Citric Acid Passivation of Water Wells

(based on Water Well Rehabilitation by Neil Mansuy),

✅ Citric Acid Protocol for Steel Casing Passivation in Wells

📌 Objective:

• Remove iron scale, rust, and bacterial byproducts.

• Passivate the cleaned steel surface to inhibit further corrosion.

🧪 1. Citric Acid Concentration

Purpose	Citric Acid Concentration (% by weight in water)	Notes
Light cleaning / passivation only	1%–2%	Mild action; suitable for newer or lightly scaled wells
Moderate iron scale & biofilm	3%–5%	Effective for general rehabilitation jobs
Heavy scale, rust, biofouling	5%–10%	For wells with severe iron fouling and corrosion products

🧰 2. Equipment & Materials

• Clean water (preferably dechlorinated or softened)

• Citric acid (food grade or technical grade)

• Mixing tank (poly or stainless, not carbon steel)

• Recirculation pump or surge block

• Airlift or pump for flushing

• pH meter or test strips

🔄 3. Procedure

Step 1: Pre-Treatment Prep

• Measure water volume in the well (depth × casing diameter).

• Calculate citric acid dose based on selected concentration.

• Prepare citric acid solution in a mixing tank using warm water if possible (increases solubility and reactivity).

Step 2: Injection

• Pump or pour the citric acid solution into the well.

• Use a tremie pipe for deep injection if necessary to distribute evenly.

Step 3: Agitation & Contact Time

• Recirculate or surge the well for 4–8 hours to enhance contact.

• Leave the solution static in the well for an additional 12–24 hours.

• Optional: Use brushes, bailers, or swabs to help clean the casing wall.

Step 4: Flushing

• Remove spent solution via airlifting or pumping to a waste tank or disposal area (follow local discharge regulations).

• Continue flushing with clean water until:

  • pH returns to near neutral (6.5–7.5).

  • Water runs clear and free of visible debris or foam.

Step 5: Optional Post-Treatment

• Apply a mild sodium hypochlorite (chlorine) shock or bactericide if biofouling was present.

• Consider a follow-up phosphate or silicate corrosion inhibitor if long-term protection is needed.

⚠️ Safety & Compatibility Notes

• Avoid mixing citric acid with chlorine or oxidizers — this can release harmful gases.

• Do not store citric acid in carbon steel containers.

• Always add acid to water, never the reverse.

🔍 Field Tips

• pH will drop to ~2–3 in a strong citric acid solution — this is expected and helps dissolve iron scale.

• If the solution turns dark orange or brown quickly, that’s a good sign it’s chelating iron.

• Monitor effluent water color and pH during flushing — they indicate cleaning progress.