| The combustion of fossil fuels is not only causing serious threats to the environment but also the reserves of such hydrocarbon fuels are depleting day by day. So, researchers around the world are trying to find suitable replacement of fossil fuels which should be environment friendly and also available as a renewable source of energy. In this regard, hydrogen got more attention of the scientists and researchers because of its high energy contents of 122kJ/g and environment friendly nature, as during the combustion of hydrogen, only water is produced.Bio-hydrogen production by dark fermentation requires a feedstock and source of microorganism. Rice straw is abundantly available as 1.35 tons of rice straw are produced for every ton of rice grain harvested, which makes rice straw is a suitable feedstock for bio-hydrogen production through anaerobic digestion. On the other hand, mix consortia of Clostridium in the form of sludge is the best option to be used as a source of microorganism.Keeping in view all these facts, this research work was carried out to produce bio-hydrogen by utilizing the rice straw. For this purpose, a 20L anaerobic bio reactor was developed to produce bio-hydrogen from co-digestion of pretreated straw and sludge in equal proportion. The feedstock was added to the reactor along with water in such ratio that maintains total solids (TS) at 10%. The process was carried out under mesophilic and thermophilic conditions in order to compare the results. The bio-hydrogen production, drop in pH and production of volatile fatty acids were studied during the incubation period. The kinetic parameters of bio-hydrogen production were calculated with the help of modified Gompertz equation. The bio-hydrogen yield and specific hydrogen production rate (SHPR) were calculated by dividing cumulative bio-hydrogen production and bio-hydrogen production rate with removed quantity of volatile solids (VS rem) respectively. Response surface methodology was opted through quadratic modeling for better representation of the results. The results are generalized as following;1. Rice straw, rice husk, rice bran and rice waste (part of food waste) were co-digested with heat shocked sludge in order to compare the bio-hydrogen production potential of said wastes under mesophilic and thermophilic conditions by using anaerobic bio reactor. It was observed that the bio-hydrogen production potential increased with an increase in temperature from 37? to 55? for all wastes, except for rice waste. The bio-hydrogen yield from rice straw,rice husk,rice bran and waste rice was 36.62, 23.05,31.25 and 30.54 mL/VSrem under mesophilic conditions, and 40.04, 30.27, 38.60 and 23.75 mL/VSrem under thermophilic conditions respectively. The optimum pH range of bio-hydrogen production from all tested wastes except rice waste was observed at pH 7 to pH 6. The average yield of wastes produced from rice crop was 30.36 and 33.16 mL/VSrem under mesophilic and thermophilic conditions respectively.2. The effect of three common pretreatments (mechanical, steam explosion and chemical) on bio-hydrogen production potential of rice straw was compared under mesophilic(37?) and thermophilic (55?) temperature. Results showed that the solid state NaOH pretreatment returned the highest experimental reduction of LCH (lignin, cellulose and hemi-cellulose) contents and highest bio-hydrogen production from rice straw. The increase in incubation temperature from 37? to 55? increased the bio-hydrogen yield and the highest experimental yield of 60.6mL/VS removed was obtained under chemical pretreatment at 55?.The time required for maximum bio-hydrogen production was found on the basis of kinetic parameters as 36h to 47h of incubation which can be used as a hydraulic retention time for continuous bio-hydrogen production from rice straw. The optimum pH range of bio-hydrogen production was observed to be 6.7±0.1 to 5.8±0.1 and 7.1 ±0.1 to 5.8±0.1 under mesophilic and thermophilic conditions respectively.3. The impact of three concentrations (3%, 6% and 9%) of NaOH during solid state treatment of rice straw was studied lignocellulosic properties of rice straw as well as on bio-hydrogen production. It was observed that the increase in NaOH concentration from 3% to 9%increased the reduction rate of cellulose, hemicellulose and lignin by 3.82%-10.332%, 10.78%-50.40%, and 8.12%-43.31% respectively as compared to untreated straw. The increase in NaOH concentration from 3% to 6 % increased the bio-hydrogen yield from 43.53 to 51.18 mL/VS rem under mesophilic and 49.10 to 60.60 mL/VS rem under thermophilic conditions. The further increase from 6% to 9% NaOH concentration decreased 11.5% and 6.4% bio-hydrogen yield under mesophilic and thermophilic conditions respectively. The reduction was observed due to possible over dose of NaOH causing higher level of Na+. As a whole, pH from 7.3 to 5.6 was found optimum for bio-hydrogen production from NaOH pretreated rice straw. On the other hand, the VFA production was also increased with incubation time, NaOH concentration and temperature.4. In order to conserve the input energy, the effect of heating 12h/day and 24/day was studied on 6% NaOH treated rice straw under thermophilic conditions (55?). It was found that the decrease in the heating interval from 24h/day to 12h/day, decreased the cumulative bio-hydrogen production by 39%. The corresponding bio-hydrogen yield was decreased 17% from 60.60 mL/VS rem to 50.45 mL/VS rem due to decrease in heating interval from 24h/day to12h/day. The decrease in heating interval from 24h/day to 12h/day was found suitable for controlling VFA production as VFA production at 12h/day increased by 21.11 % ±2.14% when heating was done for 24h/day. As a whole, the interval heating was found a suitable option for treatment plants as by saving 50% input energy, the VS removal efficiency was decreased by 27% only.5. The quadratic modelling was used to develop surface plots for cumulative bio-hydrogen production, drop in pH and volatile fatty acids production, which provided better representation of the impact of different pretreatments on bio-hydrogen production, drop in pH and production of volatile fatty acids. |
PDF Full Text Request