by Professor C. Visvanathan from the School of Environment, Resources and Development Asian Institute of Technology, Thailand. Posted 10/27/2011.

In 2009, there were 27 million displaced people due to military conflicts alone. Cyclone Nargis in Myanmar (2009), the floods in Pakistan (2010), and the 2011 earthquake and tsunami in Japan highlight the number of devastating disasters occurring around the world in the recent past. Apart from deaths, the number of displaced communities due to these anthropogenic or natural disasters is a huge issue to tackle. Provision for safe drinking water is among the highest priorities during and after any disaster situation.

On-site water treatment is considered an important strategy to cope up with prolonged disaster recovery efforts. Water taken from surface water sources such as rivers and lakes needs some treatment before it can be safe for drinking. Fallout from disasters often limits access to various resources such as chemicals, electricity, and treated water from treatment plants. When people are displaced from their homes and are gathered at one location, such as a rehabilitation camp, unavailability of resources becomes quickly apparent. Such conditions highlight the necessity of having reliable drinking water treatment systems running on alternative energy sources such as human-generated power. With the prime objective of providing safe drinking water using human-generated power (using hand pumps rather than electric pumps) in these situations, a microfilter- (MF) based, hand-pump operated water treatment unit was developed. The low-operating, trans-membrane pressure of microfiltration provided the applicability of hand-pumps to develop a sufficient driving force for filtration.

Emergency Potable Water Supply System

A dead-end, outside-in hollow fiber MF [200 kDa MWCO (molecular weight cut-off) with a 3.4 m² surface area] made of PVDF and a rotating hand pump are the most important units of the system. Pretreatment consists of a bar screen and a cloth-bag filter with pore sizes of 45 µm. The schematic diagram of the system and the actual system are given in Figures 1 and 2, respectively. In its operation, surface water is poured through a coarse screen, then a cloth screen, and finally stored in the feed tank. From there, the feed water is pumped by the hand pump through the membrane, and the filtrate is collected and stored in the filtrate tank. The system is capable of providing 400-650 L/day of treated water, sufficient to meet the daily drinking water requirement of 50-100 people under normal operating conditions.

Figure 1: Schematic diagram of the emergency potable water supply system.

Actual emergency potable water supply system:
Figure 2A: Front

 

Figure 2B: Rear

System Performances

The system was operated and tested with two types of raw water typical to those found in tropical regions. These two types include water from a surface water collection pond and water from a river. The basic properties of the water sources are indicated in Table 1.

Table 1

The emergency water supply system has shown excellent performances under both types of water sources. However, removal efficiencies and maintenance requirements vary with the quality of the raw water. Table 2 summarizes the system performances and operation details of the unit.

Table 2

Treated Water Quality

Treated water quality satisfies not only emergency water supply standards but also drinking water quality standards. Some of these water quality parameters are given in Table 3. Irrespective to raw water turbidity, the unit is capable of providing low turbid water, well below the upper limits of drinking water quality standards. A major advantage of this low turbid product is low requirement of disinfectants for the post disinfection processes.

The membrane separation process (PVDF membrane having 200 kDa MWCO) provides complete rejection of bacterial and protozoa pathogens in the water. The removal of protozoa and protozoa cysts is very important because of the resistance of those under a typical chemical disinfection process with chlorine compounds.

Table 3: Water Quality Parameters of the Treated Water 

However, there are possibilities of growing pathogenic bacteria in the treated water line or in storage containers. Also, pathogenic viruses that are smaller than membrane pores may escape through the membrane. To counter this, the system includes a post disinfection using a chlorine compound, Ca(OCl)₂. The treated water quality with low turbidity provides excellent conditions for further disinfection with this chlorine compound, or other forms of Cl₂. Apart from the chemical disinfection, techniques such as solar water disinfection (SODIS), can be used.

The emergency water supply systems can be operated and maintained with simple instructions—consisting of an operation and troubleshooting manual with pictorial illustrations. Further improvements to suit the system for different field conditions are under progress at the moment, with the collaboration of industrial partners.

Some additional details of the emergency water supply system are given in the next sections.

 Operating Procedure of the System

A. Pour the Surface Water Into the Feed:

(Figure 3)

 

 

 

(Figure 4)

 

 

B.  Rotate hand pump (clockwise). During the rotation of the hand pump, press the gas release valve until water comes out from it:

(Figure 5)

 

 

 

 

(Figure 6)

 

 

 

 

 

c. Collect treated water.

(Figure 7)

 

 

 

 

 

Figure 8

 

 

 

(Above) This Picture shows the comparison between feed water and treated water.

D. Disinfect using chlorine.

Daily Draining Out and Maintenance

To remove the impurities accumulated in the membrane after one working day, draining the concentrated water can be performed by opening a valve at the bottom of the housing.

• Open the draining valve for about five minutes to drain out the concentrated water.
• Rotate the rotating hand of the hand pump to let the feed water pass through the membrane for about one minute.
• Close the draining valve.
• Continue rotating the hand pump to fill the membrane housing completely.
•  Press the air release valve on the housing until water exits from this valve.

Figure 9

Cleaning frequency of the fine screen depends on the feed water quality. Normally, it is recommended to clean whenever membrane chemical cleaning is done.

Step 1: Take out the coarse screen, and then the fine screen from the system.

Figure 10

Figure 11

Figure 12

Step2: Remove the particles inside the fine screen.

Figure 13

Figure 14

Figure 15

Step 3: Shake and rub the screen in a small feed water tank, then rinse the screen with the treated water.

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Bibliography and References:

Abeynayaka A., Nguyen T. T., Visvanathan C. & Ariyamethee P. (2010). Chemical-free and carbon neutral membrane based emergency water supply system. 8th International Symposium on Southeast Asian Water Environment, Phuket, Thailand. October 24 to 26, 2010. pp. 59-66.

Nguyen T. T.  (2010). Development of a water treatment system for emergency situations. Master thesis, Environmental Engineering and Management, Asian Institute of technology. Thailand.