Effect of silver nanoparticles on an integrated fixed-film activated sludge-sequencing batch reactor: Performance and community structure

Strong suppression of silver nanoparticles on antibiotic resistome in anammox process

This study comprehensively deciphered the effect of silver nanoparticles (AgNPs) on anammox flocculent sludge, including nitrogen removal performance, microbial community structure, functional enzyme abundance, antibiotic resistance gene (ARGs) dissemination, and horizontal gene transfer (HGT) mechanisms. After long-term exposure to 0-2.5 mg/L AgNPs for 200 cycles, anammox performance significantly decreased (P < 0.05), while the relative abundances of dominant Ca. Kuenenia and anammox-related enzymes (hzsA, nirK) increased compared to the control (P < 0.05). For antibiotic resistome, ARG abundance hardly changed with 0-0.5 mg/L AgNPs but decreased by approximately 90% with 1.5-2.5 mg/L AgNPs. More importantly, AgNPs effectively inhibited MGE-mediated HGT of ARGs. Additionally, structural equation model (SEM) disclosed the underlying relationship between AgNPs, the antibiotic resistome, and the microbial community. Overall, AgNPs suppressed the anammox-driven nitrogen cycle, regulated the microbial community, and prevented the spread of ARGs in anammox flocs. This study provides a theoretical baseline for an advanced understanding of the ecological roles of nanoparticles and resistance elements in engineered ecosystems.

Enhanced mutualism: A promotional effect driven by bacteria during the early invasion of Phytolacca americana

The enhanced mutualism hypothesis postulates that invasive plants promote self-growth by enriching beneficial microbes to establish a positive soil feedback. However, the roles of soil microorganisms may vary with increasing time for plant growth. Research on changes in soil microbial communities over time has important implications for understanding the mechanisms underlying plant invasion. Due to the difficulty in evaluating the duration of plant growth, few studies have quantified the changes in soil microorganisms with increasing plant age. This study focuses on the invasive weed Phytolacca americana L., which has growth rings in the main root. We conducted a two-stage experiment in the field and greenhouse to explore the soil feedback changes with duration of plant growth. We determined the effects of P. americana at different ages on the soil microbial community and soil properties and performed a soil inoculation experiment to quantify the influence of soil microbes on seed germination and seedling performance. We found that the content of some soil nutrients, namely total nitrogen, total phosphorus, nitrate-N, and available phosphorus, significantly decreased with increasing growth age of P. americana, whereas the available potassium showed an opposite increasing trend. The P. americana growth age also significantly influenced the soil bacterial community structure. However, this phenomenon did not occur in the fungal community. In the bacterial community, the relative abundance of plant growth-promoting bacteria showed an increasing trend. The soil inoculation experiment had high seed germination rates and biomass accumulation when the plants were grown in conditioned soil from P. americana growth within 5 years, suggesting a positive plant-soil feedback. However, the promoting effect disappeared in conditioned soil from 10 years of age. Our findings demonstrate that plant growth-promoting bacteria significantly accumulated in the soil during the early stages of P. americana invasion, and that the strength of enhanced positive feedback may play a crucial role in facilitating P. americana invasion. This study highlights the changing nature of plant-microbe interactions during biological invasion and illustrates how bacteria could contribute to the initial success of P. americana, providing new insights into the underlying mechanisms of plant invasion.

Comprehensive response of microbes to Ag and Ag2S nanoparticles and silver spatial distribution in constructed wetlands

This study investigated functional bacteria, key enzymes, and nitrogen metabolism in vertical flow constructed wetlands (CWs) after exposing to silver, silver sulfide nanoparticles (Ag NPs and Ag2S NPs), and silver iron (Ag+), and silver spatial distribution in CWs for 155 days. Ag NPs and Ag2S NPs affected species richness and diversity whereas Ag+ showed the higher the species diversity indices. Sequencing analysis exhibited that Ag NPs or Ag+ significantly inhibited nitrogen metabolic process by hindering the relative activity of functional enzymes, downregulating relative abundances of nrfA, norB and napA for Ag NPs, nxrA gene for Ag+, while Ag2S NPs inhibited relative abundance of nirA. The above results confirmed that NPs or Ag+ significantly reduced nitrogen removal and Ag NPs mainly inhibited NO3--N removal while Ag+ significantly suppressed NH4+-N removal. This study also found that CWs could effectively remove NPs or Ag+ (about 98 %), and nanoparticles showed higher translocation factors (TFs) values (0.81-1.15 or 0.36), indicating nanoparticles transported easily through substrate layers.

Effect of Operating Parameters on the Performance of Integrated Fixed-Film Activated Sludge for Wastewater Treatment

Integrated fixed-film activated sludge (IFAS) is a hybrid wastewater treatment process that combines suspended and attached growth. The current review provides an overview of the effect of operating parameters on the performance of IFAS and their implications for wastewater treatment. The operating parameters examined include hydraulic retention time (HRT), solids retention time (SRT), dissolved oxygen (DO) levels, temperature, nutrient loading rates, and aeration. Proper control and optimization of these parameters significantly enhance the treatment efficiency and pollutant removal. Longer HRT and appropriate SRT contribute to improved organic matter and nutrient removal. DO levels promote the growth of aerobic microorganisms, leading to enhanced organic matter degradation. Temperature influences microbial activity and enzymatic reactions, impacting treatment efficiency. Nutrient loading rates must be carefully managed to avoid system overload or inhibition. Effective aeration ensures uniform distribution of wastewater and biofilm carriers, optimizing contact between microorganisms and pollutants. IFAS has been used in water reuse applications, providing a sustainable and reliable water source for non-potable uses. Overall, IFAS has proven to be an effective and efficient treatment process that can provide high-quality effluent suitable for discharge or reuse. Understanding the effects of these operating parameters helps to optimize the design and operation for efficient wastewater treatment. Further research is needed to explore the interactions between different parameters, evaluate their impact under varying wastewater characteristics, and develop advanced control strategies for improved performance and sustainability.

Modified integrated fixed-film activated sludge process: Advanced nitrogen removal for low-C/N domestic wastewater

Actual low-C/N domestic wastewater was treated using the high-concentration powder carrier bio-fluidized bed (HPB) process comparing diatomite and Fe-C as the carriers. The total nitrogen removal efficiencies were increased from 50.08% to 65.40% and 78.58%, respectively. The diatomite HPB process increased the relative abundance of autotrophic N-cycle bacteria to more than twofold and the sludge size. Therefore, the contributions for nitrogen removal by anammox and simultaneous nitrification-denitrification were increased. The Fe-C HPB process improved the nitrogen removal efficiency mainly by increasing the biodegradability and activities of electron transfer system and key enzymes. The key device (hydrocyclone separator) of the HPB process significantly improved the recovery efficiency of the carriers. It also improved the capacity of microbial aggregations for adsorbing pollutants. Furthermore, it reduced the relative abundance of filamentous bacteria. This study demonstrated the feasibility and mechanism of the HPB process for improving the nitrogen removal efficiency for low-C/N wastewater.

Effect of biochar and hydrochar from cow manure and reed straw on lettuce growth in an acidified soil

Soil acidification has become a major environmental and economic concern worldwide. Char materials (e.g biochar, hydrochar) have attracted considerable attention as soil amendments to restore degraded soil. However, the comparative study of biochar and hydrochar on plant growth in acidified soil is limited. In this study, a microcosmic experiment was used to compare the effect of biochar and hydrochar from cow manure (CBC, CHC) and reed straw (RBC, RHC) on the growth of lettuce in the acidified soil. CBC and RHC significantly increased and decreased the biomass of lettuce by 18.7% and 32.5% in the acidified soil, respectively. The increase of the lettuce growth by CBC primarily attributed to the enhancement of soil properties (SOM and pH) and soil nutrient content (Olsen-P, K, Ca, Mg, Zn, Fe and Mn). Moreover, CBC enhanced the microbial activity and complexity and increased the abundance of beneficial genera like Gemmatimonas, Ramlibacter and Haliangium, which improved soil health and might indirectly benefited the lettuce growth. Our findings highlighted the priority of char materials feedstock and preparation technology for remediating the acidified soil.

Unveiling changes of microbial community involved in N and P removal in constructed wetlands with exposing to silver nanoparticles

Constructed wetlands (CWs) are environmentally friendly engineered systems to purify wastewater, with low-cost and easy maintenance. However, it is not clear on responses of functional microbes for nitrogen (N) and phosphorus (P) biotransformation in CWs to silver nanoparticles (Ag NPs). The high throughput sequencings were employed to reveal microbial communities in vertical flow subsurface CWs with stable operation for 120 days. The results indicated that NH₄⁺-N, TN and TP removal of soil layer decreased by 43.56%, 15.7% and 22.7% under stress of Ag NPs. Microbial richness index and compositions were affected, and control wetland enriched Sulfurospirillum, Desulfarculaceae and Flavobacterium whereas CWs exposed to Ag NPs enriched Desulfosporosinus and Desulfurispora from LEfSe analysis. Moreover, after dosing Ag NPs, relative abundances of functional genes amoA and hao for nitrification, nirK and norB for denitrification and ppx and phoA/phoD for phosphorus conversions in upper soil were significantly downregulated. Inhibition on functional bacteria and genes of Ag NPs explained poor removal efficiencies of nitrogen and phosphorus pollutants in CWs. Our findings give an insight into ecological toxicity of Ag NPs on CWs with N and P bioconversions and provide the understanding of response of nitrifiers, denitrifies and PAOs.

Long-Term Exposure and Effects of rGO-nZVI Nanohybrids and Their Parent Nanomaterials on Wastewater-Nitrifying Microbial Communities

Single nanomaterials and nanohybrids (NHs) can inhibit microbial processes in wastewater treatment, especially nitrification. While existing studies focus on short-term and acute exposures of single nanomaterials on wastewater microbial community growth and function, long-term, low-exposure, and emerging NHs need to be examined. These NHs have distinctly different physicochemical properties than their parent nanomaterials and, therefore, may exert previously unknown effects onto wastewater microbial communities. This study systematically investigated long-term [∼6 solid residence time [(SRT)] exposure effects of a widely used carbon-metal NH (rGO-nZVI = 1:2 and 1:0.2, mass ratio) and compared these effects to their single-parent nanomaterials (i.e., rGO and nZVI) in nitrifying sequencing batch reactors. nZVI and NH-dosed reactors showed relatively unaffected microbial communities compared to control, whereas rGO showed a significantly different (p = 0.022) and less diverse community. nZVI promoted a diverse community and significantly higher (p < 0.05) biomass growth under steady-state conditions. While long-term chronic exposure (10 mg·L^-1) of single nanomaterials and NHs had limited impact on long-term nutrient recovery, functionally, the reactors dosed with higher iron content, that is, nZVI and rGO-nZVI (1:2), promoted faster NH₄⁺-N removal due to higher biomass growth and upregulation of amoA genes at the transcript level, respectively. The transmission electron microscopy images and scanning electron microscopy─energy-dispersive X-ray spectroscopy analysis revealed high incorporation of iron in nZVI-dosed biomass, which promoted higher cellular growth and a diverse community. Overall, this study shows that NHs have unique effects on microbial community growth and function that cannot be predicted from parent materials alone.

The impacts of metal-based engineered nanomaterial mixtures on microbial systems: A review

The last decade has witnessed tremendous growth in the commercial use of metal-based engineered nanomaterials (ENMs) for a wide range of products and processes. Consequently, direct and indirect release into environmental systems may no longer be considered negligible or insignificant. Yet, there is an active debate as to whether there are real risks to human or ecological health with environmental exposure to ENMs. Previous research has focused primarily on the acute effects of individual ENMs using pure cultures under controlled laboratory environments, which may not accurately reveal the ecological impacts of ENMs under real environmental conditions. The goal of this review is to assess our current understanding of ENM effects as we move from exposure of single to multiple ENMs or microbial species. For instance, are ENMs' impacts on microbial communities predicted by their intrinsic physical or chemical characteristics or their effects on single microbial populations; how do chronic ENM interactions compare to acute toxicity; does behavior under simplified laboratory conditions reflect that in environmental media; finally, is biological stress modified by interactions in ENM mixtures relative to that of individual ENM? This review summarizes key findings and our evolving understanding of the ecological effects of ENMs under complex environmental conditions on microbial systems, identifies the gaps in our current knowledge, and indicates the direction of future research.

Microbial nitrogen removal in synthetic aquaculture wastewater by fixed-bed baffled reactors packed with different biofilm carrier materials

Fixed-bed baffled reactors packed with carbon fiber (CFBR), polyurethane, or non-woven fabrics were developed to support microbial nitrification-denitrification reactions for nitrogen removal from synthetic aquaculture wastewater. The CFBR showed the best performance, with a short hydraulic retention time and low C/N ratio. Microbial communities in the reactor's biofilms and deposited sludge were analyzed using high-throughput sequencing and quantitative polymerase chain reactions. The biofilms efficiently enriched the nitrifying and denitrifying bacteria in the CFBR. Moreover, bacteria capable of denitrification under aerobic conditions were detected in the aerobic chamber biofilm, showing positive correlations with the main nitrifiers and denitrifiers, which provides potential synergistic interactions for simultaneous nitrification-denitrification in the aerobic chamber. A network analysis revealed that the CFBR had more complex cooperative interactions than others. This study provides insights into the influence of different carrier materials on biofilm formation, proving that the CFBR has potential applications in aquaculture wastewater treatment.

Biological fixed-film systems

The technical papers published in 2019 regarding wastewater treatment and microbial films were classified into two categories: biofilm and biofilm reactors. The biofilm category includes biofilm formation, biofilm consortia, bacterial signals, biofouling, extracellular polymeric substances, and biofilm membrane bioreactors. The biofilm reactors category provides recent information on rotating biological contactors, fluidized-bed biofilm reactors, integrated fixed-film activated sludge, moving-bed biofilm reactors, packed-bed biofilm reactors, sequencing biofilm batch reactors, and trickling filters.

Sequencing batch reactor technology for landfill leachate treatment: A state-of-the-art review

Landfill has become an underlying source of surface and groundwater pollution if not efficiently managed, due to the risk of leachate infiltration into to land and aquifers. The generated leachate is considered a serious environmental threat for the public health, because of the toxic and recalcitrant nature of its constituents. Thus, it must be collected and appropriately treated before being discharged into the environment. At present, there is no single unit process available for proper leachate treatment as conventional wastewater treatment processes cannot achieve a satisfactory level for degrading toxic substances present. Therefore, there is a growing interest in examination of different leachate treatment processes for maximum operational flexibility. Based on leachate characteristics, discharge requirements, technical possibilities, regulatory requirements and financial considerations, several techniques have been applied for its degradation, presenting varying degrees of efficiency. Therefore, this article presents a comprehensive review of existing research articles on the pros and cons of various leachate degradation methods. In line with environmental sustainability, the article stressed on the application and efficiency of sequencing batch reactor (SBR) system treating landfill leachate due to its operational flexibility, resistance to shock loads and high biomass retention. Contributions of integrated leachate treatment technologies with SBR were also discussed. The article further analyzed the effect of different adopted materials, processes, strategies and configurations on leachate treatment. Environmental and operational parameters that affect SBR system were critically discussed. It is believed that information contained in this review will increase readers fundamental knowledge, guide future researchers and be incorporated into future works on experimentally-based SBR studies for leachate treatment.

Recent progress in integrated fixed-film activated sludge process for wastewater treatment: A review

Integrated fixed-film activated sludge (IFAS) process is considered as one of the leading-edge processes that provides a sustainable solution for wastewater treatment. IFAS was introduced as an advancement of the moving bed biofilm reactor by integrating the attached and the suspended growth systems. IFAS offers advantages over the conventional activated sludge process such as reduced footprint, enhanced nutrient removal, complete nitrification, longer solids retention time and better removal of anthropogenic composites. IFAS has been recognized as an attractive option as stated from the results of many pilot and full scales studies. Generally, IFAS achieves >90% removals for combined chemical oxygen demand and ammonia, improves sludge settling properties and enhances operational stability. Recently developed IFAS reactors incorporate frameworks for either methane production, energy generation through algae, or microbial fuel cells. This review details the recent development in IFAS with the focus on the pilot and full-scale applications. The microbial community analyses of IFAS biofilm and floc are underlined along with the special emphasis on organics and nitrogen removals, as well as the future research perspectives.

Stronger Stimulation of Waste Activated Sludge Anaerobic Fermentation by a Particular Amount of Micron-Sized Zero Valent Iron

An emerging contaminant, micron-sized zero valent iron (mZVI) has been reported to be accumulated in waste activated sludge (WAS). In the present study, the potential effects of mZVI on WAS anaerobic fermentation performance, as well as the shift of the microbial community composition and function, were assessed. Results from batch experiments indicated that a particular concentration of mZVI (1.5 g/L, in the range of 0.0 to 5.0 g/L) improved volatile fatty acids (VFA) accumulation by 4.84 times that in the control group, the ability (dosage dependent) to remove phosphorus, and the dewaterability of fermented WAS from 126 ± 5 s (control group) to 104 ± 3 s (group with 1.5 g/L mZVI). Furthermore, high-throughput sequencing revealed that mZVI had no significant impact on the shift of microbial community structure, but directly stimulated the functional performance related to anaerobic fermentation. This study will provide new insights into the mZVI application and its effect on WAS utilization.

Integrated effects of temperature and COD/N on an up-flow anaerobic filter-biological aerated filter: Performance, biofilm characteristics and microbial community

The integrated effects of temperature and COD/N ratio on performance, biofilm characteristics and microbial community in up-flow anaerobic filter-biological aerated filters (UAF-BAFs) were investigated. Results indicated that the UAF-BAF system could achieve excellent COD, NH₄⁺-N and TN removal, in which effluent quality well met the Class 1A standard. Biofilm physicochemical characteristics showed that the biomass, biofilm thickness and extracellular polymeric substance (EPS) content in the UAF-BAFs reduced with the decrease in COD/N ratio, but were enhanced under low temperature. The biofilm structure characterized by CLSM in the UAF-BAFs significantly shifted, which was closely correlated with operational conditions. Sequencing analysis revealed that Proteobacteria, Epsilonbacteraeota, Bacteroidetes and Firmicutes were dominant in the UAFs and the abundance of ammonium oxidizing bacteria (AOB) was responsible for nitrification performance in the BAFs. Functions analysis indicated that amino acid metabolism, carbohydrate metabolism, energy metabolism and lipid metabolism were clearly regulated by parameters changes.