Environmental Engineering Reference
In-Depth Information
A second form of tertiary recycling is the conversion of plastic waste into fuels.
This comprises mainly liquefaction and gasification. Both methods can be used for
mixed waste fractions containing plastics, biomass, and other materials. In lique-
faction, mainly heat is used in the absence of oxygen to break down the molecular
structure of polymers. The aim is to obtain a synthetic crude oil (syncrude) with
a high content of hydrocarbons that could be processed in petrochemical facili-
ties. Gasification aims for the conversion of waste plastics and biomass into carbon
monoxide and hydrogen. Steam, oxygen, or carbon dioxide are used as reactants.
Both carbon monoxide and hydrogen can then be used for the synthesis of hy-
drocarbons (Fisher-Tropsch process), ammonia (Haber-Bosch process) and other
important substances. The chemical information is mainly destroyed during these
processes.
The term quaternary recycling is used in an ambiguous way. Often it is used for
the recovery of energy as we describe below. Sometimes composting of biodegrad-
able polymers is implied, referring to the conversion of polymeric materials into
new biomass.
Recovering energy: energy recovery is the last step in the utilization of waste ma-
terials. Incineration of waste in power plants results in electricity and usable heat.
Waste plastics can also be converted in coke ovens into coke, which is used in blast
furnaces. Moreover, waste plastics are also directly introduced into blast furnaces
for the reduction of iron ore. In cement kilns, waste plastics are also used for the de-
carbonation of limestone. In the latter cases, the production of steel and cement are
the new materials obtained. Materials used for these purposes have the lowest re-
quirements since any material with sufficient carbon content can be utilized. Often
materials are used that were not found suitable for recycling and separated as refuse
derived fuel (RDF). Both structural and molecular order are destroyed. Remaining
inorganic ashes are commonly landfilled.
With a few exceptions, the reduction or handling of waste streams incurs finan-
cial costs, which means that waste management is expensive. As a consequence,
the motivation in economy and society to put efforts into waste processing is quite
limited. For this reason, many countries have put regulations in place to control the
waste flow. Such regulations comprise rules for materials that have to be collected,
sorted, and processed, may ban certain materials and substances, and apply other re-
quirements. Regulatory structures might be very different from country to country.
In the USA, the responsibility is divided between states and local authorities, lead-
ing to a patchwork of competences. In Europe, the European Commission took over
many competences from the member states and released directives, which have to
be put into national law by member states. In Japan, regulations were centralized
by the Japanese government and most date from the beginning of this century. The
Basic Law for Establishing the Recycling-Based Society acts as the framework for
measures that should lead to a sustainable handling of resources. Under this basic
law, are laws for the Promotion of Effective Utilization of Resources, for Waste
Management Regulation and Recycling, and waste management supported by vari-
ous subsidiary recycle laws for individual waste groups such as automotive waste
and electric and electronic waste (see Chap. 2).
