Introduction to Papermaking Wastewater Treatment Methods

The papermaking industry is an important part of the national economy, but it is also a typical high water‑consumption and high‑pollution industry. As environmental regulations become increasingly stringent and water resources grow ever scarcer, papermaking wastewater treatment has become a core issue for the sustainable development of the industry. So, what are the main methods for treating papermaking wastewater? This article provides a systematic overview.

Key Characteristics of Papermaking Wastewater

The wastewater generated during paper production is characterised by large volumes, high concentrations of organic pollutants, and complex composition. It contains difficult‑to‑degrade organic substances such as lignin, cellulose and hemicellulose, as well as suspended solids, colour and other pollutants. It is widely recognised as one of the more challenging types of industrial wastewater to treat. Current industry standards specify that the discharge of water pollutants from the papermaking industry must meet limits for key indicators such as Chemical Oxygen Demand (COD) and Suspended Solids (SS). The COD limit has been tightened to 50–80 mg/L.

Mainstream Treatment Technology: The “Three‑Stage” System

At present, the most widely applied technical route for papermaking wastewater treatment is the “three‑stage” system, with biochemical treatment at its core. This system consists of three interlinked stages: pre‑treatment, biochemical treatment and advanced treatment.

First stage: Pre‑treatment. This mainly includes screening, sedimentation or flotation to remove large particles such as suspended solids, fibres and colloids. Through coagulation sedimentation or flotation, a large proportion of suspended solids and part of the COD load can be removed, creating favourable conditions for subsequent biochemical treatment.

Second stage: Biochemical treatment. This is the core of the three‑stage system and includes both anaerobic and aerobic biological treatment. Anaerobic treatment uses microorganisms under oxygen‑free conditions to degrade high‑concentration organic matter into small molecules, while producing biogas (methane) that can be recovered and used. Aerobic treatment further degrades pollutants using aerobic microorganisms. At present, the combined anaerobic‑aerobic process is the most widely used, effectively removing organic pollutants from the wastewater.

Third stage: Advanced treatment. After biochemical treatment, some refractory organic matter and colour remain in the wastewater, and further physical‑chemical purification is needed. Common advanced treatment technologies include coagulation sedimentation, flotation, advanced oxidation processes (such as Fenton oxidation and ozone catalytic oxidation), and membrane separation. Among these, the Fenton oxidation method is the most widely applied in the advanced treatment of papermaking wastewater, accounting for about 70‑80% of advanced treatment capacity. These technologies convert refractory organic compounds into small molecules or even mineralise them into CO₂ and H₂O, achieving effective purification.

Technology Frontiers: Multi‑Process Integration and Resource Recovery

Current developments in papermaking wastewater treatment are moving towards the integration of multiple technologies and efficient resource recovery. Studies have shown that combining various technologies such as anaerobic hydrolysis, aerobic degradation, bio‑augmentation and membrane separation enables stepwise treatment of pollutants with different molecular weights. This approach achieves significantly better removal efficiency and effluent stability than traditional single‑process systems, with short payback periods and good engineering application prospects.

At the same time, practices at advanced enterprises also show that wastewater treatment is not only an environmental responsibility but can also become a new source of value. For example, Jinfeng Paper invested RMB 270 million to build a three‑stage wastewater treatment facility. Using advanced processes, its water reuse rate exceeds 95%. The plant recovers 6.5 million tonnes of clean water from wastewater every year, and converts resources such as biogas and pulp residues from sludge into energy and raw materials, achieving a win‑win situation for both economic and environmental benefits.

Policy Drivers and Industry Trends

In recent years, China’s environmental requirements for the papermaking industry have become increasingly stringent. The Discharge Standard of Water Pollutants for Pulp and Paper Industry has been revised several times, with significantly tightened COD limits and more comprehensive pollutant control indicators. Industry experts call on papermaking enterprises to increase investment in environmental technology research and application, and resolutely phase out backward, low‑efficiency processes. In the future, new technologies such as advanced oxidation coupled with bio‑augmentation, electrochemical treatment and sludge resource recovery will be gradually promoted and applied.

In summary, papermaking wastewater treatment has now formed a whole‑chain technology system covering source reduction, process control, end‑of‑pipe treatment and resource recovery. With technological progress and stricter policies, the industry is accelerating its transformation towards green, low‑carbon and circular economy models. If you would like to learn more about the technical details of wastewater treatment, please continue to follow our content updates.