A plastic recycling facility in Croatia processes used plastics for reuse. Intensive washing represents a key stage in the recycling process. It removes dirt, residues and adhering organic matter from the surface of the plastic.
This process generates heavily contaminated industrial wastewater. Its composition varies according to the incoming material and the production process. The high concentration of organic compounds places particularly demanding requirements on wastewater treatment. Mechanical treatment alone does not provide sufficient removal.
The client had already installed a physicochemical treatment stage from a local provider. This system pre-treated the washwater and reduced part of the pollutant load. However, it failed to achieve the effluent quality required for discharge into the municipal sewer network.
The operator therefore needed an additional biological treatment stage. The new system had to integrate downstream of the existing physicochemical process and reliably reduce the remaining COD. At the same time, the site required a compact solution with straightforward operation.
The system design accounted for a wastewater volume of approximately 50 m³ per day. Based on 20 operating hours, this corresponds to an average flow rate of around 2.5 m³ per hour. PPU Umwelttechnik developed a modular ClearFox® containerised wastewater treatment system for this purpose.
The plastic recycling washwater contained a COD concentration of more than 10,000 mg/l. This organic load significantly exceeded the permitted discharge limit. Before releasing the wastewater into the municipal sewer network, the operator had to reduce the COD to below 1,000 mg/l.
The existing chemical treatment process failed to achieve this target reliably. It also required large quantities of chemicals and generated correspondingly high operating costs. Despite this considerable expenditure, the effluent quality remained insufficient. This ruled out regular discharge into the municipal sewer network. Instead, the facility collected the non-compliant wastewater and arranged daily removal by tanker. This disposal method resulted in high ongoing costs and added considerable logistical demands at the site.
The variable composition of the wastewater presented a further treatment challenge. Plastic washing lines do not generate a consistent pollutant load because the incoming material, level of contamination and production volume continually vary. The biological treatment stage therefore had to handle both high organic loads and fluctuating influent conditions.
Biological degradation also produces secondary sludge. Without effective clarification, these biological solids enter the outlet together with the treated water. In addition to biological treatment, the client therefore required a compact and reliable solids separation stage.
Large conventional settling tanks would have required extensive space and significant civil works. The limited footprint at the site called for a compact system solution. The operator also wanted straightforward operation with minimal input from site personnel.
PPU Umwelttechnik supplied a containerised biological treatment system based on ClearFox® FBR technology. The system operates hydraulically downstream of the existing physicochemical treatment stage, where it provides the additional biological degradation of the remaining organic load.
A 40-foot High Cube container forms the heart of the treatment system. It houses three ClearFox® FBR modules, each with an effective volume of approximately 13 m³. Every module contains fixed-bed media that provides around 1,650 m² of biologically active surface area. A stable biofilm develops on this carrier material. The microorganisms within the biofilm use the organic compounds as a source of nutrients and break them down biologically. Fine-bubble diffusers beneath the fixed-bed media supply the biomass with a consistent flow of oxygen.
The wastewater passes through the three FBR modules in sequence. This cascade arrangement supports the development of different microbial communities within each reaction zone, each adapted to the pollutant load at that particular stage. As a result, the system maintains a high biological degradation rate throughout the entire treatment process.
The firmly established biofilm responds reliably to fluctuating influent conditions and sudden load peaks. This process principle is particularly well suited to demanding industrial wastewater with a variable composition. The ClearFox® FBR also requires little operator input and eliminates the need for continuous adjustment of complex process parameters.
After biological treatment, the wastewater flows into a ClearFox® lamella clarifier. PPU integrated this clarification stage into a separate AP tank with a volume of 3,500 litres. Hydraulically, the clarifier follows the three FBR modules. Inside the lamella clarifier, sedimentation separates the secondary sludge from the clear water. The water flows evenly upwards through lamella plates positioned at an angle of 60 degrees. Sludge flocs settle on the inclined surfaces and then slide downwards into the sludge hopper.
The clear water collects above the lamella plates. From there, it flows over an overflow weir towards the outlet. The enlarged settling surface significantly reduces the required footprint compared with a conventional sedimentation tank.
Together, the FBR and lamella clarifier reduce the COD reliably to below 1,000 mg/l. The treated wastewater therefore meets the required standard for discharge into the municipal sewer network. The operator avoids daily tanker disposal and significantly reduces ongoing treatment, disposal and operating costs.
The compact design also simplifies integration into the existing treatment infrastructure. At the same time, the modular concept provides flexibility for future expansion. The plastic recycling facility now benefits from a robust, economical and straightforward solution for treating its challenging washwater.
During plastic washing, organic residues, dirt, label fragments, adhesives, fats and fine plastic particles enter the wastewater. The type and concentration of these contaminants depend heavily on the incoming material and the washing process. As a result, influent characteristics often fluctuate considerably.
The ClearFox® FBR is particularly well suited to industrial wastewater with high organic loads. At the Croatian facility, the COD concentration exceeded 10,000 mg/l. The combination of pre-treatment, biological treatment and clarification reliably reduced this value to below 1,000 mg/l.
Microorganisms colonise the fixed-bed media and form a stable biofilm. They biologically break down the organic compounds contained in the wastewater. Fine-bubble diffusers supply the biomass with a consistent flow of oxygen and create ideal conditions for the treatment process.
The firmly established biofilm adapts to changing influent conditions. As a result, the ClearFox® FBR reliably handles varying organic loads and short-term load peaks. This process stability provides a major advantage for plastic washing lines that process materials with different contamination levels.
The modular design supports demand-based expansion. PPU adds further FBR modules or containers in series or parallel to increase the treatment capacity. This allows the system to grow alongside production without requiring the operator to replace the entire wastewater treatment plant.
