Nitrogen And Phosphorus Purification From Low C/N Ratio Wastewater By Composite Carrier Immobilized Algae-bacteria

As China’s economy changes from high-speed development to high-quality development,the amount of sewage discharged from cities is increasing,and the sewage discharge standards are improving.The traditional biological nitrogen and phosphorus removal process is difficult to effectively remove the nutrients in the low carbon and nitrogen ratio wastewater to make it discharge up to the standard.In view of the shortcomings of traditional biological carbon and phosphorus removal technology,it is imperative to develop a new carbon and phosphorus removal process with low energy consumption,low cost and high efficiency.In recent years,immobilized microorganism technology has been widely concerned because of its many advantages.In this paper,five kinds of inorganic materials（volcanic stone,vermiculite,medical stone,chlorolite and clinoptilolite）and five kinds of organic materials（corncob,pine sawdust,rice husk carbon,corncob carbon and coconut husk carbon）were used to explore the nitrogen and phosphorus removal effects of immobilized algae,immobilized bacteria and immobilized algae on low carbon and nitrogen ratio wastewater.The best inorganic and organic carrier materials（chlorolite and corncob）were selected.Then,based on the two materials,a composite carrier immobilized algae-bacteria coupling system was constructed to explore its nitrogen and phosphorus removal capacity and its influencing factors in low carbon/nitrogen ratio wastewater under flowing water.This paper aims to explore an efficient and energy-saving nitrogen and phosphorus removal way and provide theoretical basis and technical support for the development and application of carrier materials.（1）Among the five inorganic materials,the removal rate of total nitrogen were shown in a descending order:chlorolite（44%）,clinoptilolite（40%）,vermiculite（29%）,medical stone（9%）,and volcanic stone（-2%）.The order of phosphate removal rate is vermiculite（23%）>clinoptilolite（10%）>volcanic stone（8%）>chlorite（6%）>medical stone（4%）.Immobilized algae can significantly improve the removal rate of nitrogen and phosphorus by five materials,of which the removal rate of total nitrogen by clinoptilolite immobilized algae is the highest,up to 57%,and the removal rate of phosphate by vermiculite immobilized algae is the highest,up to 91%.The removal rate of total nitrogen were shown in a descending order:clinoptilolite immobilized algae（57%）>chlorolite immobilized algae（53%）>vermiculite immobilized algae（40%）>volcanic stone immobilized algae（24%）>medical stone immobilized algae（17%）;The order of phosphate removal rate is vermiculite immobilized algae（91%）>clinoptilolite immobilized algae（89%）>chlorolite immobilized algae（88%）>volcanic stone immobilized algae（87%）>medical stone immobilized algae（78%）.Since the five inorganic materials cannot release enough organic carbon,and activated sludge occupies a part of the specific surface area of the material,affecting the adsorption performance,the removal rate of total nitrogen by the five materials decreased after the immobilized bacteria.Immobilized algal bacteria can improve the nitrogen removal rate of five inorganic materials,of which the growth rate of algal bacteria clinoptilolite is the largest,up to 14%.Only vermiculite immobilized algae-bacteria can improve the removal of phosphate,with an increase of 57%.（2）Among the five organic materials,corncob has the largest TOC release,reaching 62 mg·L^-1.Rice husk carbon,corncob carbon and coconut husk carbon have low TOC release and cannot be used as a solid carbon source.The total nitrogen removal rate of the five organic materials were shown in a descending order:pine sawdust（30%）>rice husk carbon（27%）>corn cob（25%）>corn cob carbon（19%）>coconut husk carbon（11%）,and the phosphate removal rate were shown in a descending order:rice husk carbon（33%）>corn cob（21%）>pine sawdust（-10%）>corn cob carbon（-18%）>rice husk carbon（-57%）.Immobilized algae can improve the nitrogen removal capacity of corncob,pine sawdust and coconut husk carbon,with an increase of 23%,1%and 15%respectively.At the same time,immobilized algae can effectively improve the phosphorus removal rate of the material,and the increase of corncob immobilized algae is the largest,up to 42%.Immobilized bacteria can significantly increase the removal rate of total nitrogen from corncob,with an increase of 61%,and also inhibit the other four materials.The nitrogen removal effect of immobilized algae-bacteria corncob and coconut husk carbon increased by 54%and 7%respectively.Immobilized algal-bacteria significantly increased the phosphorus removal effect of corncob carbon by 60%,while the removal rate of the other four materials decreased.（3）Based on the experimental results of inorganic carrier materials and organic carrier materials in the previous two chapters,the inorganic carrier material chlorolite and organic carrier material corncob were selected as the components of the composite carrier materials for immobilization of algae and bacteria in the subsequent experiments,and the purification effect of nitrogen and phosphorus in wastewater by immobilized algae and bacteria in the composite carrier under different ratio conditions was studied.The experimental results showed that with the increase of the proportion of chlorolite in the composite carrier material,the removal rate of nitrogen from wastewater by immobilized algal bacteria on the composite carrier increased first and then decreased.The removal rate of ammonia nitrogen and total nitrogen in the chlorolite:corncob 10:1（mass ratio）group was the highest,reaching 62%and 77%respectively.chlorolite:the phosphate removal rate of corncob 17:1 group can reach 57%,but the nitrogen removal effect is significantly lower than that of 10:1 group.Based on the factors such as nitrogen and phosphorus removal effect,cost and secondary pollution,the ratio of chlorolite to corncob 10:1 is selected as the composite ratio of materials in the subsequent column experiment.（4）The column experiment results show that the composite carrier material immobilized algal bacteria coupling system can effectively remove nitrogen and phosphorus from low carbon and nitrogen wastewater.During the operation of the device,the removal rate of nitrate and nitrite nitrogen always remains above 70%,and with the increase of hydraulic retention time,the nitrogen concentration in the effluent gradually decreases.With a residence time of 6 hours,the removal rate of total nitrogen from low carbon nitrogen ratio wastewater reached a maximum of 82%at the beginning of the experiment,and then gradually decreased with time.By the end of the experiment,the removal rate decreased to 52%.With a residence time of 6 hours,the maximum removal rate of phosphate from wastewater was only 12%.With a residence time of 12hours,the removal rate of total nitrogen reached 95%at the beginning of the experiment,and then gradually decreased over time.At the end of the experiment,the removal rate of total nitrogen was 80%,and the removal rate of phosphate reached 18%on the last day.The removal rate of total nitrogen from wastewater by a device with a residence time of 18 hours increases with time,and remains high throughout the entire experimental process.By the end of the experiment,the total nitrogen removal rate reached 98%.With a residence time of 18 hours,the phosphate removal rate of the device increased to 27% at the end of the experiment.