Circuit closure in the pulp manufacturing process may mitigate water scarcity. This work aimed to analyse the feasibility of reusing the alkaline filtrate (carryover) from the (EP) stage of producing hardwood pulp in the A/D(EP)DP bleaching sequence. Pulp from Eucalyptus grandis and Eucalyptus grandis × Eucalyptus urophylla wood and the alkaline effluent from (EP) bleaching stage were collected in a pulp mill. Bleaching was conducted both without this effluent (as a control) and with 15 kg odt -1 of the alkaline filtrate from the (EP) stage. The consumption of reagents during bleaching and the chemical, physical, mechanical and optical pulp properties were evaluated. The alkaline filtrate increased the pulp kappa number from 1.4 to 2.2 with a fixed reagent dosage. The consumption of chlorine dioxide, sulfuric acid and the brightness reversion were 13.7, 17.3 and 20.1% higher in treatments using carryover, respectively to achieve a brightness level of 89 ± 0.2% ISO in the bleaching process. The viscosity, hemicelluloses content and the pulp properties did not vary between these two treatments. The adoption of effluent recirculation should consider the environmental and economic gain of reducing the water consumption and the negative effect of pulp chemical changes and the increase in reagent consumption.

The effects of alkaline fi ltrate recirculation towards the properties of long fi ber pulps with od(epo)ded bleaching sequence. CERNE, v. 24, n. 3, p. 233-239, 2018. HIGHLIGHTS The alkaline fi ltrate recirculation increased the reagents load during bleaching. The alkaline fi ltrate recirculation did not alter the quality of the refi ned pulp. The alkaline fi ltrate recirculation increased calcium, chloride, sodium and sulfate levels in the D stage and sodium and sulfate levels after the (EPO) stage ABSTRACT Circuit closure can reduce water consumption, but negative effects on pulp quality and equipment wear may make it unfeasible. This study aimed to evaluate how the alkaline fi ltrate of the recirculation stage (EP) affects bleaching, pulp quality and characteristics of the fi ltrates produced. Pre-delignifi ed cellulose pulp from a mixture of three coniferous woods was used. Bleaching followed the D(EPO)DED sequence, with the addition of 5, 10 and 15 kg. odt-1 of the alkaline fi ltrate (EP) to the pre-O 2 pulp. The physical and mechanical cellulosic pulp properties were evaluated in the control and with 10 kg. odt-1 of the alkaline fi ltrate. The inorganic compound accumulation in the system was evaluated in the control pulp and with 15 kg. odt-1 of the alkaline fi ltrate. The fi ltrate use increased the ClO 2 consumption for bleaching and sulfuric acid and NaOH to adjust the pH of the stages. The pulp tensile index was higher and the tear index lower with the fi ltrate use in pulp without refi nement, however the properties of refi ned pulp were similar between treatments. The fi ltrate increased the calcium, chloride, sodium and sulfate levels in the D stage and that of sodium and sulfate after the (EPO) stage. Filtrate recirculation can reduce water use, but it increases bleaching costs and metal accumulation in the system. v.24 n.3 2018 THE EFFECTS OF ALKALINE FILTRATE RECIRCULATION TOWARDS THE PROPERTIES OF LONG FIBER PULPS WITH OD(EPO)DED BLEACHING SEQUENCE 234 CERNE SOUZA et al.