Chemical and Biochemical Sensors for Pollution Prevention

Chapter 5

Chemical and Biochemical Sensors for Pollution Prevention Jess S. Eldridge, Keith M. Hoffmann, Jeff W. Stock, and Y. T. Shih

Downloaded by UNIV OF PITTSBURGH on May 3, 2015 | http://pubs.acs.org Publication Date: October 6, 1992 | doi: 10.1021/bk-1992-0508.ch005

3M Environmental Engineering and Pollution Control and 3M Occupational Health and Environmental Safety, St. Paul, MN 55133

A successful pollution prevention program depends upon monitoring chemical and biochemical information in a timely manner before or at the point of emission or discharge. Industry calls for product and technology developments for chemical/biochemical sensors needed for air, liquid, and soil. Sensor technology should be viewed as complementary to laboratory instruments and human senses. Fast response, reliability and compact size are essential to perform in-situ analysis or real-time monitoring. A broad sensing principle or mechanism is often more desirable than a compound-specific device, however, compound speciation is frequently needed. Also, selectivity should be balanced by minimizing interferences associated with complex chemical matrices. Sensors should be rugged and able to operate under varying conditions. Calibration must be performed on a routine basis to insure that results obtained are indicative of the conditions present at the time the measurements are taken; therefore, the calibration technique must be simple to implement and all encompassing. Current Practices How do chemical and biochemical sensors relate to pollution prevention? Basically speaking most sensors and analytical instrumentation are assessment tools. The data generated from this equipment provides the information necessary to make decisions regarding the matrix being monitored. Ultimately the decisions made are pertinent to defining concentrations of what pollutants are being emitted relative to the project objectives. The key to pollution prevention is to reduce or eliminate pollution at it's source which tends to affect compliance issues as a side benefit. Many industries are going through a transition from a compliance only mentality toward a more progressive approach to pollution. The

0097-6156/92/0508-0040$06.00/0 © 1992 American Chemical Society

In Pollution Prevention in Industrial Processes; Breen, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.


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outdated attitude of simply complying is giving way to a more integrated proactive philosophy about pollution. The new approach is to prevent or reduce pollution at the source for one major reason; it's good business! Raw materials that are utilized on one end of the plant become waste products on the other end. In order to dispose of these wastes costly treatment processes may be necessary which cut into profit margins. Also by factoring in pollution preventive design and management early in the planning of various processes many retrofit modifications can be minimized. The outcome of preventive measures can be dramatic and very effective. The current perspective for the application of chemical and biochemical sensors is mostly from the less inclusive view point of compliance monitoring. Fortunately, by broadening the view to include preventive techniques their uses can be even more varying. With these thoughts in mind the use of sensors, probes, and instrumentation have many potential uses. Hopefully, this will outline the intent of this paper. Sample collection and flow measurements are the major thrust of the field services group. The standard practice for a majority of collected samples dictates that analyses be conducted in a laboratory setting. The laboratory utilizes the required instrumentation for sample analysis, and appropriate Q A / Q C routines are common practice. The normal turnaround time for laboratory results ranges from several days to several weeks depending on the complexity of the requested analysis. However, test results are often needed instantaneously. The driving force behind acquiring more timely data is necessitated by two main challenges: the dramatic increase in environmental regulations, and the environmentally conscious attitude adopted by 3M. Faster analytical turnaround is a current requirement, and real time data is essential in many environmental monitoring schemes. Unfortunately, technology has not advanced as fast as government regulations and corporate sentiment have, so an urgent need for real time data is apparent. The goal of the field services group is to collect information that accurately represents the overall composition of the matrix under test. The overall composition of the test matrix is not always apparent, so monitoring is often performed to determine what elements and compounds are present. The data is used to assess the impact of the effluent stream on the environment and to determine compliance with applicable regulations, optimization criteria, or preventive techniques. The presence of undefined components makes the design of a sampling and analytical scheme difficult. Collecting representative information becomes a challenge if unforeseen constituents are present or expected constituents are not present. Things get even more complicated if transitional compounds exist due to conditions in the matrix during a monitoring event. In many cases, this predicament is unavoidable, but the affects of such an occurrence can be lessened by previous experiences, utilizing broadly inclusive methods, and some luck. Often, repeat sampling trips may be needed to collect the desired information. Portable monitoring equipment is utilized to aid in the collection of representative data. Many monitoring programs employ on line sensors/instrumentation to obtain representative data. The use of portable gas chromatographs, transportable mass spectrometers, portable Fourier



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POLLUTION PREVENTION IN INDUSTRIAL PROCESSES

transform infrared analyzers, and in situ water quality probes has increased the overall integrity of sampling and analytical schemes. In terms of on site response they offer additional capabilities not possible with lab equipment and occasionally they facilitate technical advantages as well. Many times the major consideration in whether to utilize portable equipment is the need for reduced turn around time as compared to a laboratory setting. The use of field déployable analyzers supplements the existing resources that can be applied to any given environmental investigation or assessment. Portable monitors are primarily meant to aid us in our abilities to make value decisions about environmental matters based on additional information otherwise not attainable. Using portable equipment in the proper context, and in conjunction with laboratory resources may produce benefits that neither could offer exclusively where one does not necessarily replace the other. Many monitoring programs require flow measurement as one of the defining parameters. This is a basic yet critical requirement in determining mass loadings of effluent streams. Mass loadings are determined by incorporating the analytical results with the flow measurement. Emission permits are frequently established based on mass rather than concentration, so flow monitoring is essential. Equipment manufacturers have made great strides in the development of flow measurement by exploiting various sensing techniques such as ultrasonic, pressure, capacitance, magnetic, and thermal sensors. Many of the sensors developed are intended for portable applications, so the sensors fit well into monitoring schemes. Current monitoring programs use battery operated flow meters for lengthy time periods in remote locations. The flow meters are capable of long term data storage, instantaneous and totalized flow measurement, and are capable of initializing samplers when the desired conditions exist. Flow monitor control and interrogation can be conducted directly or by remote access via cellular phone modem, conventional modem, infrared, radio, or satellite telemetry. The type of telemetry utilized depends on the monitoring application. There is a need for improving conduit flow measurement by integrating multiple velocity readings simultaneously with a sensor array and computing power to match. Currently, in the absence of such a device, manual traverses or a single discrete reading is made to determine average velocity.

Challenge of Real Time Monitoring The challenges that face effective real time data acquisition are sensitivity, operational range, reliability, and portability. Also, it should be stated that the interferences associated with analysis of any kind must be minimized. The calibration of the instrumentation must be conducted such that adequate accuracy is attainable. Possibly the largest hurdle to overcome in implementing more wide spread use of real time data acquisition, is the process of validation and acceptance. The process of correlating new instrumentation to existing methodologies can be laborious and time consuming. The importance of low level detection is fortified by industry and by regulators, so sensitivity of in situ instrumentation is significant to the evaluation of real time data. Instrument sensitivity is a widely varying



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concern. Sensitivity requirements range from part per million to per cent levels, yet part per trillion levels are frequently desired and often essential. Field instrumentation must have the ability to isolate the analyte of interest from other analytes that may be present. Cross-sensitivity potential must be eliminated. Field instrumentation is often deployed in situations where the total composition of the effluent streams are largely unknown. The instrumentation must have the ability to selectively monitor for the specific analyte(s) of interest, but the instrumentation must not be affected by unexpected biases that could be present in the effluent stream. It is common to experience varying conditions during field operations, so the instrument must be capable of handling wide physical and analytical operating ranges. Elemental and compound specific detectors must be able to compensate for changes of the composition in the matrix stream and for changes in ambient conditions. For example, an exhaust duct from a combustion source can change in composition each time the input or the operation variables are affected. If hydrocarbons are present, the instrumentation must be able to respond to variations in ratio deflections in the hydrocarbon output. The moisture content and source temperature is also subject to instantaneous changes, so the monitoring instrumentation must be able to respond immediately to changes in the composition of the gas stream. The location and ambient conditions near the field monitor must also be considered. Frequently, testing is needed in remote areas where A C power is not available, so battery or solar power may be needed. The ambient temperature can easily vary from - 3 0 ° F to 100° F, and temperature changes of 5 0 ° F in an hour are not uncommon. The ambient conditions can also be extremely corrosive or moist, so field instrumentation must be able to exist in and respond to varying conditions. Real time field monitors will be used to document emission violations and to monitor process variations, so field monitors must exhibit a high level of reliability and durability. During the design stages, manufacturers should take steps to insure that all components of the field monitors are easily accessible, and a supply of spare parts and consumables must be readily available. In order to document the instruments reliability, the instrument must be easily calibrated and maintained. Before field monitors can be utilized in a monitoring scheme, the reliability of the instrumentation must be proven. Extended instrument downtimes cannot be tolerated. The reliability issue is further compounded by the application of the monitoring programs. Field monitors will frequently be deployed in remote areas, so the time that a competent technician can devote to the instrumentation will be limited. Operational reliability is a limiting factor in the application of leading edge technologies to field monitoring, but field monitors that are both reliable and durable must evolve from technological advancements. The use of in situ instrumentation and real time analyzers requires that portability be included as a major factor in the design of field instrumentation. Monitoring programs vary in duration from several minutes to several months. Frequently, monitoring programs are process dependent, and field monitors must be moved rapidly from site to site. Sample introduction and sample conditioning systems will also be needed for most field monitors. The sample interface system must also be compact


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and appropriate for the anticipated effluent streams. The need for compact, transportable monitoring equipment is governed by both time and logistical limitations. A field monitor that is too large, or too hard to transport will suffer limited use.


Categories of Real Time Data Acquisition In terms of real time data acquisition usage, the basic distinctions to be made are between sensors and on line instrumentation. The notion of sensors can be described as devices such as ion specific probes that essentially measure a single parameter or phenomena directly without additional chemical processing. These type of sensors lend themselves to in situ deployment because of their basic simplicity. There is a dramatic increase in the development of these devices. For example, water monitoring applications utilize an in situ water quality probe that can integrate, store, and transmit six (6) directly readable parameters: dissolved oxygen, pH, oxidation reduction potential, specific conductance, temperature, and depth. Various specific sensors, a pressure transducer, and a thermocouple are incorporated into a single probe. The probe integrates the effects of one parameter on others when relevant. For example, pH is temperature sensitive and is automatically adjusted to compensate for changes in temperature as measured by the probe. The probe is specifically programmed by the user to perform virtually any combination of measurements for data storage and transmission via remote telemetry or direct connection. The sensors are calibrated prior to deployment through direct computer interface with the instrument using the proper procedures. The probe is cylindrically configured in such a way to permit access through a four inch diameter pipe; thus, broadening it's application range to include down-hole groundwater monitor wells. The probe meets the criteria for real time monitoring discussed above. On line instrumentation is generally more sophisticated. On line instrumentation requires a dynamic interactive process of sequential events leading to a final output, such as temperature adjustments, addition of reagents, and extractions. The process leading to the analysis of a sample under these circumstances would typically require automatic integration and control of the components of such an instrument. Historically, the human element was in control of this process. However, with the advent of computer processing, and automated control equipment, close involvement of the human element can be reduced and the instrument can be placed on site to facilitate practical real time data acquisition and dissemination. There seems to be a steady increase in the development of these type instruments. Various manufacturers of equipment such as total organic carbon analyzers, volatile organic analyzers, portable FTIR, X-Ray fluorometer, gas chromatograph with flame ionization, photoionization, electron capture, mass spectrophotometer detectors, etc. are on the market. On line analyzers and in situ sensors will probably never fully replace the need for the classical lab analyses but will augment the general study of our environment by providing more tools with unique capabilities. On site monitors will help to characterize different matrices by providing supplemental information preparatory to the


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laboratory setting. In addition, interactive control of process/waste treatment equipment will be possible. This would greatly reduce the time lapse between knowledge of a problem, quantifying it, locating it's source, and correcting it. In the extreme case, it may be possible to entirely avert problems that would otherwise go undetected.


General and Specific Sensing In the environmental field, both regulators and industry require specific or generalized analyses of given emissions or discharges. An emission source or discharge is characterized by identifying and quantifying a set of specific and general parameters defined beforehand by parameter or afterwards by the methods used. It is common to perform a set of tests which define the project. Generally, when planning a project, one works backwards from the purpose for which monitoring is desired to design the appropriate steps to accomplish the objectives. For example, one may be required to analyze the matrix of interest for five specific compounds each in a specific detection range and each requiring different procedures. The methods used to perform this testing will look only at the five parameters in the specified ranges and ignore all else. This is an example where the discharge is defined by parameter. Alternately, the objective may be to perform a certain method in a given detection range, and to report quantifiable results. This method may only be sensitive to chlorinated compounds in the parts per million range and preclude all others. The results are reported as having conformed to the prescribed method. This is an example where the discharge was defined by method. Sometimes a certain parameter cannot be directly measured; it may be possible to establish a correlation between a different parameter and thereby provide a way to meet the monitoring requirements. In order for real time data acquisition to be a viable resource in environmental evaluations, there must be a broad base of specific and general testing to successfully utilize real-time data acquisition on a diverse practical basis.

Future Many technologies are being developed including infrared, lasers, fiber optics, radioactive, X-ray, magnetic, ultrasonic, thermal, radar, microwave, ultraviolet, potentiometric, the list goes on and on. The trend in the environmental testing area is changing; mainly due to new regulatory guidelines and industry demands. The laboratory must adjust to these changes even though the differences may conflict with today's accepted technology. Sampling specific locations require an intensive plan to ensure that samples are representative and that integrity is maintained. Often, decisions regarding waste stream profiles are a result of one time sampling and analyses which may or may not be consistent over a specific time period. Ideally, access to real-time information allows for appropriate decision making and problem solving. The current practice of taking samples and delivering them to the analytical lab takes a great amount of coordination in the sampling, preservation, and shipping within specified holding times. Once at the lab, data generation may take days or even weeks, depending


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upon the analytical methodologies required. This delay in information could result in decisions being made after the fact. On site data gathering is increasingly important as waste streams become more complex. A waste treatment facility will benefit from the ability to rapidly identify a change in the waste profile. Multiple sensor and instrumentation systems would serve the need in generating real time data. On demand interrogation coupled with limit alarms will announce changing conditions, and facilitate a response action. A s more systems become available the emphasis on sample collection may diminish, and a greater significance will be placed on calibration and maintenance. The skills and training for personnel utilizing these technologies will also change accordingly. In conclusion, the need for real time data generation has become a priority in the decision making process. The objective of the future will be to answer the question before it is asked. Hopefully, changing technologies and awareness will meet the challenges of real-time monitoring for pollution prevention. RECEIVED December 12,1991


Chemical and Biochemical Sensors for Pollution Prevention

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