- What septic tanks are in use in the domestic market
- Volume of effluent and salvo discharge
- Required degree of purification
- Features of the housing design
- Septic tank technological equipment
Local treatment facilities for a private house, which we used to call a septic tank, are part of the basic engineering systems of a house, and one must approach its purchase with knowledge of the matter. Today we will deal with how the equipment should be arranged and how to choose the right septic tank for a private house or summer cottage.
What septic tanks are in use in the domestic market
The market for local treatment facilities is full of variety. Almost every manufacturer seeks to supplement their device with a number of “gadgets” that can either really be useful, or unreasonably increase the cost of already expensive equipment. Nevertheless, there are only two main types of treatment plants, and there is always the same option for assembling a septic tank with your own hands..
Flow-through septic tanks (TOPAS, Termit, Flotenk-STA) are multi-chamber devices with a classic wastewater treatment scheme. In such stations, wastewater is sequentially moved from one chamber to another. In each of them, gravitational sedimentation of ever smaller suspended particles occurs, in parallel, biological cleaning mechanisms are included in the work..
An alternative to flow-through are septic tanks of a cyclic type (AK-47, EuroBion, One2Clean), in which the SBR (Sequence Batch Reactor) mechanism is involved. Septic tanks of this type are single-chamber and require a mandatory connection to the electrical network for the operation of aerators and pumps. Wastewater treatment occurs due to the inclusion in the work of the widest range of microorganisms of both aerobic and anaerobic types. Once or twice a day, such a septic tank stops aeration to settle solid particles to the bottom and pumps out the upper clarified layer of water.
The advantage of flow-through septic tanks is the ability to operate in a completely autonomous mode, albeit with lower productivity, using only anaerobic bacteria for biological purification. At the same time, SBR complexes have a slightly lower capacity, which is reflected in a reduction in the amount of excavation and preparatory work, while not inferior in performance to multi-chamber systems. However, such a septic tank will not work without electricity, plus, in addition to everything, it implements a rather complex automatic control scheme, which means there are more vulnerabilities in the equipment than in flow stations..
Volume of effluent and salvo discharge
Of primary importance for absolutely any septic tank is the volume of wastewater that the station can handle. But do not rush to study SNiP 2.04.03–85 in search of regulated norms: for each septic tank, the manufacturer independently makes calculations and indicates the number of residents the station is designed to service.
In addition, the daily volume of wastewater is so relative that all families simply cannot be matched with one size fits all. It all depends on the lifestyle, the abundance of household appliances, and therefore it is much better to calculate the discharged effluents empirically and independently. The average benchmark is about 150-200 liters per day per person: this includes a single use of the shower, 3-4 flushes of the toilet bowl plus washing dishes and daily wet cleaning..
For the treatment plant, the volume of the salvo discharge is also important, which cannot be less than five times the nominal discharge. A septic tank, which has an even larger margin, has a much lower probability of going into emergency operation and differs in a deep degree of purification due to a longer biological reaction time. In case of insufficient resistance to volley discharge in a septic tank, it is possible to raise sludge from the bottom and carry it out together with clarified water.
Required degree of purification
Wastewater treatment plants that clarify water to 95–98% of the initial content of suspended particles are considered effective. In actual figures, this is approximately 3-5 g / l of water, such a liquid can be used for watering the garden and technical needs, discharged into the drainage / storm / reclamation system or the nearest reservoir. Septic tanks with an efficiency of 80% require additional treatment, which is performed either by a sequentially installed infiltrator, or by a specially equipped discharge field into the soil.
An example of the organization of a drainage field for a septic tank in clayey soils
Let’s try to figure out the contaminants present in the effluent and the permissibility of their presence in water clarified by a septic tank. The main volume of contamination falls on solid particles of fecal mass, which serve as a breeding ground for bacteria. It is good if the septic tank has a device that takes into account the need for crushing the coarse fraction for the most complete and rapid entry of solid particles into a reaction with activated sludge. This can be done either by dropping the liquid from a height onto a large sieve, or by using a forced mixing mechanism.
A less obvious point is fatty deposits that settle on the parts of the septic tank and sewer pipeline. At the inlet of the septic tank, there must be a grease trap that traps floating residues and increases their response time until they are completely cleaned..
If the discharge from the septic tank is carried out into a water carrier or reservoir, then it is necessary by all means to exclude the presence of phosphates and nitrates in the clarified water. The former come together with detergents dissolved in the effluent, the latter are formed from urea during aeration of the waste masses. Both classes of substances can be eliminated by increasing the response time and increasing the population of bacterial colonies, especially anaerobic ones..
It will not be superfluous to take a sample of clarified water for analysis of the substances it contains before discharging it into public water bodies. Note also that it takes a time for the septic tank to reach its rated capacity, usually 2 to 4 weeks. The process can be accelerated by forcing the introduction of enzymes and bacteria.
Features of the housing design
Almost all modern septic tanks are made of cross-linked polyethylene, although variations with metal or reinforced concrete bodies are possible. Polymer materials are preferred due to their high resistance to corrosion and aggressive chemical compounds present in waste masses.
But it is not without its drawbacks: due to the low weight of the plastic, the septic tank can literally float up when the soil softens with groundwater. Therefore, in swampy, mudflow soils and sandy loam, a special anchoring system or a reinforced concrete sarcophagus is required.
The most important factor is the hull manufacturing process. There are many precedents when welded septic tanks simply vomited from pressure, especially multi-chamber stations often sin. The septic tank itself is by no means a cheap installation, so the durability of the equipment should not be lower than its efficiency. Be sure to check with the manufacturer or distributor for details of the production of the case, the most reliable are plastic products made by cold winding.
The resistance of the septic tank body to pressure and heaving of the soil is determined by the shape, aspect ratio and the presence of stiffening ribs. The most stable are vertical columns and trapezoidal tanks with profiled walls..
Septic tank technological equipment
The internal filling of the treatment plant can be attributed to the aeration complex, the movement of effluents and the electrical communications unit, which controls the operation of all other components. The latter also includes a system of sensors: level, water clarity and others.
Electrical equipment must be made of quality components available on the market. In case of failure of such units as a power relay or a timer, the possibility of their independent replacement should remain, service repair will cost at least 2-3 times more. For example, a conventional float sensor costing 600-800 rubles, when replaced by specialists of the service company, can rise in price to 3-4 thousand.
Of the equipment for the movement of waste masses, airlifts are considered the most reliable and trouble-free. Centrifugal faecal pumps can also be used successfully, but they are more sensitive to the ingress of coarse fractions and are prone to rapid wear due to operation in aggressive environments.
The septic tank aeration complex consists of a compressor and an aerator. The power of the first should correspond to the volume of the processed mass, approximately 35–40 W for each cubic meter of the septic tank capacity. Of the aerators, linear air atomizers with variable pore sizes are considered the most durable and effective. Such elements are not susceptible to siltation, unlike ceramic ones, at the same time they have a very high performance and are not subject to corrosion..