Algae-laden canals have the potential to provide an efficient means of treating human effluent while simultaneously transforming it into a green source of energy.
While algae has been used to treat human waste since time immemorial, and efforts to convert its biomass into energy commenced as early as the 1940s, an environmental engineer in California is now working on a system which pairs the two processes, thus achieving cost efficiencies which could give the algal fuels industry a viable future.
Tryg Lundquist, an associate professor in environmental engineering at the California State Polytechnic University, has spent more than two decades designing sewage "raceway" systems and says the technology is now cheap and efficient enough to serve as a viable means of both treating waste water and manufacturing biofuel.
Lundquist's system consists of an intricate, maze-like network of shallow canals and looping ponds designed to foster the growth of algae colonies by maximizing their exposure to sunlight and aeration.
Paddle wheels impel the movement of waste water which enters the system, mixing it with the algae as it proceeds through the network of raceways.
According to Lundquist, this system harbours major advantages compared to existing methods for the treatment of sewage and waste water. It is inexpensive to build and operate, particularly compared to prevailing mechanical systems which can be costly and energy-intensive. The algae-based treatment process entails less use of electricity, and permits the recycling of water as well as nitrogen and phosphorus.
On top of reduced costs and heightened energy efficiency, the process also provides the added boon of biofuel in the form of the algal colonies. The system, purpose tailored to facilitate algae growth, generates sufficient biomass to make conversion into fuels such as algal oil economically feasible.
According to estimates made by Dr David Batten, a former scientist with CSIRO's Energy Flagship and currently an industrial ecologist with the Temaplan Group, algal oil can be made via conversion from waste water for under US$160 per barrel, or US$1 per litre. Even in a country with a relatively modest population like Australia, the use of sewage-derived algal fuel could replace as much as 10 per cent of current diesel use.
Despite his long-term commitment to the new processing method, Lundquist concedes it suffers from a few disadvantages, the large amount of land required to house the maze-like networks of raceways being it chief shortcoming. This land must also be situated in close proximity to treatment plants in order to ensure that electricity and transportation costs remain low, while suitable climate conditions are also required to spur algae growth.
For these reasons, the method may not be suitable for high-density urban environments, or in countries with cold climates and modest sunlight. In the antipodean nations of Australia and New Zealand, however, which enjoy strong levels of sunlight as well as ample space, the system could certainly abet efforts to transition to green sources of energy.
A waste water treatment centre in the New Zealand town of Cambridge is already conducting trials of a full-scale raceway system, which will be permanently incorporated into the centre's treatment process should it prove successful.