Minimising losses to predation during microalgae cultivation

We explore approaches to minimise impacts of zooplanktonic pests upon commercial microalgal crops using system dynamics models to describe algal growth controlled by light and nutrient availability and zooplankton growth controlled by crop abundance and nutritional quality. Losses of microalgal crops are minimised when their growth is fastest and, in contrast, also when growing slowly under conditions of nutrient exhaustion. In many culture systems, however, dwindling light availability due to self-shading in dense suspensions favours slow growth under nutrient sufficiency. Such a situation improves microalgal quality as prey, enhancing zooplankton growth, and leads to rapid crop collapse. Timing of pest entry is important; crop losses are least likely in established, nutrient-exhausted microalgal communities grown for high C-content (e.g. for biofuels). A potentially useful approach is to promote a low level of P-stress that does not adversely affect microalgal growth but which produces a crop that is suboptimal for zooplankton growth

Infrastructure Support for Bioenergy Development in Cities

Worldwide, bioenergy production is increasing. However, there is still a lack of understanding of the types of infrastructural modifications necessary to support further bioenergy development in ways that are both cost effective and environmentally sustainable. This paper provides an overview of the infrastructure support crucial for enabling large-scale bioenergy production in cities. Three waste-to-bioenergy pathways to produce biodiesel from waste oils, syngas from plasma gasification of municipal solid waste (MSW), and bioenergy from algae are reviewed. (i) To produce biodiesel from waste oils, a cost-effective feedstock collection system is key as feedstock cost, including transportation cost, is the single largest contributor to total cost. (ii) To promote the production of syngas from MSW by plasma gasification, a decentralized approach is recommended in the near to medium term. This is because at present, there is still little experience operating large MSW plasma gasification plants. A decentralized approach creates opportunities for public-private partnerships, leading to investments to gain operational experience. Soft infrastructure in the form of a well-developed recycling program or legislation is also necessary to ensure the gasification does not compete with recycling for recyclables. (iii) To produce bioenergy from algae, two infrastructures are vital. The first is infrastructure to integrate wastewater treatment and algae cultivation with nutrients and carbon dioxide recycling. The second is infrastructure to create large surface areas from sides of buildings and/or rooftops that are well exposed to sunlight for algae growth. Provided these infrastructures are in place, the three pathways, combined, have the potential to supply up to 12–16 % of Hong Kong’s electricity demand if converting the energy products from the pathways to electricity. Further, the pathways create new interdependencies between the waste and energy sectors. The interdependencies, while synergistic, could lead to new vulnerabilities such that a failure of one sector will cause a failure in the other as well. Care must be taken when designing systems to minimize this