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Wastewater treatment from PET bottles Recycling processes

05.08.2024

A practical report

A well-known PET recycler in the European market produces the highly organically contaminated effluent typical of the industry. Most of the water is generated during the washing and sorting of shredded PET. The contamination is characterised by the beverage residues introduced, but also contains various chemical additives and cleaning additives such as surfactants. The waste water is turbid, the collected pollutants form emulsions with the wash water and have a high COD and TOC content, both parameters describing the contamination with organic carbon compounds. These include surfactants, but also, for example, sugar, fruit acids and all sorts of products that result from weeks of fermentation in the bottles after they have been discarded by the consumer.

Like many recyclers in this sector, the wastewater treatment process relies on basic chemicals such as polyaluminium chloride (PAC) and/or ferric chloride and polymer flocculants. In most cases, the aim of the treatment is to achieve certain COD levels before the water is discharged, which can vary from site to site. In the past, problems have arisen with sludge composition, flocculation behaviour and the quality of the clear phase. If the emulsion cannot be sufficiently broken down, or if the precipitated carbon cannot be properly separated during flotation due to insufficient flocculation, the achievement of the COD target is severely compromised. On the plant side, there was heavy scaling in the tanks, resulting in increased weekly cleaning and maintenance costs, particularly in the area of the lamellae in the flotation tank.

By using EVO-Flock Clear-07 and a water-based flocculant FAP-50W, Färber & Schmid achieved a significant improvement in emulsion splitting and flocculation. As a result, the COD value could be maintained with an extremely low dosage, which was immediately visible in the very clear water after treatment. In the case of more heavily polluted waste water, the process can be optimally adjusted by increasing the dosage of EVO-Flock Clear-07 and controlled by simple visual assessment of the clear water. In addition, there were no more deposits in the tanks, which was very much appreciated by the plant operators.

A further advantage of this process is that there is no need for acidification, e.g. with hydrochloric acid, to support the splitting of the emulsion in the waste water. For our customer, this has led to a significant reduction in the cost of basic chemicals and a simplification of the treatment process. Plant operators appreciate the simplicity of the process, the lower maintenance costs and the reduction in chemicals used.

The process is used not only in PET recycling but also in the related food industry, such as dairies. EVO-Flock Clear-07 is also used very successfully in the metal processing industry for rinsing water of cleaning and degreasing surfaces. EVO-Flock Clear-07 is extremely effective and works in waste water even in small quantities. The strengths of this product lie in the splitting and clarification of organically contaminated waste water.

Overall, a financial saving of 30 to 40% on the products used could be achieved by changing the process. The COD value is reliably maintained, there are no deposits in the flotation process, the system runs with a very high level of process reliability and is extremely easy to operate.