| Utilizing the synergistic effect lied in photosynthetic microalgae and aerobic bacteria has been become a new way for purifying piggery wastewater in recyclable and harmless.In this study,Chlorella vulgaris and Bacillus licheniformis were selected to construct the microalgae-bacterial consortia?C.v-B.l?.On this basis,the purification effects of C.v-B.l consortia for piggery wastewater and the synergetic mechanism between C.vulgaris and bacteria during the process were studied,which can provide a reference for utilizing the microalgae-bacterial consortia to realize the livestock and poultry wastewater purification,and the wastewater can be as a resource.The detailed research contents and results are as follows:?1?The effect of Chlorella vulgaris-Bacillus licheniformis consortia on purifying the anaerobic piggery wastewater and its influencing factorsIn order to investigate the growth adaptability and pollutant removal ability of the C.v-B.l consortia,the growth of microorganism and the pollutant index was measured during the wastewater treatment process.Result showed that the C.v-B.l consortia which was constructed by the C.vulgaris and Bacillus licheniformis can promote the growth of microorganism obviously compared with the axenic microalgae consortia and the axenic bacteria consortia.The chlorophyll content in C.v-B.l consortia can be up to 13.2 mg·L-1,which was increased by 48.9%than the pure microalgae consortium significantly.The final removal rates of C.v-B.l consortia in total nitrogen?TN?,total phosphorus?TP?,ammonia nitrogen?NH4+-N?,and chemical oxygen demand?COD?were34.3%,64.5%,69.1%,and 57.5%,respectively,the purification effect was better than that of the axenic microalgae consortia and the axenic bacteria consortia,and the TP concentration in C.v-B.l consortia after the purification,which can meet emission standards?GB18596-2001?.The result indicated that the C.v-B.l consortia was well adapted to grow in anaerobic piggery wastewater,and the synergistic effect on growth promotion is existed between Chlorella and Bacillus licheniformis.The effects of initial adding carbon source type and concentration for the C.v-B.l consortia in removing the pollutant of wastewater were investigated respectively,the result showed that,compare the two carbon sources,sodium acetate was more effective in nitrogen and phosphorus removal than that of the glucose,and in the sodium acetate concentration 5.0 g·L-1,C.v-B.l consortia removal rates of TN,TP and NH4+-N reached to 48.7%,93.1%,and 90.1%,respectively,especially the NH4+-N removal rate was 12.4%higher than that of the glucose group.The TP and NH4+-N concentration in C.v-B.l consortia can meet emission standards after the purification.When adding the sodium acetate,in the concentration range of 0.0-5.0 g·L-1,the overall pollutant removal rate of C.v-B.l consortia was positively correlated with the carbon source concentration.When adding the glucose,the highest pollutant removal rate was concentration 1.25g·L-1,the removal rates of TN,TP and NH4+-N reached to 48.0%,87.2%,and 80.2%,respectively.And the TP and NH4+-N concentration in C.v-B.l consortia can meet emission standards after the purification.The results indicated that the types and concentration of carbon sources had significant effects on the nitrogen and phosphorus removal of C.v-B.l consortia.?2?The synergistic mechanism of C-O exchange between microalgae and bacteriaIn order to investigate the synergistic mechanism of carbon dioxide and oxygen exchange between microalgae and bacteria,the growth of microalgae and bacteria,rubisco activity,the chlorophyll content,the change of microalgae net photosynthesis activity,pH,the dissolved oxygen concentration,and the total inorganic carbon?TIC?concentration were measured.The result showed that the chlorophyll content,the change of microalgae net photosynthesis activity,the dissolved oxygen concentration,and the bacterial biomass in the C.v-B.l consortia was increased by 71.2%,57.4%,1.6times,and 34.8%,significantly,compared with the axenic microalgae consortia?P<0.05?.The result indicated that the light reaction intensity of microalgae in the co-culture system was significantly increased,the amount of O2 released was increased,and the dissolved oxygen concentration in the water was improved,which had a promoting effect on the growth of aerobic bacteria in the co-culture system.Detecting the change of total inorganic carbon?TIC?concentration,pH,Rubisco activity and the microalgae biomass,which showed that,in the C.v-B.l consortia,the TIC content,Rubisco activity,and the microalgae biomass was significantly increased by 74.4%,69.8%,and 74.6%,that compared with the pure microalgae system?P<0.05?,and the pH value was lower than that of the axenic microalgae consortium and remained below 7.6 for a long time.The result indicated that co-culture bacteria release CO2through respiration to improve the TIC content of water,at the same time stimulate the secretion of microalgae Rubisco to strengthen the microalgal fixation and transformation of CO2,and promote the growth of microalgae.The above results verified that microalgae and bacteria could achieve synergistic promotion through gas exchange between O2 and CO2.?3?Research on the synergistic mechanism based on the change of enzyme activity related to nitrogen metabolism between microalgae and bacteriaThe nitrogen elimination effect in wastewater was related to the enzyme activity,which were involved in the nitrogen absorption,conversion and other related metabolic pathways in microorganism cells.In this study,the synergistic mechanism between Chlorella and it's co-cultured bacteria was investigated by measuring the enzyme activity related to nitrogen metabolism in microalgae-bacteria consortia.The results are as follows:Detecting the microalgal urease?UE?activity and the urea concentration change of the C.v-B.l consortia,the result showed that,in the C.v-B.l consortia,the maximum enzyme activity of microalgal UE reached 0.07 U·10-6 cell on day 6,which was 40.7%higher than that in axenic microalgae consortia?P<0.05?.The urea content in C.v-B.l consortia was 3.2 mg·L-1 at the later stage,and the removal rate was 97.7%,which was1.4 times higher than that of axenic microalgae consortia?P<0.05?.The result indicated in the metabolic pathway that urease catalyzes the decomposition of urea into NH3 and CO2,bacteria can stimulate the secretion of microalgal UE,enhance the enzyme activity,and accelerate the decomposition of urea.The determination of enzyme activity related to the absorption and transformation of ammonia nitrogen showed that,in the C.v-B.l consortia,the maximum enzyme activity of glutamate dehydrogenase?GDH?,glutamate synthase?GOGAT?,and glutamine synthetase?GS?in microalgae could be up to 0.1 U·10-4 cell,0.01 U·10-4 cell,1.1 U·g-1,respectively.And the GDH activity was 11.9 times higher than that of the axenic microalgae consortia?P<0.05?.The GOGAT peak activity was 6 days earlier than that in axenic microalgae consortia,there was no significant difference between the two peaks?P>0.05?.The GS activity was significantly decreased by 57.1%than that of the axenic microalgae consortia?P<0.05?.But the three enzymes reached their peak activity at different times.The ammonia nitrogen content in the microalgae-bacterial consortia reached the lowest concentration of 124.2 mg·L-1,the removal rate was 66.9%,which was 19.1%higher than that of the pure microalgae system?P<0.05?.The result indicated that the bacteria could significantly stimulate and regulate the secretion of enzymes related to ammonia nitrogen absorption and transformation,and improved the removal effect of ammonia nitrogen from wastewater.The determination of enzyme activity related to nitrate and nitrite conversion showed that,in the C.v-B.l consortia,the maximum enzyme activity of nitrate reductase?NR?and nitrite reductase?NiR?reached 6.8 U·g-1 and 3.5×10-4?mol·h-1·10-4cell respectively.The NR activity peak was 3 days later than that appeared in axenic microalgae consortia,and there was no significant difference between the two peaks?P>0.05?.The NiR activity was 1.1 times higher than that of the axenic microalgae consortia?P<0.05?.The nitrate content in the microalgae-bacterial consortia reached the lowest concentration of 173.4 mg·L-1,the removal rate was 28.1%,and that was68.2%higher than the pure microalgae consortia?P<0.05?.The nitrite content reached the lowest concentration of 127.4 mg·L-1,and the removal rate was 23.5%,79.3%higher than that of the pure microalgae system?P<0.05?.The results indicated that stimulating and enhancing the activity of enzymes related to nitrate and nitrite absorption and transformation could improve the removal effect of nitrate and nitrite. |
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