The majority of codes require vents to rise at least 2 feet above the roofline. However, you can extend them up to 5 feet if necessary to clear an overhanging branch or tree. A vent pipe with 100 mm diameter and a wire mesh cover is required to be installed above the first chamber. If the tank is within 15 m of the building, the vent pipe should be at least 2 m high. The vent pipe should be 2 m high if the tank is closer to the building. The pipe’s height can be increased to allow the gasses and odors to be released at a higher level. This allows for the ventilation air to blow over the structure during windy days.
These Are The General Principles To Be Followed When Building Large-Sized Septic Tanks:
1. Maximum capacity is 100 liters per person. The minimum design number should be five people. Minimum retention time should be between 24 and 36 hours.
2. Minimum inner width should not exceed 75 cm (2.25 ft). The length should be three-times the width. A medium-sized to large tank should be divided into three equal chambers. Two divisions might be sufficient for small tanks such as those in smaller residences that house 4 to 5 people.
3. The liquid level should not exceed 1 to 2m (normally 1.5m or 5ft). The tank’s top level should be at least 30cm above the liquid level. This creates an air space.
4. The outlet level should be 50 nuns higher than the inlet.
5. Above the first chamber, a vent pipe measuring 100 mm in diameter and covered with a wire mesh cover is required. The vent pipe should be at least 2m high if the septic tank lies 15m from the building. The vent pipe should be 2 m higher than the roof if the tank is closer.
6. An outlet should be equipped with a dispersion ditch so that the effluent can flow to a trench at least 15cm below ground level. To allow for easy dispersal of outflowing water, the stoneware pipes should be laid in the dispersion ditch with loose joints and sockets (different than the normal). below).
7. Inside the tank, there will be three chambers and two cross walls. The first wall should be built on an R.C.C. (1) lintel placed 30cm above the tank’s bottom. It should be 15 cm higher than the liquid level. Sometimes, this chamber is called the grit chamber.
The second cross wall should extend from the floor to 15 cm above liquid level. This wall should be constructed with holes made of honeycombed brickwork at a depth 40 cm below the liquid level. The water will flow through the holes into the third chamber, and the scum will remain on top of the second chamber. [A small tank with two chambers can be equipped without the second cross wall, as shown in Fig. Above
8. R.C.C. is required for the base slab. (1:2:4) and walls can be made of one-brick for tanks up to 3.6m (12ft) in length. It can also be constructed as twin tanks with a common wall. Precast slabs can be used as top covers. They can be lifted up with ease and covered with earth. Manholes can also be installed for cleaning if the top is a continuous slab.
9. Plaster the outside and inside with 1:3 cement mortar (12mm thick). To collect the sludge, the concrete floor below is sloped at 1-in-20 towards the inlet. The ground should not be covered with the sludge. It should be removed from site or buried in a pit.