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As to inorganic and carbonaceous nanomaterials considerable scope exists for a variety of recycling called resource cascading. Resource cascading aims at the maximum exploitation of quality and service time of natural resources. Extension of product use, product reuse, remanufacturing, and the reuse of materials are important elements in resource cascades. Options for resource cascading are available regarding nanomaterials applied in reactors, used as recoverable analyte, and for nanomaterials embedded in, or bound to the surface of, large-sized materials. Important research issues for nanomaterials applied in reactors are: recovery of nanomaterials in commercial processes, preventing aggregation of nanomaterials, kinetics of catalysts and adsorbents and preventing and reversing poisoning of catalysts and adsorbents. Options facilitating extended use and reuse of nanocomposites with large-sized materials include: preventing loss of nanomaterials, preventing poisoning of nanomaterials, preventing degradation of polymers and introducing self-healing properties. For the recycling of nanomaterials and nanocomposite materials a wide range of technologies has been investigated. Performance of thermoplastic polymeric nanocomposites often deteriorates on reprocessing. There is also scope for recycling of nanomaterials and sacrificed nanomaterials present in wastes. There can be good reasons for resource cascading of nanomaterials and recycling of wastes linked to functionality, resource savings and hazard minimization. Much work is still needed to extend our knowledge about options for resource cascading and the minimization of the environmental burden thereof, and to make resource cascading of nanomaterials fully operational.

Life cycle assessment (LCA) of greenhouse gas emissions has been developed for analyzing environmental burdens and impacts of products “from cradle to grave”: from resource extraction to waste disposal. Life cycle assessments of greenhouse gas emissions are often part of wider environmental assessments, which also cover other environmental burdens or impacts. Such wider-ranging assessments allow for considering “trade-offs” between reduction of greenhouse gas emissions and other environmental impacts and co-benefits of reduced greenhouse gas emissions. Data about greenhouse gas emissions used as input in assessments of current product life cycles do allow for substantial uncertainties in life cycle emission estimates. Estimates of life cycle greenhouse gas emissions linked to new processes and products are subject to even greater data-linked uncertainty. Variability in outcomes of life cycle assessments of greenhouse gas emissions may originate in different choices regarding system boundaries, time horizons, and the allocation of emissions to outputs in multi-output processes. Life cycle assessments can include other interventions than the emission of well-mixed greenhouse gases, which can affect climate such as changes in tropospheric ozone and aerosol concentrations, changes in albedo, and the generation of contrails and cirrus clouds. Life cycle assessments may be useful in the identification of life cycle stages that are major contributors to life cycle greenhouse gas emissions and of major reduction options, in the verification of alleged climate benefits, and to establish major differences between competing products. Main findings from available life cycle assessments of greenhouse gas emissions are summarized for products ranging from buildings to unconventional fossil fuels, and from food to vehicles. Guidance for reducing greenhouse gas emissions is presented. Future directions in developing life cycle assessment and its application are indicated. These include better handling of indirect effects, of uncertainty, and of changes in ecosystem carbon stocks and improved comprehensiveness in dealing with climate change by including, where appropriate, climate effects of changes in albedo, tropospheric ozone, and aerosols and the generation of contrails and cirrus clouds.

Life cycle assessment (LCA) assesses the environmental burdens or impacts of products from cradle to grave. It is also possible to assess such burdens or impacts for parts of the life cycle. A brief overview is given of LCA methodology. A number of choices have to be made in the goal and scope definition, inventory analysis, and impact assessment stages of life cycle assessments. Such choices can have substantial impacts on LCA outcomes. There are uncertainties in outcomes linked to inventory data and modeling. In the case that future biofuels and production processes are studied, assessment outcomes are characterized by relatively large uncertainties. Choices and uncertainties should be considered in the interpretation stage of life cycle assessments. Methodologies applied to several important environmentally relevant aspects of biofuel life cycles are discussed. These aspects are: emissions of substances impacting climate, depletion of virtually nonrenewable abiotic resources, primary energy demand, and water footprint. LCA can be useful in identifying life cycle stages and processes that are major contributors to environmental burdens, for determining the energetic return on energy invested in biofuels, for the identification of environmental trade-offs, and for comparing the life cycle environmental burdens of products.

Safer-by-design strategies for engineered inorganic and carbonaceous nanomaterials mainly aim at reducing hazard and the release of nanomaterials to the environment. In practice, the focus as to hazard is often on aspects of the overall hazard or specific hazards. Important constraints for safer-by-design are: limited toxicological knowledge, differences between tested nanomaterials and the nanomaterials that organisms or cells are exposed to in the real world, and trade-offs between functionality and safety. Proposed strategies to reduce (aspects of) hazard for nanomaterials include: coating, control of size, doping, grafting, loading, managing shape and crystallinity, reducing the presence of substances at the surface of nanomaterials that contribute to hazard, reduced persistence, and substitution. Isolation of nanomaterials production and processing, in situ synthesis of nanomaterials, enhanced integrity and durability of nanocomposites, design for disassembly of products and efficient recycling of materials may contribute to reducing nanomaterial releases to the environment.

Environmental sustainability is defined here as near-constancy of natural capital and resources derived thereof, that are to be transferred to future generations. Contributions to natural capital considered here include: Fresh water, soil and soil carbon, plant nutrients, ecosystem services, fossil fuels and climate The current production of biofuels often has a substantial negative effect on natural capital that is to be transferred to future generations. Biofuels are renewable but do not necessarily mitigate the greenhouse effect or carbon footprint, if compared with fossil fuels. Options that can reduce the negative impact of biofuels on natural capital are outlined.

Life cycle assessment (LCA) assesses the environmental impacts of products from cradle to grave. It is also possible to assess parts of the life cycle. Available peer-reviewed LCAs dealing with microalgae-based products and processes are reviewed. In processes that require extraction of dry algae, the combined harvesting, drying, and extraction steps are associated with relatively large environmental impacts. In addition, the cultivation stage has been identified as linked to relatively large environmental impacts. Proteins derived from cyanobacteria tend to have larger estimated life cycle environmental impacts than proteins derived from cultivated terrestrial plants such as maize and soybean. Microalgal biomass-based feed for carnivorous fish might have a lower life cycle environmental burden than conventional fish meal. Whether commercial microalgal fuels will have a climate benefit compared with fossil fuels appears to be uncertain. The energetic return on energy invested (EROI) of all microalgal fuels for which peer-reviewed LCAs are available does not meet the criterion of 5–8, which would allow for widespread application.