Applied Mechanics and Materials Vol. 768

Abstract: With the increasing of plastic consumption, the recycling of plastic waste has become an important problem with huge environmental impact. In order to analyze the environmental impact of plastic waste recycling, this study presents a systematic evaluation framework for plastic waste’s recycling process in China. Based on the framework, theoretical analysis and experimental research are made to evaluate the relationship of scale volume and environmental impact of plastic waste recycling. Cost and energy consumption of typical processing of plastic wastes have been calculated. And an optimization research is made to reduce the environmental impact, and increase recycling output efficiency for enterprise and local region.

Abstract: Non-methane volatile organic compounds (NMOCs) are important precursors of the photochemical reactions which produce ozone and secondary organic aerosols. An accurate emission inventory is essential for air-quality simulations and policy making. The NMOC emission from landfill is an important sector in the anthropogenic source. When estimating anthropogenic NMOC inventory the emission factor for refuse disposal originates from the European study or the estimation for this sector is discarded due to no other referenced data. This research is reviewed the NMOC yields from refuse landfill and the emission factor is from 0.0775 to 3.7625 kg/t. Besides, this paper was particularly concerned with correction of the emission factor by estimating the effects of waste characteristics and the various technologies for landfill. Compared NMOC yields under anaerobic and aerobic conditions for each kind of wastes, only the difference for food waste was obvious.

Abstract: Contrast experiment was developed on the semi-aerobic and anaerobic landfill treatment. Leachate nitrate nitrogen concentrations in different landfill layers spatially were monitored regularly in two landfill equipments, and variations and differences of leachate nitrate nitrogen concentration of different landfills were discussed. The results showed that differences on the variation characteristics of nitrate nitrogen concentration in space and time were obvious in the landfill treatments with different structures. In 73 weeks of monitoring period, nitrate nitrogen concentration in the middle and the lower layer of semi-aerobic landfill treatment was in turn stable within 55.40 mg/L and 40.80 mg/L; The concentration fluctuations in both layers were small in general. Nitrate nitrogen concentration decreased respectively to 9.26 mg/L, 6.82 mg/L and 4.69 mg/L at the 73th week from 28.51 mg/L, 4.44 mg/L and 5.85 mg/L at the initial landfill stage in the lower , middle and the upper layer of anaerobic landfill treatment. When degradation of the landfill treatments went into relatively stable stage, nitrate nitrogen concentration in the upper, middle and the lower layer of semi-aerobic landfill treatment was located respectively in 30-240 mg/L, 2.5-11.0 mg/L and 5.5-13.5 mg/L respectively, and the spatial distribution difference of nitrate nitrogen concentration in the upper layer of semi-aerobic landfill treatment was relatively big, but those of the middle and the lower layer were relatively small, and they were both lower than the upper layer. Nitrate nitrogen concentration in the upper, middle and the lower layer of anaerobic landfill treatment was located in 1.6-7.4 mg/L, 3.8-7.2 mg/L and 7.5-15 mg/L respectively, and showing a performance of spatial nitrate nitrogen concentration that was the lower layer> the middle layer >the upper layer. Under the experimental conditions, seim-aerobic landfill treatment was favorable to the nitrification and denitrification of leachate in contrast with the anaerobic landfill treatment.

Abstract: With the acceleration of urbanization and industrialization, the amount of MSW in China generated is growing fast, while the pollutants generated in the disposal process of MSW has gradually attracted people’s attention. This paper presents the generation and composition status of MSW in China, summarizing the problems during MSW incineration disposal, providing an assumption of kitchen waste separation and using heat balance calculation to analysis the impact of kitchen waste separation on MSW incineration. Results shows that after kitchen waste separated from MSW, the amount of MSW reduced obviously, moisture content dropped, calorific value improved, auxiliary fuel is not need to ensure the proper incineration process and combustion efficiency improved; meanwhile, the generation of greenhouse gases and air pollutants is reduced significantly. Overall, the separation of kitchen waste not only reduced the difficulty and handling stress of MSW incineration, but also improved the incineration efficiency, reduced the generation of pollutants during incineration process.

Abstract: As new and efficient dehydration technology and equipment needs to be applied to the recycling of Chinese urban garbage urgently, this study discusses the differences and similarities between spiral-extrusion and screw-extrusion physical model on dehydration technology. Based on the research on screw-extrusion dehydration technology, the factors that affect dehydration production volume and efficiency of urban garbage’s recycling have been analyzed. Using screw-extrusion theoretical model, the paper further discusses the influence of some parameters such as operation factors, geometric structure and urban garbage’s material performance. Finally, experiment research is made to examine the screw-extrusion theoretical model. The results show that appropriate screw speed can balance the production volume and dehydration efficiency. The main factors of geometric parameters are screw diameter, screw groove depth and helix angle, and all of these three factors can influence dehydration output and efficiency.

Abstract: The variations of daily biogas yields, cumulative biogas yields, biogas composition analysis, total solids (TS) and volatile solids (VS) were studied in the process of mesophilic and dry anaerobic digestion of food waste under different oil contents (0%, 2%, 4%, 6%, 8%, 10%) at 35 °C. The gas production raised and then went down with the oil content, followed by 243.14, 245.64, 256.09, 269.25, 276.54, 284.22mL /g TS respectively. The research provided a reference for the pretreatment of food waste in follow-up continuous fermentation. Results showed that the period of the process of mesophilic dry anaerobic digestion under oil content of 0% was the shortest, with the total biogas production of 1275.5mL. During the process of the digestion, methane content of the biogas raised and then went down, up to a maximum of 77.62%. The removal rate of TS and VS in food waste with the oil content of 6% was the highest, obtained as 11.2% and 13.2%, respectively.

Abstract: Food waste was a troublesome organic waste stream, but a highly desirable substrate for anaerobic digestion to recover energy. Among the diverse reactor configurations, the leaching-bed reactor was reported to be best choice to treating the particular organic waste for platform compounds (volatile fatty acid). In this study, we carried out a series of experiments to investigate the bulking agent and pH control on process performance, and special focus was put on the biodegradability of bulking agent. The supplement of bulking agent greatly improved the leaching rate by 3.6 folds. Although the hydrolytic and acidogenic bacteria were resistant to low pH, the pH control (neutralization) caused a significantly increased volatile fatty acid (VFA) productions from 39.1 g COD/kg VS_added to 183.4 g VFA/kg VS_added. Comparing with the undegradable bulking agent, the case with supplementing corncob as a bulking agent showed superior VFA yields (225 g COD/kg VS_added) which could be ascribed to the good adhesive properties for microorganisms and biodegradability. The ultimate analysis of the substrate (excluding the bulking agent) also showed that most of food waste was degraded with relative short reaction time. In addition, the TG/DTA and FTIR of residual corncob results indicated some components (cellulose, hemi-cellulose) were degraded, which could contribute to the additional VFA production (14 g COD/kg VS_added). This study suggested that the corncob could be considered as a good bio-compatible bulking agent for leaching-bed reactor, which not only increased the VFA productivity, but provided additional VFA production.

Abstract: Flush and chemical cleaning were applied to remove foulants on UF membrane fouled by lactic acid fermentation of food waste. Flushing methods, flushing time and agents for chemical cleaning were studied. The obtained results indicated that backwash at 0.1 MPa for 10s and chemical cleaning with NaClO could gain the best cleaning effect.

Abstract: Considering the refuse and leachate as one whole system, a conventional landfill (CL) was set as a control, transformation of dioctyl phthalate (DOP) in recirculated landfill (RL) and bioreactor landfill (BL) was studied. Results showed that DOP was detected in both leachate and refuse from CL, RL and BL. The initial DOP amount was 0.8 μg g^-1 in the landfill refuse. At the day of 310, refuse sedimentation rates were 7.0%, 11.9% and 24.3% in CL, RL and BL, respectively. DOP removal rates were 17.4%, 30.8% and 31.7% in the refuse from CL, RL and BL, respectively. The residual amounts of DOP with significant differences well fitted exponential decay models in CL, RL and BL. DOP biodegradation was accelerated with the operation of leachate recirculation compared to the conventional operation, and it was further promoted with the introduction of methanogenic reactor.

Abstract: In this study, aerobic-anaerobic landfill method (AANM) is focused on as a new way to speed up landfill stabilization, inhibit landfill gas flux, and ameliorate on leachate quality. Numerical simulation model is developed to guide the air injection craftwork and study its effect on achieving above goals. On basis of work finished in last period (0~310 days), air was injected into Lysimeters A (Lys.A) at 0.5 m, and at 2.5 m in Lys.B with the same rate of 1 L/min. In Lys.C there is no air injected. In order to interview the influence by air injection manners changing, from 310 days till 360 days, air injection manners are changed from Mono-site into Double-site in Lys.A and in Lys. B it will be changed from bottom-site (2.5m) into middle-site (1.5m). In Lys.C there will be no changing. By interviewing the comparisons on simulated results in 50 days with and without air injection manners changing, it was found that air injection manners changing in Lys.A causes TOC discharging amount increase more than 6 times, but T-N and GHE resulted from landfill gas decrease 24.1% and 71 % respectively. Air injection manners changing in Lys.B resulted in discharged TOC and T-N increase 108.1 % and 53.5 % respectively, while T-N decreases 3.7 %. On basis of mechanism assumption, mathematical model was developed and according to the simulated results for 5 years, air injected at 2.5 m achieved improvements on stabilization of solid phase organic carbon and nitrogen for 34 % and 13 %, amelioration on leachate quality for 35 % and 62 % of TOC and T-N, and the restraint of GHE for 14 times compared with no air injection case.