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In this study, Myriophyllum elatinoides growth under different nitrogen (N) concentrations (2, 250, 300, 350 and 400 mg L-1) and changes in rhizosphere bacterial community structure were investigated. High N (>300 mg L-1) concentrations caused reduction in M. elatinoides biomass. Growth tended to stabilize at 49 days. N concentration in roots were higher than that in stems and leaves under high N conditions. TN and NH4+ removal efficiencies reached 84.0% and 87.2%, respectively, in M. elatinoides surface flow constructed wetlands (SFCWs). Rhizosphere bacterial diversity increased over time. Proteobacteria, Firmicutes, Cyanobacteria, and Bacteroidetes dominated at the phylum level. Genera Turicibacter, Allochromatium, and Methylocystis increased at low N (<300 mg L-1) concentrations, while Pseudomonas increased at high N concentrations over the experimental period. Redundancy analysis showed that pH was strongly correlated with changes in rhizosphere bacterial community structure. These findings helped to insight into N removal mechanism in M. elatinoides.

Abstract In arid areas, dry cooling technology is a preferable alternate of wet cooling mainly owing to the scarcity of abundant water supply. However, the supercritical CO2 power cycle still offers considerable thermal performance even at higher ambient temperature using dry cooling. The novelty of this work is the exhaustive designing of dry cooler for supercritical CO2 cycles (recompression and partial cooling) in concentrating solar power application. Prior to the design of tower, a preliminary analysis is conducted in achieving the optimum main compressor inlet temperature (33 °C-recompression and 40 °C-partial cooling) at which the cycle delivers the maximal efficiency. The comparison is performed at same higher and lower pressure and for the partial cooling, the intermediate pressure is optimized. At relatively higher compressor inlet temperatures (above 50 °C), the partial cooling achieves higher efficiency while at lower temperatures (30–49 °C), the recompression shows superior performance. An iterative nodal method is used for the air-cooled finned tube heat exchanger units that takes account of the dramatic variation in thermodynamic properties of CO2 with the bulk temperature. Kroger’s detailed methodology of designing dry cooler is adapted with the implementation of nodal approach for CO2 property variation. A dry cooling tower with 52.45 m height is essential for the recompression cycle, whereas the partial cooling requires two towers of the height of 35.4 m and 38.7 m. A thermal assessment is carried out on the dry cooler under various cycle fluid inlet temperatures and ambient temperatures. During hot and humid ambient conditions, lower compressor inlet temperatures (up to 53.1 °C) are obtained with the recompression cycle compared to partial cooling (up to 64.5 °C). In extreme climate condition of 50 °C air temperature, the recompression cycle provides superior thermal efficiency (46.5% against 45.5%). For future commercialization of dry cooled sCO2 power plant, the recompression cycle is preferred due to its superior performance and lower capital cost for cooling tower design and solar field. The work demonstrates the impact of dry cooling tower design strategy in the context of cycle thermal assessment under various working condition.

AbstractBy using the data of 30 provinces from 1998 to 2016 in China, this paper estimates the water rebound effect in the agricultural crop farming by combining Slacks‐based Measure (SBM‐based) of Malmquist Index and Logarithmic Mean Divisia Index (LMDI) method. We find that the average water rebound effect is 70.3%, implying that over two‐thirds of the water saving from irrigation technology improvement is offset by higher water consumption. We find evidence on the regional heterogeneity in terms of the magnitude of rebound: Southwest is the highest, whereas Northwest is the lowest. The heterogeneous rebound effect across regions is mainly due to the difference in water endowment and irrigation land availability. Our results indicate that irrigation technology improvement is not necessarily sufficient for achieving agricultural water conservation. In particular, the difference in natural geography conditions across regions needs to be considered in designing water conservation policies at a sub‐regional level.

Abstract Fouling is one of the most significant problems for internally enhanced tubes installed in the shell and tube condensers. Due to the lack of long-term test data, current fouling models are developed based on accelerated particulate fouling tests that have the low precision and hence are inapplicable for predicting combined fouling in most practical cooling tower systems. In addition, the constant values of fouling resistance (factor) recommended by the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) are extremely limited under different operating conditions. To overcome these challenges, this research developed and validated two fouling prediction models based on experimental long-term tests. One of the models was in the form of a ratio of asymptotic fouling resistance of the enhanced tube to that of the plain tube ( R f ∗ / R f , p ∗ ), and the other one was in the form of the asymptotic fouling resistance of the directly enhanced tube ( R f ∗ ). Both models considered water quality, water velocity, and the tube geometries as the variables with the acceptable accuracy for prediction. 1) For the water quality, the parameter of valid concentration ( C com ) of cooling water was defined in this study, which reflected the potential amount of valid components to form the fouling. 2) For the water velocity, its impacts on the two critical parameters of the fouling process: sticking probability ( P ) and deposit bond strength ( ξ ) were investigated using experimental studies. Test results showed that in enhanced tubes with the increased water velocity the sticking probability ( P ) decreased continuously while the deposit bond strength (ξ) initially increased, and then, decreased. 3) For the tube geometries, by taking the parameters of tube geometries as variables the multi-variable correlations of the sticking probability ( P ) and deposit bond strength ( ξ ) were developed. From the results the generalized fouling prediction model as a ratio of asymptotic fouling resistance ( R f ∗ / R f , p ∗ ) was recommended for the application in HVAC&R industry due to its suitability and accuracy in practical project applications.

Abstract Coal water slurry (CWS) with high solid content and low viscosity can allow for efficient and environmentally friendly gasification. In the process of CWS preparation, water will enter pores of coal particle to form inner water, resulting in a decrease in free water among particles and an increase in viscosity. However, pre-absorption of moisture from air was found to result in a sharp decrease of suspension viscosity, since small amount of air were sealed in particle pores. Coal particles have many polar functional groups, and pre-absorbed water sealed the entrance of pores through hydrogen bonds like a “bottle stopper”, which effectively inhibited the diffusion of water from slurry into the pores of coal particles. Pre-absorption of water from air was also found to improve the efficiency of the second fluid (immiscible with water), and cause a further decrease in viscosity and yield stress.

Mass finishing processes have widely industrial application, and in most conditions these processes are used with empiricism and trial and error. Based on basic concept of mass finishing, its category is presented. Main aspects of motion and force analysis, material removal model, equipment and consumables, process experiments and industrial application are induced. Finally, development trends are recommended from quantified models, process database, new mass finishing processes and surface integrity. This will provide full investigation and further development and research to improvement part surface integrity.

Antibiotics removal and ARGs control in microbial fuel cell (MFC) has received extensive attention. In particular, the critical role of bioelectrochemical characteristics deserves further study. Bioelectrochemical characteristics significantly affected sulfamethoxazole (SMX) removal and ARGs fate, in which the current intensity played a more critical role than anode potential. High-concentration SMX (2 mg/L and 10 mg/L) facilitated the anode potential tend to be close, and thus, the strengthening effect of current on the system was highlighted. However, the SMX degradation pathway under different bioelectrochemical characteristics was not affected. Furthermore, the higher current intensity was preferable to antibiotic removal, but unfavorable for ARGs control might be due to the oxidative stress on microorganisms. Low-concentration SMX (0.5 mg/L) contributed to improving higher electricity generation because of Geobacter enrichement. This study suggested that appropriate bioelectrochemical characteristics regulation in MFCs was essential in removing antibiotics and controlling ARGs.

Abstract Standardization of biogas technology is immensely important for the promotion of the biogas industry worldwide. China has built a complete biogas standard system, which is divided into common, household biogas, biogas engineering, biogas digester for domestic sewage treatment, output utilization, and service system standards. The problems and potential barriers for biogas standardization in China are analyzed and come down to sluggish standard, overlapped standard, government-dominated standard, and lagging international standard. Accordingly, all potential biogas standards should be evaluated and placed under the same department. China Biogas Society and China Association of Rural Energy Industry play leading roles in developing enterprise or group/association biogas standards and ISO biogas standards. The bio-natural gas standard system and experimental standardization should be developed as well to replenish biogas standard system. A paradigm shift in biogas standardization should be from government-dominated to market-oriented model. The lessons learned for other developing countries includes expanding standardization to multi-aspects to realize full lifecycle control and management, building rapid responding mechanism of standardization to adopt industry transformation, integrating outdated standards into new versions, and establishing market-based standard system.

In this study, KOH and ZnCl2 were impregnated into sewage sludge as activation agents to produce activated sludge char in the pyrolysis step for the De-NOx process. The emission characteristics of volatile combustion from the pyrolysis of raw sewage sludge (SS-Raw), sewage sludge spiked with KOH (SS-KOH), and sewage sludge spiked with ZnCl2 (SS-ZnCl2) were investigated. In addition, the De-NOx effects and the characteristics of the prepared chars, including specific surface areas, pore distributions, functional groups, were explored. The exploration results showed that the pollutants generated during the volatile combustion process could be divided into primary pollutants (SO2, NO, N2O, and HCl) and minor pollutants (CO, NH3, and HCN). Under the conditions of oxygen-rich combustion, SO2 and NOx emissions from SS-KOH were 0% and 113.2% of those from SS-Raw respectively. SS-ZnCl2 exhibited the similar SO2 and NOx emissions to those of SS-KOH. However, SS-ZnCl2 released considerable HCl during the pyrolysis process, thus limiting its application. Sludge char from SS-KOH (SC-KOH) also exhibited the best De-NOx performance compared to the chars from SS-Raw and SS-ZnCl2 and the De-NOx efficiency was 56% higher than that of sludge char from SS-Raw (SC-Raw). Therefore, with KOH-impregnated SS, activated sludge char can be produced via one pyrolysis step and used in the De-NOx process.