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- Ｑ 1 ）So the soil treatment unit doesn’t use infiltration? Doesn’t blockage occur then?
- Ｑ 2 ）Do scum and sludge in the digester tank have to be frequently extracted?
- Ｑ 3 ）Doesn’t anaerobic treatment produce a foul odor?
- Ｑ 4 ）Doesn’t rainwater flow into the digester tank where it is in contact with the soil or into the soil treatment equipment?
- Ｑ 5 ）Evapotranspiration doesn’t function when it’s raining or snowing, does it?
- Ｑ 6 ）Doesn’t the equipment freeze up in cold districts?
- Ｑ 7 ）So should we plant vegetation?
- Ｑ 8 ）Moss has grown in the soil treatment unit – should I treat this as a kind of vegetation?
- Ｑ 9 ）Doesn’t the soil or filtering media have to be changed periodically?
- Ｑ10）Is there no need to disinfect the system?
- Ｑ11）How are nitrogen and phosphorus, for example, treated?
- Ｑ12）Can the sewage be purified just by passing through the soil?
- Ｑ13）What is permeable soil? Can’t any other soils be used?
- Ｑ 1 ）So the soil treatment unit doesn’t use infiltration? Doesn’t blockage occur then?
- ‘Infiltration’ and ‘seepage’ may appear to be the same, but in fact they are quite different.
- While the two terms are often confused by the layperson, in the field of soil hydrology they are clearly differentiated.
- What is more, both infiltration and seepage are closely connected to blockage, which is an important aspect of
- water treatment that utilizes soil.
- ‘Infiltration’ refers to the case where the ‘saturated flow’ method of water movement is employed.
- This movement is achieved by filling the spaces between soil (soil particles) with water, so that the force holding
- the interstitial water in the soil is lost, and the water then succumbs to gravity and moves down
- into the underground water layer. As a result, sewage may find its way into the groundwater arteries.
- When the spaces between the soil particles are filled with water, the internal pressure exceeds one atmosphere,
- and external air (oxygen) cannot be dissolved in the water. If this condition continues for a long period of time,
- the level of oxygen necessary for the aerobic microorganisms required to decompose the organic material
- in the sewage cannot be maintained, and a membrane material produced by anaerobic microorganisms
- which thrive under conditions of low oxygen concentration gradually results in a gradual occlusion of the soil
- from a considerable depth, which eventually makes the trench unusable.
- This phenomenon becomes increasingly apparent as the amount of organic material in the sewage increases
- (i.e., as the BOD concentration increases).
- ‘Seepage’ refers to the case where ‘unsaturated flow’ method of water movement is employed.
- This movement occurs naturally when there is interstitial water in the soil. In this condition the spaces between
- the soil (soil particles) are not filled completely with water, and water moves horizontally and to the surface
- under conditions in which the meniscus in the soil water is maintained. Since the mutual attraction due to the
- meniscus in the soil water remains, movement of water against gravity is possible.
- With unsaturated flow, water can move in a capillary action, which allows it to move close to the ground surface.
- Under these conditions the internal pressure in the soil water is negative, external air (oxygen) is readily dissolved,
- and sufficient oxygen necessary for the aerobic microorganisms required to decompose the organic material
- in the sewage can be maintained. As a result, imbalance between organic material and aerobic microorganisms t
- hat causes blockage is avoided, and a long-term stable food-chain for soil microorganisms is thus able to develop.
- Ｑ 2 ）Do scum and sludge in the digester tank have to be frequently extracted?
- Anaerobic treatment liquefies and gasifies the sludge, so during the treatment process the volume is constantly
- being reduced. The ideal retention rate of sludge in the case of anaerobic treatment is generally considered to be
- 30% or less of the volume of the digester tank, so as long as it does not exceed this level then there is no need to
- extract the sludge. Under normal conditions, you can expect to have to extract the sludge every 3-5 years,
- or every 5-10 years if the digester tank is out of operation during the winter months. Of course,
- if the volume does not reach the stipulated level, there is no need to extract at all.
- What is more, the extracted sludge has excellent dehydration properties, and has the benefit of no unpleasant odor
- from hydrogen sulfide, so that it makes a high quality compost material.
- Also, the amount of scum in contact with the soil is fixed, and the microbes in the earth ensure that the layer of scum
- does not become too thick. (However, this does not apply in the case where the digester tank is hermetically sealed.)
- Where a covering of earth is not maintained, for example Chamber #1 in the digester tank that doubles as a tank for
- human excrement, a large volume of scum is produced. In this type of facility, the volume of scum can be controlled
- by adding digestive oxygen once or twice per year.
- Ｑ 3 ）Doesn’t anaerobic treatment produce a foul odor?
- People’s sensitivity to odors varies, but as the digester tank does not employ aeration in the treatment process,
- most people will not notice a foul odor. Since the inside of the tank is basically equal to the outside air pressure,
- odors do not leak from the manhole as, for example, in the case of a septic tank.
- (A deodorized type manhole is used.) However, an odor will be noticeable when the manhole is opened.
- The top of the digester tank is also covered with earth, so the odor from the part in contact with the soil is
- broken down through oxidation and does not therefore leak to the outside.
- This also applies to the soil treatment equipment part.
- When using non-flush toilets, measures need to be taken to counteract the odor from the human excrement pipe.
- Ｑ 4 ）Doesn’t rainwater flow into the digester tank
- where it is in contact with the soil or into the soil treatment equipment?
- The part of the digester tank that is in contact with the soil is positioned higher than the design G.L., and the soil
- heaped on the top of the tank has the effect of removing rainwater, so it is difficult for rainwater to flow into the
- digester tank.
- In the case of the soil treatment equipment, efforts are made at the design stage to ensure that its position
- minimizes the possibility of water flowing in from the outside. Since the finished shape of the installed part is
- around 100 mm higher than the circumference, the design ensures that surface water is removed promptly to
- the outside of the system by means of a drainage tube for the purpose of removing rainwater near the ground
- surface inside the equipment.
- The SOBIO Sewage Treatment System employs two types of materials for removing rainwater, one for removing
- rainwater from the surrounding area and the other for removing spring water from gradients. This ensures that
- water flowing in from the outside is removed as far as possible, while at the same time taking care not to hinder
- the evapotranspiration function.
- In addition, under normal usage, the system can be affected by rainwater until such time as the volume of rainwater
- around the SOBIOmat is commensurate with the volume of rainwater that penetrates from the surface area, but the
- natural pressure balance ensures that any penetration over and above that is impossible.
- (When the system is closed there is no water around the SOBIOmat, so rainwater penetration may occur. However,
- as soon as use recommences, it returns to its normal usage state.)
- For both the digester tank and the soil treatment equipment, it is important to be constantly alert to the possibility
- of external water penetration. While the penetration of rainwater may not be a priority at the design and building
- stages, by taking certain precautionary measures it is possible to minimize the impact on the equipment of
- rainwater, water flowing down gradients, and so forth.
- 5 ）Evapotranspiration doesn’t function when it’s raining or snowing, does it?
- Evapotranspiration refers to evaporation from the ground surface, plants, and so forth.
- Broadly speaking, there are only two conditions that cause evapotranspiration of the soil treatment unit to stop
- functioning: when the atmospheric humidity has become 100%, and when the soil treatment unit has flooded.
- Let us suppose that the atmospheric humidity were 90%. In this case, evapotranspiration would occur in order to
- compensate for the difference between the saturated flow of the underground water layer (100%).
- If flooding occurs, the ground surface turns into a state of saturated flow, so evapotranspiration does not occur.
- Under normal use, it is practically inconceivable that such a situation should occur, so evapotranspiration is
- considered to function according to the circumstances at all times. However, the effectiveness of
- evapotranspiration is naturally lowered, so there is a need to take this into consideration at the design stage.
- Also, in the case of accumulated snow, evapotranspiration is more active than usual due to the difference between
- the ground temperature and the snow temperature.
- This kind of evapotranspiration is known as water vapor movement. You may be surprised to know that a similar
- phenomenon can be seen on the Japan Sea coast in the winter.
- However, just as measures for dealing with the penetration of rainwater are needed, so too there is a need to
- consider from the design stage ways of removing surface water in the form of snowmelt to the outside of the
- system, using a removal tube for example, in order to guard against problems arising when using the facility.
- Ｑ 6 ）Doesn’t the equipment freeze up in cold districts?
- Treated water contains salt, so it does not freeze at the same temperature as fresh water, but even so it is still
- possible for the surface soil to freeze because of cold winds.
- (See Q5. concerning evapotranspiration when snow accumulates.)
- One way of dealing with this would be to change the thickness of the SOBIOmat cover from the usual 400 mm to
- 700 mm, so the equipment is not directly impacted, and we are currently considering this option.
- Another way of curbing the effects of freezing is to plant thick vegetation, and for this reason it is recommended
- that planting be carried out at the time of installation. In the case of mountainous areas, the option of planting is
- not possible due to the danger of bringing in introduced species. However,
- since inflow is expected to be minimal during the winter period, this is dealt with using the measures for cold
- districts previously described.
- Ｑ 7 ）So should we plant vegetation?
- Plants constantly draw up water from the earth through their roots, and transpire from the leaf surface.
- So planting is the best way of aiding evapotranspiration. The surface area of the leaves of plants that transpire
- the water drawn up from the roots is equivalent to several tens to several hundred times the area of the soil
- treatment equipment.
- The SOBIO System does not carry out 100% evapotranspiration into the air. Rather, it disseminates water partly into
- the soil, so in fact the mechanism may be more correctly termed partial evapotranspiration.
- In order to bring about more efficient evapotranspiration of the water disseminated in the soil, planting is incorporated
- at the design stage. (The exception is in the case of mountainous areas, which have their own native species.)
- Ｑ 8 ）Moss has grown in the soil treatment unit – should I treat this as a kind of vegetation?
- In the case of a facility where planting was not incorporated at the design stage, a thick growth of moss
- appears on the surface after several months of use. Since the pH of the permeable soil is inclined to alkaline,
- it is thought that this creates favorable conditions for moss to grow. However, the moisture retention of moss
- is high, so if it covers the surface, it has the effect of inhibiting evapotranspiration.
- The moss should therefore be cut away completely.
- Ｑ 9 ）Doesn’t the soil or filtering media have to be changed periodically?
- As well as being a necessary material for evapotranspiration to function, permeable soil is the home of
- microorganisms. Beginning with worms, soil microorganisms form the food chain over time.
- When SOBIOmat is functioning normally, the balance of organic matter, oxygen, and microorganisms is
- maintained, so there is no need to replace the soil. What is more, SOBIOmat gradually develops a greater
- affinity with the soil, and thus it functions in a more stable way over time. In the case of filtering media
- that use intergravel aeration, which is a kind of activated sludge method, blockages occur in a short space
- of time, but with anaerobic filter bed, no blockage occurs.
- With the SOBIO Sewage Treatment System, therefore, basically none of the parts need to be changed
- periodically.
- Ｑ10）Is there no need to disinfect the system?
- Intestinal bacteria, dominated by colon bacillus, are sterilized by methane bacteria in the digester tank.
- Soil bacteria too have the power to combat intestinal and pathogenic bacteria, thus colon bacillus can barely be
- detected in soil more than 50 cm away from SOBIOmat. If colon bacillus cannot be detected, it is safe to say
- there are no other bacteria present.
- Ｑ11）How are nitrogen and phosphorus, for example, treated?
- Nitrogen moves with water, so it exists in the soil close to the ground surface, but it is consumed by vegetation
- where this exists. To date, no new non power-based measures to combat nitrogen have emerged.
- While it can sometimes be washed away by the rain, the incorporation into the equipment of an oxidation-reduction
- device that uses as a catalyst iron as a denitrification device is a more reliable option.
- As far as phosphorus is concerned, this is combined with the iron, calcium, alumina, etc. in the soil and does not
- move with water. Phosphorus is also consumed as plant food for vegetation.
- Ｑ12）Can the sewage be purified just by passing through the soil?
- The pedosphere is home to a variety of organisms, from animals such as worms to microorganisms such as
- bacteria. Soil content varies depending on conditions, but in the case of soil near the ground surface, hundreds of
- millions of microorganisms, from bacteria to protozoa, live in just one gram of earth.
- Predatory decomposition of organic matter contained in the sewage has a high purification capacity, much higher
- than we think. However, this means it is extremely important to ensure that the production of sewage does not
- destroy the conditions that microorganisms present in the soil in the natural environment need to function.
- In other words, oxygen, which is the source of microorganism activity, needs to be supplied to the sewage in the
- volume required. SOBIOmat solves this problem by the use of a siphon phenomenon, which results in an excellent
- quality of treated water.
- In addition, research has shown that purification of the sewage occurs in exactly the same place where SOBIOmat
- has watered the soil.
- Ｑ13）What is permeable soil? Can’t any other soils be used?
- Actually, we refer to it as ‘soil’ for the sake of convenience, but it is not the same as the soil found in the natural
- environment. Our company has selected a number of soils that produce the same effect, taking into account a
- range of conditions. What these all currently have in common is the raw material used, which is wood-based fiber
- that has been incinerated and processed at high temperatures. So even if these are used in toilets in mountain
- areas, national parks, and suchlike, there is no danger of contamination from the seeds of introduced species.
- Such characteristics cannot be obtained with other soils, and for this reason we do not use them.
Q&Aの最終更新日 :
2010-01-17
