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Biochar (BC) addition to soil is a strategy to enhance soil fertility, which may also affect microbial activity. However, little information is available on the responses of soil nutrients and microbial activities to BC in a calcareous soil. This study investigated the changes of soil nutrient contents and microbial activities in a calcareous soil two years after application of biochar at rate of 0, 2.5, 7.5 and 22.5 t/ha. The results showed that the contents of soil organic carbon (SOC), total nitrogen (TN), dissolved organic carbon (DOC), total dissolved nitrogen (TDN), and available phosphorus and potassium increased significantly with increasing BC addition rate, but no significant effect on soil pH. Soil microbial biomass carbon and nitrogen (MBC and MBN) had an increased and then decreased trend. BC amendment increased microbial biomass and promoted soil carbon- and nitrogen-cycling enzyme activities, the ratios of β-glucosaminidase/phosphomonoesterase, N-acetyl-β-glucosaminidase plus leucine aminopeptidase/phosphomonoesterase increased significantly with increasing BC addition rate. Redundancy analysis confirmed that DOC and MBN were dominant factors affecting soil microbial biomass, and soil pH, TDN, DOC, MBN and SOC were main factors regulating soil enzyme activities. Besides, principal component analysis revealed that difference in microbial community composition in one year after BC addition was mainly associated with the relative abundance of bacteria and fungi, the relative abundance of bacteria increased, while the ratios of Gram-negative/Gram-positive bacteria and fungi/bacteria, and relative abundance of fungi and arbuscular mycorrhizal fungi decreased in BC-amended soils with control. However, BC had no significant effect on microbial community composition after two years. These results suggest that application of maize BC to calcareous soils may have a great potential for improvements in the soil nutrients and enzyme activity, the changes in soil microbial composition deserve further studies.

Abstract Non-uniform sand retention behavior often occurs to the serviced screen deteriorating erosion. However, this phenomenon is poorly understood. This paper presents a numerical study of the sand retention on wire-wrapped screens, with special reference to non-uniform behaviors. This is done by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM). The validity of the model has been validated for dry and wet sand screen systems. It is used here to study sand retention behaviors at different solid concentrations and particle size distributions (PSD). Via this model, five distinct sand retention modes are identified: No sand retention (Mode I), partial sand retention (Mode II), sand retention with slow sequential bridging (Mode III), sand retention with fast sequential bridging (Model IV) and sand retention with instantaneous bridging (Mode V). Modes II and III belong to non-uniform sand retention, which develops strong local flows that induce local erosion or hot spot on the screen. A phase diagram is introduced to predict these five modes and their transition with respect to solid concentration and PSD. Additionally, the predicted flow and force structures are analyzed in detail. The results indicate that the bridging over a slot heavily relies on the particle accumulation on the screen. A new screen with a converging slot configuration is proposed to improve this particle accumulation. This improvement helps develop uniform sand retention on the screen.

The aim of this work was to investigate the acid inhibition during the anaerobic digestion of kitchen waste. Four biodegradable substrates of soybean, fat meat, rice, and celery cane were considered in this paper. A series of anaerobic co-digestion tests were performed on the four substrates at the load of 1.0 gVS/(l·day) and anaerobic granular sludge. The results show that the acid inhibition was occurred at the load of 1.0 gVS/(l·day) for the soybean and rice; the corresponding pH values at the lowest acidification points were 5.03 and 3.73, respectively. There was no acid inhibition during the whole digestion period for the celery cane substrate. And the results also reveal that the order of the cumulative gas yields for different substrates from highest to lowest is: celery cane > soybean > fat meat > rice; while the order of the average methane (CH4) percentage from highest to lowest is: celery cane > fat meat > soybean > rice. Finally, the method to calculate the lowest acidification points of the four substrates was provided by the least squares method, and it is verified by the measured data, and good agreement is found.

The emission of fine particles, especially those with an aerodynamic diameter of less than 2.5 μm named PM2.5, from coal combustion is an important source of atmospheric PM2.5. To improve the removal of PM2.5 by an electrostatic precipitator (ESP), an agglomerant solution prepared by dissolving agglomerant in process water or desulfurization wastewater was sprayed at the inlet of the ESP. The number concentration and diameter distribution of the particles were investigated before and after the agglomeration solution addition based on a coal-fired thermal system, and the effects of the operating parameters, such as the species and concentration of the agglomeration solution, flue gas temperature, pH value of the agglomeration solution, and diameter of the spray droplets, on the fine particle removal efficiency were analyzed. The results show that the average diameter of the particles could grow more than 4 times as a result of the effects of wetting, the liquid bridge force, and adsorption bridging, and th...

With increasing attention on sulfuric acid emission, investigations on the removal characteristics of sulfuric acid aerosols by the limestone gypsum wet flue gas desulfurization (WFGD) system and the wet electrostatic precipitator (WESP) were carried out in two coal-fired power plants, and the effects of the WFGD scrubber type and the flue gas characteristics were discussed. The results showed that it was necessary to install the WESP device after desulfurization, as the WFGD system was inefficient to remove sulfuric acid aerosols from the flue gas. The removal efficiency of sulfuric acid aerosols in the WFGD system with double scrubbers ranged from 50% to 65%, which was higher than that with a single scrubber, ranging from 30% to 40%. Furthermore, the removal efficiency of WESP on the sulfuric acid aerosols was from 47.9% to 52.4%. With increased concentrations of SO3 and particles in the flue gas, the removal efficiencies of the WFGD and the WESP on the sulfuric acid aerosols were increased.Investigations on removal of sulfuric acid aerosols by the WFGD and the WESP in the power plants were aimed at the control of sulfuric acid emission. The results showed that the improvement of the WFGD system was beneficial for the reduction of sulfuric acid emission, while the WESP system was essential to control the final sulfuric acid aerosol concentration.

In this study, we constructed a three-chamber microbial fuel cell (TC-MFC) that avoided the adverse effects of H+ diffusion on anode microorganisms in the acidic catholyte and the precipitation of heavy metals in the soil near the cathode side (S4), while also achieving migration of copper from the soil and reduction of Cu2+ in the catholyte. The removal efficiency of acid-soluble Cu from the soil near the anode region reached 42.5% after 63 days of operation at an external resistance of 100 Ω and electrode spacing of 10 cm, and Cu2+ in the catholyte was completely removed within 21 days. Heavy metal mobility index (MF) values indicated that the bioavailability and mobility of heavy metals were reduced by the TC-MFC. We found that changing the cathode potential and external circuit current in TC-MFC would affect the type (via XRD) and morphology (via SEM) of cathode deposits and the average removal rate of heavy metals. At the meantime, it should be noted that the interaction between the electric-field-dependent soil heavy metal migration and electron-dependent copper reduction in TC-MFC occurred, which was confirmed to have a relationship with the negative correlation between voltage and current during the test.

Hydrological processes in lowland polders, especially those for paddy rice planting, are affected by complicated factors. The improved Wageningen Lowland Runoff Simulator (WALRUS) model incorporates an irrigation and drainage scheme, and a new stage–discharge relationship to account for hydrological processes in multi-land-use polder with paddy fields and pumping stations. Here, this model was applied to assess how climate and land use changes affected the runoff of a Chinese polder in Poyang Lake basin in the past two decades. Simulated results showed that the runoff in the autumn–winter transition and midsummer months increased significantly, whereas those in the other months decreased slightly during the period of 1996–2005, primarily affected by climate change. For the period of 2006–2014, the runoff in the autumn–winter transition and midsummer increased, while that in the other months declined, affected by both climate and land use/cover changes. The land use/cover change resulting from the conversion of rice–wheat rotation to dominantly double-rice cropping and the expansion of residential area, increased the runoff during this period by demanding more irrigation water from the outside basin.

A coupled system consisting of a double-anode microbial fuel cell (MFC) unit and a biofilm electrode reactor (BER) has been applied to degrade the azo dye reactive brilliant red X-3B. In this system, the MFC effluent was used as the input of the BER. The MFC preliminarily degraded X-3B while generating electricity, and the BER obtained electrons from the MFC through the external circuit to continue degrading pollutants without the need for an external power supply. The X-3B removal efficiency was 41.93% higher in the coupled system than the control when the X-3B concentration was 3000 mg/L. The analysis of intermediate products showed that the azo bond of X-3B broke in the MFC, generating a large number of complex intermediates such as anthraquinones, which were further degraded into simple organic compounds in the BER. Meanwhile, the abundance of microbial taxa related to the degradation of refractory organics in the MFC was high, as was that of microbial taxa related to the degradation of simple organics in the BER. Furthermore, the abundance of microorganisms related to power generation in the MFC increased. These results provided an efficient strategy for improving electron utilization efficiency in the coupling system of bioelectrochemical system.

In the current study, three roadside bioretention systems with different configurations were constructed to investigate their pollutant removal efficiency in different rainfall recurrence intervals. The bioretention systems (referred as units) (unit A: 700 mm height material without submerged zone; unit B: 400 mm height material with 300 mm submerged zone; unit C: 400 mm height material without submerged zone) were used to conduct the rainfall events with uniform 120 min rainfall duration for 2-, 5-, 10-, 15-, and 30-year recurrence intervals. Results reveal that the gradual increase of rainfall return period would have negative effects on TN and NH4+-N removal. The higher filler layer may increase pollutant removal efficiency. Setting a submerged zone could improve the CODMn and TN removal compared to TP and NH4+-N removal. The values for comprehensive reduction rate of pollutant load in the three bioretention systems were recorded as follows: 64% in SS, 50%~80% in TP, 69% in NH4+-N, and 28%~53% in NO3-N separately. These results provide greater understanding of the design and treatment performance of bioretention systems.

Abstract The utilization of the solar water heating system can reduce the conventional energy consumption of a building. A good inlet of the solar storage tank can enhance the thermal stratification and improve the thermal storage efficiency and discharging efficiency. Experiments were carried out to investigate the discharging performance of a rectangular storage tank with different inlet structures which were slotting-type inlet, direct inlet and shower-type inlet. This study aimed to provide guidance for the optimization of the inlet structure of water tank so that the efficiency of solar water heating system (SWHS) could be improved further. The effective discharging efficiency and effective discharging time were introduced to evaluate the performance of water tank with different inlet structures. The results showed that the slotting-type inlet exhibited the best thermal stratification and improved the discharging performance of the tank more effectively than the other two inlets. Energy saving potential of new inlet was also presented.