International Research Journal of Environment Sciences________________________________ ISSN 2319–1414Vol. 2(6), 71-75, June (2013) Int. Res. J. Environment Sci. International Science Congress Association 71 Application of a Multichannel Respirometer to Assess the Biokinetic Parameters of Industrial WastewaterM.S. Rahman1* and M.A. Islam2 Dept. of Civil and Environmental Engineering, Shahjalal University of Science and Technology (SUST), Sylhet, BANGLADESH Dept. of Chemical Engineering and Polymer Science, Shahjalal University of Science and Technology (SUST), Sylhet, BANGLADESH Available online at: www.isca.in Received 3rd May 2013, revised 13th May 2013, accepted 12th June 2013 AbstractIn this study, some important biokinetic parameters of industrial wastewater were assessed by a locally fabricated multichannel respirometric device. A revised theoretical approach has also been incorporated in the determination of biokinetic coefficients (yield coefficient, reaction rate and biodegradability) using the concept of headspace gas respirometry. Wastewater samples from different industrial sources were studied by the device in presence of freshly cultured seed inoculums as biomass agent. It is found that the results obtained from the respirometric bioassay can easily evaluate the overall operation and treatment efficiency achieved by an industrial effluent treatment plants (ETPs). Keywords: Multichannel respirometer, wastewater, yield coefficients, OUR, biodegradation, ETPs. IntroductionWastewater disposal is a burning issue of the day in Bangladesh. Different programs are being undertaken to reduce the severity of the problems. Environmental laws and legislations are being customized for proper application. Various guidelines are enforced to follow. Industrialists are very much concern to handle this problem soundly. However, selecting an efficient and low-cost treatment option is a very crucial matter1-3. Industrial wastewater could be treated by physical, chemical and or biological processes. The biological system in form of activated sludge can be a cheapest and feasible choice in the context of our country since it solely depends on the natural biodegradation process and requires less operation and maintenance efforts. However, the space requirements are much higher for this particular type of treatment in compare to other conventional options. The amount of space depends on the biodegradability of organic matters of the wastewater which actually associated with the biokinetic parameters of the microbes and gravitational settling characteristics of activated sludge. A typical biological unit of wastewater treatment consists of two parts i. aeration reactor ii. sludge separation unit. The size of the reactor solely depends on the microbial growth kinetics. So in order to optimize the reactor volume, this kinetics should be studied thoroughly3,4. In the present study, a low cost respirometric device fabricated in the Laboratory of Center for Environmental Process Engineering (SUST, Bangladesh) has been used for the determination of wastewater biokinetic coefficients. The respirometric device measures the oxygen concentration in the gas phase by manometric method. Its performance has been tested with a standard Glucose-Glutamic acid (GGA) solution, and the oxygen uptake data acquired from the biodegradation of the solution have been compared with those reported in the literature5-7. Efforts have been made to correlate various biokinetic parameters with the oxygen uptake data revealed form the experimental respirograms8,9. These parameters can assist users in decision making with regard to treatment efficiency improvements and optimization of the ETPs. Biokinetic parameters: Biodegradability and rate of biodegradation: The concept‚ ’biodegradability’ expresses the capability of an object to undergo biodegradation (manifested by the decrease in the chemical oxygen demand, COD8,10. The COD has both biodegradable and non-biodegradable components as follows:  \n \r   (1) The subscripts In, sI and sB denote respectively the insoluble, soluble inert and soluble biodegradable constituents of the COD. The subscript symbolizes substrate concentration in the sample. In a biodegradation process, the insoluble and inert constituents of the COD remain unaffected and the oxygen uptake is only related to the biodegradable constituents, CODsB. Thus,  \n \r     (2) Where the subscript 0 stands for the parameter at the time =0. The biodegradability, , of an effluent could be defined as follows:   (3) Where the subscript stands for the parameter at the time . In a biodegradation process, CODsB is assumed zero at the time . Conventionally a BOD-COD ratio is taken as a measure International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 2(6), 71-75, June (2013) Int. Res. J. Environment Sci. International Science Congress Association 72 for the biodegradability of an effluent. The BOD of an effluent is defined as the oxygen uptake (OU) in a biodegradation process in a given time . The BOD value increases with the biodegradation time, and conventionally, the criterion for the effluent quality is accepted to be BOD (with biodegradation time = 5 days) and the biodegradability is defined as  (4) Where BOD known as ‚ultimate BOD’ is the oxygen uptake for . From the way of definition of the biodegradability, it becomes evident that is a seed-independent and is a seed-dependent parameter. But if the oxygen uptake is measured for the biodegradation with naturally grown or adapted microorganism, the biodegradability, defined by the equation (4) is quite sound for practical purposes. The biodegradability,, defined by the equation (3) is of theoretical interest and could also be used for practical purposes. Relationship among COD, activated biomass concentration, X, yield coefficient, Y and oxygen uptake, OU: In a biodegradation process, the biodegradable portion of the substrate COD is partly oxidized (measured as OU) and partly included as microbial cell-COD growth, (measured as CODequivalent of ). Thus   !"" (5) For the simplicity of the analysis, the effect of decay rate of the microorganism is ignored and the following linear relations are assumed:  !""$ (6) $% (7) Where is the yield coefficient; mass of cells produced per unit mass of substrate utilized (mg /mg COD), and is the oxidative potential of the biomass. Combining equation (5-7) we obtain &'()'*\n +,-. )//0' (8) And 23'*\n +,-. 30/0' (9) The COD vs. (equation 7) and COD vs. OU (equation 8) (or vs. OU (equation 9)) data could be fitted to straight lines to give the parameters, Y and . Thus, Y can be determined from individual batch kinetic tests for vs. CODdata using a laboratory fermentator. A rough estimation of , assuming an average value of in the range of 1.42-1.48, however, seems satisfactory for respirometric analysis of biodegradation using two measured values of COD at a given time-interval and the corresponding oxygen uptake11. Then for the calculation of the parameter , the equation (8) is rewritten as follows: %/\n \r /456/457 (10) It is difficult to collect samples for COD from a respirometric device without affecting the preciseness of the measurement of oxygen uptake. Thus, it is recommended that the COD be measured initially and after the respirometric experiment is completed. For the present analysis, the COD was measured initially and after an experimental period of 120 h and was calculated by the following relation: %8/9:;=&#x-6.4;匈9?@&#x-6.4;匈9?AB;= C\n \r /45D (11) Where OU120 is the cumulative oxygen uptake for the time = 120 h. Having the value of , the value of can be estimated (see equation 9). Calculation of biodegradability and the rate of biodegradation: For effective operation of an activated sludge plant, the biodegradability (defined by the Eq. (3) or (4)), and the biodegradation rate must be high. Combining the equation (3) and (8), and the equations (4) and (8), we haveF (12) GF (13) And combining the equation (3) and (8), for the rate of biodegradation, we have  HHF (14) Thus practically and are equivalent (simply multiple by a factor, ). As the Eq. (14) shows the biodegradation rate is equivalent to oxygen uptake rate. Thus, the biodegradation process (resulting in the gradual decrease in the COD) is manifested by the OU uptake from the system and its control could be done following the OU profile only. The OU vs. data are usually found to be described by a first order rate equation of the type: I/J@KL (15) Correspondingly, the COD-decreasing rate (biodegradation rate) is given by the following relation: FHFN@KL (16) Thus, the whole task of evaluating the biodegradability of a wastewater is reduced to the determination of (or ) and to collect OU vs. data. Material and MethodsBIOSUST multichannel manometric respirometric system (MRMR)--principle of operation and data treatment: The present unit is a specially designed device based on the principle of headspace gas respirometry. It consists of six respirometric units (RU), each of which can operate independently. The oxygen consumption of the reference and the sample solutions with different dilutions can be studied simultaneously with the MRMR. Each RU of the device is identical to that in figure 1 and comprises a constantly stirred batch reactor (CSBR) and an open tube manometer unit.