First-order Decay Rate Research Articles

Study of pollutant transport under linear sorption in a groundwater reservoir

Abstract Pollutant dispersion in a porous medium can be modelled mathematically to forecast its concentration distribution profile. The governing equation of pollutant transport is modelled as a partial differential equation. Effects of sorption, zero-order production rate and first-order decay rate on pollutant transport are incorporated in the present study. The temporarily dependent pulse-type input source decaying exponentially is assumed at the origin of the domain. The solution of the proposed transport equation is derived by Laplace transform method for the respective time split domain. Matlab algorithm is developed to illustrate the obtained analytical solutions graphically for various hydrological input data. The pollutant distribution profiles in the medium are obtained for different times and porosities. The pollutant transport nature is examined for various forms of velocity flow pattern in presence and absence of input source. Also, the derived solution is compared graphically under special case with the existing solution and found the results with good agreement.

A data-driven approach for simplifying the estimation of time for contaminant plumes to reach their maximum extent

Globally there exist a very large number of contaminated or possibly contaminated sites where a basic preliminary assessment has not been completed. This is largely, among others, due to limited simple methods/models available for estimating key site quantities such as the maximum plume length, further denoted as Lmax and the corresponding time T=TLmax, at which the plume reaches its maximum extent L=Lmax. An approach to easily obtain an estimate of TLmax in particular is presented in this work. Limited availability of high-quality field data, particularly of TLmax, necessitates the use of synthetic data, which constrains the overall model development works. Taking BIOSCREEN-AT (transient 3D model) as a base model, this work proposes second-order polynomial models, with only two parameters, for estimating Lmax and TLmax. This reformulation of the well established solution significantly reduces data requirement and workload for initial site assessment purposes. A global sensitivity analysis (Morris, 1991), using a large number of random synthetic data, identifies the first-order decay rate constants in the plume λEFF and at the source γ as dominantly most influential for TLmax. For Lmax, the first-order decay rate constant λEFF and groundwater velocity v are the two important parameters. The sensitivity analysis also identifies that these parameters non-linearly impact TLmax or Lmax. With this information, the proposed polynomial models (each for Lmax and TLmax) were trained to obtain model coefficients, using a large amount of synthetic data. For verification, the developed models were tested using four datasets comprising over 100 sample sets against the results obtained from BIOSCREEN-AT and the developed BIOSCREEN-AT-based steady-state model. Additionally, the developed models were evaluated against two well documented field sites. The proposed models largely simplify estimation, particularly, of TLmax, for which only very limited field or literature information is available.

Cu fractions in Shiraz and Pinot Noir wines during bottle aging: rates of changes and capacity for conversion

The Cu fraction in wine associated with Cu(II)-organic acid complexes can suppress detrimental aromas attributed to hydrogen sulfide and methanethiol. However, the long-term stability of this Cu fraction (known as Cu fraction I) during bottle aging of red wine is not well understood. This study utilised Pinot Noir and Shiraz wines containing 0.43 ± 0.01 and 0.56 ± 0.02 mg/L respectively of total Cu, to which 0, 0.3 or 0.6 mg/L Cu(II) was further added immediately before bottling. The bottles were then stored at 14 °C for 1 yr. Cu fraction I concentrations were measured using two independent methods: i) stripping potentiometry, and ii) ICP-OES analysis of filtrate after diatomaceous earth depth filtration. Within the first 6 months of storage, Cu fraction I was found to decrease in all wines. Using stripping potentiometry, the first-order decay rates were found to be 0.012 ± 0.001 day-1 and 0.010 ± 0.001 day-1 for Pinot Noir and Shiraz respectively, corresponding to half-lives of 55 ± 4 and 67 ± 9 days. The decay rates for Shiraz versus Pinot Noir were similar for wines with different Cu addition rates, or when rates were determined using the different analysis techniques. Both wines had a high capacity for conversion of Cu fraction I to Cu fraction III during the 1-yr storage period, with 0.4-0.8 mg/L Cu forming Cu fraction III in the Pinot Noir, and 0.3-0.6 mg/L in the Shiraz. These conversion capacity ranges are higher than the typical Cu(II) additions made to wine during production. Overall, the results show that red wine has a large capacity for enabling the sulfide-binding of Cu-organic acid complexes during bottle aging and the conversion occurs at a relatively uniform rate with the concentration halving approximately every 2 months.

Machine-learning-assisted prediction and optimized kinetic modelling of residual chlorine decay for enhanced water quality management

The quality of water changes from source to tap, presenting challenges in maintaining consistent water quality across the system. Predicting water quality in distribution systems, including disinfectant residual loss and by-product formation, has been the subject of research since the early 1990s. Although numerous models have been proposed to predict residual chlorine decay, disputes exist among researchers and experts over the superiority of certain models. Accordingly, this study modified the existing process-based bulk decay models by replacing the initial Total Residual Chlorine (TRC) concentration parameter with TRC demand, leading to an improvement in the models' performance. The modification resulted in a 38.03%, 28.02%, 23.11%, and 33.29% average improvement in Mean Squared Error (MSE) values for the First Order Model (FOM), Parallel First Order Model (PFOM), Second Order Model (SOM), and Parallel Second Order Model (PSOM), respectively. The study also introduced an online predictive method based on a Machine Learning (ML) algorithm that predicts the first-order TRC bulk decay rate by using water quality parameters as inputs. A Gaussian Process Regression (GPR) model was used to predict the kinetic parameters in FOM, which accurately predicted the test sets for most of the cases. In addition, a new methodology was proposed in this study for predicting TRC in water distribution systems that incorporates the variability of source natural organic matter, operational actions, and water demands. This method seeks to develop high-fidelity and robust water quality predictions that provide operational decision support for optimized distribution system management. In conclusion, this study emphasizes the importance of understanding water quality changes from source to tap and the challenges of maintaining consistent water quality across the system. The study suggests modifying existing models and introducing a novel methodology for predicting residual chlorine in water distribution systems that can improve water quality management and, ultimately, better public health outcomes.

Sunlight photolysis of SARS-CoV-2 N1 gene target in the water environment: considerations for the environmental surveillance of wastewater-impacted surface waters.

Wastewater surveillance of SARS-CoV-2 has been used around the world to supplement clinical testing data for situational awareness of COVID-19 disease trends. Many regions of the world lack centralized wastewater collection and treatment infrastructure, which presents additional considerations for wastewater surveillance of SARS-CoV-2, including environmental decay of the RT-qPCR gene targets used for quantification of SARS-CoV-2 virions. Given the role of sunlight in the environmental decay of RNA, we evaluated sunlight photolysis kinetics of the N1 gene target in heat-inactivated SARS-CoV-2 with a solar simulator under laboratory conditions. Insignificant photolysis of the N1 target was observed in a photosensitizer-free matrix. Conversely, significant decay of the N1 target was observed in wastewater at a shallow depth (<1 cm). Given that sunlight irradiance is affected by several environmental factors, first-order decay rate models were used to evaluate the effect of water column depth, time of the year, and latitude on decay kinetics. Decay rate constants were found to decrease significantly with greater depth of the well-mixed water column, at high latitudes, and in the winter. Therefore, sunlight-mediated decay of the N1 gene target is likely to be minimal, and is unlikely to confound results from wastewater-based epidemiology programs utilizing wastewater-impacted surface waters.

On the increasing competitiveness of UV/Cl to UV/H2O2 advanced oxidation as the organic carbon concentration increases

UV/Cl and UV/H2O2 are advanced oxidation processes (AOPs) used for drinking water treatment and water reuse. This work explored the hypothesis that UV/Cl becomes more competitive to UV/H2O2 at neutral-to-high pH as the concentration of total organic carbon (TOC) increases. Lab experiments and kinetic modelling were used to compare initial pseudo first-order contaminant decay rate coefficients between the AOPs at various pH and TOC conditions. The relative effect of increasing TOC concentrations on UV/Cl vs. UV/H2O2 depended on the pH, contaminant, and organic matter reactivity towards radicals. For example, while the reaction rate coefficients during both AOPs generally decreased with increasing TOC, the UV/Cl reaction rate coefficients for the solely •OH-reactive sucralose decreased 41–138% less than the UV/H2O2 coefficients as the TOC concentration was increased from 0 to 5 mg-C L−1. However, UV/Cl was more affected than UV/H2O2 when targeting caffeine (a contaminant reactive to chlorine radicals). The data were used to define TOC-pH conditions for which either AOP would be more energy-efficient, under a set of standard conditions. The results suggest that UV/Cl may be competitive to UV/H2O2 under a wider range of treatment scenarios than has been conventionally thought based on tests in pure water.

Decay of enveloped SARS-CoV-2 and non-enveloped PMMoV RNA in raw sewage from university dormitories.

Although severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) RNA has been frequently detected in sewage from many university dormitories to inform public health decisions during the COVID-19 pandemic, a clear understanding of SARS-CoV-2 RNA persistence in site-specific raw sewage is still lacking. To investigate the SARS-CoV-2 RNA persistence, a field trial was conducted in the University of Tennessee dormitories raw sewage, similar to municipal wastewater. The decay of enveloped SARS-CoV-2 RNA and non-enveloped Pepper mild mottle virus (PMMoV) RNA was investigated by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) in raw sewage at 4°C and 20°C. Temperature, followed by the concentration level of SARS-CoV-2 RNA, was the most significant factors that influenced the first-order decay rate constants (k) of SARS-CoV-2 RNA. The mean k values of SARS-CoV-2 RNA were 0.094 day-1 at 4°C and 0.261 day-1 at 20°C. At high-, medium-, and low-concentration levels of SARS-CoV-2 RNA, the mean k values were 0.367, 0.169, and 0.091 day-1, respectively. Furthermore, there was a statistical difference between the decay of enveloped SARS-CoV-2 and non-enveloped PMMoV RNA at different temperature conditions. The first decay rates for both temperatures were statistically comparable for SARS-CoV-2 RNA, which showed sensitivity to elevated temperatures but not for PMMoV RNA. This study provides evidence for the persistence of viral RNA in site-specific raw sewage at different temperature conditions and concentration levels.

Experimental study of the disinfection performance of a 222-nm Far-UVC upper-room system on airborne microorganisms in a full-scale chamber

222-nm Far-UVC light is an emerging and promising tool for rapidly inactivating airborne pathogens. In this study, we experimentally evaluated the performance of a 222-nm Far-UVC upper-room disinfection system with a 15 W Far-UVC lamp in a full-scale chamber (11.9 m3). One gram-positive bacteria, namely Staphylococcus epidermidis and two gram-negative bacteria, namely Escherichia coli and Salmonella enterica were selected for the experiments. The aerosolized bacteria were injected into the chamber and exposed to 222-nm Far-UVC light. The first-order decay rates of indoor bioaerosols concentration with and without Far-UVC treatment were estimated. According to the results, the 222-nm Far-UVC induced decay rates of three bacteria were 0.0611 ± 0.003, 0.409 ± 0.048, and 0.474 ± 0.015 min−1, respectively. Besides, the UV susceptibility constants (Z-values) of these three bacteria were estimated as 0.157, 0.974, and 1.18 m2/J, respectively. The gram-positive bacteria, S. epidermidis, showed higher resistance to Far-UVC light as compared to the gram-negative bacteria, E. coli and S. enterica. In addition, a case study on airborne SARS-CoV-2 indoor transmission was simulated, and the infection risk of SARS-CoV-2 was compared using the Far-UVC and enhanced ventilation approaches. The results showed that both UV inactivation and ventilation approaches can significantly reduce the infection risk. More importantly, the Far-UVC may be a feasible and sustainable solution for reducing infection risk and improving indoor air quality.

Influence of temperature and water quality on the persistence of human mitochondrial DNA, human Hf183 Bacteroidales, fecal coliforms and enterococci in surface water in human fecal source tracking context.

Mitochondrial DNA (mtDNA) is used as a genetic marker to track fecal contamination in surface water. Its potential to effectively discriminate between the nonpoint sources of fecal pollution (e.g. human, livestock) in water environments is relevant for water quality management. However, there is a lack of knowledge about the environmental persistence of mtDNA in relation to those of other microbial parameters, such as fecal indicator bacteria (FIB). In this study, mesocosms composed of water collected from four rivers and tap water were spiked with raw wastewater to mimic human fecal contamination. Mesocosms composed of raw wastewater were also studied. The mesocosms were incubated at 4 °C or at 22 °C for 189 days, from which the levels of human mtDNA (HumtDNA) and human Bacteroidales (Hf183) were measured by qPCR. The levels of FIB (fecal coliforms and enterococci) and heterotrophs were determined by culture methods along with the determination of physicochemical attributes. The decay rates of the genetic markers and FIB were determined with first-order decay rate models. The decay rates of HumtDNA (0.004-0.059 d-1), Hf183 (0.007-0.082 d-1), and the two FIBs (0.005-0.066 d-1) were similar at 4 °C, while the genetic markers both had higher decay rates (0.013-0.919 d-1) at 22 °C. Different HumtDNA decay rates were observed between the river mesocosms (0.043-0.919 d-1) and the wastewater and tap water mesocosms (0.004-0.095 d-1). Covariations of pH and conductivity among the HumtDNA, Hf183 and FIB decay rates were observed. HumtDNA and Hf183 had similar environmental persistence, whereas fecal coliforms and enterococci persisted longer at 22 °C. Finally, HumtDNA had the same trends of persistence in the four river mesocosms, suggesting a relative stability of this marker in different rivers. Our results suggest that HumtDNA could be more suitable for tracking the source of a recent fecal contamination in complement to FIB.

Denitrification kinetics during aquifer storage and recovery of drainage water from agricultural land

An aquifer storage transfer and recovery (ASTR) system was studied in which tile drainage water (TDW) was injected with relatively high NO3 (about 14 mg/L) concentrations originating from fertilizers. Here we present the evolution of denitrification kinetics at 6 different depths in the aquifer before, and during ASTR operation. First-order denitrification rate constants increased over time before and during the first days of ASTR operation, likely due to microbial adaptation of the native bacterial community and/or bioaugmentation of the aquifer by denitrifying bacteria present in injected TDW. Push-pull tests were performed in the native aquifer before ASTR operation. Obtained first-order denitrification rate constants were negligible (0.00–0.03 d−1) at the start, but increased to 0.17–0.83 d−1 after a lag-phase of about 6 days. During the first days of ASTR operation in autumn 2019, the arrival of injected TDW was studied at 2.5 m distance from the injection well. First-order denitrification rate constants increased again over time (maximum >1 d−1). Three storage periods without injection were monitored in winter 2019, fall 2020, and spring 2021 during ASTR operation. First-order rate constants ranged between 0.12 and 0.61 d−1. Denitrification coupled to pyrite oxidation occurred at all depths, but other oxidation processes were indicated as well. NO3 concentration trends resembled Monod kinetics but were fitted also to a first-order decay rate model to facilitate comparison. Rate constants during the storage periods were substantially lower than during injection, probably due to a reduction in the exchange rate between aquifer solid phases and injected water during the stagnant conditions. Denitrification rate constants deviated maximally a factor 5 over time and depth for all in-situ measurement approaches after the lag-phase. The combination of these in-situ approaches enabled to obtain more detailed insights in the evolution of denitrification kinetics during AS(T)R.

Persistence of Endogenous SARS-CoV-2 and Pepper Mild Mottle Virus RNA in Wastewater-Settled Solids.

Limited information is available on the decay rate of endogenous SARS-CoV-2 and pepper mild mottle virus (PMMoV) RNA in wastewater and primary settled solids, potentially limiting an understanding of how transit or holding times within wastewater infrastructure might impact RNA measurements and their relationship to community COVID-19 infections. In this study, primary settled solids samples were collected from two wastewater treatment plants in the San Francisco Bay Area. Samples were thoroughly mixed, aliquoted into subsamples, and stored at 4, 22, and 37 °C for 10 days. The concentrations of SARS-CoV-2 (N1 and N2 targets) and PMMoV RNA were measured using an RT-ddPCR. Limited decay (<1 log10 reduction) was observed in the detection of viral RNA targets at all temperature conditions, suggesting that SARS-CoV-2 and PMMoV RNA can be highly persistent in solids. First-order decay rate constants ranged from 0.011 to 0.098 day–1 for SARS-CoV-2 RNA and from 0.010 to 0.091 day–1 for PMMoV RNA depending on the temperature conditions. A slower decay was observed for SARS-CoV-2 RNA in primary settled solids compared to previously reported decay in wastewater influent. Further research is needed to understand if solid content and wastewater characteristics might influence the persistence of viral RNA targets.

Modelling of autogenerative high-pressure anaerobic digestion in a batch reactor for the production of pressurised biogas

BackgroundPressurised anaerobic digestion allows the production of biogas with a high content of methane and, at the same time, avoid the energy costs for the biogas upgrading and injection into the distribution grid. The technology carries potential, but the research faces practical constraints by a.o. the capital investment needed in high-pressure reactors and sensors and associated sampling limitations. In this work, the kinetic model of an autogenerative high-pressure anaerobic digestion of acetate, as the representative compound of the aceticlastic methanogenesis route, in batch configuration, is proposed to predict the dynamic performance of pressurised digesters and support future experimental work. The modelling of autogenerative high-pressure anaerobic digestion in batch configuration, which is not extensively studied and simulated in the present literature, was developed, calibrated, and validated by using experimental results available from the literature.ResultsUnder high-pressure conditions, the assessment of the Monod maximum specific uptake rate, the half-saturation constant and the first-order decay rate was carried out, and the values of 5.9 kg COD kg COD−1 d−1, 0.05 kg COD m−3 and 0.02 d−1 were determined, respectively. By using the predicted values, excellent fittings of the final pressure, the CH4 molar fraction and the specific methanogenic yield calculation were obtained. Likewise, the variation in the gas–liquid mass transfer coefficient by several orders of magnitude showed negligible effects on the model predictive values in terms of methane molar fraction of the produced biogas, while the final pressure seemed to be slightly influenced.ConclusionsThe proposed model allowed to estimate the Monod maximum specific uptake rate for acetate, the half-saturation rate for acetate and the first-order decay rate constant, which were comparable with literature values reported for well-studied methanogens under anaerobic digestion at atmospheric pressure. The methane molar fraction and the final pressure predicted by the model showed different responses towards the variation of the gas–liquid mass transfer coefficient since the former seemed not to be affected by the variation of the gas–liquid mass transfer coefficient; in contrast, the final pressure seemed to be slightly influenced. The proposed approach may also allow to potentially identify the methanogens species able to be predominant at high pressure.

Estimation of chloramine decay in drinking water distribution systems

When compared to free chlorine, chloramines represent an established secondary disinfectant that may be utilized to reduce disinfection by-product formation and improve residual stability. Maintaining an acceptable residual in distribution systems however may be challenging due to potential high maintenance costs associated with uni-directional flushing and swabbing. This study was designed to identify the primary sources of chloramine demand for a distribution system receiving surface and groundwater. Decay in the bulk water was quantified using a bottle point method. Bench-scale pipe section reactors (PSRs) were utilized to evaluate decay associated with cast‑iron and polyvinyl chloride (PVC) pipe sections that had been harvested from a distribution system, as well as to allow comparisons with new pipe material. Bulk water decay was compared to that observed in PSRs at flow rates of 0.03 m/s and 0.09 m/s, representative of distribution system conditions. Pipe material type and associated surface conditions were identified as the most critical factors influencing decay. Observed first-order decay rates for harvested cast‑iron pipe with an established microbial community and metal/silicate scale were significantly higher than those for PVC. In contrast, first-order decay rates for harvested PVC were comparable to new pipe, with water velocity exerting a negligible impact. Overall, these results reinforce the importance of determining the primary sources of chloramine decay in distribution systems.

Evaluation of multiple analytical methods for SARS-CoV-2 surveillance in wastewater samples

In this study, 14 virus concentration protocols based on centrifugation, filtration, polyethylene glycol (PEG) precipitation and ultrafiltration were tested for their efficacy for the quantification of SARS-CoV-2 in wastewater samples. These protocols were paired with four RNA extraction procedures resulting in a combination of 50 unique approaches. Bovine respiratory syncytial virus (BRSV) was used as a process control and seeded in each wastewater sample subjected to all 50 protocols. The recovery of BRSV obtained through the application of 50 unique approaches ranged from <0.03 to 64.7% (±1.6%). Combination of centrifugation as the solid removal step, ultrafiltration (Amicon-UF-15; 100 kDa cut-off; protocol 9) as the primary virus concentration method, and Zymo Quick-RNA extraction kit provided the highest BRSV recovery (64.7 ± 1.6%). To determine the impact of prolonged storage of large wastewater sample volume (900 mL) at −20 °C on enveloped virus decay, the BRSV seeded wastewaters samples were stored at −20 °C up to 110 days and analyzed using the most efficient concentration (protocol 9) and extraction (Zymo Quick-RNA kit) methods. BRSV RNA followed a first-order decay rate (k = 0.04/h with r2 = 0.99) in wastewater. Finally, 21 wastewater influent samples from five wastewater treatment plants (WWTPs) in southern Maryland, USA were analyzed between May to August 2020 to determine SARS-CoV-2 RNA concentrations. SARS-CoV-2 RNA was quantifiable in 17/21 (81%) of the influent wastewater samples with concentration ranging from 1.10 (±0.10) × 104 to 2.38 (±0.16) × 106 gene copies/L. Among the RT-qPCR assays tested, US CDC N1 assay was the most sensitive followed by US CDC N2, E_Sarbeco, and RdRp assays. Data presented in this study may enhance our understanding on the effective concentration and extraction of SARS-CoV-2 from wastewater.

Preferential removal of benzene, toluene, ethylbenzene, and xylene (BTEX) by persulfate in ethanol-containing aquifer materials.

The effective approaches to eliminate impacts of ethanol on the biodegradation of benzene, toluene, ethylbenzene, and xylene (BTEX) are concerned in the bioremediation of groundwater contaminated with ethanol-blended gasoline. In situ chemical oxidation (ISCO) is a common technique widely used for the remediation of contaminated groundwater. However, the selectivity of ISCO for BTEX and ethanol removal is poorly understood. Therefore, a batch experiment was performed with different aquifer materials, including calcareous soil, basalt soil, granite soil, dolomite, and sand. Gasoline was used to provide dissolved BTEX and ethanol reagent was used as additive to improve the quality of gasoline and to reduce the possibility of air pollution caused by gasoline. Persulfate (PS) was used as a chemical oxidant to oxidize organic contaminants. The target concentrations of BTEX and ethanol were 20mg/L and 1000mg/L, respectively. The results showed that ethanol could be preferentially degraded in the absence of PS and inhibit BTEX biodegradation. However, BTEX could be preferentially removed prior to ethanol in all aquifer materials used at ambient temperature, when PS was added at a PS/BTEX molar ratio of 150. Over 94% BTEX in sand, dolomite, and granite soil was preferentially removed with the first-order decay rate constants of 0.890-2.703day-1 within the first ~ 10days, followed by calcareous and basalt soil at the constants of 0.123-0.371day-1. Ethanol could compete with BTEX for sulfate radical at the first-order decay rate constants of 0.005-0.060day-1 for the first 25days, which was slower than that of BTEX. The pH quickly decreased to < 2.5 in dolomite, sand, and granite soil, but maintained > 6.2 in calcareous soil. Rich organic matter in calcareous and basalt soil had an inhibition effect on BTEX oxidation by PS. The pH buffer in calcareous soil may imply the potential of PS oxidation combined with bioremediation in carbonate rock regions.

Anammox enrichment: impact of sludge retention time on nitrogen removal

ABSTRACT Enrichment of anammox bacteria has long been considered to be time-consuming because of the slow growth rate. This study evaluated the impact of sludge retention time (SRT) on the enrichment of anammox bacteria with a focus on nitrogen removal and specific anammox activity (SAA) in sequencing batch reactors (SBR). A total of eight different SRTs in the range of 30–1280 days at nitrogen loading rates (NLR) range from 12.1 to 122.1 mg/L-d were used to evaluate the anammox activity. SAA was negligible during the first 105 days due to denitrification and continued to increase thereafter to peak at 0.22 g N/g VSS-d on day 530 as the solids and hydraulic retention times (SRT and HRT) decreased from 120 to 80 days and 10 to 2 days, respectively. The stability of SAA (0.21 ± 0.02 g N/g VSS-d) from day 503 to day 670 indicates that anammox bacteria should be enriched at SRTs ranging from 30 to 80 days and NLR of 122.1 mg N/L-d. Moreover, the SBR achieved a maximum nitrogen removal efficiency of 86.6% at an SRT of 30 days and an NLR of 122 mg/L-d. Microbial analysis indicated that the two most abundant microorganisms accounting for 48% of the bacterial population are Anammoxoglobus followed by the heterotrophic denitrifier Rhizobiales. The maximum specific growth rate (was estimated as 0.062 d−1, consistent with typical of 0.057 d−1. The average first-order decay rate was estimated as 0.008 d−1, and the half-saturation constants (ks) averaged 16.2 mg NH4–N/L.

Remediation of weathered diesel-oil contaminated soils using biopile systems: An amendment selection and pilot-scale study

Weathered diesel oil (WDO) has less biodegradable and volatile characteristics, and its bioremediation could be a challenge. In this study, the effectiveness of enhanced bioremediation via biopile processes for the cleanup of WDO-contaminated soils was evaluated. Six biopiles were constructed and operated with the following six different amendments addition: red bran (12 kg), water-soluble fertilizer (20 L/week), highly oxygenated water (20 L/d, dissolved oxygen = 25 mg/L), petroleum hydrocarbon-degrading bacterial culture (20 L/week), mixture of the above amendments, and natural attenuation (no amendment). Each biopile contained 5 m3 [2.5 m (L) × 2 m (W) × 1 m (H)] of WDO-contaminated soils [initial total petroleum hydrocarbon (TPH) concentrations = 3015 to 3785 mg/kg]. Soils were mixed with amendments and tilled for air supplement twice a week with soil moisture around 25%. Metagenomics analyses were applied to determine the microbial biodiversity and strains responsible for hydrocarbon biodegradation. Results show that the biopile system with mixed supplements (mixture group) had the highest TPH removal efficiency (79% of TPH removal) followed by red bran addition group with a removal efficiency of approximately 73% during the 42-day operation. The first-order TPH decay rates in mixture and red bran biopiles were around 3.2 × 10−2 1/d, which was 4.8 times higher than that obtained from natural attenuation biopile. Biopiles with red bran and mixture supplements contained carbon substrates and nutrients, which could effectively activate microbial activities and accelerate the TPH biodegradation. High carbon number compounds (C > 20) in WDO could be biodegraded within 24 days in the biopile with mixed amendments. Results from metagenomics study indicate that Sphingomonas and Pseudomonas might cause removal of heavy components (C24–30) and light components of petroleum hydrocarbons (C10–16), respectively.

Survival of animal and human-associated Listeria monocytogenes in drinking water and biofilms

Abstract Land slugs are occasionally observed as contaminants in groundwater wells and drinking water treatment plants including storage tanks. Slugs may feed on carrion and feces, and they are potential vectors of pathogens such as Listeria monocytogenes. We isolated L. monocytogenes from the pest slug Arion vulgaris and examined the persistence and survival of human- and slug-derived L. monocytogenes in groundwater-based drinking water and biofilms. L. monocytogenes survival was evaluated using cultivation and cultivation-independent techniques. L. monocytogenes remained culturable for 35–47 days in drinking water with first-order decay rates between 0.314 and 0.457 h−1 (T99 ≥10 days). Attachment of L. monocytogenes to filter sand delayed washout from drinking water filters and increased persistence 2–3-fold. Indigenous biofilms stimulated initial surface attachment 10–100-fold but L. monocytogenes declined more rapidly in drinking water biofilms compared with virgin filters not colonized by microorganisms. Grazing by protozoa likely attenuated L. monocytogenes survival in some drinking water biofilms. A comparable survival pattern was observed for L. monocytogenes and the fecal indicator bacterium E. coli. The study suggests that live L. monocytogenes can persist for weeks as sessile organisms in groundwater-based drinking water supplies and may subsequently be released to the drinking water.

Complex interactions between environmental DNA (eDNA) state and water chemistries on eDNA persistence suggested by meta-analyses.

Understanding the processes of environmental DNA (eDNA) persistence and degradation is essential to determine the spatiotemporal scale of eDNA signals and accurately estimate species distribution. The effects of environmental factors on eDNA persistence have previously been examined; however, the influence of the physiochemical and molecular states of eDNA on its persistence is not completely understood. Here, we performed meta-analyses including 26 previously published papers on the estimation of first-order eDNA decay rate constants, and assessed the effects of filter pore size, DNA fragment size, target gene, and environmental conditions on eDNA decay rates. Almost all supported models included the interactions between the filter pore size and water temperature, between the target gene and water temperature, and between the target gene and water source, implying the influence of complex interactions between the eDNA state and environmental conditions on eDNA persistence. These findings were generally consistent with the results of a reanalysis of a previous tank experiment which measured the time-series changes in marine fish eDNA concentrations in multiple size fractions after fish removal. Our results suggest that the mechanism of eDNA persistence and degradation cannot be fully understood without knowing not only environmental factors but also cellular and molecular states of eDNA in water. Further verification of the relationship between eDNA state and persistence is required by obtaining more information on eDNA persistence in various experimental and environmental conditions, which will enhance our knowledge on eDNA persistence and support our findings.

Characteristics of indoor air pollutants and estimation of their exposure dose

Rural areas of developing countries have various indoor air pollution sources along with solid fuels used for cooking. This study aims to compare five indoor air pollution sources, viz., incense stick, dhoop, mosquito coil, cigarette, and cooking fuel charcoal, with respect to their pollution potential. The monitoring of PM, CO, CO2, NO2, and particulate bound heavy metals was carried out. Dhoop (DH1) was found to be emitting the highest concentration of metal Sb among all the analyzed metals. Dhoop, incense sticks, mosquito coil, and charcoal were found to be having high pollution potential. The first-order decay rate equation indicated that the highest decay rate constant per hour was observed with dhoop (DH1) for PM10 and PM2.5 and with mosquito coil (M1) for CO. The highest half-life of PM10 and PM2.5 was observed for cigarette (CG1) and charcoal (C1) respectively indicating their slow decay in air. The average daily dose values indicated that the age group 6 to < 11 years, 11 to < 16 years, and 31 to < 51 years will be more vulnerable to PM emissions from dhoop (DH1) and incense stick (IS1). The highest hazard index was estimated for incense stick (IS1) and charcoal. Significant carcinogenic risk was observed from cigarette and charcoal. The multiple-path particle dosimetry (MPPD) model was used to estimate the deposition of PM fractions in various regions of the human body.