Frequently Asked Questions

How does the Green Rock 15 work?

Green Rock 15, like all the other Green Rock small-scale treatment units that operate without electricity (like GR Mini 05 S, Green Rock 10 S and Green Rock 20), function with so-called two-layer filtration. To the upper filtration right after the septic tanks remain the rough particles. The first filter removes most of the impurities. Under the upper filter is the so-called biological unit, where the water oxidises and forms drops on the plastic substrate material. On the surface of the plastic grid rings grows a micro-organism, which removes soluble organic matter from the wastewater.

Phosphorous, bound in the solid matter, can effectively be removed in the filtration process, but the soluble phosphorous comes trough. In order to precipitate the soluble phosphorous we have developed a chemicalizing device, AquaStone Block, which is fastened to the toilet seat. Every time the toilet is flushed, aluminium sulphate is released into the water. This coagulant makes soluble inorganic phosphorous turn into sparingly soluble metallic phosphates that settle easily in the septic tank.

Aeration pipe is led through the plastic grid rings and this allows the air to circulate through the treatment unit with gravitational ventilation. The sewage ventilation is led onto the roof, above the ridge.

Under the plastic substrate material is another filtration unit, which adsorbs the solids, micro-organism and other particles. The lower filtration unit also functions as a bio film, which establishes into the biological unit the widest possible surface for the micro-organisms to grow on.

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How often should I replace the filters and how is it done?

Small-scale treatment units should be maintained in every three to five years. Emptying the septic tanks has the fundamental effect on the treatment unit performance. Sludge and grease must be removed from the septic tanks at least twice a year. When the septic tanks are emptied, you should check that the inlet and outlet pipes and the t-tubes are open. When the septic tanks are at least partly empty, it is easy to evaluate their condition and especially how watertight they are.

If there accumulates a lot of over-aged sludge into the septic tanks, the acid fermentation begins. It causes gas and simultaneously mixes the sedimentated sludge and the grease from the surface. This allows solids and grease to slip from the septic tanks to the treatment unit and they will block the treatment unit fairly quickly. At the same time this process loosens nutrients, which possibly are sedimentated to the sludge. When the septic tanks work properly and they are regularly maintained, the load which comes from them to the treatment unit is mainly organic matter in liquid or fine colloidal form. It causes only a small amount of sludge in the biological process. Using the Aqua Stone –chemicalizing devices regularly in the toilet seats reduces the load that comes into the treatment unit.

On the average the filters of the treatment unit last about three years. At best they will last from five to six years. Emptying the septic tanks regularly, their condition and volume also have an effect. The living habits of the residents play a significant roll. If the sewage is used as a litter box, the maintenance period will shorten evidently. The way the residents live, the treatment unit lives accordingly.

Maintaining the treatment unit is manual work. Old filters are removed with a pitchfork and new filters are replaced. Maintenance takes about two hours (max.). Filtration material can be composted, because the fibre binders are made of decomposing material. When they vanish there remains only rock fibre, which is dust in practice.

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How do I know, when the filters should be changed?

On the top of the filters fastens some solid material, which slowly blocks the surface. The horizontal surfaces are blocked first. This causes that the filtered water first infiltrates through the lamella or the filtration cartridges. Blocking of the vertical surfaces is slower, because the particles tend to sink downwards and not straight on the wool. Also the changes in water level ”rinse” the wool surface and clean it from the solids.

When the water level rises on the same level with the inlet pipe leading into the filtration unit, it is important to observe it more frequently. Because the water level in the filter varies, there is no immediate trouble. The most reliable way to check the filter situation is to peek in it in the morning, when no water has been run yet. If the water surface is still on the same level with the inlet pipe, it is time to change the filters.

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Where should I put the used filters?

The used filter is entirely of decomposing material. The binders that are used to fasten the fibres together will decompose into compost. When they vanish, there remains only rock fibre, which is dust in practice. The filters contain a lot of nutrients and organic material, so they work well as soil improvement material. The smaller you crush the filters after the use, the quicker they will decompose. If you have only small household waste compost, it is no use to put the used filtration material into it, because there is so much of it.

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How often should the septic tanks be emptied?

Septic tanks must be emptied at least twice a year. There is more detailed information about this in answer 2.

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Which treatment unit should I choose to an old house?

If the existing septic tanks are undamaged, you can choose whichever treatment plant with the matching capacity. Normally Green Rock 15 is enough. It is designed for larger detached houses and treats about 1000 l/day, if the septic tanks are matching size for this amount of water.

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Can I use old concrete septic tanks in front of the treatment plant?

Old concrete tanks can be used in front of the treatment units. However first must be checked, that the inlet and outlet pipes of the septic tanks are undamaged and that the t-tubes are on their places and open. When the septic tanks are empty, it is easy to evaluate their condition and assure how watertight they are.

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Can I place for example a concrete septic tank in front of Green Rock 10 S?

If the daily wastewater amount is close to the maximum, i.e. 700 litres a day, an additional separate septic tank can be placed in front of Green Rock 10 S. Then the first septic tank will collect most of the solid material and this gives more time for the septic tank of the treatment unit to settle the wastewater before letting it pass to the filters. A bigger septic tank does not however reduce the need of emptying the septic tanks. Still, the tanks must be emptied at least twice a year.

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Can the treatment unit be buried into the ground if the inlet is deep?

Most of the Green Rock small-scale treatment plants are buried into the ground so that only the lid remains on the surface. The inlet pipe coming from the house however defines in most cases how deep the plant must be buried. When installing the treatment unit one must remember that the deeper the plant is installed the bigger is the earth pressure directed to it. If the installation depth is more than 50 cm below the earth surface, one should prevent excessive earth pressure by building a shelter around the plant. Also note manufacturers recommendations of the installation depth. Most basic tanks may only be installed in 60–100 cm deep (max.) There might gather surface water and rainwater into the shelter, which must be prevented from happening and the surface waters should be led away from the treatment plant by using drainage pipes.

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My house is on flatland. Where could I lead the discharge pipe?

If differences in water level are not sufficient enough to lead the discharge water into a ditch, you can install a pump well after the treatment plant. The pump well raises the water on the right level so that the water can float forward.

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Can the rainwater and the drainpipes be led into the treatment unit?

Drainpipes and rainwater may not be led in the septic tanks or in the treatment unit. Additional water is useless burden for the treatment plant and it mixes the operations of the septic tank and in this way causes blockings in the filtration.

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Is a soaking field necessary after the treatment plant?

The outlet water from the treatment unit must not be soaked into the ground, unless the local authorities require it. It is true though that it formerly reduces the environmental burden. Part of the outlet pipe can be replaced with an absorbing pipe. This minimizes the strain caused to the watercourses. It is however good to lead the outlet water from the treatment unit for example into a ditch. This allows the impurities in the wastewater to continue dispersing in the oxygenous conditions. It also allows the nutrients to be transferred for the flora etc. It is easy to control the quality of the outlet water from an open discharge pipe.

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Can the treated water be led directly into the watercourse?

Wastewaters, even treated ones, should rather not be led directly into watercourses. Transporting the water through the soil or in the ditch lengthens the treatment process and gives for example the phosphorous a chance to join the nature’s normal circle, which prevents it from burdening the environment. When choosing the discharge place it is recommended to contact the local environmental authorities.

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How does the installing of the treatment plant succeed on a rocky building site?

On a rocky building site there usually is a place, where there is enough soil to sink the treatment plant. If an appropriate place cannot be found, the treatment unit can be buried only halfway and in that case the top part of it should be isolated. Even in this case the altitude of the outlet is significant. Even the drainage pipe can be left near the earth’s surface or even on the ground, if only it is isolated against frost.

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Can the toilet waters also be led into the treatment unit?

All Green Rock small-scale treatment units are designed to treat also toilet waters. It depends on the building site and the authority regulations, if the toilet waters may be treated on your own property.

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Can I get some financial support to install the treatment plant?

This matter must be checked from your local authorities, for example from the environmental authorities.

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How close to water well can the treatment unit be placed?

Because it is a question about a treatment plant, which is designed to treat wastewaters, the plant must be located so that it cannot ruin the drinking water in the well. It is worth to analyse the shape of the ground and the quality of the soil before installing the plant. The minimum distance should be at least 30 meters.

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How close to the neighbouring site can I install the treatment plant?

The minimum distance from the boundary is five (5) metres. The same distance concerns also the discharge place. It is however possible to use the boundary ditch, if the parties concerned agree to it.

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Why does the treatment unit stink?

The treatment plant treats the outlet wastewater coming from the facilities. Treatment plants are designed so that the air floats from the air intake pipe into the biological unit and keeps it oxidized. Ventilation continues through the drainage pipe to the aeration pipe, which ends on the top of the roof. The aeration pipe ventilates the stink from the treatment unit and the treatment plant and smells are mixed in to largest possible amount of air. Sometimes, because of the low pressure, aeration doesn’t work effectively and then there might be an odd smell near the treatment unit outside the house. If this happens often, you should check that the air passes free from the treatment unit above the roof.

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How should the treatment unit be anchored?

Treatment unit and septic tanks are anchored to the ground in order to prevent them from moving. Movements can be caused for example by surface water that cumulates in the excavation. Water causes buoyancy, especially during maintenance when the treatment unit and the septic tanks are empty. In the products there are specific anchorage links, from which they are fastened either to the concrete plate (cast under the products) or to smaller anchorage weights.

As anchorage weights you can use for example separate concrete blocks. In addition to the anchorage, on the bottom of the excavation it is good to install drainage pipes, which are led as separate lines either to an appropriate place or they can be combined to the outlet pipe. Using the drainage assures that the product doesn’t move and it minimizes the load that is directed to the anchorage.

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Do we need a treatment plant also on our summer cottage?

At least in Finland you do. According to the Finnish environmental law all facilities must have an organized wastewater treatment system. You get further information from your local environmental authorities.

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