Performance of a haloalkaliphilic bioreactor under different NO3(-)/SO4(2-) ratios

Pollution Control of Industrial Mariculture Wastewater: A Mini-Review

With the rapid development of intensive mariculture, lots of mariculture wastewaters containing residual feed and excrements are discharged into marinelands, leading to coastal pollution. Recently, the environmental problems caused by the discharge of mariculture wastewater have been paid much attention, as have other breeding industries in China. In fact, organic solid waste accounts for most of the pollutants and can be reduced by precipitation or filtration technologies, after which the supernatant can be easily treated by ecological methods. Some national guidelines and relevant local standards have been issued to strictly control the mariculture wastewater, but there are still few effective technologies for mariculture wastewater treatment due to its high salinity and extremely low pollutant concentration. This paper aims to propose feasible pollution control methods of mariculture wastewater according to the wastewater characteristics from different mariculture modes. For raw ammonia-based wastewater, it should be sequentially treated by precipitation, nitrification and denitrification and ecological methods, which would target solid waste, organic carbon/nitrogen and phosphorus removal, respectively. For the nitrate-based wastewater, this just needs denitrification filters and ecological methods for nitrate and phosphorus removal. After an overview of pollution control strategies for different types and scales of industrial mariculture wastewater treatment, some challenges are also mentioned.

Haloalkaliphilic denitrifiers-dependent sulfate-reducing bacteria thrive in nitrate-enriched environments

As bridge in global cycles of carbon, nitrogen, and sulfur, sulfate-reducing bacteria (SRB) play more and more important role under various environments, especially the saline-alkali environments with significant increase in area caused by human activities. Sulfate reduction can be inhibited by environmental nitrate. However, how SRB cope with environmental nitrate stress in these extreme environments still remain unclear. Here, after a long-term enrichment of sediment from saline-alkali Qinghai Lake of China using anaerobic filter reactors, nitrate was added to evaluate the response of SRB. With the increase in nitrate concentrations, the inhibition on sulfate reduction was gradually observed. Interestingly, extension of hydraulic retention time can relieve the inhibition caused by high nitrate concentration. Mass balance analysis showed that nitrate reduction is prior to sulfate reduction. Further metatranscriptomic analysis shows that, genes of nitrite reductase (periplasmic cytochrome c nitrite reductase gene) and energy metabolisms (lactate dehydrogenase, formate dehydrogenase, pyruvate:ferredoxin-oxidoreductase, and fumarate reductase genes) in SRB was down-regulated, challenging the long-held opinion that up-regulation of these genes can relieve the nitrate inhibition. Most importantly, the nitrate addition activated the denitrification pathway in denitrifying bacteria (DB) via significantly up-regulating the expression of the corresponding genes (nitrite reductase, nitric oxide reductase c subunit, nitric oxide reductase activation protein and nitrous oxide reductase genes), quickly reducing the environmental nitrate and relieving the nitrate inhibition on SRB. Our findings unravel that in response to environmental nitrate stress, haloalkaliphilic SRB show dependency on DB, and expand our knowledge of microbial relationship during sulfur and nitrogen cycles.

Improving confirmed nanometric sulfur bioproduction using engineered Thioalkalivibrio versutus

Complicated production procedures and superior characteristics of nano-sized sulfur elevate its price to 25-40 fold higher than micrograde kind. Also, natural gas hydrogen sulfide levels are restricted because of its toxic environmental consequences. Thioalkalivibrio versutus is a polyextremophilic industrial autotroph with high natural gas desulfurization capability. Here, nanometric (>50 nm) sulfur bioproduction using T. versutus while desulfurizing natural gas was validated. Also, this production was enhanced by 166.7% via lowering sulfate production by 55.1%. A specially-developed CRISPR system, with 42% editing efficiency, simplified the genome editing workflow scheme for this challenging bacterium. In parallel, sulfur metabolism was uncovered using proteins mining and transcriptome studies for defining sulfate-producing key genes (heterodisulfide reductase-like complex, sulfur dioxygenase, sulfite dehydrogenase and sulfite oxidase). This study provided cost-effective nanometric sulfur production and improved this production using a novel CRISPR strategy, which could be suitable for industrial polyextremophiles, after uncovering sulfur pathways in T. versutus.

Deep and high-efficiency removal of sulfate through a coupling system with sulfate-reducing and sulfur-oxidizing capacity under haloalkaliphilic condition

Sulfide from anaerobic treatment of high-sulfate wastewater would always have some adverse effects on downstream processes. In this study, a coupling anaerobic/aerobic system was developed and operated under haloalkaliphilic condition to realize deep and high-efficiency removal of sulfate without production of sulfide. A haloalkaliphilic sulfur-oxidizing strain, Thioalkalivibrio versutus SOB306, was responsible for oxidation of sulfide. The anaerobic part was first operated at optimum condition based on a previous study. Then, its effluent with an average sulfide concentration of 674 ± 33 mg·l^-1 was further directly treated by a set of 1 l biofilter with SOB306 strain under aerobic condition. Finally, 100% removal rate of sulfide was achieved at aeration rate of 0.75 l·l^-1·min^-1, ORP of - 392 mV and HRT of 4 h. The average yield of elemental sulfur reached 79.1 ± 1.3% in the filter, and the CROS achieved a conversion rate of sulfate to sulfur beyond 54%. This study for the first time revealed the characteristics and performance of the haloalkaliphilic CROS in deep treatment of high-sulfate wastewater, which paved the way for the development and application of this method in the real world.

Enhanced growth-driven stepwise inducible expression system development in haloalkaliphilic desulfurizing Thioalkalivibrio versutus

Highly toxic and flammable H₂S gas has become an environmental threat. Because of its ability to efficiently remove H₂S by oxidation, Thioalkalivibrio versutus is gaining more attention. Haloalkaliphilic autotrophs, like the bio-desulfurizing T. versutus, grow weakly. Weak growth makes any trial for developing potent genetic tools required for genetic engineering far from achieved. In this study, the fed-batch strategy improved T. versutus growth by 1.6 fold in maximal growth rate, 9-fold in O.D₆₀₀ values and about 3-fold in biomass and protein productions. The strategy also increased the favorable desulfurization product, sulfur, by 2.7 fold in percent yield and 1.5-fold in diameter. A tight iron-inducible expression system for T. versutus was successfully developed. The system was derived from fed-batch cultivation coupled with new design, build, test and validate (DPTV) approach. The inducible system was validated by toxin expression. Fed-batch cultivation coupled with DPTV approach could be applied to other autotrophs.

The mutual influence between corrosion and the surrounding soil microbial communities of buried petroleum pipelines

Buried petroleum pipeline corrosion and leaks cause inevitable changes in the microbial communities of the surrounding soils. In addition, soils with different microbial communities can make different contributions to buried pipeline corrosion. Three kinds of soil samples of buried petroleum pipelines under different corrosion and petroleum contamination conditions were collected from the Shengli Oilfield of China to investigate the mutual influence between corrosion and the microbial communities of the surrounding soil. The 16S rRNA gene high-throughput Illumina MiSeq sequencing was used to analyze the microbial communities of different surrounding soils. Electrochemical tests were performed for steel corrosion investigation. The results showed that the microbial diversity of the surrounding soils of corroded pipelines with/without petroleum contamination (O-soil and C-soil, respectively) decreased significantly as compared with that of the non-corroded and non-contaminated ones (NC-soil). The C-soil contained more abundant Balneolaceae (Balneola, KSA1), Flavobacteriaceae (Muricauda, Gramella) and Desulfuromonadaceae (Pelobacter, Geoalkalibacter). The O-soil possessed a greater abundance of Halomonas, Pseudoalteromonas, Psychrobacter and Dietzia, which were reported to have a capacity for hydrocarbon degradation. Moreover, electrochemical measurements indicated that the microcosm of the C-soil and NC-soil promoted steel corrosion, while the C-soil community showed a slightly higher corrosion rate. However, the O-soil community mitigated the steel corrosion. These observations suggested that pipeline corrosion increased proportions of microorganisms, which are likely related to fermentation, sulfur respiration, iron respiration and manganese respiration in surrounding soils and enhanced the soil corrosivity, while petroleum contamination weakened the corrosion ability and promoted the growth of hydrocarbon-degrading organisms in the microbial community.

Microbial communities in the native habitats of Agaricus sinodeliciosus from Xinjiang Province revealed by amplicon sequencing

Agaricus sinodeliciosus is an edible species described from China and has been successfully cultivated. However, no studies have yet reported the influence factors implicated in the process of fructification. To better know abiotic and biotic factors, physiochemical characteristics and microbial communities were investigated in five different soil samples collected in the native habitats of specimens from northern Xinjiang, southern Xinjiang, and Zhejiang Province, respectively. There are major differences in texture and morphology among different specimens of A. sinodeliciosus from Xinjiang Province. A. sinodeliciosus from southern Xinjiang was the largest. Concentrations of DOC and TN and C/N ratio are not the main reason for the differences. Microbial communities were analyzed to find out mushroom growth promoting microbes (MGPM), which may lead to the differences. Functional microbes were picked out and can be divided into two categories. Microbes in the first category may belong to MGPM. There may be symbiotic relationships between microbes in the second category and A. sinodeliciosus. Certain analyses of microbial communities support the hypothesis that interactions between microbes and mushrooms would be implicated in morphological variation of the collected mushrooms. Redundancy analysis results indicate that high DOC/NH₄⁺-N ratio and NH₄⁺-N concentration can improve the yield of A. sinodeliciosus.

Pyrosequencing reveals microbial community dynamics in integrated simultaneous desulfurization and denitrification process at different influent nitrate concentrations

Integrated simultaneous desulfurization and denitrification (ISDD) process has proven to be feasible for the coremoval of sulfate, nitrate, and chemical oxygen demand (COD). In this study, we aimed to reveal the microbial community dynamics in the ISDD process with different influent nitrate (NO₃^-) concentrations. For all tested scenarios, full denitrification was accomplished while sulfate removal efficiency decreased along with increased influent NO₃^- concentrations. The proportion of S⁰ to influent SO₄^2- maintained a low level (5.6-17.0%) regardless of the increased influent NO₃^- concentrations. Microbial community analysis results showed that higher influent NO₃^- concentrations affected the microbial community structure greatly. Phyla Proteobacteria, Spirochaetae, Firmicutes, Synergistetes, and Chloroflexi dominated in all the community compositions, of which Proteobacteria exhibited a clear difference among eight microbial samples. Members of δ-Proteobacteria, with 16S rRNA gene sequences related to Desulfobulbus, were clearly decreased at influent NO₃^- = 3000 and 3500 mg/L, suggesting an inhibitory effect of NO₃^- on sulfate reduction. In contrast, as influent NO₃^- concentration increased, microbial community was notably enriched in γ-Proteobacteria and ε-Proteobacteria, which revealed the enrichment of 16S rRNA gene sequences related to Pseudomonas (γ-Proteobacteria), and Arcobacteria and Sulfurospirillum (ε-Proteobacteria).

Mathematical modeling of simultaneous carbon-nitrogen-sulfur removal from industrial wastewater

A mathematical model of carbon, nitrogen and sulfur removal (C-N-S) from industrial wastewater was constructed considering the interactions of sulfate-reducing bacteria (SRB), sulfide-oxidizing bacteria (SOB), nitrate-reducing bacteria (NRB), facultative bacteria (FB), and methane producing archaea (MPA). For the kinetic network, the bioconversion of C-N by heterotrophic denitrifiers (NO₃^-→NO₂^-→N₂), and that of C-S by SRB (SO₄^2-→S^2-) and SOB (S^2-→S⁰) was proposed and calibrated based on batch experimental data. The model closely predicted the profiles of nitrate, nitrite, sulfate, sulfide, lactate, acetate, methane and oxygen under both anaerobic and micro-aerobic conditions. The best-fit kinetic parameters had small 95% confidence regions with mean values approximately at the center. The model was further validated using independent data sets generated under different operating conditions. This work was the first successful mathematical modeling of simultaneous C-N-S removal from industrial wastewater and more importantly, the proposed model was proven feasible to simulate other relevant processes, such as sulfate-reducing, sulfide-oxidizing process (SR-SO) and denitrifying sulfide removal (DSR) process. The model developed is expected to enhance our ability to predict the treatment of carbon-nitrogen-sulfur contaminated industrial wastewater.

Bacterial communities in haloalkaliphilic sulfate-reducing bioreactors under different electron donors revealed by 16S rRNA MiSeq sequencing

Biological technology used to treat flue gas is useful to replace conventional treatment, but there is sulfide inhibition. However, no sulfide toxicity effect was observed in haloalkaliphilic bioreactors. The performance of the ethanol-fed bioreactor was better than that of lactate-, glucose-, and formate-fed bioreactor, respectively. To support this result strongly, Illumina MiSeq paired-end sequencing of 16S rRNA gene was applied to investigate the bacterial communities. A total of 389,971 effective sequences were obtained and all of them were assigned to 10,220 operational taxonomic units (OTUs) at a 97% similarity. Bacterial communities in the glucose-fed bioreactor showed the greatest richness and evenness. The highest relative abundance of sulfate-reducing bacteria (SRB) was found in the ethanol-fed bioreactor, which can explain why the performance of the ethanol-fed bioreactor was the best. Different types of SRB, sulfur-oxidizing bacteria, and sulfur-reducing bacteria were detected, indicating that sulfur may be cycled among these microorganisms. Because high-throughput 16S rRNA gene paired-end sequencing has improved resolution of bacterial community analysis, many rare microorganisms were detected, such as Halanaerobium, Halothiobacillus, Desulfonatronum, Syntrophobacter, and Fusibacter. 16S rRNA gene sequencing of these bacteria would provide more functional and phylogenetic information about the bacterial communities.

Regeneration of elemental sulfur in a simultaneous sulfide and nitrate removal reactor under different dissolved oxygen conditions

A continuous reactor in microaerobic conditions was adopted for sulfide-oxidizing, nitrate-reducing and elemental sulfur (S(0)) regenerating, simultaneously. The results showed that appropriate dissolved oxygen (DO) enhanced S(0) regeneration efficiency, sulfide oxidation efficiency, and nitrate reduction efficiency. When the DO concentration was 0.1-0.3 mg L(-1), the microaerobic bioreactor simultaneously converted 8.16 kg-Sm(-3)d(-1) of sulfide to S(0) and 2.48 kg-Nm(-3)d(-1) of nitrate to nitrogen with the sulfide and nitrate removal efficiency of 100% and 90% respectively. Compared with anaerobic sulfide and nitrate removal process previously reported, the loading sulfide was higher and more S(0) was generated during the operation in microaerobic reactor. Analysis using the 16S rDNA gene clone library revealed that Azoarcus, Thauera, Paracoccus, Sulfurospirillum, Arcobacter and Clostridium were the dominant microorganisms in the sulfide and nitrate removal system.

Sulfate reduction in a hydrogen fed bioreactor operated at haloalkaline conditions

Biological sulfate reduction is used as a biotechnological process to treat sulfate rich streams. However, application of biological sulfate reduction at high pH and high salinity using H₂ was not thoroughly investigated before. In this work the sulfate reduction activity, biomass growth, microbial community and biomass aggregation were investigated in a H₂-fed gas lift bioreactor at haloalkaline conditions. The process was characterized by low sulfate reduction volumetric rates due to slow growth and lack of biomass aggregation. Apparently, the extreme conditions and absence of organic compounds prevented the formation of stable aggregates. The microbial community analysis revealed a low abundance of known haloalkaliphilic sulfate reducers and presence of a Tindallia sp. The identified archaea were related to Methanobacterium alcaliphilum and Methanocalculus sp. The biomass did not attach to metal sulfides, calcite and magnesite crystals. However, biofilm formation on the glass bioreactor walls showed that attachment to glass occurs.

Performance of a haloalkaliphilic bioreactor and bacterial community shifts under different COD/SO₄²⁻ ratios and hydraulic retention times

Sulfur dioxide from flue gas was converted into sulfate after the absorption of alkaline solutions. Haloalkaliphilic microorganisms have been used in reducing sulfate to decrease expenses and avoid sulfide inhibition. The effects of different COD/SO4(2-) ratios and hydraulic retention times (HRTs) on the sulfate removal efficiency and bacterial community were investigated in model experiments. Ethanol showed better performance as an electron donor than lactate. The optimum COD/SO4(2-) ratio and HRT were 4.0 and 18 h, respectively, with respective sulfate removal efficiency and rate of 97.8 ± 1.11% and 6.26 ± 0.0710 g/Ld. Sulfide concentrations reached 1,603 ± 3.38 mg/L. Based on denaturing gradient gel electrophoresis analysis of 16S rDNA, the major sulfate-reducing bacterium (SRB) was Desulfonatronovibrio sp., which was only detected at a COD/SO4(2-) ratio of 4.0 using ethanol as an electron donor. Different HRTs had no significant effect on the band corresponding to this species. PCR results show that methane-producing archaea (MPA) were from the acetoclastic methanogenic family Methanosarcinaceae. Quantitative real-time PCR did not demonstrate any significant competition between SRB and MPA. The findings of this study indicate that sulfate reduction, nitrate reduction, and sulfide oxidization may occur in the same bioreactor.