Paper industry is one of the world's six major industrial pollution sources, accounting for 10% of China's total industrial waste water. Papermaking wastewater is mainly high concentration of organic wastewater, and containing lignin, residual alkali, sulfide, chloride and other pollutants. It is characterized by large amount of waste water, high COD concentration, waste water in the fiber suspended solids, and containing divalent sulfur elements, high color, mercaptans odor.
In the pulping (chemical method) and papermaking production process mainly produces three types of wastewater: black (red) liquid, the middle of the waste water and paper white water. Black (red) liquid is mainly cooking pulp wastewater, the middle of the water, including pulp washing, screening, bleaching wastewater, paper machine white water for the papermaking workshop waste water. Which is the most serious environmental pollution of cooking wastewater, accounting for 90% of the entire paper industry pollution.