Succession of sulfur-oxidizing bacteria in the microbial community on corroding concrete in sewer systems

Bio-corrosion in concrete sewer systems: Mechanisms and mitigation strategies

The deterioration of concrete sewer structures due to bio-corrosion presents critical and escalating challenges from structural, economic and environmental perspectives. Despite decades of research, this issue remains inadequately addressed, resulting in billions of dollars in maintenance costs and a shortened service life for sewer infrastructure worldwide. This challenge is exacerbated by the absence of standardized test methods and universally accepted mitigation strategies, leaving industries and stakeholders confronting an increasingly pressing problem. This paper aims to bridge this knowledge gap by providing a comprehensive review of the complex mechanisms of bio-corrosion, focusing on the formation and accumulation of hydrogen sulfide, its conversion into sulfuric acid and the subsequent deterioration of concrete materials. The paper also explores various factors affecting bio-corrosion rates, including environmental conditions, concrete properties and wastewater characteristics. The paper further highlights existing corrosion test strategies, such as chemical tests, in-situ tests and microbial simulations tests along with their general analytical parameters. The conversion of hydrogen sulfide into sulfuric acid is a primary cause of concrete decay and its progression is influenced by environmental conditions, inherent concrete characteristics, and the composition of wastewater. Through illustrative case studies, the paper assesses the practical implications and efficacy of prevailing mitigation techniques. Coating materials provide a protective barrier against corrosive agents among the discussed techniques, while optimised concrete mix designs enhance the inherent resistance and durability of the concrete matrix. Finally, this review also outlines the future prospects and challenges in bio-corrosion research with an aim to promote the creation of more resilient and cost-efficient materials for sewer systems.

Sulfur-containing substances in sewers: Transformation, transportation, and remediation

Sulfur-containing substances in sewers frequently incur unpleasant odors, corrosion-related economic loss, and potential human health concerns. These observations are principally attributed to microbial reactions, particularly the involvement of sulfate-reducing bacteria (SRB) in sulfur reduction process. As a multivalent element, sulfur engages in complex bioreactions in both aerobic and anaerobic environments. Organic sulfides are also present in sewage, and these compounds possess the potential to undergo transformation and volatilization. In this paper, a comprehensive review was conducted on the present status regarding sulfur transformation, transportation, and remediation in sewers, including both inorganic and organic sulfur components. The review extensively addressed reactions occurring in the liquid and gas phase, as well as examined detection methods for various types of sulfur compounds and factors affecting sulfur transformation. Current remediation measures based on corresponding mechanisms were presented. Additionally, the impacts of measures implemented in sewers on the subsequent wastewater treatment plants were also discussed, aiming to attain better management of the entire wastewater system. Finally, challenges and prospects related to the issue of sulfur-containing substances in sewers were proposed to facilitate improved management and development of the urban water system.

Biomineralization To Prevent Microbially Induced Corrosion on Concrete for Sustainable Marine Infrastructure

Microbially induced corrosion (MIC) on concrete represents a serious issue impairing the lifespan of coastal/marine infrastructure. However, currently developed concrete corrosion protection strategies have limitations in wide applications. Here, a biomineralization method was proposed to form a biomineralized film on concrete surfaces for corrosion inhibition. Laboratory seawater corrosion experiments were conducted under different conditions [e.g., chemical corrosion (CC), MIC, and biomineralization for corrosion inhibition]. A combination of chemical and mechanical property measurements of concrete (e.g., sulfate concentrations, permeability, mass, and strength) and a genotypic-based investigation of formed concrete biofilms was conducted to evaluate the effectiveness of the biomineralization approach on corrosion inhibition. The results show that MIC resulted in much higher corrosion rates than CC. However, the biomineralization treatment effectively inhibited corrosion because the biomineralized film decreased the total and relative abundance of sulfate-reducing bacteria (SRB) and acted as a protective layer to control the diffusion of sulfate and isolate the concrete from the corrosive SRB communities, which helps extend the lifespan of concrete structures. Moreover, this technique had no negative impact on the native marine microbial communities. Our study contributes to the potential application of biomineralization for corrosion inhibition to achieve long-term sustainability for major marine concrete structures.

Establishing a green biodesulfurization process for iron ore concentrates in stirred tank and leaching column bioreactors using Acidithiobacillus thiooxidans

The presence of sulfur impurities in complex iron ores represents a significant challenge for the iron mining and steel-making industries as their removal often necessitates the use of hazardous chemicals and energy-intensive processes. Here, we examined the microbial and mineralogical composition of both primary and secondary iron concentrates, identifying the presence of Sulfobacillus spp. and Leptospirillum spp., while sulfur-oxidizing bacteria were absent. We also observed that these concentrates displayed up to 85% exposed pyrrhotite. These observations led us to explore the capacity of Acidithiobacillus thiooxidans to remove pyrrhotite-sulfur impurities from iron concentrates. Employing stirred tank bioreactors operating at 30°C and inoculated with 5·106 (At. thiooxidans cells mL-1), we achieved 45.6% sulfur removal over 16 days. Then, we evaluated packed leaching columns operated at 30°C, where the At. thiooxidans enriched system reached 43.5% desulfurization over 60 days. Remarkably, sulfur removal increased to 80% within 21 days under potassium limitation. We then compared the At. thiooxidans-mediated desulfurization process, with and without air supply, under potassium limitation, varying the initial biomass concentration in 1-m columns. Aerated systems facilitated approximately 70% sulfur removal across the entire column with minimal iron loss. In contrast, non-aerated leaching columns achieved desulfurization levels of only 6% and 26% in the lower and middle sections of the column, respectively. Collectively, we have developed an efficient, scalable biological sulfur-removal technology for processing complex iron ores, aligning with the burgeoning demand for sustainable practices in the mining industry.

Evaluation of commercial moving bed media and sugarcane bagasse as packing material in biotrickling filter for hydrogen sulfide removal

This study compared two biotrickling filter packing materials for hydrogen sulfide removal. Inlet H2S concentrations and empty-bed retention time were tested on the two biotrickling filters. First reactor (BT1) had immobilized sulfur-oxidizing bacteria on commercial moving-bed media, whereas second reactor (BT2) had sulfur-oxidizing bacteria on sugarcane bagasse. The study found that BT1 performed best at 120 s empty-bed retention time, 422.39 g/m3·h hydrogen sulfide loading rate, resulted in 416 g/m3·h hydrogen sulfide elimination capacity. In contrast, BT2 performed best at 180 s empty-bed retention time, 278.77 g/m3·h hydrogen sulfide loading rate, and 273 g/m3·h elimination capacity was achieved. High-throughput sequencing showed Acidithobacillus spp. dominated the sulfur-oxidizing bacteria consortium. Sugarcane bagasse may receive less hydrogen sulfide loading than moving bed medium under optimal conditions, but its low cost and reasonable removal capacity of hydrogen sulfide -containing industrial gases in a biotrickling filter system make it an excellent alternative packing material.

Microbially Influenced Corrosion of Steel in Marine Environments: A Review from Mechanisms to Prevention

Microbially influenced corrosion (MIC) is a formidable challenge in the marine industry, resulting from intricate interactions among various biochemical reactions and microbial species. Many preventions used to mitigate biocorrosion fail due to ignorance of the MIC mechanisms. This review provides a summary of the current research on microbial corrosion in marine environments, including corrosive microbes and biocorrosion mechanisms. We also summarized current strategies for inhibiting MIC and proposed future research directions for MIC mechanisms and prevention. This review aims to comprehensively understand marine microbial corrosion and contribute to novel strategy developments for biocorrosion control in marine environments.

Review on Microbially Influenced Concrete Corrosion

Microbially influenced concrete corrosion (MICC) causes substantial financial losses to modern societies. Concrete corrosion with various environmental factors has been studied extensively over several decades. With the enhancement of public awareness on the environmental and economic impacts of microbial corrosion, MICC draws increasingly public attention. In this review, the roles of various microbial communities on MICC and corresponding protective measures against MICC are described. Also, the current status and research methodology of MICC are discussed. Thus, this review aims at providing insight into MICC and its mechanisms as well as the development of protection possibilities.

A critical review of chemical uses in urban sewer systems

Chemical dosing is the most used strategy for sulfide and methane abatement in urban sewer systems. Although conventional physicochemical methods, such as sulfide oxidation (e.g., oxygen/nitrate), precipitation (e.g., iron salts), and pH elevation (e.g., magnesium hydroxide/sodium hydroxide) have been used since the last century, the high chemical cost, large environmental footprint, and side-effects on downstream treatment processes demand a sustainable and cost-effective alternative to these approaches. In this paper, we aimed to review the currently used chemicals and significant progress made in sustainable sulfide and methane abatement technology, including 1) the use of bio-inhibitors, 2) in situ chemical production, and 3) an effective dosing strategy. To enhance the cost-effectiveness of chemical applications in urban sewer systems, two research directions have emerged: 1) online control and optimization of chemical dosing strategies and 2) integrated use of chemicals in urban sewer and wastewater treatment systems. The integration of these approaches offers considerable system-wide benefits; however, further development and comprehensive studies are required.

Hydrogen sulfide control in sewer systems: A critical review of recent progress

In sewer systems where anaerobic conditions are present, sulfate-reducing bacteria reduce sulfate to hydrogen sulfide (H₂S), leading to sewer corrosion and odor emission. Various sulfide/corrosion control strategies have been proposed, demonstrated, and optimized in the past decades. These included (1) chemical addition to sewage to reduce sulfide formation, to remove dissolved sulfide after its formation, or to reduce H₂S emission from sewage to sewer air, (2) ventilation to reduce the H₂S and humidity levels in sewer air, and (3) amendments of pipe materials/surfaces to retard corrosion. This work aims to comprehensively review both the commonly used sulfide control measures and the emerging technologies, and to shed light on their underlying mechanisms. The optimal use of the above-stated strategies is also analyzed and discussed in depth. The key knowledge gaps and major challenges associated with these control strategies are identified and strategies dealing with these gaps and challenges are recommended. Finally, we emphasize a holistic approach to sulfide control by managing sewer networks as an integral part of an urban water system.

O2 partitioning of sulfur oxidizing bacteria drives acidity and thiosulfate distributions in mining waters

The acidification of water in mining areas is a global environmental issue primarily catalyzed by sulfur-oxidizing bacteria (SOB). Little is known about microbial sulfur cycling in circumneutral pH mine tailing impoundment waters. Here we investigate biological sulfur oxidation over four years in a mine tailings impoundment water cap, integrating aqueous sulfur geochemistry, genome-resolved metagenomics and metatranscriptomics. The microbial community is consistently dominated by neutrophilic, chemolithoautotrophic SOB (relative abundances of ~76% in 2015, ~55% in 2016/2017 and ~60% in 2018). Results reveal two SOB strategies alternately dominate across the four years, influencing acid generation and sulfur speciation. Under oxic conditions, novel Halothiobacillus drive lower pH conditions (as low as 4.3) and lower [S₂O₃^2-] via the complete Sox pathway coupled to O₂. Under anoxic conditions, Thiobacillus spp. dominate in activity, via the incomplete Sox and rDSR pathways coupled to NO₃^-, resulting in higher [S₂O₃^2-] and no net significant acidity generation. This study provides genomic evidence explaining acidity generation and thiosulfate accumulation patterns in a circumneutral mine tailing impoundment and has significant environmental applications in preventing the discharge of sulfur compounds that can impact downstream environments. These insights illuminate opportunities for in situ biotreatment of reduced sulfur compounds and prediction of acidification events using gene-based monitoring and in situ RNA detection.

Inhibition Effect of Pseudomonas stutzeri on the Corrosion of X70 Pipeline Steel Caused by Sulfate-Reducing Bacteria

Microbiologically influenced corrosion (MIC) is a common phenomenon in water treatment, shipping, construction, marine and other industries. Sulfate-reducing bacteria (SRB) often lead to MIC. In this paper, a strain of Pseudomonas stutzeri (P. stutzeri) with the ability to inhibit SRB corrosion is isolated from the soil through enrichment culture. P. stutzeri is a short, rod-shaped, white and transparent colony with denitrification ability. Our 16SrDNA sequencing results verify the properties of P. stutzeri strains. The growth conditions of P. stutzeri bacteria and SRB are similar, and the optimal culture conditions are about 30 °C, pH 7, and the stable stage is reached in about seven days. The bacteria can coexist in the same growth environment. Using the weight loss method, electrochemical experiments and composition analysis techniques we found that P. stutzeri can inhibit the corrosion of X70 steel by SRB at 20~40 °C, pH 6~8. Furthermore, long-term tests at 3, 6 and 9 months reveal that P. stutzeri can effectively inhibit the corrosion of X70 steel caused by SRB.

Effect of Pseudomonas aeruginosa on corrosion of X65 pipeline steel

Microbiologically influenced corrosion (MIC) has caused great losses to many industries. This paper aimed to study the corrosion behavior of P. aeruginosa on X65 steel. The corrosion behavior of P. aeruginosa on X65 steel under aerobic and anaerobic conditions was studied by scanning electron microscopy, energy dispersive spectrometer and electrochemical analysis techniques. The results showed that the corrosion rate of X65 steel in bacterial environment is higher than that in sterile environment. In anaerobic environment, the corrosion of P. aeruginosa is mainly secreted acidic metabolites, and alkaline substances are corroded in aerobic environment. In general, the corrosion of X65 steel by P. aeruginosa in aerobic environment is more serious than that in anaerobic environment.

The fate of tetrathionate during the development of a biofilm in biogenic sulfuric acid attack on different cementitious materials

The biodeterioration of cement-based materials in sewer environments occurs because of the production of sulfuric acid from the biochemical oxidation of H₂S by sulfur-oxidizing bacteria (SOB). In the perspective of determining the possible reaction pathways for the sulfur cycle in such conditions, hydrated cementitious binders were exposed to an accelerated laboratory test (BAC test) to reproduce a biochemical attack similar to the one occurring in the sewer networks. Tetrathionate was used as a reduced sulfur source to naturally develop sulfur-oxidizing activities on the surfaces of materials. The transformation of tetrathionate was investigated on materials made from different binders: Portland cement, calcium aluminate cement, calcium sulfoaluminate cement and alkali-activated slag. The pH and the concentration of the different sulfur species were monitored in the leached solutions during 3 months of exposure. The results showed that the formation of different polythionates was independent of the nature of the material. The main parameter controlling the phenomena was the evolution of the pH of the leached solutions. Moreover, tetrathionate disproportionation was detected with the formation of more reduced forms of sulfur compounds (pentathionate, hexathionate and elemental sulfur) along with thiosulfate and sulfate. The experimental findings allowed numerical models to be developed to estimate the amount of sulfur compounds as a function of the pH evolution. In addition, biomass samples were collected from the exposed surface and from the deteriorated layers to identify the microbial populations. No clear influence of the cementitious materials on the selected populations was detected, confirming the previous results concerning the impact of the materials on the selected reaction pathways for tetrathionate transformation.

Two New Species of Filamentous Sulfur Bacteria of the Genus Thiothrix, Thiothrix winogradskyi sp. nov. and ‘Candidatus Thiothrix sulfatifontis’ sp. nov

The metagenome of foulings from sulfidic spring “Serovodorodny” (Tatarstan, Russia), where members of the genus Thiothrix was observed, was sequenced. Representatives of the phyla Gammaproteobacteria, Cyanobacteria and Campilobacteriota dominated in the microbial community. The complete genome of Thiothrix sp. KT was assembled from the metagenome. It displayed 93.93–99.72% 16S rRNA gene sequence identity to other Thiothrix species. The average nucleotide identity (ANI) и digital DNA-DNA hybridization (dDDH) showed that the genome designated KT represents a new species within the genus Thiothrix, ‘Candidatus Thiothrix sulfatifontis’ sp. nov. KT. The taxonomic status has been determined of the strain Thiothrix sp. CT3, isolated about 30 years ago and not assigned to any of Thiothrix species due to high 16S rRNA gene sequence identity with related species (i.e., 98.8–99.4%). The complete genome sequence of strain CT3 was determined. The ANI between CT3 and other Thiothrix species was below 82%, and the dDDH values were less than 40%, indicating that strain CT3 belongs to a novel species, Thiothrix winogradskyi sp. nov. A genome analysis showed that both strains are chemo-organoheterotrophs, chemolithotrophs (in the presence of hydrogen sulfide and thiosulfate) and chemoautotrophs. For the first time, representatives of Thiothrix showed anaerobic growth in the presence of thiosulfate.

Rapid start of high-concentration denitrification and desulfurization reactors by heterotrophic denitrification sulphur-oxidising bacteria

High sulphide concentrations can be toxic to denitrifying and desulphurising microorganisms. In this study, bioaugmentation was used to solve this problem. Pseudomonas sp. gs1 can tolerate 400 mg/L sulphide and converts most of the sulphide into elemental sulphur after 4 h. A solid inoculum of Pseudomonas sp. h1 was prepared. Two reactors, that is, one with and one without inoculum, were simultaneously run for 60 days. Bioreactor II to which bacterial inoculum was added reached a good treatment performance on day 3. The elemental sulphur concentration of the effluent was 342.6 mg/L. It was maintained at 245.3-333.8 mg/L during the subsequent operation. In contrast, reactor I without inoculants achieved the same performance on day 50. High-throughput sequencing shows that Pseudomonas and Azoarcus are the dominant genera. The abundance of the genus Pseudomonas and related denitrifying sulphur-oxidising bacteria in reactor I increases with the operation time. This phenomenon was confirmed by testing the sqr and gltA genes. The quantitative fluorescence PCR test also proves that the addition of bacteria leads to a rapid increase in the sulphur oxidation and carbon metabolism of the activated sludge in the reactor.

Characterization and Comparison of Corrosion Layer Microstructure between Cement Mortar and Alkali-Activated Fly Ash/Slag Mortar Exposed to Sulfuric Acid and Acetic Acid

In this study, we investigated the formation and evolution of the corrosion layers in alkali-activated mortar and ordinary Portland cement mortar exposed to sulfuric acid and acetic acid environments with different pH values, and explored the differences in the deterioration mechanisms. The experimental results indicated that ordinary Portland cement (OPC) mortars experienced more severe deterioration in terms of appearance, mass loss, and strength loss as compared with alkali-activated mortars exposed to an acetic acid environment, but their neutralization depths were smaller. Alkali-activated fly ash (AAF) mortar had a the relatively intact appearance but the greatest neutralization depth, which was due to its stable three-dimensional network but highly porous structure. To sum up, alkali-activated fly ash/slag (AFS) mortar had the best resistance to acid attack. In addition, the mortars exposed to acetic acid suffered greater deterioration than those exposed to sulfuric acid with the same pH values, which was mainly due to the highly porous corrosion layer formed in acetic acid, whereas crystallization of gypsum in sulfuric acid had a pore filling effect. However, for alkali-activated slag (AAS) and OPC mortars exposed to a sulfuric acid environment, extensive gypsum resulted in the formation of micro-cracks, and the corrosion layer of OPC mortar was more prone to fall off. OPC mortar also had the greatest resistance difference values of the continuously connected micro-pores before and after acid corrosion, followed by AAS, AAF, and AFS mortars, and these values for all the specimens were smaller in sulfuric acid. Furthermore, the gaps between acetic and sulfuric acid attacks increased with increased calcium content in binders, which were 7%, 13%, 21%, and 29% for AAF, AFS, AAS, and OPC mortars, respectively. Thus, it can be inferred that an appropriate amount of gypsum existed in the corrosion layer which could act as a barrier to some extent ina sulfuric acid environment.

Corrosion mitigation by nitrite spray on corroded concrete in a real sewer system

Microbially influenced concrete corrosion (MICC) in sewers is caused by the activity of sulfide-oxidizing microorganisms (SOMs) on concrete surfaces, which greatly deteriorates the integrity of sewers. Surface treatment of corroded concrete by spraying chemicals is a low-cost and non-intrusive strategy. This study systematically evaluated the spray of nitrite solution in corrosion mitigation and re-establishment in a real sewer manhole. Two types of concrete were exposed at three heights within the sewer manhole for 21 months. Nitrite spray was applied at the 6th month for half of the coupons which had developed active corrosion. The corrosion development was monitored by measuring the surface pH, corrosion product composition, sulfide uptake rate, concrete corrosion loss, and the microbial community on the corrosion layer. Free nitrous acid (FNA, i.e. HNO₂), formed by spraying a nitrite solution on acidic corrosion surfaces, was shown to inhibit the activity of SOMs. The nitrite spray reduced the corrosion loss of concrete at all heights by 40-90% for six months. The sulfide uptake rate of sprayed coupons was also reduced by about 35%, leading to 1-2 units higher surface pH, comparing to the control coupons. The microbial community analysis revealed a reduced abundance of SOMs on nitrite sprayed coupons. The long-term monitoring also showed that the corrosion mitigation effect became negligible in 15 months after the spray. The results consistently demonstrated the effectiveness of nitrite spray on the MICC mitigation and identified the re-application frequencies for full scale applications.

A novel granular sludge-based and highly corrosion-resistant bio-concrete in sewers

Bio-concrete is known for its self-healing capacity although the corrosion resistance was not investigated previously. This study presents an innovative bio-concrete by mixing anaerobic granular sludge into concrete to mitigate sewer corrosion. The control concrete and bio-concrete (with granular sludge at 1% and 2% of the cement weight) were partially submerged in a corrosion chamber for 6 months, simulating the tidal-region corrosion in sewers. The corrosion rates of 1% and 2% bio-concrete were about 17.2% and 42.8% less than that of the control concrete, together with 14.6% and 35.0% less sulfide uptake rates, 15.3% and 55.6% less sulfate concentrations, and higher surface pH (up to 1.8 units). Gypsum and ettringite were major corrosion products but in smaller sizes on bio-concrete than that of control concrete. The total relative abundance of corrosion-causing microorganisms, i.e. sulfide-oxidizing bacteria, was significantly reduced on bio-concrete, while more sulfate-reducing bacteria (SRB) was detected. The corrosion-resistance of bio-concrete was mainly attributed to activities of SRB derived from the granular sludge, which supported the sulfur cycle between the aerobic and anaerobic corrosion sub-layers. This significantly reduced the net production of biogenic sulfuric acid and thus corrosion. The results suggested that the novel granular sludge-based bio-concrete provides a highly potential solution to reduce sewer corrosion.

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.

Metagenomics and metatranscriptomics uncover the microbial community associated with high S0 production in a denitrifying desulfurization granular sludge reactor

The denitrification desulfurization process is a promising technology for elemental sulfur (S⁰) production from sulfide containing wastewater. However, the microbial community associated with high S⁰ production still is not well studied. This study describes an efficient denitrification S⁰ production bioreactor based on inoculation with anaerobic granular sludge. At an optimal S/N molar ratio of 7:2, 80 % of the influent sulfide was transformed to high quality elemental sulfur with a purity of 92.5% while the total inorganic nitrogen removal efficiency was stable at ∼80%. Metatranscriptomic analysis found that community expression of the gene encoding the sulfide-quinone reductase (SQR) was 10-fold greater than that of the flavocytochrome-c sulfide dehydrogenase subunit B (fccB). Moreover, the expression level of SQR was also significantly higher than the Dsr gene encoding for dissimilatory sulfate reductase, which encodes a critical S⁰ oxidation enzyme. Metagenomic binning analysis confirmed that sulfide-oxidizing bacteria (SOB) utilizing SQR were common in the community and most likely accounted for high S⁰ production. An unexpected enrichment in methanogens and high expression activity of bacteria carrying out Stickland fermentation as well as in other bacteria with reduced genomes indicated a complex community supporting stable sulfide oxidation to S⁰, likely aiding in performance stability. This study establishes this treatment approach as an alternative biotechnology for sulfide containing wastewater treatment and sheds light on the microbial interactions associated with high S⁰ production.

Evaluation of the Protection Ability of a Magnesium Hydroxide Coating against the Bio-Corrosion of Concrete Sewer Pipes, by Using Short and Long Duration Accelerated Acid Spraying Tests

The Microbiologically Induced Corrosion (MIC) of concrete sewer pipes is a commonly known problem that can lead to the destruction of the system, creating multiple public health issues and the need for costly repair investments. The present study focuses on the development of a magnesium hydroxide coating, with optimized properties to protect concrete against MIC. The anti-corrosion properties of the respective coating were evaluated by using short and long duration accelerated sulfuric acid spraying tests. The coating presented satisfying adhesion ability, based on pull-off and Scanning Electron Microscopy (SEM) analysis measurements. The surface pH of the coated concrete was maintained at the alkaline region (i.e., >8.0) throughout the duration of all acid spraying tests. The consumption of the coating, due to the reaction (neutralization) with sulfuric acid, was confirmed by the respective mass and thickness measurements. The protection ability of this coating was also evaluated by recording the formation of gypsum (i.e., the main corrosion product of concrete) during the performed tests, by X-ray Diffraction (XRD) analysis and by the Attenuated Total Reflectance (ATR) measurements. Finally, a long duration acid spraying test was additionally used to evaluate the behavior of the coating, simulating better the conditions existing in a real sewer pipe, and the obtained results showed that this coating is capable of offering prolonged protection to the concrete substrate.

The role of pH on sewer corrosion processes and control methods: A review

The production and emission of hydrogen sulfide (H₂S) in sewer systems is associated with the corrosion of sewer structures and harmful odour. Numerous studies have been conducted to find the best solution to overcome this issue. The pH plays a critical role not only on microbial and chemical processes that are responsible for all processes of corrosion but also on the efficiency of several control methods. This paper first critically reviews the literature on the interplay between pH and various chemical and microbial in-sewer processes, followed by a review of the control methods that depend on pH or indirectly alter pH. The paper argues that proper evaluation of each method should include the impact the control method has on downstream processes. This paper concludes the raising of pH has several benefits but is operationally difficult to implement. It also emphasises single control method may not be as efficient as combination of one or two methods in controlling the production and emission of H₂S. Finally, the research requirements and future directions in relation to emerging and potential methods that are not heavily reliant on pH control are discussed.

Microbial sulfur metabolism and environmental implications

Sulfur as a macroelement plays an important role in biochemistry in both natural environments and engineering biosystems, which can be further linked to other important element cycles, e.g. carbon, nitrogen and iron. Consequently, the sulfur cycling primarily mediated by sulfur compounds oxidizing microorganisms and sulfur compounds reducing microorganisms has enormous environmental implications, particularly in wastewater treatment and pollution bioremediation. In this review, to connect the knowledge in microbial sulfur metabolism to environmental applications, we first comprehensively review recent advances in understanding microbial sulfur metabolisms at molecular-, cellular- and ecosystem-levels, together with their energetics. We then discuss the environmental implications to fight against soil and water pollution, with four foci: (1) acid mine drainage, (2) water blackening and odorization in urban rivers, (3) SANI® and DS-EBPR processes for sewage treatment, and (4) bioremediation of persistent organic pollutants. In addition, major challenges and further developments toward elucidation of microbial sulfur metabolisms and their environmental applications are identified and discussed.

Evaluation of Three Prokaryote Primers for Identification of Prokaryote Community Structure and Their Abode Preference in Three Distinct Wetland Ecosystems

The ultimate role of prokaryote (bacteria and archaea), the decomposer of the wetland ecosystem, depends on its community structure and its interaction with the environment. The present study has used three universal prokaryote primers to compare prokaryote community structure and diversity of three distinctly different wetlands. The study results revealed that α-diversity indices and phylogenetic differential abundance patterns did not differ significantly among primers, but they did differ significantly across wetlands. Microbial community composition revealed a distinct pattern for each primer in each wetland. Overall comparison of prokaryote communities in sediments of three wetlands revealed the highest prokaryote richness and diversity in Bhomra (freshwater wetland) followed by Malencho (brackish-water wetland) and East Kolkata wetland (EKW) (sewage-fed wetland). Indicator genus analysis identified 21, 4, and 29 unique indicator genera, having preferential abode for Bhomra, EKW, and Malencho, respectively. Prediction of potential roles of these microbes revealed a preference for sulfate-reducing microbes in Malencho and methanogens in Bhomra. The distinct phylogenetic differential abundance pattern, microbial abode preference, and their potential functional role predict ecosystem variables shaping microbial diversity. The variation in community composition of prokaryotes in response to ecosystem variables can serve as the most sensitive bioindicator of wetland ecosystem assessment and management.

Bacterial Communities in Concrete Reflect Its Composite Nature and Change with Weathering

Concrete is an extreme but common environment and is home to microbial communities adapted to alkaline, saline, and oligotrophic conditions. Microbes inside the concrete that makes up buildings or roads have received little attention despite their ubiquity and capacity to interact with the concrete. Because concrete is a composite of materials which have their own microbial communities, we hypothesized that the microbial communities of concrete reflect those of the concrete components and that these communities change as the concrete ages. Here, we used a 16S amplicon study to show how microbial communities change over 2 years of outdoor weathering in two sets of concrete cylinders, one prone to the concrete-degrading alkali-silica reaction (ASR) and the other having the risk of the ASR mitigated. After identifying and removing taxa that were likely laboratory or reagent contaminants, we found that precursor materials, particularly the large aggregate (gravel), were the probable source of ∼50 to 60% of the bacteria observed in the first cylinders from each series. Overall, community diversity decreased over 2 years, with temporarily increased diversity in warmer summer months. We found that most of the concrete microbiome was composed of Proteobacteria, Firmicutes, and Actinobacteria, although community composition changed seasonally and over multiyear time scales and was likely influenced by environmental deposition. Although the community composition between the two series was not significantly different overall, several taxa, including Arcobacter, Modestobacter, Salinicoccus, Rheinheimera, Lawsonella, and Bryobacter, appear to be associated with ASR.

IMPORTANCE Concrete is the most-used building material in the world and a biologically extreme environment, with a microbiome composed of bacteria that likely come from concrete precursor materials, aerosols, and environmental deposition. These microbes, though seeded from a variety of materials, are all subject to desiccation, heating, starvation, high salinity, and very high pH. Microbes that survive and even thrive under these conditions can potentially either degrade concrete or contribute to its repair. Thus, understanding which microbes survive in concrete, under what conditions, and for how long has potential implications for biorepair of concrete. Further, methodological pipelines for analyzing concrete microbial communities can be applied to concrete from a variety of structures or with different types of damage to identify bioindicator species that can be used for structural health monitoring and service life prediction.

Laboratory Test to Evaluate the Resistance of Cementitious Materials to Biodeterioration in Sewer Network Conditions

The biodeterioration of cementitious materials in sewer networks has become a major economic, ecological, and public health issue. Establishing a suitable standardized test is essential if sustainable construction materials are to be developed and qualified for sewerage environments. Since purely chemical tests are proven to not be representative of the actual deterioration phenomena in real sewer conditions, a biological test–named the Biogenic Acid Concrete (BAC) test–was developed at the University of Toulouse to reproduce the biological reactions involved in the process of concrete biodeterioration in sewers. The test consists in trickling a solution containing a safe reduced sulfur source onto the surface of cementitious substrates previously covered with a high diversity microbial consortium. In these conditions, a sulfur-oxidizing metabolism naturally develops in the biofilm and leads to the production of biogenic sulfuric acid on the surface of the material. The representativeness of the test in terms of deterioration mechanisms has been validated in previous studies. A wide range of cementitious materials have been exposed to the biodeterioration test during half a decade. On the basis of this large database and the expertise gained, the purpose of this paper is (i) to propose a simple and robust performance criterion for the test (standardized leached calcium as a function of sulfate produced by the biofilm), and (ii) to demonstrate the repeatability, reproducibility, and discriminability of the test method. In only a 3-month period, the test was able to highlight the differences in the performances of common cement-based materials (CEM I, CEM III, and CEM V) and special calcium aluminate cement (CAC) binders with different nature of aggregates (natural silica and synthetic calcium aluminate). The proposed performance indicator (relative standardized leached calcium) allowed the materials to be classified according to their resistance to biogenic acid attack in sewer conditions. The repeatability of the test was confirmed using three different specimens of the same material within the same experiment and the reproducibility of the results was demonstrated by standardizing the results using a reference material from 5 different test campaigns. Furthermore, developing post-testing processing and calculation methods constituted a first step toward a standardized test protocol.

Case study of H2S release and transport in a trunk sewer with drops

Field work was performed to investigate the release of hydrogen sulphide (H₂S) and its transport in the sewer trunk with drops in the Bonnie Doon area in Edmonton, Alberta, Canada, in order to develop a proper odor control strategy. The liquid sulfide concentration in the upstream trunk was low (less than 1.0 mg/L), and no H₂S gas was detected in the head space under this low concentration. However, high H₂S gas concentration was detected in the middle reach of the trunk due to the stripping effect of the three drops (2.7 m, 5.2 m and 2.0 m) along the trunk. The released H₂S at drops was then transported in the sewer system and emitted at various locations and caused odor concerns. These drops played an important role in H₂S release, and the overall H₂S mass transfer coefficient at drops was much higher than that in normal gravity sewers. The overall oxygen and H₂S mass transfer coefficient (K_La) was estimated to be around 200 h^-1 and 300 h^-1 at the first two drops, respectively. Field sampling of biofilm indicates that Desulfomicrobium was identified as the sulfate-reducing bacteria (SRB) responsible for sulfide generation in sewer wall biofilm and Thiobacillus was the only predominant member in manhole wall biofilm contributing to sewer manhole corrosion.

"Bacterial consortium from hydrothermal vent sediments presents electrogenic activity achieved under sulfate reducing conditions in a microbial fuel cell"

PURPOSE

The aim of the present work was to assess the electrogenic activity of bacteria from hydrothermal vent sediments achieved under sulfate reducing (SR) conditions in a microbial fuel cell design with acetate, propionate and butyrate as electron donors.

METHODS

Two different mixtures of volatile fatty acids (VFA) were evaluated as the carbon source at two chemical oxygen demand (COD) proportions. The mixtures of VFA used were: acetate, propionate and butyrate COD: 3:0.5:0.5 (stage 1) and acetate - butyrate COD: 3.5:0.5 (stage 2). Periodical analysis of sulfate (SO₄ ^-2), sulfide (HS^-) and COD were conducted to assess sulfate reduction (SR) and COD removal along with measurements of voltage and current to assess the global performance of the consortium in the system.

RESULTS

Percentage of SR was of 97.5 ± 0.7 and 74.3 ± 1.5% for stage 1 and 2, respectively. The % COD removal was of 91 ± 2.1 and 75.3 ± 9.6 for stage 1 and 2, respectively. Although SR and COD removal were higher at stage 1, in regards of energy, stage 2 presented higher current and power densities and Coulombic efficiency as follows: 741.7 ± 30.5 μA/m², 376 ± 34.4 μW/m² and 5 ± 2.7%, whereas for stage 1 these values were: 419 ± 71 μA/m², 52.7 ± 18 μW/m² and 0.02%, respectively. A metagenomic analysis - stage 2 - in the anodic chamber, demonstrated that SR was due to Dethiosulfovibrionaceae (HA73), Desulfobacter and Desulfococcus and the electrogenic microorganisms were Planococcus, SHD-231, Proteiniclasticum, vadinCA02, and families Porphyromonadacea and Pseudomonadaceae.

CONCLUSIONS

It was demonstrated that microorganisms prevenient from hydrothermal vent sediments adapted to a microbial fuel cell system are able to generate electricity coupled to 74.3 ± 1.5 and 75.3 ± 9.6% of SR and COD removal respectively, with a mixture of acetate - butyrate.

Microbial Communities and Sulfate-Reducing Microorganisms Abundance and Diversity in Municipal Anaerobic Sewage Sludge Digesters from a Wastewater Treatment Plant (Marrakech, Morocco)

Both molecular analyses and culture-dependent isolation were combined to investigate the diversity of sulfate-reducing prokaryotes and explore their role in sulfides production in full-scale anaerobic digesters (Marrakech, Morocco). At global scale, using 16S rRNA gene sequencing, Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, Synergistetes, and Euryarchaeota were the most dominant phyla. The abundance of Archaea (3.1–5.7%) was linked with temperature. The mcrA gene ranged from 2.18 × 105 to 1.47 × 107 gene copies.g−1 of sludge. The sulfate-reducing prokaryotes, representing 5% of total sequences, involved in sulfides production were Peptococcaceae, Syntrophaceae, Desulfobulbaceae, Desulfovibrionaceae, Syntrophobacteraceae, Desulfurellaceae, and Desulfobacteraceae. Furthermore, dsrB gene ranged from 2.18 × 105 to 1.92 × 107 gene copies.g−1 of sludge. The results revealed that exploration of diversity and function of sulfate-reducing bacteria may play a key role in decreasing sulfide production, an undesirable by-product, during anaerobic digestion.

Microbial and Geochemical Dynamics of an Aquifer Stimulated for Microbial Induced Calcite Precipitation (MICP)

Microbially induced calcite precipitation (MICP) is an alternative to existing soil stabilization techniques for construction and erosion. As with any biologically induced process in soils or aquifers, it is important to track changes in the microbial communities that occur as a result of the treatment. Our research assessed how native microbial communities developed in response to injections of reactants (dilute molasses as a carbon source; urea as a source of nitrogen and alkalinity) that promoted MICP in a shallow aquifer. Microbial community composition (16S rRNA gene) and ureolytic potential (ureC gene copy numbers) were also measured in groundwater and artificial sediment. Aquifer geochemistry showed evidence of sulfate reduction, nitrification, denitrification, ureolysis, and iron reduction during the treatment. The observed changes in geochemistry corresponded to microbial community succession in the groundwater and this matched parallel geophysical and mineralogical evidence of calcite precipitation in the aquifer. We detected an increase in the number of ureC genes in the microbial communities at the end of the injection period, suggesting an increase in the abundance of microbes possessing this gene as needed to hydrolyze urea and stimulate MICP. We identify geochemical and biological markers that highlight the microbial community response that can be used along with geophysical and geotechnical evidence to assess progress of MICP.

The performance and microbial community in a slightly alkaline biotrickling filter for the removal of high concentration H2S from biogas

In this study, high concentration of H₂S (i.e., 5000 ppmv) in biogas was effectively removed by a slightly alkaline biotricking filter (BTF) with Polypropylene rings as packing material and oxygen from air as the electron acceptor. The results showed that when the inlet loading of H₂S increased from 101.7 to 422.0 g/m³/h, the removal efficiency of H₂S decreased from 100.0% to 91.4%, and the maximum elimination capacity (EC) was 386.0 ± 10.5 gH₂S/m³/h when empty bed retention time (EBRT) was 1.0 min. The slightly alkaline condition could increase the mass transfer of H₂S from gas to liquid phase and avoid the toxic effect of high concentration of H₂S, resulting in high removal performance of H₂S in the system. With the increase of H₂S inlet loading, the ratio of SO₄^2- in bio-desulfurization products gradually decreased, while that of S⁰ increased. At 101.7-210.7 gH₂S/m³/h of inlet loading, SO₄^2- was the dominant product with the ratio of above 50.00%, while S⁰ became the dominant product with 62.96% at 422.0 gH₂S/m³/h of inlet loading. The 16S rDNA sequencing results showed that the dominant genus in the BTF was sulfide-oxidizing bacteria (SOB), with the abundance of SOB decreased with the increase of inlet loading. The dominant genus were Pseudomonas, Halothiobacillus and Sulfurimonas in the BTF at 101.7, 139.8 and 210.7 gH₂S/m³/h of inlet loading, respectively. The SOB Sulfurimonas might play an important role for bio-desulfurization of high concentration of H₂S in a slightly alkaline BTF under high inlet loading of H₂S.

Enhancing the removal of H2S from biogas through refluxing of outlet gas in biological bubble-column

Biological bubble-column (BBC) is beneficial for elemental sulfur recycle from H₂S, but it's difficult to remove high concentration of H₂S in biogas efficiently due to the mass transfer limitation of H₂S from gas to liquid. In this study, a novel method with refluxing outlet gas in BBC was investigated. The results showed that gas reflux greatly enhanced the removal of high concentration of H₂S (about 5000 ppmv) from biogas. The removal efficiency of H₂S was 88.0 ± 4.1% with the reflux ratio at 1.0, which was higher than those without gas reflux (58.4 ± 1.0%), when the inlet H₂S loading was 143.1 ± 4.5 g/(m³·h). Moreover, the removal capacity of H₂S improved significantly with the increase of the reflux ratios from 1.0 to 4.0 and achieved the maximum at 271.8 ± 2.4 g/(m³·h). This might mainly be attributed to longer residence time and enhanced the mass transfer of O₂ and H₂S from gas to liquid through gas reflux.

Increased Resistance of Nitrite-Admixed Concrete to Microbially Induced Corrosion in Real Sewers

Microbially induced concrete corrosion is a major deterioration process in sewers, causing a huge economic burden, and improved mitigating technologies are required. This study reports a novel and promising effective solution to attenuate the corrosion in sewers using calcium nitrite-admixed concrete. This strategy aims to suppress the development and activity of corrosion-inducing microorganisms with the antimicrobial free nitrous acid, which is generated in situ from calcium nitrite that is added to the concrete. Concrete coupons with calcium nitrite as an admixture were exposed in a sewer manhole, together with control coupons that had no nitrite admixture, for 18 months. The corrosion process was monitored by measuring the surface pH, corrosion product composition, concrete corrosion loss, and the microbial community on the corrosion layer. During the exposure, the corrosion loss of the admixed concrete coupons was 30% lower than that of the control coupons. The sulfide uptake rate of the admixed concrete was also 30% lower, leading to a higher surface pH (0.5-0.6 unit), in comparison to that of the control coupons. A negative correlation between the calcium nitrite admixture in concrete and the abundance of sulfide-oxidizing microorganisms was determined by DNA sequencing. The results obtained in this field study demonstrated that this novel use of calcium nitrite as an admixture in concrete is a promising strategy to mitigate the microbially induced corrosion in sewers.

The rapid chemically induced corrosion of concrete sewers at high H2S concentration

Concrete corrosion in sewers is primarily caused by H₂S in sewer atmosphere. H₂S concentration can vary from several ppm to hundreds of ppm in real sewers. Our understanding of sewer corrosion has increased dramatically in recent years, however, there is limited knowledge of the concrete corrosion at high H₂S levels. This study examined the corrosion development in sewers with high H₂S concentrations. Fresh concrete coupons, manufactured according to sewer pipe standards, were exposed to corrosive conditions in a pilot-scale gravity sewer system with gaseous H₂S at 1100 ± 100 ppm. The corrosion process was continuously monitored by measuring the surface pH, corrosion product composition, corrosion loss and the microbial community. The surface pH of concrete was reduced from 10.5 ± 0.3 to 3.1 ± 0.5 within 20 days and this coincided with a rapid corrosion rate of 3.5 ± 0.3 mm year ^-1. Microbial community analysis based on 16S rRNA gene sequencing indicated the absence of sulfide-oxidizing microorganisms in the corrosion layer. The chemical analysis of corrosion products supported the reaction of cement with sulfuric acid formed by the chemical oxidation of H₂S. The rapid corrosion of concrete in the gravity pipe was confirmed to be caused by the chemical oxidation of hydrogen sulfide at high concentrations. This is in contrast to the conventional knowledge that is focused on microbially induced corrosion. This first-ever systematic investigation shows that chemically induced oxidation of H₂S leads to the rapid corrosion of new concrete sewers within a few weeks. These findings contribute novel understanding of in-sewer corrosion processes and hold profound implications for sewer operation and corrosion management.

Microbial Ecology of Biofiltration Units Used for the Desulfurization of Biogas

Bacterial communities’ composition, activity and robustness determines the effectiveness of biofiltration units for the desulfurization of biogas. It is therefore important to get a better understanding of the bacterial communities that coexist in biofiltration units under different operational conditions for the removal of H2S, the main reduced sulfur compound to eliminate in biogas. This review presents the main characteristics of sulfur-oxidizing chemotrophic bacteria that are the base of the biological transformation of H2S to innocuous products in biofilters. A survey of the existing biofiltration technologies in relation to H2S elimination is then presented followed by a review of the microbial ecology studies performed to date on biotrickling filter units for the treatment of H2S in biogas under aerobic and anoxic conditions.

Influence of Dissolved-Aluminum Concentration on Sulfur-Oxidizing Bacterial Activity in the Biodeterioration of Concrete

Several studies undertaken on the biodeterioration of concrete sewer infrastructures have highlighted the better durability of aluminate-based materials. The bacteriostatic effect of aluminum has been suggested to explain the increase in durability of these materials. However, no clear demonstration of the negative effect of aluminum on cell growth has been yet provided in the literature. In the present study, we sought to investigate the inhibitory potential of dissolved aluminum on nonsterile microbial cultures containing sulfur-oxidizing microorganisms. Both kinetic (maximum specific growth rate) and stoichiometric (oxygen consumption yield) parameters describing cells activity were accurately determined by using respirometry measurements coupled with modeled data obtained from fed-batch cultures run for several days at pH below 4 and with increasing total aluminum (Al_tot) concentrations from 0 to 100 mM. Short-term inhibition was observed for cells poorly acclimated to high salinity. However, inhibition was significantly attenuated for cells grown on mortar substrate. Moreover, after a rapid adaptation, and for an Al_tot concentration up to 100 mM, both kinetic and stoichiometric growth parameters remained similar to those obtained in control culture conditions where no aluminum was added. This argued in favor of the impact of ionic strength change on the growth of sulfur-oxidizing microorganism rather than an inhibitory effect of dissolved aluminum. Other assumptions must therefore be put forward in order to explain the better durability of cement containing aluminate-based materials in sewer networks. Among these assumptions, the influence of physical or chemical properties of the material (phase reactivity, porosity, etc.) might be proposed.IMPORTANCE Biodeterioration of cement infrastructures represents 5 to 20% of observed deteriorations within the sewer network. Such biodeterioration events are mainly due to microbial sulfur-oxidizing activity which produces sulfuric acid able to dissolve cementitious material. Calcium aluminate cement materials are more resistant to biodeterioration compared to the commonly used Portland cement. Several theories have been suggested to describe this resistance, and the bacteriostatic effect of aluminum seems to be the most plausible explanation. However, results reported by the several studies on this exact topic are highly controversial. This present study provides a comprehensive analysis of the influence of dissolved aluminum on growth parameters of long-term cultures of sulfur-oxidizing bacterial consortia sampled from different origins. Kinetic and stoichiometric parameters estimated by respirometry measurements and modeling showed that total dissolved-aluminum concentrations up to 100 mM were not inhibitory, but it is more likely that a sudden increase in the ionic strength affects cell growth. Therefore, it appears that the bacteriostatic effect of aluminum on microbial growth cannot explain the better durability of aluminate based cementitious materials.

Periodic deprivation of gaseous hydrogen sulfide affects the activity of the concrete corrosion layer in sewers

Sulfide induced concrete corrosion significantly reduces the service life of the sewer systems. Gaseous hydrogen sulfide (H₂S) levels are a key factor affecting the corrosion rate and these fluctuate due to the diurnal flow pattern of sewers. Currently, there is little known about how such fluctuations, in particular the periodic deprivation of H₂S, may affect the corrosion activity. This study investigated the impact of the deprivation of H₂S on the sulfide uptake rate (SUR) of concrete coupons incubated in laboratory corrosion chambers. After systematic evaluation of the gaseous H₂S concentration profiles of two sewer systems, two types of profiles, i.e. short- (1 h) and long- (12 h) term deprivation of H₂S, were applied to the concrete coupons. In comparison to the baseline SUR, exposing the concrete coupon to 0 ppm of H₂S for 1 h consistently caused a temporary increase of the SUR (i.e. 3.2%-12.5%) following re-supply of H₂S at baseline levels. With the continuous re-supply of H₂S, there was gradual and steady decrease of SUR to the level close to the baseline SUR. However, for the case after deprivation of H₂S for 12 h, the SUR was 5.1% lower than baseline SUR and gradually increased to a level similar to the baseline SUR during the 20-30 min of continuous re-supply of H₂S. In addition, the simultaneous deprivation of H₂S and O₂ for 1 h had negligible impact on the SUR. Further analysis suggests that the historically accumulated intermediates of sulfide oxidation could act as electron donors for sulfide oxidizing bacteria (SOB). The replenishment of the intermediates upon the re-supply of H₂S could play a key role in the increase of SUR after short-term deprivation of H₂S. However, the activity of SOB could be diminished after long-term deprivation of H₂S, although the sulfur intermediates still could be available. Estimating the sulfide uptake by concrete using the SUR of the average H₂S concentration could lead to overestimation of the sulfide uptake. There could be more significant overestimation for the case with longer deprivation of H₂S.

Wastewater microbial community structure and functional traits change over short timescales

Wastewater contains microorganisms coming from various sources, e.g. feces discharges, soil infiltrations and sewer biofilms and sediments. The primary objective of this work was to determine if end-of-pipe wastewater microbial community structures exhibits short-timescale variation, and assess possible microbial origins. To this end, we measured hourly physicochemical characteristics of wastewater influent for 2 days and analyzed the microbial community at 4-h intervals using 16S rRNA gene amplicon sequencing. Results showed large variations in the microbial community composition at phylum and genus levels, i.e. Proteobacteria ranged from 44 to 63% of the total relative abundance and Arcobacter ranged from 11 to 22%. Diurnal patterns were observed in the alpha-diversity, beta-diversity and the prevalence of several taxa. Wastewater physicochemical characteristics explained 61% of the total microbial community variance by Canonical Correspondence Analysis (CCA), with flow rate being the main explanatory variable exhibiting a clear diurnal profile. Comparison with public databases using closed reference OTUs revealed that only 7.3% of the sequences were shared with human gut microbiota and 21.7% with soil microbiota, the majority being from the sewer biofilms and sediments. The functional trait, weighted average ribosomal RNA operon (rrn) copy number per genome, was found to be relatively high in the wastewater microbiota (average 3.6, soil 2.1, and human gut 2.6) and significantly correlated with flow, inferring active microbial enrichments in the sewer. The prevalence of Methylophilaceae, methanol oxidation genes and denitrification genes were related to high influent methanol and NO₃^- concentration in the influent wastewater. These functional organisms and genes indicate important carbon and nutrient removal related functions in the sewer. Together, the observed temporal patterns of the microbial community and functional traits suggest that high wastewater flow causes greater transport of active sewer microorganisms which are functionally important.

Molecular biological tools in concrete biodeterioration - a mini review

Concrete structures develop biofilms when exposed to various environments. At a certain stage, the microbial films destroy the concrete structures leading to significant deterioration. Culture-dependent techniques give an incomplete picture of the microbial communities on the concrete surface. Culture-independent techniques or molecular biological tools pave a new way to analyse microbial communities involved in concrete biodeterioration. This study highlights the need to 'build' a database, for Microbiologically Influenced Concrete Corrosion (MICC) involving microbial groups that are being identified using culture-dependent and independent techniques. The role of molecular tools such as 16S rRNA sequencing, denaturing gradient gel electrophoresis (DGGE), Fluorescent in situ hybridization (FISH), Real-time Polymerase Chain Reaction (RT-PCR), microarray analysis, 2-Dimensional gel electrophoresis (2-DE) in analysing microbial communities on the concrete structures have been reviewed in this paper.

Metabolic Activity of Micromycetes Affecting Urban Concrete Constructions

Concrete resistance to the destructive action of microorganisms is considered as a measure of its durability and is increasingly being raised as an important issue. We focused our study on the biodeterioration of concrete specimens widely used as a building material of urban houses by micromycetes isolated from the inner wall surface of the former military hospital in Kazan city, Tatarstan, Russia. Fungal community consists of 9 Penicillium isolates, 6 Aspergillus, 2 Trichoderma, and 1 isolate of Alternaria. First, we have identified two dominant isolates, Aspergillus fumigatus and Penicillium brevicompactum, and characterized their destructive properties according to the radial growth rate, antagonistic activity towards bacterial habitants of concrete, and production of organic acids. Then, we have demonstrated that five tested brands of high-strength concrete differ in bioreceptivity. The alterations in concrete resistances to compression and flexure after fungal attack were recorded at the trend level, mainly due to a short exposure time of concrete to fungal destructors in tests recommended by national Russian standard. Finally, using scanning electron microscopy we have shown that colonization of concrete by the dominant fungi includes their penetration into the thickness of concrete and germination in cracks. Elementary analysis revealed the decrease of calcium content on about 41% after fungal growth on the concrete in liquid phase and on 32% by superficial growth in comparison with the samples without fungal treatment.

Subsea tunnel reinforced sprayed concrete subjected to deterioration harbours distinct microbial communities

Deterioration of concrete is a large societal cost. In the Oslofjord subsea tunnel (Norway), deterioration of sprayed concrete and corrosion of reinforcing steel fibres occur under biofilm formed at sites with intrusion of saline groundwater. In this study, the microbial community structure, in situ environmental gradients and chemical composition of the biofilms were examined at three tunnel sites. Ammonia- and nitrite-oxidising microorganisms, in particular Nitrosopumilus sp., and iron-oxidising bacteria within Mariprofundus sp., were omnipresent, together with a diversity of presumably heterotrophic bacteria. Alpha- and beta diversity measures showed significant differences in richness and community structure between the sites as well as over time and null-models suggested that deterministic factors were important for the community assembly. The superficial flow of water over the biofilm had a strong effect on oxygen penetration in the biofilm and was identified as one major environmental gradient that varied between the sites, likely being important for shaping the microbial communities.

ZnO-SiO2 nanohybrid decorated sustainable geopolymer retaining anti-biodeterioration activity with improved durability

Geopolymer, consists of industrial by-product fly ash, and alkaline activator, possesses similar strength along with durability like conventional cement composite, is an alternative construction substantial of Portland cement in current scenario. Corrosion of the concrete materials resulted mainly from the chemical degradation. Besides chemical degradation, biogenic-deterioration is also another alarming issue especially in the sewer systems, bridge piers, several pipelines and offshore platforms and the need to act on it is long-standing. In this study, application of zinc oxide-silica nanohybrid based sustainable geopolymer (GM_ZnO-Si) has been investigated for the development of a sustainable, anti-biodeteriorate cementitious material having significant mechanical strength and durability. Initially, zinc oxide nano-rods (ZnO NRs) have been synthesized and spherical silica nanoparticles were decorated on the surface of ZnO NRs. The ZnO-SiO₂ composite was characterized by various techniques (FTIR, XRD, FESEM, EDS, TEM, and XPS). Ambient temperature cured GM_ZnO-Si mortar was further explored in terms of mechanical strength, durability, mechanistic anti-microbial (E. coli, S. aureus, A. niger) influences. Mechanical properties of GM_ZnO-Si are found significantly higher than that of control samples. MIC, MBC, and MFC results demonstrate enhanced anti-microbial efficacy of GM_ZnO-Si. Inner permeability assay, reactive oxygen species generation and microscopic images of cell wall rupture and DNA damage studies supported the detailed understanding of anti-microbial activities. These experimental findings suggest that incorporation of ZnO-SiO₂ hybrid in geopolymer will pave the way for biodeterioration resistant concrete with enhanced mechanical and structural behaviour.

Codon usage bias reveals genomic adaptations to environmental conditions in an acidophilic consortium

The analysis of codon usage bias has been widely used to characterize different communities of microorganisms. In this context, the aim of this work was to study the codon usage bias in a natural consortium of five acidophilic bacteria used for biomining. The codon usage bias of the consortium was contrasted with genes from an alternative collection of acidophilic reference strains and metagenome samples. Results indicate that acidophilic bacteria preferentially have low codon usage bias, consistent with both their capacity to live in a wide range of habitats and their slow growth rate, a characteristic probably acquired independently from their phylogenetic relationships. In addition, the analysis showed significant differences in the unique sets of genes from the autotrophic species of the consortium in relation to other acidophilic organisms, principally in genes which code for proteins involved in metal and oxidative stress resistance. The lower values of codon usage bias obtained in this unique set of genes suggest higher transcriptional adaptation to living in extreme conditions, which was probably acquired as a measure for resisting the elevated metal conditions present in the mine.

Advances in concrete materials for sewer systems affected by microbial induced concrete corrosion: A review

Microbial induced concrete corrosion (MICC) is recognized as one of the main degradation mechanisms of subsurface infrastructure worldwide, raising the demand for sustainable construction materials in corrosive environments. This review aims to summarize the key research progress acquired during the last decade regarding the understanding of MICC reaction mechanisms and the development of durable materials from an interdisciplinary perspective. Special focus was laid on aspects governing concrete - micoorganisms interaction since being the central process steering biogenic acid corrosion. The insufficient knowledge regarding the latter is proposed as a central reason for insufficient progress in tailored material development for aggressive wastewater systems. To date no cement-based material exists, suitable to withstand the aggressive conditions related to MICC over its entire service life. Research is in particular needed on the impact of physiochemical material parameters on microbial community structure, growth characteristics and limitations within individual concrete speciation. Herein an interdisciplinary approach is presented by combining results from material sciences, microbiology, mineralogy and hydrochemistry to stimulate the development of novel and sustainable materials and mitigation strategies for MICC. For instance, the application of antibacteriostatic agents is introduced as an effective instrument to limit microbial growth on concrete surfaces in aggressive sewer environments. Additionally, geopolymer concretes are introduced as highly resistent in acid environments, thus representing a possible green alternative to conventional cement-based construction materials.

High growth potential and nitrogen removal performance of marine anammox bacteria in shrimp-aquaculture sediment

Anaerobic ammonium oxidation (anammox) bacteria were enriched in continuous packed-bed columns with marine sediment. One column (SB-C) was packed with only marine sediment collected from a shrimp-aquaculture pond, and another column (SB-AMX) was inoculated with marine anammox bacteria (MAB) as a control. These columns were continuously fed with natural or artificial seawater including ammonium (NH₄⁺) and nitrite (NO₂^-). The SB-AMX showed anammox activities from the beginning and continued for over 200 days. However, the SB-C had no nitrogen removal performance for over 170 days. After adding a bicarbonate solution (KHCO₃) to the sediment-only packed column, anammox activity was observed within 13 days. The column exhibited a nitrogen removal efficiency (NRE) of 88% at a nitrogen loading rate (NLR) of 1.0 kg-N·m^-3·day^-1, which was comparable to the control one. A next-generation sequencing analysis revealed the predominance of MAB related to "Candidatus Scalindua spp.". In addition, the co-occurrence of sulfur-oxidizing denitrifiers was observed, which suggests their symbiotic relationship. This study suggests the applicability of MAB for in-situ bioremediation of nitrogen-contaminated marine sediments and reveals a potential microbial interaction between anammox and sulfur-oxidizing communities responsible for nitrogen and sulfur cycling in marine aquaculture systems.

Co-Variation between Distribution of Microbial Communities and Biological Metabolization of Organics in Urban Sewer Systems

Distribution characteristics and biodiversity of microbial communities were studied in a 1200 m pilot sewer system. Results showed that the dominant microorganisms, fermentation bacteria (FB), hydrogen-producing acetogen (HPA), sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) changed significantly along the sewer systems, from start to the end. The distribution of the functional microorganisms could induce substrate transformation and lead to the accumulation of micromolecular organics (i.e., acetic acid, propionic acid and amino acid). However, substrate transformation induced by these microbes was affected by environmental factors such as oxidation-reduction potential, pH and dissolved oxygen. Changes in environmental conditions along the sewer resulted in the variation of dominant bioreactions. FB were enriched at the beginning of the sewer, while SRB and MA were found toward the end. Furthermore, based on Spearman rank correlation analysis of microbial communities, environmental factors and substrates, covariation between microbial community distribution and organics metabolization along the sewer was identified. This study could provide a theoretical foundation for understanding wastewater quality variation during transportation from sewers to treatment plants, therefore, promoting optimization of design and operation of wastewater treatment.

Microbiomes in extremely acidic environments: functionalities and interactions that allow survival and growth of prokaryotes at low pH

Extremely acidic environments have global distribution and can have natural or, increasingly, anthropogenic origins. Extreme acidophiles grow optimally at pH 3 or less, have multiple strategies for tolerating stresses that accompany high levels of acidity and are scattered in all three domains of the tree of life. Metagenomic studies have expanded knowledge of the diversity of extreme acidophile communities, their ecological networks and their metabolic potentials, both confirmed and inferred. High resolution compositional and functional profiling of these microbiomes have begun to reveal spatial diversity patterns at global, regional, local, zonal and micro-scales. Future integration of genomic and other meta-omic data will offer new opportunities to utilize acidic microbiomes and to engineer beneficial interactions within them in biotechnologies.

Draft genome sequence of Acidithiobacillus thiooxidans CLST isolated from the acidic hypersaline Gorbea salt flat in northern Chile

10.1601/nm.2199 CLST is an extremely acidophilic gamma-proteobacteria that was isolated from the Gorbea salt flat, an acidic hypersaline environment in northern Chile. This kind of environment is considered a terrestrial analog of ancient Martian terrains and a source of new material for biotechnological applications. 10.1601/nm.2199 plays a key role in industrial bioleaching; it has the capacity of generating and maintaining acidic conditions by producing sulfuric acid and it can also remove sulfur layers from the surface of minerals, which are detrimental for their dissolution. CLST is a strain of 10.1601/nm.2199 able to tolerate moderate chloride concentrations (up to 15 g L-1 Cl-), a feature that is quite unusual in extreme acidophilic microorganisms. Basic microbiological features and genomic properties of this biotechnologically relevant strain are described in this work. The 3,974,949 bp draft genome is arranged into 40 scaffolds of 389 contigs containing 3866 protein-coding genes and 75 RNAs encoding genes. This is the first draft genome of a halotolerant 10.1601/nm.2199 strain. The release of the genome sequence of this strain improves representation of these extreme acidophilic Gram negative bacteria in public databases and strengthens the framework for further investigation of the physiological diversity and ecological function of 10.1601/nm.2199 populations.