Evolution of river-aquifer disconnections and the migration and transformation of iron and manganese under non-time-varying/time-varying riverbed permeability.

Changes in the composition, structure, and thickness of riverbed sediments caused by riverbed clogging strongly affect the hydraulic connection, migration and transformation of nutrients between river water and groundwater in groundwater source areas. However, previous studies have not extensively investigated the mechanisms of river-aquifer disconnection and the migration and transformation processes of iron and manganese under non-time-varying and time-varying conditions of riverbed permeability. This study developed a model using the COMSOL Multiphysics platform to characterize the riverbed clogging-groundwater exploitation-disconnection process, considering microbial growth and related biogeochemical processes, and investigated feedbacks between the reactive migration of iron and manganese and physical clogging-groundwater exploitation processes or bioclogging processes. The research findings showed that under non-time-varying conditions of riverbed permeability, the evolution of river-aquifer disconnection was strongly affected by the thickness and permeability coefficient of riverbed sediments. The dissolved oxygen attenuation rate in the disconnection zone decreased by up to 88.8 %. Additionally, the Mn2+ and Fe2+ generation rates in sediment pore water decreased by 65.8 % and 62.7 %, respectively. In contrast, during the riverbed bioclogging process, as the biofilms on the surface of the riverbed sediments developed, the sediment pores gradually clogged, leading to a significant reduction in the porosity and permeability coefficient. Consequently, the hydraulic connection between the river and aquifer transitioned from a saturated connection to a disconnection. However, reduced permeability due to riverbed bioclogging primarily controlled the release of Fe and Mn. When the river-aquifer was in complete disconnection, compared to the saturated connection state, the Mn2+ and Fe2+ generation rates increased by up to 5.8 and 3.8 times, respectively. This study deepens our understanding of the biogeochemical cycling mechanisms of Fe and Mn under riverbed clogging conditions in groundwater source areas and contributes to ensuring a secure and stable water supply in these areas.

Biogeochemical modelling to assess the effect of bioclogging on multiple electron acceptor-mediated petroleum hydrocarbon bioremediation in vadose zone.

Bioremediation is an economically viable and sustainable clean-up strategy. Hydrodynamic, as well as transport characteristics of the porous medium, can evolve over the period as a result of biological clean-up activities. The present study proposes a 2-D numerical framework to simulate the effect of bioclogging on multiple electron acceptor-mediated petroleum hydrocarbon bioremediation in the vadose zone. For modelling, a spill of BTEX (benzene, toluene, ethylbenzene and xylene) is assumed near source zone. The developed model results are validated using three previously published datasets on flow, transport and biodegradation in the vadose zone. Simulations are performed for three types of soil, including clay, sand and loam. The analysis shows that sand has a maximum infiltration rate and clay has a minimum. Hydraulic conductivity and saturation profile peaks reach their minimal value at a shallower depth (around four times) when bioclogging is present compared to when it is absent. The migration depth and concentration of BTEX are observed to be restricted to a shallower depth in aquifers with the presence of microbial clogging. The outcome shows that electron acceptor consumption is more (around sevenfold for oxygen, fourfold for nitrate and threefold for sulphate) in the presence of bioclogging at the shallower zone. Zeroth order spatial moment and sensitivity analyses show that biological clogging, number of electron acceptors and inhibition constant substantially affect BTEX bioremediation in the vadose zone.

Acetylene Tunes Microbial Growth During Aerobic Cometabolism of Trichloroethene.

Microbial aerobic cometabolism is a possible treatment approach for large, dilute trichloroethene (TCE) plumes at groundwater contaminated sites. Rapid microbial growth and bioclogging pose a persistent problem in bioremediation schemes. Bioclogging reduces soil porosity and permeability, which negatively affects substrate distribution and contaminant treatment efficacy while also increasing the operation and maintenance costs of bioremediation. In this study, we evaluated the ability of acetylene, an oxygenase enzyme-specific inhibitor, to decrease biomass production while maintaining aerobic TCE cometabolism capacity upon removal of acetylene. We first exposed propane-metabolizing cultures (pure and mixed) to 5% acetylene (v v-1) for 1, 2, 4, and 8 d and we then verified TCE aerobic cometabolic activity. Exposure to acetylene overall decreased biomass production and TCE degradation rates while retaining the TCE degradation capacity. In the mixed culture, exposure to acetylene for 1-8 d showed minimal effects on the composition and relative abundance of TCE cometabolizing bacterial taxa. TCE aerobic cometabolism and incubation conditions exerted more notable effects on microbial ecology than did acetylene. Acetylene appears to be a viable approach to control biomass production that may lessen the likelihood of bioclogging during TCE cometabolism. The findings from this study may lead to advancements in aerobic cometabolism remediation technologies for dilute plumes.

Rhamnolipid-induced alleviation of bioclogging in Managed Aquifer Recharge (MAR): Interactions with bacteria and porous media.

The prevention and treatment of bioclogging is of great significance to the application of Managed Aquifer Recharge (MAR). This study investigated the alleviating effect of biosurfactant rhamnolipid (RL) on bioclogging by laboratory-scale percolation experiments. The results show that the addition of RL greatly reduced bioclogging. Compared with the group without RL, the relative hydraulic conductivity (K') of the 100 mg/L RL group increased 5 times at the end of the experiment (23 h), while the bacterial cell amount and extracellular polymeric substances (EPS) content on the sand column surface (0-2 cm) decreased by 60.8% and 85.7%, respectively. In addition, the richness and diversity of the microbial communities within the clogging matter decreased after the addition of RL. A variety of bacterial phyla were found, among which Proteobacteria were predominant in all groups. At the genus level, RL reduced the relative abundance of Acinetobacter, Bacillus, Klebsiella, and Pseudomonas. These microbes are known as strong adhesion, large size, and easy to form biofilms, therefore playing a critical role during MAR bioclogging. Moreover, RL changed the surface properties of bacteria and porous media, which results in the increase of electrostatic repulsion and decrease of hydrophobic interaction between them. Therefore, RL mediated the bacteria-porous media interaction to reduce biomass in porous media, thereby alleviating bioclogging. This study implies that RL's addition is an environmentally friendly and effective method to alleviate the bioclogging in MAR.

Bio-clogging mitigation in constructed wetland using microbial fuel cells with novel hybrid air-photocathode.

Excessive accumulation of extracellular polymeric substances (EPS) in constructed wetland (CW) substrate can lead to bio-clogging and affect the long-term stable operation of CW. In this study, a microbial fuel cell (MFC) was coupled with air-photocathode to mitigate CW bio-clogging by enhancing the micro-electric field environment. Because TiO2/biochar could catalyze and accelerate oxygen reduction reaction, further promoting the gain of electric energy, the electricity generation of the tandem CW-photocatalytic fuel cell (CW-PFC) reached 90.78 mW m-3. After bio-clogging was mitigated in situ in tandem CW-PFC, the porosity of CW could be restored to about 62.5 % of the initial porosity, and the zeta potential of EPS showed an obvious increase (-14.98 mV). The removal efficiencies of NH4+-N and chemical oxygen demand (COD) in tandem CW-PFC were respectively 31.8 ± 7.2 % and 86.1 ± 6.8 %, higher than those in control system (21.1 ± 11.0 % and 73.3 ± 5.6 %). Tandem CW-PFC could accelerate the degradation of EPS into small molecules (such as aromatic protein) by enhancing the electron transfer. Furthermore, microbiome structure analysis indicated that the enrichment of characteristic microorganisms (Anaerovorax) for degradation of protein-related pollutants, and electroactive bacteria (Geobacter and Trichococcus) promoted EPS degradation and electron transfer. The degradation of EPS might be attributed to the up-regulation of the abundances of carbohydrate and amino acid metabolism. This study provided a promising new strategy for synergic mitigation and prevention of bio-clogging in CW by coupling with MFC and photocatalysis.

Isolation and characterization of quorum quenching bacteria from municipal solid waste and bottom ash co-disposal landfills.

Co-landfilling of bottom ash (BA) accelerates the clogging of leachate collection systems (LCSs) and increases the risk of landfill failure. The clogging was mainly associated with bio-clogging, which may be reduced by quorum quenching (QQ) strategies. This communication reports on a study of how isolated facultative QQ bacterial strains from municipal solid waste (MSW) landfills and BA co-disposal landfills. In MSW landfills, two novel QQ strains (Brevibacillus agri and Lysinibacillus sp. YS11) can degrade the signal molecule hexanoyl-l-homoserine lactone (C6-HSL) and octanoyl-l-homoserine lactone (C8-HSL), respectively. Pseudomonas aeruginosa could degrade C6-HSL and C8-HSL in BA co-disposal landfills. Moreover, P. aeruginosa (0.98) was observed with a higher growth rate (OD600) compared to that of B. agri (0.27) and Lysinibacillus sp. YS11 (0.53). These results indicated that the QQ bacterial strains were associated with leachate characteristics and signal molecules and could be used for controlling bio-clogging in landfills.

Application of filter media surface hydrophobic modification to reduce bioclogging in the infiltration system.

Bioclogging is a commonly encountered operational issue that lowers hydraulic conductivity and the overall performance of the infiltration systems. In this paper, a novel processing for alleviating bioclogging by filter media surface hydrophobic modification was presented. Two-dimensional porous media cells were used to observe the influence of hydrophobic modification on biofilm growth in the pore structure. Moreover, two continuous-flow columns packed with gravel, one of which half gravel was hydrophobically modified, were operated with artificial wastewater to verify the effect of hydrophobic modification on bioclogging alleviation. The results showed that the biofilm growth in the cell with hydrophobic modification was slow, and the biomass was less and liable to wipe off after hydrophobic treatment. Meanwhile, the hydraulic efficiency of the flow seepage field was also improved after hydrophobic treatment. The column tests results showed that the hydraulic conductivity of the filter bed with hydrophobic modification (Column B) decreased more slowly than that of another without hydrophobic modification (Column A). Column B had the hydraulic conductivity (k) of 0.66 cm/s in the final stage of the experiment, while the k of Column A was 0.14 cm/s. It verified that hydrophobic modification of partial filter media can alleviate the bioclogging problem of the infiltration systems to some extent. The results provide a new idea and potential technical support for solving bioclogging problem.

Bioclogging alleviation for constructed wetland based on the interaction among biofilm growth and hydrodynamics.

Bioclogging is the most crucial operation problem of the constructed wetlands, which reduce its removal efficiency and life span. A strategy through properly increasing hydraulic loading is proposed in this study to alleviate the bioclogging for CWs. The two-dimensional porous media flow cell (2D PMFC) test indicated that a quadratic correlation was found between local biofilms growth rate and the near-wall Reynolds number (r > 0.765, p < 0.05). The biofilm growth rate declined with the flowrate when Re exceeded about 6.0. It was also found that the higher flowrate (6 mL/min) lead to the homogeneous biofilm and velocity distribution in the PMFC. The column test indicated that the highest hydraulic loading (9.2 cm/h) produced the smallest decrease in hydraulic conductivity, which was 80 times more than that of low hydraulic load (3.0 cm/h) at the end (40 days) of experiment. Moreover, the relatively homogenized distribution of biofilm was found along the column with the highest hydraulic loading, which confirmed that the proper increase in hydraulic loading can alleviate bioclogging.

Fluid transport in porous media based on differences in filter media morphology and biofilm growth in bioreactors.

To elucidate the effect of pore structure on bioclogging and seepage flow in bioreactors, we used X-ray computed tomography (X-CT) to investigate the changes in seepage flow of porous media in zeolite, gravel and ceramsite bioreactors with biofilm growth by injecting a non-ionic contrast medium iohexol. Based on the X-CT images using a ball-and-stick model, the highest average pore radius (R‾) and the average pore throat radius (r‾) in the ceramsite column were found under the initial conditions, which facilitated its permeability. The pore and throat of the gravel column were small and homogeneous relatively. Biofilm growth decreased the pore and pore throat in the columns. The total throat area of zeolite, gravel and ceramsite columns declined by 74%, 73% and 79% respectively. The zeolite column had the highest average pore throat, which contributed to its maximum conductivity subsequently after biofilm growth. Further, the fractal dimensions of the pore structure increased with biofilm growth, especially in the zeolite and ceramsite columns. The heterogeneity of the porous media was reinforced by the biofilm growth in the zeolite and ceramsite columns due to their higher heterogeneity initially. We also observed that an increase in heterogeneity of porous medium amplified the preferential flow and flow heterogeneities, especially in the zeolite and ceramsite columns.

Influence of pH on bioclogging in porous media during managed aquifer recharge (MAR): Effectiveness and mechanism.

To investigate the effect of pH on bioclogging process during managed aquifer recharge, three laboratory-scale column experiments were conducted and the relative hydraulic conductivity, bacterial cell number and the concentrations of polysaccharide, protein and EPS were measured under pH 5, 7, and 9, respectively. High-throughput sequencing was also used to determine the characteristics of bacterial community under different pH conditions. The development of bioclogging was rather different for the case of pH 5. 7, and 9; i.e., the growth process and number of bacteria differed with pH. The shortest growth period and lowest number of bacteria were observed at pH 5. In addition, the difference in bacterial EPS concentration was mainly associated with the polysaccharides. The variation in pH led to different bacterial community composition and diversity. The acid-resistant Elizabethkingia and Bacillus were abundant at pH 5, while Chryseobacterium and Klebsiella had relatively high abundances at pH 7. In contrast, the basophilic Exiguobacterium accounted for >80% of the total bacterial abundance at pH 9. This work is of great significance to explore bioclogging mechanism during MAR process, and provides insights and guidances for field-based managed aquifer recharge.

Role of surface physicochemical properties of pipe materials on bio-clogging in leachate collection systems from a thermodynamic perspective.

Bio-clogging in pipes poses a significant threat to the operation of leachate collection systems. Bio-clogging formation is influenced by the pipe materials. However, the relationship between bio-clogging and the physicochemical properties of different pipe materials has not been clarified yet, especially from a thermodynamic aspect. In this study, the dynamic bio-clogging processes in pipes of different materials (high-density polyethylene (HDPE), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE)) were compared, and their correlation with the physicochemical properties was investigated. Results showed that the bio-clogging in HDPE and PVC pipes was more severe than that in PP and PE pipes. In bio-clogging development, the predominant factor changed from the surface roughness to the electron donator parameter (γ-). In the initial phase, the most severe bio-clogging was observed in the HDPE pipe, which exhibited the highest roughness (432 ± 76 nm). In the later phase, the highest γ- (2.2 mJ/m2) and protein content (2623.1 ± 33.2 µg/cm2) were observed in the PVC simultaneously. Moreover, the interaction energy indicated that the bacteria could irreversibly and reversibly adhere to the HDPE, whereas irreversible adhesion was observed in the PVC, PP, and PE cases. The findings clarify the thermodynamic mechanism underlying bio-clogging behaviors and provide novel insights into the bio-clogging behaviors in pipes of different materials, which can facilitate the development of effective bio-clogging control strategies.

Spatial Variation of the Microbial Community Structure of On-Site Soil Treatment Units in a Temperate Climate, and the Role of Pre-treatment of Domestic Effluent in the Development of the Biomat Community.

The growth of microbial mats or "biomats" has been identified as an essential component in the attenuation of pollutants within the soil treatment unit (STU) of conventional on-site wastewater treatment systems (OWTSs). This study aimed to characterize the microbial community which colonizes these niches and to determine the influence of the pre-treatment of raw-domestic wastewater on these communities. This was achieved through a detailed sampling campaign of two OWTSs. At each site, the STU areas were split whereby half received effluent directly from septic tanks, and half received more highly treated effluents from packaged aerobic treatment systems [a coconut husk media filter on one site, and a rotating biodisc contactor (RBC) on the other site]. Effluents from the RBC had a higher level of pre-treatment [~90% Total Organic Carbon (TOC) removal], compared to the media filter (~60% TOC removal). A total of 92 samples were obtained from both STU locations and characterized by 16S rRNA gene sequencing analysis. The fully treated effluent from the RBC resulted in greater microbial community richness and diversity within the STUs compared to the STUs receiving partially treated effluents. The microbial community structure found within the STU receiving fully treated effluents was significantly different from its septic tank, primary effluent counterpart. Moreover, the distance along each STU appears to have a greater impact on the community structure than the depth in each STU. Our findings highlight the spatial variability of diversity, Phylum- and Genus-level taxa, and functional groups within the STUs, which supports the assumption that specialized biomes develop around the application of effluents under different degrees of treatment and distance from the source. This research indicates that the application of pre-treated effluents infers significant changes in the microbial community structure, which in turn has important implications for the functionality of the STU, and consequently the potential risks to public health and the environment.

Competition between growth and shear stress drives intermittency in preferential flow paths in porous medium biofilms.

Bacteria in porous media, such as soils, aquifers, and filters, often form surface-attached communities known as biofilms. Biofilms are affected by fluid flow through the porous medium, for example, for nutrient supply, and they, in turn, affect the flow. A striking example of this interplay is the strong intermittency in flow that can occur when biofilms nearly clog the porous medium. Intermittency manifests itself as the rapid opening and slow closing of individual preferential flow paths (PFPs) through the biofilm-porous medium structure, leading to continual spatiotemporal rearrangement. The drastic changes to the flow and mass transport induced by intermittency can affect the functioning and efficiency of natural and industrial systems. Yet, the mechanistic origin of intermittency remains unexplained. Here, we show that the mechanism driving PFP intermittency is the competition between microbial growth and shear stress. We combined microfluidic experiments quantifying Bacillus subtilis biofilm formation and behavior in synthetic porous media for different pore sizes and flow rates with a mathematical model accounting for flow through the biofilm and biofilm poroelasticity to reveal the underlying mechanisms. We show that the closing of PFPs is driven by microbial growth, controlled by nutrient mass flow. Opposing this, we find that the opening of PFPs is driven by flow-induced shear stress, which increases as a PFP becomes narrower due to microbial growth, causing biofilm compression and rupture. Our results demonstrate that microbial growth and its competition with shear stresses can lead to strong temporal variability in flow and transport conditions in bioclogged porous media.

Characteristics and origin of clogging-functional bacteria during managed aquifer recharge: A laboratory study.

Owing to serious influences on well performance, bacteria-induced clogging has become a dilemma for managed aquifer recharge (MAR). During MAR, surface river water is inoculated into aquifer and mixed with groundwater. Therefore, the clogging-functional bacteria may originate from the river water or the groundwater. However, the origin of the clogging-functional bacteria in the aquifer has not yet been well understood. This study conducted a series of laboratory-scale column experiments involving different recharge modes (using river water, groundwater) to simulate the processes of bacteria-induced clogging and used the high-throughput sequencing technology, aiming to elucidate the community characteristics and the origin of the clogging-functional bacteria involved in MAR bioclogging. Analyses of the bacterial-community characteristics showed significant differences between the river water and groundwater. The bacterial-community characteristics of the clogging aquifer in the different recharge modes were similar to each other and have common genera, namely, Acinetobacter, Brevundimonas, Exiguobacterium, Porphyrobacter, Cloacibacterium, and Sphingobium, which suggests that MAR activity could promote bacterial communities to become identical during surface water infiltration into aquifers, despite differences in the bacterial communities present in the subsurface- and surface systems. This knowledge will assist greatly in targeted treatment and prophylaxis of clogging-functional bacteria during managed aquifer recharge.

Insight into the effect of calcium on bio-clogging behavior via quartz crystal microbalance with dissipation monitoring.

Bio-clogging of leachate collection systems has attracted much attention because of its threat to landfill slope stability and landfill landslide events. Calcium in leachate plays a vital role in the formation of bio-clogging. However, the influence of calcium on bio-clogging remains unclear. This study examined the effects of calcium concentration on bio-clogging, including 0, 1.25, 5, 25, and 75 mM CaCl2 groups. A technique involving quartz crystal microbalance with dissipation monitoring (QCM-D) was applied to evaluate the bacteria adhesion behaviors in real time. The results showed that the presence of Ca2+ accelerated the bacterial attachment and increased the viscoelasticity of deposited layers. The deposition mass for 75 mM CaCl2 was 1442 ± 260 ng/cm2, which is 1.5 times that for 1.25 mM CaCl2. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory could explain the bacterial adhesion behaviors in low calcium concentrations (<25 mM). In comparison, the effect of calcium bridge was shown in high calcium concentrations (>25 mM). The development of biofilms was a dynamic process, and the Ca2+ concentration was positively related to the amount of biofilm generated. In low CaCl2 concentration (less than 5 mM) groups, the degree of bio-clogging increased from the exponential growth phase to the decline phase; in contrast, in high CaCl2 concentration (above 25 mM) groups, the degree of bio-clogging increased and later declined. Therefore, the calcium concentration should be controlled at a low level in leachate to mitigate bio-clogging in LCSs.

An appraisal of the hydro-mechanical behaviour of polysaccharides, xanthan gum, guar gum and ß-glucan amended soil.

The study aims to investigate the hydro-mechanical behaviour of the polysaccharide amended sand-clay mixture and analyse the soil - biopolymer interaction. Parameters like permeability, strength and heavy metal attenuation capacity of the amended soil were characterized and studied particularly for its use in landfill applications. The permeability of the soil was investigated for a period of one year. The results of the investigation show that all the selected polysaccharides significantly reduce the permeability and improve the heavy metal adsorption capacity of the sand-clay mixtures. The biopolymer also contributes to the increase in the strength of the soil. The improved mechanical properties of the amended soil can be ascribed to the bio-clogging through gel plug formation and bonding action of the biopolymers. Xanthan gum amended soil showed the least permeability, highest strength and adsorbed the selected heavy metals almost entirely, showing the best performance as a liner material.

Impact of compost reactive layer on hydraulic transport and C & N cycles: Biogeochemical modeling of infiltration column experiments.

Managed Aquifer Recharge (MAR) is a key strategy to increase freshwater resources in many regions facing water scarcity. MAR issues are related to both quantity and quality of the infiltrating water. In most countries, very high quality of the infiltrating water is required, to limit the impact on the aquifer geochemistry. In this paper, the possibility of injecting water of lower quality in the aquifer and letting the biogeochemical reactions take place in order to enhance its quality is explored. Here, we present the fate of nutrients (C, N) in the biogeochemical system of a reactive barrier formed by mixture of different proportions of sand and compost, supplied with treated wastewater to mimic MAR. An integrated conceptual model involving the nutrient cycles and biomass dynamics (auto- and heterotrophic) was developed, and then tested with a number of solute transport experiments in columns with different compost fraction in the column filling. The model incorporated both saturation and inhibition processes (regarding the nutrients and their byproducts) to provide a comprehensive picture of the nutrient dynamics within the column. The model developed (three if considering the 3 column setups) allowed to discriminate the processes that govern the fate of nutrients in relation with the compost enhancing long-term nutrient degradation, yet hindering hydraulic parameters that affect infiltration rates.

Deciphering acyl-homoserine lactones-mediated quorum sensing on geotextile bio-clogging in municipal solid waste and bottom ash co-disposal landfills.

Bottom ash co-disposed in landfills accelerates geotextile clogging and decreases landfill stability. As the main contributor to clogging, bio-clogging may be associated with quorum sensing (QS) in microbial communities. This study investigated the potential roles of acyl-homoserine lactones (AHLs)-mediated QS in geotextile bio-clogging under different landfill conditions, including municipal solid waste landfill and bottom ash co-disposal landfill. The unit area of geotextile bio-clogging mass in the municipal solid waste landfill (MSW_G) ranged from 5.2 × 10-3 to 8.2 × 10-3 g/cm2, while it was in the range of 8.4 × 10-3 to 1.2 × 10-2 g/cm2 in the bottom ash co-disposal landfill (BA_G). Two types of AHLs were detected and the total AHLs content in the MSW_G (1,616.9 ± 103.8 ng/g VSS) was half of that in the BA_G (3,233.0 ± 646.8 ng/g VSS). High contents of the AHLs could increase bio-clogging. The bio-clogging was also attributed to QS genes and extracellular polymeric substances (EPS). EPS aggregation was stimulated due to the higher Ca2+ and Mg2+ in the BA_G. These results suggested that the co-disposal of bottom ash could increase the AHLs content, resulting in accelerated bio-clogging.

Comparison of bio-clogging characteristics of geotextiles in MSW and bottom ash co-disposal landfills.

Bio-clogging of geotextile is a big challenge for the leachate collection system in landfills. It is important to understand the characteristics of geotextile bio-clogging to develop control technologies. This study investigated the characteristics of geotextile bio-clogging in municipal solid waste landfill (MSW_G) and bottom ash (BA) co-disposal landfill (BA_G). Results showed that the bio-clogging mass of per area in MSW_G and BA_G was 49 ± 5 g/m2 and 57 ± 3 g/m2, respectively. Bio-clogging was dominated by live cells in both MSW_G and BA_G. The confocal laser scanning microscopy images revealed that live cells percentage was 46% in MSW_G, while it increased to 77% in BA_G. In contrast, the percentage of the dead cells was 47% and 9% in MSW_G and BA_G, respectively. The biofilm formed in BA _G was thinner and denser than that in MSW_G. Based on the microbial analysis, the biofilms of BA_G had a higher genetic amount and diversity than these of MSW_G. The total amount of extracellular polymeric substances in BA_G was 45.29 ± 4.52 mg/g volatile suspended solids, which was 1.5 times of that in MSW_G. The co-disposal of BA increased the microbial diversity and accelerated bio-clogging due to the high calcium concentration. These findings provide a better understanding of the bio-clogging characteristics, which is helpful to control bio-clogging in co-disposal landfills.

Laboratory investigation on Bacillus subtilis addition to alleviate bio-clogging for constructed wetlands.

Bio-clogging is a major problem in the operation of constructed wetlands (CWs) and is caused by accumulation of biofilm and extracellular polymeric substances (EPS) in the substrate. B. subtilis can successfully produce α-amylase and endoglucanase, which can degrade polysaccharides and, consequently, disperse the EPS. Therefore, the addition of B. subtilis was used to decrease the bio-clogging of lab-scale vertical-flow constructed wetlands (VFCW) in this study, and the feasibility and performance of VFCWs were assessed. The results indicate that the addition of B. subtilis can degrade the polysaccharides in the clogging matter and thereby increase the porosity of the substrate. The hydraulic conductivity of Column 1 (with addition) increased by six times, which was 57 times that of control (Column 2). Meanwhile, the chemical oxygen demand (COD) removal rate also increased after the addition of B. subtilis. The microbial communities show that the richness and diversity within the substrate increased after addition. The relative abundance of functional groups of chemoheterotrophy, aerobic chemoheterotrophy, as well as that connected to N cycles also increased, which implied the improvement of the pollution removal efficiency. Meanwhile, the copy number of α-amylase and endoglucanase increased significantly in Column 1 with the addition of B. subtilis, which offers further support for a hydrolase-induced reduction of polysaccharides and the efficiency of B. subtilis on bio-clogging alleviation. The results showed that B. subtilis addition is an effective and safe solution to control the bio-clogging for CWs. However, further research about long-term effect assessment and dosing strategy optimization should be conducted.