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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Abstract
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.