The table below shows the potential biogas yield, in $[$m$3/$t wet mass of substrate$]$ for different substrates, along with their respective total solids $($TS$)$ content and volatile solids $($VS$)$ content.

Cow manure Chicken manure Food waste Grease trap Bread

TS content, $\%$ wb

$9$

$15$

$205090$

VS content, $\%$ db

$80$

$65$

$909690$

Potential biogas yield, m$3/$t wet mass of substrate $30$

$60$

$220$

$500$

$580$

$1)$ Calculate the biogas yields, in $[$m$3/$t total solids$]$ and $[$m$3/$t volatile solids$]$ for the substrates.

$2)$ Rank the substrates based on the biogas yields that are expressed in the three different units. Briefly comment on your results.