Evaluation of extracellular polymeric substances extracted from waste activated sludge as a renewable corrosion inhibitor

Abstract

Background Waste activated sludge (WAS) has recently gained attention as a feedstock for resource recovery. The aim of this study is to investigate the corrosion inhibition efficiencies of extracellular polymeric substances (EPS) extracted from WAS. Methods The studied corrosion inhibitors were tested with carbon steel in 3.64% NaCl saturated with CO2 at 25 °C, which is the typical oilfield environment. They were first prepared by EPS extraction (heating at 80 °C), followed by centrifugation for solid and liquid separation, then the supernatant was freeze-thawed five times for sterilization of microorganisms in WAS to terminate metabolic activities in the test inhibitors to ensure consistency in corrosion inhibition. The EPS mixture (supernatant) was then deemed as the test corrosion inhibitor. The inhibition performance was determined using potentiodynamic polarization scans. Results Waste activated sludge alone showed unsatisfactory inhibition. However, EPS extracted from WAS showed an optimum inhibition of approximately 80% with 1,000 mg/L of inhibitor. The average total solid (TS) and EPS contents of the WAS were 7,330 mg TS/L WAS and 110 mg EPS/g TS, respectively. Three sets of extracted EPS were scanned with fourier-transform infrared spectroscopy (FTIR) and showed almost overlapping curves, yielding the consistent inhibition performance. Discussion The potentiodynamic polarization results indicated that EPS acts as a mixed-type inhibitor which inhibits corrosion on both anode and cathode sites of metal surfaces. Based on the FTIR results, it was assumed that major chemical groups O–H, N–H, C–N, C=O, and C–H contributed to the inhibition by adsorbing on the metal surface, forming a biofilm that acts as a protective barrier to isolate the metal from its corrosive environment. Results show that WAS EPS corrosion inhibitors have inhibition performance comparable to commercial products, signifying their potential in commercialization. This corrosion inhibitor is renewable, biodegradable, non-toxic, and free from heavy metal, making it a superior green corrosion inhibitor candidate. Additionally, turning biomass into value-added product can be beneficial to the environment and, in this case, deriving new materials from WAS could also transform the economics of wastewater treatment operations.

Peer Review #2 of "Kinetic and thermodynamic analyses of the corrosion inhibition of synthetic extracellular polymeric substances (v0.1)"

“…The corrosion inhibition capability of synthetic EPS was proven significant in this study. The trend in the IR spectrum of the synthetic EPS followed closely to the natural WAS EPS [8] as expected because it is formulated based on the chemical composition of natural WAS EPS. Similar to the natural WAS EPS, the FTIR results of synthetic EPS showed that functional groups O-H, N-H, C-N, C=O, and C-H were present.…”

“…At 25°C, the maximum inhibition protection of synthetic EPS was 82% at a concentration of 153 mg/L. The previous study of WAS EPS inhibitor demonstrated an optimum inhibition performance of about 79% at a concentration of 1000 mg/L [8]. Even though the inhibition performance showed only a mere improvement of 3%, the inhibitor concentration was reduced by about 6.5 times.…”

“…This article is an extension of a previous study that showed the potential of EPS extracted from waste activated sludge (WAS) of wastewater treatment operations as a green corrosion inhibitor for CO 2 corrosion. A maximum inhibition performance of about 80% was achieved with the application of 1000 mg/L of this inhibitor [8] [9]. The major flaw in this corrosion inhibitor is that the inhibition performance is not consistent due to the variation in wastewater compositions.…”

“…Small amounts of humic substances [5], uronic acids, and nucleic acids [1] [6] [7] were also detected in EPS. A previous study [8] [9] showed the potential of EPS extracted from waste activated sludge (WAS) of wastewater treatment operations as a green corrosion inhibitor for CO 2 corrosion. A maximum inhibition performance of about 80% was achieved with the application of 1000 mg/L of this inhibitor.…”

A Review of Recent Advances in the Inhibition of Sweet Corrosion

“…It was also reported that natural products are used to either synthesize [37,104–105,107c,118b,119‐120,131a‐c,e,144] or modify other compounds [128c,f,131d] that have been tested as CIs in a CO 2 environment (Table S10 in Supplementary Material). In addition, the corrosion inhibition effectiveness of extracellular polymeric substances extracted from waste activated sludge [77] and berberine extracted from Coptis chinensis [67c] was evaluated for CS immersed in CO 2 ‐saturated 3.64 wt.% NaCl solution and for L360 steel immersed in CO 2 ‐saturated 3.5 wt.% NaCl solution, respectively. There were also studies on the corrosion inhibition role of gum arabic, [82] aqueous solutions of caffeine and nicotine, [94] and sophorolipids (a mixture produced by Starmerella bombicola with a carbon source of glucose and rapeseed oil) in CO 2 ‐saturated brine solutions (Table S11 in Supplementary Material).…”