Several food and beverage companies have been participating in a community diges

Question

Several food and beverage companies have been participating in a community digester pilot program within the UMD Industrial Park. The following waste stocks are currently treated in the anaerobic digester: potato waste, cooking oil, cow manure, and bakery waste. Assumptions: 30 % of the volatile solids are converted 15 ft3 of biogas per lbs volatile solids destroyed 65 % methane in biogas.

1. a. If the food waste is 9% total solids and 7% volatile solids, what is the concentration of TS and VS in g/L?

b. The digester is a 1000 L. If 30% of the VS are destroyed, what is the biogas production expected per day?

c. The generated biogas is used for heating purposes in the security trailer. If the trailer requires being supplemented with 700 ft3 of methane per day, does the anaerobic digester meet the heating requirements for the security trailer?

Explanation / Answer

a) It is well known that 1% equals to 1g/100 mL

So, 9% means 9 g/100 mL

hence, for 1000 mL,

90g/1000mL

= 90g/L

Similarly, for 7% volatile solids,

7% = 70g/L

b) First calculate the volume of VS in 1000 L digester using the concentration of 70 g/L

so, 1 liter = 70 g

1000L = 70*1000

= 70,000 g VS

calculating 30% of this,

30% of 70,000

= 21000 g VS

As given in the problem, 15 ft3 biogas per Kg or 1000 g

hence, for 21000 g or 21Kg VS, the produced gas will be = 21*15

= 315 ft3

c) No,

The digester doesn't meet the security trailer requirements as the quantity of produced gas (315 ft3) is lower than the reuired quantity (700 ft3)

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