Use of Sensors in Wastewater Quality Monitoring—A Review of Available Technologies
Abstract
Wastewater treatment involves removing nutrients from wastewater before discharging it to water courses. Many technologies have been developed for this purpose, such as the activated sludge process and others. This process is a biological method performed by a mixed community of microorganisms in an aerobic aquatic environment. These microorganisms derive energy from carbonaceous organic matter in aerated wastewater for the production of new cells in a process known as synthesis, while simultaneously releasing energy through the conversion of this organic matter into compounds that contain lower energy, such as carbon dioxide and water, in a process called respiration. As well, a variable number of microorganisms in the system obtain energy by converting ammonia nitrogen to nitrate nitrogen in a process termed nitrification. This consortium of microorganisms, the biological component of the process, is known collectively as activated sludge. EBPR (Enhanced biological phosphorus removal) is a wastewater treatment configuration applied to activated sludge systems for the removal of phosphate. The common element in EBPR implementations is the presence of an anaerobic stage (nitrate and oxygen are absent) prior to the aeration stage. Under these conditions a group of heterotrophic bacteria, called polyphosphate-accumulating organisms (PAO) are selectively enriched in the bacterial community within the activated sludge. These bacteria accumulate large quantities of polyphosphate within their cells and the removal of phosphorus is said to be enhanced (R. G. Benedict et al. 1971). SBR (Sequencing batch reactors) is a fill-and-draw activated sludge system which is used in most lab-scale systems in order to enrich the sludge with PAO. The management of these reactors is mostly based on off-line measurements such as volatile fatty acids and phosphorus. However, off-line monitoring of the SBR cycle implies low frequency data sampling and delay between sampling and availability of the results. This is an obstacle for a proper process monitoring and makes difficult the application of control strategies to the process. For this reason, the on-line monitoring of the SBR cycle would improve the daily process management, as well as facilitate the "on-line" detection of abnormal situations and the implementation of new control strategies. Moreover the control of these processes has become more complex and the demand on continuous monitoring has increased. This may cause difficulties if this is handled manually and an online control system should make the process more controllable and less complex. In recent years there has been a lack of a proper sensor which can be used for on-line real time monitoring. This paper will review the available technologies for online monitoring outlining their advantages and disadvantages. The paper will also present current developments at Liverpool John Moores University with regards to the development of such a sensor and investigate the possibility of applying it to in-situ applications. In addition, the use of microwave technology is investigated for enhancing sensor performance.
... In the world, there are some works [10][11][12][13][14][15][16] interested in this issue. The work [10,13,14] introduces an overview of the parameters of wastewater and the basic equipment of the remote wastewater quality monitoring system following in real-time approach. ...
... The work [12] presents the designing hardware and software of water quality monitoring system using CC2430-F128 processor based on wireless sensor network and ZigBee technology. The work [15] presents about some sensors for design a monitoring system including on-line monitoring and data accessing. The work [16] introduces the block diagram of general real-time remote wastewater quality monitoring system. ...
... Photosensors are mainly used to detect water composition [11], and it can be done through the determination of the wavelength for a distinct color; for instance, detection of the phosphorus can be proceeded using blue or yellow, which is the consequence of a chemical reaction between special reagent and phosphorus. The intensity of phosphorus in the sample can be noticed by the concentration of the resulting dye [12]. Some available commercial systems for water quality checks are Hach Lange, EnviroTech, TresCon, and ChemScan UV-6100 Analyzer System [1]. ...
... This method is used both for phosphate detection in laboratory based and online monitoring systems. Here color change of a reagent (molybdenum blue or vanadate/molybdate yellow) upon reaction with phosphate in acidic medium is used to detect and quantify it [18]. The colorimetric approach provides accurate measurements but it requires toxic reagents, sophisticated instrumentation, sample preparation and skilled personnel for operation [19]. ...
Phosphate is an important analyte to monitor in various water bodies. Cobalt based sensors are attractive for this application as they are solid-state, have a quick response time, are easy to fabricate and can perform reagent-less measurements. However, these sensors have lower sensitivity, limited dynamic range and require a chemical conditioning in a standard solution before measurement. In this study, an in situ anodic current pretreatment method in sample solution itself is used to enhance the sensitivity of the sensor and alleviate the need of chemical conditioning before measurement. With electrical pretreatment, the sensor exhibited a linear range from 10-6 M to 10-3 M with a sensitivity of -91.4 mV/decade of change in dihydrogen phosphate concentration. No significant interference was detected with common interfering anions that are typically present in field water samples such as nitrate, sulphate and chloride. Finally, the sensor was also responsive when tested real water samples such as tap water, lake water and creek water spiked with phosphate.
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... The sewage treatment process needs long-lasting and competent tools to enhance online monitoring of several important factors including pH, BOD, COD, Chlorine, Ammonium, Phosphorus, and other important gases such as Methane (CH 4 ), H 2 S etc. [10]. The aforementioned parameters influence the quality of treated water and also have adverse effects on the structural health of the plant. ...
Adverse effects of wastewater on the hygiene of human and circumstances is a major issue in society. Appropriate refining systems with high efficiency is required to treat the wastewater. Sewage treatment plant plays a major and important role in conserving incredible nature of the environment. Microbiologically Induced Corrosion (MIC) is an important phenomenon in sewage structures which causes the deterioration of infrastructures. Huge capital has been spent and efforts have been made on wastewater treatment infrastructure to increase operating efficiency and reliability of compliance. The investments in reimbursement and maintenance of sewer structures upsurge with an increase in the rate of MIC. The focus of this review is to describe MIC in sewer structure and the factors influencing the corrosion such as the generation of Sulfuric acid (H2SO4), Relative Humidity (RH), pH of the concrete structure and temperature. Modern developments in the design of Fiber Optical Sensors (FOSs) for observing the parameters including pH, Hydrogen Sulfide (H2S), RH and temperature will be discussed.
... In wastewater treatment processes, sensors pose major difficulties [15]. This is due to the requirements of the environment in which they must work (contact with biochemical components) but especially because of the physical variables they are supposed to measure: molecular concentration in a gas or a liquid, air, biomass concentration, sterilizing value, etc. ...
This paper presents a thorough review of control technologies that have been applied to wastewater treatment processes in the environmental engineering regime in the past four decades. It aims to provide a comprehensive technological review for both water engineering professionals and control specialists, giving rise to a suite of up-to-date pathways to impact this field in light of the classified technology hubs. The assessment was conducted with respect to linear control, linearizing control, nonlinear control, and artificial intelligence-based control. The application domain of each technology hub was summarized into a set of comparative tables for a holistic assessment. Challenges and perspectives were offered to these field engineers to help orient their future endeavor.
... BOD is a typical parameter that has been measured in monitoring wastewater systems. It can be characterized as the quantity of dissolved oxygen in milligrams per litre, needed by the microorganism to break down the degradable organic carbonaceous that exist in the water through their bioprocess or biochemical under the reaction situation [49]. ...
Chemical-sensor and bio-sensor technologies commonly used for quality management of wastewater have been critically reviewed. The applications of electrochemical, opto-chemical, piezoelectric, acoustic wave, Biochemical Oxygen Demand (BOD), amperometric BOD, bio-enzymatic, bio-acetylcholinesterase and bio-optical algal sensors are detailed. The effectiveness of sensor measurement in terms of accuracy, selectivity, overall cost, and practicality are the main attributes for appropriate selection of sensor technologies in wastewater quality management. This study provides up-to-date information for researchers who look forward to developing better improved and improvised sensors for the future.
Industrial and population expansion in the last few decades has been a critical contributor to water quality degradation. Some of the gases emanating from water treatment plants are toxic and flammable, which need to be identified, such as hydrogen sulphide, carbon dioxide, methane, and carbon monoxide. Water quality monitoring systems must be developed to meet legal, environmental, and social requirements. Monitoring water quality is difficult due to the variability, nature, and low concentrations of contaminants that need to be detected. The gas emanating from these treatment processes plays an essential role in water treatment, monitoring, and control. Gas sensors can be used as a safety device in the water purification process. The gas sensors receive input signals in chemical, physical, and biological stimulus and convert them into electrical signals. The gas sensors can be installed in different wastewater treatment processes. In this review, we present state-of-the-art progresses, landmark developments, and technological achievements that led to the development of gas sensors for evaluating water quality. The role of gas sensors in water quality maintenance and monitoring is discussed, and different analytes and their detection technologies and sensing materials outlining their advantages and disadvantages have been summarized. Finally, a summary and outlook for future directions of gas sensors in water quality monitoring and maintenance are provided.
The primary mandate of wastewater treatment facilities is the limitation of pollutant discharges, however both continued tightening of permit limits and unique challenges associated with improving sustainability (i.e., resource recovery) demand innovation. Enabling increasingly sophisticated treatment processes in a cost-effective and energy-efficient way requires expanding capabilities for rapid, accurate real-time quantification of a broadened range of wastewater constituents as well as envisioning novel feedback control strategies based on these signals. This manuscript quantitatively compares results of early adoption of instrumentation and process upgrades at operating wastewater treatment facilities and proof-of-concept research results, with a focus on leveraging real-time sensing of wastewater chemistry for process monitoring and control. Up to 10% improvement in nutrient removal and energy savings are already being achieved, yet shortfalls in hardware readiness, lack of field-relevant context of research results, and a widening gap between the training of environmental engineers and the skillsets required to develop and maintain sensor-driven solutions present challenges. A forward-looking roadmap highlights opportunities for accelerating innovation, including (1) ensuring research results are published in units and context that allow operators to make an informed cost–benefit analysis with explicit comparison to existing operational baselines, (2) promoting integrated design of hardware and software to generate novel approaches for improved sensing of target analytes, (3) strengthening partnerships nationally, including for data sharing, field testing of new hardware, and expanding educational curricula, and (4) building forums for sharing of expertise and data among plant operators to enable smaller facilities to more cost-effectively collect information required to design and evaluate upgrades.
A newly developed non-contact high resolution real-time microwave sensor was used to determine the breakthrough time and adsorption capacity for adsorbents/adsorbates with different dielectric properties. The sensor is a microwave microstrip planar resonator with enhanced quality factor using a regenerative feedback loop operating at 1.4 GHz and adjustable quality factor of 200 to 200,000. Beaded activated carbon (BAC, microwave absorbing) and a polymeric adsorbent (V503, microwave transparent) were completely loaded with 1,2,4-trimethylbenzene (non-polar) or 2-butoxyethanol (polar). During adsorption, variations in the dielectric properties of the adsorbents were monitored using two microwave parameters; quality factor and resonant frequency. Those parameters were related to adsorption breakthrough time and capacity. Adsorption tests were completed at select relative pressures (0.03, 0.1, 0.2, 0.4, and 0.6) of adsorbates in the influent stream. For all experiments, the difference between the breakthrough time (t5%) and the settling time of the quality factor variation (time that the quality factor was 0.95 of its final value), was less than 5%. Additionally, a linear relationship between the final value of the resonant frequency shift and adsorption capacity was observed. The proposed non-contact sensor can be used to determine breakthrough time and adsorption capacity.
We have developed, in conjunction with Solartron ISA, an electromagnetic cavity resonator based sensor for multiphase flow measurement through an oil pipeline. This sensor is non-intrusive and transmits low power (10 mW) radio frequencies (RF) in the range of 100–350 MHz and detects the pipeline contents using resonant peaks captured instantaneously. The multiple resonances from each captured RF spectrum are analysed to determine the phase fractions in the pipeline. An industrial version of the sensor for a 102 mm (4 inch) diameter pipe has been constructed and results from this sensor are compared to those given by simulations performed using the electromagnetic high frequency structure simulator software package HFSS.
The objectives of this study were to establish an on-line controlling system for nitrogen and phosphorus removal synchronously of municipal wastewater in a sequencing batch reactor (SBR). The SBR for municipal wastewater treatment was operated in sequences: filling, anaerobic, oxic, anoxic, oxic, settling and discharge. The reactor was equipped with on-line monitoring sensors for dissolved oxygen (DO), oxidation-reduction potential (ORP) and pH. The variation of DO, ORP and pH is relevant to each phase of biological process for nitrogen and phosphorus removal in this SBR. The characteristic points of DO, ORP and pH can be used to judge and control the stages of process that include: phosphate release by the turning points of ORP and pH; nitrification by the ammonia valley of pH and ammonia elbows of DO and ORP; denitrification by the nitrate knee of ORP and nitrate apex of pH; phosphate uptake by the turning point of pH; and residual organic carbon oxidation by the carbon elbows of DO and ORP. The controlling system can operate automatically for nitrogen and phosphorus efficiently removal.
For efficient energy consumption and control of effluent quality, the cycle duration for a sequencing batch reactor (SBR) needs to be adjusted by real-time control according to the characteristics and loading of wastewater. In this study, an on-line information system for phosphorus removal processes was established. Based on the analysis for four systems with different ecological community structures and two operation modes, anaerobic-aerobic process and anaerobic-anaerobic process, the characteristic patterns of oxidation-reduction potential (ORP) and pH were related to phosphorous dynamics in the anaerobic, anoxic and aerobic phases, for determination of the end of phosphorous removal. In the operation mode of anaerobic-aerobic process, the pH profile in the anaerobic phase was used to estimate the relative amount of phosphorous accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), which is beneficial to early detection of ecology community shifts. The on-line sensor values of pH and ORP may be used as the parameters to adjust the duration for phosphorous removal and community shifts to cope with influent variations and maintain appropriate operation conditions.
Homogenized activated sludge samples from a laboratory activated sludge unit and a domestic activated sludge sewage treatment plant were plated out on two non-selective agars to compare laboratory and field populations. Following viable cell counts, 129 colonies were picked from high-dilution countable plates. Subcultures were subjected to a wide variety of macro- and micromanipulations to determine the approximate number of cultures representing each genus, and in a few cases, species of heterotropic bacteria and yeasts present. The bacteria included species in the genera Acinetobacter, Alcaligenes, Brevibacterium, Caulobacter, Comomonas, Cytophaga, Flavobacterium, Hyphomicrobium, Microbacterium, Pseudomonas and Sphaerotilus. One yeast, Debaromyces species, also occurred in the domestic sludge in significant numbers. The absence of Zoogloea is discussed.
The in situ monitoring of phosphate has been of great importance in many environmental applications, particularly those involving biological treatment processes and eutrophication monitoring. A microelectrode with small tip size (~10 mum) was fabricated with cobalt wire, characterized and evaluated for in situ and in vivo environmental analysis of phosphate in biological applications. The electrochemical performance of this cobalt-based microelectrode was fully examined for its characteristics, including detection limit, response time, selectivity, reproducibility, life time, interference with pH, ions and dissolved oxygen (DO), and the stirring effect. The microelectrode showed excellent selectivity for the orthophosphate ions (HPO(4) (2-), H(2)PO(4) (-)) in various environmental conditions. Alkalinity and DO were found to interfere with electrode response to phosphate. The phosphate microelectrode was also evaluated with Scanning Electron Microscopy (SEM) and Cyclic Voltammetry (CV). The developed microelectrode was used for in situ monitoring of phosphate in microbial flocs. Well-defined phosphate profiles across the flocs were observed under anaerobic (phosphorus release) conditions. This full characterization and successful application showed that the cobalt-based phosphate microelectrodes can be a very useful tool for in situ measurement of phosphate in various environmental conditions, including within microbial flocs.
A moisture sensor is described that consists of a microwave
circuit working at 2.45 GHz. The system is an interferometer, a part of
which is formed on a Duroid substrate. The characteristics of the system
are analysed and discussed. Preliminary experiments, made on different
materials, for moisture contents smaller than 16%, show the accuracy of
the sensor to be better than within ±0.1%