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Wastewater chemical treatment: our expert Q&A on heavy metal removal

By: Pete Cranney on Jul 6, 2023

The removal of metal ions from industrial effluent is critical to ensure protection of human health and the environment.  Here's how you can manage that process more efficiently and cost-effectively. 

In this Q&A session, we asked Pete Cranney, technical manager at WCS Environmental Engineering, how chemical treatment can offer a robust, practical and cost-effective solution for trade effluent management. Here's what he told us:

Why is effective metal removal critical in wastewater treatment?

Over the decades, the presence of metals in effluent has been increasing alongside industry growth. Heavy metals are non-biodegradable and if not removed effectively during the industrial wastewater treatment process, could eventually be discharged into the environment. If unsafe volumes find their way into freshwater sources, there is a serious risk to human health, as well as to the ecosystem. As a result, metal removal during industrial effluent treatment should always be the front of minds for businesses. 

What kind of industries typically need chemical treatment?

Chemical treatment is ideal for industries that use metals in either the manufacture, finishing or as part of the finished product, such as metal finishing and plating, semiconductor and electronics assembly and mining and chemical manufacturing.

What water treatment chemicals are used?

Both chelants and sequestrants are used for the chemical removal of contaminants, predominantly heavy metals, from wastewater effluent. Chelants are organic molecules which can bind to metal ions such as lead, mercury, cadmium, copper, iron and zinc, preventing these metals undergoing their normal reactions and forming insoluble compounds. 

Each chelant molecule can only bind to one metal ion at a time, with certain chelants binding preferentially with different metals, therefore the chelating agents are chosen to match whatever contaminant needs to be removed to meet discharge consent.

Sequestrants similarly bind to metal ions but are larger molecules and can therefore bind to multiple heavy metal ions simultaneously. They can also bind a variety of other contaminants such as calcium and magnesium. Like chelants, sequestrants can prevent these contaminants from interfering with the chemical wastewater treatment process, breaching discharge consent limits or causing environmental harm – which can all result in large fines or prosecutions.

At what stage of the process are chemicals used?

Chelants and sequestrants can be introduced into wastewater treatment systems at different stages of the treatment process, depending on the particular contaminants and the treatment objectives.

Before the process is established, a qualified chemical and wastewater consultant should examine the whole cycle as pH, temperature and contact time must be considered to achieve the desired results. Improper chemical dosing and disposal can harm the environment, which again can lead to serious penalties, and, of course, reputational damage.

Is chemical treatment cost-effective?

Yes, as well as being reliable, practical and robust, chemical treatment is seen as one of the most cost-effective methods of wastewater treatment. By integrating chelants or sequestrants into the process, you may avoid installation of alternative, more expensive processes such as further filtration, or a biological treatment method. 

Additionally, higher-quality discharges into the public sewer will lead to lower trade effluent charges from water companies. Before a new chemical regime is introduced, we offer trials which can assess costings.

How are chemical trials managed?

A trial ensures the correct chemical combination is applied when embedding new, or enhancing existing, wastewater treatment processes. Onsite trials of the entire chemical range, including sustainable chemicals, are offered as standard by WCS Environmental Engineering (WCSEE). 

Initial testing is undertaken in a lab, and then upscaled for a trial onsite using hire equipment if required. Trials can be set up quickly, take approximately one week to run and provide tangible evidence of how the process will work at full-scale. 

An initial survey of the wastewater treatment process, including jar testing, would determine the potential for introduction of the organic chemical ranges. The team would submit a detailed report on each site surveyed and would then carry out an onsite trial to demonstrate the effectiveness of the new chemistry regime. All trials are designed to remove any risk to the client’s existing process and are managed by qualified engineering and chemical consultants.

Trial results will also give an accurate picture of the cost of a permanent solution, taking into account ongoing chemical and physical process costs. Decision-making is not only about the price per litre of chemical – clients need to know the whole-life cost of any required investment.  The cost-benefit of having the correct process in place can be significant.

This information can also demonstrate a return on investment, enabling clients to look at the bigger picture. How much do you need to use for the treatment system to work effectively? What are the associated energy costs of treatment? 

Trials are used to assess and project annual cost savings, which can then be presented to decision-makers to help build the case for a permanent scheme. We always encourage clients to take a lifecycle view of their chemical consumption, and the overall cost-benefit, from initial purchase to disposal of the final waste product, post-treatment. 

What are the health and safety considerations?

As with all chemicals handling, operators should be knowledgeable about the chemical properties, handling procedures, and safety precautions associated with these chemical processes to prevent accidents and ensure the well-being of personnel. 

What support does WCSEE offer?

WCSEE can design the treatment process and train operators. Once up and running, chemical treatment systems are straightforward to manage, but we do provide ongoing monitoring and control checks to ensure you are compliant with regulations and limits.

For more information about the water technology solutions that can protect your business from breaching discharge consent and damaging the environment, contact us today.

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Topics: Wastewater Treatment

Pete Cranney

Written by Pete Cranney

Pete Cranney has worked for Atana (now part of WCSEE) since 2003 and has experience across every part of the business. Specialising in food & drink manufacturing, Pete can recommend the most practical and cost-effective treatment processes, designing onsite solutions that achieve strict discharge consents. In previous roles, Pete has managed full treatment plants for clients such as PepsiCo and Kraft Heinz. He has also led on laboratory testing of client samples. In process design, Pete provides clients with the most effective blends of chemical and mechanical treatments to ensure their sites offer full environmental protection 24/7.

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