The effect of voltage gradient on microorganisms in electrokinetic process in sandy soil

Electrokinetic remediation is introduced as a promising process to remediate both organic andmetallic contaminants. Coupling the electrokinetic process with the ability of microorganisms inaffecting different types of pollutants is the subject of interest to enhance their final removal [۱-۳].Electrokinetic remediation is the technology for migration, separation, and removal of pollutantsin soil and sediment by applying an electric field, which is cost-efficient and has low environmentalimpacts [۴]. The final effectiveness of electrokinetics in soil remediation depends on three mechanisms including electromigration, electroosmosis, and electrophoresis. Moreover, the redoxin soil induced by electrochemical oxidation plays an important role in this process [۵].These electrochemical reactions make changes in soil characteristics, such as pH, water content,and ions. This may have impact on the viability of microbial community, and thus affect pollutantremoval. For example, the H+ and OH− produced by water electrolysis can migrate into the soilunder the electric field and change the soil pH which leads to microbial population reduction [۵].One of the most important requirements for coupled bio-electrokinetic processes is an active andviable microbial community under the electric field during electrokinetic treatment [۶]. The aim of this study is to evaluate the effect of voltage gradient on soil microbial population during the electrokinetic process and evaluate recovery of it after the experiments in sandy soil.In this regard, ۲ experiments were designed for voltage gradients of ۱ and ۲ V/cm, applied for ۸days on a sandy soil with initial microbial population of ۳×۱۰۸ CFU/kg soil. Control experiment wasconducted with the same microbial number without applying electric field to observe the microbialgrowth without tension of electric field.In electrokinetic setup, soil was compacted in soil chamber. Distilled water was used as electrolyteand two graphite electrode were used as anode and cathode. Electrolytes were refreshed daily.During the experiment, soil samples were collected daily for the measurements. The microbialpopulation was determined by conventional methods of colony counting.As expected, as a higher voltage is applied to the soil, the current through it is also higher. Thus, itis expected that the negative effect of electrical current on microorganisms is greater at this voltage.Based on obtained results, in both voltages, a decrease in the microbial population was observedby applying them. This reduction in population is greater in the case where a higher voltage isapplied (Fig. ۱). On the other hand, the recovery of the microbial population was faster in the case where a lower voltage was applied. In the control condition, the microbial population was observed to be steadily increasing. Based on this, it can be concluded that applying high voltage to the soilcan have a negative effect on the structure of microorganisms and lead to their death and reduce their ability to re-increase the population after removing the environmental harsh conditions.Electroporation, disruption of cell membranes, oxidative stress, and cell death due toelectrochemically generated oxidants have been identified to be responsible for cell death duringelectrochemical exposure [۶].

کلیدواژه ها:

Electrokinetics ، Microbial population ، Cell damage ، Electrical stress.