Thursday, October 29, 2015

Garden Irrigation With Sewage Water Prevents Drought

In the dry season the water so scarce and it is not economical if used for watering the garden. Sewage water is suitable for garden irrigation if there are a lot of plants around the sewer, and a lot of fishes live in that sewer water. Usually sewer water is more suitable for garden irrigation instead of fresh water, because it contains nutrients suitable for plants. Perhaps it is equal to a liquid organic fertilizer.

Pumping sewer water for garden irrigation can increase groundwater volume. It will raise ground water level and prevent drought in the dry season. The costs would be enormous if it had to buy water in the dry season.

As ground water level raises, fresh water pump will work lighter, thereby reducing the electric power consumed by the fresh water pump. So in addition to saving water, this system can also save electricity cost.

The main constraints of sewage pump is difficult to use one-way valve (foot valve) at the end of the suction pipe. Because dirt and mud from the gutter will make the valve always leaking. The water in the suction pipe and in the pump impeller housing always fall back to the gutter. Then the pump must always be filled with water (primed) just before turned on. The pump also does not have a one-way valve inside the impeler housing.

Photo below shows a small and inexpensive pump that I use, the pump power of about 125 watts. No need to use an expensive big power jet pump. Because of the difference in height of water being pumped (total head) is not too high. Total head is about 1 meter only. I am using a jet pump with 250 watts for fresh water pump. Of course there will be a significant electricity cost savings if I am watering the garden with sewer water with a small 125 watts pump, compared watering the garden with fresh water from the 250 watts jet pump.

Submersible pump can also be used. Submersible pump does not need to be primed before start. But submersible pump price can be three times more expensive than a pump in the above photo. Submersible pump must also be immersed in the gutter in order to operate. My gutter is positioned outside the fence. So, there is a risk of theft when using a submersible pump.

Pump motor coil is wetted with about 2-3 tablespoons oil to protect coil from water seepage into the motor housing, see photo below. This often occurs in small cheap pump because the motor housing has unprecise sealing. So it is easy for water to enter motor housing when the pump is primed, and the coil will be damaged if exposed to water. Pump oil filled and shaken up for the oil to spread evenly coat the entire motor coil. The oil inside motor housing also helps to absorb heat. Cheap pump has a small-sized cooling fins and can be easily overheating. The oil used was SAE 40 (engine oil), which is formulated to absorb heat. Transformer oil can also be used.

CAUTION: beware of electric shock when opening motor coil cover. Make sure the pump power cable is disconnected from the grid. Make sure all wiring connections are well insulated. As shown in the photo, wiring connections are insulated with yellow plastic caps.

As we know that the air is elastic, it is compressible and also can be stretched. The air inside impeller housing will be stretched if sucked by impeller, and will be compressed if blown by impeller.

Water pump works by pushing the liquid contained inside impeller housing, to go out through the exit pipe. Furthermore, there will be a low pressure inside the impeller housing, this pressure is lower than the air pressure in the atmosphere. The nature of air or gas will always fill the empty space. The air in the atmosphere will be trying to get into the impeller housing through inlet pipe. Atmospheric air pressure will push the surface of the water to be sucked, so the water will fill the impeller housing through the inlet pipe. In daily language we call it 'the pump to suck water', but actualy atmospheric air pushes the water into the pump.

If there is plenty air inside impeller housing, the impeller can not blow or push it out. Because the air is compressed inside impeller housing, not blown out through the exit pipe. So nothing low pressure is happening inside impeller housing.

Goose neck or U pipe system is applied too avoid air to enter into suction pipe and impeller housing. It is also called as water valve. Water valve system is also applied to toilet or WC (water closet). With goose neck pipe, some of water will be trapped in the suction pipe. The pump is positioned in the lowest part of goose neck, so the water is also trapped in the impeller housing.

Goose neck system is also applied to vehicle brake bleeding by only one mechanic , to remove air from brake hydraulic system.

Please refer to the following schematic. It is shown in the schematic that suction pipe (I) have a knee that is higher than the pump. Difference in height is about 20 cm. The height difference makes the water trapped in the suction pipe and the pump. This trapped water can not fall back to the filter (Sc) and into the gutter. My suction pipe (I) is about 5 meters long, not include the vertical suction pipe section. Vertical suction pipe is about 80 cm long. Differences gutter water level to the pump is about 50 cm high.

In the vertical section of the suction pipe, air is accumulated when the pump is not working. Because of this vertical section is only 80 cm in length, while the declining pipe towards the pump is much longer (5 meters). The volume of air accumulated in the vertical pipe is much smaller than the volume of water that is accumulated or trapped in the declining pipe. Trapped water volume is plenty enough so that the pump can start and immediately remove the air from the pipe, no need pump priming.

Output pipe (O) is positioned vertically. It is also to trap water inside impeller housing. Output pipe (O) is high enough to help to remove air bubbles from pump (P) impeller housing, when air is sucked by impeller. Because the air is lighter than water, air will always move up when mixed with water, while the water will always seek and fill the lowest place. If there is a small amount of air sucked by impeller, the air will try to rise to the top of output pipe (O), while the water in the output pipe (O) will go down back to impeller housing. Water that returned back to impeller housing will help the impeller to suck water from the suction pipe (I). Thus the air will not be accumulated in impeller housing, but the water will always be accumulated in impeller housing. Output pipe (O) is about 50 cm height, this pipe is connected by hose to the sprinkler (Sp). If using a transparent hose for output pipe (O), it will be clearly visible air bubbles go out of impeller housing, and the water flows back into the impeller housing.

In order to prevent mud and dirt enter into the pump, a screener (Sc) is fitted at the end of the suction pipe. Screener is made of PVC pipe which has opening cuts along the side, as the photo below.

Those cuts are deliberately tilted to avoid pipe strength greatly reduced. Cuts are positioned at the left and the right side of pipe. If those cuts are at the upper sidea and the lower side of the pipe, dirt and mud will easily enter. Because dirt in water usually moves from top to bottom, dirt will be collected or settled at lower part of water.

Screener is placed in the gutter with supporting bricks to make it slightly higher than gutter base. Screener must always be below the water level, to avoid air is sucked by the pump. It is needed to check and ensure the minimum water level. A buoy can be used to make screener always follow water level, and the screener always be slightly lower than the water level. But because my gutter is a public facility and the size is not big enough, then the buoy system is not suitable to be applied. Other citizens could questioning the buoy in the gutter, as it could block water flow in the gutter.

I am using PVC pipe with 1 inch diameter and 70 cm length. Since the suction pipe has 3/4 inches diameter, it is necessary to add an adapter socket 1 inch to 3/4 inches. End of the screener pipe which has no knee is left open.

Knee which connects vertical suction pipe to declining suction pipe (I) is not glued. This way will make it easy to remove screener (Sc) for cleaning, if the screener is too dirty or clogged. That knee is smeared with oil or grease to avoid leaking.

Knee at screener end is also not glued, to make it easy to remove to clean the screener. Knee at the end of screener is always submerged in water, so the air can not enter although it is not glued.

If screener is positioned in the same direction to gutter water flow, in the schematic from right to left as shown by arrow (F). Then the dirt inside the screener can be cleaned by that water flow. Water will flow into the screener through opening cuts and exit through the other end of the pipe which has no knee, while carrying the dirt. In other words, the screener can be cleaned by itself.

After 3 weeks operation, it was found that the water usually smelly if sprayed in the morning. While spraying during the afternoon or evening is not too smelly. Maybe because in the afternoon and evening, the smelly gases from the sewer have been evaporated because exposed to hot sun. Sewer aroma will be smelled when using sprinkler which spray water into the air. If sewage directly discharged into the ground, then it is not too smelly. Because water is directly absorbed by the soil and less time to release smelly gases into the air. The pump operates about 15-30 minutes for each test.

Due to hygienic reasons, I do not spray this sewage water directly with hand-held hose. I use a sprinkler (Sp) as sprayers which is placed on grass or tied to a tree. This way prevents sewage water contact with my body when watering the garden. Yellow plastic sprinkler in the top picture can spray to the left and to the right at an angle of about 60 degrees automatically, so water spreads in wide area. With pump power of 125 watts, the total area of the sprayed water can reach about 4x4 square meters. Similar to artificial rain with water sourced from the gutter. The sprinkler has a filter at input section, this filter is usually clogged by dirt. After some time dirt will be accumulated inside hose just before sprinkler input, can be seen clearly as the blackish water if using a transparent hose. Disconnect the sprinkler, turn the pump on to spray the dirt out of the hose. Clean the sprinkler filter with water spray from the hose.

Although the sewer water sprinkler is positioned just a few meters from the clean water pump well, pumped clean water does not change color, taste, and odorless. Thanks to a good casing pipe in the clean water well. Sewer water that seeps into the soil is well filtered by the soil. The sewer water will enter into fresh water well after pervasive dozen meters from ground level. Sewer water can not enter directly into fresh water well because it is obstructed by casing pipe.

Small water pump that is used in this design can directly spray water in less than 5 seconds after power on. The pump does not need to be primed, even if the pump has been rested for 1-2 days. With proper application techniques, this small and inexpensive pump is proven quite reliable.

If too much mud inside impeller housing, the pump will be difficult to start or jammed. Connect and disconnect the electric power quickly (intermittently) sometime could help to start the pump. Intermittent electric power will vibrate pump shaft to free jammed impeller. Usually the pump can be started after 5 times the electric power turned on and off quickly. If the impeller is hard to move, the pump shaft should be rotated manually by hand. For the pump that I use, simply remove the cooling fan cover behind the pump by hand, no need tool as nothing screw to hold that cooling fan cover. Then turn the cooling fan by hand until it feels lighter, no longer jammed. The pump will rotate smoothly as soon as the power cord is connected to the grid.

If a lot of people use this garden irrigation by sewage water, it will reduce load of city's waste water system and prevent flooding. It will also raise the volume of ground water, which can prevent the intrusion of sea water.


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