Which household treatment plant to choose? 

The law requires every property owner to connect to the sewage system. If the construction of a sewage system is technically or economically unjustified, a non-drainage tank for liquid waste or a household sewage treatment plant should be installed on the property.

Pursuant to the legal acts in force, sewage, before it is discharged into water or soil, must undergo appropriate treatment for its treatment. This is to reduce the negative impact on the environment and human health, as sewage is a habitat of microorganisms, including those that are dangerous to life (Escherichia coli, Salmonella spp). Until recently, the only way to remove sewage from the property was to use septic tanks. This solution requires the removal of waste with septic car, so often as to prevent the tank from overfilling and, consequently, pouring the sewage into your own yard. (if such a situation occurs, the property owner commits an offense punishable by a fine of up to PLN 5,000. The constantly increasing costs of neutralizing and discharging wastewater increasingly tend to abandon this method in favor of cheaper, less burdensome and more ecological solutions.

An alternative are household sewage treatment plants that are becoming more and more popular. Their purpose is to neutralize sewage at the production place, and then to discharge the treated sewage by means of a drainage system into the ground or a ditch.

Drainage wastewater treatment plants

The treatment process consists in carrying the sewage through a sewage pipe to the septic tank, where the sewage is treated under anaerobic conditions. The bacteria present there break down some of the pollutants in the wastewater into minerals, water and gas. The next stage of the process is oxygen cleaning. The pre-treated wastewater is evenly distributed through the separation pit to the drainage threads. . The process of aerobic wastewater treatment takes place in the drainage pipes, from where the neutralized sewage can freely seep into the ground. At the end of the infiltration drainage, there is a collecting well, whose task is to aerate all drains. Drainage sewage treatment plant is the simplest type of sewage treatment plant. 

Selection of a septic tank for a drainage treatment plant

High-quality tanks are most often made by rotomoulding. Due to their monolithic structure, they are 100% tight, as they do not have any welds or connections. They are made of ecological polyethylene, thanks to which they are characterized by low weight, high mechanical strength, corrosion resistance and high durability. The sedimentation tank should be placed as close as possible to the outlet of the sewage pipe, because thanks to this there is no significant drop in the temperature of the waste water. If the distance between the sewage pipe and the sedimentation tank is large, thermal insulation should be applied to the sewage inlet pipe to prevent it from freezing in winter. In order to properly select the tank, the number of people who permanently live in the building should be determined. The concept of the equivalent number of inhabitants was introduced to standardize the calculations related to the amount of discharged sewage (EH habitat equivalent). This indicator determines the amount of sewage discharged from households by one inhabitant during the day.

V = RLM · L · T

where:

V - minimum tank volume, liters

L - the amount of sewage discharged by one inhabitant, liters / day (average 150 liters / day)

T - time of keeping sewage in the tank, day (most often sewage is subjected to a 3-day treatment process)

Example: V = 4 people· 150 liters / day ·3 days = 1800 liters

Hence, the optimal capacity of the settler for a family of 4 is about 2000 liters.

Selection of standard infiltration drainage

Drainage is a system of several parallel connected perforated plastic pipes, aimed at even distribution of pre-treated sewage to the filtration layer made of gravel or fine crushed stone. When designing the installation, it is necessary to maintain a minimum distance of 1.5 meters from the highest annual groundwater level. Individual drainage pipes should be at least 1.5 m apart and led with a slope of 1 to 3 per mille. The maximum length of one drainage thread should not exceed 25 meters, and the depression depends on the soil freezing zone. The length of drainage in well-drained soils is about 8 m / person, in poorly permeable soils 12 m / person, while in hard-to-drain soils - 16m / person. The area on which the drainage is installed should be absolutely excluded from vehicles traffic. It is also not allowed to plant in this area plants with a developed root system as this could damage the drainage installation. It is also important to respect the following dimensions:

• distance of the treatment plant from the plot border - 2 meters,
• distance of the treatment plant from the nearest well - 15 meters,
• distance of drainage from a residential building - 3 meters,
• distance of drainage from trees and shrubs - 3 meters,
• distance of drainage from the nearest well - 30 meters,
• distance of drainage from the plot border - 2 meters.

Selection of drainage - infiltration boxes

This system works in the same way as a standard wastewater treatment plant. Pre-treated sewage is directed from the tank to the sump, then through a drainage pipe it is led to the infiltration boxes. They are an alternative to the traditional method of infiltrating water which uses gravel. They are small, light and easy to install. In the case of well-drained soils, 2 drainage boxes per person are enough (the amount of drainage calculated on the example of GEOdek boxes), in soils with medium permeability, 4 boxes should be used per person, and in soils with moderate permeability (sandy loam) - 6 boxes per person. The dimensions of one box are 1200 x 600 x 325 mm (L x H x W).

Summary of the selection of traditional drainage treatment plants

Home sewage treatment plants with drainage drainage should be built (due to low investment costs), if soil and water conditions allow it, which include: a large plot of land, low level of groundwater and good soil permeability (sandy soils or sandy loam). Unfortunately, this type of solution makes it difficult to control the effectiveness of wastewater treatment and, therefore, the possibility of determining whether the treated wastewater discharged into the environment meets the guidelines contained in the regulation of the Minister of the Environment of 2014. For this reason, this method has been abandoned in several countries in Western Europe.

Types of biological wastewater treatment plants

The methods of biological wastewater treatment are based on the intensification of the self-purification processes of water and soil naturally occurring in the environment by engineering methods. 

Wastewater treatment plant type SBR

SBR technology is based on sequential reactors in which the purification process takes place cyclically. The wastewater is temporarily stored and then it undergoes biological treatment. The entire process takes place cyclically every 8, 12 or 24 hours and consists of five phases. The first chamber plays the role of a preliminary settling tank and a buffer tank, in which there is a preliminary mechanical treatment of sewage by sedimentation of easily settling suspensions, flocculation of fats and equalization of loads caused by uneven sewage inflow. The pre-treated sewage goes to the SBR chamber, where it is aerated and treated. The first phase of the process is to supply the wastewater to the SBR reaction chamber via pumps. In the second phase, the wastewater is aerated by means of diffusers in order to ensure optimal living conditions for the microorganisms. The next step in the process is the deposition phase. The accumulated activated sludge undergoes the process of sedimentation, creating a layer of sludge at the bottom of the tank. As a result, clean water is separated in the upper part of the tank, which is discharged into the receiver in phase four. After clear water is discharged to the receiver, the active sludge accumulated at the bottom of the SBR reactor is discharged to the primary settling tank. After discharging the sludge, the plant is ready for the next cycle. The purified water is directed to the separating sump and then discharged to the infiltration system. 

Waste water treatment plant - type activated sludge

Wastewater treatment with activated sludge involves introducing special microorganisms into the wastewater, forming flocs. These flocks adsorb organic pollutants on their surface, which are mineralized as a result of the metabolism of microorganisms. For the proper course of the process, it is necessary to aerate the sewage with a special pump. After the end of aeration, the sewage is directed to the secondary settling tank, where the liquid is separated from the activated sludge. In a further stage, the purified liquid is directed to the infiltration system, as in the case of the SBR treatment plant.

Hybrid type sewage treatment plant

The hybrid sewage treatment plant works on the principle of active sludge and biological bed. The tank combines the aerobic and anaerobic processes of wastewater treatment. Thanks to the mixed technology the treatment plant achieves a very high degree of pollution reduction. The system is resistant to vacation periods and short-term interruptions in electricity supply. Thanks to the use of advanced automation, high comfort of use has been guaranteed.

Purified water infiltration system from biological wastewater treatment plants

The number of boxes is calculated on the basis of GEOdek infiltration boxes. The length of drainage in well-drained soils is 2 drainage boxes per person. In soils with medium permeability, we use 2 boxes per person, while in soils with moderate permeability (sandy loam), we install 4 boxes per person. Infiltration box dimensions: 1200 x 600 x 325 mm (L x H x W).

Advantages and disadvantages of household sewage treatment plants

Drainage		Biological
Advantages	Disadvantages	Advantages	Disadvantages
The treatment plant is fully maintenance-free	A large plot of land on which drainage will be distributed is required	Environmentally friendly	The need to supply electricity
There is no need to supply electricity	Possibility of clogging drainage	Possibility to control the quality of treated wastewater
Installation costs on average after 3 years of use	/ Inability to check the quality of the system operation	Ease of assembly
Ease of assembly	The need to add bacteria	High pollution reduction
		Cleaning the sedimentation tank once a year

Valuable tips before starting the construction of a household wastewater treatment plant

1. Before starting the construction of a household sewage treatment plant, it is worth going to the Commune Office. Often, communes have funds to finance investments. Then the construction is more financially beneficial. You can also get a grant from the National Fund for Environmental Protection and Water Management or a low-interest loan from Environmental Protection Bank.
2. It is worth consulting with a company that specializes in home sewage treatment plants. The company will determine the water and ground conditions, the building area and the most effective technology of wastewater treatment. The selection of the right technology is very important because then you can count on many years of trouble-free operation.
3. When planning the construction of a household sewage treatment plant, it should be reported to the Poviat Starosty. In accordance with applicable regulations, when building a sewage treatment plant up to 7.5 m³/d, it is required to submit an investment notification to the Department of Civil Engineering and Architecture of the Poviat Starosty. The application should be accompanied by the required documents: a situational and altitude map with the location of the sewage treatment plant, a statement on the right to dispose of the property and a draft design describing the type and operation of the technology. The County Office has 30 days to raise an objection, if this does not happen, construction can begin.
4. If a construction permit for a septic tank (septic tank) is issued, you can apply for a replacement permit for the construction of a home sewage treatment plant. The process of obtaining such consent is the same as in point 3.