Study On The Degradation Of Lignin In Cotton Pulp Black Liquor By Pleurotus Ostreatus

Large quantities of cotton pulp black liquor are produced in chemical fiber factories. Toxic and intensively colored cotton pulp black liquor causes severe pollution. The primary contributor to the color and toxicity of cotton pulp black liquor is the high-molecular-weight lignin, which is refractory to biodegradation. The conventional biological methods are not effective in treating cotton pulp black liquor. Pleurotus ostreatus was studied to treat alkali lignin and cotton pulp black liquor in a bubble-column reactor (BCR). The operation conditions, degradation kinetics and degradation products were studied and analyzed systematically under non-sterile conditions. Combinations of P. ostreatus with other processes for the treatment of cotton pulp black liquor were discussed. This study provides a theoretical and technical supports for the treatment of wastewater by P. ostreatus.Pre-cultures of the fungal pellets were added in the BCR under non-sterile conditions. In batch experiments, strain B1 and B2 were investigated. The pellets state of strain B1 is better than that of strain B2. The alkali lignin decolorization rate and COD removal rate of strain B1 are higher than those of strain B2. Thus, strain Bl is selected for further studies. The retention time is 3-4 days in continuous experiments. The BCR was run for 55 days with ultimate decolorization rate and COD removal rate of 50% and 76%, respectively. The growth model of strain B1 C_x(t)=0.01e^0.94t/{1-0.0087[1-e^0.94t]) was obtained. There appearedinhibition when the substrate concentration reached up to a certain degree. The equation of substrate inhibition v = 1.46/(1 + 36.7 /S + S/308.30) was also obtained. The depolymerisation products of alkali lignin were identified using UV-Vis spectrophotometer, Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS). Low-molecular-mass compounds such as aromatic alcohols, phenols and aromatic acids were detected. Strain B1 is able to breakdown the benzene ring linkages between the alkali lignin. It is presumed that the degradation of alkali lignin may be initiated by the cleavage of C_α-C_βbond andβ-O-4 ether bond.Consumption of different carbon source and nitrogen source by strain B1 was studied. The optimal conditions are as follows: glucose (10 g·L^-1) as carbon source and ammonium tartrate (0.2 g·L^-1) as nitrogen source. In reactor experiment, the optimal conditions for the running of BCR are as follows: 30℃, pH 6.0, aeration rate 0.24 m³Â·m^-2·h^-1, mycelial age 7 d and dilution rate 0.2. Under the optimal conditions, BCR was run for 4 cycles (each cycle, 12 days) and the same mycelial pellets were reused. The ultimate decolorization rate and COD removal rate are 76% and 80%, respectively. Even after four cycles, strain B1 can still decolorize cotton pulp black liquor effectively. The substrate degradation kinetics of stain Bl can be expressed by Andrew equation as v = 0.594/(1 + 3865 /S + S/17038).P. ostreatus-activated sludge process was investigated aiming to effectively treat cotton pulp black liquor. Two treatment methods were studied. The results showed that the COD removal rate was 94%-97% after being treated by the process of P. ostreatus as a pretreatment and the activated sludge as a post-treatment. The residual COD in black liquor is less than 1000 mg·L^-1, which meets the national integrated wastewater discharge standardâ…¢. When the influent organic loads are gradually increased, the COD removal rate of activated sludge added with P. ostreatus is 55%-83%, which is higher than that using activated sludge treatment process alone.P. ostreatus-Fenton process was proposed to treat cotton pulp black liquor. The optimal conditions of Fenton process are as follows: initial pH 7.0, FeSO₄ 80 mmol·L^-1, H₂O₂0.15 mol·L^-1, 40 min. Under the optimal conditions, the ultimate COD removal rate is 98%. The residual COD of black liquor is 45 mg·L^-1, which meets national chemical fiber wastewater discharge standards I (COD < 100 mg·L^-1). Ultrasound is studied as a pre-treatment process. Ultrasound-P.ostreatus process was also proposed to treat cotton pulp black liquor. The optimal conditions are as follows: dilution times 10, frequency 20 KHz, power 225 W, 120 min. Treatment efficiency of black liquor by P. ostreatus was increased after ultrasound pretreatment. A 16% increase of COD removal is achieved. It was indicates that ultrasound pre-treatment is feasible for application in cotton pulp black liquor treatment.