The Influence of Stock Consistency on the Pollution Load in Washing Process

The influences of stock consistency on the kappa number, residual alkali of pulp, flow direction of lignin, chemical oxygen demand, oxidation with dichromate (CODCr), and five-day biochemical oxygen demand (BOD5) in effluents were investigated in a washing process. Compared with 15% stock consistency, 35% stock consistency could lead to a decrease of at least 25% in the consumption of washing water while cutting 75.27% and 46.29% of CODCr and BOD5 in washing effluents, respectively. Moreover, the residual lignin in effluents were reduced greatly from 39.35 g·t to 12.76 g·t, which will be beneficial to treatment of washing and bleaching effluent. All the results showed that a higher stock consistency in the washing process could decrease the consumption of washing water, the generation of pollution, and the toxicity in bleaching effluent.