Different transport behaviors of Bacillus subtilis cells and spores in saturated porous media: Implications for contamination risks associated with bacterial sporulation in aquifer

Transport and removal of spores of Bacillus subtilis in an alluvial gravel aquifer at varying flow rates and implications for setback distances

To guarantee proper protection from fecally transmitted pathogen infections, drinking water wells should have a sufficiently large setback distance from potential sources of contamination, e.g. a nearby river. The aim of this study was to provide insight in regards to microbial contamination of groundwater under different flow velocities, which can vary over time due to changes in river stage, season or pumping rate. The effects of these changes, and how they affect removal parameters, are not completely understood. In this study, field tracer tests were carried out in a sandy gravel aquifer near Vienna, Austria to evaluate the ability of subsurface media to attenuate Bacillus subtilis spores, used as a surrogate for Cryptosporidium and Campylobacter. The hydraulic gradient between injection and extraction was controlled by changing the pumping rate (1, 10 l/s) of a pumping well at the test site, building upon previously published work in which tracer tests with a 5 l/s pumping rate were carried out. Attachment and detachment rate coefficients were determined using a HYDRUS-3D model and ranged from 0.12 to 0.76 and 0-0.0013 h^-1, respectively. Setback distances were calculated based on the 60-day travel time, as well as a quantitative microbial risk assessment (QMRA) approach, which showed similar results at this site; around 700 m at the highest pumping rate. Removal rates (λ) in the field tests ranged from 0.2 to 0.3 log/m, with lower pumping rates leading to higher removal. It was shown that scale must be taken into consideration when determining λ for the calculation of safe setback distances.

Mechanism insights into bacterial sporulation at natural sphalerite interface with and without light irradiation: The suppressing role in bacterial sporulation by photocatalysis

Unveiling the mechanisms of bacterial sporulation at natural mineral interfaces is crucial to fully understand the interactions of mineral with microorganism in aquatic environment. In this study, the bacterial sporulation mechanisms of Bacillus subtilis (B. subtilis) at natural sphalerite (NS) interface with and without light irradiation were systematically investigated for the first time. Under dark condition, NS was found to inactivate vegetative cells of B. subtilis and promote their sporulation simultaneously. The released Zn2+ from NS was mainly responsible for the bacterial inactivation and sporulation. With light irradiation, the photocatalytic effect from NS could increase the bacterial inactivation efficiency, while the bacterial sporulation efficiency was decreased from 8.1 % to 4.5 %. The photo-generated H2O2 and O2- played the major roles in enhancing bacterial inactivation and suppressing bacterial sporulation process. The intracellular synthesis of dipicolinic acid (DPA) as biomarker for sporulation was promoted by NS in dark, which was suppressed by the photocatalytic effect of NS with light irradiation. The transformation process from vegetative cells to spores was monitored by both 3D-fluerecence EEM and SEM observations. Compared with the NS alone system, the NS/light combined system induced higher level of intracellular ROSs, up-regulated antioxidant enzyme activity and decreased cell metabolism activity, which eventually led to enhanced inactivation of vegetative cells and suppressed bacterial sporulation. These results not only provide in-depth understanding about bacterial sporulation as a new mode of sub-lethal stress response at NS interface, but also shed lights on putting forward suitable strategies for controlling spore-producing bacteria by suppressing their sporulation during water disinfection.

Distribution, Genesis, and Human Health Risks of Groundwater Heavy Metals Impacted by the Typical Setting of Songnen Plain of NE China

Heavy metals pollution in groundwater and the resulting health risks have always been an environmental research hotspot. However, the available information regarding this topic and associated methods is still limited. This study collected 98 groundwater samples from a typical agricultural area of Songnen Plain in different seasons. The pollution status and sources of ten heavy metals (As, Ba, Cd, Co, Cr (VI), Cu, Fe, Mn, Ni, Pb, and Zn) were then analyzed and compared. In addition, the human health risks assessment (HHRA) model was used to calculate human health risks caused by heavy metals in groundwater. The results revealed that heavy metals were mainly distributed in the northwest of the study area and along the upper reaches of the Lalin river and that the concentrations of heavy metals were higher during the wet season than the dry season. Industrial and agricultural activities and natural leaching are the main sources, and each kind of heavy metal may have different sources. Fe and Mn are the primary pollutants, mainly caused by the native environment and agricultural activities. The exceeding standard rates are 71.74% and 61.54%, respectively based on the Class III of Quality Standard for Groundwater of China (GB/T 14848-2017). The maximum exceeding multiple are 91.45 and 32.05, respectively. The health risks of heavy metals borne by different groups of people were as follows: child > elder > young > adult. Carcinogenic heavy metals contribute to the main risks, and the largest risks sources are Cr and As. Therefore, the government should appropriately restrict the use of pesticides and fertilizers, strictly manage the discharge of enterprises, and control man-made heavy metals from the source. In addition, centralized water supply and treatment facilities shall be established to prevent the harm of native heavy metals.

Physical Clogging Characteristics and Water Quality Variations by Injecting Secondary Effluent into Porous Media: A Laboratory Column Study

Artificial recharge engineering has been widely used to solve the water resource crisis. However, there are still some safety hazards regarding reclaimed water quality. Here, chlorinated secondary effluent (SE) was injected into saturated porous media composed of high–purity quartz sands. The column experiment was conducted and modeled through a developed numerical model to predict the evolution of physical clogging. Some representative inorganic and organic indicators were measured both at different times and in different column sections. The study showed that the relative hydraulic conductivity (K/K0) decreased significantly by approximately 63.5% in 40 h. Especially for the first 3 cm of the column, the clogging was the most serious, with a decrease of approximately 85.8%. The porous media has a certain degree of filtration effect on turbidity, TOC, protein (Pr) and polysaccharide (PS) but has slight removal for other water quality indicators. Pr is the main component of the intercepted TOC, and its content is higher than that of Ps. Moreover, the inorganic and organic parameter variations along the column further verified that the organic floc particles were mainly retained in the first 3 cm. The 3D excitation/emission matrix (3DEEM) fluorescence spectra illustrated that the humic acids and fulvic acids were easy to release and that their injection may be harmful to groundwater quality. The study will lay a theoretical foundation and provide a guiding scheme for optimizing China’s reclaimed water reuse technology, ensuring the safety of reclaimed water quality.

Detection of low numbers of bacterial cells in a pharmaceutical drug product using Raman spectroscopy and PLS-DA multivariate analysis

Fast and non-invasive approach to detect drug product (DP) samples with low numbers of bacteria within the primary packaging. The method combines Raman spectroscopy and partial least squared discriminant analysis (RS-PLS-DA).

Bactericidal efficiency and photochemical mechanisms of micro/nano bubble-enhanced visible light photocatalytic water disinfection

Microbial contamination of water in the form of highly-resistant bacterial spores can cause a long-term risk of waterborne disease. Advanced photocatalysis has become an effective approach to inactivate bacterial spores due to its potential for efficient solar energy conversion alongside reduced formation of disinfection by-products. However, the overall efficiency of the process still requires significant improvements. Here, we proposed and evaluated a novel visible light photocatalytic water disinfection technology by its close coupling with micro/nano bubbles (MNBs). The inactivation rate constant of Bacillus subtilis spores reached 1.28 h^-1, which was 5.6 times higher than that observed for treatment without MNBs. The superior performance for the progressive destruction of spores' cells during the treatment was confirmed by transmission electron microscopy (TEM) and excitation-emission matrix (EEM) spectra determination. Experiments using scavengers of reactive oxygen species (ROSs) revealed that H₂O₂ and •OH were the primary active species responsible for the inactivation of spores. The effective supply of oxygen from air MNBs helped accelerate the hole oxidation of H₂O₂ on the photocatalyst (i.e. Ag/TiO₂). In addition, the interfacial photoelectric effect from the MNBs was also confirmed to contribute to the spore inactivation. Specifically, MNBs induced strong light scattering, consequently increasing the optical path length in the photocatalysis medium by 54.8% at 700nm and enhancing light adsorption of the photocatalyst. The non-uniformities in dielectricity led to a high-degree of heterogeneity of the electric field, which triggered the formation of a region of enhanced light intensity which ultimately promoted the photocatalytic reaction. Overall, this study provided new insights on the mechanisms of photocatalysis coupled with MNB technology for advanced water treatment.

Transport and Retention of Free-Living Amoeba Spores in Porous Media: Effects of Operational Parameters and Extracellular Polymeric Substances

Amoebas are protists that are widespread in water and soil environments. Some species are pathogenic, inducing potentially lethal effects on humans, making them a major threat to public health. Nonpathogenic amoebas are also of concern because they have the potential to carry a mini-microbiome of bacteria, either transiently or via more long-term stable transport. Due to their resistance to disinfection processes, the physical removal of amoeba by filtration is necessary to prevent their propagation throughout drinking water distribution networks and occurrence in tap water. In this study, a model amoeba species Dictyostelium discoideum was used to study the transport and retention behavior of amoeba spores in porous media. The key factors affecting the transport behavior of amoeba spores in fully saturated media were comprehensively evaluated, with experiments performed using a quartz crystal microbalance with dissipation monitoring (QCM-D) and parallel plate chamber system. The effects of ionic strength (IS) on the deposition of spores were found to be in contrast to the predicted Derjaguin-Landau-Verwey-Overbeek (DLVO) theory that more deposition is observed under lower-IS conditions. The presence of extracellular polymeric substances (EPS) was found to be the main contributor to deposition behavior. Overall, these results provide plausible evidence for the presence of amoeba in tap water. Furthermore, this is one of the first studies to examine the mechanisms affecting the fate of amoeba spores in porous media, providing a significant baseline for future research to minimize the safety risk presented by amoeba in drinking water systems.

Acceleration of saturated porous media clogging and silicon dissolution due to low concentrations of Al(III) in the recharge of reclaimed water

The recharge of reclaimed water is an effective strategy for addressing the issues of water quality deterioration and groundwater level decline simultaneously. Residual Al coagulants are normally remained in the recovered water at low concentrations, and may induce clogging problems during the recharging process. However, this issue has been ignored in the past. In this study, we investigated the mechanisms of Al(III)-induced aquifer bio-clogging, the role of Al(III) in quartz sand media (SiO₂) dissolution and re-precipitation in the series of aquifer columns. We determined that Al(III) resulted in serious clogging in ∼140 h at low concentrations that satisfied the national drinking water standard of China. The corresponding hydraulic conductivity decreased by more than ∼90% in the bacteria-containing aquifer, which was ∼30% greater than that for the bacteria-free trials. The enhanced Al(III)-related clogging was caused by modifying quartz sand to form Si-O-Al(OH)n and improving microbes attachment. Microbes retention kinetic coefficients (k) of the Al recharged simulated aquifer could increase by 3.0-8.3 times. The Al(III) also enhanced biomass production and clogging by binding to microbial extracellular polymeric substances. In turn, the greater amount of biomass accelerated the Si dissolution and re-precipitation, this may potentially damage the stability of aquifer structure. The results showed that reclaimed water treated with Al coagulation should be employed with caution for recharging.