certain types of waste, such as waste aqueous solvent blends , drilling mud, mining sludge and some tars.
Waste containing heavy metals should never be incinerated, as these metals remain in the incinerator ash and are a health hazard, requiring specialist disposal. Heating hazardous materials in the absence of oxygen to speed up the chemical decomposition of waste is another technique often used, called pyrolysis.
Biological Treatment Methods
Biological treatment methods use a wide variety of microorganisms, primarily bacteria, to degrade organic compounds in wastewater streams. These microorganisms convert the biodegradable organic matter found in wastewater into simpler substances and additional biomass.
Biological treatments (a.k.a. bioremediation) can largely be split into aerobic and anaerobic reactions, i.e. in the presence of oxygen and the absence; though it is generally a combination of the two that will prove most effective at treating wastewater.
Land farming is a bioremediation technique used to treat contaminated soils, whereby bulking agents and nutrients are tilled into the soil, often with additional tilling for aeration, as well as controls over moisture levels, and soil pH, to promote decomposition.
It’s absolutely vital that any chemical waste is treated and disposed of effectively, not just due to health and environmental implications, but also from legal standpoint. We always recommend having an expert partner to look after chemical waste management on your behalf; one who can be trusted to maintain your compliance with regulations and keep your site safe. Visit the chemical waste page of the Enva website to learn more about our hazardous waste management, treatment and disposal service.