ABE TUTORIALS

PROBLEM 18:

THE MINIMUM SIZE FOR A BIOGAS DIGESTER HANDLING THE MANURE OF 100 PIGS WITH AN AVERAGE OF 2.25 KG MANURE/PIG/DAY, 30 DAY RETENTION TIME, AND A MIXING RATIO OF 1:1. ASSUME THE DENSITY OF MANURE IS EQUAL TO THAT OF WATER.

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Select the minimum digester size:

a. 6,750 liters | b. 13.5 m3 | c. 6.75 liters | d. 13.5 liters | e. nota

View Solution

Step 1: Calculate Total Daily Manure (V_m).
Vm = 100 pigs × 2.25 kg/pig/day = 225 kg/day
Since density ≈ water (1 kg/L), Vm = 225 L/day

Step 2: Calculate Daily Slurry Volume (Vs).
Mixing Ratio 1:1 (1 part manure: 1 part water)
Vs = Vm + Vwater 

     = 225 L + 225 L 

     = 450 L/day

Step 3: Calculate Digester Volume (Vd).
Vd = Daily Slurry Volume × Retention Time
Vd = 450 L/day × 30 days = 13,500 Liters

Step 4: Convert to Cubic Meters.
13,500 L / 1,000 = 13.5 m³

Result: b. 13.5 cu. m.