Comparative systems analysis of thermochemical and biochemical recycling of organic waste towards industrial feedstocks

Shifting the resource base for chemical and energy production from fossil feedstocks to renewable raw materials is seen by many as one of the key strategies towards sustainable development. The utilization of biomass for the production of fuels and materials has been proposed as an alternative to the petroleum-based industry. Current research and policy initiatives focus mainly on the utilization of lignocellulose biomass, originating from agriculture and forestry, as second generation feedstocks for the production of biofuels and electricity. These activities act on the assumption that significant amounts of biomass for non-food purposes are available. However, given a certain productivity per area, the current massive growth in global biofuels demand may in the long term only be met through an expansion of global arable land at the expense of natural ecosystems and in direct competition with the food-sector. Although many studies have shown the potential of biofuels production to reduce both, greenhouse gas emissions and non-renewable energy consumption, these production routes are still linear processes which depend on significant amounts of agricultural or forestry production area. Cascading use, i.e. when biomass is used for material products first and the energy content is recovered at end-of-life, may provide a greater environmental benefit than primary use as fuel. Considering waste and production residues as alternative feedstocks could help to further reduce pressures on global arable land. This research focused on thermochemical and biochemical technologies capable of utilizing organic waste or forestry residuals for energy, chemical feedstock, and synthetic materials (polymers) generation. Routes towards synthetic materials allow a closer cycle of materials and can help to reduce dependence on either fossil or biobased raw materials. The system-wide environmental burdens of three different technologies, including (1) municipal solid waste (MSW) gasification followed by Fischer-Tropsch synthesis (FTS), (2) plasma gasification of construction and demolition (C&D) wood for syngas production with energy recovery, and (3) forest residuals use in a biorefinery for polyitaconic acid (PIA) production, were assessed using life-cycle assessment. The first two studies indicated that MSW gasification and subsequent ethylene and polyethylene production via FTS has lower environmental impacts than conventional landfilling. In the future, as societies may shift towards the use of renewable energy, power offset by conventional waste-to-energy systems would not be as significant and chemicals production routes may then become increasingly competitive (in terms of environmental burdens) also to waste incineration. While production cost of Fischer-Tropsch derived chemicals seems not yet competitive to fossil-based chemicals provision, future price increases in global oil prices as well as changes in waste tipping fees, and efficiency gains on site of the waste conversion systems, may alter the economics and allow carbon recycling routes to reach a price competitive to fossil-based production routes. The third study found that plasma gasification of C&D wood for energy recovery has roughly similar environmental impacts than conventional fossil-based power systems. However, process optimization with respect to coal co-gasified, coke used as gasifier bed material, and fuel oil co-combusted in the steam boiler, would allow to significantly lower the system-wide environmental burdens. The fourth study looked at PIA production from softwood hemicellulose in a stream integrated approach (with the partially macerated wood and lignin being used in other existing processes such as pulp & paper plants for conventional pulp and bioenergy production). The assessment indicated lower global warming potential, energy demand, and acidification, for the wood-based PIA polymer, when compared to corn-based PIA and fossil-based polyacrylic acid (PAA). However, water use associated with wood-derived PIA was found to be higher than for fossil-based PAA production and land occupation is highest for the wood-derived polymer. It is hoped that results of this dissertation will add to the current debate on sustainable waste and biomass utilization and to establish future supply chains for green and sustainable chemical products.