OPERATION OF A DRAINAGE WASTEWATER TREATMENT PLANT

Investment and operating costs of a drainage treatment plant

When deciding on the method of sewage disposal, we are often guided by the economic aspect. The analysis showed that after 10 years of use, the cheapest solution is a drainage sewage treatment plant. The following costs were assumed for the analysis: purchase of PLN 2583 gross, assembly PLN 4300 gross and operating costs (biopreparations, waste disposal). Compared to alternative solutions, the drainage treatment plant turned out to be more advantageous than the collective sewage system, not to mention the septic tank. From the first year of operation of the sewage treatment plant, we have financial benefits compared to the costs of a septic tank or collective sewage system (we avoid costs related to every monthly bills or waste disposal).

Drainage treatment plant - principle of operation

In the first stage, the so-called anaerobic, the raw sewage flows by gravity to the septic tank. Light substances are separated in the settling tank (oils, fats) from substances falling to the bottom of the tank. When using the drainage treatment plant correctly, we must remember to empty the sedimentation tank chamber periodically, once or twice a year, depending on the operation. The bacteria that are present both in the settling chamber and in the drainage pipe system are responsible for the proper operation of the treatment plant. Systematic control of the distribution well and filter will make our treatment plant work without any reservations. the operated settling tank allows the removal of up to 65% of suspended solids and 40% of BOD₅. Then, the pre-treated sewage flows through the filter to the second stage of treatment, which takes place in the drainage. At this stage, the natural aerobic process is used, consisting in the biochemical breakdown of pollutants. For this purpose bacteria are used, for which in the wastewater is food. For the cleansing process to be effective, it must take at least three days - hence, for the proper functioning of a household sewage treatment plant, the appropriate volume of the septic tank is required.

What water and ground conditions for a drainage treatment plant?

The water and ground conditions on the plot are a factor that determines the method of wastewater treatment. When we choose a drainage treatment plant, groundwater must be at a low level of min. 2m below ground level, and the surrounding land should be light and easily permeable, e.g. sand, gravel. The sewage treatment tank and drainage pipes should be placed in an area where there are no plants with a rich root system. Such plants include all fruit and coniferous trees. The infiltration system should be located in a green area. Vehicle traffic causes hardening and compaction of the soil, which reduces the permeability. An improperly selected tank for the water and ground conditions on the plot may contribute to its cracking, crushing or displacement.

Step by step assembly

When installing a household wastewater treatment plant, we must follow the guidelines provided by the manufacturer.

1. Selection of the place where the drainage treatment plant will be located. At this stage, it is worth drawing into the land development plan the settling tank with the infiltration system  and marking the outline of the house, well, plot border and larger plantings. It is necessary to maintain the correct distance from the indicated objects.

2. The depression of the sewer pipe leading from the building determines the depth of the foundation of the reservoir and drainage. The septic tank should not be placed too deep. Za optymalną głębokość przyjmuje się ok. 50 cm. The pipe supplying sewage to the settling tank should have a slope of 2-3%. Drainage should be below the ground, at a depth of 60-80 cm.

3. When assembling the tank:

- level and align the bottom of the trench, 
- make a trench 1 m larger than the tank dimensions in length and width, a larger trench will facilitate assembly work,
- exclude the occurrence of visible physical defects that may arise during transport of the tank,
- sand used to cover up the tank must not contain sharp objects that may damage the walls of the tank,
-  pour 30 cm of bedding at the bottom of the excavation,
- place a settling tank in the trench, connect it and level it,
- when backfilling the tank, evenly fill it with water and cover the tank with sand to stabilize it,
- when installing the tank in conditions with high groundwater level, a weighting plate must be made. 

4. When installing the infiltration system:

- make a trench min. 50 cm length and the required length,
- at the bottom of the excavation, pour an appropriate gravel bed, fraction of 12-32mm,
- lay the drainage pipes wrapped with geotextile in the trench with the cuts downwards,
- the width of the ditch should be min. 50 cm, pipes should be arranged at a distance of not less than 1.5 m from each other, and the drainage length must not exceed 20 m,
- connect the drainage pipes with the tank keeping a proper slope,
- cover drainage.

What biopreparations for treatment plants?

To work properly, sewage treatment plants need bacteria that cannot be ignored. Those bacterias that require a constant supply of nutrient solution for their work should receive it every 2-3 weeks. The biopreparation BIOSTART drainage, which inoculates bacteria in the drainage system, is ideally suited to instilled the bacterias in drainage system. The biopreparations used contribute to the reduction of the volume of waste. Wastewater fed with the bacterial nutrient solution does not give off an unpleasant odor, and its volume is lower by up to 30%.  Biopreparations also have a positive effect on the infiltration system and prevent its clogging. In the case of clogged drainage, we suggest BIOMAX IMPROPER DRAINAGE, which cleans overgrown pipes.The regulation also introduces the obligation to collect samples of domestic wastewater introduced into water facilities or into the ground from household sewage treatment plants. Sampling should be performed at regular intervals throughout the year, constantly at the same place where the waste water enters the waters or the ground.

Sampling from a sewage treatment plant

Sewage treatment plants should be operated in accordance with the instructions (this applies to the frequency of emptying the primary sedimentation tank) and in accordance with the Regulation of the Minister of the Environment of November 18, 2014 on the conditions to be met when discharging sewage into water or soil.

The regulation also introduces the obligation to collect samples of domestic wastewater introduced into water facilities or into the ground from household sewage treatment plants. Sampling should be performed at regular intervals throughout the year, constantly at the same place where the waste water enters the waters or the ground.

Pursuant to § 5 sec. 2 point 1 of the Regulation, the number of samples taken during the year is 4, and if it is shown that the sewage meets the required conditions - 2 samples in the next year; in the event that one sample of the two taken fails to meet the required conditions, four more samples are taken the following year.

If you decide to buy a home sewage treatment plant or a septic tank that collects waste, it is worth following the above few valuable tips. Remember that the purchase of such systems is an investment that should fulfill its functions for many years. . When choosing tanks, let's not only consider the price. Usually, the price is an indicator of quality. Let's ask sellers about all certificates, advantages and disadvantages. Let's check the products at the competition. Make a decision carefully and enjoy an efficiently  system for many years. First of all, we should follow the manufacturer's recommendations from the moment of selecting the tank, through assembly, to the moment of use.