Phytoremediation of Cd-contaminated farmland soil via various Sedum alfredii-oilseed rape cropping systems: Efficiency comparison and cost-benefit analysis.

Phytoremediation is a green technology for heavy metal removal from contaminated soil, and its remediation efficiency and economic feasibility in field trial should be evaluated before large-scale application. However, there is still lacking relevant analysis, especially for phytoremediation with different cropping patterns. In the present study, we performed phytoremediation on slightly Cd-contaminated farmland soil via three cropping systems, i.e. Sedum alfredii monoculture, oilseed rape monoculture, and S. alfredii-oilseed rape intercropping. Dry weights of S. alfredii and oilseed rape were both enhanced under intercropping pattern, while the highest total Cd extraction amount (148 g ha-1) were observed under S. alfredii monoculture. Furtherly, a cost-benefit analysis via Monta Carlo simulation in a ten-year lifetime was conducted. The benefits of S. alfredii monoculture and intercropping schemes would offset the total costs in 6 and 8 years, respectively. S. alfredii monoculture achieved a higher net present value of 1.88 × 104 US$ as compared with intercropping (9.53 × 103 US$). These results indicate that S. alfredii monoculture scheme could be a promising phytoremediation strategy for slightly Cd-contaminated soil owing to better remediation efficiency and economic feasibility. Moreover, the enhancement in mechanization level and the reduction of seedling cost could further improve its economic viability.

Assessment of biomass demineralization on gasification: From experimental investigation, mechanism to potential application.

Considering the advantages (e.g. agglomeration mitigation) and disadvantages (e.g. inorganic species catalysis removal) of biomass demineralization, it is valuable to investigate its effects on gasification performance, thus assessing its necessity prior to performing gasification. To accomplish this, corn straw (CS) was demineralized to different degrees with H2O and HCl, respectively. H2O and HCl demineralization behaved different abilities to inorganic species removal. Cellulose and hemicelluloses content decreased, while lignin content increased, especially with HCl demineralization. The experiments were investigated by using a bench-scale downdraft fixed-bed gasifier at 600-800 °C and were further analyzed via thermogravimetric coupled with Fourier transform infrared spectrometry. Demineralization demonstrated a positive effect on gasification at lower temperatures (600-700 °C) for a dominant effect of lignin content and an insignificant effect of inorganic species removal. However, the catalysis of inorganic species increased as the temperature increased, resulting in the highest H2 (11.30 vol%) and CO (16.02 vol%) production of raw CS compared to demineralized CS at 800 °C. Inorganic species had a dual positive effect on CO generation, promoting both CO2 and char generation leading to a higher CO yield following Boundouard reaction, and increasing the formation of active intermediates thus producing more CO. These effects enhanced when the gasification temperature increased. Additionally, inorganic species catalyzed the aromatic rings rearrangement to generate more H2O, thus driving the endothermic Primary water-gas to produce H2. This was also positively correlated with gasification temperature. Therefore, raw CS demonstrated higher H2 and CO production than demineralized CS at a higher gasification temperature. Moreover, the promotion effect of inorganic species on thermal devolatilization of methoxyl groups and Methanation reaction led to the higher CH4 production of raw CS. This research clarifies the effects of biomass demineralization on its gasification and suggests the potential application.

Environmental, energy, and economic analysis of integrated treatment of municipal solid waste and sewage sludge: A case study in China.

Incineration is well used to treat municipal solid wastes (MSW) but is difficult to treat sewage sludge (SS) because it requires a large amount of heat to remove high content of moisture in SS. Over 50 billion tons of SS are discharged annually in China, and the need for a better waste treatment strategy is urgent. This paper is to introduce a waste disposal technology referring to the integrated treatment of MSW and SS. Four scenarios were analyzed including Mono-incineration of MSW (Case 1) and SS (Case 2), co-incineration of SS and MSW by traditional (Case 3) and integrated ways (Case 4), in terms of environment, energy and economic impact by means of LCA, CED and TEA method. From the environmental perspective, the top four mid-point categories involving the largest effect on four cases are N-C (non-carcinogens), OLD (Ozone layer depletion), TET (Terrestrial eco-toxicity), and GWP (Global warming potential). Case 4 has the most positive effect on climate change and resources (-1.44 kg CO2 eq and -18 MJ, respectively) according to end-point categories. From the view of energy, Case 4 shows the best performance of energy efficiency, and significantly saves the non-renewable energy (0.21 t coal per ton feedstock compared with Case 3). From the economic part, Case 4 is preferentially potential with the best profit, cutting down 79.08% of cost in coal than that in Case 3. These results provide understandings of developing an effective approach for co-treating MSW and SS in the near future.

The hotspots of life cycle assessment for bioenergy: A review by social network analysis.

The purpose of this paper is to provide an up-to-date bibliometric view about the current life cycle assessment (LCA) for bioenergy. The social network analysis (SNA) method was applied to study total 2367 publications in this field. The results showed the high frequency keywords related with the "LCA" for bioenergy included three categories: (1) Bioenergy production, such as "Biodiesel", "Bioethanol", "Biogas" and "Biorefinery"; (2) Environmental problems, such as "Greenhouse gas" (GHG), "Environmental impact", "Climate change"; (3) Environmental target: "Sustainability". This means that LCA methods have been widely used in assessing the environmental impact from various types of bioenergy production process. Specially, the "GHG" attracted more attention in this research area. According to the temporal trend of the high frequency keywords, "bioethanol" is the most significant hotspot keyword of implication LCA. However, it has become colder since 2011. The environmental performance of "biogas" and "land use" began to receive attention since 2015.The evolutionary co-words network showed that the boundary of hotspots became overlapped. We also found four clusters were identified from keywords networks, i.e. the biggest cluster Cluster (I) (central cluster node linkage was "Bioethanol-GHG"), followed by Cluster (II) (central cluster node linkage was "Biodiesel-Algae"), Cluster (III) (central cluster node linkage was "Biorefinery-Sustainability") and Cluster (IV) (central cluster node linkage was "Biogas-Anaerobic digestion"). This cluster analysis also showed that the implication of LCA for the relationship between "bioethanol" and "GHG" is the most important hotspot research field. Although "biogas" is the smallest cluster now, it could be the next important hotspot of implication LCA for bioenergy. This study provides an effective approach to obtain a general knowledge of the LCA for bioenergy and supports a deeper understanding of research directions in the future.