This study focused on the removal of organic matter and nitrogen and explored the feasible operation strategies to achieve short-cut nitrification and denitrification in two constructed wetlands (CWs), which were designed to treat the actual landfill leachate from a small county in parallel. The two CWs were horizontal sub-surface flow constructed wetlands (HFCW) with partial-area aeration and vertical sub-surface flow constructed wetlands (VFCW) with full-area aeration. The experimental results showed that both CWs could achieve an excellent organic matter and nitrogen removal performance under the conditions of intermittent aeration with high frequency and medium intensity (2 h of aeration and 4 h of rest). The removal efficiencies of COD and total nitrogen by HFCW were 89.08% and 73.22%, and the corresponding values of VFCW were 84.51% and 71.44%, respectively. Meanwhile, the inhibition kinetics model indicated that HFCW with partial-area aeration could enhance the free ammonium (FA) tolerance of ammonium-oxidizing bacteria (AOB) and reduce the conversion percentage of ammonia nitrogen. In addition, the intermittent aeration mode with high frequency and medium intensity could keep the DO concentration below under 0.60 mg L⁻¹ in HFCW, which helped to achieve stable short-cut nitrification and ensure the average nitrite accumulation rate (NAR) reach 50.96%. These results suggested that the intermittent aeration in partial-area could achieve successful short-cut nitrification in HFCW, thereby improving the removal efficiency of nitrogen in landfill leachate.

Digital textile printing (DTP) is a game-changer technology that is rapidly expanding worldwide. On the other hand, process wastewater is rich in ammoniacal and organic nitrogen, resulting in relevant issues for discharge into sewer system and treatment in centralized plants. The present research is focused on the assessment of the partial nitritation/anammox process in a single-stage granular sequencing batch reactor for on-site decentralized treatment. The technical feasibility of the process was assessed by treating wastewater from five DTP industries in a laboratory-scale reactor, in one case investigating long-term process stabilization. While experimental results indicated nitrogen removal efficiencies up to about 70%, complying with regulations on discharge in sewer system, these data were used as input for process modelling, whose successful parameter calibration was carried out. The model was applied to the simulation of two scenarios: (i) the current situation of a DTP company, in which wastewater is discharged into the sewer system and treated in a centralized plant, (ii) the modified situation in which on-site decentralized treatment for DTP wastewater is implemented. The second scenario resulted in significant improvements, including reduced energy consumption (− 15%), reduced greenhouse gases emission, elimination of external carbon source for completing denitrification at centralized WWTP and reduced sludge production (− 25%).

Agriculture is the largest consumer of water, particularly in arid and semi-arid regions, so identifying and managing surface water quality in these areas is critical to preserving water resources and ensuring sustainable agriculture. Irrigation water quality (IWQ) assessment integrated with geographic information system (GIS) of West Nile Delta, Egypt, was carried out using suitability indicators such as hazards of salinity, permeability hazard, specific ion toxicity, and miscellaneous impacts on sensitive crops. In ArcGIS 10.7, inverse distance-weighted algorithms and the Model Builder function were used to categorize irrigation water quality into different classes. According to the findings, 87% and 13% of the water samples from the study area were categorized as medium and high suitability for irrigation, respectively. The heavy metal pollution index (HPI), Nemerow index (NeI), ecological risks of heavy metal index (ERI), heavy metal evaluation index (HEI), pollution load index (PLI), and modified degree of contamination (mCd) for five selected metals, namely As, Co, Cu, Ni, and Zn, were calculated to assess heavy metal contamination levels in the study area. The results showed that HPI had 3.7% medium contamination and 96.3% high contamination; NeI was 7.4% moderately contaminated and 92.6% heavily contaminated; ERI has almost 7% low risk, 30% moderate risk, 41% considerable risk, and 22% very high risk; HEI had 100% low contamination; PLI was 100% polluted; and mCd has 18.5% moderately-heavily polluted, 63% heavily polluted, and 18.5% severely polluted samples. This research can help decision-makers manage water resources more effectively for sustainable agriculture.

Feasible countermeasures to mitigate mercury (Hg) accumulation and its deleterious effects on crops are urgently needed worldwide. Selenium (Se) fertilizer application is a cost-effective strategy to reduce Hg concentrations, promote agro-environmental sustainability and food safety, and decrease the public health risk posed by Hg-contaminated soils and its accumulation in food crops. This holistic review focuses on the processes and detoxification mechanisms of Hg in whole soil–plant systems after Se application. The reduction of Hg bioavailability in soil, the formation of inert HgSe or/and HgSe-containing proteinaceous complexes in the rhizosphere and/or roots, and the reduction of plant root uptake and translocation of Hg in plant after Se application are systemically discussed. In addition, the positive responses in plant physiological and biochemical processes to Se application under Hg stress are presented to show the possible mechanisms for protecting the plant. However, application of high levels Se showed synergistic toxic effect with Hg and inhibited plant growth. The effectiveness of Se application methods, rates, and species on Hg detoxification is compared. This review provides a good approach for plant production in Hg-contaminated areas to meet food security demands and reduce the public health risk.

In this study, biochar was generated from chicken manure by using a tube furnace under different temperatures (300, 500, and 700 °C), and the treatments were noted as J300, J500, and J700, respectively. In comparison, another type of biochar was prepared under 500 °C with a muffle furnace, and the treatment was noted as JM500. Biochar in treatment group J500 was subsequently modified with HNO₃ and NaOH, and the treatments were noted as J500-HNO₃ and J500-NaOH, respectively. The sorption efficiencies of naphthalene by the above six types of biochar were evaluated. Characteristic results showed that the surface pores of the biochar were improved with the increase of temperature, and biochar under the treatments J300, J500, J700, and JM500 experienced a high speed of adsorption within 1 h after the naphthalene adsorption started. The adsorption capacity of naphthalene increased with the increase of the initial concentration of naphthalene. Treatment J700 exhibited the largest adsorption capacity since its biochar surface pore structure was more fully developed with a crystal structure formed, and its specific surface area was increased by about 20 times compared to the original chicken manure. After biochar modification using HNO₃ and NaOH, the infrared spectrum changed, and the adsorption active sites were increased. The biochar modification by HNO₃ had a high naphthalene adsorption efficiency compared to NaOH. The order of adsorption capacity was as follows: J500 ≈ JM500 < J300 < J500-NaOH < J500-HNO₃ < J700.

Boreal lakes with soft water and low buffering capacity are susceptible to excess ion loading resulting from metal mining. The impact of two Finish mining sites in downstream lakes was assessed with a chronic sediment toxicity test using a laboratory-reared freshwater Lumbriculus variegatus (Oligochaeta). The test organisms were exposed to mining-contaminated natural lake sediments and hypolimnion water (HLW) or artificial freshwater (AFW) as overlying water in two independent experimental setups. In both test setups, growth and reproduction of L. variegatus were lower in sediments from the lakes receiving high amount of mining effluents from the mines nearby. In the biomining site, the main contaminants in the recipient lakes were the ore metals Ni and Zn, while in the lakes affected by the conventional underground mine, they were Cu and Zn. These metals accumulated in L. variegatus especially in the setup with natural HLW above the sediment. Growth and reproduction were lower in the HLW than in the AFW setup. The mining-contaminated sediments did not support optimum growth or reproduction of L. variegatus in comparison to the local reference sediments. Decline of pH in the unbuffered natural sediments brought up challenges in the assessment of metal-contaminated lake sediments with high sulfur content, and a need to develop new tools for their risk assessment.

Road salt (NaCl) and acid deposition co-occur across much of North America and Europe. One such region is the Adirondack Park (AP) in New York, USA, where the effects of acid deposition have been widely studied and the effects of road salt have not. Road salt delivers 3560 Mmolc of Na to AP roads each year, which has significant potential to displace soil base cations and exacerbate ecosystem recovery from acidification. Our objective was to estimate the effect of road salt on soil base cation export for the AP. We used a simple steady state model based on estimated runoff and cation concentrations from lakes in watersheds with (n=84) and without (n=68) paved roads to estimate watershed export of Ca, Mg, K, and Na. Road salting resulted in significantly higher export for all cations, with 28, 15, 2, and 83 mmolc/m²/year more of Ca, Mg, K, and Na released, respectively, compared to watersheds without paved roads. Mineral weathering rates are insufficient to replace these lost cations and thus watershed recovery from acidification will be slower in the presence of road salt. Road salt should be included as a co-occurring stressor when assessing the impacts of pollutants on ecosystem health, not only in the AP but wherever road salt is applied.

Natural iron minerals and zero-valent metals have been widely tested as catalysts for the Fenton-like process, but the systematical comparison study about their catalytic performance was rarely conducted, and the risk of the secondary pollution of toxic heavy metals was still not uncertain. In this paper, a comparison study of applying pyrite, ilmenite, vanadium titano-magnetite (VTM), zero-valent iron (ZVI), and zero-valent copper (ZVC) as Fenton-like catalysts for the removal of imidacloprid was performed. The results showed that ZVI exhibited the highest activity among the recyclable solid catalysts with a removal rate of 96.8% at initial pH 3 using 10.78 mmol/L H₂O₂, due to iron corrosive dissolution. Vanadium titano-magnetite (VTM) exhibited the best activity at first use among tested minerals but with low reusability. Pyrite with stable morphology showed a medium but sustainable ability to degrade imidacloprid, achieving a removal rate of 10.5% in the fifth use. The reaction much favored the acidic condition of initial pH around 2 or 3. Meanwhile, there was a significant positive correlation between removal efficiency and dissolved Fe or Cu concentration. Pyrite was considered to be a promising catalyst in Fenton-like reaction. It was suggested that the system proceeded predominantly through a homogeneous route via dissolved Fe or Cu ions. Except ZVC and VTM, other tested catalysts showed the low possibility of causing secondary pollution of toxic metals in the application of Fenton-like process.

Amendments, such as biochar, compost, and iron grit, used in phytostabilization studies, showed positive effects on soil physico-chemical properties, plant growth, and the microbial community. However, assisted phytostabilization studies do not always focus on the rhizosphere area where soil, plants, and microorganisms are affected by the amendments and plants and microorganisms can also interact with each other. The aims of this study were to evaluate the effects of amendment application on the exudation of organic acids by Salix viminalis plant roots, as well as the effects of amendments and plant development on the soil CHNS contents and the microbial community activity and diversity, assessed by measuring enzyme activities and using Biolog EcoPlatesᵀᴹ tests and next-generation sequencing analyses. The results of the mesocosm experiment showed that soil C, H, and N contents were increased by amendment application, especially biochar and compost, while the one of S decreased. Enzyme activities, microbial activity, and diversity were also increased by the addition of amendments, except iron grit alone. Finally, the quantity of organic acids exuded by roots were little affected by amendments, which could in part explain the reduced effect of plant development on soil chemical and microbiological parameters. In conclusion, this study showed in particular that biochar and compost were beneficial for the soil CHN contents and the microbial community while affecting poorly Salix viminalis root exudates.

Soil microbial communities are affected by environmental factors. Contamination with heavy metals such as cadmium (Cd) can decrease soil microbial species richness and substantially alter soil microbial species composition. Investigations of the microbial communities in Cd-contaminated soils are necessary to obtain data for soil bioremediation efforts. However, depth-associated variations in microbial community composition and structure in Cd-contaminated paddy soils are not well understood. Here, the effects of various degrees of long-term Cd pollution on soil microorganisms were investigated at different soil depths within the plough layer using 16S rRNA gene amplicon sequencing. We found that, in Cd-polluted soils, microbial communities were more similar between the surface soil and the underlying soil. In addition, microbial community richness and/or diversity were significantly reduced in the Cd-polluted underlying soil as compared with the non-polluted underlying soil. However, species richness in the surface layer was significantly greater in the mildly and severely Cd-polluted soils. The soil microbial communities in the same soil layer differed significantly between the non-polluted and polluted soils. Furthermore, Cd contamination affected the microbial communities of different soil layers differently. Soil pH had a synergistic effect on microbial community abundance and composition. The potential functions of the soil microbiota were mainly related to environmental processing, genetic processing, and metabolic pathways. Notably, our identification of the phyla that were differently abundant among sites with different levels of Cd pollution will provide experimental guidance for further explorations of the effects of Cd on soil microbes in natural environments. Our results not only demonstrate that long-term Cd pollution leads to a marked reduction in microbial richness and diversity in the underlying soil layer, but they also help to clarify how long-term heavy metal contamination affects the soil bacterial community.