Abstract: The pollution characteristics of wastewater from the two-stage impregnated process of wheat straw chemimechanical pulp(CTMP) with different alkali charges were analyzed comprehensively.The relationships of the pulp yield and pollution load were discussed.The results showed that good pulp properties could be obtained at low refining energy consumption with two-stage NaOH impregnation process while the total alkali charges in the whole pulping process were 3%-5% with the pulp yields of 73.1%-78.9%.Meanwhile,the produced wastewater had the chemical oxygen demand(COD) pollution load of 270.5-446.0 kg/t,the five days' biochemical oxygen demand(BOD₅) pollution load of 181.3-228.2 kg/t and the suspended solid(SS) pollution load of 47.62-124.30 kg/t. The BOD₅/COD ratios of 0.422-0.466 meaned that the wastewater was easy to be treated by the biochemical treatment process.By the suitable ratio of m_BOD5:m_N:m_P of the wastewater,its N and P element were enough to meet the needs of microorganism in the anaerobic-aerobic biochemical treatment.With the increase of the alkali charge,the yield of wheat straw CMP pulps declined,while the corresponding pollution loads increased.The relation formula of the pulping yield(Y) and COD pollution loads(L) was L=5 884-11 670Y+5 800Y²,R²=0.995 with the total alkali charge of 0-8%.

Key words: wheat straw, chemical impregnated, CTMP pulping wastewater, pollution characteristics, pulping yield