Chhaya Sharma

Microbial influenced corrosion by thermophilic bacteria

The present study was undertaken to investigate microbial influenced corrosion (MIC) on stainless steels due to thermophilic bacteria Desulfotomaculum nigrificans. The objective of the study was to measure the extent of corrosion and correlate it with the growth of the biofilm by monitoring the composition of its extracellular polymeric substances (EPS). The toxic effect of heavy metals on MIC was also observed. For this purpose, stainless steels 304L, 316L and 2205 were subjected to electrochemical polarization and immersion tests in the modified Baar’s media, control and inoculated, in anaerobic conditions at room temperature. Scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS) were used to identify the chemicals present in/outside the pit. The results show maximum corrosive conditions when bacterial activity is highest, which in turn minimizes the amount of carbohydrate and protein along with the increase in the fraction of uronic acid in carbohydrate in EPS of the biofilm. However, although bacterial activity and corrosion rate decreases, the amount of biofilm components continue to increase. It is also observed that the toxicity of metals ions affect the bacterial activity and EPS production. It was observed that Desulfotomaculum sp. has the ability to biodegrade its own EPS.

Ce1−xCoxOy nanocatalysts: synthesis, characterization and environmental application

In the present study, Ce1−xCoxOy nanocatalysts were synthesized by a simple co-precipitation method. The synthesized catalysts were further characterized using various techniques (XRD, FTIR, N2 adsorption/desorption, SEM, TEM, and EDX) in order to study their structural, micro-structural and textural properties. The catalytic activity of the nanocatalysts along with their degradation kinetics was studied for the catalytic wet air oxidation (CWAO) of paper industry wastewater at mild reaction conditions of 90 °C and 1 atm. Interestingly, mixed oxide catalysts exhibited higher activity than the corresponding single-metal oxides, and the catalyst with a Co/Ce molar ratio of 1 : 1 exhibited maximum removal of color (79%), COD (68%), TOC (66%), AOX (59%) and CHPs (62%). The biodegradability increased appreciably from 0.27 to 0.45, indicating the degradation potential of the nanocatalyst for non-biodegradable compounds. Furthermore, the recyclability of mixed catalysts was ascertained through continuous reuse experiments.

Comparison of Biocorrosion due to Desulfovibrio desulfuricans and Desulfotomaculum nigrificans Bacteria

One observes several species of sulfate-reducing bacteria in nature. Presence of these species in a media may cause microbial influenced corrosion (MIC) of materials differently. To investigate this aspect of MIC, corrosion tests were performed on three types of stainless steels. The tests were done in modified Baar’s media inoculated separately by the two species of SRB namely Desulfovibrio desulfuricans (DD) and Desulfotomaculum nigrificans (DN). Electrochemical and immersion tests were performed to assess the extent of uniform and localized corrosion of these steels. Biofilms formed on the corroded samples were analyzed for estimating various components of its extracellular polymeric substances. Hydrogenase enzyme of these bacteria was tested to determine its nature and activity. Higher degree of corrosivity was observed in case of media inoculated with DD as compared to DN. More active nature of hydrogenase enzyme, its location in the periplasmic phase in DD and higher fraction of carbohydrate in biofilm formed due to DD have been suggested to be responsible for higher degree of corrosivity caused by them.

Microbial influenced corrosion due to Desulfovibrio desulfuricans

Purpose – The purpose of this paper is to investigate microbially induced corrosion on stainless steels due to sulfate reducing bacteria sp. Desulfovibrio desulfuricans and correlate it with the composition of extracellular polymeric substances (EPS) of the biofilm formed by these bacteria.Design/methodology/approach – Stainless steels 304L, 316L and 2205 were selected for the test. Modified Baars media, both control and inoculated, were used as test solutions in anaerobic conditions. The bacteria were identified by scanning electron microscopy and their growth was estimated by bacterial counting. Electrochemical polarization and immersion test were performed to estimate the corrosion rate and the extent of pitting attack. The degree of corrosion and the presence of chemicals present inside/outside pits were determined by SEM/EDS. Biofilm formed on corroded coupons was analyzed spectroscopically to identify its components. An attempt was made to correlate the extent of corrosion with the bacterial concen...

Effect of Host Media on Microbial Influenced Corrosion due to Desulfotomaculum nigrificans

This article reports about the tests carried to investigate microbial-induced corrosion on stainless steels due to sulfate-reducing bacteria sp. Desulfotomaculum nigrificans in different host media. Stainless steel 304L, 316L, and 2205 were selected for the test. Modified Baar’s media (BM), sodium chloride solution, and artificial sea water (SW) were used as test solutions in anaerobic conditions. Electrochemical polarization and immersion test were performed to estimate the extent of corrosion rate and pitting on stainless steels. SEM/EDS were used to study the details inside/outside pits formed on the corroded samples. Biofilm formed on corroded coupons was analyzed for its components by UV/Visible spectroscopy. Corrosion attack on the test samples was observed maximum in case of exposure to SW followed by NaCl solution, both having sulfide and chloride whereas stainless steel exposed to BM, having sulfide, showed minimum attack. Tendency of extracellular polymeric substances to bind metal ions is observed to be responsible for governing the extent of corrosion attack.

Synthesis, characterization and catalytic performance of ZnO–CeO2 nanoparticles in wet oxidation of wastewater containing chlorinated compounds

Here we report the catalytic property of ZnO–CeO2 nanoparticles towards oxidative degradation of organic pollutants present in industrial wastewater. The catalysts were prepared by co-precipitation method without using any surfactant. The physicochemical properties of catalysts were studied by XRD, Raman, XPS, N2-sorption, FE-SEM, TEM and EDX techniques. The characterization results confirmed the formation of porous ZnO–CeO2 nanocatalysts with high surface area, pore volume and oxygen vacancies. ZnO–CeO2 nanocatalysts exhibited appreciable efficiency in CWAO of industrial wastewater under mild conditions. The Ce40Zn60 catalyst was found to be most efficient with 72% color, 64% chemical oxygen demand (COD) and 63% total organic carbon (TOC) removal. Efficient removal of chlorophenolics (CHPs, 59%) and adsorbable organic halides (AOX, 54%) indicated the feasibility of using ZnO–CeO2 nanocatalysts in degradation of non-biodegradable and toxic chlorinated compounds.

Green Technology for the Removal of Chloro-Organics from Pulp and Paper Mill Wastewater.

This study evaluates the treatment efficiency of a horizontal subsurface-flow constructed wetland (HSSF-CW) for the removal of chloro-organic compounds from pulp and paper mill wastewater. The surface area of the HSSF-CW unit was 5.25 m² and was planted with Colocasia esculenta. The wastewater was characterized for different chloro-organic compounds, that is, adsorbable organic halides (AOX), chlorophenolics, and chlorinated resin and fatty acids (cRFAs). Under a hydraulic retention time of 5.9 days, the average AOX, chlorophenolics, and cRFA removal from wastewater was 87, 87, and 93%, respectively. Some of the chlorophenolics were found to accumulate in the plant biomass and soil material. The mass balance studies show that a significant fraction of chlorophenolics and cRFA was degraded in the constructed wetland system. Modeling studies were carried out to estimate the first-order area-based removal rate constants (k) for chemical oxygen demand removal. The HSSF-CW was found to be an effective treatment technology for the remediation of pulp and paper mill wastewater.

In-Plant Corrosion Study of Steels in Distillery Effluent Treatment Plant

The present study deals with corrosion and performance of steels observed in an effluent treatment plant (ETP) of a distillery. For this purpose, the metal coupons were exposed in primary (untreated effluent) and secondary tank (anaerobic treatment effluent) of the ETP. The extent of attack has been correlated with the composition of the effluent with the help of laboratory immersion and electrochemical tests. Untreated distillery effluent found to be more corrosive than the anaerobic-treated effluents and is assigned due to chloride, phosphate, calcium, nitrate, and nitrite ions, which enhances corrosivity at acidic pH. Mild steel showed highest uniform and localized corrosion followed by stainless steels 304L and 316L and lowest in case of duplex 2205.

Electrochemical Corrosion Investigations on Anaerobic Treated Distillery Effluent

Present study is focused on the corrosivity of anaerobic treated distillery effluent and corrosion performance of mild steel and stainless steels. Accordingly, electrochemical polarization tests were performed in both treated distillery and synthetic effluents. Polarization tests were also performed in synthetic solutions and it was observed that Cl− and K+ increase whereas SO4−, PO4−, NO3−, and NO2− decrease the corrosivity of effluent at alkaline pH. Further, comparison in corrosivity of distillery and synthetic effluents shows the former to be less corrosive and this is assigned due to the presence of amino acids and melanoidins. Mild steel experienced to have the highest corrosion rate followed by stainless steels—304L and 316L and lowest in case of SAF 2205. Relative corrosion resistance of stainless steels is observed to depend upon Cr, Mo, and N content.

Fuzzy-based Probabilistic Ecological Risk Assessment Approach: A Case Study of Heavy Metal Contaminated Soil

The ecological risk assessment tools, viz. index of geoaccumulation (I geo) and enrichment factor (EF), are the classical models for the assessment of risk related to the soil and sediment contamination. These models are well classified into several classes for the assessment of contamination risk. The vagueness in the estimation of risk associated with these models creates voids for computational approaches. In the present study, fuzzy-based probabilistic model was developed to restrict the vagueness of risk estimation. Both I geo and EF were taken as input variables for aggregate risk determination. The linguistic attributes were assigned for risk estimation and qualitative scale presented as trapezoidal fuzzy number. For the validation of methodology, a case study was taken into the account for risk determination. The fuzzy-based aggregate risk assessment revealed high risk of cadmium and arsenic toxicity in the study area with the risk score of 0.751 and 0.698, respectively. The fuzzy-based risk assessment is a conceptual methodology that restricts the vagueness in the estimation of risk for better decision-making approach.