| Pulp and paper making industry is an industry of high water consumption and serious pollution. Due to high toxicity and difficult treatment of pulp and paper making wastewater pollutants, it has been listed as one of the main hazards by many countries. Compared with less wastewater discharge and advanced pollution control technology in developed countries, there are serious defects in our country, such as grass fibers being used as main raw material for pulp making and huge pollutants discharged. The corresponding pollution control technology has been an important area of environmental protection technology.Pollution control technology on the middle-stage wastewater of straw pulp and paper making industry was studied in this research. The main purpose of this research is to optimize the operating parameters in micro-electrolysis-UASB-BAF pilot-scale test system. At the same time, small-scale test by addition of trace elements was established to optimize the operating process of anaerobic SBR system treating settled middle-stage wastewater of straw pulp and paper making.The results of research on micro-electrolysis-UASB-BAF pilot-scale test system treating middle-stage wastewater of straw pulp and paper making showed that:(1) During the experiment, inlet COD of pilot-scale test system is 900～3200mg/L, the outlet COD of pilot-scale system is 100～300mg/L. The COD removal rate of pilot-scale system is maintained in 82%～91%. The inlet SS of pilot-scale test system is 500～1900mg/L, the outlet SS is 20～140mg/L. The SS removal rate of pilot-scale system is maintained in above 90%. The inlet color of the pilot-scale system is 100～500 times, the outlet color is 20～60 times. The color removal rate of the pilot-scale system is about 85%. The changes of COD cumulative removal rate along the process in pilot-scale test system is analyzed. COD cumulative removal rate of sedimentation tank and micro-electrolysis tank is 50%～80%, which is the largest contribution to COD removal. The change of color cumulative removal rate along the process in pilot-scale test system is relatively uniform.(2) Within the operation parameters setting in this experiment, higher aeration, lower pH, longer HRT is benefit for organic matter removal in micro-electrolytic tank. When DO is 7mg/L, inlet pH is 5, HRT is 5h in the micro-electrolytic tank, the COD removal rate of micro-electrolysis is about 60%～75%, the color removal rate is about 43%. Influent of the pilot-scale system has low biodegradability with B/C is lower than 0.3. The B/C of micro-electrolysis outlet increased to 0.35～0.4. (3) The B/C of UASB outlet increased to 0.5 from 0.28 when the hydraulic retention time of UASB is 12h. The biodegradability of wastewater is greatly improved. In the same conditon, the color removal rate of UASB is 28%. UASB has big impacts on the color removal of BAF.(4) Within the operation parameters setting in this experiment, for BAF, under the certain reflux ratio, higher aeration is benefit for removal efficiency. When inlet reflux ratio is 3:1, filter filtration rate is 4m/h, air to water ratio is 3:1, COD removal rate of BAF is above 60%. In the same conditons, the color removal rate of BAF is 60% after UASB.The results of adding trace elements into anaerobic SBR system to treat sedimental middle-stage wastewater of straw pulp and paper making showed that:(1) The inlet COD of the two systems is 900～1000mg/L. The outlet COD of adding trace elements system is 700～750mg/L, whose COD removal rate is 25%～30%. The outlet COD of comparison system is 750～800mg/L, whose COD removal rate is 20%～25%. COD removal rate of adding trace elements system is 4% higher than comparison system.(2) The sludge settlement ratio (SV30) in adding trace elements system is 40%～45%, which is 50%～55% in comparison system. Compared with comparison system, the sludge settlement ratio in adding trace elements system decreased 10% and the sludge settling properties improved. |
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