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Reducing wastewater COD levels at plastic recycling company

Recovering and recycling plastic is crucial for achieving sustainability goals – but the process creates its own environmental problems in the form of contaminated wastewater. Destoec’s Mobicon filters are ideal for purifying wastewater so that it meets legal requirements, enabling recycling plants to grow their business and keep plastic waste out of landfill.

The problem

An Italian client recovers and recycles plastic boxes, mainly from the food industry.

The washing and recycling processes result in wastewater that contains residues of food and cleaning agents. Before this wastewater can be sent off-site for further treatment, the level of these compounds must be reduced.

If left untreated, the COD concentrations in the wastewater from this plant are around 600 mg/L. The legal limit in the region is set at 500 mg/L. Due to the client’s strong commitment to environmental sustainability and corporate social responsibility, it has set itself an even lower COD limit of just 200 mg/L.

Until recently, the client was able to filter the pollutants from the wastewater itself using fixed carbon filters. However, in 2019, it increased its rate of production and found that its filters were unable to cope. COD levels were higher than expected, and the client wasn’t sure why.

Aware that the core expertise of the business was in recycling plastic, not purifying wastewater, the client called in the specialists at Desotec.

The solution

Desotec engineers first visited the site in July 2019 to help the client investigate why the existing filters were no longer working correctly.

They found that suspended solids in the water were clogging the carbon filters. This reduced their efficiency and made it harder to pump water over them.

Working closely with the client, Desotec designed a solution that involves a two-stage filtering process.

The client’s existing filter was converted to use sand, which filters out the suspended solids from the wastewater.

Next, a Mobicon filter was installed, which uses activated carbon technology to filter the water for a second time. This treats the remaining organic compounds to reduce COD levels.

As the Mobicon filter is supplied on a rental basis, there was no major investment required.

The Mobicon was in place within just a few weeks of Desotec’s first site visit, and the filter was exchanged for the first time at the end of August.

The results

The new system has proved to be a great success.

COD levels after purification are 150 mg/L – well below the legal limits, and also comfortably within the lower limit set by the client.

Filters are exchanged on average once a month. It takes the client around an hour to disconnect the old filter and reconnect a new one, with Desotec transporting the spent filter to its own site for further treatment.

That means minimal downtime. Plus, none of the client’s employees need to handle the spent carbon themselves.

The partnership is working well, with the client praising our reliability, promptness and ongoing support.

The designated Desotec account handler is in daily contact with the client. Results and weekly analyses are shared so that Desotec experts can check that the filter continues to operate at optimum efficiency.

With an effective wastewater management solution in place, the plant is able to cope with existing business and scale up when they need to.

Sales teams have now been given the green light to approach potential new clients, growing the business and further helping to conserve the Earth’s natural resources.