Anaerobic digestion of recycled paper Mill effluent (rpme) using modified Anaerobic hybrid baffled (mahb) reactor

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Date
2016-02-01
Authors
Siti Roshayu Hassan
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Modified anaerobic hybrid baffled (MAHB) reactor is a recent reactor that widely used for rapid bioconversion of organic matter in industrial wastewater treatment process to produce methane with the help of anaerobic microorganism. A pilot scale MAHB reactor (58 L) was successfully fabricated and operated for treatment of recycled paper mill effluent (RPME). A successful start up process were achieved less than a month (28 days) with a high COD removal efficiency of 86.41 % and pH values between 7.2 – 7.4 at steady state condition. The methane content at the end of start up was recorded at 65.97 % with a total biogas volume of 0.31 L. During the process study, the MAHB reactor were run to study the performance of MAHB reactor during continuous feeding, compartment-wise profile, different organic loading rates (OLRs) and also different feeding concentrations. Result shows that the MAHB reactor successfully operated at continuous process and each compartments act as an individual reactor which gives high methane production rate. Furthermore, installation of standing and hanging baffles and introduction of packing materials into MAHB reactor provides perfect mixing between biomass and substrates. The different size and shaped of baffles also contributes to different growth of microorganism in each different compartments that leds to phase separations. The 35° ladder with inclining horizontal ladder baffled in Compartment 1 shows the best shaped of baffle that contributes to higher performances of MAHB. The effect of OLR and feeding COD concentrations shows that MAHB reactor gives high performance in terms of methane production rates and COD removal efficiencies as the OLR and feeding COD concentration increases until it reach its optimum condition. Interaction and optimization of RPME digestion were conducted using D-optimal design of response surface methodology (RSM) with two variables i.e. hydraulic retention time (HRT) and feeding COD concentrations. The optimum conditions that yield a highest COD and lignin removal efficiency as well as methane production rate was HRT of 3.93 days, feeding COD concentration of 3020.88 mg L-1 that gaves a COD removal efficiency of 97.42 %, lignin removal efficiency of 59.59 % and methane production rate of 8.07 L CH4 day-1 with desirability value of 0.897. This finding were in close agreement with the predicted optimum COD removal efficiecncy, lignin removal efficiency and methane production rate predicted by fitting analysis using artificial neural network (ANN). The optimum predicted output obained by ANN are 98.16 %, 77.29 % and 8.34 L day-1 for COD removal, lignin removal and methane production rate, respectively. Different phases of anaerobic digestion were undergo kinetic studies which revealed that hydrolysis is the rate limiting step. Applied Monod and Contois kinetic models, it shows that both give satisfactory prediction with 𝜇,􀯠􀯔􀯫 values of 1.476 and 0.6796 L day-1, respectively. Instead of kinetics, the hydrodynamic behaviours shows that dead space in MAHB reactor is between 10.13 – 10.39 % for tap water and 1.45 – 5 % for RPME. The flow pattern within the MAHB reactors showed an intermediary between the plug flows and intermediate which closer to plug flow compared to intermediate flow with a hydraulic efficiency between 0.20 – 0.64 for tap water and 1.00 – 3.95 for RPME.
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