Mechanism And Application Of The Interaction Between Electroactive Bacteria And The Bidirectional Electron Transfer In The Mixed-bacteria System

The total amount of wastewater discharged across the country continues to increase,making water pollution treatment a major national strategic issue related to people’s livelihood.Organic matter and nitrogen oxides are the main pollutants in wastewater.The development of efficient monitoring and treatment technologies for organic matter and nitrogen oxides is of great significance to protect the water environment and human health.Bioelectrochemical system（BES）is based on the electrochemical reaction of bioelectrodes to degrade pollutants while recovering energy.It is considered to be a promising water pollution control technology.However,the existing BESs do not meet the application requirements in actual wastewater.One of the important reasons is that the bioelectrode used in the BES suffers a long preparation time,poor performance and weak anti-interference ability.The above problems are particularly prominent in biocathode systems.The polarity inversion method is for rapidly preparing biocathode,which enriches EAB in the bioanode and then uses a potentiostat to reverse the electrode potential for the functional transformation from bioanode to biocathode.However,the performance and stability of the biocathode cultured by the existing polarity inversion method are poor,and the culture mechanism is not clear,forming a technical bottleneck for BES.Aiming at the problems of the polarity inversion method,this paper proposed a technical route to improve the reducing electroactivity of the bioelectrode after polarity inversion by changing the external resistance coupling substrate regulation to increase the oxidizing electroactivity of the bioelectrode in the culture stage.A high-performance biocathode was prepared,and its nitrate degradation rate was 1.3～7.9 times that reported.A positive correlation between the oxidizing and reducing electroactivity of bioelectrodes was revealed by electrochemical characterization.Through microscopy,bacterial structure analysis,antibiotic treatment and electrochemical technology,the interspecific interaction of EAB and electron transfer path were discussed.It was found that oxidizing EAB provided energy for reducing EAB through interspecies electron transfer,and oxidizing EAB formed a three-dimensional framework structure that accelerated the enrichment of reducing EAB.There were microbe-electrode electrochemical electron transfer channel,microbe-microbe interspecies electron transfer channel and microbe-electrode-microbe interspecies electron transfer channel on bioelectrodes,forming a complex electron transfer network,whose electron transfer paths were affected by EAB,substrate and electrode potential.Aiming at the shortcomings of the existing sensors in terms of the detection mechanism,detection time and accuracy,this paper developed four new bioelectrochemical sensors based on the bidirectional electron transfer mechanism and the new polarity inversion method.（1）The bioelectrochemical BOD sensor was developed with the bioanode as the detector and the linear sweep voltammetry as the detection method.The bioelectrochemical degradation coefficient（k）was proposed for the first time and used for the correction of the detection signal so as to make the bioelectrochemical BOD sensor accurately detect BOD in different actual wastewaters（relative errors<14.6%）;（2）The bioelectrochemical nitrite sensor was developed with the biocathode as the detector,the linear sweep voltammetry as the detection method and the inversion operation as the maintenance method,which could realize rapid and long-term stable detection of nitrite in wastewaters;（3）The high-precision and high-selectivity nitrite sensor was developed with a biocathode treated with metronidazole to remove oxidizing EAB and other non-functional bacteria.The detector signal of the high-precision and high-selectivity nitrite sensor was not interfered with by organic substances and ions such as NH₄⁺,NO₃^-,and the detection accuracy can reach 0.0001 mg NO₂^--N L^-1;（4）The dual-function bioelectrochemical sensor was developed based on the bidirectional electron transfer capability of the bioelectrode,the potential-step chronoamperometry and able to achieve simultaneous detection of BOD and nitrite in wastewaters.