Project Details

Project Delivery

Project Results

Discussion

Situation

Sandwich packaging, coffee packaging, packaging for pet food, and shrink film—these are the specialties of Coveris, a company based in England. The company manufactures packaging and supplies it to various food producers, enabling them to package their products safely and hygienically. Shrink films in particular—plastic films wrapped around drink cans or bottles that shrink tightly around the product under heat—are one of the Group’s core products.

Coveris is committed to sustainability and the circular economy. To this end, the company founded a subsidiary in the east of England that focuses exclusively on recycling plastics: ReCover. The recycling subsidiary has an annual capacity of around 5,000 tonnes of plastic. This quantity comes mainly from the company’s own operations, but other plastics are also purchased for recycling.

Food packaging—mainly shrink film—is printed with various colours. To remove these colours from the plastic, a process called deinking is used. The films are placed in a base bath that dissolves the ink from the plastic. The plastics then go through two or more washing processes before being chopped into fine flakes. The process results in an alkaline bath and water from the washing processes, which is primarily responsible for washing away the acid adhering to the plastic.

Coveris aims for 100 per cent recycling—not only of the plastic but also of the process water produced during recycling. For this reason, Coveris approached PPU Umwelttechnik GmbH to design a wastewater treatment plant capable of achieving this goal.

Problem

The recycling plant produces 5.7 m³ of process water per hour. Of this, 5,000 litres are used for the rinsing stages, and 700 litres are used for the acid bath in the deinking stage.

The company already had a treatment plant, but it was unable to adequately treat the entire volume of wastewater. The entire 5.7 m³ flowed into a collection tank, where the plant adjusted the pH level and removed solids. This treatment allowed the company to recycle 5 m³ back into the rinsing stages. However, the remaining 0.7 m³ had to be transported off-site for further treatment.

The objective was to treat the entire wastewater volume in such a way that 5 m³ could be returned to the recycling process, while the remaining 0.7 m³ could be discharged directly on-site. The treatment process also needed to be easy to monitor to ensure compliance with prescribed discharge values. Furthermore, the customer required the system to be highly automated, as they had limited staff available to operate it.

Solution

The high COD (chemical oxygen demand) of 7,500 mg/l mainly results from the dissolved colours, as well as small suspended plastic particles. To address this, a drum screen is used as the first step to sieve out coarse solids from the wastewater before it enters a buffer tank. This tank is aerated to ensure consistent mixing of the wastewater, preventing solids from settling at the bottom.

From the buffer tank, the wastewater flows through a mixing section where the pH level is adjusted to a neutral value. Precipitants and flocculants are then added to bind the remaining small suspended solids and colour particles into larger flocs.

To ensure the process operates effectively, PPU Umwelttechnik GmbH analysed a wastewater sample in its in-house laboratory. The analysis revealed that with the addition of precipitants and flocculants, the suspended solids could be bound and settled within seconds. As a result, a ClearFox® DAF (dissolved air flotation) system was chosen as the optimal solution.

The ClearFox® DAF can remove up to 99 per cent of suspended solids from the wastewater, significantly reducing COD. The system supersaturates the wastewater with air under pressure. When the wastewater enters the flotation reactor, the pressure drops, and the air bubbles out. These fine air bubbles attach to the flocculated suspended solids, lifting them to the surface. This mixture of air and solids forms a sludge layer at the top of the DAF reactor, which is removed via a cone opening. Meanwhile, a clear water zone forms at the bottom of the reactor and is discharged at regular intervals.

The sludge discharged by the system has a dry matter content of approximately two per cent. This is further processed by a newly developed sludge screw press, introduced by PPU at the beginning of 2024. The screw press increases the dry matter content to around 40 per cent, significantly reducing the amount of sludge waste generated.

The system has been in operation since the end of July 2024 and has been running smoothly ever since.