Exercise $3.$ Biogas generation

Table $1$ presents the general biogas properties from different biogas plant types while table $2$ shows

available feedstocks and landfills in a Finnish district Niemi $($fictional$).$

Table $1.$ Biogas properties in different biogas plant types

Table $2.$ Metaanin tuotto ja kuiva$-$aineen muodostuminen eri raaka$-$aineista sek$$ metaanin tuotto kaatopaikalla.

a$)$ What is the lower heating value of each biogas quality $($considered as ideal gas$)?$

b$)$ Calculate the biogas $($BG$)$ potential in normal cubic meters $)$ for each plant type from

available feedstocks and landfills in Niemi

c$)$ Hydraulic retention time $($HRT$,$ unit: days$)$ of a biogas plant describes the average time the

substrate remains in the digester.

$HRT=\frac{V_{\text{c}\text{a}\text{p}}}{V_{\text{f}\text{e}\text{e}\text{d}}^{}}$

Where

$V_{\text{c}\text{a}\text{p}},$ Feedstock capacity of digester $m^3$

$V_{\text{f}\text{e}\text{e}\text{d}},$ Volume flow of feed $\frac{m^3}{d}$

The combined feedstock capacity of the wastewater treatment plant $($WP$)$ digesters in Niemi is

$3$

$650$ m $.$ With HRT of $21$ days, $80\%$ of the potential methane is gained while with HRT of $25$ days

the $90\%$ of the methane. Generation of sludges is equable through the year and the density of

$3$

sewage and industrial sludge is assumed to be $1$ ton$/$m $.$ What is the yearly methane production

with HRTs of $21$ and $25$ days in WPs$?$