Environmental sustainability assessment of a new food waste anaerobic digestion and pyrolysis hybridization system.

This research conducted an environmental life cycle assessment (LCA) to evaluate an anaerobic digestion-co-pyrolysis (ADCo-Py) system in which pyrolysis was added to traditional food waste (FW) anaerobic digestion (AD) systems to treat the solid fraction and impurities separated from FW. The solid fraction, including impurities such as wooden chopsticks, plastics, eggshells, and bones, is usually incinerated, while pyrolysis can be a viable alternative to optimize FW treatment. The environmental impact of ADCo-Py was compared with stand-alone AD, pyrolysis, and ADCo-INC (AD with incineration of separated solids). The results indicated that both ADCo-Py (-1.726 kg CO2-Eq/kgFW) and ADCo-INC (-1.535 kg CO2-Eq/kgFW) outperform stand-alone AD (-0.855 kg CO2-Eq/kgFW) and pyrolysis (-0.181 kg CO2-Eq/kgFW) in mitigating global warming potential (GWP). Additionally, pretreatments were found to have the most significant influence on GWP, ecotoxicity potential (ETP), and acidification potential (AP). The two-step pretreatment in ADCo-Py, including the separation of solids and drying, significantly improved the environmental sustainability of the system when compared with standalone pyrolysis.

Experimental study and techno-economic analysis of co-processing system for treatment of food waste with various impurities.

The study assessed a co-processing system segregating food waste (FW) with different impurities into liquid (slurry) and solid fractions and treated using anaerobic digestion (AD) and pyrolysis (Py), respectively, which is defined as ADCo-Py. Biomethane potential tests showed higher methane yield from the FW slurry fraction (572.88 mL/gVSFW) compared to the whole FW (294.37 mL/gVSFW). Pyrolyzing the FW solid fraction reduced nitrogen compounds in bio-oil by 62 % compared to the whole FW. The energy balance and economic feasibility of ADCo-Py were compared with stand-alone AD, Py, and AD integrated with incineration (ADCo-INC). While all systems required extra energy, stand-alone Py and ADCo-INC needed 3.8 and 2.8 times more energy than ADCo-Py, respectively. Techno-economic analysis favored ADCo-Py, with a net present value (NPV) of $15 million and an internal rate of return (IRR) of 34 %. These findings highlighted FW separation as a promising approach, aligning with energy and economic goals in sustainable FW management.

Microecological health assessment of water environment and sediment based on metagenomics: a case study of Guixi River in Chongqing, China.

River sediment is vital in containing water pollution and strengthening water remediation. This paper has conducted a study on the microecological health assessment of the sediment and water body of Guixi River in Dianjiang, Chongqing, China, using metagenomics sequencing and microbial biological integrity index (M-IBI) technology. The analysis of physical and chemical characteristics shows that the concentration of TN varies from 2.62 to 9.76 mg/L in each sampling section, and the eutrophication of the water body is relatively severe. The proportion of Cyanobacteria in the sampling section at the sink entrance is higher than that of other sites, where there are outbreaks of water blooms and potential hazards to human health. The dominant functions of each site include carbon metabolism, TCA cycle, and pyruvate metabolism. In addition, the main virulence factors and antibiotic resistance genes in sediment are Type IV pili (VF0082), LOS (CVF494), MymA operon (CVF649), and macrolide resistance genes macB, tetracyclic tetA (58), and novA. Correlation analysis of environmental factors and microorganisms was also performed, and it was discovered that Thiothrix and Acidovorax had obvious gene expression in the nitrogen metabolism pathway, and the Guixi River Basin had a self-purification capacity. Finally, based on the microecological composition of sediment and physical and chemical characteristics of the water body, the health assessment was carried out, indicating that the main pollution area was Dianjiang Middle School and the watershed near the sewage treatment plant. The findings should theoretically support an in-depth assessment of the water environment's microecological health.

Ecological risk assessment of toxic metal(loid)s for land application of sewage sludge in China.

Sewage sludge, including those after biological or thermochemical treatments, has the potential to be used as fertilizers for recycle of resources. However, its potential ecological risk is also of great concern to policy making. This study employed comprehensive ecological risk assessment (ERA) methods to evaluate the risk caused by the toxic metal(loid)s in sewage sludge throughout China. The conventional geo-accumulation index and potential ecological risk index revealed that cadmium (Cd) and mercury (Hg) were of significant concern in treating sewage sludge before land application, but chromium (Cr) and zinc (Zn) were preferred by potential affected proportion (PAF) and overall risk probability (ORP) of species sensitivity distribution (SSD). Because SSD considered both the community and the ecotoxicity of toxic metal(loid)s, it was more advantageous and promising in assessing ecological risks caused by land application of sewage sludge. Based on the predicted no-effect concentration (PNEC) of toxic metal(loid) calculated by hazardous concentration that cause death of 50% of species (HC50) by SSD, the maximum allowable disposal amount (MADA) of sewage sludge in the whole China indicated that chromium (Cr) should be totally eliminated because of its high risks in the present background soil. After excluding Cr, the MADA of sewage sludge in China was 3.24 × 106 t and 6.47 × 107 t under land application scenarios with high and low ecological risks, respectively. Additionally, the MADA could be increased by mixing sewage sludge with deeper soil in wider areas. This study emphasized that local laws and regulations on land application of sewage sludge and the subsequent ERA system need to be addressed in the future.

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.

Life cycle assessment of bio-based levoglucosan production from cotton straw through fast pyrolysis.

This study aimed to evaluate the environmental impacts (i.e. global warming potential (GWP) and resource depletion (RD)) of the bio-based levoglucosan production process through fast pyrolysis of cotton straw via life cycle assessment (LCA). An LCA model consisting of feedstock transportation, biomass pretreatment, fast pyrolysis, bio-oil transportation, bio-oil recovery and levoglucosan extraction was developed. Results indicated that GWP and RD of bio-based levoglucosan production were approximately 2 and 32.5 times less than that of the petroleum-based counterpart. Sensitivity analysis showed that the GWP and RD of levoglucosan production were highly sensitive to plant size, hydrochloric acid usage, cooling energy, levoglucosan yield and bio-oil yield. The results of this research could provide a framework for robust decision making at an industrial level, which is useful for the commercial-scale production of levoglucosan.

Environmental Assessment of a Hybrid Solar-Biomass Energy Supplying System: A Case Study.

Local energy supply by renewable energy, such as solar energy and biomass, using distributed energy systems plays an important role in global energy structure. This study investigated the environmental performance of a hybrid solar-biomass energy supplying system by life-cycle assessment method. The results showed that in terms of environmental and energy impacts, the construction stage and the disassembly and recycling stage of the system contribute little to the whole life-cycle environmental impacts. According to the results of most of the selected impact categories, the solar subsystem contributed the most environmental emissions during construction stage, followed by the two anaerobic reactors; therefore, the excessive pursuit of high solar energy proportion can correspondingly lead to even more serious environmental problems. The integrated energy supplying system significantly reduces non-renewable energy consumption, climate change impacts, acidification as well as eutrophication effects due to the replacement of alternatives such as lignite coal, and from fertilizer production. The present hybrid solar-biomass energy supplying system not only produces clean thermal energy but also reduces the disposal of organic wastes and produces valuable agricultural products.

Reactor performance and economic evaluation of anaerobic co-digestion of dairy manure with corn stover and tomato residues under liquid, hemi-solid, and solid state conditions.

Anaerobic co-digestion of tomato residues, dairy manure, and corn stover at ratios of 20:48:32, 40:36:24, and 60:24:16 (volatile solid basis) were compared for liquid anaerobic digestion (L-AD), hemi-solid state AD (HSS-AD), and solid state AD (SS-AD) systems. The highest methane yield (353.5 L/kg-VSadded) and volumetric methane productivity (24.5 m3methane/m3reactor volume) were both obtained with 20% tomato residues addition under L-AD and HSS-AD conditions, respectively. Total solid and feedstock mixing ratio affected the degradation of protein and lipids during AD, but not cellulose and hemicellulose. Economic analysis results indicated that capital and labor costs have the dominant effect on total investment. SS-AD of tomato residues, dairy manure, and corn stover at ratios of 20:48:32 (VS basis) has the highest net present value (2.6 million US$) and shortest payback period (10.1 year), which indicated SS-AD was financially attractive under analysis conditions.