HOW TO CHOOSE A TREATMENT PLANT
When choosing a treatment plant, you need to take into account the depth of the groundwater on your site. This determines the shape of the plant.
You need to know where the treatment plant will be located, and what will be on top of it – lawn or road. In the green area, the manhole cover must be installed in such a way that it does not interfere with grass cutting with a lawnmower.
It is important to know the treatment level of the wastewater so that the correct disposal method can be chosen.
It is important to decide where and how the treated water will be disposed of – whether it will be discharged into streams, ditches or infiltrated into the ground on site.
It is important to find out how many years have the vendors or manufacturers of treatment plants been operating in the Lithuanian market and who will provide after-sales service.
Make sure you check whether the sellers or manufacturers of the cleaning equipment have a representative in your city, as it may be difficult for them to come from far away.
The treatment plant will be underground all the time, so it is important to know the thickness of the casing wall.
It is important to know how the wastewater will be treated – biochemically or biologically.
The biological principle of water treatment is perfect because it does not require any additional tools. Nothing needs to be added to such a treatment plant. Humans themselves are the best source of all the bacteria needed for water treatment, and our homes are the most suitable environment for them to grow. So the bacteria enter the treatment plant in the most natural way and completely free of charge. It takes about a month for a sufficient quantity of bacteria to grow. The more natural waste and the less chemical waste is present in the effluent, the better the conditions for bacterial activity.
It is possible to bring in bacteria by filling 10% of the volume of a new treatment plant with the contents of an existing plant, but 99% of users do not do this and the system works perfectly.
Initially, the plant is filled with clean water. Each unit needs to be refilled with special chemicals from time to time. Manufacturers ensure that the device notifies the user when it is time to refill.
In cyclical biochemical treatment plants, the whole process is controlled and the water is treated in cycles, in specific doses. The amount of water to be treated per treatment cycle is predictable. In these plants, the quality of each gram is identical.
Designers usually calculate the amount of wastewater that will be discharged in a particular house. The average rate per person is 160 l/day. One treatment plant is sufficient to treat the wastewater of a family of 5 persons.
Biochemical treatment plants struggle to cope with water treatment during the morning and evening peaks, when large volumes of water from baths and showers enter the plant at the same time. The concentration of contaminants decreases and bacteria are less able to process them.
The water treated in a domestic wastewater treatment plant doesn’t disappear by itself. There are several ways to deal with it. The simplest is to discharge it into the environment, through pipes to nearby streams or drainage ditches. No facility can treat the water completely, but it comes out clean enough not to harm the environment.
It can be absorbed into the ground through infiltration wells, or it can be pumped out and reused. After passing through a special filter, this water can be used in a toilet tank or for car washing. The water treated in the biological treatment plant retains a high level of nitrogen and phosphorus and is ideal for irrigation and lawn fertilization. It is not recommended to use this water in a pond, as it will grow algae and turn brown.
The effluent from the biochemical treatment plant contains neither nitrogen nor phosphorus in the water. It is suitable for fertilisation, but will no longer fertilise the meadows.
We will advise you on the most suitable method for your situation, so that the water is not a problem and does not cost more than necessary.
A simple and reliable way is to allow the water to accumulate in one place, from which it gradually soaks into the ground.
A well is dug to a depth of about 3 m, into which two concrete rings with a diameter of 1,5-2 m are inserted, with a volume of over 5 cubic metres. If the rings are 2 m in diameter, a surface area of approximately 4 sq m is created for water infiltration. Whether this area is sufficient for comfortable domestic water use depends on the composition of the soil and lifestyle. The infiltration coefficient of the soil, i.e. the permeability to water, is determined by geological investigations. Gravel has the highest permeability. Sand is less permeable, especially if it is very fine. Its permeability then becomes similar to that of clay, where water has difficulty or no ability to penetrate.
Once an infiltration well fills up, because the silt particles remaining in the treated water contaminate the bottom of the well over time, it has to be cleaned. Go down and remove the fouling layer. It does not seem very difficult, but this well is too narrow to do it mechanically, or even comfortably. It is heavy physical work, which makes cleaning the well an expensive service. Another thing is that it is always untimely and very unpleasant when the well becomes clogged.
We always suggest installing an infiltration well with a gravel bed at the bottom, which is several percent more expensive and many times more efficient. This involves digging a pit about 3 m in diameter, much wider and deeper than the well rings. A layer of gravel is poured into the bottom of the pit, which increases the infiltration surface to 10 square metres. The gravel is covered with a special synthetic material which serves as an additional filter to prevent contamination and blockage of the soil. The soil in such a well will never become clogged. If it does have to be cleaned, it will be infinitely less frequent and easier: a wider well is easier to clean; there is no need to dig anything up, just replace the clogged part of the synthetic material. Cleaning this well is probably 6 times cheaper than cleaning a regular well.
A well that costs just a few percent more is much more reliable.
Surprisingly, few wastewater installers offer this option.
Generally, people prefer to get some kind of signal indicating that the well has filled up. But this is not the best way to avoid problems. The alarm will not necessarily go off on Monday morning, when it is convenient to call for help. It can happen at any time, whether it’s at the weekend, at night, or when only the kids and grandparents are home and you’re away on a trip…
We suggest installing a small water pump connected to a float immersed in a well. When the water reaches a dangerous level, the pump pumps out the excess water and discharges it evenly near the well. This temporary solution allows enough time for help to arrive. Meanwhile, the alarm system only indicates that there is a problem, but does not solve it.
A popular and relatively inexpensive way of releasing used and treated water to the land is to install an infiltration field. Special water-permeable pipes are laid in several layers over a certain area of the site and the water slowly percolates into the ground. At first sight, it is attractive and simple. In reality, however, this system is completely inconvenient to use and we do not recommend it.
First of all, because it’s impossible to clean – there’s nowhere to climb and nothing to dig. The sewage treatment plants do not clean the sewage at all, so it is clear that there will be a day when the infiltration field system will be blocked. Over time, the sludge particles that remain in the water will clog both the small openings in the pipe and the soil around it. While increasing the water pressure may still clean the pipe, it may not clean the soil. The infiltration field is therefore truly a disposable device. If it becomes clogged, it must either be relined, which costs the same as installing a new one, or a well must be built at the end of the pipe to collect the water that no longer soaks into the ground. This water can then be disposed of.
There is no point in installing infiltration wells where the soil on the site is clayey or the water table is high. Water will not penetrate the ground through them. The two options are either to remove the accumulated water or to irrigate it.
If irrigation is the option, there is a solution that avoids the need to stand with a rubber hose in your hand and do the watering yourself. This is ground infiltration. Water from an infiltration well is lifted by a pump above the water table or clayey soil to a level where the soil is suitable to absorb it. Several smaller and shallower concrete rings are placed on top of the well and the whole structure is backfilled. The water gradually overflows into the cavity and spreads underground.
In Lithuania, the use of treated water for irrigation, washing cars or toilet cisterns is not common. Theoretically, this would be very convenient, but in practice it is expensive. It requires additional storage capacity, pumps and costly filters, additional water supply etc. Compared to the cost of extracting fresh, clean water from a borehole, the investment in a recycling system is not worth it. It is rare for anyone to use it to water vegetables that they will later eat, but it is perfect for watering meadows. But it is better to use collected rainwater for watering vegetables.