I am indebted to a reader for bringing a new technology to my attention, namely the "High Density Vertical Bioreactor", or HDVB in contrast to open-pond systems, as alluded to in my recent posting, "Biofuel from Algae: Photosynthetic Efficiencies." The HDVB system is marketed by Valcent Products Inc. and consists of growing plants or algae in plastic pockets on clear vertical panels that move on a conveyor-belt arrangement. The strategy is designed to maximise the amount of sunlight and provide an ideal balance of nutrients to achieve optimum growth. It is proposed that such vertical growth systems might provide a solution to the problem of feeding urban populations so that urban living becomes sustainable.
Now, I like the sound of this, as it fits with my notion that once transportation begins to fail in consequence of cheap oil supplies waning in 5 - 10 years, humanity will relocalise into relatively small communities far less dependent on transport. The lack of urban growing space is counteracted by the very high efficiency of crop production in HDVB reactors. This form of agriculture as also soil-free, and uses perhaps 5% of the amount of water that is required to grow crops by conventional means, since the whole constitutes a closed-system with far less evaporation. Since these reactors can be placed anywhere (as can open-ponds) there is no necessity to compromise arable land which can still be used for standard agriculture.
However, the HDVB offers the potential of producing fuel as well as food, since algae can be grown in these systems too, and it is claimed in higher yield than in open-ponds. Thus in principle, food is grown locally, thus eliminating much of the fuel-costs borne in the carriage of crops from one part of the country to another or even across the world, by air or by ship, and also biodiesel can be made from oil extracted from algae grown using the technology, by transesterification with methanol or ethanol, as is done with plant-derived oils. Growing food both efficiently and locally also averts much of the spoilage that occurs on long hauls, during which as much as 50% of it is thus rendered inedible.
It is claimed that 100,000 gallons (US) of diesel can be produced per acre of HDVB area, which does seem very high. I commented in my article on photosynthetic efficiencies that the figure of 20,000 gallons/acre quoted in the wikipedia entry on "permaculture" looks to be well above the theoretical efficiency for a horizontal open-pond/algal system, but higher surface areas could be attained using vertical reactor arrangements; however, to install this paraphernalia on the very large scale is going to take a lot of plastic (derived from oil) and a lot of engineering, especially since the HDVB systems are more intricate than the basis I have indicated. Irrespective of whether the algae are grown in open-ponds or HDVB systems, there will also need to be a massive construction of transesterification plants and a source of methanol or ethanol must be found, in an amount equal to perhaps 10% of the diesel that is produced.
It sounds like a great idea and sits comfortably with most of my values and projections as to what precisely we need to achieve in order to form a stable, sustainable society. However, the scale-up will be a gargantuan task. If we can cut our fuel use to say 25% in relocalised communities, we still need to produce around 700 million tonnes of biodiesel annually (15 million tonnes just for the UK and 175 million tonnes for the US) and convert most vehicles to run on diesel-engines; but can this be done quickly enough to breach the demand/supply gap facing conventional oil production?