Investigating Applicability Of A Suitable Ammonia Sensor For Waste And Wastewater

Introduction

I was studying Master of Environmental Engineering and Pollution Control at Griffith University when I completed this task. Since there are number of research investigations have been conducted on ammonia sensors, it was quite difficult to choose such ammonia sensor that could be used for diverse in waste was wastewater industry. Therefore, I will be presenting the first part of the project in this episode, while the second part, which was completed in the following semester, is presented in the second episode. The duration of this project was about three months, and was ended on June 26, 2017. Griffith University has demonstrated as one of the leading research universities in Australia, and ranked 19. The university offers a large number of quality engineering courses on bachelor, master and doctorate levels including a range of professional studies.

Project

My master degree candidature was full of adventures to me as I have experienced quality education and professional development. Although all of the courses in my degree were interesting, I decided on water and wastewater sector, as it is quite emerging in Australia especially northern areas. I had few meetings with my supervisor on selecting a suitable topic, and my supervisor advised me to work on ammonia sensor, as its application is quite diverse, but limited to topic specific. Moreover, my supervisor wanted me to start my research interests with literature review that could allow me to establish the context of future research in a smooth manner. Since ammonia itself has been extensively used in a large number of industries such as process, biological, and agricultural, an increase its concentration in water bodies was reported widely.

I found that there were several methods to measure ammonia concentration in water, and it was quite important to identify an efficient and suitable sensor that could tolerate change in the subject, and also provide reliable outcomes.

Since this was my dissertation project, so I had to work alone under my advisor’s supervision. I always had strong engagement with my supervisor to ensure that my project is well planned and tracked according to the set objective. Below is my position in this project.

Personal Engineering Activities

Before I start finding the relevant literature, it was important to me to understand the basics of ammonical-nitrogen in terms of characteristics (both physical and chemical). I knew from my courses that ammonical-nitrogen covers a wide range of nitrogen based ions such as ammonium-N, ammonia-N, nitrate-N, and nitrite-N. The ammonium, nitrate, and nitrite are normally measured with wave length method using spectrophotometer. I knew that ammonia is alkaline in nature, it is colorless at STP (standard room temperature and pressure), and bitter in odor. I further explored that it is soluble in water, with about 90g/100 ml solubility at 0 °C. Since ammonia is soluble in water, fewer ions react with water to form ammonium ion. Therefore, detection of ammonium ion is the primary parameter in water and wastewater industry, which elaborates the quality of liquid stream. I also found that, ammonium ion can also be called as aqueous ammonium. Therefore, I will be using the standard term as aqueous ammonium in this episode.

I studied various kinetic reactions involved in detecting aqueous ammonium in liquid streams such as Nessler and Berthelot. I found that this equation is mostly used in most of detection instruments, where techniques such as common-flow-based are used to calculate aqueous ammonium. This technique is widely accepted because of the sensitivity, reliability, and interpretation of measured data.

I expanded my research to further understand the importance of nitrogen globally, and found that nearly 80% nitrogen is available in the atmosphere, however, most of it is unavailable for plant and other living beings uptake. I consulted books such as “Biological Nitrogen Fixation”, “Nitrogen in the Environment”, and “Nitrogen in the Marine Environment”. I found that human activities are most likely the reason of nitrogen leaching in both atmosphere and water bodies. One of the examples is excessive application of nitrogen fertilizers to agronomic lands, and in use in industrial products. I learned that nitrification encourages algal growth in water bodies that caused eutrophication. I also reviewed a number of research papers to ensure that my knowledge is up to date according to the literature, I understood the nitrogen cycle that is given below.

I also reviewed emissions from industrial and farming lands that excessive amounts of ammonia are produced. The air quality measurement detector for indoor air quality measurement, the detection limit of ammonia detector should be set about 50 ppm. For indoor air quality measurement the sensing quality of detector should be fast. When air quality outside the vehicle is low, the inlet valve of air should be closed. The response time for the air quality detector should be in seconds. Ammonia sensors third application is to measure the automotive area NOx reduction in diesel engines. Present day diesel motors work at high air-to-fuel proportions that outcome in an abundance of oxygen in the exhaust gas, bringing about vast groupings of NO and NO2 (NOx). Poisonous NOx fixations are brought down fundamentally by particular synergist diminishment (SCR) of NOx with NH3, as indicated by response (equation below). Along these lines, ammonia is infused into the fumes framework, causing smog etc.

I found various methods on measuring ammonium in liquid streams such as an automated determination of ammonium, phenol hyper chlorite method, lab-based method, colometry indo-phenol-blue method, AA-II auto analyzer, spectrophotometric method, Cobas-Fara centrifugal analyzer, salicylate method, Berthelot method, sol-gel method, and computer-based colorimetric method. Conclusively, I reviewed more than 20 research papers to understand all available and published methods, and discussed these with my supervisor, she appreciated my efforts, and encouraged me to continue further research.

I collected the data in a sequence and systematic form that was highly considered in the research study. Selecting the data collection process from different and complexed data collection process was really challenging. Thus, I focused on keeping the data collection process as simple as the complexities might impact on the research outcomes. As per the nature of present study, I collected data for the research study from the primary sources that include; journal, articles, and past research studies.

I carefully understood various injection-based methods to measure ammonium as well. For instance a SFA (segmented flow analysis) method is used for discrete analysis that involves a reaction coil, and sample is passes through it as air bubbles, the detector then detects the ammonium. This method is widely used in oceanographic sector. Another type of ammonium analysis is carried through FIA (flow injection analysis) where only carrier gas and reagents are mixed with sample, and ammonium along with nitrate and nitrite is measured via detector following the passage through reaction coil. This method is usually used in water and wastewater sector. A SIA (sequential injection analysis) method is also a reliable method in terms of versatility and computerized control. This method uses reagent in a solenoid valve, and make the process economical in terms of chemical cost. MFCIA is an enhanced version of FIA as termed as multi-commuted FIA, where solenoid valves are used to simultaneously inject the sample, reagent and carrier. The solenoid valves can also be replaced with syringe pumps for extended number of samples. MPFS (multi-pumping flow system) comprises on using miniature solenoid valves to provide better mixing of the sample and reagent, thus increasing the reliability of results.

Following injection-based method, I extended my research on spectrophotometric-based detection for ammonium as well. I found that Nessler and Berthelot reaction are used in spectrophotometric methods. I also reviewed optical absorption ammonia detection that could detect ammonia by 1 ppb (part per billion), this making is quite reliable and diverse in application. I prepared a table (shown as plate below) to compare detection ranges, and discussed with my supervisor for further advice.

I continued my research and found that metal oxide semiconductors could also be used to detect ammonia. These are normally used for gases, and work on the principle of conductance-conversion, and are gas specific thus making them less useable for most of the other gases. This method additionally requires chemicals for reaction on the metal-oxide, which utilizes metals to create particle of tested gas. The minimum detection limit of this type of sensors is 1ppm (part per million), which is quite high in regards to the critical measurements such as for air sampling. I prepared a table on detection ranges, and it is shown below as plate.

I also found that gas-diffusion method, which uses sodium hydroxide (NaOH) as soaking medium in a benefactor conduit to convert ammonium into ammonia followed by ammonia dispersion on the gas penetrable film (a hydrophobic layer). This method could be used for less intense gas mixture, as cations (such as Mg2+ and Ca2+) could restrict the measurement by making solid residue on the film surface, this making this method less reliable due to lack of versatility. A further expansion in gas-diffusion method is the inclusion of flow-injection analyzer, but highly saline streams could also restrict its application.

I explored fluorimetric technique that detects ammonium via ortho-phthaldi aldehyde (OPA). A solid fading specialist 2-mercaptoethanol or sodium sulphate is used as a soluble medium to induce OPA. I further found that sodium sulphate is much reliable than 2-mercaptoethanol as it fades the influence of amino acids, thus adding additional benefit to ammonium detection. Plate below shows detection limits with various methods using this technique.

I found that a number of sensor can be used to detect ammonium in various instruments. The used of a particular sensor is totally application specific, and also based on the detection limits of ammonium in certain samples. The application of this sensor varies with the sample type, making the sensor economical in terms of sensing capacity, versatility, and reliance. For instance, electrochemical sensor consists of a solution called electrolyte to react with ammonium, and produces an electrical pulse that is proportional to ammonium concentration. Figure below shows the working principle of this sensor.

I presented my work in weekly meeting with my supervisor, and she appreciated my interests, and courage of getting deep knowledge on my project. I felt quite motivated, and continue my research. I also found solid state sensors can also be used for ammonium detection. These uses metal oxides such as tin or aluminium oxides. A change in conductivity shows the presence of ammonium and peak is developed to record concentration. Since this process involves oxidized metals, a variation in temperature may impact the results. Therefore, a heater is installed having a temperature sensor, to maintain the temperature of solid-state sensor. This method also needs special filters to avoid an interference from other ions if present in the sample.

I found that the introduction of infrared sensor makes the ammonium detection easier in gas samples, particularly in hydrocarbon based gases. These sensors are also used in liquid samples to detection ammonium. This basic principal of this type of sensor is that the infrared rays are assorted through the sample. However, these sensors are also dependent on the complexity of sample’s characteristics that could restrict their application in certain fields, but these are quite promising in detecting high ranges of ammonium. These sensors are quite expensive because of their sensing capacity. Another type of sensor is ion-sensitive probes, which only measure ammonium ions concentration. These probes are the membrane probes that detect specific ions and transmit data to the transmitter, thus providing immediate results.

I also compared cost of various sensors available in market, and found that analyzers are quite expansive compared to the sensors. An ammonium analyzer could cost up to US$21723 of brand Denfos (an in-situ analyzer), and it could be as lowest as US$8280 of brand Nadler.

I used licensed Microsoft Office software for writing, data analysis, and presentation. I conducted all of my work in the University premises, and complied with organizational code of conduct. I contact various suppliers and vendors to confirm the market prices. I negotiated well with my work colleagues, and maintained a healthy environment. I consistently participated in meetings, and received feedback. I corrected my work directions where required on the advice of my supervisor. I maintain my work record in in a professional manner and presented myself a genuine candidate who has a strong control on reviewing literature.

Summary

I learnt a lot from this project, and found myself quite fit in the field of environmental engineering. I found that learning basics prior to start any project is the key of success. I concluded that most of the analyzers and sensors are application specific such as flow injection analyzer is best suitable for waste and wastewater for better ammonium detection and measurement. My supervisor was happy on my understanding on measuring nitrogen based samples, and encouraged me to enhance my skills by conducted further research.