Coagulation improves water quality

Coagulation - Flash Animation

This Flash movie is about the coagulation process to improve the quality of rural water. A transcript of the dialogue is presented below.

Coagulation is a simple and inexpensive way to improve the quality of farm water and reduces levels of organic compounds, dissolved phosphorus, colour, iron, and suspended particles.

Coagulation can be useful for:

• household use
• improved operation of commercial treatment systems
• mixing of farm chemicals
• livestock watering
• agri-food processing

Test to determine how much chemical is needed

Recommended chemicals:
Dugouts: aluminum sulphate
Cells: aluminum sulphate, ferric chloride or ferric sulphate
Commercial coagulation systems: polyaluminum chloride

Materials:
2L measuring container
2 - 10 or 20 ml syringes
rubber spatula
pH meter and/or alkalinity strips (both preferred)
1% coagulation chemical solution
(to obtain a 1% solution add 5 mL of chemical to 495 mL of distilled water)

Conduct beaker test by adding 1 liter of water. Measure pH or alkalinity.Add 1% chemical solution until pH drops to 6.0 and/or alkalinity reaches 40 mg/L.

Undiluted chemical will be used when treating the entire dugout. Use the following formula to determine the amount:
1% chemical required for beaker test (mL) multiplied by the volume of the dugout (litres) and divide by 100 will result in the amount of undiluted chemical required for the entire dugout.(mL). Note: 1000 mL = 1 Litre

Size of dugout

• Measure length and width at the dugout's water surface
• Length must be equal to or greater than the width
• Slope is the number of metres in the horizontal (run) direction for each metre in the vertical (rise) direction (e.g.: run/rise = 4m/1m)

You can enter your measurements into the online calculator to determine the volume of your dugout.

Note: Most dugouts constructed with an earth mover (buggy) have 4/1 end slopes and 1.5/1 side slopes.

Coagulate

When coagulating the chemical must be sufficiently mixed.

A demonstration of a coagulation cell is shown:

Prepare by determining chemical needed, then moor boat on dugout

For coagulation cells, attach electric trolling motor to one side of the dock.Start motor, run at full throttle 20 minutes to fully circulate.

Put on protective gloves, clothing and eyewear (especially when using ferric chloride). Always follow the protective measures in the Material Safety Data Sheets for all chemicals. Refer to the Transportation of Dangerous Goods Act for transportation of chemicals.

Add chemical directly above propellor.
Dugouts: Add 8-20 litres per minute.
Coagulation cells: Add 2 litres per minute.

Monitor pH and/or alkalinity during chemical addition.
Stop adding chemical if alkalinity drops below 40 mg/L or pH drops below 6.0.

Once 75% of chemical has been added, mix for 20 minutes.
Monitor pH and/or alkalinity.
The pH should stabilize between 6.5 and 7.0.
The alkalinity should stabilize between 50 and 100 mg/L.

Stop adding chemical if levels are below what is expected.
Add more chemical if pH and alkalinity levels are high.

After enough chemical has been added, continue mixing at full throttle for 20 minutes.

Slow the motor to half speed and continue mixing for another 10 minutes.

Allow the dugout to settle for at least one day before using the water.

Dugout coagulation is a temporary solution to water quality problems in dugouts. Because poor quality surface runoff flows into the dugout, repeated applications are required. Following good land practices around the dugout improves and maintains good quality water. Coagulation will work better with higher quality raw water.

Water uses

Most water sources can be coagulated successfully and then used in a number of ways.

Coagulation can be useful for:

• household use
• improved operation of commercial treatment systems
• mixing of farm chemicals
• livestock watering
• agri-food processing

Warning: Do not drink the water until further treatment or disinfection has been done.

For technical advice, contact the PFRA district office nearest you.