Stimulation of methane yield rate from food waste by aerobic pre-treatment

Designing a Framework for Materials Flow by Integrating Circular Economy Principles with End-of-life Management Strategies

Circular economy is an upward trending notion that has drawn worldwide attention of policymakers, industry administrators, environmentalist as well as academic researchers. Though there are several tools developed for monitoring the material recovery, a very few number of research have been conducted to integrate circular economy principles with end-of-life (EOL) management strategies. This paper proposes an EOL-driven circular economy framework for the management of materials flow so as to extend the lifetime of materials through improved durability as well as to provide more social, economic and environmental benefits through less material waste. A case study from the agricultural waste industry is presented in order to test the model and validate its performance. The results show that the proposed framework has a good potential for small and medium enterprises (SME) advances.

Effect of different aerobic hydrolysis time on the anaerobic digestion characteristics and energy consumption analysis

Aerobic hydrolysis of stover before anaerobic digestion is beneficial to improve the biodegradability of corn stover. Aerobic hydrolysis of corn stover at 43 °C was conducted to investigate the effects of hydrolysis time (0 h, 8 h, 16 h, and 24 h) on the degradation of lignocellulose from corn stover and material conversion. Further anaerobic digestion and energy consumption analysis with the digestion temperature of 36 °C were carried out. The accumulation rate of volatile fatty acids began to slow down after 16 h of hydrolysis, and the concentration of acetic acid reached 221.85 mmol/L at 24 h of hydrolysis. The degradation rate of lignocellulose was obviously increased after hydrolysis. When the hydrolysis time was 16 h, it reached the maximum cumulative methane production with 268.75 ml/g VS. In terms of biogas production and energy conversion efficiency, it is more appropriate to choose 16 h as hydrolysis time in biogas engineering.

Biogas recovery from fresh landfill leachates by using a coupled air stripping-up follow anaerobic sludge blanket (UASB) process

The present study focuses on fresh leachates treatment using anaerobic digestion. To overcome the unsuitable raw characteristics, appropriate pretreatment conditions were identified based on Batch tests. A subsequently optimized pretreatment-anaerobic two stages UASB coupled treatment was studied. The performance of the overall coupled treatment was assessed by monitoring volatile fatty acids (VFA), COD and ammonium removal, and biogas performance. Results showed that combining acidity correction to short aeration gives a synergetic effect and allowed appropriate anaerobic start-up conditions. Under continuous aerobic pretreatment-UASB digestion, significant removal of NH+4 (75.87%), COD (19.14%), and VFA (20.3%) were achieved during the aeration step resulting in the total abatement of 88.66%, 83.6% and 70.39% for NH+4, COD, and VFA, respectively. The process allowed good biogas performance up to 2,470 mL biogas/L and 123 mL CH4/gCOD removed, with gradual improvement from the first to the second UASB reactor. Inlet COD and VFA feeding rate seemed to be the main key parameters with 45.37 g COD/L.d and 18.43 g VFA/L.d as a critical threshold. Therefore, the anaerobic digestion of high COD leachates is highly feasible and the aerobic–anaerobic coupled treatment is a promising technical scenario that deserves further studies.

Biochemical and microbial changes reveal how aerobic pre-treatment impacts anaerobic biodegradability of food waste

Aerobic pre-treatment of food waste (FW) was performed at different oxygen concentrations (0%, 5%, 10% and 21%O₂) and different durations (1, 2, 3 and 4 days) to investigate its impact on biochemical and microbial community characteristics of the waste and its ability to improve anaerobic biodegradability. Whatever the duration, the highest effect of pre-treatment was observed at full aerobic pre-treatment (21%O₂) while 5%O₂ and 10%O₂ showed lower transformation performances. Biochemical variations at 21%O₂ were mainly a decrease of simple carbohydrates, volatile fatty acids (VFA) and low molecular weight water soluble compounds and an increase of high weight water soluble compounds. Microbial community analysis showed a clear modification of populations after 21%O₂ aerobic pre-treatment, changing from an initial dominance of lactic acid bacteria to a final dominance of VFA consumers (like Acetobacter) and a higher presence of Fungi. Enzymatic tests showed an increase of exoenzymes content and a higher presence of protein and carbohydrates degrading enzymes. Finally, the aerobic pre-treatment did not negatively impact methane potential of FW (496 NLCH₄·kgVS^-1) which remained unchanged after two days of pre-treatment at 21%O₂. These latter optimal pre-treatment conditions are proposed to be tested in future investigation of anaerobic digestion (AD) process with low inoculum to substrate ratio in order to assess their ability to avoid acidification risk during AD of FW.