The effect of chemical oxidation on the biological sulfide oxidation by an alkaliphilic sulfoxidizing bacterial consortium

Assessing nitrous oxide emissions from algal-bacterial photobioreactors devoted to biogas upgrading and digestate treatment

Nitrous oxide (N2O) emissions in High Rate Algal Ponds (HRAP) can negatively affect the sustainability of algal-bacterial processes. N2O emissions from a pilot HRAP devoted to biogas upgrading and digestate treatment were herein monitored for 73 days. The influence of the pH (7.5, 8.5, and 9.5), nitrogen sources (100 mg L-1 of N-NO2-, N-NO3-, and N-NH4+) and illumination on N2O emissions from the algal-bacterial biomass of the HRAP was also assessed in batch tests. Significantly higher N2O gas concentrations of 311.8 ± 101.1 ppmv were recorded in the dark compared to the illuminated period (236.9 ± 82.6 ppmv) in the HRAP. The batch tests revealed that the highest N2O emission rates (49.4 mmol g-1 TSS·h-1) occurred at pH 8.5 in the presence of 100 mg N-NO2-/L under dark conditions. This study revealed significant N2O emissions in HRAPs during darkness.

Influence of pH on the Morphology and Cell Volume of Microscopic Algae, Widely Distributed in Terrestrial Ecosystems

Terrestrial algae are a group of photosynthetic organisms that can survive in extreme conditions. pH is one of the most important factors influencing the distribution of algae in both aquatic and terrestrial ecosystems. The impact of different pH levels on the cell volume and other morphological characteristics of authentic and reference strains of Chlorella vulgaris, Bracteacoccus minor, Pseudoccomyxa simplex, Chlorococcum infusionum, and Vischeria magna were studied. Chlorella vulgaris, Pseudoccomyxa simplex, and Vischeria magna were the most resistant species, retaining their morphology in the range of pH 4-11.5 and pH 3.5-11, respectively. The change in pH towards acidic and alkaline levels caused an increase in the volume of Pseudoccomixa simplex and Vischeria magna cells, according to a polynomial regression model. The volume of Chlorella vulgaris cells increased from a low to high pH according to a linear regression model. Changes in pH levels did not have a significant impact on the volume of Bracteacoccus minor and Chlorococcum infusionum cells. Low and high levels of pH caused an increase in oil-containing substances in Vischeria magna and Bracteacoccus minor cells. Our study revealed a high resistance of the studied species to extreme pH levels, which allows for us to recommend these strains for broader use in biotechnology and conservation studies of natural populations.

Short-term tuning of microalgal composition by exposition to different irradiance and small doses of sulfide

Suitability of microalgae valorization mainly depends on its biochemical composition. Overall, among all microalgal derivatives, pigments currently stand out as the major added-value component. While it is well recognized that microalgal growth conditions strongly affect biomass composition, final tuning of already grown microalgae has been scarcely studied. Herein, pigment crude extract and debris biomass composition of an already grown microalgal consortium was evaluated after a short-term exposure (90 min) to different levels of irradiance (15, 50, 120 μmol m^-2 s^-1) and sulfide concentrations (0, 3.2, 16 mg L^-1). Although lipid, protein, and carbohydrate contents of debris biomass were not decisively modified by the short-term exposures, pigments content of the crude extracts were strongly modified after 90-min exposure at given sulfide and irradiance conditions. Particularly, a higher content of chlorophyll a, chlorophyll b, and total carotenoids was estimated at an optimal sulfide concentration of 5 mg L^-1, and the higher irradiance of 120 μmol m^-2 s^-1. Contrarily, the average irradiation level of 50 μmol m^-2 s^-1 and the absence of sulfide stimulated the production of phycoerythrin and phycocyanin which could be increased by 65 and 50%, respectively. Thus, a final qualitative and quantitative tuning of pigment content is plainly achievable on grown microalgal biomass, in a reduced exposure time, at given irradiance or sulfide conditions.

Revealing sulfate role in empowering the sulfur-oxidizing capacity of Thioalkalivibrio versutus D301 for an enhanced desulfurization process

Haloalkaliphilic Thioalkalivibrio, a dominant genus for sulfide removal, has attracted growing interest. However, the bacterial biological response to this process's final product, sulfate, has not been well-studied. Here, thiosulfate oxidation and sulfur formation by T. versutus D301 were being enhanced with increasing sulfate supply. With the addition of 0.73 M sulfate, the thiosulfate utilization rate and sulfur production were improved by 68.1% and 120.1% compared with carbonate-grown control at the same salinity (1.8 M). For sulfate-grown cells, based on metabolic analysis, the downregulation of central carbon metabolism indicated that sulfate triggered a decrease in energy conservation efficiency. Additionally, the gene expression analysis further revealed that sulfate induced the inhibition of sulfur to sulfate oxidation, causing the upregulation of thiosulfate to sulfur oxidation for providing cells with additional energy. This study enhances researchers' understanding regarding the sulfate effect on the bio-desulfurization process and presents a new perspective of optimizing the biotechniques.

Simultaneous biofiltration of H2S and NH3 using compost mixtures from lignocellulosic waste and chicken manure as packing material

Biofiltration offers an efficient and economical alternative for the elimination of offensive odors caused by hydrogen sulfide, ammonia, and volatile organic compounds. Considering that packing materials affect the performance and represent the main installation cost, the purpose of this work was to evaluate the biofiltration of H₂S and NH₃ comparing three composted mixtures made from chicken manure and lignocellulosic residues (pruning waste, sugarcane bagasse, and rice husk) used as packing material. A range of gas concentrations similar to those of a municipal WWTP was used in the biofiltration of a contaminated stream performed on a laboratory scale. The results indicate that at low concentrations of H₂S (6-36 ppm) and NH₃ (0-1 ppm), the three biofilters showed 100% removal efficiency. Now, at the maximum levels of gas concentrations of H₂S (250 ppm) and NH₃ (19 ppm) while the removal efficiency of H₂S remained higher than 90% in all cases, the removal efficiency of NH₃ remained higher than 90% only in the sugarcane bagasse biofilter. Compost mixtures with sugarcane bagasse and rice husk are highly reliable as packing material for biofiltration at high concentration of H₂S. Specifically, the sugarcane bagasse mixture had the highest removal efficiency (99% H₂S and 95% NH₃) and the highest elimination capacity (15 g H₂S/m³h and 0.6 g NH₃/m³h), making it a better option for the elimination of both gases. These results represent a contribution to the construction of a low-price elimination system of offensive odors in WTTPs and other industries.

Simultaneous nitrification/denitrification and desulfurization of wastewater polluted with ammonium, COD and sulfide: effectiveness of a new up-flow vertical hybrid reactor

Industrial wastewater discharges pose an environmental risk. Here, the effectiveness of an up-flow vertical hybrid system, operating with synthetic and industrial wastewater was investigated, as a new approach to perform nitrification/denitrification and desulfurization within a single reactor. The hybrid reactor is divided in two reaction zones, the oxic and anoxic. The removal of chemical oxygen demand (COD), ammonium, and sulfide was investigated, highlighting changes in microbial diversity. The reactor was evaluated at hydraulic residence time (HRT) of 1.6 days, and its performance throughout 180 days is presented in four stages. In stages I-II, high COD and ammonium removal was obtained with synthetic wastewater. In stage-III, sulfide-rich synthetic wastewater did not alter the system, attaining COD, ammonium, and sulfide removal efficiencies of 81, 99.5, and 99.7%, respectively. In the last stage, a mixture of effluents was fed into the reactor at loading rates of 277 mg COD/L-d, 46.5 mg NH₄ ⁺-N /L-d, and 15 mg HS^--S /L-d. Sulfide and ammonium removals were 100% and 99.9%, respectively. However, low COD removal was observed, being of 51%, and the system removed 97% in terms of BOD₅. The structure and microbial diversity also changed. Sulfide feeding, induced the proliferation of sulfur oxidizers like Thiomiscropira and Thiobacillus. Industrial wastewater enhanced the abundance of Pseudomonas (15.53%) and favored the proliferation of new bacteria of the genus Truepera (2.98%) and Alicyclipilus (7.56%). This is the first study reporting simultaneous nitrification/denitrification and desulfurization to remove ammonium, COD and sulfide from complex industrial wastewater using an up-flow vertical hybrid reactor.

Revealing the role of nitrate on sulfide removal coupled with bioenergy production in Chlamydomonas sp. Tai-03: Metabolic pathways and mechanisms

Recently, simultaneous sulfide removal and bioenergy production by microalgal treatment have attracted growing attention. However, the response of nitrogen metabolism to the sulfide-removal process has yet to be explored. Here, variable levels of sulfide could be completely removed by Chlamydomonas sp. Tai-03 under both high and low nitrate conditions in synthetic wastewaters. The highest sulfide removal rate of 5.56 mg-S L^-1 h^-1 was achieved with the addition of 100 mg L^-1 sulfide in the presence of high nitrate. Meanwhile, sulfide was chemically oxidized to sulfate and then ingested by microalgae. Interestingly, sulfide-removal efficiency critically depended on nitrate concentration. Sulfide can also enhance the ability of microalgae to assimilate nitrogen. Based on the analysis of sulfur- and nitrogen-related metabolic profiling, serine as a precursor decreased by 94 % under low levels of nitrate, which induced the significant inhibition of cysteine and methionine biosynthesis. The results indicated that nitrogen source played a critical role in the sulfur cycle because of the positive relationship between the aforementioned metabolic processes and nitrate concentration. Additionally, sulfide can improve lipid and carbohydrate productivity under high levels of nitrate. This study enhances our understanding of the mechanisms underlying the simultaneous removal of sulfide and alternative bioenergy production.

The Effect of Chemical Sulfide Oxidation on the Oxygenic Activity of an Alkaliphilic Microalgae Consortium Deployed for Biogas Upgrading

The oxygenic photosynthetic activity (OPA) of an alkaliphilic microalgae consortium was evaluated at different concentrations of dissolved sulfide under room temperature and well-defined conditions of irradiance and pH in a tubular closed photobioreactor. The kinetic assays showed that it was optimal at a sulfide concentration of 3.2 mg/L under an external photosynthetically active radiation of 50 and 120 μE/m2 s together with a pH of 8.5 and 9.2. In contrast, the oxygenic photosynthetic activity was insignificant at 15 μE/m2 s with a pH of 7.3, both in the absence and presence of sulfide. Consecutive pulse additions of dissolved sulfide evidenced that the accumulation rate of dissolved oxygen was decreased by the spontaneous chemical oxidation of sulfide with dissolved oxygen in alkaline culture media, mainly at high sulfide levels. At 3.2 mg/L of sulfide, the oxygenic photosynthetic activity was improved by around 60% compared to the treatment without sulfide at external irradiances of 120 μE/m2 s, 30 °C, and pH of 8.5 and 9.2. Additionally, an even higher OPA enhancement (around 85%) was observed in the same previous conditions but using 16 mg/L of sulfide. Thiosulfate was the major end-product of sulfide by oxic chemical reaction, both in biotic and abiotic assays with yields of 0.80 and 0.68, respectively.

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.

Photorespiration in an outdoor alkaline open-photobioreactor used for biogas upgrading

The rates of oxygenic and carbon fixation photosynthetic processes of a microalgae consortium were simultaneously evaluated under steady-state performance in an bench scale alkaline open-system exposed to outdoor conditions in Mexico City. A synthetic methane-free gaseous stream (SMGS) similar to biogas was used as inorganic carbon source and model of biogas upgrading. The microalgae CO₂ fixation rates were calculated through a novel methodology based on an inorganic carbon mass balance under continuous scrubbing of a SMGS similar to biogas, where the influence of pH and temperature time-depended oscillations were successfully incorporated into the mass balances. The oxygenic activity and carbon fixation occurred at different non-stoichiometric rates during the diurnal phase, in average carbon fixation predominated over oxygen production (photosynthesis quotient PQ≈ 0.5 mol O₂ mol^-1 CO₂) indicating photorespiration occurrence mainly under dissolved oxygen concentrations higher than 10 mg L^-1. The oxygen and inorganic carbon mass balances demonstrated that photorespiration and endogenous respiration were responsible for losing up to 66% and 7% respectively of the biomass grew at diurnal periods under optimal conditions. In favoring photorespiration conditions, the microalgae biomass productivity (CO₂ effectively captured) can be severely decreased. A kinetic mathematical model as a function of temperature and irradiance of the oxygenic photosynthetic activity indicated the optimal operation zone for this outdoor alkaline open-photobioreactor, where irradiance was found being the most influential parameter.

Investigation of transient forms of sulfur during biological treatment of spent caustic

In the present study, the production of various transient forms of sulfur during biological oxidation of sulfidic spent caustics under haloalkaline conditions in a stirred tank bioreactor is investigated. Also, the effects of abiotic aeration (chemical oxidation), dissolved oxygen (DO) concentration and sodium concentration on forms of sulfur during biological treatment are demonstrated. Thioalkalivibrio versutus strain was used for sulfide oxidation in spent caustic (SC). The aeration had an important effect on sulfide oxidation and its final products. At DO concentrations above 2 mg l^-1, majority of sulfide was oxidized to sulfate. Maximum sulfide removal efficiency (%R) and yield of sulfate production [Formula: see text] was obtained in Na⁺ concentration ranging from 0.6 to 2 M. Abiotic aeration, which is the most important factor of production of thiosulfate, resulted in the formation of an undesired product-polysulfide. However, abiotic aeration can be used as a pretreatment to biological treatment. In the bioreactor the removal efficiency was obtained as 82.7% and various forms of sulfur such as polysulfide, biosulfur, thiosulfate and sulfate was observed during biological treatment of SC.

Anaerobic digestion of sulphate-rich post-tanning wastewater at different COD/sulphate and F/M ratios

Anaerobic digestion of post-tanning wastewater was performed in batch anaerobic digester to evaluate the effect of COD/sulphate ratio [0.62, 0.69, and 1.20 (w/w) %] and F/M ratio [0.2, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, and 1.5 (w/w) %)] on the removal efficiency of COD. The F/M ratio of 0.3 was found to be the optimum ratio for the removal of COD by 53, 57, and 65%, respectively at COD/sulphate ratio of 0.62, 0.69, and 1.20. The maximum sulphate removal was observed at F/M ratio of 0.2 and the removal efficiency was 48, 50, and 58% at COD/sulphate ratio of 0.62, 0.69, and 1.20, respectively. The removal efficiency of COD and sulphate was increased with increase in COD/sulphate ratio from 0.62 to 1.20 and decreased with increase in F/M ratio from 0.2 to 1.5 in anaerobic digestion of post-tanning wastewater. The maximum concentration of sulphide formation was 784 mg/L at COD/sulphate ratio of 0.62 in anaerobic digestion process and the process was inhibited at this sulphide concentration. The microbial activity in the sludge was evaluated through live and dead cell assay using fluorescent microscopy. The maximum amount of dead microbes was observed in the anaerobic digester, which was operated at COD/sulphate ratio of 0.62 than other studied ratio.

Simultaneous treatment of dimethyl disulfide and hydrogen sulfide in an alkaline biotrickling filter

Foul odors comprise generally a complex mixture of molecules, where reduced sulfur compounds play a key role due to their toxicity and low odor threshold. Previous reports on treating mixtures of sulfur compounds in single biofilters showed that hydrogen sulfide (H₂S) interferes with the removal and degradation of other sulfur compounds. In this study, hydrogen sulfide (H₂S) and dimethyl disulfide (DMDS) were fed to an alkaline biotrickling filter (ABTF) at pH 10, to evaluate the simultaneous removal of inorganic and organic sulfur compounds in a single, basic-pH system. The H₂S-DMDS mixture was treated for more than 200 days, with a gas residence time of 40 s, attaining elimination capacities of 86 g_DMDS m^-3 h^-1 and 17 g_H2S m^-3 h^-1 and removal efficiencies close to 100%. Conversion of H₂S and DMDS to sulfate was generally above 70%. Consumption of sulfide and formaldehyde was verified by respirometry, suggesting the coexistence of both methylotrophic and chemoautotrophic breakdown pathways by the immobilized alkaliphilic biomass. The molecular biology analysis showed that the long-term acclimation of the ABTF led to a great variety of bacteria, predominated by Thioalkalivibrio species, while fungal community was notoriously less diverse and dominated by Fusarium species.

A study of photosynthetic biogas upgrading based on a high rate algal pond under alkaline conditions: Influence of the illumination regime

Microalgal-bacterial processes have emerged as environmental friendly systems for the cost-effective treatment of anaerobic effluents such as biogas and nutrients-laden digestates. Environmental parameters such as temperature, irradiation, nutrient concentration and pH effect the performance of the systems. In this paper, the potential of a microalgal-bacterial photobioreactor operated under high pH (≈9.5) and high alkalinity to convert biogas into biomethane was evaluated. The influence of the illumination regime (continuous light supply vs 12h/12h light/dark cycles) on the synthetic biogas upgrading efficiency, biomass productivity and nutrient removal efficiency was assessed in a High-Rate Algal Pond interconnected to a biogas absorption bubble column. No significant differences in the removal efficiency of CO₂ and H₂S (91.5±2% and 99.5%±0.5, respectively) were recorded regardless of the illumination regime. The high fluctuations of the dissolved oxygen concentration during operation under light/dark cycles allowed to evaluate the specific growth rate and the specific partial degradation rate of the microalgae biomass by photosynthesis and respiration, respectively. The respiration reduced the net microalgae biomass productivity under light/dark cycles compared with process operation under the continuous light supply.

Fate of H2S during the cultivation of Chlorella sp. deployed for biogas upgrading

The H₂S may play a key role in the sulfur cycle among the biogas production by the anaerobic digestion of wastes and the biogas upgrading by a microalgae based technology. The biogas is upgraded by contacting with slightly alkaline aqueous microalgae culture, then CO₂ and H₂S are absorbed. The dissolved H₂S could limit or inhibit the microalgae growth. This paper evaluated the role of dissolved H₂S and other sulfured byproducts under prevailing biogas upgrading conditions using a microalgal technology. At initial stages of batch cultivation the growth of Chlorella sp. was presumably inhibited by dissolved H₂S. After 2 days, the sulfides were oxidized mainly by oxic chemical reactions to sulfate, which was later rapidly assimilated by Chlorella sp., allowing high growing rates. The fate of H₂S during the microalgae cultivation at pH > 8.5 was assessed by a mathematical model where the pentasulfide, thiosulfate and sulfite were firstly produced and converted finally to sulfate for posterior assimilation.

Study on Haloalkaliphilic Sulfur-Oxidizing Bacterium for Thiosulfate Removal in Treatment of Sulfidic Spent Caustic

Due to the disadvantages of physiochemical methods for sulfidic spent caustic treatment, attentions are drawn to the environmental-friendly biotreatments including sulfur-oxidizing halo-alkaliphiles. Thioalkalivibrio versutus DSM 13738 was grown at alkaline (pH10) autotrophic medium with sodium carbonate/bicarbonate as the sole source of carbon and amended with sodium thiosulfate as the electron and energy source. The effect of various parameters including temperature (25-40 °C), pH (8-11), NaCl concentration (0.5-5 % w/v) and sodium thiosulfate concentrations (100-750 mM) was evaluated on bacterial growth and thiosulfate removal. This strain could eliminate sodium thiosulfate at very high concentrations up to 750 mM. The results showed that the highest specific growth rate was pH 9.5 and thiosulfate removal of Thioalkalivibrio versutus occurred at pH 10.5. The optimum salt concentration for thiosulfate removal was 2.5 % w/v and 5 % NaCl and specific growth rate elevated 2.5% w/v. It was also specified that this strain thrives occurred in 37 °C and at 35 and 37 °C higher removal of thiosulfate. Following chemical oxidation of sulfide to thiosulfate, application of Thioalkalivibrio versutus could be promising for spent caustic treatment. Since thiosulfate is utilized as an energy source, highest removal efficiency occurred at marginally different conditions compared to optimal growth.

Study on Haloalkaliphilic Sulfur-Oxidizing Bacterium for Thiosulfate Removal in Treatment of Sulfidic Spent Caustic

Due to the disadvantages of physiochemical methods for sulfidic spent caustic treatment, attentions are drawn to the environmental-friendly biotreatments including sulfur-oxidizing halo-alkaliphiles.Thioalkalivibrio versutusDSM 13738 was grown at alkaline (pH10) autotrophic medium with sodium carbonate/bicarbonate as the sole source of carbon and amended with sodium thiosulfate as the electron and energy source. The effect of various parameters including temperature (25-40 °C), pH (8-11), NaCl concentration (0.5-5 % w/v) and sodium thiosulfate concentrations (100-750 mM) was evaluated on bacterial growth and thiosulfate removal. This strain could eliminate sodium thiosulfate at very high concentrations up to 750 mM. The results showed that the highest specific growth rate was pH 9.5 and thiosulfate removal ofThioalkalivibrio versutusoccurred at pH 10.5. The optimum salt concentration for thiosulfate removal was 2.5 % w/v and 5 % NaCl and specific growth rate elevated 2.5% w/v. It was also specified that this strain thrives occurred in 37 °C and at 35 and 37 °C higher removal of thiosulfate. Following chemical oxidation of sulfide to thiosulfate, application ofThioalkalivibrio versutuscould be promising for spent caustic treatment. Since thiosulfate is utilized as an energy source, highest removal efficiency occurred at marginally different conditions compared to optimal growth.

Metagenomic analysis of a desulphurisation system used to treat biogas from vinasse methanisation

We investigated the response of microbial community to changes in H2S loading rate in a microaerated desulphurisation system treating biogas from vinasse methanisation. H2S removal efficiency was high, and both COD and DO seemed to be important parameters to biomass activity. DGGE analysis retrieved sequences of sulphide-oxidising bacteria (SOB), such as Thioalkalimicrobium sp. Deep sequencing analysis revealed that the microbial community was complex and remained constant throughout the experiment. Most sequences belonged to Firmicutes and Proteobacteria, and, to a lesser extent, Bacteroidetes, Chloroflexi, and Synergistetes. Despite the high sulphide removal efficiency, the abundance of the taxa of SOB was low, and was negatively affected by the high sulphide loading rate.

Metatranscriptomic analysis of a high-sulfide aquatic spring reveals insights into sulfur cycling and unexpected aerobic metabolism

Zodletone spring is a sulfide-rich spring in southwestern Oklahoma characterized by shallow, microoxic, light-exposed spring water overlaying anoxic sediments. Previously, culture-independent 16S rRNA gene based diversity surveys have revealed that Zodletone spring source sediments harbor a highly diverse microbial community, with multiple lineages putatively involved in various sulfur-cycling processes. Here, we conducted a metatranscriptomic survey of microbial populations in Zodletone spring source sediments to characterize the relative prevalence and importance of putative phototrophic, chemolithotrophic, and heterotrophic microorganisms in the sulfur cycle, the identity of lineages actively involved in various sulfur cycling processes, and the interaction between sulfur cycling and other geochemical processes at the spring source. Sediment samples at the spring’s source were taken at three different times within a 24-h period for geochemical analyses and RNA sequencing. In depth mining of datasets for sulfur cycling transcripts revealed major sulfur cycling pathways and taxa involved, including an unexpected potential role of Actinobacteria in sulfide oxidation and thiosulfate transformation. Surprisingly, transcripts coding for the cyanobacterial Photosystem II D1 protein, methane monooxygenase, and terminal cytochrome oxidases were encountered, indicating that genes for oxygen production and aerobic modes of metabolism are actively being transcribed, despite below-detectable levels (<1 µM) of oxygen in source sediment. Results highlight transcripts involved in sulfur, methane, and oxygen cycles, propose that oxygenic photosynthesis could support aerobic methane and sulfide oxidation in anoxic sediments exposed to sunlight, and provide a viewpoint of microbial metabolic lifestyles under conditions similar to those seen during late Archaean and Proterozoic eons.

Spontaneous electrochemical treatment for sulfur recovery by a sulfide oxidation/vanadium(V) reduction galvanic cell

Sulfide is the product of the biological sulfate reduction process which gives toxicity and odor problems. Wastewaters or bioreactor effluents containing sulfide can cause severe environmental impacts. Electrochemical treatment can be an alternative approach for sulfide removal and sulfur recovery from such sulfide rich solutions. This study aims to develop a spontaneous electrochemical sulfide oxidation/vanadium(V) reduction cell with a graphite electrode system to recover sulfide as elemental sulfur. The effects of the internal and external resistance on the sulfide removal efficiency and electrical current produced were investigated at different pH. A high surface area of the graphite electrode is required in order to have as less internal resistance as possible. In this study, graphite powder was added (contact area >633 cm(2)) in order to reduce the internal resistance. A sulfide removal efficiency up to 91% and electrical charge of more than 400 C were achieved when using five graphite rods supplemented with graphite powder as the electrode at an external resistance of 30 Ω and a sulfide concentration of 250 mg L(-1).

Microbial treatment of sulfur-contaminated industrial wastes

The present study evaluated the microbial removal of sulfur from a solid industrial waste in liquid culture under laboratory conditions. The study involved the use of two bacteria Acidithiobacillus ferrooxidans ATCC 53987 and Acidithiobacillus thiooxidans AZCT-M125-5 isolated from a Mexican soil. Experimentation for industrial waste biotreatment was done in liquid culture using 125-mL Erlenmeyer flasks containing 30 mL Starkey modified culture medium and incubated at 30°C during 7 days. The industrial waste was added at different pulp densities (8.25-100% w/v) corresponding to different sulfur contents from 0.7 to 8.63% (w/w). Sulfur-oxidizing activity of the strain AZCT-M125-5 produced 281 and 262 mg/g of sulfate and a sulfur removal of 60% and 45.7% when the pulp density was set at 8.25 and 16.5% (w/v), respectively. In comparison, the strain A. ferrooxidans ATCC 53987 showed a lower sulfur-oxidizing activity with a sulfate production of 25.6 and 12.7 mg/g and a sulfur removal of 6% and 2.5% at the same pulp densities, respectively. Microbial growth was limited by pulp densities higher than 25% (w/v) of industrial waste with minimal sulfur-oxidizing activity and sulfur removal. The rate of sulfur removal for Acidithiobacillus thioxidans AZCT-M125-5 and Acidithiobacillus ferrooxidans ATCC 53987 was 0.185 and 0.0159 mg S g(-1) h(-1) with a pulp density of 16.5% (w/v), respectively. This study demonstrated that Acidithiobacillus thiooxidans AZCT-M125-5 possesses a high sulfur-oxidizing activity, even at high sulfur concentration, which allows the treatment of hazardous materials.

Microalgal-biotechnology as a platform for an integral biogas upgrading and nutrient removal from anaerobic effluents

The potential of a pilot high rate algal pond (HRAP) interconnected via liquid recirculation with an external absorption column for the simultaneous removal of H2S and CO2 from biogas using an alkaliphilic microalgal-bacterial consortium was evaluated. A bubble column was preferred as external absorption unit to a packed bed column based on its ease of operation, despite showing a comparable CO2 mass transfer capacity. When the combined HRAP-bubble column system was operated under continuous mode with mineral salt medium at a biogas residence time of 30 min in the absorption column, the system removed 100% of the H2S (up to 5000 ppmv) and 90% of the CO2 supplied, with O2 concentrations in the upgraded biogas below 0.2%. The use of diluted centrates as a free nutrient source resulted in a gradual decrease in CO2 removal to steady values of 40%, while H2S removal remained at 100%. The anaerobic digestion of the algal-bacterial biomass produced during biogas upgrading resulted in a CH4 yield of 0.21-0.27 L/gVS, which could satisfy up to 60% of the overall energy demand for biogas upgrading. This proof of concept study confirmed that algal-bacterial photobioreactors can support an integral upgrading without biogas contamination, with a net negative CO2 footprint, energy production, and a reduction of the eutrophication potential of the residual anaerobic effluents.

Isolation and identification of methanethiol-utilizing bacterium CZ05 and its application in bio-trickling filter of biogas

A bacterium capable of methanethiol (MT) degradation was enriched and isolated by employing activated sewage sludge as the inoculum in a mineral medium containing MT. The isolate was identified as Paenibacillus polymyxa CZ05 through a Biolog test and 16S rDNA sequencing. This strain can utilize both organic and inorganic media and thrives at pH 4 to 9. The batch culture showed that the strain can degrade MT better in the No. 4 medium than in the No. 1 medium. A series-operating biotrickling filter with lava stone as the carrier was employed to test the application of P. polymyxa CZ05 in the removal of MT in simulated biogas. Long-term experiments showed that a high concentration of MT (60 ppm) was efficiently removed (99.5%) by the biotrickling filters at EBRT 30 s. The addition of hydrogen sulfide decreased the MT removal rate because the dissolved oxygen competed with MT.

By-passing acidification limitations during the biofiltration of high formaldehyde loads via the application of ozone pulses

A formaldehyde airstream was treated in a biofilter for an extended period of time. During the first 133 days, the reactor was operated without ozone, whereas over the following 82 days ozone was intermittently implemented. The maximum stable elimination capacity obtained without ozone was around 57 g m(-3) h(-1). A greater load could not be treated under these conditions, and no significant formaldehyde removal was maintained for inlet loads greater than 65 g m(-3) h(-1); the activity of microorganisms was then inhibited by the presence of acidic byproducts, and the media acidified (pH<4). The implementation of ozone pulses allowed a stable elimination capacity to be obtained, even at greater loads (74 g m(-3) h(-1)). The effect of ozone on the extra cellular polymeric substances detachment from the biofilm could not be confirmed due to the too low biofilter biomass content. Thus, the results suggest that ozone acted as an in situ pH regulator, preventing acidic byproducts accumulation, and allowing the treatment of high loads of formaldehyde.

Surface neutralization and H(2)S oxidation at early stages of sewer corrosion: influence of temperature, relative humidity and H(2)S concentration

While the involvement of a range of environmental factors in sewer corrosion is known, a comprehensive understanding of the processes involved and the exact role of individual environmental factors in sewer corrosion is still lacking. The corrosion of concrete in sewer systems is reported to be initiated through chemical reactions (involving H(2)S and CO(2)) that lower the surface pH to a level then conducive for biological activity. However, the specific influence of environmental variables, such as H(2)S level, temperature, and relative humidity etc. remains unclear; although, they are expected to control these initial surface reactions of the concrete sewer pipe. We examined changes in the surface chemistry of concrete during the early stages of corrosion by exposing concrete coupons to thirty-six independent conditions in well-controlled laboratory chambers that simulated conditions typically found in various sewer environments across Australia. The conditions employed were combinations of six H(2)S levels, three gas-phase temperatures and two relative humidity levels. Our results indicate that the role of CO(2) on initial surface pH reduction is insignificant when compared to the influence of H(2)S. Within the first 12 months, a decrease in surface pH by 4.8 units was observed for coupons exposed to 30 °C and 50 ppm H(2)S, while significantly lower pH reductions of 3.5 and 1.8 units were detected for coupons exposed to 25 °C and 18 °C respectively, and 50 ppm H(2)S. Elemental sulphur was found to be the major oxidation product of H(2)S and elevated concentrations were detected at the higher levels of H(2)S, temperature and relative humidity. More significantly, the data obtained from the controlled chamber experiments correlated with those obtained from the field-exposed coupons. Hence, these findings can be extended to real sewer corrosion processes.

Application of a 2-step process for the biological treatment of sulfidic spent caustics

This research demonstrates the feasibility and advantages of a 2-step process for the biological treatment of sulfidic spent caustics under halo-alkaline conditions (i.e. pH 9.5; Na(+) = 0.8 M). Experiments with synthetically prepared solutions were performed in a continuously fed system consisting of two gas-lift reactors in series operated at aerobic conditions at 35 °C. The detoxification of sulfide to thiosulfate in the first step allowed the successful biological treatment of total-S loading rates up to 33 mmol L(-1) day(-1). In the second, biological step, the remaining sulfide and thiosulfate was completely converted to sulfate by haloalkaliphilic sulfide oxidizing bacteria. Mathematical modeling of the 2-step process shows that under the prevailing conditions an optimal reactor configuration consists of 40% 'abiotic' and 60% 'biological' volume, whilst the total reactor volume is 22% smaller than for the 1-step process.

Effects of methanethiol on the biological oxidation of sulfide at natron-alkaline conditions

The effects of methanethiol (MT) on biological sulfide oxidation were studied in a continuously operated bioreactor, in which chemolithoautotrophic bacteria belonging to the genus Thioalkalivibrio convert hydrogen sulfide (H2S) at natron-alkaline conditions. Previous bioreactor experiments have shown that always a fraction of the H2S is oxidized to sulfate and thiosulfate. This is unwanted, as it leads to caustic requirements for pH control and the formation of a bleed stream to discharge these compounds from the process. The current research shows that due to the addition of MT, sulfate formation is prevented. As a result, all supplied H2S is completely converted into elemental sulfur. Treatment of a continuous supply of 51.0 mM day(-1) H2S and 79 microM day(-1) MT was feasible for a prolonged period, with 99 mol% selectivity for sulfur formation. A part of the MT reacts with the freshly produced sulfur particles to form dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS). Results indicate that MT, DMDS, and DMTS partly adsorb onto the biosulfur particles. At concentrations above 10 microM, these volatile organic sulfur compounds induce biomass decay.

Alkaline biofiltration of H2S odors

Hydrogen sulfide (H2S) is a very common odor nuisance which is best controlled by chemical or biological scrubbing. Under alkaline pH, the amount of H2S that can be solubilized in a scrubbing liquid increases significantly, and therefore, gas-liquid mass transfer limitations can be reduced. To date, biological scrubbing of H2S has been limited to neutral or acidic pH, despite the potential benefit of reduced mass transfer limitations at alkaline pH. In the present paper, an alkaliphilic sulfoxidizing bacterial consortium was deployed in a laboratory-scale biotrickling filter treating H2S at pH 10. The gas contact time ranged from 1 to 6 s, and H2S inlet concentrations, from 2.5 to 18 ppm(v). The results showed that under most conditions, H2S removal exceeded 98% and the degradation end-product was sulfate. At the highest H2S concentrations and shortest gas contacttimes, when the loading exceeded 30 g m(-3) h(-1), the H2S removal efficiency decreased significantly due to biological reaction limitation, and incompletely oxidized sulfides were measured in the trickling liquid. An analysis of the process demonstrated that operating the biotrickling filter at high pH results in an enhancement of the mass transfer by a factor of 1700-11 000. Overall, alkaline biotrickling filtration was shown to be very effective at low concentration of H2S and very short gas contact time. This is the first demonstration of a biotrickling filter for air pollution control operated at high pH.

Evaluation of feed COD/sulfate ratio as a control criterion for the biological hydrogen sulfide production and lead precipitation

The ability of sulfate-reducing bacteria to produce hydrogen sulfide and the high affinity of sulfide to react with divalent metallic cations represent an excellent option to remove heavy metals from wastewater. Different parameters have been proposed to control the hydrogen sulfide production by anaerobic bacteria, such as the organic and sulfate loading rates and the feed COD/SO4(2-) ratio. This work relates the feed COD/SO4(2-) ratio with the hydrogen sulfide production and dissolved lead precipitation, using ethanol as carbon and energy source in an up-flow anaerobic sludge blanket reactor. A maximum dissolved sulfide concentration of 470+/-7 mg S/L was obtained at a feed COD/SO4(2-) ratio of 2.5, with sulfate and ethanol conversions of approximately 94 and 87%, respectively. The lowest dissolved sulfide concentration (145+/-10 mg S/L) was observed with a feed COD/SO4(2-) ratio of 0.67. Substantial amounts of acetate (510-1730 mg/L) were produced and accumulated in the bioreactor from ethanol oxidation. Although only incomplete oxidation of ethanol to acetate was observed, the consortium was able to remove 99% of the dissolved lead (200 mg/L) with a feed COD/SO4(2-) ratio of 1.5. It was found that the feed COD/SO4(2-) ratio could be an adequate parameter to control the hydrogen sulfide production and the consequent precipitation of dissolved lead.

A new role for sulfur in arsenic cycling

Sulfur and arsenic often coexist in the environment and share similar microbial redox transformations. We examined the effects of sulfide on aerobic arsenite oxidation in alkaline lake water samples and in laboratory enrichment cultures. Significant arsenite oxidation occurred only in treatments with bacteria present, and production of arsenate was greatly enhanced by the addition of sulfide or thiosulfate. IC-ICP-MS analysis of samples showed that mono- and dithioarsenate formed in arsenite + sulfide amended lake water. Our data indicate that these two thioarsenic compounds are fairly stable in sterile alkaline solutions, but are transformed predominantly to arsenate when bacteria are present. Enrichment culture experiments suggest that sulfur-oxidizing bacteria use free or arsenic-bound sulfur as a growth substrate and directly or indirectly transform arsenite and thioarsenates to arsenate during growth. Increases in cell density resulted in more rapid conversion of arsenite and thioarsenates. The rate and extent of these processes appearto be controlled bythe concentration of bacteria and the ratio of reduced sulfur to arsenite present. Sulfur-driven arsenite oxidation and microbial thioarsenate transformation may be important biogeochemical processes in the arsenic cycle of our study site (Mono Lake, CA, USA) and other alkaline environments as well.