======Cleaning Water With Flocculation======


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**Materials: **{{$demo.materials_description}}\\
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**Safety: **{{$demo.safety_description}}\\
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**Alternative titles:** Cleaning Water With Alum
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====Summary====                   
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====Procedure====  
 - Collect about 1 liter of turbid water per group from a nearby pond or stream, including a little bottom sediment. Cap and bring to class.
  - Prepare two stock flocculant solutions in labeled containers: dissolve a small pinch of aluminum sulfate in about 10 mL tap water; dilute a small amount of pool clarifier polymer in about 10 mL tap water.
  - Give each group seven clear cups. Draw a fill line about three-quarters up each cup and label cups 1–7.
  - Record in journals what each cup will test: 1 control; 2 alum not stirred; 3 alum stirred; 4 polymer not stirred; 5 polymer stirred; 6 alum plus lemon juice; 7 polymer plus lemon juice.
  - Shake the source water to resuspend solids and fill cups 1–5 to the fill line. Note initial appearance.
  - After the heaviest particles settle briefly, add 1 mL of the assigned flocculant to cups 2–5.
  - Stir only cups 3 and 5 for several seconds using separate stirrers to avoid cross contamination.
  - Observe cups 1–5 for about 5 minutes and record changes in clarity and any visible flocs or settled layers.
  - Re-shake the source water and fill cups 6 and 7 to the fill line.
  - Add 1 mL lemon juice to cups 6 and 7 and stir to acidify the water.
  - Add 1 mL alum to cup 6 and 1 mL polymer to cup 7. Stir both with separate stirrers.
  - Observe cups 6 and 7 for about 15 minutes, recording floc formation, settling behavior, and clarity compared to the control.
  - As a class, compare which conditions improved solids removal: flocculant type, stirring vs no stirring, and neutral vs acidic pH.
  - Conclude by ranking treatments from most to least effective based on observed settling and clarity.



====Links==== 
Flocculation - MITK12Videos: 
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📄 Things That Matter to Flocculants - Teach Engineering: [[https://www.teachengineering.org/activities/view/usf_flocculant_activity01]]\\


====Variations====
  * Try several doses of each flocculant to find an optimal amount for your local water.
  * Replace lemon juice with a mild base such as baking soda solution to test the effect of higher pH.
  * Test natural flocculants such as crushed moringa seeds or chitosan and compare to alum and polymer.
  * Add a simple measurement, such as a Secchi tube or ruler behind the cup, to semi-quantify clarity changes.
  * Repeat with water from different sites or after rain to see how source water changes results.




====Safety Precautions====
  * Treat all field-collected water as nonpotable; do not taste or touch face while working and wash hands after the activity.
  * Label all solutions clearly and keep alum, polymer, and lemon juice out of eyes and mouth; avoid splashes.
  * Use separate stirrers for different chemicals to prevent unintended reactions.



====Questions to Consider====
  * Why did stirring change the outcome for the same flocculant and dose? (Stirring increases particle collisions so more microflocs form, which then settle.)
  * Why might alum work differently from a polymer clarifier? (Alum neutralizes particle charges, while polymers bridge particles together; their mechanisms respond differently to water chemistry.)
  * How did lowering pH with lemon juice affect alum performance, and why? (Acidic conditions can shift aluminum species and reduce charge neutralization at this dose, slowing floc formation.)
  * Which treatment produced the clearest water fastest, and what evidence supports your choice? (State the cup number and specific observations such as visible flocs, settled layer height, and clarity.)
  * If you increased the dose of polymer or alum, what problems might appear? (Overdosing can restabilize particles or create tiny, fragile flocs that do not settle well.)