International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 05 Issue: 10 | Oct 2018 www.irjet.net p-ISSN: 2395-0072 © 2018, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 1934 Design and Fabrication of a Micro-respirometer to Measure the Short- Term Respiratory Quotient (RQ) of Wastewater Samples M. S. Rahman 1 , M. Z. Mousumi 2 , M. A. A. Sakib 2 , M. S. A. Fahad 2 , T. J. CHY 2 & N. M. H. Robiul 3 1 Associate Professor, Department of Civil and Environmental Engineering, Shahjalal University of Science and Technology, Sylhet, Bangladesh. 2 Student, Department of Civil and Environmental Engineering, Shahjalal University of Science and Technology, Sylhet, Bangladesh. 3 Assistant Professor, Department of Civil and Environmental Engineering, Shahjalal University of Science and Technology, Sylhet, Bangladesh. ----------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - The main objective of the study is to develop a low-cost wastewater micro-respirometer to determine some important bioactivity performance indicators such as oxygen consumption rate (OCR), carbon dioxide evolution rate (CER) and respiratory quotient (RQ) of wastewater samples collected from effluent treatment plants (ETPs) and other wastewater sources. The developed apparatus was comprised of two major parts, a reaction chamber and a measuring unit facilitated with a well type vertical volumeter. Validation of the newly fabricated respirometer was done by checking the repeatability of the test results using standard sodium sulfite deoxygenation method. The qualities of the wastewater collected from different sources of Sylhet city area of Bangladesh were characterized in terms of pH, total solid (TS), total dissolved solid (TDS) and chemical oxygen demand (COD). Finally, five wastewater samples (both municipal and industrial type) covering low range COD were tested for three hours of incubation period to obtain respirograms for calculating OCR, CER and RQ under room temperature. Similar fashion of experiments were conducted with another five wastewater samples covering high range COD. Samples originated from a pharmaceutical industry under high range COD category had shown highest value of CER (4.1 mg/L.min) and the corresponding RQ was constantly above one. Under low range category mixed type wastewater samples had shown the highest RQ (3.5). However, using the device ETP personnel could make a rough idea about the type of influent wastewater and subsequent follow-up steps could be formulated and maintained during plant operation. Key Words: Oxygen consumption rate, Carbon dioxide evolution rate, Effluent treatment plant, Low-cost, Manometer, Respirometer, Respirogram, Respiratory quotient, Wastewater. 1. INTRODUCTION In our country, biochemical oxygen demand (BOD) is being used as a unique wastewater quality index from academic to industrial level for both design and operation of effluent treatment plants (ETPs). Therefore, it is very important to develop a relatively faster and cost-effective way for understanding the biodegradation phenomena that are taken placed in a reaction tank of an ETP [1, 2, 3]. Respiration is generally considered as a general measure of the microbial activity [4, 5]. Therefore, the respiration process and its qualitative and quantitative phenomena could be an effective indicator of the on-going condition of a typical biodegradation process. Respirometric parameters such as cumulative oxygen consumption (COC), oxygen consumption rate (OCR), cumulative carbon-dioxide evolution (CCE), carbon dioxide evolution rate (CER) and respiratory quotient (RQ) can ascertain the presence of organic matters, microbes and respiration type present in wastewater by observing microbial activities [4, 5, 6]. These parameters can provide a reliable and scientifically sound assessment of biodegradable criteria. Oxygen consumption and carbon dioxide emission are directly associated with both biomass growth and substrate removal [7, 8]. It can be considered as one of the most important information sources in activated sludge process modelling and process control. Respirometry is used to assess wastewater toxicity to heterotrophic and nitrifying bacteria in activated sludge [9]. Respirometry is a direct method for measuring sludge activity and thus toxicity to sludge [10]. The method for analysing wastewater based on Respirometry and COD is comparatively new to the dominant part of higher educational institutions in Bangladesh. From this research different parameters as stated earlier like OCR, COC, CER, CCE, RQ and COD can be known which will give a clear picture about the concentration of organic matters and biodegradation status of wastewater under some treatment. Thus, the main objective of the study is to develop a low-cost wastewater micro-respirometer (named as ‘Waste respirometer’) to determine some important respirometric parameters such as oxygen consumption rate (OCR), carbon dioxide evolution rate (CER) and respiratory quotient (RQ) of wastewater samples. This study can present an improved quick test protocol for analysing wastewater with locally available materials and technology. 2. RESEARCH METHODOLOGY Before starting design and fabrication of the present respirometer, a survey was done to find the existing devices in the market and nearby laboratories. After that a prototype device was built to test the feasibility of the concept and device as well (Figure 1). Then final fabrication of the device was done following standard fabrication process (Figure 2 and Figure 3).