Paper is an essential product in daily life and widely applied in various scenarios, which promotes the development of paper manufacturing plants. Most industrial facilities produce wastewater during production processes, and paper mills are among them. In addition, papermaking wastewater is relatively difficult to treat, and the black liquor it contains brings prominent pollution risks to the ecological environment.
The papermaking industry adopts raw materials including timber, rags and rice straw. Cellulose is separated from these raw materials via high-temperature cooking to prepare paper pulp. The wastewater produced in the production process is mainly divided into three types: washing wastewater, pulping cooking liquor (also referred to as black liquor, a major pollution source of pulp mills), and bleaching wastewater.
Hazardous Substances Contained in Papermaking Wastewater
- Suspended Solids
These substances mainly come from sediment and bark generated in the raw material preparation process, as well as partial pulp fibers lost in discharged wastewater.
- BOD (Biochemical Oxygen Demand)
It is generated in the pulping and cooking process, with main components including organic acids, saccharides and other substances.
- COD (Chemical Oxygen Demand)
Similar to chromogenic substances, COD mainly comes from lignin and its derivatives produced during the pulping and cooking procedure.
- Toxic Substances
Several toxic compounds will be generated in the papermaking process, mainly including dichlorophenol, trace mercury, phenols and other harmful components.
Effective treatment is required for these contaminants, and wastewater can only be discharged after professional treatment and standard compliance inspection. Common wastewater treatment technologies include physical and chemical methods, such as membrane separation, flocculation sedimentation, adsorption, and advanced oxidation processes.
No matter which treatment technology is applied, real-time monitoring of water quality indicators is required during the entire treatment process. Staff carry out regular Wastewater Monitoring with professional Water Quality Analyzers to track various pollutant parameters stably. Wastewater discharge is allowed only when the monitoring data verifies that all indicators conform to the official discharge standards.
