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Domestic Biogas Plant Construction Complete Guide 4th Part

Helping Hands

2 Oct, 2015

Proper Construction of Domestic Biogas Plant

So for Gobar gas domestic biogas plant construction manual four parts are described, including it’s all contents, introduction, material required, benefits and installation guidelines. Now we are moving towards proper construction of biogas plant. size, construction siteselection and quality standards of construction materials are discussed in previous post, now in this post we will discuss plant layout of bio gas plant, digging of pit and construction of digester in detail.

Layout of Bio Gas Plant

Before the start of digging, the dimensions of plant on the ground are made. First Level the ground and draw the locations of the digester, outlet tank, inlet pit and a straight line in which the centers of inlet, digester and outlet are located. Insert a wooden stick in the center line. Select the outer radius of the pit including wall thickness, plaster thickness and 10 cm space for a footing projection for brick walls as shown in figure. To indicate the area of dig makes a circle. From the centre point where the central line meets with the perimeter of the digester, draw a tangent and measure a length equal to half of the size of manhole (half of 60 = 30cm) adding wall thickness and plaster thickness.

Measure size of manhole plus wall thickness plus plaster thickness in the center line to decide the positioning of Manhole. Mark the manhole ensuring that the inner size is 60 cm x 60 cm. To decide the location of outlet, take half the breadth of outlet plus wall thickness plus plaster thickness and mark the points in either side of the centre point where the central line meets with the perimeter line. From the centre, measure the length of outlet plus wall thickness plus plaster thickness to decide the outer dimension of outlet length wise. Use colored powder to mark the dimensions.

Digging of Biogas Pit

Digging is an important step of domestic biogas plant construction. Digging should be done as per layout. After digging up to the required depth level the pit bottom. Now horizontal poles have to be placed in the ground level crossing each other at 90 degree in the centre. Ensure that the poles rest at leveled ground. The vertical pole will guide the construction of digester wall.

Construction of Biogas Digester

Construction of biogas digester is the main and important step of biogas construction. First soak the brick in water for about 10-15 minutes before use and mortar it properly. The ratio of cement and sand should be 1:3. At the centre of the pit, a straight rod or pipe must be placed in an exact vertical position.

At ground level place a horizontal pipe in the centre of the pit. The vertical pipe can now be secured to the horizontal pipe. Now, fix the radius of wall at the floor with the help of a string attached to the vertical pipe.

Every brick which is laid in the round wall has to be exactly at a distance from the vertical pipe. After deciding the radius of digester, a circle has to be drawn to decide the inner circumference of the round wall. Now, the base of round wall is constructed. The construction of round wall should be started from the side of manhole. First a space of 60 cm plus plaster thickness has to be marked and then construction of wall started. Place the first brick with the help of guiding string. Go on placing the bricks in circle with the help of this string. If brick masonry, the first row of bricks must be positioned on their sides so that a 5 cm high, 20 cm wide base is made. It is essential that first row is placed on a firm, untouched and leveled soil. The next rows of bricks can be positioned on their lengths so that the wall thickness becomes 4.5". The backfilling has to be done with great care to avoid cracks in round wall and dome.

While laying bricks ensure that the joints between them are filled with mortar, properly compacted. The thickness of mortar joint should be at least 10 mm. Ensure that the mortar joints in two adjacent brick layer never fall in vertical line.

When the height of round wall reaches 30 cm, place 2 inlet pipes (one for conveying cattle dung and the other for human excreta from toilet). You can place one only for cattle dung. These pipes should drain exactly at the opposite side of the manhole opening. The slope of these pipes should at least be 60° with the ground level. Ensure that the lengths of inlet pipes are sufficient enough to construct the floor of inlet at least 15 cm in higher elevation than the level of slurry overflow at the outlet wall. To reduce the risk of blockages, the inlet pipe must be placed as vertically as practically possible.

Exactly to the opposite of the dung inlet pipe, a 60 cm wide opening must be left in the round wall which acts as manhole. The digested slurry also flows out to the outlet tank through this opening. The inlet pipe from the latrine should be placed as close as possible with the dung inlet pipe with a

maximum distance of 30 degrees from the dung inlet on the dang inlet centers manhole line.

Now the digester floor has to be constructed. For this, a flat soling of broken bricks or stones should be done in the compacted floor. After properly ramming the stone layer, a thick layer of plaster in cement mortar (1:4) has to be applied and finished properly.