Cut-Off processes without exhanges and with 0 impact score

Question

Hello, 

I have been working with some processes in the system model APOS, for example; 

treatment of biowaste by anaerobic digestion | biowaste , treatment of biowaste by anaerobic digestion | biogas ; 

 treatment of waste plastic, mixture, municipal incineration | waste plastic, mixture , treatment of waste plastic, mixture, municipal incineration | heat , treatment of waste plastic, mixture, municipal incineration | electricity

I noticed that, in the Cut-Off system model, the byproducts of these processes as biogas, heat and electricity can't be used. In the ecoinvent database site EcoQuery, they appear wihtout exchanges and with 0 impact scores. When i try to use them in OpenLCA, i always obtain an impact equal to 0.

Why can't i use these processes with the Cut-Off system model? They are only designed for APOS? What are my alternatives? In my study, i'am assessing the byproducts of waste treatment, like biogas, heat, electricity, etc. and i would like to do this with Cut-Off also.

Thank you for your help! 

Answer 1

Hello tapmbot.

The cut-off system boundary approaches waste by-products like this: When recycled/treated a waste stream will stop being waste. It will instead become a resource. When that happens, you stop and draw a fat line right after the process that made the waste stream go from waste to ressource. Everything before that line belongs to product system 1, which generated the waste stream. Everything after, belongs to product system 2, which can utilize the newly created ressource.

So why do you not get any impacts in these processes you are describing?

Simply put, these flows have just stopped being waste, and their entire past product system has been cut off (hence the name). In other words, its on purpose that these processes are empty.

Cut-off is an easy to understand, easy to communicate approach to waste and ressources. It does not however, do well in the analysis you are trying to conduct.

Is there a reason you would like to use cut-off? I would think its possible, but it would be 10x simpler to use other system models, like APOS or consequential.

I hope this sheds some light on the topic.