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Septic Tank - Doing Evaluation

Updated on November 12, 2014
Septic Tank
Septic Tank

A septic tank is an important constituent of septic system. It processes the wastewater collected in it so as to make it safe to release it to the drainfield. To keep your septic system in good condition it is very necessary to take care of the septic tank.

Nowadays there are plenty of types of septic tanks. While deciding which one to buy, it is useful to evaluate the primary and secondary treatment given by each of them to the wastewater.

The primary treatment is of anaerobic type. This means that it is without oxygen. The reason for this is oxygen in the tank is used up fast. Due to the anaerobic treatment an organic substance called biochemical oxygen demand (BOD) is released in the septic tank.

In the septic tank the wastewater collected is divided into three parts, viz. solids or sludge which settles down, liquid water which remains in the middle and oily or greasy layer called scum which floats on the watery part. Out of these, sludge and scum should not be mixed with the watery part and released into the drainfield, because if they reach the drainfield they contaminate it as well as soil. They should be pumped out periodically. Generally pumping of a septic tank should be done once in three years. If they are not pumped out, they damage the septic tank.

The primary treatment of wastewater in a septic tank can be enhanced by filters. These filters are either made up of plastic trays or a series of long tubes. They enhance the removal of solids from the watery part while the sewage moves towards the outlet of the septic tank. The filters are to be cleaned once in 2 to 3 years.

Secondary treatment is aimed at removing BOD. Removal of BOD decreases the biomat. Some advanced treatment units oxygenate the wastewater actively to decrease BOD. Among the secondary treatment options, there are recirculating media filters, aerobic wastewater treatment systems and constructed wetlands. These can bring about one or more of the tasks like reduction of size of drainfield, reduction of depth of soil required in the drainfield, allowing drainage into erstwhile unfavorable soils, like clay, giving out more nitrogen from the effluent and allowing effluent to be given out into environmentally sensitive fields.

Concrete Septic Tanks

These were installed primarily because of low cost. They include both cast-on-site as well as precast tanks. Nowadays precast concrete septic tanks are more popular because they are designed and created in a controlled environment. This makes them of uniform quality, whereas cast-on-site tanks may differ in quality because of differing skills of workers working on them. Moreover, as, it is not possible to build a tank in a single pour, there is a risk of cold joints giving rise to leaking.

Concrete Septic Tank
Concrete Septic Tank

Fiberglass Septic Tanks

These are made of fiberglass-reinforced polyester (FRP) which is a laminate, an amalgamated material. FRP is made of a liquid resin which hardens after the addition of a catalyst. The glass fibers form the strengthening material. Fiberglass septic tanks also have FRP ribs which offer the tanks enhanced structural integrity.

Fiberglass Septic Tank
Fiberglass Septic Tank

Injection-Molded Septic Tanks

This is a variation of fiberglass tanks. A fiberglass injected molding process is used while manufacturing them. The process is called resin transfer molding (RTM) and it uses a very low pressure injection. They are expensive, yet preferred at many places mainly due to the inconvenience of transporting and installing heavy concrete tanks.

Injection Molded Tank
Injection Molded Tank

Polyethylene Septic Tanks

These got bad reputation mainly because they got distorted because of the weight of soil and created problems. However they have some strong points too. They are extremely easy and cheap to buy, transport and install. No crane is required to install them. And now some manufacturers have started making these types of tanks which don’t need water in the backfill process. This is achieved by combining a high-strength engineered resin with an original multi-layer co-extrusion treatment named COEX-3 which uses high-molecular weight HDPE and a ribbed pattern. Therefore they have overcome their earlier bad reputation.

Polyethylene Septic Tank
Polyethylene Septic Tank

Copolymer Polypropylene Septic Tanks

Specialty of these tanks is they are 1/10th in weight to that of concrete tanks of same size, but are stronger than the concrete tanks. They are eco-friendly and their manufacturers claim that they can be used permanently. They are very easy to install too.

Thus there is a quite wide chance for you to choose from the septic tanks available in the market. They are particularly useful in the conditions when regulations are strict. Still while shopping for the septic tanks you should beware of substandard products and scrutinize everything.

How to build a septic tank


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