Existing forms and changes of nitrogen inside of horizontal subsurface constructed wetlands

Preparation and Screening of SRB Gel Particles Used for Deep Purification of Acid Mine Drainage

The progressive decline of the coal industry necessitates the development of effective treatment solutions for acid mine drainage (AMD), which is characterized by high acidity and elevated concentrations of heavy metals. This study proposes an innovative approach leveraging sulfate-reducing bacteria (SRB) acclimated to contaminated anaerobic environments. The research focused on elucidating the physiological characteristics and optimal growth conditions of SRB, particularly in relation to the pH level and temperature. The experimental findings reveal that the SRB exhibited a sulfate removal rate of 88.86% at an optimal temperature of 30 °C. Additionally, SRB gel particles were formulated using sodium alginate (SA) and carboxymethyl cellulose (CMC), and their performance was assessed under specific conditions (pH = 6, C/S = 1.5, T = 30 °C, CMC = 4.5%, BSNa = 0.4 mol/L, and cross-linking time = 9 h). Under these conditions, the SRB gel particles demonstrated an enhanced sulfate removal efficiency of 91.6%. Thermal analysis via differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) provided further insights into the stability and properties of the SRB gel spheres. The findings underscore the potential of SRB-based bioremediation as a sustainable and efficient method for AMD treatment, offering a novel and environmentally friendly solution to mitigating the adverse effects of environmental contamination.

Submerged plant-biochar composite system exhibits effective control over residual organic pollutants in the benthic organisms of aquaculture ponds

As of now, submerged plants and biochar have demonstrated significant benefits in aquaculture pond sediment remediation. However, there is limited research on the synergistic effects of biochar and submerged plants in mitigating hydrophobic organic contaminant (HOC) accumulation in aquaculture benthic organisms and in controlling the nutrient (nitrogen and phosphorus) levels in aquaculture water. This study assesses a submerged plant-biochar system's efficacy in removing HOCs from simulated freshwater aquaculture ponds. Vallisneria natans was planted in sediment with varying levels of wheat straw biochar, while Corbicula fluminea served as the targeted benthic organism. The bioaccumulation experiment identified the optimal biochar ratio for the Vallisneria natans-biochar system in controlling HOCs in aquaculture products. Analyses included final accumulation concentrations in benthic organisms, changes in freely-dissolved concentrations in aquaculture sediment, and a mass balance calculation to explore key factors in their removal from the system. Results indicated that the Vallisneria natans-1.5% biochar composite system achieved optimal control of HOCs in sediment and aquaculture products. Biochar addition to the sediment in the composite system demonstrated a "promotion with low addition, inhibition with high addition" effect on Vallisneria natans growth. Notably, the addition of 1.5% biochar (VN1.5 group) significantly promoted the growth of Vallisneria natans leaves and roots. Comparing the final pollutant proportions in different environmental media, concentrations in water (0.20%-1.8%), clam accumulation (0.032%-0.11%), and plant absorption (0.10%-0.44%) constituted a minimal portion of the overall pollutant load in the system. The majority of pollutants (24%-65%) were degraded in the aquaculture environment, with microbial degradation likely playing a predominant role. Bacterial phyla, particularly Proteobacteria and Firmicutes, were identified as potential direct contributors to pollutant degradation in the Vallisneria natans-biochar system.

Impact of current anthropogenic activities on Blesbokspruit wetland microbiome and functions

Till present, natural wetlands have been continuously subjected to intensive pollution stress in recent years, mainly because of the rapidly growing industrialization and urbanization that are associated with a myriad of anthropogenic activities and land use practices. These man-made sources of pollution change the chemical properties of the natural wetlands, which in turn alter their microbial ecological biodiversity and functions. For the first time, the impact of the current anthropogenic activities and land use practices on the Blesbokspruit wetland chemical status and their consequential effect on the microbial structure and functions were investigated. Sites of high pollution intensity were identified using geographic information systems mapping (GISMapping) and the wetland microbiome and functional profile were studied through the use of high throughput shotgun metagenomics sequencing analysis. The predominant phyla that stemmed along the Blesbokspruit wetland were found to be Proteobacteria which was more dominant in water (93 %) than in the sediments (89 %), followed by firmicutes which was more abundant in sediments (9 %) than in water (6 %), and Bacteroidetes were relatively low in abundance within both the sediments (2 %) and the overlying water (1 %). The genera Klebsiella (70.4 %-28.2 %), Citrobacter (52.0 %-30.6 %), Escherichia (51.0 %-8.4 %), and Lynsinibacillus (9.3 %-1.5 %) were observed in most water and sediment samples. Within the six polluted sites, Site 2 was found to be the most highly polluted site in the Blesbokspruit wetland with very high COD (900 mg/L), TOC (11.60 mg/L), NO3- (39.74 mg/L), NO2- (12.64 mg/L), PO43 (4.14 mg/L), Fl- (143.88 mg/L), Cl- (145.95 mg/L) concentrations recorded in the water and high levels of TOC (0.37 mg/L), TC (6.92 %), TN (1.82 %), TS (0.53 %) in sediments. The microbial community structure and functions were found to be strongly influenced by the high organic content from the intense agricultural activities and sewage spillages and heavy metals from the mining activities nearby.

Purification effect and microbial community structure of bio filter on rural dispersed sewage

Taking rural dispersed sewage for research objects, the treatment effect and microbial community structure characteristics of a bio filter (BF) reactor was studied. At fixed time and location, the removal efficiencies of common pollutants were investigated. By using high-throughput sequencing method, the heterogeneities of microbial community structure in fillers and plant roots were analyzed. The results showed that the average annual removal rates of CODCr, NH3-N, TN, and TP by the BF were 83.10 %, 65.67 %, 60.25 %, and 80.32 % respectively, and the effluent could reach the first grade of the water pollutant discharge standard of rural sewage treatment facility (DB51/2626-2019). During the sewage treatment process, Scindapsus could effectively establish complex and stable microbial communities, and could better degrade pollutants, especially nitrogen removal. The dominant microbial communities were more than 11 phyla and 19 classes. At the genus level, the dominant bacteria included Nitrospira, Arthrobacter, Rhodoplanes, etc.

Technical structure and influencing factors of nitrogen and phosphorus removal in constructed wetlands

Constructed wetlands purify water quality by synergistically removing nitrogen and phosphorus pollutants from water, among other pollutants such as organic matter through a physical, chemical, and biological composite remediation mechanism formed between plants, fillers, and microorganisms. Compared with large-scale centralized wastewater treatment systems with high cost and energy consumption, the construction and operation costs of artificial wetlands are relatively low, do not require large-scale equipment and high energy consumption treatment processes, and have the characteristics of green, environmental protection, and sustainability. Gradually, constructed wetlands are widely used to treat nitrogen and phosphorus substances in wastewater. Therefore, this article discusses in detail the role and interaction of the main technical structures (plants, microorganisms, and fillers) involved in nitrogen and phosphorus removal in constructed wetlands. At the same time, it analyses the impact of main environmental parameters (such as pH and temperature) and operating conditions (such as hydraulic load and hydraulic retention time, forced ventilation, influent carbon/nitrogen ratio, and feeding patterns) on nitrogen and phosphorus removal in wetland systems, and addresses the problems currently existing in relevant research, the future research directions are prospected in order to provide theoretical references for scholars' research.

Driving mechanism of farmers' green production behavior under normalization of COVID-19 prevention and control: A case study in China

China's public health emergency COVID-19 has brought great challenges to food safety. Among them, the quality and safety of agricultural products under the normalization of the COVID-19 prevention and control has become a hot issue of general concern. This study attempts to reveal the driving factors and mechanisms of farmers' green production behavior. The empirical research by collecting 673 sample data shows that: individual characteristics of farmers, government guiding factors, an industrial organization promoting factors, and market adjustment factors have a positive driving effect on farmers' green production behavior. And farmers' green production behavior has a positive influence on the quality and safety of agricultural products. Farmers' green production behavior plays an intermediary role between the quality and safety of agricultural products and individual characteristics of farmers, government guidance factors, industrial organization promotion factors, and market regulation factors. The results of the study have guiding significance for ensuring the quality and safety of agricultural products, promoting ecological environmental protection, and sustainable agricultural development under the normalization of COVID-19 prevention and control.

Technical and Economic Evaluation and Development Policy Suggestions of LNG Power Plants

The return on investment (RIO) of a Liquefied natural gas (LNG) power plant is lower than that of conventional power plants with high pollution due to the “take or pay” supply mode of natural gas and the two-shift peak shaving operation mode in the LNG power plants. . In this paper, firstly, based on the characteristics of the gas turbine combined cycle (GTCC) unit for peak shaving and standby application, it is proposed to calculate the generation cost of LNG power plants according to the depreciation of operation life. Secondly, through the sensitivity analysis of power generation cost, it is found that fuel price and average efficiency are the first influencing factors. Next, to reflect the environmental protection characteristics of LNG power plants, the on-grid price included in the environmental value is put forward innovatively based on the calculation of the environmental cost and environmental value of natural gas power generation.

Investigation on the Distribution of Yimin Lignite Pyrolysis Products and the Stability of its Char

This paper introduces the utilization of lignite in China and abroad and studies the influence of different process conditions on the pyrolysis products of lignite. The effects of pyrolysis temperature, residence time, and heating rate on the yield and stability of pyrolysis products were studied by standard lattice low-temperature distillation of coal. The results showed that the final pyrolysis temperature of lignite increases gradually, which is a key factor affecting the pyrolysis performance of lignite. At the same time, the combustible gas yield and tar yield were also significantly improved. Semichar yield and semichar volatile content showed a downward trend. From the range of pyrolysis products, the heating rate also has an important influence on the pyrolysis performance of lignite. Through the thermal stability test of lignite, it is concluded that the particle size distribution of carbon black products is not significantly different, and most of the coal particles are mainly distributed in the range of more than 6 mm.

Study on denitration and sulfur removal performance of Mn-Ce supported fly ash catalyst

Nitrogen oxides (NOx) are the main pollutants of air, which mainly come from the combustion of coal and fossil fuels. In this paper, with fly ash used as the catalyst carrier, the effects on the denitration and sulfur resistance of Mn-Ce loading sequence and molar ratio were studied. The catalyst was characterized and analyzed by XRD, XPS, SEM. The results show that when Mn-Ce bimetal is loaded at the same time, Mn ions enter the CeO₂ lattice to form a solid solution of Mn-O-Ce fluorite structure, which makes the catalyst has the best denitration and sulfur resistance. The catalyst denitration performance increases first and then decreases with the increase of Mn-Ce molar ratio. When Mn-Ce is 1:1, the denitration efficiency is higher, the total conversion rate of NO is the highest and the deactivation time is the longest, the catalyst is resistant to sulfur performance is also the best.

Remanufacturing system reliability analysis based on the uncertainty of part quality

The remanufacturing industry is one of the important means to achieve sustainable development and resource recycling. It is of great significance to study the remanufacturing production system. This paper mainly studies the reliability of remanufacturing production system based on the uncertainty of part quality. In order to rationally arrange workshop production, minimize the maximum completion time and the cost of electricity in the production process, this study established a mixed integer linear programming model for the remanufacturing of flexible workshop based on batch processing of partial stations. In order to solve this mathematical model, the traditional genetic on the basis of the algorithm, the crossover and mutation operators of the genetic algorithm conforming to the model are designed, and finally combined with actual examples, compared with traditional batch scheduling to verify the effectiveness of the system. This research takes the remanufacturing of the Steyr engine crankshaft as the research object. Based on the uncertainty of crankshaft wear, the uncertainty of the crankshaft remanufacturing process is investigated and discussed. From the three dimensions of environment, economy and technology, from the remanufacturing process. The evaluation was carried out at the level of the process chain and the modeling process and method were verified, and the sustainability value of the worn crankshaft remanufacturing process was obtained. The remanufacturing production system experiment can show that the average sustainability values of the three batches of used crankshafts are SR1 = 0.9082, SR2 = 0.8669, SR3 = 0.7803. The system reliability analysis can provide a theoretical basis for the reliability of enterprise remanufacturing systems, and has important application and research value.

Performance of nitrobenzene and its intermediate aniline removal by constructed wetlands coupled with the micro-electric field

The degradation of nitrobenzene and its intermediate aniline from wastewater by constructed wetlands coupled with the micro-electric field (CW-MEF) technology was studied. The results showed that the CW-MEF system had good degradation. With the increase of influent concentration of nitrobenzene, the removal rate of the anode was excellent which remained above 86%, but the degradation of CW-MEF for COD decreased. In different stages, the power generation capacity was different. In the second stage, the power generation voltage reached 430 V and the average power density was 85.07 MW m^-3, while the maximum reached 87.47 MW m^-3. Through high-throughput sequencing analysis, the A1 sludge layer contained 36% of thick-walled bacteria and 20% of bacteroides, the A2 contained about 20% of campylobacter green, and the A3 contained 10% of green campylobacter, pachyphyte and bacteroides.

Investigation on the treatment effect of slope wetland on pollutants under different hydraulic retention times

This work was aimed at investigating the feasibility of the slope wetland system (SWs) for improving the polluted river water. According to the characteristics of polluted river water with different hydraulic retention time (HRT) changes, a field simulation device was set up. In this experiment, a SWs simulation device was set up to study pollutant removal of SWs under different hydraulic conditions. It was found that the effect of mixed fillers (zeolite and ceramsite) as the bed was better than that of the gravel fillers as the bed. The improvement of each treatment index was about 5% (P < 0.05). When HRT = 5 days, the removal rate of chemical oxygen demand (COD) was 28.02%, total nitrogen (TN) was 32.99%, ammonia nitrogen (NH₃-N) was 32.49%, and total phosphorus (TP) was 38.15%. At the same time, it was found that the characteristic moderate extension of HRT is conducive to the removal of pollutants in SWs. The growth of plants in the environment of the gravel matrix was worse than that of mixed fillers (zeolite and ceramsite). It was found that physical adsorption was the main form of pollution removal on the SWs fillers by Fourier infrared spectrum (FTIR) analysis. Based on the analysis of the microbial community in the packing of the device, it is indicated that the enrichment of microorganisms appeared during the experiment, forming the dominant bacteria against the polluted river water.

Study on Denitration Performance of Solid Waste Blast Furnace Slag Catalysts under Different Preparation Processes

In this article, blast furnace slag, a high-yield industrial solid waste, was taken as the research object and it was used as the main material. Bentonite was used as the binder, and water was added to shape the blast furnace slag into a small column. The denitration catalyst was prepared using different methods, its denitration performances were compared and analyzed, and the best preparation method and process parameters were screened. Results showed that bentonite will clearly improve denitration performance, and 4:1 blast furnace slag and bentonite was selected as the molding ratio to reduce the effect of bentonite on its performance, combined with the hardness and surface adhesion of the prepared carrier. Separately, the catalysts were prepared using citric acid impregnation, hydrothermal decomposition, and mixing method, and active Mn was loaded. Among them, the hydrothermal decomposition method cannot completely decompose in a closed kettle, resulting in a lower denitration performance. The catalyst prepared using the mixing method is superior to that prepared using the impregnation method because the active component prepared by the former was more uniformly dispersed, and simple and easy to operate, which can meet the needs of the excess denitration catalysts of small enterprises.

The influence of flow rates and water depth gradients on the growth process of submerged macrophytes and the biomass composition of the phytoplankton assemblage in eutrophic water: an analysis based on submerged macrophytes photosynthesis parameters

Submerged macrophytes and phytoplankton assemblage play significant roles in the functioning of aquatic ecosystems. An experiment was carried out in Beijing in order to further evaluate the environmental factors that affect the growth of submerged macrophytes and phytoplankton assemblage. Submerged macrophytes (i.e., Vallisneria natans, Hydrilla verticillata, and Ceratophyllum demersum) constructed the growth system with some controllable influencing factors (i.e., the flow rate and water depth gradient). The flow rates were set separately as 4 L/h (1#), 6 L/h (2#), and 12 L/h (3#), while the water depth gradient was of 0.5-1.7 m in eutrophic water. Generally, all macrophytes could grow normally in the experiment, and the system could maintain and improve the effluent quality. The average removal rates of NH3-N, COD, NO3-N, TN, and TP were about 90%, 33%, 65%, 45%, and 40%, respectively. Seen from the results of the water depth gradient experiments, it is indicated that Vallisneria natans grows better in shallow water (0.5 m) and moderate shallow water (0.7 m) area, with an average relative growth rate (ARGA) of 57%. Hydrilla verticillata and Ceratophyllum demersum grow better in moderate deep water (1.2 m) and deep water (1.7 m) area (ARGA of 66% and 64%, respectively). Results of the flow rate experiments showed that the moderate flow rate (6 L/h) was the best for those three macrophytes' growth. As the fitting results of the rapid light curves (RLCs) showed that the utilization of light and the tolerance to strong light were different for these macrophytes, if they are ranked in the order of the utilization and the tolerance from strong to weak, they are Hydrilla verticillata, Ceratophyllum demersum, and Vallisneria natans. Microbial analyses indicated that the overall system diversity of the experimental groups have been improved after cultivation of macrophytes. However, the accumulated Cyanobacteria caused by the low flow rate (1#) would lead to the suppression of microbial organics decomposition and nutrient metabolism in the macrophytes. To sum up, the results of this study provided theoretical guidance and technical support for the restoration of submerged macrophytes in eutrophic water.

Review: recent developments of substrates for nitrogen and phosphorus removal in CWs treating municipal wastewater

Substrates are the main factor influencing the performance of constructed wetlands (CWs), and especially play an important role in enhancing the removal of nitrogen and phosphorus from CWs. In the recent 10 years, based on the investigation of emerged substrates used in CWs, this paper summarizes the removal efficiency and mechanism of nitrogen and phosphorus by a single substrate in detail. The simultaneous removal efficiency of nitrogen and phosphorus by different combined substrates is emphatically analyzed. Among them, the reuse of industrial and agricultural wastes as water treatment substrates is recommended due to the efficient pollutant removal efficiency and the principle of waste minimization, also more studies on the environmental impact and risk assessment of the application, and the subsequent disposal of saturated substrates are needed. This work serves as a basis for future screening and development of substrates utilized in CWs, which is helpful to enhance the synchronous removal of nitrogen and phosphorus, as well as improve the sustainability of substrates and CWs. Moreover, further studies on the interaction between different types of substrates in the wetland system are desperately needed.

MnOx-CuOx cordierite catalyst for selective catalytic oxidation of the NO at low temperature

Low-value solid waste cordierite honeycomb ceramics were used as carrier of SCO denitration catalyst, and the active component was supported by the impregnation method to improve the performance of the catalyst. Firstly, the effect of calcination conditions on the denitration performance of the Mn-loaded cordierite catalyst was studied for the cordierite-loaded active component MnO_X. Secondly, the preferred catalyst was reloaded with another active component to further improve its denitration performance; the bimetal ratios were affected by the denitration performance, which was, finally, characterized by XRD, XPS, and SEM. The result shows the following: (1) Mn-loaded cordierite prepared at 450 °C for 3 h has a good denitration effect; (2) the MnO_X-CuO_X/CR catalyst is superior to MnO_X-FeO_X/CR, MnO_X-CoO_X/CR, and MnO_X-CeO_X/CR; (3) the MnO₂ crystal form in the single metal-supported catalyst plays a major role, and Cu₂Mn₃O₈ in the bimetallic catalyst affects the performance and activity of the catalyst. Graphical abstract.

Gas-Modified Pyrolysis Coke for in Situ Catalytic Cracking of Coal Tar

Modified pyrolysis coke can be used as a catalyst for tar cracking. In this paper, pyrolysis coke was used as a carrier for modification by using gases (H₂O, CO₂, and NH₃), and the optimal modified gas was selected. On the basis of this, pyrolysis coke with different modified flow rates, temperatures, and times were prepared to catalyze the cracking of tar. The effect of gas-modified pyrolysis coke on tar cracking products was studied. Also, pyrolysis coke was characterized by Fourier-transform infrared spectroscopy, Brunauer-Emmett-Teller analysis, and scanning electron microscopy. The results show that the optimal gas is H₂O, and the optimal preparation conditions are 450 mL/min, 650 °C, and 60 min. The pyrolysis coke catalyst under the optimal conditions has the best cracking effect on tar. Also, the gas and tar yields have been further improved.

Study on In Situ Catalytic Cracking of Coal Tar by Plasma Preparation of the Pyrolysis Coke Catalyst

A two-stage pyrolysis fixed bed was used, and the vapor-modified pyrolysis coke was used as a carrier. A ZHPC catalyst was prepared by plasma calcination. Gas-phase tar produced by the pyrolysis of raw coal was subjected to in situ catalytic cracking to improve tar and gas yield. The effects of plasma calcination power, calcination time, and ZnO loading on in situ cracked products were studied. The prepared catalyst was characterized by X-ray electron spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller, and scanning electron microscopy. The results showed that (1) compared with traditional catalysts, the catalyst prepared by plasma has better performance; (2) the optimal calcination time of the ZHPC catalyst is 5 min, calcination power is 60 W, and ZnO loading is 10%; (3) compared with raw coal pyrolysis, the optimal ZHPC catalyst on in situ catalytic cracking tar, gas yield increased by 66.16%; the cracking rate of tar increased by 54.46%, and the content of light components increased to 60.7%; (4) in situ catalytic cracking of tar with the optimal PC, the light tar has been greatly improved, in which the light oil, phenol oil, naphthalene oil, and wash oil have increased by 93.04, 126.31, 257.28, and 108.08%, respectively. The anthracene oil and asphalt have decreased by 26.98 and 58.71%; the tar cracking rate has increased.

Assessment of pollutant removal processes and kinetic modelling in vertical flow constructed wetlands at elevated pollutant loading

Constructed wetland (CW), an ecological wastewater treatment technology, is low cost and easily to operate. Vertical flow constructed wetland (VF-CW) systems have been used to treat various wastewaters across the world. The present work exhibits the detail study of five type's multi-layered vertically constructed wetlands operated at 24 h hydraulic retention time under semi-continuous vertical flow mode. Except N-NO₃^-, all the pollutants were sufficient removal in iron scraps constructed wetland (ISs-CW). The highest average pollutant removal efficiency achieved in ISs-CW was 85.04%, 77.57%, 85.99%, 62.01% and 88.91% for N-NH₄⁺, N-NO₂⁺, total nitrogen, total phosphate and sulphate respectively. The present CWs planted with Eichhornia crassipes is a promising system for municipal wastewater treatment. The first-order kinetic modelling was best suited for the removal rate since it presents higher R², rate constant (k) and B values.