One study about pre-treatment
technologies. The investigated pre-treatment technologies were screw press,
disc screen and shredder + magnet. The average quantity of
pre-treated organic waste (biomass) produced from the incoming waste varied
between the investigated pre-treatment technologies: 59%, 66% and 98% wet
weight, respectively (41%, 34% and 2% reject, respectively). The pre-treatment
technologies showed differences with respect to distribution of the chemical
components in the waste between the biomass and the rejected material (reject),
especially for dry matter, ash, collection bag material (plastic or paper) and
easily degradable organic matter. Furthermore, the particle size of the biomass
was related to the pre-treatment technology. The content of plastic in the
biomass depended both on the actual collection bag material used in the system
and the pre-treatment technology. The sampled reject consisted mostly of
organic matter. For cities using plastic bags for the source-separated organic
waste, the expected content of plastic in the reject was up to 10% wet weight
(in some cases up to 20%).
The researchers made
batch tests for methane potential of the biomass samples showed only minor
variations caused by the factors city, pre-treatment technology, dwelling type
and season when based on the VS content of the waste (overall average
459 STP m3/t VS). The
amount of methane generated from 1 t of collected waste was therefore
mainly determined by the efficiency of the chosen pre-treatment technology
described by the mass distribution of the incoming waste between biomass and
reject.