So only focussing on biogas and electricity that are byproducts from your waste treatment, in produçao and in consumo, from what I see you modeled this as avoided product, and you have set the provider process for this in both cases - that makes sense to me.
Addition: you have of course still multifunctional processes, they treat waste and produce one product (Sumo etc.) - you will need to decide about allocation still, since the system expansion / avoided product takes care only of the third funtion of these processes.