| Abstract:In China, most pulping and paper industry takes the non-wood as material and large volumes of dark black liquor (BL) are generated as byproduct or waste. The BL contains high concentrations of lignocellulosic materials, phenolics, fatty acids and resinous compounds. The presence of the these compounds imparts extreme properties such as high pH (10-13) and high COD values (100000-250000mg/1) to the wastewater, making it one of the most difficult materials to handle in the world environmental protection.Based on the study of the four strains which were isolated from eroded bamboo slips (ancient writing tablets) for their ability of biodegrading BL, the bioaugmentation system in sequencing batch reactor (SBR) as corn treatment technology was systematically studied. According to the characteristics of BL, a novel integrated process is proposed:alkaline separating?bioaugmentation?microbiological acid-ification?Fenton process. The mechanism of bioaugmentation on degrading lignin was also studied. The study focuses on comprehensive utilization and bioprocess of BL and provides a theoretical and new technology support.The main results are as follows:According to the extreme properties of BL, a new pre-process on treatment of BL, alkali separating process is presented to remove lignin under high alkaline environment by adding Ca2+. Single-factor experiments combined with orthogonal experiment were carried out to determine the optimal conditions for removing COD concentration and lignin conten in BL. Under the following optimal conditions:pH was13, the dosage of Ca+was4.5g/l, the reaction temperature was60?, the COD concentration was78000mg/l, the removal rate of COD, lignin and color achieved to71.62%,83.21%and94.26%, respectively, meanwhile the pH of BL decreased to about11, the COD concentration decreased to about22300mg/l and massive deposited lignin was produced, which is benefit to the subsequent biological treatment. The pre-processing is helpful to conquer the disadvantages of conventional flocculation methods or acidification which needs large amount of flocculent or acid consumption and facilitates secondary pollution.Three bacteria named Pandoraea sp. B-6, Cupriavidus sp. B-8, Comamonas sp. B-9and a fungus named Aspergillus sp. F-1were screened from the seven strains, which grew well on the culture contained BL. The optimal conditions in biotreatment of BL are as follows:initial pH was between10?11, COD was under22000mg/l, temperature was between30?35?. Under the given conditions, the strains showed the strong abilities of pH adjustment and could secrete alkaline lingocellulolytic enzymes. The highest COD, color and lignin removal were about58.2%,62.4%,46.7%, respectively. The results showed the strains were well tolerated on the high alkaline environment. The results also showed adding other carbon, nitrogen sources and nutritional elements had no positive effects on biotreatment, which is much convenient in practical application.Detailed study was carried out on the bioaugmented activated sludge treatment of BL with multiple lignin-degrading microorganisms. The results showed that the best removal effeciency occured when the concentration of activate sludge was3.5g/l, initial pH was10, the COD concentration was about23000mg/l, the reaction temperature was30?and the ratio of Pandoraea B-6, Comamonas B-9and Aspergillus F-1was2:1:2. The highest COD, color and lignin removal were about62.7%,66.4%,48.1%, respectively. The results illustrated that biaugmentation of multiple lignin-degrading microorganisms with activated sludge improved the treatment efficiency. In batch experiments, the bioagu-mentation system was investigated and the activated sludge process served as a control. The biaugmentation system was found to yield better COD, lignin and color removal efficiency over20%,21%,22%than those of the activated sludge process as a result of addition of the mixed special microorganisms. The reaction time was also shortened. When COD increased from9000mg/l to24000mg/l, COD removal efficiency could keep above50%in the biaugmentaiton system, which showed the biaugmentation system has a good shock load tolerance. The mechanism of lignin degradation in BL during bioaugmentaiton system treatment was also investgated by using Fourier transform infrared spectroscopy, UV spectroscopy and GC-MS method, etc. A preliminary analysis was made of the degradation mechanism as follows:the microorganisms directly utilized the carbon and nitrogen nutrient sources in BL for growth, then secreted lignocellulolytic enzymes and promoted the breakdown the benzene ring linkages. Meanwhile, lignin trimer and dimmers such as C?-C?, ?-O-4and ?-? bond were gradually disappeared, demethoxylation and dehydroxylation reaction happened. Low-molecular-mass compounds such as aromatic aldehydes, aromatic acids and aromatic ketones were detected. Lignin monomers were gradually separated from the benzene ring, the quinone, benzene oxygen free radicals were formed by Lac and MnP secretion, and a large number of carbonyl group were produced as well as some double bonds, and even ring-opening products were formed into tricarboxylic acid cycle by LiP oxidation.On the basis of the previous experiments, the integrated processes were proposed. After15cycles'continuous operation, the BL was proved to be treated effectively. The initial conditions of treated BL were as follows:initial pH13.0, COD about78500mg/l. Under optimal conditions, the ultimate COD, color and lignin removal rate were98.5%,99.8%,95.8%, respectively.The study establishes the basis of the application of biaugmentation with multiple lignin-degrading microorganisms and provides a new possible method in BL treatment process, which also improves the disadvantages of BL process by multiple physicochemical methods. |
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