The effect of activated sludge treatment and catalytic ozonation on high concentration of ammonia nitrogen removal from landfill leachate

Performance investigation of cutoff wall and permeable reactive barriers at a landfill: Multiscale experiments and numerical analyses

Environmental issues from waste management require reliable remediation techniques to prevent groundwater and soil pollution. Cut-off walls and permeable reactive barriers (PRBs) have been widely used for the control and remediation of groundwater pollution. However, the performance of the newly modified barrier materials and site remediation was not well explored. Therefore, in-depth and comparative analyses of 2 % carboxymethyl cellulose (CMC)-modified bentonite and 2 % unmodified sodium bentonite used in vertical barriers are required. Curtain and high-pressure jet grouting composed of CMC-modified bentonite were investigated in a field scale. Additionally, laboratory experiments were conducted to examine the permeability and adsorption properties of the PRB comprised of natural zeolite. The performances of vertical barriers and the PRB were compared by a three-dimensional numerical simulation based on the hydrogeological characteristics of a municipal solid waste landfill (MSWL) in southeastern China. The hydraulic conductivities of CMC-modified bentonite barriers could range from 21.9 %-50.5 % of those of unmodified sodium bentonite barriers, and could be as low as 1.02 × 10-8 cm/s. Contaminant fluxes through the cut-off wall and PRB were 38.67 % and 44.97 % of that without protection after 10 years in the polluted stratum. It was indicated that the removal rate of NH3-N can be 52.30 % at the 10th year by using PRBs. These results demonstrated the long-term performance of CMC-modified bentonite vertical barriers combined with PRBs is quite good at landfills or contaminated sites.

Effects of ozonation sludge reduction on nutrient removal and microbial community diversity of conventional A2/O and reversed A2/O processes

To optimise ozonation sludge reduction in the activated sludge process, it is crucial to monitor nutrient removal and pay particular attention to the influential biological species. This study employed high-throughput sequencing to examine the microbial composition and diversity in the anaerobic-anoxic-oxic (A2/O) process, the A2/O process with ozonation, and the reversed A2/O process with ozonation. The diversity analysis aimed to identify discrepancies and similarities in microbial communities among these groups, thereby elucidating the varying biological efficiencies. Furthermore, the results from Illumina MiSeq sequencing revealed significant diversification in microbial community structures in different processes. Ozonation sludge notably inhibited certain species, including the order Bacteroidales within the class Bacteroidia, as well as the orders Rhizobiales and Rhodospirillales within the class Alphaproteobacteria. Additionally, ozonation sludge exerted a notable impact on specific orders within the class Gammaproteobacteria, including Aeromonadales, Chromatiales, and HOC36. In contrast, it stimulated the proliferation of other microbial groups, such as Lactobacillales, Clostridiales, as well as Burkholderiales and Rhodocyclales. The inhibition and promotion of ozonation sludge in conventional and reversed A2/O processes resulted in various microbial richness and diversity, which rendered the distinctive biochemical activities and wastewater treatment performances. Betaproteobacteria increased significantly, especially in the reversed A2/O process, and Betaproteobacteria played an important role in the nitrogen removal and phosphorus removal process. These findings are useful for guiding the ozonised sludge system to reduce carbon, denitrification, and phosphorus removal to meet the emission standards, and the identification and enhancement of the construction of potential key biological flora for better wastewater treatment and sludge reduction.

Effective denitrification from landfill leachate using magnetic PVA/CMC/DE carrier immobilized microorganisms

Ammonia nitrogen (NH4+-N) discharge has caused eutrophication of water bodies and harm to humans and organisms. In this work, polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), diatomite (DE), and Fe3O4 were used to prepare magnetic immobilized carriers by encapsulating microorganisms for the treatment of NH4+-N wastewater. The response surface methodology was used to explore the optimal ratio of the immobilized carriers. The obtained optimal raw material ratio was 99.10 %. The obtained carriers are spherical (4-5 mm in diameter) with a rich honeycombed pore structure. The magnetic carrier improves the ammonia oxidation activity, and the carrier achieved 99.0 % of NH4+-N and 86.7 % of total nitrogen (TN) removal rates from the simulated wastewater (NH4+-N concentration: 300 mg/L) through nitrification and denitrification under aerobic conditions. Upon applied for a 60 days' treatment of landfill leachate (NH4+-N concentration of 300 mg/L), the daily removal rates for NH4+-N and TN reached 93.7 % and 78.3 %, respectively. The analysis of the microbial community showed that the abundances of heterotrophic nitrifying-aerobic denitrifying bacteria including Enterobacter, Pseudomonas, and Bacillus increased with prolonging treatment days, which accelerated nitrification and denitrification, consequently promoting the nitrogen removal effect.

Electrocoagulation of landfill leachate: Transforming a hazardous residue into a source of irrigation water

Electrocoagulation of landfill leachate has been widely investigated, however, only few reports include the reuse of the treated water. In this work, treated leachate is evaluated as irrigation water. The main obstacle is the high Sodium Absorption Ratio (SAR=Na+/(Ca2++Mg2+)/2. Reducing this indicator involves decreasing Na+ and increasing Mg2+ or Ca2+. Sodium concentration reduction is difficult by electrochemical methods (E0 = -2.71 V); Ca2+ increasing is not feasible as it precipitates. Hence, the use of different Al-Mg anodes was tested tending to increase Mg2+ concentration in the treated water The alloy 88%wtAl-12%wtMg was able to remove 52.9% of COD, 98.1% of turbidity, 97.9% of color, obtaining a SAR of 8.2 meq·L-1, total hardness (TH) of 64.2 meq·L-1 and a soluble sodium percentage (SSP) of 75.8 meq·L-1. This was achieved by working at a current density of 15 mA cm-2, a treatment time of 15 min and a pH 5.0. The phytotoxicity of the treated leachate was evaluated by the germination index using Lactuca Sativa L., reaching a value of 83.2%, which is considered excellent for irrigation water. During growth, 3-4 primary leaves were observed in seedings after 21 days, similar to when potable water was used. The results demonstrate that electrocoagulation is an adequate treatment technique for the reuse of landfill leachate if appropriated materials are used as anodes working in well selected operational variables.

Intermittent aeration mitigating carbon emission from landfills with gas-water joint regulation

Landfill is a significant source of atmospheric CH4 and CO2 emissions. In this study, four landfill reactor systems were constructed to investigate the effects of different ventilation methods, including continuous aeration (20 h d-1) and intermittent aeration (continuous aeration for 4 h d-1 and 2 h of aeration every 12 h, twice a day), on properties of landfilled waste and emissions of CH4 and CO2, in comparison to a traditional landfill. Compared with continuous aeration, intermittent aeration could reduce the potential global warming effect of the CH4 and CO2 emissions, especially multiple intermittent aeration. The CH4 and CO2 emissions could be predicted by the multiple linear regression model based on the contents of carbon, sulfur and/or pH during landfill stabilization. Both intermittent and continuous aeration could enhance the methane oxidation activity of landfilled waste. The aerobic methane oxidation activity of landfilled waste reached the maximums of 50.77-73.78 μg g-1 h-1 after aeration for 5 or 15 d, which was higher than the anaerobic methane oxidation activity (0.45-1.27 μg g-1 h-1). CO2 was the predominant form of organic carbon loss in the bioreactor landfills. Candidatus Methylomirabilis, Methylobacter, Methylomonas and Crenothrix were the main methane-oxidating microorganisms (MOM) in the landfills. Total, NO2--N, pH and Fe3+ were the main environmental variables influencing the MOM community, among which NO2--N and pH had the significant impact on the MOM community. Partial least squares path modelling indicated that aeration modes mainly influenced the emissions of CH4 and CO2 by affecting the degradation of landfilled waste, environmental variables and microbial activities. The results would be helpful for designing aeration systems to reduce the emissions of CH4 and CO2, and the cost during landfill stabilization.

Central Countries' and Brazil's Contributions to Nanotechnology

Abstract:

Nanotechnology is a cornerstone of the scientific advances witnessed over the past few years. Nanotechnology applications are extensively broad, and an overview of the main trends worldwide can give an insight into the most researched areas and gaps to be covered. This document presents an overview of the trend topics of the three leading countries studying in this area, as well as Brazil for comparison. The data mining was made from the Scopus database and analyzed using the VOSviewer and Voyant Tools software. More than 44.000 indexed articles published from 2010 to 2020 revealed that the countries responsible for the highest number of published articles are The United States, China, and India, while Brazil is in the fifteenth position. Thematic global networks revealed that the standing-out research topics are health science, energy, wastewater treatment, and electronics. In a temporal observation, the primary topics of research are: India (2020), which was devoted to facing SARS-COV 2; Brazil (2019), which is developing promising strategies to combat cancer; China (2018), whit research on nanomedicine and triboelectric nanogenerators; the United States (2017) and the Global tendencies (2018) are also related to the development of triboelectric nanogenerators. The collected data are available on GitHub. This study demonstrates the innovative use of data-mining technologies to gain a comprehensive understanding of nanotechnology's contributions and trends and highlights the diverse priorities of nations in this cutting-edge field.

Effect of sulfide on the nitrogen removal performance and microbial community of low-substrate Anammox process

Anammox is one of the most innovative nitrogen removal technologies, while its functional bacteria-anaerobic ammonia-oxidizing bacteria (AAOB) is sensitive to the impurities in the wastewater. In this study, the long-term effects of sulfide at different concentrations (0, 5, 10, 20, 30, 50, 25 mg L-1) on low substrate Anammox process were studied. The results showed that when the sulfide was 25-30 mg L-1, AAOB was well coupled with sulfide-denitrifying bacteria and the total nitrogen removal efficiency (TNRE) reached a maximum of 91.0%. The hydroxylamine oxidoreductase activity and Heme-c reached 1.678 EU g-1 SS and 0.0023 mmol g-1 SS, respectively, with the hzo and nosZ gene concentrations as 2.52 × 108 and 4.45 × 107 copies mL-1. 50 mg L-1 sulfide inhibited the nitrogen removal by AAOB, resulting in the TNRE decreasing to 81.7%. The experimental results provide a reference for the practical application of Anammox in treating sulfur-containing wastewater.

Maximizing bio-methane potential from municipal landfill leachate through ultrasonic pretreatment

In the quest for sustainable waste management solutions, this study explores the integration of ultrasonic pretreatment as a preparatory step for the anaerobic digestion of landfill leachate. Employing response surface methodology (RSM) coupled with central composite design (CCD), we systematically optimize the process parameters, including pH, inoculum volume, and ultrasonic pretreatment duration, to maximize the yield of bio-methane potential (ml CH4/g VS). The results demonstrate the effective application of RSM-CCD for predicting and modelling methane generation, with a highly significant model (R2 = 0.899). The optimized conditions reveal a remarkable biomethane potential of 177 ml CH4/g VS. Additionally, this study contributes to the understanding of the positive effect of ultrasound pretreatment on the anaerobic digestion of landfill leachate, and the quality of the digestate obtained after anaerobic digestion was studied and different valorisations were proposed.

Synthetic microbial consortia to enhance the biodegradation of compost odor by biotrickling filter

Composting generates odorous gases, including ammonia (NH3), hydrogen sulfide (H2S), and volatile organic compounds (VOCs). The Biological Trickling Filter (BTF) is effective for odor treatment, but it may have limitations with hydrophobic VOCs. In this study, a strain of Bacillus subtilis with ammonia-reducing ability, a strain of Bacillus cereus with desulfurization ability and a strain of Schizophyllum commune with the ability to degrade dimethyl disulfide were isolated and screened. The three strains were combined to create synthetic microbial consortia for enhancing odor treatment in the BTF. Compared to the activated sludge control, the BTF with synthetic microbial consortia removed 92.43% ammonia, 92.75% hydrogen sulfide. Furthermore, it demonstrated a significant improvement in the removal rates of p-methyl mercaptan, methyl sulfide, and dimethyl disulfide. High-throughput sequencing was conducted on the fillers of the synthetic microbial consortia-inoculated BTF to analyze the microbial community composition.

Simultaneous methanogenesis and denitrification in an anaerobic moving bed biofilm reactor for landfill leachate treatment: Ameliorative effect of rhamnolipids

In this study, an anaerobic moving bed biofilm reactor (AnMBBR) was developed for simultaneous methanogenesis and denitrification (SMD) to treat high-strength landfill leachate for the first time. A novel strategy using biosurfactant to ameliorate the inhibition of landfill leachate on the SMD performance was proposed and the underlying mechanisms were explored comprehensively. With the help of rhamnolipids, the chemical oxygen demand (COD) removal efficiency of landfill leachate was improved from 86.0% ± 2.9% to 97.5% ± 1.6%, while methane yields increased from 50.1 mL/g-COD to 69.6 mL/g-COD, and the removal efficiency of NO3--N was also slightly increased from 92.5% ± 1.9% to 95.6% ± 1.0%. The addition of rhamnolipids increased the number of live cells and enhanced the secretion of extracellular polymeric substances (EPS) and key enzyme activity, indicating that the inhibitory effect was significantly ameliorated. Methanogenic and denitrifying bacteria were enhanced by 1.6 and 1.1 times, respectively. Analysis of the microbial metabolic pathways demonstrated that landfill leachate inhibited the expression of genes involved in methanogenesis and denitrification, and that their relative abundance could be upregulated with the assistance of rhamnolipids addition. Moreover, extended Deraguin - Landau - Verwery - Oxerbeek (XDLVO) theory analysis indicated that rhamnolipids reduced the repulsive interaction between biofilms and pollutants with a 57.0% decrease in the energy barrier, and thus accelerated the adsorption and uptake of pollutants onto biofilm biomass. This finding provides a low-carbon biological treatment protocol for landfill leachate and a reliable and effective strategy for its sustainable application.

The efficiency and mechanism of excess sludge-based biochar catalyst in catalytic ozonation of landfill leachate

In this study, biochar was produced based on dehydrated excess sludge from the municipal wastewater treatment plant, which was used for catalytic ozonation of pollutants derived from landfill leachate. The necessary catalytic sites in the structure of biochar were originated from the inorganic metals and organic matters in the sludge, which included a large number of functional groups (e.g., C-C, CO, etc.), adsorbed oxygen (Oads accounted for 44.82%) and electron defects (ID/IG=1.01). These active sites could promote the generation of reactive oxygen species (ROS) (e.g., ·OH,·O2-, etc.). The synergistic interaction between the microorganisms in the activated sludge also facilitated the removal rates of pollutants. Proteobacteria, Bacteroidetes, and Deinococcu-Thermus were crucial in the bioreactor. In 16 days of reaction, the removal ratios of NH+4-N and COD were 98.95 ± 0.11% and 90.89 ± 0.47%, respectively. This study not only explains the mechanism of catalytic ozonation of biochar, but also provides a new way of the practical treatment of landfill leachate.

Effect of salinity stress on nitrogen and sulfur removal performance of short-cut sulfur autotrophic denitrification and anammox coupling system

The effects of salinity on anaerobic nitrogen and sulfide removal were investigated in a coupled anammox and short-cut sulfur autotrophic denitrification (SSADN) system. The results revealed that salinity had significant nonlinear effects on the nitrogen and sulfur transformations in the coupled system. When the salinity was <2 %, the anammox and SSADN activities increased with increasing salinity, and the total nitrogen removal rate, S⁰ production rate, and nitrite production rate were 0.41 kg/(m³·d), 0.37 kg/(m³·d), and 0.28 kg/(m³·d), respectively. With continuous increase of salinity, the performances of the anammox and SSADN gradually decreased, and the three indicators decreased to 0.14 kg/(m³·d), 0.22 kg/(m³·d), and 0.14 kg/(m³·d) at 5 % salinity, respectively. When the salinity reached 5 %, the nitrogen removal contribution of anammox decreased to 68.4 %, while the contribution of the sulfur autotrophic denitrification increased to 31.6 %. The coupled system recovered in a short time after alleviation of the salinity stress, and the SSADN activity recovery was faster than anammox. The microbial community structure and functional microbial abundance in the coupled system changed significantly with increasing salinity, and the functional microbial abundance after recovery was considerably different from the initial state.