Removal Effect And Mechanism Of Corncob-Microorganism On Inorganic Nitrogen And Copper Compound Pollution In Water

With the rapid development of my country’s economy,the amount and types of pollutants are also increasing,resulting in the occurrence of heavy metals,nitrogen,phosphorus and other pollutants exceeding the standard in many water bodies.Pollutants in the water environment often do not exist in the form of single pollution,but in the form of compound pollution.The coexistence of multiple pollutants will produce synergistic or antagonistic effects,which complicates the problem of water pollution.Therefore,compound pollution control has attracted more and more attention.Nutrients and heavy metals are common pollutants in the water environment.In this paper,the composite pollution of inorganic nitrogen and copper in the water body is taken as the removal object.Then,the adsorption characteristics of corncob combined activated sludge on inorganic nitrogen and copper single pollutants and composite pollutants were studied,and on this basis,a bacterial feed（corncob-microbe）coupling system was constructed;Finally,the effect of synchronous removal of nutrient salt and heavy metal composite pollution by the corncob-microbe coupling system and its influencing factors were further studied in the state of running water.The purpose of this paper is to provide theoretical basis and technical support for the simultaneous removal of water complex pollution.The main conclusions of this paper are as follows:（1）In the case of single pollution,the adsorption amount of corncob to NH₄⁺and Cu²⁺reached 0.058 mg·g^-1and 0.018 mg·g^-1,respectively.No obvious adsorption ability was shown for NO₃^-under single pollution condition;In the case of binary composite pollution,the presence of Cu²⁺had a very significant promoting effect on the adsorption of NH₄⁺on the corncob（P<0.01）,and the presence of NO₃^-showed a very significant inhibitory effect on the adsorption of NH₄⁺on corncob（P<0.01）.However,the presence of NH₄⁺and NO₃^-could significantly promote the adsorption of Cu²⁺on corncob（P<0.01）;In the case of ternary compound pollution,the coexisting ions NO₃^-and Cu²⁺showed a very significant inhibitory effect on the adsorption of NH₄⁺（P<0.01）,while the coexisting ions NH₄⁺and NO₃^-had a significant promoting effect on the adsorption of Cu²⁺.Further,the adsorption process of NH₄⁺on corncob conforms to the Langmuir adsorption isotherm model.Both the pseudo-first-order kinetic equation and the pseudo-second-order kinetic equation provide high correlation to the data;The adsorption process of Cu²⁺follows the pseudo-second-order kinetic model with the best correlation,and the fitting effect is fairly consistent with Langmuir adsorption model.（2）In the case of single pollution,the adsorption amount of activated sludge to NH₄⁺and Cu²⁺reached 6.30 mg·g^-1and 1.38 mg·g^-1,respectively.No obvious adsorption ability was shown for NO₃^-under single pollution condition;In the case of dual compound pollution,When Cu²⁺,NO₃^-and NH₄⁺coexisted,they could promote the adsorption of NH₄⁺by activated sludge,and NO₃^-showed a more significant promoting effect,and the existence of NH₄⁺and NO₃^-would significantly inhibit the adsorption of Cu²⁺by activated sludge（P<0.01）;In the case of ternary compound pollution,the existence of NO₃^-and Cu²⁺would promote the adsorption of NH₄⁺in activated sludge,and the presence of NH₄⁺and NO₃^-would significantly inhibit the adsorption of Cu²⁺in activated sludge（P<0.05）.Further,the adsorption process of Cu²⁺and NH₄⁺on activated sludge conforms to the Langmuir adsorption isotherm model,both the pseudo-first-order kinetic equation and the pseudo-second-order kinetic equation provide high correlation to the data.（3）In the case of single pollution,the removal rate of Cu²⁺by corncob combined with activated sludge can reach 86.65%,and the removal rate of NH₄⁺nitrogen is54.47%,but it has no adsorption capacity for NO₃^-;In the case of binary compound pollution,the coexistence of Cu²⁺,NO₃^-and NH₄⁺,respectively,would inhibit the adsorption of NH₄⁺on the corncob combined with activated sludge to different degrees,while the ternary coexistence of NH₄⁺,NO₃^-and Cu²⁺shows a very significant effect,and the existence of NH₄⁺and NO₃^-would significantly inhibit the adsorption of Cu²⁺in corncob combined activated sludge;in the case of ternary compound pollution,NH₄⁺,NO₃^-The presence of NO₃^-would significantly inhibit the adsorption of Cu²⁺by the corncob combined activated sludge,and the presence of Cu²⁺and NO₃^-would also inhibit the adsorption of NH₄⁺by the corncob combined activated sludge.The maximum removal rates of NH₄⁺,NO₃^-and Cu²⁺by the constructed bacteria-material coupling system were 73.61%,91.86%and 86.48%,respectively.The results of microbial community structure analysis showed that the abundance and diversity of the microorganisms on the seventh day of operation of the coupled system decreased compared with those used in the construction of the coupled system.The dominant microbial populations used in the construction were Chloroflexi（30.17%）,Proteobacteria（22.59%）,Bacteroidota（20.60%）and Firmicutes（28.45%）,the dominant species after the experiment were Bacteroidota（42.10%）,Firmicutes（37.29%）and Proteobacteria（16.18%）.（4）The removal rate of the compound pollutants by the corncob-microorganism coupling system decreased with the increase of the influent flow rate.During the process of increasing the flow rate from 20 m L·min^-1to 50 m L·min^-1,the removal rate of NH₄⁺-N decreased from the highest 81.81%to 32.49%;the removal rate of NO₃^--N decreased from the highest 81.73%to 30.66%;TN removal rate decreased from the highest 76.34%to 29.4%;Cu²⁺removal rate decreased from the highest 87.78%to29.4%.Meanwhile,the increase of the initial Cu²⁺concentration would reduce the removal rate of the compound pollutants by the coupling system.During the process of increasing the initial Cu²⁺concentration from 2 mg·L^-1to 8 mg·L^-1,the removal rate of NH₄⁺-N decreased from the highest 81.81%to 20.25%;the removal rate of NO₃^--N decreased from the highest 81.73%to 27.90%;TN removal rate decreased from the highest 76.34%to 29.65%;Cu²⁺removal rate decreased from the highest 87.78%to28.57%.In addition,the increase of water temperature could promote the removal rate of compound pollutants by the corncob-microbe coupling system.the removal rates of various composite pollutants by the coupling system increased with the increase of water temperature.During the process of increasing the water temperature from 15℃to 35℃,the removal rate of NH₄⁺-N increased from the lowest 23.02%to 95.03%;the removal rate of NO₃^--N increased from the lowest 27.00%to 92.42%;the TN removal rate increased from the lowest 29.65%increased to 85.34%;Cu²⁺removal rate increased from the lowest 30.26%to 98.88%.To sum up,in the actual application process,in order to ensure the removal efficiency of pollutants by the coupling system,it is recommended that the influent flow rate should not be higher than 50 m L·min^-1,the temperature should not be lower than 15℃,and the initial Cu²⁺concentration should not be higher than 8 mg·L^-1.