| China is a big pulp and papermaking country with a huge paper consumption. Although the straw pulp and paper industry with straw, stalk and reed grasses as raw materials accounts for only 15% in paper industry, COD emission of straw pulp and paper industry accounts for more than 80% of the total emissions of paper industry. Taking Liaoning province as an example, there are more than 200 straw pulp and paper enterprises in Liaohe basin. The COD emission accounts for 40% of the total COD emissions in industrial wastewater, which becomes a major pollution sources in Liaohe basin and presses for solutions. This study was supported by the water conservation, waste reduction and the key clean production technologies of papermaking industry research project-Water conservation and waste reduction of cleaner production technology integration and demonstration project of heavy chemical industry in Liao river-Key state science and technology projects (2009ZX07208-002-003). The main research contents and conclusions are listed as follows:(1) In this study, the internal and external catalysts of the super-circulation driving force in water recycling economy system of straw pulp and paper industry were analysed based on super-circulation mode. The industrial policy and regulation were identified as the external catalysts, and the clean production and sustainable wastewater treatment technology were identified as the internal catalysts. Paper industry was considered as the main pollution factor in the industry framework of Liaoning after the pollution contribution analysis of each industry in Liaoning province. Through revising of integrated wastewater discharge standard of liaoning province, the elimination of industry with backward production capacity in Liaohe basin and adjustment of industrial structure was prompted, the development and application of clean production and of water-saving technology of paper industry were improved, and the important function of emissions reduction in construction and management was implemented.(2) The super-circulation mode of water recycling economy in straw pulp and paper industry was established based on super-circulation theory. From the level of reaction cycle, source reduction of paper industry was realized through carrying out clean production. The water saving and emission reduction was fulfilled after the improvement of water usage efficiency at water intaking-usage-drainage links. From the level of the catalytic cycle, the reduction of fresh water usage and sharp rise in the water recycling efficiency was realized based on papermaking wastewater reuse and water network optimization. From the super-circulation level, a reed wetland-paper pulp integrated compound ecological system was built. The benign binary natural water cycle was realized through the advanced treatment papermaking wastewater of the reed wetland.(3) The technical supporting system of super-circulation mode was constructed. From the aspect of source reduction in clean production, the clean pulping method with alkaline/H2O2 degesting at low temperature was studied. The optimal process condition obtained in this study included:(i) the optimal dosage of NaOH and H2O2 were 10%?11% and 15%?18% respectively, (ii) the feeding interval of 1 h, and (iii) the total cooking time of 2.5 h. Compared to traditional caustic soda pulping proceses, COD and discharge load of papermaking black liquor generated in above NaOH/H2O2 clean pulping method were low, and the paper property and quality were significantly improved. From the aspect of black liquior recycling, the synthesis of calcium lignosulphonate adhesive using black liquior was studied. The optimal reaction condition was listed as below. Adding solids with formaldehyde content of 5% in the reaction kettle after concentrated, heating 1 h (60?). After then, supplying the solids with calcium sulfite content of 10%, and reacting 2 h at 130?. The optimal process condition to prepare activated carbon included phosphorus/material ratio of 3.5:1, activation temperature of 500? and activation time of 60 min. The property of adhesive comfirmed to the product quality standard.From the aspect of water recycling economy treatment technique in straw pulp and paper industry, the optimization of trapezoid flat membrane in SMBR was studied. Based on the analysis and calculation of the interaction mode between bubbles and vertical flat membrane proposed by Vries, a new mathematical model was established to describe the interaction between bubbles and trapezoid flat membrane. The optimization design for trapezoid flat membrane in SMBR and enhancement of the aeration scour utilization under equivalent conditions were obtained. The results showed that the optimal rake angle of trapezoid membrane was 8.1° and 6.8° for small bubbles (diameter,0.5?1.5 mm) and big bubbles (diameter,1.5?2.5 mm),respectively. The average COD and SS removal efficiencies of SMBR with trapezoid membrane module were 90.5% and 95.1%, respectively. Trapezoid membrane module was verified to have a better antifouling ability compared to flat membrane module. From the aspect of research on water recycling technique in straw pulp and paper industry, the advanced treatment of papermaking wastewater with multistage tandem wetland system was proposed. The multistage tandem wetland system could effectively deal with the wastewater generated in straw pulp and paper industry, and the treatment efficiency was siganificantly and a little influenced by influent load and temperature, respctively. The stable water quality in effluent was realized after treatment by triple combination process (coagulation-oxidation ditch-air flotation-oxidation pond-ashimita wetland). COD and SS contained in the effluent fluctuated between 20?50 mg/L and 10?20 mg/L respectively, which comfirmed to the emission limit value (50 mg/L for COD and 20 mg/L for SS) stipulated by standard of sewage comprehensive discharge in Liaoning province. After biochemical and oxidation pond treatment, the papermaking wastewater which flowed into ashimita depth irrigation reed wetland had a little influence on the quality of soil and groundwater environment. On the contrary, the raised organic content could improve the growth of reed.(4) The water usage network optimization of straw pulp and paper industry was studied. A water usage network model was established based on material flow tracking model. With the aid of the above model, the problems existing in the water system of sraw pulp papermaking enterprises could be identified. In addition, the water usage system of straw pulp and paper industry could be effectively analyzed and optimized. A large reed pulp and papermaking enterprise in Liaoning(namely A) was chosen as study object. After water network optimization, the water consumption per ton paper reduced by 49 m3/t, fresh water consumption per ton paper reduced by 98 m3/t paper, wastewater per ton paper reduced to 0 m3/t, water resources efficiency, water environment efficiency and water circulation efficiency were improved by 268.1%,+?, and 24.2%. |
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