Life cycle assessment of the integration of anaerobic digestion and pyrolysis for treatment of municipal solid waste.

The integration of anaerobic digestion (AD) and pyrolysis (Py) could be a solution to economically utilize the organic fraction of municipal solid waste (OFMSW). However, it is not clear whether the environmental impact of the integrated pathway always outperforms the two single technologies. In this study, two integrated pathways (AD-Py, Py-AD) were compared with single AD and Py from the life cycle environmental impacts point of view. The results indicate that the environmental impacts of the four pathways are heavily dependent on their energy inputs and outputs. AD-Py is more environmentally friendly (-11.53 of total environmental impact /kg OFMSW) than single AD or Py. Py-AD exhibites the heaviest environmental burden (2.75 of total environmental impact /kg OFMSW) in all pathways. Therefore, AD-Py can be the top priority of treating OFMSW among the four pathways from the environmental viewpoint. This work could provide a theoretical support for the utilization of OFMSW.

A critical review on energy recovery and non-hazardous disposal of oily sludge from petroleum industry by pyrolysis.

This review systematically reports the pyrolysis of oily sludge (OS) from petroleum industry in regards to its dual features of the energy recovery potential and the environmental risks. The petroleum hydrocarbons are the nonbiodegradable fractions in OS that possess hazardous properties, i.e. ignitability and toxicity. Besides, complicated hazardous elements (i.e. N, S and Cl) and heavy metals inherently existing in OS further aggravate the environmental risks. However, the high oil content and heating value of OS contribute to its huge energy resource potential. Considering the energy demand and the environmental pressure, the ultimate purposes of the OS management are to enhance the oil recovery efficiency to minimize the oil content as well as to stabilize the hazardous elements and heavy metals into the solid residue. Among various OS management technologies, pyrolysis is the most suitable approach to reach both targets. In this review paper, the pyrolysis principle, the kinetics and the product distribution in three-phases are discussed firstly. Then the effects of operating parameters of the pyrolysis process on the quality and the application potential of the three-phase products, as well as the hazardous element distribution are discussed. To further solve the dominant concerns, such as the oil content in the solid residue, the pyrolytic oil quality and the migration of hazardous elements and heavy metals, the potentials of the catalytic pyrolysis and the co-pyrolysis with additives are also summarized. Also, the typical pyrolysis reactors are then presented. From the perspective of the energy efficiency and the non-hazardous disposal, the integrated technology combining the pyrolysis and the combustion for the OS management is recommended. Finally, the remaining challenges of OS pyrolysis encountered in the research and the industrial application are discussed and the related outlooks are itemized.

Hazardous elements flow during pyrolysis of oily sludge.

Oily sludge (OS) is a hazardous waste and pyrolysis is a promising technology to achieve energy recovery and non-hazardous disposal simultaneously. However, the distribution of hazardous elements, including N/S/Cl and heavy metals, in pyrolytic products possibly causes secondary pollution. This study conducted a systematic research on hazardous elements flow during OS pyrolysis under variant temperature. Results showed that N/S/Cl in OS were distributed 44.77-15.51 wt%, 83.29-80.22 wt%, and 78.59-73.41 wt% into the solid residues after pyrolysis, respectively. Elevating pyrolysis temperature facilitated more N/S/Cl flowing into pyrolytic oil and gas. The macromolecular N-/S-/Cl-containing compounds, including amides, amines, nitriles, sulfonates, chloroalkanes, etc., were widely distributed in pyrolytic oil and gas products. The micromolecular N-/S-/Cl-containing pollutants released between 200 and 400 °C included HCN, NH3, NOx, H2S, CH4S, CS2, SO2, and HCl, which originated from the decomposition of the amine N, organic sulfide and sulfone-S, and inorganic Cl, respectively. The main pollutants released at above 400 °C included NH3, HCN, NOx, CS2, and SO2, which were derived from the decomposition of heterocyclic N and inorganic pyritic-S and sulfate-S. Moreover, the solid residues intercepted more than 60.0 wt% of total heavy metals, which should be concerned in the future.