Proces obrade otpadnih voda iz linija za pranje recikliranja plastike

Wastewater from recikliranje plastike and washing is a major source of pollution in the plastic recycling and regeneration process, primarily originating from the cleaning, separation, and wet crushing of waste plastics. The concentration of pollutants in the wastewater is closely related to the characteristics of the raw waste plastics. For mixed, low-grade materials containing significant amounts of impurities such as paper and soil particles, the wastewater generation can reach up to 10 tons per ton of waste plastic. The wastewater produced during the cleaning and crushing stages contains high levels of organic matter and suspended solids, with chemical oxygen demand (COD) reaching up to 2000 mg/L and suspended solids (SS) up to 500 mg/L.

In contrast, the use of imported primary and secondary plastic pellets often eliminates the need for intensive pre-treatment. Even if cleaning is required, the wastewater generation is significantly lower, approximately 2 tons per ton of raw material, with relatively low pollutant concentrations. In these cases, COD is typically around 500 mg/L and SS around 200 mg/L.

Biochemical experiments indicate that wastewater generated from different raw materials exhibits significant variations in biochemical characteristics, with generally poor biodegradability. If discharged without proper treatment, this wastewater could pose serious environmental risks.

Characteristics of Wastewater Quality

The engineering wastewater generated during the plastic washing process exhibits the following key characteristics:

1. High Organic Pollutant Content:

The wastewater contains significant amounts of organic pollutants such as organic amines, chemical oxygen demand (CODcr), and biochemical oxygen demand (BOD5), primarily originating from residues on the surface of waste plastics. The complex composition of these pollutants increases the difficulty of treatment.

2. Good Biodegradability:

The BOD5/CODcr (B/C) ratio of the wastewater is approximately 0.30, which generally meets the requirements for biological treatment. However, effective bio-oxidation treatment requires adjustments to parameters such as pH, temperature, water quality, and flow rate.

3. High Solid Impurity Content:

The wastewater contains a large amount of solid impurities and suspended solids, necessitating pre-treatment.

4. Complex Compound Composition:

The wastewater contains a variety of compounds, some of which may be toxic and inhibit microbial growth.

5. Significant Fluctuations in Water Quality and Quantity:

This requires the wastewater treatment system to have strong adaptability to handle variations in both quality and flow rate.

Wastewater Treatment Process Design

The main pollutants in the project’s wastewater can be classified into two categories:

1. Suspended Solids (SS)

2. Organic Pollutants (including COD, BOD, and color)

According to the reuse requirements, only the removal of SS is necessary. The treatment process involves a two-stage filtration system:

1. Immersion-Type Microfilter:

This is used to remove the majority of solid impurities.

2. Combined Water Purifier:

This step further removes fine suspended particles.