Sensors for measuring biodegradable and total organic matter in water

Urchin-like Co3O4 microspheres-boosted catalytic oxidation: Environmentally-friendly CO2 vapor generation for total organic carbon detection by microplasma optical emission spectrometry

Total organic carbon (TOC) is a crucial indicator of organic pollutants, widely used in environmental water quality monitoring and risk assessment. Conventional TOC detection methods often require high temperatures, complex equipment, and inefficient oxidation processes, limiting their field application due to time consumption, intricate operations, and limited sensitivity. Therefore, we developed a novel approach for TOC measurement using catalytic oxidation vapor generation coupled with miniaturized point discharge optical emission spectrometry (μPD-OES). This method employs urchin-like Co3O4 microspheres to convert organic pollutants to carbon dioxide during persulfate catalytic oxidation, followed by collection and quantification via carbon atomic emission line (λ = 193.0 nm). Standard or sample solutions were acidified with phosphoric acid and purged with Ar before quantification. Under optimal conditions, the proposed method achieved a detection limit of 0.01 mg L-1, offering precision (RSD, n = 11) better than 3.7 %. The feasibility of the system was tested using a certified reference material (GBW(E)082053) and environmental water samples, achieving satisfactory recoveries (98-102 %). This method provides high oxidation efficiency, sensitivity, and accuracy, while also reducing the demand for expensive and bulky instruments and minimizing energy consumption, making it suitable for rapid, sensitive field analysis of TOC.

Current state and future prospects of sensors for evaluating polymer biodegradability and sensors made from biodegradable polymers: A review

Since the invention of fully synthetic plastic in the 1900s, plastics have been extensively applied in various fields and represent a significant market due to their satisfactory properties. However, the non-biodegradable nature of most plastics has contributed to the accumulation of plastic waste, which poses a threat to both the environment and living beings. Given this, biodegradable polymers have emerged as eco-friendly substitutes for non-biodegradable polymers, and standard test methods have been established to evaluate polymer biodegradability. Technological advancement and the weaknesses of conventional test methods drive the invention of sensors that enable real-time monitoring of biodegradability. Besides, biodegradable polymers have been utilized to make sensors with different functionalities. Given this, the current paper is the first to compare and contrast sensors capable of identifying biodegradable polymers. The detection using sensors represents an innovative perspective for real-time monitoring of biodegradability. Besides, sensors made from biodegradable polymers are included, and these sensors are of different types and show various applications. Finally, the challenges associated with developing these sensors are described to advance future research.

Miniaturized TOC analyzer using dielectric barrier discharge for catalytic oxidation vapor generation and point discharge optical emission spectrometry

Total organic carbon (TOC) is an important parameter describing organic pollution degree of waters. Due to the increasing need of field analysis and drawbacks of conventional TOC analytical instruments, miniaturized TOC analyzers are still demanding. In this work, a dielectric barrier discharge (DBD) microplasma was utilized for catalytic oxidation vapor generation (COVG) of organic compounds into CO₂, and a point discharge (PD) microplasma was employed to excite the carbon atomic emission spectra for quantification. Sample solution with phosphoric acid and persulfate solution was injected into the DBD-COVG reactor by a syringe to convert organic compounds into CO₂ efficiently and quickly, which was subsequently transported into the point discharge optical emission spectrometer (PD-OES) for detecting carbon at 193.09 nm. Under optimal experimental conditions, high oxidation efficiencies for several organic compounds were achieved, i.e., 96.4%, 95.1% and 94.3% for 50 mg L^-1 potassium hydrogen phthalate (KHP), sodium laurylsulfonate and phenol, respectively. A limit of detection (LOD) of 0.02 mg L^-1 (as C) was obtained, with a precision of 3.9% (relative standard deviation, RSD) at 15 mg L^-1 TOC standard (as C). The possible catalytic oxidation mechanism was proposed with the characteristic results of electron paramagnetic resonance (EPR). Its potential environmental application was demonstrated by successfully analyzing TOC in underground water, surface river water and surface sedimentary water samples from oil fields, with analytical results agreed well with those obtained by the commercial high-temperature combustion coupled nondispersive infrared absorption (HTC-NDIR) technique.

A Current Sensing Biosensor for BOD Rapid Measurement

In order to improve the practicality of the rapid biochemical oxygen demand (BOD) method, a highly sensitive rapid detection method for BOD that is based on establishing the correlation between current and dissolved oxygen (DO) was developed. In this experiment, Bacillus subtilis was used as the test microorganism, and the embedding method was used to achieve quantitative fixation of microorganisms, which could increase the content of microorganisms and prolong the service life of the biological element. The conductivity (COND) probe is used as a sensing element, so that the testing value can be read every second. In the program, the moving average method is used to process the collected data so that the value can be read every minute. National standard samples were detected to test the accuracy and stability of the method. The results showed that relative error and analytical standard deviations were less than 5%. Different polluted water was tested to evaluate its application range. The results showed that relative error was less than 5%. The results of the method are consistent with the results of the wastewater sample obtained by the BOD₅ standard method. The proposed rapid BOD current sensing biosensor method should be promising in practical application of wastewater monitoring.

In situ Decolorization Monitoring of Textile Dyes for an Optimized UV-LED/TiO2 Reactor

Heterogeneous photocatalysis, using photocatalysts in suspension to eliminate diverse contaminants, including textile wastewater, has several advantages. Nevertheless, current absorbance and decolorization measurements imply sample acquisition by extraction at a fixed rate with consequent photocatalyst removal. This study presents online monitoring for the decolorization of six azo dyes, Orange PX-2R (OP2), Remazol Black B133 (RB), Procion Crimson H-EXL (PC), Procion Navy H-EXL (PN), Procion Blue H-EXL (PB), and Procion Yellow H-EXL (PY), analyzing the spectrum measured in situ by using the light scattering provided by the photocatalyst in suspension. The results obtained have corroborated the feasibility of obtaining absorbance and decolorization measurements, avoiding disturbances in the process due to a decrease in the volume in the reactor.

Current status of water environment and their microbial biosensor techniques - Part II: Recent trends in microbial biosensor development

In Part I of the present review series, I presented the current state of the water environment by focusing on Japanese cases and discussed the need to further develop microbial biosensor technologies for the actual water environment. I comprehensively present trends after approximately 2010 in microbial biosensor development for the water environment. In the first section, after briefly summarizing historical studies, recent studies on microbial biosensor principles are introduced. In the second section, recent application studies for the water environment are also introduced. Finally, I conclude the present review series by describing the need to further develop microbial biosensor technologies. Graphical abstract Current water pollution indirectly occurs by anthropogenic eutrophication (Part I). Recent trends in microbial biosensor development for water environment are described in part II of the present review series.

Continuous and Inexpensive Monitoring of Nonpurgeable Organic Carbon by Coupling High-Efficiency Photo-oxidation Vapor Generation with Miniaturized Point-Discharge Optical Emission Spectrometry

Currently, no applicable analyzers are available to accomplish online continuous monitoring of organic pollution, which is one of the most important factors contributing to water shortages around the world, particularly in developing countries. In this work, a sensitive, miniaturized, inexpensive, and online nonpurgeable organic carbon (NPOC) analysis system was developed for continuous monitoring of such organic pollution. This system consists of a specially designed high-efficiency UV photo-oxidation vapor generation (HE-POVG) reactor and a miniaturized, low-power (7 W) point-discharge microplasma optical emission spectrometer (PD-OES). Organics present in sample or standard solutions are pumped to the HE-POVG and efficiently converted into CO₂, which is separated and further transported to the PD-OES for NPOC analysis via highly sensitive detection of carbon atomic emission at 193.0 nm. Under optimal conditions, a limit of detection of 0.05 mg·L^-1 (as C) is obtained, with precision better than 5.0% (relative standard deviation) at 5 mg·L^-1. This system overcomes many shortcomings associated with conventional chemical oxygen demand or total organic carbon analyzers such as long analysis time, use of expensive and toxic chemicals, production of secondary toxic waste, requirement of large, power consuming and expensive instrumentation and difficulties implementing continuous online monitoring. The system was successfully applied to sensitive and accurate determination of NPOC in various water samples and for continuous monitoring of such organic pollution in tap water.

Quantifying biodegradable organic matter in polluted water on the basis of coulombic yield

Biodegradable organic matter (BOM) in polluted water plays a key role in various biological purification technologies. The five-day biochemical oxygen demand (BOD₅) index is often used to determine the amount of BOM. However, standard BOD₅ assays, centering on dissolved oxygen detection, have long testing times and often show severe deviation (error ≥ 15%). In the present study, the coulombic yield (Q) of a bio-electrochemical degradation process was determined, and a new index for BOM quantification was proposed. The Q value represents the quantity of transferred electrons from BOM to oxygen, and the corresponding index was defined as BOM_Q. By revealing Q-BOM stoichiometric relationship, we were able to perform a BOM_Q assay in a microbial fuel cell involved technical platform. Experimental results verified that 5-500mgL^-1 of BOM_Q toward artificial wastewater samples could be directly obtained without calibration in several to dozens of hours, leaving less than 5% error. Moreover, the BOM_Q assay remained accurate and precise in a wide range of optimized operational conditions. A ratio of approximately 1.0 between the values of BOM_Q and BOD₅ toward artificial and real wastewater samples was observed. The rapidity, accuracy, and precision of the measurement results are supported by a solid theoretical foundation. Thus, BOM_Q is a promising water quality index for quantifying BOM in polluted water.

A simple model for estimating the concentrations of natural estrogens in raw wastewater

This study provides a tool for predicting the concentrations of the natural estrogens (NEs) estrone, 17β-estradiol and estriol in raw wastewater (WW). Data characterizing the biochemical oxygen demand (BOD), NE concentrations, and discharges of raw sewage to wastewater treatment plants (WWTPs) were collected from various publications and used in the model formulation. A strong correlation was found between the log transformed BOD and the log transformed estrone load (r²=0.84, n=61), the log transformed 17β-estradiol load (r²=0.89, n=52) and the log transformed estriol load (r²=0.80, n=40). The models are reasonably accurate when compared to the measured concentrations and slightly better than previous modeling efforts. The relative amounts of data falling within ±50% error were 67% for estrone, 63% for 17β-estradiol, and 55% for estriol. Because the model was developed from a wide array of WWTPs from five continents, it is universal and can be used for projecting concentrations of NEs from a wide range of mixed domestic and industrial sources, but may be less precise when sources contain high levels of NEs or BOD (e.g., WW from dairy farms and food processing plants). The model is expected to improve our ability to predict the fate of NEs in WWTPs and in the receiving environment, which currently relies on estimating the concentrations of NEs in raw wastewater. Its application is especially valuable since direct measurement of NEs in raw WW is expensive and practically impossible in many developing countries due to the lack of expertise and funds.

A review of practical tools for rapid monitoring of membrane bioreactors

The production of high quality effluent from membrane bioreactors (MBRs) arguably requires less supervision than conventional activated sludge (CAS) processes. Nevertheless, the use of membranes brings additional issues of activated sludge filterability, cake layer formation and membrane fouling. From a practical standpoint, process engineers and operators require simple tools which offer timely information about the biological health and filterability of the mixed liquor as well as risks of membrane fouling. To this end, a range of analytical tools and biological assays are critically reviewed from this perspective. This review recommends that Capillary Suction Time (CST) analysis along with Total Suspended and Volatile Solids (TSS/VSS) analysis is used daily. For broad characterisation, total carbon and nitrogen analysis offer significant advantages over the commonly used chemical and biological oxygen demand (COD/BOD) analyses. Of the technologies for determining the vitality of the microbial biomass the most robust and reproducible, are the second generation adenosine-5'-triphosphate (ATP) test kits. Extracellular polymer concentrations are best monitored by measurement of turbidity after centrifugation. Taken collectively these tools can be used routinely to ensure timely intervention and smoother operation of MBR systems.

Toxicity measurement in biological wastewater treatment processes: a review

Biological wastewater treatment processes (WWTPs), by nature of their reliance on biological entities to degrade organics and sometimes remove nutrients, are vulnerable to toxicants present in their influent. Various toxicity measurement methods have been adopted for biological WWTPs, but most are performed off-line, and cannot be adapted to on-line monitoring tools to provide an early warning for WWTP operators. However, the past decade has seen a rapid expansion in the research and development of biosensors that can be used for toxicity assessment of aquatic environments. Some of these biosensors have also been shown to be effective for use in biological WWTPs. Nevertheless, more research is needed to: examine the sensitivity of assays and sensors based on single organisms to various toxicants and develop a matrix of biosensors or a biosensor incorporating multiple organisms that can protect WWTPs; test the micro fuel cell (MFC)-based biosensors with real wastewaters and correlate the results with the well-established oxygen uptake rate (OUR)-based or CH4-based toxicity assay; and, develop advanced data processing methods for interpreting the results of on-line toxicity sensors in real WWTPs to reduce the noise due to the normal fluctuation in influent quality and quantity.

Plasmonic swings during the Fenton reaction: catalytic sensing of organics in water via fullerene-decorated gold nanoparticles

A sensor for organics in water was developed by the plasmonic swings of gold acting as catalysts of the Fenton process.

Novel environmental analytical system based on combined biodegradation and photoelectrocatalytic detection principles for rapid determination of organic pollutants in wastewaters

This work describes the development of a novel biofilm reactor-photoelectrocatalytic chemical oxygen demand (BFR-PeCOD) analytical system for rapid online determination of biodegradable organic matters (BOMs). A novel air bubble sample delivery approach was developed to dramatically enhance the BFR's biodegradation efficiency and extend analytical linear range. Because the air bubble sample delivery invalidates the BOD quantification via the determination of oxygen consumption using dissolved oxygen probe, the PeCOD technique was innovatively utilized to resolve the BOD quantification issue under air bubble sample delivery conditions. The BFR was employed to effectively and efficiently biodegrade organic pollutants under oxygen-rich environment provided by the air bubbles. The BOD quantification was achieved by measuring the COD change (Δ[COD]) of the original sample and the effluent from BFR using PeCOD technique. The measured Δ[COD] was found to be directly proportional to the BOD5 values of the original sample with a slope independent of types and concentrations of organics. The slope was used to convert Δ[COD] to BOD5. The demonstrated analytical performance by BFR-PeCOD system surpasses all reported systems in many aspects. It has demonstrated ability to near real-time, online determining the organic pollution levels of wide range wastewaters without the need for dilution and ongoing calibration. The system possesses the widest analytical liner range (up to 800 mg O2 L(-1)) for BOD analysis, superior long-term stability, high accuracy, reliability, and simplicity. It is an environmentally friendly analytical system that consumes little reagent and requires minimal operational maintenance.

A reagent-free tubular biofilm reactor for on-line determination of biochemical oxygen demand

We reported a reagent-free tubular biofilm reactor (BFR) based analytical system for rapid online biochemical oxygen demand (BOD) determination. The BFR was cultivated using microbial seeds from activated sludge. It only needs tap water to operate and does not require any chemical reagent. The analytical performance of this reagent-free BFR system was found to be equal to or better than the BFR system operated using phosphate buffer saline (PBS) and high purity deionized water. The system can readily achieve a limit of detection of 0.25 mg O2 L(-1), possessing superior reproducibility, and long-term operational and storage stability. More importantly, we confirmed for the first time that the BFR system is capable of tolerating common toxicants found in wastewaters, such as 3,5-dichlorophenol and Zn(II), Cr(VI), Cd(II), Cu(II), Pb(II), Mn(II) and Ni(II), enabling the method to be applied to a wide range of wastewaters. The sloughing and clogging are the important attributes affecting the operational stability, hence, the reliability of most online wastewater monitoring systems, which can be effectively avoided, benefiting from the tubular geometry of the reactor and high flow rate conditions. These advantages, coupled with simplicity in device, convenience in operation and minimal maintenance, make such a reagent-free BFR analytical system promising for practical BOD online determination.

Electrochemically active biofilms: facts and fiction. A review

This review examines the electrochemical techniques used to study extracellular electron transfer in the electrochemically active biofilms that are used in microbial fuel cells and other bioelectrochemical systems. Electrochemically active biofilms are defined as biofilms that exchange electrons with conductive surfaces: electrodes. Following the electrochemical conventions, and recognizing that electrodes can be considered reactants in these bioelectrochemical processes, biofilms that deliver electrons to the biofilm electrode are called anodic, ie electrode-reducing, biofilms, while biofilms that accept electrons from the biofilm electrode are called cathodic, ie electrode-oxidizing, biofilms. How to grow these electrochemically active biofilms in bioelectrochemical systems is discussed and also the critical choices made in the experimental setup that affect the experimental results. The reactor configurations used in bioelectrochemical systems research are also described and the authors demonstrate how to use selected voltammetric techniques to study extracellular electron transfer in bioelectrochemical systems. Finally, some critical concerns with the proposed electron transfer mechanisms in bioelectrochemical systems are addressed together with the prospects of bioelectrochemical systems as energy-converting and energy-harvesting devices.