Sink–float density separation of post-consumer plastics for feedstock recycling

The paper focuses on current mechanical waste processing technologies and out-of-the-box processes linked to the processing of coal and mineral resources, to ensure high-quality feedstock recycling of polyolefin-rich post-consumer plastic fractions. Moreover, the study aims to provide the basis for the technical and economic feasibility of the chemical recycling route of this plastic fraction. When evaluating common mechanical processes, either dry or wet ones, sink–float separation in a cylindrical centrifugal force separator achieves the best results. It combines the advantages of a simple, robust apparatus of low complexity and high capacity with selective separation through the accelerated settling of particles in the centrifugal field. Furthermore, the disconnection of the separation medium feed from the solid input increases residence times. Based on the above findings, a pilot-scale plant was constructed which consists of a centrifugal force separator and a hydro jig for the pre-separation of heavy waste components. Several test campaigns were conducted to separate polyolefins from various waste fractions. Two-stage processing in the centrifugal force separator rendered almost 90 wt% of polyolefin content in the produced lightweight fraction and of polyolefin recovery. One-stage processing, on the other hand, resulted in reduced polyolefin content in the lightweight fraction.

     

Climate-related hydrological change and human vulnerability in remote mountain regions: a case study from Khumbu, Nepal

Inhabitants of mountainous regions in least developed countries are recognized to be among the most vulnerable to climate change globally. Despite this, human dimensions work is in its infancy in mountain regions where we have limited understanding of who is vulnerable (or adaptable), to what stresses, and why. This study develops a baseline understanding of vulnerability to climate-related hydrological changes in the mountainous Khumbu region of eastern Nepal. Using a vulnerability approach, 80 interviews combining fixed and open-ended questions were conducted in four communities representing the geographic and livelihood variability of the region. The study identifies four region-wide vulnerabilities currently affecting residents: reduced water access for household uses, declining crop yields, reduced water access for meeting the high water demands of tourists, and reduced hydro-electricity generation. These vulnerabilities are widespread among the population but arrange spatially as a function of varying exposure-sensitivity to hydrological change, livelihood opportunities, and access to foreign financial assistance. Our findings indicate that precipitation change (not glacial change) is the greatest biophysical driver of vulnerability.     

Urban sharing in smart cities: the cases of Berlin and London

ABSTRACT

Addressing urban sustainability challenges requires changes in the way systems of provision and services are designed, organised and delivered. In this context, two promising phenomena have gained interest from the academia, the public sector and the media: “smart cities” and “urban sharing”. Smart cities rely on the extensive use of information and communications technology (ICT) to increase efficiencies in urban areas, while urban sharing builds on the collaborative use of idling resources enabled by ICT in densely populated cities. The concepts have many similar features and share common goals, yet cities with smart city agendas often fail to take a stance on urban sharing. Thus, its potentials are going largely unnoticed by local governments. This article addresses this issue by exploring cases of London and Berlin – two ICT-dense cities with clearly articulated smart city agendas and an abundance of sharing platforms. Drawing on urban governance literature, we develop a conceptual framework that specifies the roles that cities assume when governing urban sharing: city as regulator, city as provider, city as enabler and city as consumer. We find that both cities indirectly support urban sharing through smart agenda programmes, which aim to facilitate ICT-enabled technical innovation and emergence of start-ups. However, programmes, strategies, support schemes and regulations aimed directly at urban sharing initiatives are few. We also find that Berlin is sceptical towards urban sharing organisations, while London took more of a collaborative approach. Implications for policy-makers are discussed in the end.     

BP墨西哥湾漏油事故折射出什么?

距离2010年4月的英国石油公司(BP)美国墨西哥湾漏油事故已经过去整整一年了.在这不平静的一年中,此次堪称历史上最为严重的原油泄漏事件似乎已逐渐淡出了媒体的视野.然而,它带给我们的教训是绝不应淡忘的.事故所暴露出的企业环境责任意识淡漠、监管机构失职等问题,更是令人感到似曾相识.