Apparatus
1. One pH meter
2. One adjustable hot plate
3. Two Burettes and stand
4. One 100ml beaker
Reagents
1. pH 7.0 buffer solution
2. pH 4.0 buffer solution
3. Standard acid
Procedure
1. Separate solids by centrifuging or removing water above settled sample.
2. Measure 50ml of sample and place in beaker.
3. Titrate with sulfuric acid to a pH of 4.0
4. Note acid used, and continue titrating to pH 3.5 to 3.3
5. Slightly boil sample for 3 minutes
6. Cool in water bath
7. Titrate to pH of 4.0 with 0.05 N NaOH, note burette reading ‘a’ ml and complete titration to pH of 7.0, note burette reading ‘b’ ml (If this titration consistently takes more than 10ml of the standard hydroxide, use 0.1 N NaOH)
8. Calculate total alkalinity. Take answer in m/s from titration to pH 4.0 and calculate alkalinity according to formula on Alkalinity of formula on alkalinity of wastewater and sludge, remembering that there will be discrepancy between titration of sample to pH 4.5 and this titration to 4.0.
9. Calculate volatile acid alkalinity Alkalinity between pH 4.0 AND 7.0 as mg/L CaCO3
10. Calculate volatile acids
Case 1.
Volatile acid alkalinity >180mg/L
Volatile Acid = Volatile acid alkalinity times 1.50
11. Calculate bicarbonate alkalinity
i.e. Volatile acid alkalinity in mg/L (stap9) total alkalinity in mg/L
(step 8) = Bicarbonate alkalinity in mg/L.
Example & Calculation
Titration from pH 4.0 to 7.0 of 50ml sample required 8ml of 0.05 N NaOH (a= 1.1 ml, b= 9.1ml)
Volatile Acid Alkalinity, mg/L = (b-a) x 2500/50
= 8ml x 2500/50
= 400mg/L
Step 6: Calculate Volatile Acids
Case 1:
400 mg/L >180mg/L, therefore.
Volatile Acid, mg/L
= Volatile acid alkalinity x 1.50
= 400 mg/L X1.50
= 600mg/L
Note: This is an acceptable method for digester control to determine the volatile acid/Alkalinity relationship, but not of sufficient accuracy for research work.