Department of farm power & machinery

Anaerobic co-digestion is considered to be an efficient way of disposing solid wastes which can not only reduce environmental burden, but also produce bioenergy. Co-digestion of solid wastes in the absence of bacteria inoculums with variable mixing ratios of three wastes has been experimentally tested for 35 days digestion time to determine the biogas potential. The temperature remained relatively constant at a mesophilic range of 29–36°C throughout the study. An average pH of 7.4 was recorded from all digesters. The average biogas yields obtained from the four digesters (D1, D2, D3 and D4) were 13.31, 15.67, 16.52 and 19.12 L/day, respectively. The cumulative result showed that from co-digestion of D4 43.67%, 22.02% and 15.71% more biogas was produced, respectively, than others. The maximum and average COD reduction was 57% and 31%, respectively, in co-digestion wastes. The biogas comprised average of 61% CH 4 , 33.5% CO 2 , 222 ppm H 2 S, and 4.7% H 2 O, respectively.

Although, Biogas generated from anaerobic digestion process is a clean, carbon neutral and environmental friendly energy alternative, raw biogas needs to be purified necessarily before using. The removal of CO 2 from raw biogas ensures its better applications in engines, heating purposes and electricity generation. Reduction of CO 2 content also enhances the calorific value. Biogas generated from vegetable, fruit and cafeteria wastes for duration of 30 days with the average concentration for CH 4 and CO 2 as 62 and 34%, respectively have been observed. The CO 2 content was possible to reduce significantly by treating the raw biogas with purifying agents as: solid CaO, CaO solution and activated carbon. Purifying agent's mass and concentration and treatment time dependent biogas upgradation profile reveals that these novel purification processes are effective and affordable.

To cite this article: Muhammad Rashed Al Mamun & Shuichi Torii (2017): Comparison effect of feedstock to inoculum ratios on biogas yields of cafeteria, vegetable, fruit wastes with cattle manure using co-digestion process, International Journal of Green Energy,

We report a laboratory scale combined absorption and adsorption chemical process to remove contaminants from anaerobically produced biogas using cafeteria (food), vegetable, fruit, and cattle manure wastes. Iron oxide (Fe 2 O 3), zero valent iron (Fe o), and iron chloride (FeCl 2) react with hydrogen sulfide (H 2 S) to deposit colloidal sulfur. Silica gel, sodium sulfate (Na 2 SO 4), and calcium oxide (CaO) reduce the water vapour (H 2 O) and carbon dioxide (CO 2). It is possible to upgrade methane (CH 4) above 95% in biogas using chemical or physical absorption or adsorption process. The removal efficiency of CO 2 , H 2 S, and H 2 O depends on the mass of removing agent and system pH. The results showed that Ca(OH) 2 solutions are capable of reducing CO 2 below 6%. The H 2 S concentration was reduced to 89%, 90%, 86%, 85%, and 96% for treating with 10 g of FeCl 2 , Fe o (with pH), Fe 2 O 3 , Fe o , and activated carbon, respectively. The H 2 O concentration was reduced to 0.2%, 0.7%, 0.2%, 0.2%, and 0.3% for treating raw biogas with 10 g of silica gel and Na 2 SO 4 for runs R1, R2, R3, R4, and R5, respectively. Thus, given the successful contaminant elimination, the combined absorption and adsorption process is a feasible system for biogas purification.

This paper presents an experimental study on the application of chemical technology to biogas purifying before utilization. The presence of H 2 S, CO 2 and H 2 O in the biogas has corrosion effects on metallic components and may also lead to detrimental effects on health and lowering the heating calorific value. Removal of these contaminants from biogas can therefore significantly improve the gas quality. A chemical purification process was investigated for removal of contaminants from biogas. Two types of chemical mixtures were used: phase 1 (Fe o , CaO and silica gel) and phase 2 (Fe 2 O 3 , CaO and Na 2 SO 4) mixtures. The results show that the removal efficiency of H 2 S, CO 2 and H 2 O from biogas mixtures of 83.2%, 83.8%, 95.4% and 79.8%, 80.4%, 81.7%, in phase 1 and 2, respectively with a corresponding CH 4-concentration enriched of 95.5% and 89.7%. We propose that this methane enrichment process might be useful for cleaning and upgrading of biogas quality.

The presence of H2S and H2O in biogas affects the pipeline and engine performance adversely. Reducing H2S and H2O content will significantly improve the quality of biogas. A lab-scale chemical process was performed efficiently using FeCl2, Fe2O3, activated carbon, CaO, Na2SO4 and silica gel to remove corrosive H2S and H2O for enriched of methane content in biogas, to produce upgrade biomethane. H2S is to react with FeCl2, Fe2O3 and reversibly bound on the surface of activated carbon, the silica gel, CaO, Na2SO4 is to reduce the presence of water vapor. Results obtained in this study, investigate that it is possible to achieve 90-98% removal of H2S and H2O from biogas using chemical absorption or adsorption process. The removal of H2S and H2O depends on the use of chemical agent's mass, concentration and pH conditions. The results showed that for both FeCl2 and Fe2O3 solutions, the degree of acidity appeared to have a noticeable influence on the desulfurization performance. Among all adsorbents activated carbon performed best, successfully enriched CH4-concentration almost 76%. However, the best removal efficiency shows silica was 98%. Thus, given the successful H2S and H2O elimination, these chemical processes is a feasible method for biogas purification.

Co-digestion of cafeteria, vegetable and fruit wastes was anaerobically digested, in order to recover methane as a source of renewable energy. Here we report the optimal biogas production and methane yields from variable mixing ratios without bacteria inoculums added using batch digesters under mesophilic conditions. The lab scale digestion experiment was carried out in 200 L polypropylene digesters. The result showed that the co-digestion process significantly influenced the biogas and methane yields. The maximum biogas yield obtained for the mixing ratio CW:VW:FW of (0.5:1.0:1.5, 1.0:1.5:0.5, 1.5:0.5:1.0 and 1.0:1.0:1.0) were 33.92, 35.52, 36.55 and 43.87 L/d, at the 25th, 24th, 24th, and 21th day, respectively. The cumulative result showed that an increase of 48.3%, 19.95%, and 8.61% gas yields of mixing ratio CW:VW:FW (1.0:1.0:1.0) compared with other ratios of CW:VW:FW (0.5:1.0:1.5, 1.0:1.5:0.5, and 1.5:0.5:1.0), respectively. It was observed that the average methane concentration CW: VW: FW of (0.5:1.0:1.5, 1.0:1.5:0.5, 1.5:0.5:1.0 and 1.0:1.0:1.0) were 59.95%, 60.07%, 61.41%, and 63.61%, respectively. Thus, the optimum mixing ratio suggested that the co-digestion technique can be promising to produce valuable gas products and to reduce environmental pollutions simultaneously.

The majority of paddy is still processed through Engelberg hullers in Bangladesh, which are usually low capacity mills with a very high percentage of broken rice for simultaneous both the shelling and polishing operations.
This study was conducted to improve the shelling and polishing in such a way that less rice is broken and quality rice can be produced in an economical manner. In this regard, an air blowing type Engelberg rice mill has been developed in the BRRI research workshop based on AutoCAD design during 2012-2013. A cast iron roller is used in the Engelberg rice mill. The sharp and square edge Engelberg roller of the conventional Engelberg rice mill was modified to a curved edge in one side with a less sharp edge to reduce the breakage during milling by reducing the friction and sharing force during milling operation. In the Engelberg rice mill, a round type screen (without ambush) is normally used which requires higher pressure resulting more breakage. To avoid breakage and get a higher yield, ambush type, round and hexagonal screens were designed for the modified air blowing type Engelberg rice mill. It was found that the hexagonal type screen performs better than the round type. The angle of each corner of the hexagonal screen is 60
0
. In air blowing type of Engelberg rice mill, a blower is used to remove the husk and bran from rice inside the cylinder. The radius of the blower fan is 121 mm. The inlet and outlet radius of the blower is 77 mm. The blower not only cleans the rice from the husk and bran, but also reduces the temperature inside the cylinder, resulting in less breakage and higher head rice recovery as well as high milling yield. The husk and bran collection hopper used in the lower part of the Engelberg rice mill. In the outlet pipe, there is an air hole used to supply air so that the blower can get sufficient air for the suction of husk and bran. The modified rice mill were evaluated and compared with the conventional rice mill. BRRI dhan29 was used as parboiled paddy. The operational cost per hour of the two machines is almost the same, but the capacity of the modified air blowing type Engelberg rice mill is two and half times more than that of the traditional one. To process one ton of paddy by air blowing type mill, about 800 taka is needed, whereas 2,100 taka is needed for processing one ton of paddy with the traditional Engelberg rice mill. However, milling yield also increased by 2%. The modified air blowing type needs only one pass while the Engelberg rice mill needs at least two passes to get the white rice, and almost 1% paddy remains with the end product. With the modified air blowing type Engelberg, rice mill head rice recovery was increased by 1% compared to the traditional Engelberg rice mill. The modified rice mill is a promising technology for small scale farmers and rice traders in Bangladesh.