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Microbial nitrate reduction can be driven by organic carbon oxidation, as well as by inorganic electron donors, such as reduced forms of sulfur and iron. An apparent inverse oxygen isotope fractionation effect was observed during nitrate reduction in sediment incubations from five sampling sites of a freshwater lake, Hongze Lake, China. Incubations with organic and inorganic electron donor additions were performed. Especially, the inverse oxygen isotope effect was intensified after glucose addition, whereas the incubations with sulfide and Fe

Constructed wetlands (CWs) have been widely used for ecological remediation of micro-polluted source water. Nitrous oxide (N

Denitrification is one of the major sources of N

As an emerging material, graphene oxide (GO) has been widely used in recent years and will inevitably enter into natural water bodies, and it may have an impact on lake microbial communities owing to its potential toxicity and denitrification-enhancing ability. This study simulated the effect of 0.1 g/L GO on denitrification in lake sediments under summer (28 °C) and winter temperatures (8 °C). GO promoted carbon source metabolism and denitrification. Phylogenetic bin-based null model analysis suggested that GO significantly altered the contribution of heterogeneous selection in bacterial and archaeal community assembly. The co-occurrence network indicated that bacterial communities responded to the enhancement of heterogeneous selection by strategies of enhancing positive correlation and shared niche, whereas archaeal communities adopted strategies of enhancing negative correlation and competition. Bacterial networks also emerged with more non-hub connector species that could drive changes in community structure. Our study contributed to the understanding of different ecological strategies adopted by bacterial and archaeal communities in response to changes in ecological selection driven by GO.

The microbial food web (MFW) is a material and energy source in lake water ecosystems. Although it is crucial to determine its structure and function for water ecological health, MFW changes during lake melt period have not been well studied. In this study, the MFW was divided into three categories by analyzing its structure and trophic transfer efficiency using hierarchical C/N stable isotopes and eDNA sequencing techniques, including the detrital food web (DFC, 15 %), classical grazing food web (CFC, 60 %), and mixed trophic food web (MFC, 25 %). The trophic structure and type of MFW in ice-melting lakes are always in the process of succession and adaptation, which is in a relatively low trophic transfer efficiency stage under stable conditions (i.e. CFC), whereas the input of exogenous debris and organic pollutants may lead to an increase in MFW trophic transfer efficiency (i.e. MFC, DFC). The trophic transfer efficiency from the previous trophic level to protozoa and micrometazoa was 16.32 % and 20.77 % in DFC and 10.20 % and 29.43 % in MFC, respectively. Both are obviously higher than those of the CFC (11.69 % and 9.45 %, respectively). In terms of trophic structure, the community interaction and trophic cascade effect of DFC and MFC were enhanced but easily changed with environmental factors. In contrast, the core species and cascading effects of the CFC were clearer, and the MFW structure was relatively stable. Overall, this study reveals that the explosive increase in MFW trophic transfer efficiency induced by exogenous input during the lake melt period may subsequently lead to the destabilization of the microbial community structure and cause potential ecological risks. These are manifested in the absence of ecological trophic processes, the decrease in trophic structure complexity and stability, and the weakening of microecology self-adaptive regulation ability.

Nature challenges microbes with change at different frequencies and demands an effective response for survival. Here, we used controlled laboratory experiments to investigate the ecological success of different response strategies, such as post-translational modification, transcriptional regulation, and specialized versus adaptable metabolisms. For this, we inoculated replicated chemostats with an enrichment culture obtained from sulfidic stream microbiomes 16 weeks prior. The chemostats were submitted to alternatingly oxic and anoxic conditions at three frequencies, with periods of 1 day, 4 days and 16 days. The microbial response was recorded with 16S rRNA gene amplicon sequencing, shotgun metagenomics, transcriptomics and proteomics. Metagenomics resolved 26 nearly complete genomes of bacterial populations, mainly affiliated with Proteobacteria and Bacteroidetes. Almost all these populations maintained a steady growth rate under both redox conditions at all three frequencies of change. Apparently, oscillating oxic/anoxic conditions selected for generalistic species, rather than species specializing in only a single condition. Rapid (1-day) dynamics yielded more stochasticity, both in community dynamics and gene expression, indicating that bet-hedging might be an effective coping strategy for relatively rapid environmental change. Codon-usage bias, previously associated with copiotrophic and oligotrophic lifestyles, was found to be a powerful predictor of ecological success at different frequencies, with copiotrophs and oligotrophs more successful at a rapid and a slow pace of change, respectively, independent of growth rate.

Endogenous contamination from the newly submerged sediment may have an impact on the water quality of the Danjiangkou Reservoir, the water source of the middle route of the South-to-North Water Diversion Project. In this study, in situ sediment samples were collected at different locations (Guojiashan (DJK1), Kongqueyuan (DJK2), Shijiagou (DJK3), Shiqiao Wharf (DJK4), and Songgang Wharf (DJK5) from the north to the south) of the Danjiangkou Reservoir and the upstream tributary using a columnar sediment sampler and statically cultured in laboratory, and the distribution and release of endogenous N and P from the sediment were investigated based on a double-membrane diffusion model. The results showed that the P contents in the main reservoir and the upstream tributary followed the order of inorganic phosphorus IP > organic phosphorus OP > calcium − phosphorus Ca − P > iron − phosphorus Fe − P > labile phosphorus LP . IP accounted for the largest proportion (47.10-59.70%) of total phosphorus (TP), while LP accounted for only a small proportion (0.10-0.90%) of TP. There is a significant difference in the spatial distribution of P at different sampling points, especially for the OP content (226.90 mg·kg-1) with a coefficient of variation of 26.90%. The contents of different forms of P and NH4+-N decreased from the upstream tributary to the main reservoir, which was mainly attributed to the land use type. In the vertical distribution, the contents of different forms of P in DJK4 and DJK5 decreased with the increase of sediment depth. The contents of NH4+-N and PO43--P in the sediment interstitial water of DJK4 and DJK5 were higher than those in the overlying water. In addition, the contents of NH4+-N and PO43--P were higher in DJK5 than that in DJK4. The static culture experiments showed that N and P were mainly released from the sediment-overlying water interface to the overlying water. The release rate of NH4+-N and PO43--P ranged from 13.08 mg·(m2·d)-1 to 21.39 mg·(m2·d)-1 and from 3.06 mg·(m2·d)-1 to 6.02 mg·(m2·d)-1, and the release amount calculated based on the double-membrane diffusion model was 1.17 × 10 3 t·a-1 and 0.53 × 10 3 t·a-1, respectively. Thus, endogenous contamination from the newly submerged land is an important factor affecting the water quality of the Danjiangkou Reservoir.

Antibiotics are pollutants that are constantly discharged into ocean and coastal wetlands and affect the growth and activity of microorganisms. Ammonia‐oxidizing archaea (AOA) and bacteria (AOB), which are very important in the global nitrogen cycle, are affected by antibiotics in the environment as well. Antibiotics have different influences on AOA and AOB microbial communities due to their different biochemical compositions and metabolic mechanisms, which change the ammonia‐oxidizing process in different environments. In this study, 62 samples from four typical coastal wetland types along the Bohai Rim were collected and treated with streptomycin sulfate and penicillin in the laboratory. The total ammonia oxidation rate decreased by 61.2–84.0% with streptomycin sulfate and decreased by 50.0–74.5% with penicillin. The significant change in abundance and community structure indicated that AOB were more inhibited than AOA by streptomycin sulfate and penicillin. Nevertheless, ecological network analysis verified that the internal association in the AOA community was more fragile than that in the AOB community. Moreover, the relationship between AOA and other nitrogen‐transforming functional archaea weakened in the presence of antibiotics, while AOB established relationships with more nitrogen‐transforming functional bacteria in the presence of antibiotics. Streptomycin sulfate had a stronger effect than penicillin due to the different inhibiting mechanisms of these antibiotics and the promotion of interspecific cooperation induced by penicillin in AOA.

Ammonia oxidation is mainly performed by ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). Allylthiourea (ATU) has been found to specifically inhibit ammonia oxidation. However, the effect of ATU on AOA and AOB transcription has been infrequently studied. In the present study, we examined the responses of AOA and AOB activity and DNA/cDNA community structure to ATU exposure. The ammonia oxidation activity in the 100-mg/L ATU group was 4.3% of that in the control group after 7 days. When exposed to ATU, the gene abundance of AOA was favored compared with that of AOB, and there were no statistically significant differences in the abundance of AOB amoA in DNA and cDNA between the two groups. Compared with the control group, the gene abundance of AOA significantly increased by 5.23 times, while the transcription of AOA significantly decreased by 0.70 times. Moreover, the transcriptional ratio of AOA in the ATU group was only 0.05 times as high as that in the control group. ATU selectively affected AOB and completely inhibited Nitrosomonas europaea and Bacterium amoA.22.HaldeII.kultur at the genetic level. Under ATU exposure, all AOA clusters were transcribed, but three AOB clusters were not transcribed. Our results indicated that the ammonia oxidation potential of the soil of water level fluctuation areas, based on ATU inhibition, was associated mainly with AOA amoA gene abundance and AOB community shifts in DNA and cDNA.

Lignite activated coke (LAC) has been modified in situ by adsorbing the biodegradation effluent of super heavy oil wastewater (SHOW) to extract organic pollutants from raw SHOW before biodegradation is investigated. Results showed that, in comparison with LAC, modified lignite activated coke (MLAC) exhibited a higher COD removal amount and adsorption capacity with the increase of dosage. The modification process also contributed to a dramatic COD decrease in the final effluent of SHOW from 128.9 mg L−1 to below 50 mg L−1. Particularly, characterization methods, GC-MS, FTIR, XPS and Boehm titration, were performed to investigate the relationship between the modification and the treatment performance. Results indicated that some basic substances were extracted from the biodegradation effluent by LAC during the modification process. Thus the alkali-nitrogen base abundant MLAC could remove larger acidic fractions from the raw SHOW during the adsorption process, leading to a higher adsorption capacity for MLAC. Furthermore, this clean and low cost in situ modification method also provides more reliable disposal effects for SHOW.

Oily sludge is a pollutant associated with the petrochemical industry, and its harmfulness and resource disposal are urgent problems to be solved. Nano-TiO2 was used to catalyze HTL to treat oily sludge and showed excellent technical advantages in this study. When T = 230°C and w = 1.5%, the total oil removal efficiency reaches 82.69%, of which 77.68% can be extracted and utilized. Compared with the blank group without TiO2, the oil removal efficiency is increased by nearly 35%, and the oil extraction efficiency is increased by more than 55%. The result imply that TiO2 might can be excited by HTL to generate h+ and e−, which will react with subcritical water produced by HTL to produce O2 and H2. H2 can promote the degradation and lightening of organic matter through hydrocracking, O2 can promote the oxidative cracking of organic hydrocarbons. TiO2 catalysis obviously changes the distribution trend of oil in HTL. Without TiO2 catalysis, the removed oil is mostly oxidized or coked to form coke. The H2 produced by TiO2 can inhibit the coking reaction and form liquid petroleum hydrocarbons that can be extracted and utilized. Due to gas release and coke reduction, which can create pathways to promote the release of oil and water. Nano-titanium dioxide hydrogen production catalysts can obviously improve the treatment efficiency of oily sludge and have broad application prospects in the harmless and resourceful treatment of organic solid wastes.

Microbial denitrification is a main source of nitrous oxide (N

The drag coefficient CD plays an important role in studying the interaction forces between individual particles and fluid. Due to the irregular particle shape of natural sands, studying the sedimentation characteristics and drag coefficient model of irregular particles is of great significance in explaining natural phenomena, predicting the sedimentation process, and calculating the interphase forces between individual particles and fluid. In this paper, firstly, an experimental system for measuring the settling velocity was built, the settling velocity of 67 tests of spheres with different particle Reynolds number Res in the Newtonian fluid were obtained, and the CD–Res correlation of sphere settling in the Newtonian fluid was established. The proposed CD–Res correlation was in good agreement with the existing classical CD–Res correlations, which proves the reliability of the experimental system and data processing method. Existing literature shows that the previous models are only suitable for irregular-shaped particles with three-dimensional shape-described parameters. However, the three-dimensional shape information of sand particles can only be obtained through accurate laboratory measurements, and it is often impossible to calculate accurately. By introducing the two-dimensional shape-described parameter (circularity c), using image analysis technology, the two-dimensional shape information of natural sands was obtained. The settling velocity of 221 tests of natural sands in the Newtonian fluid was obtained experimentally. It is found that the sand particles’ drag force exerted by the fluid is more significant than its equivalent sphere. With the increase in the particle Reynolds number, the shape irregularity’s influence on sand particle drag coefficient is more significant, and the CD–Res correlation of natural sand was proposed by fitting. The established CD–Res correlation has good prediction accuracy and can better predict the drag coefficient and terminal settling velocity of natural sand with irregular shapes.

The fate of nitrogen is controlled by the competition between nitrate reduction pathways. Denitrification removes nitrogen in the system to the atmosphere, whereas dissimilatory nitrate reduction to ammonia (DNRA) retains nitrate in the form of ammonia. Different microbes specialize in the oxidation of different electron donors, thus electron donors might influence the outcomes of the competition. Here, we investigated the fate of nitrate with five forms of sulfur as electron donors. Chemoautotrophic nitrate reduction did not continue after the passages of the enrichments with sulfide, sulfite and pyrite. Nitrate reduction rate was the highest in the enrichment with thiosulfate. Denitrification was stimulated and no DNRA was observed with thiosulfate, while both denitrification and DNRA were stimulated with elemental sulfur. Metagenomes of the enrichments were assembled and binned into ten genomes. The enriched populations with thiosulfate included Thiobacillus, Lentimicrobium, Sulfurovum and Hydrogenophaga, all of which contained genes involved in sulfur oxidation. Elemental sulfur-based DNRA was performed by Thiobacillus (with NrfA and NirB) and Nocardioides (with only NirB). Our study established a link between sulfur sources, nitrate reduction pathways and microbial populations.

This study found that graphene oxide (GO) improved microbial denitrification at low temperatures (~12 °C), and the optimal concentration was 10 mg/L as the removal rate of NO3-N increased by 17%. At the optimal concentration, GO improved the electron transport system activity of the microbes and enhanced the activity of nitrate reductase and nitrite reductase while exhibited low microbial toxicity. The addition of GO increased the content of tightly bound extracellular polymeric substances (EPS). The results of fluorescence spectrometer indicated that GO accelerated the renewal of bound EPS (B-EPS). Fourier Transform infrared spectroscopy (FTIR) results showed that GO affected the secondary structure of the protein in B-EPS, making B-EPS more hydrophobic and promoting microbial aggregation. B-EPS affected by GO can promote the electron transfer process of microorganisms. However, high concentration (>25 mg/L) of GO may inhibit denitrification by competing for electrons, which was not conducive to denitrification thermodynamically.

This study aimed to evaluate which environmental factors and genetic groups were important in explaining measured activity of Ammonia-oxidizing archaea (AOA) and bacteria (AOB), which play important roles in global nitrogen cycle, providing a new insight into the mechanism of archaeal and bacterial ammonia oxidation. We sampled 62 soil/sediment samples from coastal wetlands of the Bohai area of China and assessed the abundance of functional genes involved in the nitrogen cycle, soil/sediment characteristics and the potential activity of AOA (PAOA) and AOB (PAOB) using specific inhibitors. At last, we introduced the structure equation model (SEM) to infer direct and indirect effects of variables on potential activities. The results indicated that the change in AOA-amoA gene abundance may be more independent, while AOB-amoA was closely associated with the change in abundance of amx and denitrifier. PAOA was mainly defined by AOA-amoA abundance and partially influenced by the norA gene, suggesting coupling of archaeal ammonia oxidation with nitrite oxidation. PAOB was significantly defined by the abundance of amx and denitrifier, indirectly mediated by AOB-amoA. The activity of AOA seemed to be more independent of other microbial activities, while the activity of AOB varied closely with fluctuations of other microbial species. PAOA was mediated directly by the C/N ratio and indirectly by nitrite concentration and TOC value, while PAOB was mediated directly by ammonium concentration and TOC value and indirectly by C/N ratio. The activity of AOB may be determined by several other functional gene groups and had little correlation with AOB abundance while the activity of AOA was mostly controlled by itself.

In this study, the spatial and seasonal bacterioplankton community dynamics were investigated in the main channel of the Middle Route of the South-to-North Water Diversion Project (MRP) using Illumina HiSeq sequencing. Water samples were collected in spring and summer from south to north at eight water quality monitoring stations, respectively. The results showed that seasonal changes had a more pronounced effect on the bacterioplankton community compositions (BCCs) than spatial variation. The diversity analysis results indicated that samples of summer have more operational taxonomic units (OTUs), higher richness and diversity than those in spring. The main phyla, Proteobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria and Chloroflexi, displayed significant differences (P 0.05) between spring and summer in the main channel. The Redundancy analysis (RDA) targeting all samples indicated that specific conductivity (SPC), dissolved oxygen (DO), pH and temperature (T) might be key factors in driving BCCs, while trophic status showed no significant correlation (P 0.05). The present study provides important insights into the potential ecological roles of specific taxa in the new artificial ecosystem and it offers reference for studies on ecosystem succession of other giant interbasin water diversion project in the world.

The effect of adding rice husk as an electron donor on the genetic and metabolic diversity of denitrifying communities in a long-term flooded constructed wetland (D1) was compared with the control group without external carbon source addition (D2). The underlying molecular mechanisms responsible for nitrate removal were quantified under different nitrate loading rates. The results showed that D1 achieved higher and more stable removal efficiencies for NO3−-N (90–97%) and total nitrogen (73–87%) under different nitrate loading rates, which were approximately 10 times higher than those of D2. This corresponded with much higher absolute abundances of bacterial and nitrogen functional genes in D1 than D2. Additionally, the vertical distribution of microbial communities in D1 and D2 showed significant differences. This pattern suggested that adding rice husk in flooded CWs had beneficial effects on the denitrifying community. Quantitative response relationships and network analysis indicated that denitrification was the dominant nitrogen removal pathway. Moreover, the present study indicated that using rice husk as an external carbon source could be conducive to completing the nitrification process, which was first confirmed at the molecular level. The present study indicated that using rice husk as an external carbon source can significantly enhance denitrification rates and thus improve nitrogen removal in CWs for wastewater treatment process.

The dominance of different nitrate-reducing pathways determines nitrogen cycling patterns. Denitrification (DNF) has been widely studied, but assimilatory nitrate reduction (ANR) and dissimilatory nitrate reduction to ammonium (DNRA) have received much less attention. Their ecological patterns and responsible microbes are poorly understood. Here, we studied the structure and function succession of the three functional groups in the middle route of the South-to-North Water Diversion Project, which is a 1230 km canal spanning 8 degrees of latitude. The results reflected a nitrogen-removing pattern dominated by DNF in the summer and a nitrogen-retaining pattern dominated by ANR and DNRA in the winter. Stenotrophomonas, a typical denitrifier, was the keystone species in the summer and contributed to N2O production. Clostridium, a genus able to conduct ANR and DNRA, was the keystone species in the winter. Notably, a significant zonation pattern was discovered. According to the community structure, the system could be separated into two biogeographic zones, and the Yellow River (about latitude 35°N) is an important cut-off line. This bacterial biogeography followed different water characteristics and ecological processes. ANR was found to be an important process and seasonally transformed its habitat from the northern zone to the southern zone. DNRA bacteria were acclimated to the northern zone and favored at this region in both seasons. The generation of N2O, a strong greenhouse gas, also exhibited this zonation pattern. This is the first study to consider assimilatory and dissimilatory nitrate reducers together at a molecular level, and provides new insights into the underlying patterns of a nitrate-reducing bacterioplankton community.

The horizontal section length of shale gas horizontal wells in Sichuan Basin in the south-west of China generally exceeds 2000m. Cuttings are apt to accumulate and form cuttings beds along such long and curve horizontal sections due to low cuttings carrying capacity, which often results in excessive torque and drag or even stuck pipes during drilling process. According to the statistics dada inthe period of Jan. - Oct. 2019, more than 25 stuck pipe incidents and 15 rotary steering tools loss in borehole were reported due to inefficient cuttings transportation in the long horizontal wells in Sichuan Basin. This paper studies the cuttings transportation and cuttings bed formation in horizontal wells. A prediction model for the distribution of cuttings bed was established. A monitoring and analysis software for the cuttings bed and cuttings cleaner with V-shaped spiral blades that is used to agitate the cuttings bed wasdeveloped. The software calculates the distribution and thickness of the cuttings bed according to the well trajectory, wellbore structure, drilling fluid characteristics, etc., and provides the optimal operating parameters for the removal of the cuttings bed by the rotating and reciprocating drill string. Then, the drill cuttings remover in the drill string moves to the predicted position of the drill cuttings, scrapes the drill cuttings and creates a swirling flow during the pipe rotation. The combined application of software and makeup remover can effectively solve the issue of borehole cleaning in long horizontal wells. One of the field applications was carried out in the well Ning 209H12, a shale gas horizontal well in Sichuan Basin. The well experienced excessive torque and drag issue during the tripping of drill string of long horizontal section. Thesoftware ran based on oil well data, and it determines the placement and thickness of cuttings beds in the well and calculates the optimal operating parameters for a flow rate of about 32L/s and a speed of 100rpm to remove them. By rotatingand reciprocating the drill string with recommended operating parameters along the cuttings bed interval, the removers helped cleaning the cuttings bed efficiently and significant amount of cuttings was observed at vibration screen. After cleaning the cuttings bed interval, the trip smoothly ran to the bottom without any excessive torque and drag, and then continues to drill in cooperation with the removers to the total depth. During the well completion, there was no problem with the operation of electrical logging and production casing. This cuttings removal technology has been used in other shale gas formations and tight gas formations where horizontal wells are widely used.

Partitioning between nitrate reduction pathways, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) determines the fate of nitrate removal and thus it is of great ecological importance. Sulfide (S2−) is a potentially important factor that influences the role of denitrification and DNRA. However, information on the impact of microbial mechanisms for S2− on the partitioning of nitrate reduction pathways in freshwater environments is still lacking. This study investigated the effects of long-term (108 d) S2− addition on nitrate reduction pathways and microbial communities in the sediments of two different freshwater lakes. The results show that the increasing S2− addition enhanced the coupling of S2− oxidation with denitrification instead of DNRA. The sulfide-oxidizing denitrifier, Thiobacillus, was significantly enriched in the incubations of both lake samples with S2− addition, which indicates that it may be the key genus driving sulfide-oxidizing denitrification in the lake sediments. During S2− incubation of the Hongze Lake sample, which had lower inherent organic carbon (C) and sulfate (SO42−), Thiobacillus was more enriched and played a dominant role in the microbial community; while during that of the Nansi Lake sample, which had higher inherent organic C and SO42−, Thiobacillus was less enriched, but increasing abundances of sulfate reducing bacteria (Desulfomicrobium, Desulfatitalea and Geothermobacter) were observed. Moreover, sulfide-oxidizing denitrifiers and sulfate reducers were enriched in the Nansi Lake control treatment without external S2− input, which suggests that internal sulfate release may promote the cooperation between sulfide-oxidizing denitrifiers and sulfate reducers. This study highlights the importance of sulfide-driven denitrification and the close coupling between the N and S cycles in freshwater environments, which are factors that have often been overlooked.

Microbial denitrification is a main source of nitrous oxide (N2O) emissions which have strong greenhouse effect and destroy stratospheric ozone. Though the importance of sulfide driven chemoautotrophic denitrification has been recognized, its contribution to N2O emissions in nature remains elusive. We built up long-term sulfide-added microcosms with sediments from two freshwater lakes. Chemistry analysis confirmed sulfide could drive nitrate respiration in long term. N2O accumulated to over 1.5% of nitrate load in both microcosms after long-term sulfide addition, which was up to 12.9 times higher than N2O accumulation without sulfide addition. Metagenomes were extracted and sequenced during microcosm incubations. 16 S rRNA genes of Thiobacillus and Defluviimonas were gradually enriched. The nitric oxide reductase with c-type cytochromes as electron donors (cNorB) increased in abundance, while the nitric oxide reductase receiving electrons from quinols (qNorB) decreased in abundance. cnorB genes similar to Thiobacillus were enriched in both microcosms. In parallel, enrichment was observed for enzymes involved in sulfur oxidation, which supplied electrons to nitrate respiration, and enzymes involved in Calvin Cycle, which sustained autotrophic cell growth, implying the coupling relationship between carbon, nitrogen and sulfur cycling processes. Our results suggested sulfur pollution considerably increased N2O emissions in natural environments.

Newly developed hydrothermal jet drilling technology has the potential of being economically advantageous over conventional drilling techniques for drilling deep wells in hard formations. By applying coiled tubing techniques and modulating fluid media in the bottomhole reaction chamber, there can be a high temperature and high velocity jet striking and conducting heat to break the rock. So far, there has been no specific study on the influence of nozzle structure on the flow field of multiple hydrothermal jets. This paper presents hydrothermal jet models with different numbers of orifices to investigate the features of flow field, carrying capacity, drilling ability and cooling effect. Results show that for two models in the absence of cooling water, the bottomhole center temperature and pressure are higher than the two sides under multiple hydrothermal jets conditions. This is similar to the flow pattern for a single jet. Additionally, for the five-orifice nozzle with cooling water injected, the entire high temperature region is cylindrical. Ambient cooling water envelops the inner hot water. By comparing different models, the five-orifice nozzle model without cooling water shows a circular symmetric distribution of the bottomhole temperature. With cooling water injected, the central high temperature region becomes rectangular, while the margin of the well bottom is cooled by the peripheral cooling water. The bottom rock average temperature in five-orifice model is lower than for the four-orifice model due to more drastic thermal and kinetic transfer between the hydrothermal jet and the cooling water. The five-orifice nozzle model is better than the four-orifice nozzle model in terms of bottomhole temperature, bottomhole pressure and carrying capacity. Therefore, the five-orifice nozzle should be adopted for hydrothermal jet drilling. It is also feasible to pump down relatively high temperature cooling water to guarantee the high temperature downhole environment. Meanwhile, the cooling water pressure should be controlled during the drilling process for better cooling efficiency. All results in this paper are relevant to the parameters design for multi-orifice hydrothermal jet drilling technology.

Three-dimensional graphene-assembled monoliths (GAs) are emerging materials used in supercapacitors, catalysis, etc. However, GAs prepared by mainstream reduction methods (reduced GAs, RGAs) have fewer functional groups and display poor adsorption capacity of heavy metals. In this paper, we developed a new method of preparing amide-functionalized GAs (AGAs) with high degree of modification by the reaction of carboxyl-functionalized graphene oxides and ethylenediamine. AGAs contained multiple functional groups and exhibited dendritic structure at micron scale. Benefiting from these properties, the maximum adsorption capacities Cd 2 + on AGAs at T = 303 K were about 56.6 mg/g, which was twice that of RGAs and higher than that of graphene ( ∼ 10 mg/g) and biochar ( ∼ 18 mg/g) at the same conditions. By calculating the Gibbs free energies ( Δ G), the adsorption of Cd 2 + on AGAs was proved a spontaneous process, while the adsorption of Cd 2 + on RGAs was not spontaneous X-ray photoelectron spectroscopy analysis demonstrated that AGAs contained more adsorption sites and Cd 2 + adsorbed on AGAs through coordination bond. Thus, AGAs exhibited good application potentials as adsorbents for the removal of Cd 2 + from contaminated water.

Thermal spallation drilling is a non-contact and efficient technology, which is suitable for hard rock formations. It uses downhole combustion to generate high temperature media to heat the bottom rock, which leads to the spallation of the rock. However, no investigation has been carried out in combustion of thermal spallation drilling. In this paper, three combustion models (eddy dissipation model, eddy dissipation concept model and non-premixed model) are applied and compared to simulate the reaction in the combustion chamber. Through modifying Magnussen constants, the eddy dissipation model is optimized and validated. Results show that under high velocity conditions, combustion models based on infinite fast reaction mechanism may not be accurate. An additional reaction step in eddy dissipation model may significantly improve the accuracy. Besides, there is a linear relationship between the average outlet temperature and Magnussen constant in eddy dissipation model. Moreover, through modifying the Magnussen constants, the accuracy of the results can be significantly improved. The optimized eddy dissipation model with two reaction steps not only has the advantages of small computational cost, but also may reflect the actual situation of the combustion reaction. Results in this paper could provide guidance in the design of combustion chamber in thermal spallation drilling.

Increased nitrous oxide (N2O) in the atmosphere is of global concern. Biofiltration has been studied for gaseous nitrogen treatments in drinking water environments; however, the molecular mechanisms mediating N2O accumulation in denitrification biofilters have not been quantified. Five denitrification biofilters were developed in this study and all achieved high removal efficiencies for total nitrogen (TN: 72.4–92.7%), nitrate nitrogen (NO3−-N: 88.6–98.2%) and chemical oxygen demand (COD: 79.3–90.0%) across a low-temperature gradient (5–25 °C). Denitrification coupling with anaerobic ammonium oxidation (ANAMMOX) and dissimilatory nitrate reduction to ammonium (DNRA) processes yielded the presently robust treatment performance. Nitrite availability limited TN removal at 5–15 °C. Our findings indicate that temperature affected N2O accumulation indirectly by controlling the balance of nitrite versus N2O reductase carrying microorganisms. In addition, our results demonstrated that genetic association was an important index reflecting the relative intensity of N2O accumulation at low temperatures.

Heterotrophic denitrification is usually inhibited by insufficient carbon sources; however, the underlying mechanisms responsible for nitrous oxide (N 2 O) accumulation within denitrification at low carbon:nitrogen (C/N) ratios have not been quantified from a molecular level. In this study, five denitrification biofilters were developed and exhibited efficiency (total nitrogen: 18.5%–92.2%; nitrate nitrogen: 42.9%–99.5%; chemical oxygen demand: 50.5%–93.7%) in remediating micro-polluted water with C/N ratios ranging between 0.65 and 3.0. A combined analysis revealed that the coupling of anaerobic ammonium oxidation (ANAMMOX) and denitrification accounted for N 2 O accumulation in the biofilters, and the key drivers of the N 2 O accumulation rates were qnorB/nirK , nosZ/(narG + napA) , amx/(nirS + nirK) , narG/bacteria and qnorB/bacteria . Our study demonstrated that genetic association was indicative of microbial processes relative to nitrogen cycling and reflected N 2 O flux within denitrification biofilters at low C/N ratios.

Volcanic rock with the α-Fe 2 O 3 nanoparticles coating was fabricated to be an efficient and low-cost adsorbent for Cd(II) ions in water. ESEM, TEM, XPS and BET characterizations of the coated volcanic rock showed that the α-Fe 2 O 3 nanoparticles were successfully and homogeneously disseminated throughout the rock, including penetration into rock pores. Batch experiments were conducted to examine adsorption performance. The highest adsorption values were observed in a pH range of 4.0-7.0; hence, a pH value of 6.0 was used in this study. The maximum adsorption capacities of Cd(II) ions were found to be 127.23 mg/g, 146.41 mg/g and 158.48 mg/g at 293 K, 303 K and 313 K, respectively. The adsorption kinetic features of Cd(II) ions were found to be fitted best by a pseudo-second-order model, suggesting the presence of chemisorption processes. Intra-particle diffusion model results show that the adsorption processes can be divided into different stages, and the adsorption of the exterior and interior surfaces reached saturation at approximately 40 and 240 min, respectively. The adsorption process was also found to be endothermic and spontaneous. Hence, volcanic rock coated with α-Fe 2 O 3 nanoparticles serves as a high-efficiency and low-cost adsorbent.

Optimization of drilling parameters during drilling operations is a key component to obtain maximum rate of penetration (ROP) as well as minimizing the drilling cost. Advancement in computer technologies and communication are among the most important factors that can contribute to drilling optimization. In the current work, a novel rig advisory system is developed to continually improve ROP and the drilling performance. Conventionally, drillers apply drilling parameters (weight-on-bit, rotary speed and pump rate) according to past experience or to parameters specified in the drilling program. These parameters are usually kept constant over a long interval regardless of the formations being drilled. However, it is well-known that keeping constant drilling parameters to drive the bit will lead to redundant depth of cut (DOC), inducing stick-slip vibration that leads to low ROP, higher drilling specific energy (DSE), and potential damage to the bottom-hole assembly (BHA). An intelligent drilling advisory system (IDAS), based on a soft-closed-loop solution with multiple regression analysis called optimum parameters global retrieval, has been established. Integrated with machine-learning methodology (Principal component analysis), the response of the drilling parameters with lithology changes was analyzed in real time. Additionally, the optimum control parameters direction were obtained from the gradient search and decision tree algorithms. This system monitored the relationship between the ROP and input energy delivered to the bit in real time, and calculated the optimized drilling parameters. The work presented how the IDAS procedures were applied in China, how the data was interpreted, and how optimum working parameters were obtained to guide drillers to improve drilling performance and reduce non-productive time (NPT). IDAS has been introduced to hard formation drilling, which proved to be a success in real-time advisory aiding drillers applying proper working parameters for maximum ROP. Field applications of IDAS guidance showed significant ROP improvement compared to that of conventional drilling. As an effective tool for further achieving the optimum DOC, a novel control system achieved satisfactory outcomes that overcome the drilling challenges in Saudi Arabia and China, which will serve as a step forward towards automated drilling operations.