Maximizing pollutant removal and greenhouse gas emission reduction in vertical flow constructed wetlands: an orthogonal experimental approach.

Owing to the impact of the effluent C/N from the secondary structures of urban domestic wastewater treatment plants, the denitrification efficiency in constructed wetlands (CWs) is not satisfactory, limiting their widespread application in the deep treatment of urban domestic wastewater. To address this issue, we constructed enhanced CWs and conducted orthogonal experiments to investigate the effects of different factors (C/N, fillers, and plants) on the removal of conventional pollutants and the reduction of greenhouse gas (GHG) emission. The experimental results indicated that a C/N of 8, manganese sand, and calamus achieved the best denitrification efficiencies with removal efficiencies of 85.7%, 95.9%, and 88.6% for TN, NH4+-N, and COD, respectively. In terms of GHG emission reduction, this combination resulted in the lowest global warming potential (176.8 mg/m2·day), with N2O and CH4 emissions of 0.53 and 1.25 mg/m2·day, respectively. Characterization of the fillers revealed the formation of small spherical clusters of phosphates on the surfaces of manganese sand and pyrite and iron oxide crystals on the surface of pyrite. Additionally, the surface Mn (II) content of the manganese sand increased by 8.8%, and the Fe (III)/Fe (II) and SO42-/S2- on pyrite increased by 2.05 and 0.26, respectively, compared to pre-experiment levels. High-throughput sequencing indicated the presence of abundant autotrophic denitrifying bacteria (Sulfuriferula, Sulfuritalea, and Thiobacillus) in the CWs, which explains denitrification performance of the enhanced CWs. This study aimed to explore the mechanism of efficient denitrification and GHG emission reduction in the enhanced CWs, providing theoretical guidance for the deep treatment of urban domestic wastewater.

Efficient rural sewage treatment with manganese sand-pyrite soil infiltration systems: Performance, mechanisms, and emissions reduction.

The application of soil infiltration systems (SISs) in rural domestic sewage (RDS) is limited due to suboptimal denitrification resulting from factors such as low C/N (<5). This study introduced filler-enhanced SISs and investigated parameter impacts on pollutant removal efficiency and greenhouse gas (GHG) emission reduction. The results showed that Mn sand-pyrite SISs, with hydraulic load ratios of 0.003 m3/m2·h and dry-wet ratios of 3:1, achieved excellent removal efficiency of COD (92.7 %), NH4+-N (95.8 %), and TN (76.4 %). Moreover, N2O and CH4 emission flux were 0.046 and 0.019 mg/m2·d, respectively. X-ray photoelectron spectroscopy showed that the relative concentrations of Mn(Ⅱ) in Mn sand and Fe(Ⅲ) and SO42- in pyrite increased after the experiment. High-throughput sequencing indicated that denitrification was mainly performed by Thiobacillus. This study demonstrated that RDS treatment using the enhanced SIS resulted in efficient denitrification and GHG reduction.

Suitability evaluation of rural sewage treatment facilities in China considering lifcycle environmental impacts and regional differences.

Centralized vs. decentralized sewage treatment is one of the key issues in the planning of rural sewage treatment (RST) in China due to the country's diverse regional characteristics. There are very limited comprehensive evaluation models for selecting regionally suitable schemes and facilities, particularly for national or provisional scale planning. As a scenario-based multi-attribute decision-making (MADM) issue, this paper develops a novel RST suitability evaluation model by integrating the multi-attribute analytic hierarchy process (AHP) with the technique for order preference by similarity to an ideal solution (TOPSIS). The suitability evaluation model sets up 3 small-centralized and 4 decentralized RST facilities as candidates and includes 12 evaluation indicators that cover economic cost, life cycle environmental impacts, technical features and operations management. Eight generic scenarios are classified for Chinese rural areas based on differences in three major characteristic factors, i.e., population density (PD), the economic development level (EDL), and topographic slope (TS). The universal evaluation results show that a centralized sewage treatment scheme is more suitable for areas with a high PD/high EDL/low TS, while a decentralized scheme is more suitable for areas with a low PD/low EDL/high TS. Sensitivity analysis shows that in regions with a high PD/low EDL, the indicator weight of the construction investment cost in the model has a great influence on the facility suitability ranking. However, in regions with a high PD/high EDL, the ranking is the most sensitive to the indicator weights of the global warming potential and sewage treatment effect. Furthermore, as a spatial decision issue, an RST suitability map of Hunan Province in China is produced at the county level of resolution, and the map is generally consistent with our field knowledge of several counties in Hunan Province. The presented evaluation framework can be integrated into environmental decision support systems in the future to help local and central governments, water utilities, design institutes and other stakeholders scientifically plan RST projects.

Synthesis of Ag/BiOBr/CeO2 composites with enhanced photocatalytic degradation for sulfisoxazole.

A novel Ag/BiOBr/CeO2 composite was successfully prepared for the first time, which had excellent performance in degrading sulfisoxazole (SSX) under visible light irradiation. The as-prepared samples were characterized by SEM, XRD, UV-vis DRS and BET et al. The composite of 10% Ag/BiOBr/CeO2 showed the best photocatalytic activity and more than 99.5% SSX can be removed within 20 min. It exhibited the highest k value of 0.2428 min-1, which was about 39.7 times higher than pure BiOBr (6.11 × 10-3 min-1) and 22.1 times higher than BiOBr/CeO2 (1.09 × 10-2 min-1), respectively. The addition of Ag significantly improved the absorption rate of visible light and the separation rate of photogenerated electron-hole pairs. The initial pH and dosage of samples could have an influence on the photocatalytic activity. The radical trapping experiments proved that ·O2- and h+ were the main active species involved in photocatalytic degradation. Finally, the synthesized catalyst maintained excellent photocatalytic activity after 5 repeated cycles, which indicated the extraordinary stability and recyclability of Ag/BiOBr/CeO2.

[Preparation of pg-C3N4/BiOBr/Ag Composite and Photocatalytic Degradation of Sulfamethoxazole].

A pg-C3N4/BiOBr/Ag composite was successfully prepared by simple high-temperature calcination and co-precipitation methods. The composite was characterized by means of XRD, SEM, TEM, XPS, UV-Vis, BET, and photocurrent analyses alongside other detection methods, and the degradation of 10 mg·L-1 sulfamethoxazole was investigated under simulated visible light irradiation. The results showed that the pg-C3N4/BiOBr/Ag composite had the best degradation effect on sulfamethoxazole when the loading ratio of silver was 5%. Compared with pg-C3N4, BiOBr monomer, and pg-C3N4/BiOBr composite, the photocatalytic degradation effect of the pg-C3N4/BiOBr/Ag (5%) was significantly improved, and the degradation rate was almost 100% within 30 min. The reaction rate constant (0.21016 min-1) was 13.15 times that of pg-C3N4/BiOBr. Through radical quenching experiments, it was shown that the main active substances in the photocatalytic degradation were holes (h+), superoxide radicals (·O2-), and singlet oxygen (1O2), among which superoxide radicals (·O2-) contributed the most. Cyclic tests of pg-C3N4/BiOBr/Ag showed that the synthesized material has good recyclability and application prospects.

Enhanced activation of peroxydisulfate by strontium modified BiFeO3perovskite for ciprofloxacin degradation.

A series of Sr-doped BiFeO3 perovskites (Bi1-xSrxFeO3, BSFO) fabricated via sol-gel method was applied as peroxydisulfate (PDS) activator for ciprofloxacin (CIP) degradation. Various technologies were used to characterize the morphology and physicochemical features of prepared BSFO samples and the results indicated that Sr was successfully inserted into the perovskites lattice. The catalytic performance of BiFeO3 was significantly boosted by strontium doping. Specifically, Bi0.9Sr0.1FeO3 (0.1BSFO) exhibited the highest catalytic performance for PDS activation to remove CIP, where 95% of CIP (10 mg/L) could be degraded with the addition of 1 g/L 0.1BSFO and 1 mmol/L PDS within 60 min. Moreover, 0.1BSFO displayed high reusability and stability with lower metal leaching. Weak acidic condition was preferred to neutral and alkaline conditions in 0.1BSFO/PDS system. The boosted catalytic performance can be interpreted as the lower oxidation state of Fe and the existence of affluent oxygen vacancies generated by Sr doping, that induced the formation of singlet oxygen (1O2) which was confirmed as the dominant reactive species by radical scavenging studies and electron spin resonance (ESR) tests. The catalytic oxidation mechanism related to major 1O2 and minor free radicals was proposed. Current study opens a new avenue to develop effective A-site modified perovskite and expands their application for PDS activation in wastewater remediation.

Enhanced degradation of atrazine by nanoscale LaFe1-xCuxO3-δ perovskite activated peroxymonosulfate: Performance and mechanism.

Cu-doped LaFeO3 perovskite (LaFe1-xCuxO3-δ, LFCx) synthesized using a sol-gel method was introduced in the heterogeneous activation of peroxymonosulfate (PMS) for atrazine degradation. The obtained LFCx catalysts were characterized by several technologies and the results showed that Cu was incorporated into the perovskites lattice successfully. In addition, the introduction of Cu resulted in the mixed valence state of Fe(III)/Fe(II) and Cu(II)/Cu(I) in perovskite structure. LaFe0.8Cu0.2O3-δ (LFC0.2) exhibited excellent catalytic activity and stability towards the degradation of atrazine. Atrazine (23 µM) was removed completely within 60 min in the presence of 0.5 g/L catalyst and 0.5 mM PMS. The efficient degradation was obtained when the initial pH ranged from 2 to 10. Sulfate radicals (SO4•-) and hydroxyl radicals (HO•) generated during activation process were determined as the main reactive species based on the electron spin resonance (ESR) studies and radical quenching experiments. The enhanced catalytic activity derived from the lower valence state of Fe and Cu as well as the synergetic effect between them. A surface catalyzed-redox cycle between Fe(III)/Fe(II) and Cu(II)/Cu(I), along with surface hydroxyl groups (-OH), were all responsible for the decomposition of PMS. The oxygen vacancies could promote the chemical bonding with PMS and enhance the reactivity of Fe and Cu. The 12 transformation products were determined by LC-MS and the degradation mechanisms were further proposed, which involved five different pathways. The perovskite that possesses bimetallic active sites can be a promising catalyst for PMS activation towards the degradation of persistent organic pollutants with high-efficiency.

Effect of inoculation with a microbial consortium that degrades organic acids on the composting efficiency of food waste.

In order to overcome the excessive acidification problem, a microbial consortium for the degradation of organic acids (MCDOA), which acts synergistically in degrading organic acids, was developed and used as an inoculum to improve the efficiency of food waste composting. MCDOA could eliminate the initial lag phase of the pile temperature rise because of excessive acidification and effectively shorten the composting period. Fluorescence regional integration analysis of the excitation-emission matrix spectra of dissolved organic matter showed that compared with raw material, in compost with MCDOA inoculation, the percent fluorescence response (Pi,n ) values of Regions I, II and IV decreased by 95.11%, 94.19% and 87.41%, respectively, and Pi,n of Region V increased by 172.57%. The decreased and increased levels were markedly higher than in the two control groups (MgO and K2 HPO4 treatment, and uninoculated compost). These findings revealed that MCDOA accelerated the degradation of proteinaceous compounds and the formation of complicated humic-like materials. Bacterial profiles implied that MCDOA could improve the indigenous bacterial community structure and diversities of acetic and propionic acid-degrading and lignin-degrading bacteria, which might account for the high composting efficiency and degree of humification of the inoculated compost.

Impact of anti-acidification microbial consortium on carbohydrate metabolism of key microbes during food waste composting.

This study investigated the effect of anti-acidification microbial consortium (AAMC), which act synergistically for rapid bioconversion of organic acids on carbohydrate metabolism of key microbes in the course of food waste (FW) composting by metaproteomics. AAMC was inoculated to the composting mass and compared with treatment with alkaline compounds and the control without any amendment. Inoculating AAMC could effectively accelerate carbohydrate degradation process and improve composting efficiency. Carbohydrate metabolic network profiles showed the inoculation with AAMC could increase significantly the types of enzymes catalysing the degradation of lignin, cellulose and hemicellulose. Furthermore, AAMC inoculum could increase not only diversities of microbes producing key enzymes in metabolism pathways of acetic and propionic acids, but also the amounts of these key enzymes. The increase of diversities of microbes could disperse the pressure from acidic adversity on microorganisms which were capable to degrade acetic and propionic acids.

Life cycle energy efficiency and environmental impact assessment of bioethanol production from sweet potato based on different production modes.

The bioethanol is playing an increasingly important role in renewable energy in China. Based on the theory of circular economy, integration of different resources by polygeneration is one of the solutions to improve energy efficiency and to reduce environmental impact. In this study, three modes of bioethanol production were selected to evaluate the life cycle energy efficiency and environmental impact of sweet potato-based bioethanol. The results showed that, the net energy ratio was greater than 1 and the value of net energy gain was positive in the three production modes, in which the maximum value appeared in the circular economy mode (CEM). The environment emission mainly occurred to bioethanol conversion unit in the conventional production mode (CPM) and the cogeneration mode (CGM), and eutrophication potential (EP) and global warming potential (GWP) were the most significant environmental impact category. While compared with CPM and CGM, the environmental impact of CEM significantly declined due to increasing recycling, and plant cultivation unit mainly contributed to EP and GWP. And the comprehensive evaluation score of environmental impact decreased by 73.46% and 23.36%. This study showed that CEM was effective in improving energy efficiency, especially in reducing the environmental impact, and it provides a new method for bioethanol production.

Environmental sustainability of bioethanol produced from sweet sorghum stem on saline-alkali land.

Life cycle assessment was conducted to evaluate the energy efficiency and environmental impacts of a bioethanol production system that uses sweet sorghum stem on saline-alkali land as feedstock. The system comprises a plant cultivation unit, a feedstock transport unit, and a bioethanol conversion unit, with 1000L of bioethanol as a functional unit. The net energy ratio is 3.84, and the net energy gain is 17.21MJ/L. Agrochemical production consumes 76.58% of the life cycle fossil energy. The category with the most significant impact on the environment is eutrophication, followed by acidification, fresh water aquatic ecotoxicity, human toxicity, and global warming. Allocation method, waste recycling approach, and soil salinity significantly influence the results. Using vinasse to produce pellet fuel for steam generation significantly improves energy efficiency and decreases negative environmental impacts. Promoting reasonable management practices to alleviate saline stress and increasing agrochemical utilization efficiency can further improve environmental sustainability.

Biogas production improvement and C/N control by natural clinoptilolite addition into anaerobic co-digestion of Phragmites australis, feces and kitchen waste.

Anaerobic co-digestion (A co-D) performance of Phragmites australis, feces and kitchen waste with addition of clinoptilolite (one main kind of zeolite) was investigated to evaluate the improvement of biogas/methane production and internal mechanism of nitrogen and organics control. A better biogas/methane production was observed by 10% clinoptilolite (v/v) than bentonite and diatomite, with the shortest lag phase of 0.070d(-1), the max rate of 15.89L/(kgVSday) and ultimate biogas production of 308.2L/kgVS as the modified Gompertz equation predicted. Accordingly, the content of methane in the biogas was increased from 44.10% to 65.30%. Furthermore, the clinoptilolite inhibited the acidification of digestion liquid (optimum pH 7.0-7.5) and enhanced the VFAs (acetic acid, propionic acid and butyric acid) destruction. Moreover, 10% of clinoptilolite optimally enhanced the microbial utilization of Ca(2+)/Mg(2+), controlled the C/N ratio, and improved the biogas production as well as NH3-N/NO3-N inhibition efficiency.

Energy efficiency and environmental performance of bioethanol production from sweet sorghum stem based on life cycle analysis.

Life cycle analysis method was used to evaluate the energy efficiency and environmental performance of bioethanol production from sweet sorghum stem in China. The scope covers three units, including plant cultivation, feedstock transport, and bioethanol conversion. Results show that the net energy ratio was 1.56 and the net energy gain was 8.37 MJ/L. Human toxicity was identified as the most significant negative environmental impact, followed by eutrophication and acidification. Steam generation in the bioethanol conversion unit contributed 82.28% and 48.26% to total human toxicity and acidification potential, respectively. Fertilizers loss from farmland represented 67.23% of total eutrophication potential. The results were significantly affected by the inventory allocation methods, vinasse reusing approaches, and feedstock yields. Reusing vinasse as fuel for steam generation and better cultivation practice to control fertilizer loss could significantly contribute to enhance the energy efficiency and environmental performance of bioethanol production from sweet sorghum stem.

Extraction, purification, and characterization of a trypsin inhibitor from cowpea seeds (Vigna unguiculata).

Protease inhibitors against trypsin were extracted from cowpea seeds, purified, and characterized. After the seed powder was defatted with hexane, the cowpea trypsin inhibitor (CpTI) was extracted with 0.15 M NaCl for 30 min. The crude extracts were then heated at 90°C for 10 min, followed by precipitation with 40-65% saturation ammonium sulfate, by which the protein purity increased approximately 15-fold. The CpTI had approximate 88-fold and 186-fold purification after anion-exchange chromatography (Super-Q) and gel filtration (Sephadex G-200), respectively. A broad band of the purified CpTI on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) indicates a degree of heterogeneity and partial denaturation of CpTI, having a molecular mass of ∼8000 kD. Multiple peaks between 7451 and 8898 by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy also suggest heterogeneity. The purified CpTI was stable at 90°C for 60 min, pH 5-10, and 0-3.0% of NaCl. The purification method described here can be used to obtain highly purified CpTI for its studies such as risk assessment of CpTI genetically modified foods.

[Characterizing composition and transformation of dissolved organic matter in subsurface wastewater infiltration system].

In the present study, the soil column with radius of 30 cm and height of 200 cm was used to simulate a subsurface wastewater infiltration system. Under the hydraulic loading of 4 cm x d(-1), composition and transformation of dissolved organic matter (DOM) from different depths were analyzed in a subsurface wastewater infiltration system for treatment of septic tank effluent using three-dimensional excitation emission matrix fluorescence spectroscopy (3D-EEM) with regional integration analysis (FRI). The results indicate that: (1) from different depth, the composition of DOM was also different; influent with the depth of 0.5 m was mainly composed of protein-like substances, and that at other depths was mainly composed of humic- and fulvic-like substances. (2) DOM stability gradually increased and part of the nonbiodegradable organic matter can be removed during organic pollutants degradation process. (3) Not only the organic pollutants concentration was reduced effectively, but also the stability of the DOM improved in subsurface wastewater infiltration system.

Polybrominated diphenyl ethers occurrence in major inflowing rivers of Lake Chaohu (China): characteristics, potential sources and inputs to lake.

Eight commonly occurring polybrominated diphenyl ethers (PBDEs), including BDE 28, 47, 99, 100, 153, 154, 183, 207, and 209, were investigated in water samples from seven major inflowing rivers of Lake Chaohu to determine the distribution characteristics, potential sources and inputs to the lake. The sum of 8 BDE congeners (Σ8PBDEs) had a concentration varied from 0.31 to 84 ng L(-1), with those of BDE 209, BDE 47, BDE 99, and BDE 153 being 0.31-83, <0.012-0.36, <0.012-1.3, and <0.012-0.77 ng L(-1), respectively. These levels were in the high range of the global PBDEs concentrations in the water environments. The highest concentrations of Σ8PBDEs were detected in the western rivers, of which the main pollution sources were strongly related to human activities in urban centers, such as automobile-derived wastes. A sewage treatment plant was likely an important source of the lower brominated BDEs input to one western river. The correlation analyses (all p<0.05) between PBDEs and DOC, TN, TP, and EC, suggested that the distributions and sources of PBDEs in rivers might also be related with the soil erosion by heave floods. Σ8PBDEs input to Lake Chaohu from the rivers outlets was estimated at 344 kg yr(-1) during the flood season. BDE 209 was the dominant contributor with an input of 340 kg yr(-1), followed by BDE 99 (1.3 kg yr(-1)), BDE 47 (0.83 kg yr(-1)) and BDE 153 (0.60 kg yr(-1)).

Synthesis, characterization, and mercury adsorption properties of hybrid mesoporous aluminosilicate sieve prepared with fly ash.

A novel hybrid mesoporous aluminosilicate sieve (HMAS) was prepared with fly ash and impregnated with zeolite A precursors. This improved the mercury adsorption of HMAS compared to original MCM-41. The HMAS was characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, Fourier transform infrared (FTIR) analysis, transmission electron microscopy (TEM) images and 29Si and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra. These showed that the HMAS structure was still retained after impregnated with zeolite A. But the surface area and pore diameter of HMAS decreased due to pore blockage. Adsorption of mercury from aqueous solution was studied on untreated MCM-41and HMAS. The mercury adsorption rate of HMAS was higher than that of origin MCM-41. The adsorption of mercury was investigated on HMAS regarding the pH of mercury solution, initial mercury concentration, and the reaction temperature. The experimental data fit well to Langmuir and Freundlich isotherm models. The Dublin-Radushkevich isotherm and the characterization show that the mercury adsorption on HMAS involved the ion-exchange mechanisms. In addition, the thermodynamic parameters suggest that the adsorption process was endothermic in nature. The adsorption of mercury on HMAS followed the first order kinetics.

Life-cycle energy efficiency and environmental impacts of bioethanol production from sweet potato.

Life-cycle assessment (LCA) was used to evaluate the energy efficiency and environmental impacts of sweet potato-based bioethanol production. The scope covered all stages in the life cycle of bioethanol production, including the cultivation and treatment, transport, as well as bioethanol conversion of sweet potato. Results show that the net energy ratio of sweet potato-based bioethanol is 1.48 and the net energy gain is 6.55 MJ/L. Eutrophication is identified as the most significant environmental impact category, followed by acidification, global warming, human toxicity, and photochemical oxidation. Sensitivity analysis reveals that steam consumption during bioethanol conversion exerts the most effect on the results, followed by sweet potato yields and fertilizers input. It is suggested that substituting coal with cleaner energy for steam generation in bioethanol conversion stage and promotion of better management practices in sweet potato cultivation stage could lead to a significant improvement of energy and environmental performance.

MCM-41 impregnated with A zeolite precursor: Synthesis, characterization and tetracycline antibiotics removal from aqueous solution.

In this paper, the MCM-41 has been modified by impregnation with zeolite A to prepare a kind of new adsorbent. The adsorption of TC from aqueous solutions onto modified MCM-41 has been studied. It was discovered that the adsorption capability of zeolite A modified MCM-41 (A-MCM-41) increased dramatically after modification. The modified MCM-41 was characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, Fourier Transform Infrared (FTIR) analysis, Transmission electron microscopy (TEM) images, and 29Si and 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectra. The modified MCM-41 structure was still retained after impregnated with zeolite A but the surface area and pore diameter decreased due to pore blockage. The adsorption of TC on modified MCM-41 was discussed regarding various parameters such as pH, initial TC concentration, and the reaction time. The pH effects on TC adsorption indicated that the adsorbents had better adsorption performances in acidic and neutral conditions. The adsorption isotherms were fitted well by the Langmuir model. The adsorption kinetics was well described by both pseudo-second order equation and the intra-particle diffusion model. The adsorption behavior in a fixed-bed column system followed Thomas model. The adsorption behavior of TC was the chemical adsorption with an ion exchange process and electrostatic adsorption.

Using fluorescence excitation-emission matrix spectroscopy to monitor the conversion of organic matter during anaerobic co-digestion of cattle dung and duck manure.

In this study, the removal of volatile solids (VSs) and soluble chemical oxygen demand (SCOD) by co-digesting cattle dung (CD) and duck manure (DM) was determined and compared with the reduction achieved with CD or DM digestion alone. Moreover, fluorescence excitation-emission matrix spectroscopy was utilised to characterise the conversion mechanisms of organic nitrogen. It was found that the co-digestion provided 71% VS reduction compared with 58% for CD and 61% for DM. The amounts of COD removed were 28%, 23% and 31% for CD, DM and the mixture, respectively. Tyrosine-like/fulvic-like fluorescence intensity (FI) ratios increased during the initial 15days of co-digestion and were associated with an increase in total nitrogen in the supernatant. After 15days, CD and DM exhibited a lower tryptophan-like/fulvic-like FI ratio (0.8-1.6), whereas the co-digestion remained stable at a high level (3.0-3.6), rendering an improved microbial population and biochemical activity.