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The paper starts by reviewing the increasing production of waste and the growing importance of its thermal treatment, which aims at volume reduction of the waste, at the destruction, capture, and concentration of hazardous substances, and at the recovery of energy (WtE).

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Over the past few decades, the sharp rise in post-consumer plastic and biomass waste has resulted in an ever growing challenge to treat such waste sustainably. Co-pyrogasification of plastics and biomass mixtures, as opposed to separately converting these waste streams, offers several advantages including an improvement in syngas quality and composition (H2/CO ratio) in relation to the desired application, and an easier reactor feeding of plastics. Furthermore, many studies have shown that co-pyrogasification promotes the conversion of waste to gas rather than char and tar. However, in order to achieve the desired product distribution or syngas composition, operating parameters such as the reactor temperature, equivalence ratio (air or oxygen), steam/fuel ratio and catalyst, have to be optimized. Thus, this paper aims to review literature studies on the co-pyrogasification of plastics and biomass by considering various aspects including the process principle, reactors, influence of feedstock characteristics and operating parameters on the products, as well as the synergies observed during the thermoconversion of plastics and biomass mixtures with some reference to coal mixtures when necessary.

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The amount of different persistent organic pollutants (POPs) in the input of waste incinerators was compared to that in the output. Three cases were considered: a rotary kiln incinerating hazardous waste, a grate furnace incinerating municipal solid waste (MSW) and the same grate furnace co-incinerating plastics of waste of electrical and electronic equipment (WEEE) and automotive shredder residue (ASR) with MSW. The mass balance for PCBs in the rotary kiln indicates that these POPs are destroyed effectively during incineration. The grate furnace can be a sink or source of PCDD/Fs and PCBs depending on the concentrations in the incinerated waste. In order to compare the total amount of POPs in input and output, a methodology was developed whereby the amount of POPs was weighed according to minimal risk doses (MRDs) or cancer potency factors. For both incinerators the PCDD/Fs, PCBs and polyaromatic hydrocarbons (PAHs) are the main contributors to total weighed POP output. In MSW, the PCDD/Fs, PBDD/Fs and polybrominated diphenylethers (PBDEs) are the main contributors to the weighed POP input. The ratios of the weighed POP-input over -output clearly indicate that the rotary kiln incinerating hazardous waste is a weighed POP sink. The grate furnace incinerating MSW is a weighed POP sink or source depending on the POP-concentrations in the waste, but the difference between output and input is rather limited. When e.g. ASR and plastics of WEEE, containing high concentrations of PBDEs and PCBs, are co-incinerated in the grate furnace, it is clearly a weighed POP sink.