| With the development of technology of equipment and national energy-saving and emission reduction policies, the unit water consumption in pulp and paper industry is decreasing year by year, wastewater discharge concentration is getting higher and higher, on the other hand, discharge concentration required according to Wastewater Discharge Standard is become more and more stringent, which advance wastewater treatment facilities to a higher demand. Anaerobic biological treatment technology has many adventages of "higher loading, lower investment, lower energy consumption, recyclable use of biogas energy etc.and which is extraordinary suitable for the current situation in China, technology of anaerobic biological , high-efficiency low-cost ,should be strongly advocated and promotion, research and development and promote technology of anaerobic biological treatment has become one of focus and hot research in China's environmental protection field.With pulping and paper-making facility modernization and its process technology development, The water consumption in whole process of pulp and paper-making are significantly decreased, on other hand, the pollutant concentration of effluent increased as well. Since the rapid development of economic conditions and requirement of eco-environment protection, the government of China had issued series of regulations to control the air-emission, solid waste and effluent discharges. Recently, the nation start up an action plan, namely"Energy-Saving & Pollutant-Reducing", therefore, pulp and paper-making mills in China have been being faced upon very strict regulations for environment-protection. With accordance to newly issued waste-water discharge standard GB3544-2008, most of pulp and papermaking enterprises in China have to be seeking some new and efficient effluent treatment technologies to update their current effluent-treatment plants. It has been proven that, Anaerobic biological process had more advantages comparing with aerobic process, such as good ability of endurance of high pollutant load, less energy consumption, energy recovery (nature gas generation) ,less sludge production and so on. Anaerobic biological treatment has been widely applied, at the mean time, some disadvantage points occur, for instance, intensive capital investment, high operation cost, low capacity resisting impact of pollutant load and so on. The development and application of low cost anaerobic biological treatment have been becoming one of reasonable options applied to effluent treatment for clean production and sustainable development of pulp and papermaking industry.For the literature study, several typical anaerobic reactors, i.e. IC, EGSB, UASB etc., were compared carefully in aspects of their structures, efficiencies , and advantages……, with combination of the advantages of the Staged Multi-phase Anaerobic Reactor (SMPA). Therefore, the goals of this study can be described as follows: to design three-stage Anaerobic Reactor(3S-AR); characterization of the wastewater from poplar P-RC APMP pulping line; to evaluate the efficiencies of pollutant removal for treatment of such kind effluent using the designed reactor.The followed design concepts were considered for these targets as, to compact the system structure, to enhance the capacity of resisting impact, to decrease operation cost:(1) Using large ratio of height to diameter of reactor to minimize the occupation area and three-section-connection design to follow the SMPA concept;(2) To form regional reverse-flow in the hydraulic flow-regime, with movement pattern of plug-flow; to improve mixing effect of waste-water with granulated sludge along the flow direction;(3) To localize different dominant bacteria along the flow direction in the reactor, so the separation of biology community can be carried out to adapt to the different locations and substrates.There are several results have been obtained and illustrated as follows, by characterizing the target wastewater and the treatment experimental trials using a self-developed 3S-AR reactor and UASB reactor as contrast:(1) COD production of the wastewater from Poplar P-RC APMP line is 238.25kg COD/t pulp, used as furnish for copper paper, the rate of BOD/COD 0.43, which indicates that this type effluent is biodegradable. With containing of trace metals in this effluent, it could be self-sufficient for the demand of salt nutrients for anaerobic treatment process.(2) Among all organic pollutants, 95% portion are contributed by various organic acids, of which, 54% from fatty acid (monoacid such as acetic acid, mono-prop acid and butyric acid etc. ; dicarboxylic acid such as oxalic acid etc. ), 41% from aromatic acids and 4%-5% from other substances as alcohol ,phenol and lipid. (3) Operation trials of effluent treatment using 3S-AR reactor were carried. The results show that, COD removal is above 75% with changeable volume loads at the range of 15g COD/l. d to 25g COD/l. d, and COD removal above 70% at the range of 25g COD/l.d to 28g COD/l.d. HRT is one of the affective factors on COD removal, in this study, 75% COD removal can be achieved while HRT > 7.42h and VLR < 25 g COD/l.d.(4) The effects of reflux ratio, as the formula: (volume of inlet flow - volume of outlet flow)/ volume of inlet flow, and velocity of fluid in reactor: it was suggested to control the velocity within a range of 1.33 m/h to 2.07 m/h while volume loads of greater than 15gCOD/ l.d.(5) The effectivities of different type reactors were compared, the results show that: 3S-AR reactor could provide the treated effluent with a COD removal above 72.91% while volume load of 28g COD/l.d , as a contrast, UASB does with a COD removal only around 52.44% at the same volume load; While volume loads between a range of 20 g COD/l.d to 28g COD/ l.d COD, 3S-AR reactor could provide the treated effluent with an average COD removal above 70%;(6) The effect of effluent PH of inlet have been investigated: With variety of pH range of 6 to 8, COD removals of 3S-AR reactor are kept above 75%; if COD removal kept below 68%, the 3S-AR reactor could self buffer variety of effluent pH.(7) The effect of operation temperature were evaluated: COD removals of both 3S-AR and UASB reactors were increased with increment of operation temperature from 20oC to 40 oC, and the optimized temperature was proposed at the range of 35 oC to 38 oC to support both reactors with excellent COD removals.(8) The operation parameters of effluent treatment process using 3S-AR reactor were optimized, reasonable operation process conditions were proposed as: VLR 20～28gCOD/l.d,HRT≥7.42h,reflux ratio 13～20, velocity 1.33～2.07m/h, influent pH 6～8, temperature 35 oC～38 oC.(9) Most of organic substances in the effluent are able to be decomposed into low molecular acids, for example, acetic acid, used directly by methanogen to form nature gas. The mechanism of degradation might be explained as bond breaking of molecules or opening of benzene-rings. After reaction in 3S-AR reactor, the main organic substances in effluent can be classified as phenyl organics and long chain ester by GC-MS determination.(10) The average size of sludge grains in each unit of the reactor varied from 611um, 462um and 676um, and the average sludge consistency did from 32.87g/l,43.37g/l and 33.67g/l respectively.(11) Easy phase disengagement of different micro-organisms in different section of this reactor should be emphasized in this paper, and each section could play its own roles, as hydrolytic acidification reaction occurs in the first phase, the decomposition and conversion of organic substances happened in the second phase, and the methanogenesising reaction in the third phase.(12) Hydraulic flow regime of 3S-AR reactor performs both plug-flow and reflux flow which consist of flow performances of CSTR reactor (idol model for fully reflux flow) and PFR reactor (idol model for typical plug-flow). With a maximum up-flow velocity of 1.33m/h, the flow regime in the reactor is approaching to fully plug-flow; while a minimum up-flow velocity of 1.33m/h, the flow regime in the reactor is changing forward to fully reflux-flow. With increment of flow velocity from 0.95m/h to 2.45m/h, the dead-zone volume rate decreased from 12.30% to 1.06% gradually. |
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