Application of photoelectrochemical oxidation of wastewater used in the cooling tower water and its influence on microbial corrosion.

Background: Cooling towers are specialized heat exchanger devices in which air and water interact closely to cool the water's temperature. However, the cooling water contains organic nutrients that can cause microbial corrosion (MC) on the metal surfaces of the tower. This research explores the combined wastewater treatment approach using electrochemical-oxidation (EO), photo-oxidation (PO), and photoelectrochemical oxidation (PEO) to contain pollutants and prevent MC. Methods: The study employed electro-oxidation, a process involving direct current (DC) power supply, to degrade wastewater. MC studies were conducted using weight loss assessments, scanning electron microscopy (SEM), and x-ray diffraction (XRD). Results: After wastewater is subjected to electro-oxidation for 4 h, a notable decrease in pollutants was observed, with degradation efficiencies of 71, 75, and 96%, respectively. In the wastewater treated by PEO, microbial growth is restricted as the chemical oxygen demand decreases. Discussion: A metagenomics study revealed that bacteria present in the cooling tower water consists of 12% of Nitrospira genus and 22% of Fusobacterium genus. Conclusively, PEO serves as an effective method for treating wastewater, inhibiting microbial growth, degrading pollutants, and protecting metal from biocorrosion.

Bio-approach: preparation of RGO-AgNPs on cotton fabric and interface with sweat environment for antibacterial activity.

This study aims to develop a reduced graphene oxide (RGO)-silver nanoparticles (AgNPs) coating on the cotton fabric (CT) surface using photoreduction with a hydrothermal process and evaluate the antibacterial activity in a sweat environment. An ureolytic bacterium of Bacillus subtilis (HM475276) was used to generate ammonia from synthetic urine. RGO-AgNPs were synthesized on the CT surface using a moderate dosage of 1% silver ammonium complex. The analytical study reveals that spherical-shaped AgNPs of 10-50 nm size were uniformly anchored throughout the RGO sheet on the CT, further supported by X-ray photoelectron spectroscopic analysis (XPS). X-ray powder diffraction (XRD) and Energy-dispersive X-ray absorption spectroscopy (EDAX) elemental mapping confirmed Ag/AgCl formation on CT treated with sweat. The sustained release of Ag+ ions from the treated CT in the sweat solution was assessed by atomic absorption spectroscopy (AAS) and ranged from 2 to 8 ppm, correlated with antibacterial activity. The agar diffusion and solution suspension method to demonstrate the combat bacterial species were greater on RGO-AgNPs-CT than sweat-treated CT due to the suppression of Ag+ ion release caused by the deposition of Ag/AgCl. Hence, sweat-treated RGO-AgNPs-CT proved to have higher inactivation activity (45 min) than sweat-treated AgNPs-CT (60 min) due to the RGO-Ag/AgCl serving photocatalyst influencing hydroxyl radical (OH·) formation under sunlight. The RGO-AgNPs-CT has confirmed that it retains antibacterial activity after passing the laundry durability test. Together, the results showed an opportunity for improved functional fabrics that are exceptional at combating bacterial pathogens and holding up well to laundry durability tests.

Biofilm formation on copper and its control by inhibitor/biocide in cooling water environment.

The present study has successfully identified the nitrate reducing bacteria present in the cooling water system and also investigated the performance of industrially applied biocide and inhibitor on the bacterial inhibition. In order to carry out the objective of this study, facilities and methods such as 16S rRNA gene sequencing, Lowry assay, SEM, EIS, ICP-MS and weight loss analysis were being utilized. In this study, two out of the five morphologically dis- similar colonies identified through 16S rRNA gene sequencing, namely the Massilia timonae and the Pseudomonas, were being utilized in the biocorrosion study on copper metal. From the surface analysis using SEM demonstrated the phenomenon of biofilm formation on the copper surface. 2-methylbenzimidazole has the addition of methyl group in the diazole ring position of benzimidazole it has create basicity environment and inhibit the metal deterioration. Meanwhile, it is also deducible from the EIS and protein analysis that com- bination of biocide with either of the inhibitors gives rise to better biocorrosion suppression (0.00178 mpy and 0.00171mpy) as compared to the sole effect of either biocide or inhibitor (0.00219 mpy, 0.00162 and 0.00143). Biocorrosion system biocide with MBM was found to exhibit 65% corrosion inhibition efficiency. Moreover, adoption of 2-Methylbenzimidazole seems to display better performance as compared to Multionic 8151, which is adopted in cooling water system.

Microbial influenced corrosion of processing industry by re-circulating waste water and its control measures - A review.

In this review article, illustrating the impact and fundamental stuff of microbially influenced corrosion (MIC) along with mechanism, maintenance of materials, human life, wellbeing and inhibitors for cooling towers. Corrosion is a natural mechanism of oxidation and reduction of metal ions by chemical and electrochemical processes and microorganism accumulation. MIC occurs through the aggregation of microbes which can be secreting the extra polymeric substances (EPS) that oxidation of the metal surface. According to the reviews, in the cooling water system, the corrosion begins in the anode charge because its oxidation reaction quickly takes place on the metal surface than the cathode charge. Annihilate the corrosion process needs certain helper substances such as chemical or green compounds, called inhibitors. Corrosion inhibitors typically adopt the adsorption mechanism due to the presence of organic hetero atoms. Chemical and green inhibitors are used to prevent corrosion processes and since ancient times, vast quantities of chemical inhibitors have been used in industry due to their effectiveness and consistency. But still, the chemical inhibitors are more toxic to humans and the environment. Instead of chemical inhibitors, green inhibitors (natural products like plant leaves, flowers, stem, buds, roots and sea algae) are developed and used in industries. Generally, green inhibitors contain natural compounds, high inhibition efficiency, economic, eco- and human-friendly, and strong potential features against corrosion. Thus, a lot of research is ongoing to discover the green inhibitors in various parts of plants and seaweeds.

Bacillus megaterium-induced biocorrosion on mild steel and the effect of Artemisia pallens methanolic extract as a natural corrosion inhibitor.

Methanolic extract of Artemisia pallens (MEAP) (Asteraceae) was explored as greenbiocorrosion inhibitor for mild steel 1010 in 1.5% sodium chloride environment. Bacillus megaterium SKR7 induces the development of biofilm on the metal surface and forms the pitting corrosion. MEAP was showed (25 ppm) optimum inhibition effect of biocorrosion and further corrosion rate was highly reduced (0.3335 mm/year) than the control system (0.009 mm/year). The electrochemical study has supported the results with a higher value of total resistance (34 Ω cm2) when compared to control systems. It reveals the formation of a protective layer on the metal surface and reduces the adsorption of biofilm. This was due to the antimicrobial effect of MEAP. Overall, the results recognized that MEAP used as a green corrosion inhibitor for MS 1010 with 83% inhibition efficiency.