Biodegradation of low aqueous concentration pentachlorophenol (PCP) contaminated groundwater

Interpretable machine learning for predicting the fate and transport of pentachlorophenol in groundwater

Pentachlorophenol (PCP) is a commonly found recalcitrant and toxic groundwater contaminant that resists degradation, bioaccumulates, and has a potential for long-range environmental transport. Taking proper actions to deal with the pollutant accounting for the life cycle consequences requires a better understanding of its behavior in the subsurface. We recognize the huge potential for enhancing decision-making at contaminated groundwater sites with the arrival of machine learning (ML) techniques in environmental applications. We used ML to enhance the understanding of the dynamics of PCP transport properties in the subsurface, and to determine key hydrochemical and hydrogeological drivers affecting its transport and fate. We demonstrate how this complementary knowledge, provided by data-driven methods, may enable a more targeted planning of monitoring and remediation at two highly contaminated Swedish groundwater sites, where the method was validated. We evaluated 6 interpretable ML methods, 3 linear regressors and 3 non-linear (i.e., tree-based) regressors, to predict PCP concentration in the groundwater. The modeling results indicate that simple linear ML models were found to be useful in the prediction of observations for datasets without any missing values, while tree-based regressors were more suitable for datasets containing missing values. Considering that missing values are common in datasets collected during contaminated site investigations, this could be of significant importance for contaminated site planners and managers, ultimately reducing site investigation and monitoring costs. Furthermore, we interpreted the proposed models using the SHAP (SHapley Additive exPlanations) approach to decipher the importance of different drivers in the prediction and simulation of critical hydrogeochemical variables. Among these, sum of chlorophenols is of highest significance in the analyses. Setting that aside from the model, tetra chlorophenols, dissolved organic carbon, and conductivity found to be of highest importance. Accordingly, ML methods could potentially be used to improve the understanding of groundwater contamination transport dynamics, filling gaps in knowledge that remain when using more sophisticated deterministic modeling approaches.

DynSus: Dynamic sustainability assessment in groundwater remediation practice

Decision-making processes for clean-up of contaminated sites are often highly complex and inherently uncertain. It depends not only on hydrological and biogeochemical site variability, but also on the associated health, environmental, economic, and social impacts of taking, or not taking, action. These variabilities suggest that a dynamic framework is required for promoting sustainable remediation. For this, the decision support system DynSus is presented here for integrating a predeveloped contaminant fate and transport model with a sustainability assessment tool. Implemented within a system dynamics framework, the new tool uses model simulations to provide remediation scenario analysis and handling of uncertainty in various data. DynSus was applied to a site in south Sweden, contaminated with pentachlorophenol (PCP). Simulation scenarios were developed to enable a comparison between alternative remediation strategies and combinations of these. Such comparisons are provided for selected sustainability indicators and remediation performance (in terms of concentration at the recipient). This leads to identifying the most critical variables to ensure that sustainable solutions are chosen. Simulation results indicated that although passive practices, e.g., monitored natural attenuation, were more sustainable at first (5-7 years after beginning remediation measures), they failed to compete with more active practices, e.g., bioremediation, over the entire life cycle of the project (from the beginning of remedial action to achieving the target concentration at the recipient). In addition, statistical tools (clustering and genetic algorithms) were used to further assess the available hydrogeochemical data. Taken together, the results reaffirmed the suitability of the simple analytical framework that was implemented in the contaminant transport model. DynSus outcomes could therefore enable site managers to evaluate different scenarios more quickly and effectively for life cycle sustainability in such a complex and multidimensional problem.

INSIDE-T: A Groundwater Contamination Transport Model for Sustainability Assessment in Remediation Practice

Current sustainability assessment (SA) tools to help deal with contaminated groundwater sites are inherently subjective and hardly applied. One reason may be lack of proper tools for addressing contaminant spread which are basically objective. To fill this gap, there is a need for contaminant transport models that provide site managers with needed room for applying their judgments and considerations about the efficiency of each remediation method based on their experiences in similar cases. INSIDE-T uses trend analysis and inverse modeling to estimate transport parameters. It then simulates contaminant transport both with and without the inclusion of remedial actions in a transparent way. The sustainability of each remedy measure can then be quantified based on the underlying SA tool (INSIDE). INSIDE-T was applied to a site in south Sweden, contaminated with pentachlorophenol. Simulation scenarios were developed to enable comparison between various remediation strategies and combinations of these. The application indicated that natural attenuation was not a viable option within the timeframe of interest. Although pump-and-treat combined with a permeable reactive barrier was found to be just as effective as bioremediation after five years, it received a much lower sustainability score overall. INSIDE-T outcomes enable site managers to test and evaluate different scenarios, a necessity in participatory decision-making practices such as remediation projects.

In-situ generated H₂O₂ induced efficient visible light photo-electrochemical catalytic oxidation of PCP-Na with TiO₂

In this study, we developed a novel photo-electrochemical catalytic oxidation wastewater treatment system by interacting the cathodic in-situ generated H₂O₂ with TiO₂ suspension to form interfacial ≡ Ti(IV)OOH species, which endowed the PEC system with superior efficiency for degrading sodium pentachlorophenate (PCP-Na) under visible light irradiation at neutral pH. The apparent PCP-Na degradation rate constant of the PEC system was more than 10 times that of the electrochemical oxidation counterpart. In the PEC system, the interfacial ≡ Ti(IV)OOH species injected electrons to the conduction band of TiO₂ to initiate the activation of O₂ and the in-situ generated H₂O₂ adsorbed on the surface of TiO₂, lead to producing reactive oxygen species of superoxide anions and hydroxyl radicals, which were responsible for the dechlorination and mineralization of PCP-Na during the PEC process, respectively. The dosage of TiO₂ catalyst and the current intensity applied on PCP-Na degradation were optimized. This study develops a high efficient PEC oxidation system for wastewater treatment and provides new insight into the role of cathodic in-situ generated H₂O₂ on PEC oxidation of PCP-Na with TiO₂ under visible light irradiation.

Simultaneous removal of nitrate and pentachlorophenol from simulated groundwater using a biodenitrification reactor packed with corncob

Both nitrate and pentachlorophenol (PCP) are familiar pollutants in aqueous environment. This research is focused on the simultaneous removal of nitrate and PCP from simulated contaminated groundwater using a laboratory-scale denitrification reactor packed with corncob as both carbon source and biofilm support. The reactor could be started up readily, and the removal efficiencies of nitrate and PCP reached up to approximately 98% and 40-45% when their initial concentrations were 50 mg N/L and 5 mg/L, respectively, after 15-day continuous operation at 10 h of hydraulic retention time (HRT) and 25 °C. Approximately 91% of PCP removal efficiency was achieved, with 2.47 mg/L of chloride ion release at 24 h of HRT. Eighty-two percent of chlorine in PCP removed was ionized. The productions of 3-chlorophenol and phenol and chloride ion release indicate that the reductive dechlorination reaction is a major degradation pathway of PCP under the experimental conditions.

Enhancing the antibacterial activity of biomimetic HA coatings by incorporation of norvancomycin

BACKGROUND

Bacterial infections associated with the use of biomaterials remain a great challenge for orthopedic surgery. The main purpose of the work discussed in this paper was to improve the antibacterial activity of a biomimetic calcium phosphate (CP) coating widely used in orthopedic biomaterials by incorporation of norvancomycin in the biomimetic process.

METHODS

CP coating and CP coating containing norvancomycin were produced on a titanium alloy (Ti6Al4V) surface by a biomimetic process. The morphology, surface crystal structure, and concentrations of elements in the coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX), respectively. The amount of norvancomycin and its release were investigated by UV-visible spectroscopy. MTT was used to investigate cell behavior. The morphology of adhered bacteria was observed by SEM. Antibacterial activity was expressed as inhibition zone by using Staphylococcus aureus (ATCC 25923) as model bacteria.

RESULTS

Results from SEM, EDX, and XRD revealed formation of a hydroxyapatite (HA) coating. The amount of antibiotic in the CP coating increased with increasing concentration of norvancomycin in the coating solution, followed by a plateau when the concentration of norvancomycin in the coating solution reached 600 mg/l. Approximately 2.16 μg norvancomycin per mg coating was co-precipitated with the CP layer onto titanium alloy discs when 600 mg/l norvancomycin coating solution was applied. The norvancomycin had a fast release profile followed by slow release. The MTT test of osteoblast cell cultures suggested that coatings containing norvancomycin did not cause any cytotoxicity compared with the CP coating and control titanium plate. The antibacterial activity test showed that the norvancomycin released from the coatings inhibited the growth of Staphylococcus aureus; more bacteria were found on the CP coating than on the norvancomycin-loaded coating.

CONCLUSIONS

A norvancomycin-loaded HA-like coating was successfully obtained on titanium surfaces. The norvancomycin incorporated had no negative effects on osteoblast cell behavior. The released norvancomycin results in excellent antibacterial activity of Ca-P coatings. Therefore, incorporation of norvancomycin can enhance antibacterial activity and the norvancomycin-loaded CP coating can be used to inhibit post-surgical infections in orthopaedics.

The role of decision support for bioremediation strategies, exemplified by hydrocarbons for in site and ex situ procedures

Despite the widespread availability of state-of-the-art biological techniques, remediation practitioners have been slow to adopt these technologies to assist in designing or indeed monitoring remediation strategies. In part, this is because practitioners are driven by cost and fail to see the benefit of emerging technologies, and in part because most companies have only a small portfolio of procedures available to them. Here, we review the component parts required to design a decision support tool, appraise one that the authors have developed and critically evaluate its application to case studies. If bioremediation is to become adopted, then it is likely to have to operate in parallel with other remediation methods. Furthermore, remediation strategies must couple effective technology with a transparency of information such that all parties (practitioners, developers and stakeholders) understand how decisions were reached.

In situ bioremediation of monoaromatic pollutants in groundwater: a review

Monoaromatic pollutants such as benzene, toluene, ethylbenzene and mixture of xylenes are now considered as widespread contaminants of groundwater. In situ bioremediation under natural attenuation or enhanced remediation has been successfully used for removal of organic pollutants, including monoaromatic compounds, from groundwater. Results published indicate that in some sites, intrinsic bioremediation can reduce the monoaromatic compounds content of contaminated water to reach standard levels of potable water. However, engineering bioremediation is faster and more efficient. Also, studies have shown that enhanced anaerobic bioremediation can be applied for many BTEX contaminated groundwaters, as it is simple, applicable and economical. This paper reviews microbiology and metabolism of monoaromatic biodegradation and in situ bioremediation for BTEX removal from groundwater under aerobic and anaerobic conditions. It also discusses the factors affecting and limiting bioremediation processes and interactions between monoaromatic pollutants and other compounds during the remediation processes.

E. coli adhesion to silica in the presence of humic acid

The influence of humic acid on the adhesion of Escherichia coli to silica particles or glass surfaces was investigated. After adsorbing various amounts of humic acid to the particles or surfaces, bacteria were added to the sample and allowed to adhere. For the silica particles the number of bacteria-particle couplets formed were counted from video microscopy images. For the glass surfaces, a differential electrophoresis force was applied, and the force required to detach the bacteria was quantified. These experiments showed a slight increase in the number of couplets formed in the presence of humic acid, and also showed a slight increase in the force required for detachment of the bacteria. Although an increase in adhesion number and strength was measured, the magnitude of the increase was small, indicating that humic acid plays a small role in bacterial adhesion to silica or glass surfaces.