| With the development of economy and the improvement of people’s living standard,the yield of food waste(FW)increases every year.Anaerobic digestion(AD)is one of the important ways for centralized treatment and energy conversion of FW.However,it is difficult to further promote and develop due to the bottleneck problems such as difficult consumption of byproduct digestate and low overall resource utilization efficiency.The conventional disposal method of food waste solid digestate(FD)has high environmental pollution risk,limited absorption,and the energy contained in FD cannot be fully utilized.Therefore,it is urgent to develop the reduction,energy and resource treatment technology for FD.In addition,FW is often doped with a large amount of waste plastic(WP),it usually be sorted out before AD due to its unbiodegradable property,which become another difficulty faced by FW biogas plant.Based on the above problems,the pyrolysis mechanism and product distribution of FD were studied in this paper,and the potential approaches for resource utilization of FD were proposed.At the same time,the FD and sorting WP were co-pyrolyzed to realize the efficient collaborative treatment of multi-source solid waste and the full component utilization of the leftovers of AD of FW.The life cycle assessment(LCA)method was used to comprehensively evaluate the feasibility of the AD coupled co-pyrolysis process of FW from the perspectives of matter,energy and environment,which laid a foundation for the realization of green and sustainable full resource conversion of FW.The main contents and conclusions are as follows:(1)The pyrolysis characteristics of FW,FD and WP were studied from the perspective of pyrolysis thermodynamics and kinetics.The results showed that the pyrolysis process of FW can be divided into four stages,including water evaporation stage,protein and carbohydrate decomposition stage,lipid decomposition and residue secondary pyrolysis stage,and ash pyrolysis stage.Compared with FW,the devolatilization stage of FD is relatively delayed,and its weight loss peak is more complex.Besides the above weight loss peak,there is also a significant lignin weight loss peak.However,the thermogravimetric characteristics of WP are relatively simple,which has only one weight loss peak,and mainly caused by the release of hydrocarbons and the generation of volatile aromatic compounds.In addition,due to the different pyrolysis characteristics of feedstocks,the kinetic characteristics also showed certain differences.The average apparent activation energy(Eα)of FW is the lowest,which is149.18～159.21 k J/mol,followed by FD(185.49～195.64 k J/mol),and the Eαof WP is the highest.Up to 283.32～295.55 k J/mol.(2)The products distribution and release of FW and FD at different temperatures were compared and analyzed,and the influence mechanism of AD process on the thermochemical transformation of feedstocks was revealed.The results showed that AD consumed some organic matters in FW,changed the apparent structure and physical and chemical properties of feedstocks,and then affected the pyrolysis performance of FD.The lower heating value(LHV)of pyrolytic gas of FW is high,which can reach 20.52 k J/Nm~3.The pyrolytic oil of FD has high content of aliphatics and low content of oxygen and nitrogen compounds,so it is more suitable for liquid fuel.The specific surface area of FD biochar is 10 times that of FW biochar,which is suitable to be used as carbon-based adsorbent.In addition,the nitrogen-containing pollutants in the pyrolysis process of FD were less,which indicated that the pyrolysis technology was more environmentally friendly for FD treatment.(3)Co-pyrolysis of FD and WP experiment was carried out to systematically investigate the effects of mixing ratio and pyrolysis temperature on the generation characteristics and distribution of co-pyrolysis products,and further reveal the synergistic mechanism of multi-source substrates.The results showed that the LHV(36.97 MJ/Nm~3)of the co-pyrolytic gas of WP and FD is close to that of natural gas,which can be used as a substitute for natural gas in industrial and civil buildings.Co-pyrolysis at medium temperature(500℃)can significantly improve the quality of bio-oil,significantly increase the content of aliphatics,and significantly reduce the content of oxygen and nitrogen compounds.After adding 33%WP,the specific surface area of biochar was 2.10 times that of FD biochar.Pyrolytic kinetics showed that a moderate ratio of FD and WP would produce a synergistic effect and reduce the activation energy required for pyrolysis.When the mass ratio of WP was 33%,the Eαwas the lowest(189.63 k J/mol),which was much lower than that required for the pyrolysis of FD(236.83k J/mol)and WP(299.50 k J/mol)alone.(4)Based on the LCA method,the differences and similarities between the AD coupled co-pyrolysis process and conventional FW disposal process were comprehensively evaluated from the perspectives of matter,energy and environment.Four research cases for FW of AD system,pyrolysis system,AD coupled pyrolysis system and AD coupled co-pyrolysis system were constructed respectively.The results showed that compared with the process of AD,pyrolysis and AD coupled pyrolysis of FW,the coupled process of AD and co-pyrolysis of FW showed a negative environmental impact category,which showed a better overall positive effect on the environment.The standardized analysis of end-point damage category showed that the negative impact of AD system on ecosystem quality was 0.0065 m Pt.The negative effect of pyrolysis system on human health was 0.054 m Pt.The negative effect of AD coupled pyrolysis system on resource consumption was the highest,which was 0.0394 m Pt.The AD coupled co-pyrolysis system showed positive environmental effects on all the environmental indicators,indicating that it is the most suitable process for the treatment of FW.This paper explored the pyrolysis mechanism and product distribution of FW,FD and WP through thermogravimetric analysis,kinetic analysis and calculation,tubular furnace pyrolysis experiment and other research methods.The feasibility of collaborative disposal of FD and WP was cleared.A new idea for the collaborative disposal of FD and its accompanying pollutants was put forward.It also laid a theoretical foundation for the full resource conversion and utilization of FW. |
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