| According to the kind of raw material, pulping and papermaking process and wastewater treatment methods, the COD and BOD removal rate of papermaking wastewater treated by secondary biochemical was between 65%-85% and 60%-90% respectively and the chroma removal rate was between 50%-85%. The outlet COD concentration of secondary biochemical was between 450-150mg/L. The quality analysis of the wastewater after treatment showed that the main pollutants were organic compounds existed in the papermaking wastewater and there is still a potential for residual pollutants to be degraded continuously.Based on the characteristic analysis of papermaking wastewater and according to the features and nutritional needs of aerobic microbial degradation, a kind of bio-stimulant (BS) product for papermaking wastewater was developed and the aerobic treatment mechanism of papermaking wastewater using bio-stimulant was investigated in this thesis.BS can enhance the biodegradability of wastewater, optimize microbial community and increase the degradation efficiency of activated sludge. The water quality analysis of wastewater before and after treatment showed that composition of outlet wastewater includes a huge amount of benzene, phenols as well as alkanes. The content of calcium ion and aluminium ion existed in the papermaking wastewater after bio-treatment are relatively high due to the recirculation and reuse of wastewater in the pulp and papermaking process. And there were no trace elements that could promote the growth of microorganisms in the after treatment wastewater. Based on the results of wastewater quality analysis, the formula of BS contains degrading enzyme of fiber cell wall (lignin, cellulose and hemicellulose enzymes), nitrogen and phosphorus elements, trace elements, hormones and growth factors. Investigation on the effects of different formulas of bio-stimulant on COD, chroma and biodegradability of wastewater found that the optimum formula of BS is BS7. The formula is as follows:Lassase 50U/mg+Cellulase U/mg+ Hemi cellulase 10 U/mg+Gibberellins 1μg/mg+Fulvic acid 10μg/mg+ NH4C1 0.5mg/mg+NaH2PO4 0.08mg/mg.The thesis investigated the effects of continuous addition of BS in the process of papermaking wastewater treatment for 15 days and found that the COD, chroma and biodegradability increased. The maximum COD and chroma removal rate reached 85.2% and 74.8%,10.5% and 5.9% higher than the value of blank group respectively. The average value of BOD/COD increased from 0.29 to 0.39.The MLSS, SVI and SOUR value of the activated sludge also increased and the cycle of sludge discharge shortened. The average value of MLVSS/MLSS reached 0.724 after addition of BS,7.58% higher than that of blank group and the value of SOUR reached 4.3 mgO2/(g MLVSS),15.82% higher than the value of blank group.The UV spectrum of wastewater showed a shift of E band absorption peak and the Infrared spectrum showed two absorption peaks at 2730cm-1、1738cm-1 disappeared and the intensity of peaks at 2046cm-1、 1640cm-1、1384cm-1、676cm-1 decreased after addition of BS. The results demonstrated that the content of aromatics, carboxylic acids, aldehydes and alcohols decreased in the biochemical treatment process due to the degradation and transformation of these organic compounds. The GC-MS analysis results showed that the species of organic pollutants are tow less than that of the blank group and the relatively content of benzene, alkanes and lipids that are hard to degrade decreased. The aforementioned study indicated that the residual pollutants of wastewater can be sufficiently degraded using BS and BS can enhance the biodegradability of wastewater.The granularmetric analysis of stimulant and activated sludge showed that favorable absorption results and significant influence on effluent effect are observed if the particle sizes of BS are well distributed, smaller or close to that of activated sludge. Raman spectrum of the sludge before and after treatment showed that the Raman spectrum of activated sludge changed after separately addition of gibberellins, trace elements and N/P salts. While the spectrum of sludge did not change much after addition of fulvic acid due to fulvic acid□good conp atitility with mincroorg anisns that can contributes to the absorption and uptake of nutrients and degradation of organics. The microscope observation found that the bulk density of the flocculating constituents of activated sludge increased significantly, the structure of zoogloea became compact and the color of flocculating constituents deepened after the addition of BS, which indicated that BS can prolong the aging time of sludge. The SEM analysis of sludge after addition of BS in bulking sludge for 15 days found that more clearly skeleton structure of sludge are observed and the expansive sludge disappeared. Besides the structure of zoogloea became clear and good recovery condition of the morbid sludge are obtained. The aforementioned study showed that BS can boost the integral nutritional status of microorganisms, accelerate the propagation of microorganisms per unit time and prolong the sludge age in hydraulic retention time to optimize the microbial community.Effects of BS on the compositions and structure of extracellular polymer (EPS) of microorganisms showed that the total EPS, the content of protein and polysaccharide increased after addition of BS and the EPS value is 2 times of that of the blank group. The value of PN/PS decreased from original 4.81 to 3.37 and the lower the value of PN/PS, the better the settling performance of the flocculating constituents of activated sludge. The content of DNA in EPS decreased to 6.276mg/g, far lower than the original value 10.336 mg/g. Besides, healthier cells, better metabolism and nutrition conditions would lead to lower DNA ratio in total EPS. The analysis of EPS layer structure showed that BS can significantly increase the ratio of TB-EPS layer, which could improve the microbial adsorption ability for pollutants. The Raman mapping analysis of EPS found that the concentration of EPS increased especially the large volume EPS polymer after addition of BS. The content of carboxylilc acid and phenols of EPS are higher than that of the blank group. EPS2 structure is found in most EPS polymer and the EPS2 structure can boost the reaction activity of the sludge in the process of degradation and the absorption property of the zoogloea. The aforementioned study indicated that BS can optimize the composition of EPS, adjust the layer structure of EPS, improving the overall health status of the cell and the absorption and flocculation property of the zoogloea to increase the degradation efficiency of the activated sludge per unit.The COD removal rate was 90% after using BS for 22 days in the treatment process of papermaking wastewater, approximately 6% higher compared with original value. Moreover, the outlet COD removal rate continues to increase to 92.5% after stopping using BS. The MLSS value of the sludge increased steadily during the period of using BS. While the Ammoia nitrogen value of the outlet dropped steadily and stood at a lower level, lower than the Ammoia nitrogen discharge value 10mg/LThe study on the effects and mechanism of BS in the treatment process of papermaking wastewater showed that using BS can effectively avoid issues like ecological competition caused by the addition of exogenous microorganism and can improve the treatment effects by means of restoration of original microorganisms in the water environment. The addition of BS can improve the outlet water quality, enhance the biodegradability of the outlet water and reduce the cost of further treatment of the wastewater, which will finally boost the efficiency of papermaking wastewater treatment. |
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