PROCESS

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Food waste has a higher solid content than municipal wastewater, meaning that it is a more efficient use of digerester volume aka the digester can be smaller.

Peak methane production in a 15-day cycle, themophyllic digester was 10.8L/hr but averaged 4.8L/hr.

for 100 tons of “input”, 30 tons of “output” will then be composted Thus, 30% of input volume can be used for compost--> design constraint for a compost bin or hints at how many plants to have.

Biogas composition is about 67% methane (CH4), 33% CO2 thus the heat capacity is 670 BTU/Ft3 burned.

CH4 production rate (ft3/lb)= CH4% X Gas Production ( ft3/day) TS% X Feed (gal/day) X 8.34 lbs per gal

peak values near 8.5 ft3 CH4/ lb food waste. 5ft3/lb average.

1 ft3 CH4 at 67% methane = 670 BTUs and 13,400 BTUs = 1 kWh. this value is better than coal ( 10, 500btu/kwh)

av. of 2,300 ft3 per day/ 1,000 ft3 digester volume range (in ft3/day) = (1,100–3,200) with these figures, 4.79 kw/h of energy are created daily in a 1000ft3 digester! thats enough to run 48 100-watt lightbulbs continuously*

• these figures are the optimal output based on the chemical energy of the gas, not the conversion into electric energy by burning.

1000ft3= 28.3 cubic meters

There are certain minimum dimensions that a digester must have. First, it needs constant teperature, the most important thing. the first decision to make is to specify above or below ground. For our proposal, there is a decision to make.

1) below ground, and we also ditch the idea of a plinth and incorporate our fire spaces into the earth as well.

2) above ground, and the digester is integrated into the plinth running parallel to the fire pit, but the difference in height of the digester (minumum 1 M tall)must be accommodated in our ‘wall system’

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