Treatment of river water into domestic water is very necessary for demands of daily life and production today. Currently, there are some different processes that have been invented and applied. So, what is the most effective, safe and economical process? Let’s find out with UCE Co., Ltd through the article below!

Please refer to the article “Understanding the quality and treatment of groundwater and surface water”

1.   Why is it necessary to treat river water into domestic water?

Surface water such as river, stream, lake, and pond water has been increasingly polluted, increasing the harmful content of inorganic, organic, and non-biodegradable substances and suspended microorganisms (virus, bacteria, algae…) in water source.

Some rivers are cavitated by seawater, which increases salinity significantly; many streams contain large amounts of mud, soil, sand, heavy metals due to uncontrolled exploitation of forest trees and surface land, shrinking forest area, etc.,  of which the most dangerous is the  directly discharge from factories, traditional craft villages, agricultural pesticides… Since then, surface water is both lacking in quantity and not in quality.

Therefore, the design of a system to treat surface water into domestic water needs to consider the above polluted factors and changed seasonly in year and treated quality meets the new standards of the Ministry of Health QCVN 01-1:2018. /BYT.

Good stream (lake) water while heavily polluted river water  due to wastewater direct discharge
Good stream (lake) water while heavily polluted river water  due to wastewater direct discharge

Good stream (lake) water while heavily polluted river water  due to wastewater direct discharge

1- Select the best technology to treat river water into domestic water (city water)

Because the surface water source varies widely from region to region, it depends on the capacity and specific conditions of each place to choose the suitbale technology that low cost for invest and operating while keep the stable treated quality

There are places with good water sources, especially large reservoirs containing upstream water, the treatment of river water into domestic water just only needs to be settled and sterilized. However, for places near cities or industrial zones, the water on the surface is polluted, so the treatment must go through many steps.

Note: The design of the system to treat river water into domestic water needs to ensure stable treated quality although a changed water from source

The following are the basic steps that commonly applied in the process of treating river water into domestic water.

Process of treating river water into domestic water

Process of treating river water into domestic water

Step 1: Garbage screen

– Remove all kinds of garbage, dead animal, plant, algae,…

– Should design automatic garbage collection to avoid clogging or frequent cleaning and collection.

– Stainless steel material to avoid corrosion.

Step 2: Receiving tank for river or stream water

– The larger the tank the better for 2 functions of stabilization and preliminary settling tank to reduce the amount of impurities and chemicals for the next treatment step. Water retention time is 1-2 days.

– Design a tank with a certain inclination or overflow type with a periodic sludge collection pit.

– Use chlorine (liquid, powder, chlorine generator, gas) to kill algae, bacteria and partially oxidize iron, manganese, and organic substances.

Step 3: Mix chemicals

– Use agitator for small tank, low capacity or directly injected into the main pipeline with built-in mixers or directly dosed into mixing ditches if strong enough flow

– Commonly used chemicals to aid sedimentation such as PAC, aluminum alum, and iron alum.

– The pH adjustment ensures the optimum level for settling and ensures a stable pH output, caustic soda or lime to raise and control the pH. Lime is used to increase calcium hardness, avoiding corrosion of steel pipes but high hardness also make scale to water piping, so need to control harndess. Note: Sulfuric acid can also be used but is mostly standby.

– Activated carbon can be used to absorb organic matter, arsenic, ammonium from the water for the next stage of treatment.

– Chemicals that have been mixed with the flow will be put into the next settling tank.

Step 4: Sedimentation and clarification

– This is the most important step of the process of treating river water into domestic water. The efficiency settling depends  much on the settling tank. Using a laminate plates with 60 degree inclinationwill to increase the efficiency of separating suspended matter from water. It is also possible to perform centrifugal settling of water entering from the bottom to top, the flocculated sludge will be further settled in the secondary tank. Sludge is removed from the bottom, clean water will be put into the center of the settling tank again.

– Sludge from the clarifier has chemical components, must be collected from the high sludge  storage tank, then will be dehydrate with filtering press or belt press

– Turbidity after sedimentation  tank can be less than 5 NTU.

From left: river water, at coagulation tank and outlet of sedimentation tank

From left: river water, at coagulation tank and outlet of sedimentation tank

Steps 5: Microfilter

– Sand filtration is a traditional filtering technique. In particular, quartz sand, manganese sand are used for filtration if unstable water quality from source or the high required for result. Open filtering tank for large capacity, pressured filtering tank for small capacity. In addition, filtration can be faster with high tech of 10 – 20 micrometer filtering discs or 0.1 – 0.03 micrometer UF membrane with stable quality.

– Using the compressed air stream or pressured water to soften dirty layer at op before backwashing with water pump will shorten the time and save water for the washing process.

– For magnetic resin beads, it will be extracted continuously and regenerated the Cl base of the plastic beads with NaCl. Recycled water cannot be reused but must be disposed of as wastewater.

– To evaluate the effective filtration, it must be based on the turbidity of the current modern treatment systems, after this filtration step, the turbidity can be <1 NTU.

Steps 6: Active carbon filter

– Absorbing of organic impurities that causing color, odor from the water. In case good water source and high safety design factor, this step can be no need. Pressured active carbon filtration is often used for small and medium systems because it is easy to backwash or regenerate with hot steam

– For large systems, active carbon filtration also has a large cost, so this step can be absent. Instead, it is to improve the level of safety and efficiency at the previous settling and filtering step.

– Backwash water of active carbon filter, sand filter can be returned to the original raw water tank.

Step 7: Sterilizing and make up Fluoride

Bacterial control is essential, as the amount of sterilizing chemicals introduced from beginning has been much reduced, especially through the active carbon filtration step. Therefore, to prevent bacteria, it is necessary to maintain chlorine or use Ozone, UV light.

City water (domestic water)

–  Treated water quality with criteria of chemistry, physical, and microbiological must be ensured according to the new standard QCVN 01-1:2018/BYT before putting in water supply network or used for each plant.

– For Fluorine parameter, there are still opposing opinions that maintain the WHO standard (0.5 – 1.5 mg/l), the other opinion is that  concentration of 0.9 – 1.2 mg/l for a long time will affect health due to over Fluorine in body because Fluorine is assumed to be obtained from food, so no need to be supplemented

2- Treatment of river water into domestic water with high quality, lowest investment and operating costs

By improving and incorporating the settling tank, the sludge collection has compartments to minimize movement. Thereby increasing of sedimentation rate by gravity downwards and the adhesion ability of the upper laminate to optimize the settling tank, wil have high efficiency and saving area.

In the Microfilter tank: The main filter material is still quartz sand, but using an automatic hydraulic siphon option for backwashing will not need to invest in a backwash pump, reducing operating costs and consuming less water for backwashing for sands

Water quality after treatment can be obtained as follows:

No Parameter Unit Limit – QCVN 01-1:2018/BYT Treated result
1 Odour, taste   No Odour, no taste No Odour, no taste
2 Color TCU 15 0
3 pH   6.0 – 8.5 7.68
4 Turbidity NTU 2 0.3
5 Chlorine – Clo, Cl2   0.2 – 1.0 0.67
6 Ammonium (NH4 + NH3) as N mg/l 0.2 KPH (< 0.006)
7 Nitrate/ NO3 as N mg/l 0.3 KPH (< 0.003)
8 Chloride – Clorua, Cl mg/l 250 10.65
9 Ferrum – Fe mg/l 0.3 KPH (< 0.017)
10 Hardness – CaCO3 mg/l 300 45
11 Mangan – Mn mg/l 0.1 KPH (< 0.015)
12 Plumbum – Pb mg/l 0.01 KPH (< 0.006)
13 Arsenic – As mg/l 0.01 KPH (< 0.006)
14  Total Dissolved solid mg/l 1000 66.6
15 Flour – Fl   1.5 0.21
16 Coliform CFU/100ml <3 KPH ( not detected)
17 Ecoli CFU/100ml <1 KPH
  • Note: KPH: Not detected or Not detectable

Note: The treated quality depends much on water source

Just contact us – UCE Co. Ltd will help and free of charge to analyze and evaluate, proposase your water treatment.