Department of Agricultural Engineering

Bangladesh is a country of natural resources, but it is facing necessary energy supply difficulties for its low economical condition. Biogas can be used a substitute energy generating source in Bangladesh for its suitable climate. About 35°C temperatures are suitable for biogas production. In Bangladesh, the essential materials for biogas production can be arranged very easy and cheapest way depending on country temperature (4°C-41°C) as it is an agricultural country. About 64 study data was collected from different biogas plants from three Upazila under Jessore district named Jessore sadar, Jhikargachha and Noapara paurasava. Three sizes of biogas plants have been observed in the study areas, which are based on cow dung. The constructional costs of these plants were from 36000 taka to 52000 taka. Biogas is beneficial to human health and environment assistances. Approximately 86% and 80.3% male informed that biogas has improved their mental and physical health respectively. This response has reached more than 95% for female. Maximum male and female thought that not only physical and mental health but also their financial conditions are also benefited by using biogas. About 85.4% to 97.65% male and 88.69% to 98.72% female realized that it has the capability to decrease various waste materials that may have contrary effect on environment. From this survey, it is able to be stated that Bangladesh has an amazing potentiality to adopt more plant life particularly in rural areas for easing the existing environmental degradation, gas power storage, and developing financial situations with suitable health.

To suit to the management practices of the farmers of this region, an experiment was conducted to dewater eZuent slurry from biogas plants by Wltering its water content in a Wltration chamber/unit or pit under lab and Weld conditions. Under lab conditions, the mesh having a hole size of 3 mm £ 4 mm was found to be the best Wltering net among all other meshes studied. Dewatering in this mesh was studied in the Wltration unit of 0.6 m 3 capacity in the Weld and compared to a mesh of size 3.2 mm £ 5.67 mm. It is found that the performance of 3 mm £ 4 mm mesh was slightly better to dewater slurry (6%) and for lesser TS content of Wltered water. On an average, 27± 29% dewatering of slurry can be obtained from an eZuent slurry having a TS content of 93± 94% and 13± 14%. TS contents of the dewatered slurry can be obtained with Wltration unit that is suitable for transportation to the farms or to storage.

Direct-current electrical conductivity of single crystals of KHSO, doped with 5, 11, 30, and 437 ppm of cobalt-II is studied in the temperature range 25 to 165°C. The point defect parameters are calculated by graphical analysis of the conductivity data. Various parameters are obtained: enthalpy for the migration of proton (referred to as the enthalpy for the rotation of HSO., ion), H, = 0.55 k 0.01 eV; the enthalpy for the formation of the intrinsic defects (referred to as the enthalpy for the breaking of the HSO, dimers), HF = 1.30 f 0.01 eV; and the enthaipy for the impurity-vacancy association H. =-0.14 + 0.01 eV. The tritium diffusion studies in the pure KHSO, single crystals give 0.22 + 0.01 eV and-1.09 x 10m3 eV K-l as the activation enthalpy and entropy for the process, respectively. The Nernst-Einstein relation is not obeyed. The mechanisms for the conduction and diffusion processes in this crystal are discussed.

Direct-current conductivity of ferric-doped (138,267, and 490 ppm) single crystals of KHS04 has been studied. The mechanism for the dc conduction process is discussed. It is observed that the ferric ion forms a (Fe3+-two vacancies) complex and the enthalpy for its formation is 0.09 f 0.01 eV. It is proposed that each ferric ion removes two protons from each HS04 dimer. The conductivity plot shows the presence of intrinsic and extrinsic regions. It is proposed that in the intrinsic region the dimer of HSO; breaks reversibly to form a long-chain monomer-type structure. The conductivity in the KHS04 crystal is proposed to be controlled by the rotation of HSO; tetrahedra along the axis which contains no hydrogen atom. Isotherm calculation for the trivalent-doped system is applied to this crystal and the results are compared with Co'+-doped KHS04 crystal. The distribution coefficient of ferric ion in the KHS04 single crystal is calculated to be 4.5 x 10-l. Ferric ion causes tapering in the crystal growth habit of KHS04 and it is believed to be due to the presence of (Fe3+-two vacancies) complex. The enthalpy values for the various other processes are as follows: enthalpy for the breakage of HSO; dimer (Hi) = 1.28 f 0.01 eV; enthalpy for the rotation of HSO; tetrahedron (H,,,) = 0.58 f 0.01 eV.

Production of biogas from mixtures of fresh and partially-decomposed Ageratum with cattle dung were studied in batch digesters at 30 +_ I°C. Partially decomposed Ageratum produced 319.4 litres of gas per kg dry matter as compared to 222.4 litres of gas per kg dry matter from pure cattle dung. Fresh Ageratum supplemented with cattle dung in a ratio of 3:2 (wet weight basis) did not produce any gas, because of the accumulation of excess acids. In contrast, similar mixtures of partially decomposed Ageratum and cattle dung yielded about 9% more biogas than did pure cattle dung. The methane contents of the gas obtained from Ageratum mixtures were 62-77% as compared to 5640% from pure cattle dung.

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