Development of an ATP luminescence-based method for assimilable organic carbon determination in reclaimed water

Use of Bioluminescence for Monitoring Brown Coal Mine Waters from Deep and Surface Drainage

Open-pit mines can cause environmental changes, such as alterations of landscape structure, hydrology, air quality, and river sediments; they can also generate cones of depression. We propose a new method for surveys of mine waters using the example of an open-pit mine in central Poland. This study examines the correlations between bioluminescence and the color of brown coal mine waters and tests whether values of the three-color coordinate system reflected the physicochemical quality of mine waters measured in real-time and in the field. Our results show that alkalinity, pH reaction, and conductivity are higher in surface drainage, while values of trophic parameters (soluble reactive phosphates, total phosphorus, nitrates) are greater in samples representing subsurface drainage. Correlation analysis of bioluminescence with mine water quality parameters showed that only water color had a strong association with bioluminescence. This correlation is stronger for surface drainage, than for mine waters from subsurface drainage. Direct measurement of bioluminescence, resulting from adenosine 5`-triphosphate (ATP) using a luminometer, is a fast and reliable method for evaluation of the characteristics of mine waters in real-time.

Soil microbial communities-mediated bioattenuation in simulated aquifer storage and recovery (ASR) condition: Long-term study

This study evaluated the long-term organic removal performance and microbial community shift in simulated aquifer storage and recovery (ASR) conditions. For this purpose, anoxic soil box systems were operated at 15 °C for one year. The results showed that the assimilable organic carbon (AOC) concentration in the anoxic soil box systems was successfully decreased by 79.1%. The dissolved organic carbon (DOC) concentration increased during the initial operational periods; however, it subsequently decreased during long-term operation. Readily biodegradable organic fractions (i.e., low-molecular weight (LMW) neutrals and LMW acids) decreased along with time elapsed, whereas non-biodegradable fraction (i.e., humic substances) increased. Proteobacteria and Acidobacteriota were predominant in the anoxic box systems throughout the operational periods. Firmicutes and Bacteroidota suddenly increased during the initial operational period while Gemmatimonadota slightly increased during prolonged long-term operation. Interestingly, the microbial community structures were significantly shifted with respect to the operational periods while the effects of AOC/NO₃^- addition were negligible. Various bacterial species preferring low temperature or anoxic conditions were detected as predominant bacteria. Some denitrifying (i.e., Noviherbaspirillum denitrificans) and iron reducing bacteria (i.e., Geobacter spp.) appeared during the long-term operation; these bacterial communities also acted as organic degraders in the simulated ASR systems. The findings of this study suggest that the application of natural bioattenuation using indigenous soil microbial communities can be a promising option as an organic carbon management strategy in ASR systems.

Occurrence and risk assessment of volatile halogenated disinfection by-products in an urban river supplied by reclaimed wastewater

The reuse of the sewage is an effective way to solve the shortage of water resources, but disinfection by-products (DBPs) caused by chlorination may bring potential ecological and health risks to the supplied water. In this study, the occurrence and potential ecological risk of DBPs in SH River in Beijing were evaluated. Four kinds of DBPs were detected in 84 samples by GC-MS, including THM, CH, CTC and TCAN, whose detection rates were 100%, 100%, 100% and 2.38%, respectively. Combining with the relevant standard limitation and corresponding threshold values in China, and the reported concentration in domestic and foreign literatures, the results showed that the number of samples which [THM], [CTC] and [CH] exceeded the threshold values in relevant standard for 23.81%, 100.00% and 89.29%, respectively. CTC showed the highest excess times than the threshold value with [CTC]_max was 356.46 μg/L. In addition, the temporal and spatial characteristics of identified DBPs were studied. [THM], [CTC] and [CH] all exhibited the highest concentration in Aug., which was as the same as the variation trend of air and water temperature. With the increase of sampling distance, [THM] and [CTC] fluctuated greatly, and the background values in SH River were higher due to the supplement of the reclaimed water. [CH] and [TCAN] gradually decreased, which may be due to that they were more prone to volatilize in the channel and be degraded by aquatic microorganisms. In addition, the occurrence situation in S2 and S7, were in the order of CTC > CH > THM. Hence, the rank of the occurrence situation of identified DBPs was CTC > CH > THM > TCAN. Multivariate analysis showed that THM was significantly positively correlated with CTC and their sources were similar. Moreover, they were all affected by solution pH and DO. Potential ecological risk assessment indicated that the rank of identified DBPs ecological risk was CTC > THM > CH > TCAN. Among them, the risk level of CTC and THM were high in both daily and extreme situations. Therefore, the potential ecological risk caused by DBPs should be fully considered in the process of reclaimed water supplying landscape water, such as urban river. If a higher level of the ecological risk management is needed, THM, CTC and CH, especially CTC, should be considered firstly.

Assessment and mechanisms of microalgae growth inhibition by phosphonates: Effects of intrinsic toxicity and complexation

The effects of phosphonates, the heavily-used antiscalants in reverse osmosis systems, on microalgae are controversial, although they are harmless to most aquatic organisms. Herein, we assessed the inhibitory effects of etidronic acid (HEDP) and diethylenetriamine penta(methylene phosphonic acid) (DTPMP) on algal growth and revealed the mechanisms involved in both intrinsic toxicity and complexation. The phosphonates showed weak influences on Scenedesmus sp. LX1 in the first 4 d of cultivation. In contrast, a significant growth inhibition was observed subsequently with half maximal effective concentrations of 57.6 and 35.7 mg/L for HEDP and DTPMP, respectively, at 10 d. The phosphonates had little effect on cellular energy transfer and oxidative stress, quantified by adenosine triphosphate level and superoxide dismutase activity, respectively, demonstrating weak intrinsic toxicities to algal cells. Phosphonates blocked the algal assimilation of iron ions through complexation. Severe iron deficiency limited photosynthetic activity and caused chlorophyll decline, resulting in a functional loss of the photosystem followed by complete algal growth inhibition at the late cultivation stage. Our findings point to a potential ecological impact wherein harmful algal blooms are induced by the natural degradation of phosphonates due to the release of both iron and phosphate ions that stimulate algal regrowth after disinhibition.

Using rapid quantification of adenosine triphosphate (ATP) as an indicator for early detection and treatment of cyanobacterial blooms

Early detection of harmful cyanobacterial blooms allows identification of potential risk and appropriate selection of treatment techniques to prevent exposure in recreational water bodies and drinking water supplies. Here, luminescence-based adenosine triphosphate (ATP) analysis was applied to monitor and treat cultured and naturally occurring cyanobacteria cells. When evaluating lab-cultured Microcystis aeruginosa, ATP concentrations (≤252,000 pg/mL) had improved sensitivity and correlated well (R² = 0.969) with optical density measurements at 730 nm (OD730; ≤0.297 cm^-1). Following one year of monitoring of a surface water supply, ATP concentrations (≤2000 pg/mL) correlated (R² = 0.791) with chlorophyll-a concentrations (≤50 μg/L). A preliminary early warning threshold of 175 pg ATP/mL corresponded with 5 μg/L chlorophyll-a to initiate increased monitoring (e.g., of cyanotoxins). Following oxidation processes (i.e., chlorine, chloramine, ozone, permanganate), ATP was demonstrated as an indicator of cell lysis and a threshold value of <100 pg/mL was recommended for complete release of intracellular cyanotoxins. ATP was also used to assess efficacy of copper (Cu(II)) treatment on cyanobacteria-laden surface water. While 24-h exposure to 2.5 mg Cu(II)/L did not impact chlorophyll-a, ATP decreased from 13,500 to 128 pg/mL indicating metabolic activity was minimized. Ultimately, ATP analysis holds promise for early detection and mitigation of potentially harmful algal blooms based on superior sensitivity, independence from cell morphology artifacts, rapid time for analysis (<10 min), and ease of deployment in the field compared to conventional methods.

Characterization of released metabolic organics during AOC analyses by P17 and NOX strains using 3-D fluorescent signals

Assimilable organic carbon (AOC) serves as an indicator of the biostability of drinking water distribution systems; however, the properties of the released organic metabolites by Pseudomonas fluorescens (P17) and Spirillum (NOX) used in AOC bioassays are seldom discussed. In this study, fluorescence excitation emission matrix (FEEM) was selected to characterize organic metabolites after substrate biotransformation and their divergences at different growth stages of both strains in AOC bioassay. Excellent correlation between ATP and colony-forming units (CFUs) was observed for both strains. The concentration of ATP per colony was six times higher in the P17 strain than in the NOX strain. A retarding phenomenon was observed for the NOX strain in the presence of high acetate-C content (100-150 μg acetate-C/L). The fluorescence wavelength peaks were wider for the protein-like substance released by the P17 strain than for those released by the NOX strain. However, fluorescent fulvic-like substances only existed in the NOX strain. Relative humus accumulation (RHA), the ratio of protein-like fluorescence intensity to humus-like fluorescence intensity, decreased in the P17 strain but substantially increased in the NOX strain in the logarithmic growth phase. RHA showed a descending trend for the P17 strain as compared to that of the NOX strain during the progress from logarithmic to stationary growth phase at three different acetate-C concentrations; however, the opposite was observed at 100 μg acetate-C/L, indicating that high acetate-C content may affect the properties of released organic matter from both strains.

A novel method: using an adenosine triphosphate (ATP) luminescence-based assay to rapidly assess the biological stability of drinking water

The rapid and credible evaluations of the microbial stability of a drinking water distribution system (DWDS) are of great significance for ensuring the safety of drinking water and predicting microbial pollution. Conventional biostability assessment methods mainly focus on bacterial regrowth or evaluation of the level of nutrients that support bacterial regrowth. However, such methods are time-consuming and have many limitations. An adenosine triphosphate (ATP) assay can rapidly measure all active microorganisms and is known to be a useful method to assess the microbial activity of drinking water. The measurement of ATP has been used for more than a decade in the field of drinking water research. This article reviews the application of an ATP luminescence-based method to assess the biostability of drinking water and discusses the feasibility of ATP measurement as a parameter for quickly evaluating this criterion. ATP measurement will help researchers and water managers better monitor the biological stability of drinking water from the source to the consumer's tap. This review covers the: (1) principle and application of the ATP measurement in drinking water quality assessment; (2) comparison of the merits and demerits of several methods for evaluating the biostability of drinking water; (3) discussions on using ATP measurement in evaluating biostability; and (4) improvements in the use of ATP measurement in evaluating biostability. At the end of this review, recommendations were given for better application of the ATP measurement as a parameter for monitoring the microbial quality of drinking water.

Interaction between 1,2-benzisothiazol-3(2H)-one and microalgae: Growth inhibition and detoxification mechanism

Isothiazolinones, such as 1,2-benzisothiazol-3(2H)-one (BIT), are widely used as biocides for bacterial growth control in many domestic and industrial processes. Despite their advantages as biocides, they are highly toxic and pose a potential risk to the environment. This study investigated the inhibition process and detoxification mechanism involved in microalgal survival and growth recovery after BIT poisoning. BIT could seriously inhibit the growth of Scenedesmus sp. LX1, Chlorella sp. HQ, and Chlamydomonas reinhardtii with half maximal effective concentrations at 72 h (72h-EC₅₀) of 1.70, 0.41, and 1.16 mg/L, respectively. The primary inhibition mechanism was the BIT-induced damage to microalgal photosynthetic systems. However, the inhibited strains could recover when their growth was not completely inhibited. The influence of this inhibiting effect on subsequent algal regrowth was negligible or weak. BIT consumption was the primary reason for their recovery. Notably, algae did not die even if their growth was completely inhibited. If the BIT concentration did not exceed a certain high level, then the inhibited algae could recover their growth relatively well. Microalgal generation of reduced glutathione (GSH) and the oxygen radical scavenging enzymes, superoxide dismutase (SOD) and catalase (CAT), played a key role in detoxification against BIT poisoning.

A uniform bacterial growth potential assay for different water types

The bacterial growth potential is important to understand and manage bacterial regrowth-related water quality concerns. Bacterial growth potential depends on growth promoting/limiting compounds, therefore, nutrient availability is the key factor governing bacterial growth potential. Selecting proper tools for bacterial growth measurement is essential for routine implementation of the growth potential measurement. This study proposes a growth potential assay that is universal and can be used for different water types and soil extract without restrictions of pure culture or cultivability of the bacterial strain. The proposed assay measures the sample bacterial growth potential by using the indigenous community as inocula. Flow cytometry (FCM) and adenosine tri-phosphate (ATP) were used to evaluate the growth potential of six different microbial communities indigenous to the sample being analyzed, with increasing carbon concentrations. Bottled mineral water, non-chlorinated tap water, seawater, river water, wastewater effluent and a soil organic carbon extract were analyzed. Results showed that indigenous bacterial communities followed normal batch growth kinetics when grown on naturally present organic carbon. Indigenous bacterial growth could detect spiked organic carbon concentrations as low as 10 μg/L. The indigenous community in all samples responded proportionally to the increase in acetate-carbon and proportional growth could be measured with both FCM and ATP. Bacterial growth was proportional to the carbon concentration but not the same proportion factor for the different water samples tested. The effect of inoculating the same water with different indigenous microbial communities on the growth potential was also examined. The FCM results showed that the highest increase in total bacterial cell concentration was obtained with bacteria indigenous to the water sample. The growth potential assay using indigenous bacterial community revealed consistent results of bacterial growth in all the different samples tested and therefore providing a fast, more stable, and accurate approach for monitoring the biological stability of waters compared to the previously developed assays. The growth potential assay can be used to aid in detecting growth limitations by compounds other than organic carbon.

Tolerance and resistance characteristics of microalgae Scenedesmus sp. LX1 to methylisothiazolinone

Methylisothiazolinone (MIT) has been widely used to control bacterial growth in reverse osmosis (RO) systems. However, MIT's toxicity on microalgae should be determined because residual MIT is concentrated into RO concentrate (ROC) and might have a severe impact on microalgae-based ROC treatment. This study investigated the tolerance of Scenedesmus sp. LX1 to MIT and revealed the mechanism of algal growth inhibition and toxicity resistance. Scenedesmus sp. LX1 was inhibited by MIT with a half-maximal effective concentration at 72 h (72 h-EC₅₀) of 1.00 mg/L, but the strain recovered from the inhibition when its growth was not completely inhibited. It was observed that this inhibition's effect on subsequent growth was weak, and the removal of MIT was the primary reason for the recovery. Properly increasing the initial algal density significantly shortened the adaptation time for accelerated recovery in a MIT-containing culture. Photosynthesis damage by MIT was one of the primary reasons for growth inhibition, but microalgal cell respiration and adenosine triphosphate (ATP) synthesis were not completely inhibited, and the algae were still alive even when growth was completely inhibited, which was notably different from observations made with bacteria and fungi. The algae synthesized more chlorophyll, antioxidant enzymes of superoxide dismutase (SOD) and catalase (CAT), and small molecules, such as reduced glutathione (GSH), to resist MIT poisoning. The microalgae-based process could treat the MIT-containing ROC, since MIT was added for only several hours a week in municipal wastewater reclamation RO processes, and the MIT average concentration was considerably lower than the maximum concentration that algae could tolerate.

Potential risks from UV/H2O2 oxidation and UV photocatalysis: A review of toxic, assimilable, and sensory-unpleasant transformation products

UV based advanced oxidation processes (UV-AOPs) that efficiently eliminate organic pollutants during water treatment have been the subject of numerous investigations. Most organic pollutants are not completely mineralized during UV-AOPs but are partially oxidized into transformation products (TPs), thereby adding complexity to the treated water and posing risks to humans, ecological systems, and the environment. While the degradation kinetics and mechanisms of pollutants have been widely documented, there is little information about the risks associated with TPs. In this review, we have collated recent knowledge about the harmful TPs that are generated in UV/H₂O₂ and UV photocatalysis, two UV-AOPs that have been studied extensively. Toxic and assimilable TPs were ubiquitously observed in more than 80% of UV-AOPs of organic pollutants, of which the toxicity and assimilability levels changed with variations in the reaction conditions, such as the UV fluence and oxidant dosage. Previous studies and modeling assessments showed that toxic and assimilable TPs may be generated during hydroxylation, dealkylation, decarboxylation, and deamination. Among various reactions, TPs generated from dealkylation and decarboxylation were generally less and more toxic than the parent pollutants, respectively; TPs generated from decarboxylation and deamination were generally less and more assimilable than the parent pollutants, respectively. There is also potential concern about the sensory-unpleasant TPs generated by oxidations and subsequent metabolism of microorganisms. In this overview, we stress the need to include both the concentrations of organic pollutants and the evaluations of the risks from TPs for the quality assessments of the water treated by UV-AOPs.

Assimilable organic carbon (AOC) determination using GFP-tagged Pseudomonas fluorescens P-17 in water by flow cytometry

One of the newly developed methods for Assimilable organic carbon (AOC) determination is leveraged on the cell enumeration by flow cytometry (FC) which could provide a rapid and automated solution for AOC measurement. However, cell samples staining with fluorescence dye is indispensable to reduce background and machine noise. This step would bring additional cost and time consuming for this method. In this study, a green fluorescence protein (GFP) tagged strain derived of AOC testing strain Pseudomonas fluorescens P-17 (GFP-P17) was generated using Tn5 transposon mutagenesis. Continuous culture of this mutant GFP-P17 showed stable expression of eGFP signal detected by flow cytometry without staining step. In addition, this GFP-P17 strain displayed faster growth rate and had a wider range of carbon substrate utilization patterns as compared with P17 wild-type. With this strain, the capability of a new FC method with no dye staining was explored in standard acetate solution, which suggests linear correlation of counts with acetate carbon concentration. Furthermore, this FC method with GFP-P17 strain is applicable in monitoring GAC/BAC efficiency and condition as similar trends of AOC level in water treatment process were measured by both FC method and conventional spread plating count method. Therefore, this fast and easily applicable GFP-P17 based FC method could serve as a tool for routine microbiological drinking water monitoring.

Assimilable organic carbon (AOC) variation in reclaimed water: Insight on biological stability evaluation and control for sustainable water reuse

This review highlights the importance of conducting biological stability evaluation due to water reuse progression. Specifically, assimilable organic carbon (AOC) has been identified as a practical indicator for microbial occurrence and regrowth which ultimately influence biological stability. Newly modified AOC bioassays aimed for reclaimed water are introduced. Since elevated AOC levels are often detected after tertiary treatment, the review emphasizes that actions can be taken to either limit AOC levels prior to disinfection or conduct post-treatment (e.g. biological filtration) as a supplement to chemical oxidation based approaches (e.g. ozonation and chlorine disinfection). During subsequent distribution and storage, microbial community and possible microbial regrowth caused by complex interactions are discussed. It is suggested that microbial surveillance, AOC threshold values, real-time field applications and surrogate parameters could provide additional information. This review can be used to formulate regulatory plans and strategies, and to aid in deriving relevant control, management and operational guidance.