Remediation Of Atrazine-contaminated Black Soils By Maize Straw-based Biochar Loaded With Arthrobacter Sp. DNS10

Atrazine,a triazine herbicide commonly used in the North East,poses a serious threat to the environment as it is difficult to degrade and has long residual characteristics.Biodegradation methods are considered to be more effective and safe methods for atrazine removal due to their environmental friendliness and complete degradation.However,the function of pollution remediation microorganisms is easily limited by the complex soil environment,and loading microorganisms onto suitable carriers can effectively mitigate the impact of microorganisms on the complex soil environment.Biochar has properties such as a porous surface structure,making it a good choice as a microbial carrier and pollutant adsorbent.Corn straw and rice husk are common agricultural wastes in the main grain producing areas of Northeast China.It is unclear whether biochar prepared from these agricultural wastes can be used as loading materials for atrazine degrading microorganisms and enhance the removal effect on atrazine.In this experiment,corn straw biochar and rice husk biochar were used as test carriers to investigate the differences in the adsorption performance of the above-mentioned biochar on atrazine,and a biochar was selected as a suitable carrier and loaded with functional microorganisms（DNS10）to produce a biochar-loaded microbial agent.The above research can provide an efficient and safe technical tool for the stabilisation and reduction of residual atrazine in black soils in Northeast China.The main conclusions obtained from this study are summarised below:（1）The characterisation of the biochar showed that the pore size of the maize straw biochar（12.38 nm）was larger than that of the rice husk biochar（7.71 nm）,while the total pore volume of the maize straw biochar(0.022 cm·g^-1)was slightly larger than that of the rice husk biochar(0.017cm·g^-1)Infrared spectroscopy showed that both the corn straw biochar and the rice husk biochar had characteristic peaks on their surfaces caused by hydroxyl radicals,and that the corn straw biochar also had characteristic peaks on its surface caused by asymmetric stretching vibrations of-CH2 in fatty acids,and the rice husk biochar also had groups corresponding to C-H,which could facilitate the adsorption of atrazine by both.The results of the adsorption kinetics tests showed that the adsorption of atrazine by corn straw biochar and rice husk biochar both reached equilibrium at12 h.The adsorption amounts were 14.64 mg·g^-1and 12.82 mg·g^-1,respectively,and the adsorption processes of both were in accordance with the proposed secondary kinetic model.The results of the isothermal adsorption tests showed that the Langmuir model was able to better describe the isothermal adsorption process of atrazine on both biochar at a temperature of 25°C（R²of 0.924and 0.906 respectively）.In summary:the larger pore size and total pore volume of maize straw biochar compared to rice husk biochar is one possible reason for the higher atrazine adsorption capacity exhibited.（2）The characterisation results of the biochar loaded with microbial agents showed that the number of bacteria loaded by the two biochar and rice husk biochar was 1.10×10⁶CFU·mg^-1and0.76×10⁶CFU·mg^-1at 24 h loading with strain DNS10,respectively.Meanwhile,the removal rate of corn straw biochar-loaded microbial agent was higher（84.10%）than that of rice husk biochar-loaded microbial agent（78.37%）for an initial concentration of 20 mg·L^-1atrazine.The results of IR spectroscopy showed that oxygen-containing functional groups such as carboxyl-COOH and carbonyl C=O appeared on the surface of maize straw biochar loaded with the bacterium,while C=O stretching vibration of carboxylic acid and strong absorption vibration of C=C appeared on the surface of rice husk biochar loaded with the bacterium,indicating that more functional groups appeared on the surface of the above two types of biochar loaded with the bacterium.Laser confocal results showed that the survival rate of the bacteria in the corn straw biochar-loaded microbial agent（92.8%）was higher than that of the rice husk biochar-loaded microbial agent（86.16%）.Combining the removal of atrazine by two biochar-loaded microorganisms and the characterisation results,maize straw biochar was preferred as the microbial carrier for the soil remediation trials.（3）The results of the remediation trials on atrazine-contaminated soil showed that the concentration of atrazine in atrazine-contaminated soil decreased from 17.72 mg·kg^-1to 13.60mg·kg^-1throughout the incubation period（21 d）.The removal of atrazine from the soil was 33.80%in the group treated with corn stover biochar,while the removal of atrazine was 60.50%and71.78%in the group treated with strain DNS10（the same number of strains as the corn stover biochar loaded microorganisms）and the above mentioned corn stover biochar loaded microbial agent,respectively.The results showed that the corn stover biochar-loaded strain DNS10 was the most effective in removing atrazine compared to the other treatments.The addition of biochar-loaded microbials also increased the organic matter,total nitrogen and total phosphorus content of the soil by 4.53%,6.46%and 5.34%,respectively,at day 21 compared to the atrazine treatment.The addition of biochar-loaded microbial agents stimulated urease and phosphatase activity in the soil,increasing soil urease activity and phosphatase activity by 35%and 12.15%,respectively compared to the atrazine treatment.High throughput sequencing results showed that biochar-loaded microbial agents altered the community structure of microorganisms in atrazine soils compared to atrazine treatments and biochar-only treatments,increasing the abundance of bacterial clades that can degrade complex organic molecules.Thus indicating that maize straw biochar loaded with microbial agents can modulate the bacterial community structure in atrazine soils,stimulate soil enzyme activity and enhance the removal of atrazine from the soil.