The effect of TiO2 nanoparticles on sulfate-reducing bacteria and their consortium under anaerobic conditions

Control and prevention of microbially influenced corrosion using cephalopod chitosan and its derivatives: A review

Microbially influenced corrosion (MIC) of metals is an important industrial problem, causing 300-500 billion dollars of economic loss worldwide each year. It is very challenging to prevent or control the MIC in the marine environment. Eco-friendly coatings embedded with corrosion inhibitors developed from natural products may be a successful approach for MIC prevention or control. As a natural renewable resource, cephalopod chitosan has a number of unique biological properties, such as antibacterial, antifungal and non-toxicity effects, which attract scientific and industrial interests for potential applications. Chitosan is a positively charged molecule, and the negatively charged bacterial cell wall is the target of its antimicrobial action. Chitosan binds to the bacterial cell wall and disrupts the normal functions of the membrane by, for example, facilitating the leakage of intracellular components and impeding the transport of nutrients into the cells. Interestingly, chitosan is an excellent film-forming polymer. Chitosan may be applied as an antimicrobial coating substance for the prevention or control of MIC. Furthermore, the antimicrobial chitosan coating can serve as a basal matrix, in which other antimicrobial or anticorrosive substances like chitosan nanoparticles, chitosan silver nanoparticles, quorum sensing inhibitors (QSI) or the combination of these compounds, can be embedded to achieve synergistic anticorrosive effects. A combination of field and laboratory experiments will be conducted to test this hypothesis for preventing or controlling MIC in the marine environment. Thus, the proposed review will identify new eco-friendly MIC inhibitors and will assay their potential in future applications in the anti-corrosion industry.

A review on the generation, discharge, distribution, environmental behavior, and toxicity (especially to microbial aggregates) of nano-TiO2 in sewage and surface-water and related research prospects

This article reviews the nano-effects and applications of different crystalline nano‑titanium dioxide (nano-TiO₂), identifies their discharge, distribution, behavior, and toxicity to aquatic organisms (focusing on microbial aggregates) in sewage and surface-water, summarizes related toxicity mechanisms, and critically proposes future perspectives. The results show that: 1) based on crystal type, application boundaries of nano-TiO₂ have become clear, extending from traditional manufacturing to high-tech fields; 2) concentration of nano-TiO₂ in water is as high as hundreds of thousands of μg/L (sewage) or several to dozens of μg/L (surface-water) due to direct application or indirect release; 3) water environmental behaviors of nano-TiO₂ are mainly controlled by hydration conditions and particle characteristics; 4) aquatic toxicities of nano-TiO₂ are closely related to their water environmental behavior, in which crystal type and tested species (such as single species and microbial aggregates) also play the key role. Going forward, the exploration of the toxicity mechanism will surely become a hot topic in the aquatic-toxicology of nano-TiO₂, because most of the research so far has focused on the responses of biological indicators (such as metabolism and damage), while little is known about the stress imprint caused by the crystal structures of nano-TiO₂ in water environments. Additionally, the aging of nano-TiO₂ in a water environment should be heeded to because the continuously changing surface structure is bound to have a significant impact on its behavior and toxicity. Moreover, for microbial aggregates, comprehensive response analysis should be conducted in terms of the functional activity, surface features, composition structure, internal microenvironment, cellular and molecular level changes, etc., to find the key point of the interaction between nano-TiO₂ and microbial aggregates, and to take mitigation or beneficial measures to deal with the aquatic-toxicity of nano-TiO₂. In short, this article contributes by 1) reviewing the research status of nano-TiO₂ in all aspects: application and discharge, distribution and behavior, and its aquatic toxicity; 2) suggesting the response mechanism of microbial aggregates and putting forward the toxigenic mechanism of nanomaterial structure; 3) pointing out the future research direction of nano-TiO₂ in water environment.

On the incorporation of nano TiO2to inhibit concrete deterioration in the marine environment

To develop high deterioration resistance concrete for marine infrastructures, two types of nano TiO₂(NT) including anatase phase NT and silica surface-treated rutile phase NT were incorporated into concrete. The fabricated NT modified concrete was then put into the marine environment for 21 months in this study. The effects and mechanisms of two types of NT on the deterioration of concrete in the marine environment were investigated from three aspects, including seawater physical and biological as well as chemical actions on concrete with NT. Under the seawater physical action, the exposed degree of coarse sand particles on the surface of control concrete is greater than that of concrete with NT. Owing to the microorganism biodegradation property of NT, the elimination and inhibition rates of concrete with NT on microorganisms can reach up to 76.98% and 96.81%, respectively. In addition, the surface biofilm thickness of concrete can be reduced by 49.13% due to the inclusion of NT. In the aspect of seawater chemical action, NT can increase the pH value inside concrete by 0.81, increase the degree of polymerization of C-S-H gel, and improve the interfacial transition zone between cement paste and aggregate in concrete. Compared to anatase phase NT, silica surface-treated rutile phase NT is more effective in improving the deterioration resistance of concrete in the marine environment. It can be concluded that incorporating NT can inhibit the deterioration of concrete in the marine environment.

Novel Approaches for Biocorrosion Mitigation in Sewer Systems

Concrete sewer pipes can be corroded by the biogenic sulfuric acid (H2SO4) generated from microbiological activities in a process called biocorrosion or microbiologically induced corrosion (MIC). In this study, inhibitors that can reduce Acidithiobacillus thiooxidans growth and thus may reduce the accumulation of biofilm components responsible for the biodegradation of concrete were used. D-tyrosine, tetrakis hydroxymethyl phosphonium sulfate (THPS) and TiO2 nanoparticles were investigated as potential inhibitors of sulfur-oxidizing bacteria (SOB) growth. Results showed that most of the chemicals used can inhibit SOB growth at a concentration lower than 100 mg/L. TiO2 nanoparticles exhibited the highest biocide effect and potential biocorrosion mitigation activity, followed by D-tyrosine and THPS.

Changes in bacterial diversity of activated sludge exposed to titanium dioxide nanoparticles

The rapid growth of the use of nanomaterials in different modern industrial branches makes the study of the impact of nanoparticles on the human health and environment an urgent matter. For instance, it has been reported that titanium dioxide nanoparticles (TiO₂ NPs) can be found in wastewater treatment plants. Previous studies have found contrasting effects of these nanoparticles over the activated sludge process, including negative effects on the oxygen uptake. The non-utilization of oxygen reflects that aerobic bacteria were inhibited or decayed. The aim of this work was to study how TiO₂ NPs affect the bacterial diversity and metabolic processes on an activated sludge. First, respirometry assays of 8 h were carried out at different concentrations of TiO₂ NPs (0.5-2.0 mg/mL) to measure the oxygen uptake by the activated sludge. The bacterial diversity of these assays was determined by sequencing the amplified V3-V4 region of the 16S rRNA gene using Illumina MiSeq. According to the respirometry assays, the aerobic processes were inhibited in a range from 18.5 ± 4.8% to 37.5 ± 2.0% for concentrations of 0.5-2.0 mg/mL TiO₂ NPs. The oxygen uptake rate was affected mainly after 4.5 h for concentrations higher than 1.0 mg/mL of these nanoparticles. Results indicated that, in the presence of TiO₂ NPs, the bacterial community of activated sludge was altered mainly in the genera related to nitrogen removal (nitrogen assimilation, nitrification and denitrification). The metabolic pathways prediction suggested that genes related to biofilm formation were more sensitive than genes directly related to nitrification-denitrification and N-assimilation processes. These results indicated that TiO₂ NPs might modify the bacteria diversity in the activated sludge according to their concentration and time of exposition, which in turn impact in the performance of the wastewater treatment processes.

Cumulative effects of titanium dioxide nanoparticles in UASB process during wastewater treatment

Titanium dioxide nanoparticles (TiO₂ NPs) are widely used in consumer products and one of their major fate is the wastewater treatment plants. However, NPs eventually arrive to aquatic and terrestrial ecosystems via treated water and biosolids, respectively. Since low concentration of NPs is accumulating in the upflow anaerobic sludge blanket (UASB) reactors that treat wastewater and reclaim water quality, the accumulation of TiO₂ NPs in these reactors may impact in their performance. In this work, the long-term effects of TiO₂ NPs on the main benefits of treating wastewater by UASB reactors such as, biogas production, methane fraction in biogas and organic matter removal were evaluated. Evaluation consisted of monitoring such parameters in two identical UASB reactors, one UASB-Control (without NPs) and the experimental one (UASB-TiO₂ NPs) that received wastewater with TiO₂ NPs. The fate of NPs in the UASB reactor was also determined. Results indicated that biogas production increased by 8.8% due to the chronic exposure of UASB reactor to TiO₂ NPs during the first 44 days of experiment. However, the methane content in the biogas had no significant differences between both UASB, ranging between 78% and 90% of methane during the experiment. The removal of organic matter in both UASB was similar and ranged 92-98% along the experimental time. This means that accumulation of TiO₂ NPs did not altered the biogas production and organic matter removal. However, the content of total volatile solids (TVS) in UASB-TiO₂ NPs dropped off from 137.8 g to 64.2 g in 84 days, while for control reactor that decreased from 141.6 g to 92.4 g in the same period. Hence, the increased biogas production in the UASB exposed to TiO₂ was attributed to hydrolysis of the TVS in this reactor. The main fate of TiO₂ NPs was the granular sludge, which accumulated up to 8.56 mg Ti/g, which represent around 99% of the Ti spiked to the reactor and the possible cause of the biomass hydrolyzation in the UASB. Disposal of UASB sludge containing NPs from may raise ecotoxicological concerns due to the use of biosolids in agricultural activities.

Chitosan/Lignosulfonate Nanospheres as "Green" Biocide for Controlling the Microbiologically Influenced Corrosion of Carbon Steel

In this work, uniform cross-linked chitosan/lignosulfonate (CS/LS) nanospheres with an average diameter of 150–200 nm have been successfully used as a novel, environmentally friendly biocide for the inhibition of mixed sulfate-reducing bacteria (SRB) culture, thereby controlling microbiologically influenced corrosion (MIC) on carbon steel. It was found that 500 µg·mL⁻¹ of the CS/LS nanospheres can be used efficiently for the inhibition of SRB-induced corrosion up to a maximum of 85% indicated by a two fold increase of charge transfer resistance (R_ct) on the carbon steel coupons. The hydrophilic surface of CS/LS can readily bind to the negatively charged bacterial surfaces and thereby leads to the inactivation or damage of bacterial cells. In addition, the film formation ability of chitosan on the coupon surface may have formed a protective layer to prevent the biofilm formation by hindering the initial bacterial attachment, thus leading to the reduction of corrosion.