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Xu S.,Tsinghua University | Kong X.,Tsinghua University | Liu J.,Tsinghua University | Zhao K.,BESG Environmental Engineering Co. | And 2 more authors.
Waste Management | Year: 2016

High-pressure extruding (HPE) is an efficient technology used to separate municipal solid waste (MSW) into wet (biodegradable) and dry (combustible) fractions. Effects of pressure, 10, 20, 30, and 40MPa on quality upgrading of the MSW and hydrolysis of the wet fraction were examined. TS of the dry fraction increased from 48.5% to 59.4% when the extruding pressure increased from 10 to 40MPa, meanwhile the biochemical methane potential (BMP) of the wet fraction extruded under 40MPa was 674mL CH4/g·VS, 33% higher than that of the organic fraction of the MSW (OFMSW) control. Furthermore, in the initial stage of hydrolysis experiment, the extruded wet fractions had lower pH and higher COD, volatile fatty acids (VFAs) and COD/VFA than those of the OFMSW control. The results confirmed that HPE upgraded the MSW and enhanced hydrolysis of the wet fractions. However, high extruding pressure as 40MPa aggravated the excessive acidification of the wet fractions. © 2016 Elsevier Ltd. Source


Zhang Y.,Tsinghua University | Yue D.,Tsinghua University | Liu J.,Tsinghua University | He L.,BESG Environmental Engineering Co. | Nie Y.,Tsinghua University
Waste Management | Year: 2012

Odor pollution caused by municipal solid waste (MSW) treatment plants has become a growing public concern. Although aerobic pretreatment of MSW has advantages in accelerating landfill stabilization, the property of non-methane organic compound (NMOC) emissions from aerobically pretreated MSW (APMSW) during landfilling is unknown. To investigate NMOC emissions from anaerobic degradation of APMSW and to study the impact of organic compositions of APMSW and their decomposition stages, five simulative anaerobic bioreactors (R1-R5) were filled up with APMSW of different original organic compositions in a laboratory. For NMOC analysis, samples were collected from the gas that accumulated separately during two successive independent stages of the whole experiment. The results showed that the cumulative quantities of NMOCs from R1 to R5 were 1.11, 0.30, 0.18, 0.28, and 0.31. mg/kg DM, respectively, when volatile solid was degraded by 34.8-47.2%. As the organic content of the original waste was lower, the proportion of NMOCs generated in the early stage of anaerobic degradation became higher. Multiple linear regression analyses of the relationship between the quantities of degraded organics and generated NMOCs showed that lipid and protein have a strong effect on NMOC amount. The effect of lipid on NMOC quantity lasts longer than that of protein. This observation suggests that controlling the lipid and protein contents in MSW can reduce the odor from landfills. © 2012 Elsevier Ltd. Source


Kong X.,Tsinghua University | Xu S.,Tsinghua University | Liu J.,Tsinghua University | Li H.,Tsinghua University | And 2 more authors.
Journal of Environmental Management | Year: 2016

The inoculation for extruded food waste anaerobic digestion (AD) was optimized to improve methane (CH4) yield. The inoculum of acclimated anaerobic sludge resulted in high biodegradability, producing CH4 yields from 580 mLCH4 g-1·VSadded to 605 mLCH4 g-1·VSadded, with corresponding BDCH4 ranging from 90% to 94%. We also investigated inoculum to substrate ratios (ISRs). With regards to digested slurry as inoculum, we found that a decrease in ISR improved CH4 yield, while a lower ISR prolonged the lag time of the initial AD stage due to lipid inhibition caused by excessive food waste. These results demonstrate that minimal inocula are required to start the AD system for high-pressure extruded food waste because it is easily biodegraded. High ammonia concentration had a negative effect on CH4 production (i.e., when free ammonia nitrogen [FAN] increased from 20 to 30 mg L-1 to 120-140 mg L-1, the CH4 yield decreased by 25%), suggesting that FAN was a significant inhibitor in CH4 yield reduction. In terms of CH4 yield and lag time of the AD process, the optimal inoculation of digested slurry for the extruded food waste had an ISR of 0.33 with CH4 yield of 505 mLCH4 g-1VSadded, which was 20% higher than what was found for higher ISR controls of 2, 1 and 0.5. © 2015 Elsevier Ltd. Source


Qi G.,Tsinghua University | Yue D.,Tsinghua University | Liu J.,Tsinghua University | Li R.,Tsinghua University | And 5 more authors.
Journal of Environmental Management | Year: 2013

Waste samples at different depths of a covered municipal solid waste (MSW) landfill in Beijing, China, were excavated and characterized to investigate the impact of intermediate soil cover on waste stabilization. A comparatively high amount of unstable organic matter with 83.3gkg-1 dry weight (dw) total organic carbon was detected in the 6-year-old MSW, where toxic inorganic elements containing As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn of 10.1, 0.98, 85.49, 259.7, 530.4, 30.5, 84.0, and 981.7mgkg-1dw, respectively, largely accumulated because of the barrier effect of intermediate soil cover. This accumulation resulted in decreased microbial activities. The intermediate soil cover also caused significant reduction in moisture in MSW under the soil layer, which was as low as 25.9%, and led to inefficient biodegradation of 8- and 10-year-old MSW. Therefore, intermediate soil cover with low permeability seems to act as a barrier that divides a landfill into two landfill cells with different degradation processes by restraining water flow and hazardous matter. © 2013 Elsevier Ltd. Source

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