Study On The Early Warning And Prediction Of Pollution Based On The Microbial Electrochemical Signal Response

Early warning technology of environmental pollution plays a vital role in protecting human health and ecological safety.The early warning system can provide quick feedback on the toxicity of environmental pollution and trigger the alarm when it occurs,providing reference for quick emergency measures.Microbial electrochemical system is a new kind of biological early warning technolog,which used the electroactive microorganism as the sensitive element.The biggest advantage of this kind of broad-spectrum sensor is that all factors that can affect the activity of electroactive microorganisms can be directly feedback in the form of current changes.However,it also has the disadvantages of long preparation period(slow enrichment of electroactive microorganisms),low sensitivity(high concentration of detection limit),poor stability(poor resistance in reverse environment)and so on,which limit the application and development of this kind of sensor.In this study,the above bottlenecks were optimized by changing the microbial enrichment rate at the initial stage of the reactor,controlling the biofilm structure,and coating materials on the biofilm.Furthermore,a new plant rhizosphere bioelectrochemical sensor was invented to expand its application in the future.For the long preparation period of microbial electrochemical sensors,it is found that enrich more electroactive microorganisms in a short time is critical to the current output and startup of microbial electrochemical systems.Here we demonstrated that a simple method,the gravity settling(GS)of planktonic bacteria,is cost effective to improve MFC performance instead of physical and chemical treatment of anodes.The startup time is 12%shorter,and the maximum current density increases by 29%to8.41±0.13 A/m~2 than that of the control.Cyclic voltammetries at different growth stages show that GS has a remarkable improvement(66%)on limiting current at the lag stage than at exponential(32%)and mature stages(24%),which was due to the 73%decrease in charge transfer resistance.Biofilm analysis further reveals that the GS promotes biofilm electroactivity per protein in addition to the accumulation of more biomass by gravitational settling,especially at the very beginning of electroactive biofilm formation.The output current per unit biomass can be increased from 334±5 mA/g to 480±8 mA/g,and the electric activity can be increased by nearly30%.This method is simple and can significantly increase the enrichment rate and electroactivity.It provides a reliable method for accelerating the startup of microbial electrochemical sensors,which is also important to enhance power densities of large scale MFCs in the future.Electroactive biofilm has low tolerance to accidental shocks,such as extreme acid shock,which is a potential limitation for the application of bioelectrochemical systems(BESs),especially as a sensor for water quality monitoring.Here we encapsulated electroactive biofilms with biocompatible polydopamine(PDA)to protect against extreme acid shock.The bacterial cells were completely capsuled in～50 nm films formed by PDA spheres,which kept their viability and current recoverability even after pH 0.5 and 1.5 shocks.The limiting current densities of PDA encapsulated anode was 0.20±0.05 A/m~2,which was 20 times than the unprotected control(0.01±0.01 A/m~2)after strong acid shock(pH=0.5,30 min).Without PDA encapsulation,the biofilm partly disintegrated with a thickness decreased by 68%from 72 to 23μm,where 92%of them were dead.Our findings reported a novel and effective method to protect electroactive biofilm at extreme conditions,which greatly extends the use of microbial electrochemical sensor in the future.A microbial electrochemical system is promising as a broad-spectrum sensor for early-warning detection of toxicants in a water environment.However,the poor sensitivity of heterotrophic microbial electrochemical sensors comparing to autotrophic sensors was reported.It is still unknown how to improve the sensitivity of heterotrophic sensors and to what level the sensitivity will be.Here,an optimized heterotrophic sensor was formed to response trace formaldehyde by controlling initial substrate concentration during electroactive biofilm(EAB)formation.The dense EAB formed with 0.1 g/L of acetate(EAB-0.1)exhibited a 1.1 times higher current density than the one that formed with 1.0 g/L acetate(EAB-1.0)in a shortened acclimation time,leading to a significant toxicity response to 0.0001%of formaldehyde in 70 s,which is the lowest concentration detected so far using EAB-based biosensors.Compared to EAB-1.0,EAB-0.1 formed a limited substrate that had a 20%thinner thickness,a 44%lower porosity,a 54%lower EPS contents,but an 81%higher electroactivity per biomass.The relatively low acetate concentration imposed a selective pressure to enrich Geobacter and suppress the activity of nonexoelectrogens to form an optimized EAB structure,and the diffusion coefficient of formaldehyde increased with the decrease in the initial acetate concentration,resulting in a 6.3 times higher value in EAB-0.1 than that in EAB-1.0.Our findings demonstrate that the EAB-based biosensors can be further optimized by the biofilm control to achieve super sensitivity for trace toxicants,providing a broader understanding of the EAB formation process,ecology of exoelectrogens and potential applications of EABs for trace toxicant detection in the future.Based on the research of the key performance of microbial electrochemical sensors,this paper explores the application of microbial electrochemical sensors.Acid rain poses significant threats to crops and causes decline in food production,but current monitoring and response to acid rain damage is either slow or expensive.The direct damage observation on plants can take several hours to days when the damage is irreversible.This study presents a real time bioelectrochemical monitoring approach that can detect acid rain damage within minutes.The rhizospheric bioelectrochemical sensor(RBS)takes advantage the fast chain responses from leaves to roots then to the microbial electrochemical reactions in the rhizosphere.Immediate and repeatable current fluctuations were observed within 2 minutes after acid rain,and such changes were found well corresponded to the changes in,rhizospheric organic concentration,and electrochemical responses.Such correlation not only can be observed during acid rain events that can be remedied via rinsing,it was also validated when such damage is irreversible,resulted in zero current,photosynthetic efficiency,and electrochemical signals.The alanine,aspartate and glutamate metabolism and galactose metabolism in leaves and roots were inhibited by the acid rain,which resulted in the decrease of rhizodeposits such as fumaric acid,D-Galactose and D-Glucose.These changes resulted in reduced electroactivity of anodic microorganisms,which was confirmed by a reduced redox current,a narrower spectrum in differential pulse voltammetry and the loss of peak in Bode plot.These findings indicate the RBS process can be a simple,swift,and low-cost monitoring tool for acid rain that allows swift remediation measures and its potential may be broadened to other environmental monitoring applications.