Persistent conductive membrane in an electro-membrane reactor for nitrate removal in the electrocoagulation process

The United Nations (UN) has set "Clean Water and Sanitation" as its sixth Sustainable Development Goal to be accomplished by ۲۰۳۰ in response to the freshwater issue (SDG) [۱]. Nitrate (NO۳-), one of the anionic environmental pollutants, is a worldwide issue for groundwater contamination. Due to the use of chemical fertilizers, the conversion of grasslands to arable land, and the release of residential sewage into rivers, there is now more nitrate readily accessible. Although a rise in nitrate concentration is not particularly detrimental for adults, it can cause a blue baby syndrome in infants less than six months when it reaches a high concentration, which interacts with blood hemoglobin to form methemoglobin [۲]. Because of this, the World Health Organization (WHO) has established the maximum amount of this anion that is permitted in drinking water at ۱۰(...) [۳]. Electrocoagulation is one of the most efficient methods for nitrate removal, but it requires post-treatment processes and microfiltration membranes cannot separate nitrate molecules alone [۴]. In this work, we use a conductive stainless steel/PVC membrane as a cathode to synergistically remove nitrate by electrocoagulation and repulsive force and obtain cleaner production as drinking water [۵][۶]. The effects of variables such as voltage, current, and time will be investigated. Non-solvent- induced phase separation was used to create the membrane (Figure ۱). After preparing ۱۵% PVC solution with ۸۳% DMF as a solvent and mixing it for ۱۵ minutes, ۲% PEG was added as a pore-forming agent. The mixture was then agitated at ۲۰۰ rpm for ۲۴ hours to achieve homogeneity, and enough time was allowed for the bubbles to completely deflate. A portion of the completed solution was applied to stainless steel mesh using an automatic film applicator at a speed of ۱۵ mm/s and a thickness of ۲۵۰ m. To start phase inversion, the polymeric solution was submerged in a water bath. As a cathode in the electrocoagulation process, the generated membrane was employed within a home-fabricated module after its characterization. Circular aluminum measuring ۱۲.۵ cm۲ and conductive membranes spaced ۱ cm apart serve as the anodeand cathode, respectively. The pH of the solution was adjusted using HCl and NaOH, and ۱ mol/l NaCl was added to improve conductivity and lessen cathode passivation. The DC power supply provided the needed potential. We utilize a vacuum pump to extract a sample from aninitial solution of nitrate with a concentration of ۲۲.۵ (...)in deionized water undervarious circumstances (transmembrane pressure of ۰.۴ bar). Nitrate concentration was calculated using a UV-vis instrument (Gen Way۶۷.A) as Eq. ۱.Minitab software was used to do a Box-Benken statistical analysis to examine how current, voltage, and time affected the removal of nitrate. To reduce nitrate concentration and energy use, the variables voltage (۲۲, ۲۴, and ۲۶ volts), current (۰.۲, ۰.۲۶, and ۰.۳۲ amperes), and time(۶۰, ۱۲۰, and ۱۸۰ minutes) were used. At ۲۲.۶ V, ۰.۲ A, and ۶۰ min, which corresponds to ۵۵% nitrate removal and ۶.۱۲ kwh/m۳ energy consumption, the best option in terms of nitrate removal and energy consumption was discovered. The outcome demonstrates the efficacy of the electrocoagulation procedure as well as the repulsive force in removing negatively charged nitrate. Additionally, the membrane was able to successfully separate the flocs that were produced and lower the turbidity, TDS, and water hardness. Additionally, the mass of the sacrificed anode complies with the faraday law. Moreover, the bubbles produced from the surface of the membrane can reduce the membrane fouling and occupied space compare to a separated system.

کلیدواژه ها:

Nitrate removal ، electric field ، conductive membrane ، electrocoagulation