Algal Ponds as a source of protein supplementation

Summary

This project was about producing a cheap protein source in the form of microalgae to supplement cattle in northern Australia during the dry season. Microalgae were proposed as they offer high areal productivities (up to 110 t dry matter (DM) per ha per year) and can be grown on-farm with almost any water source (including brackish), making farmers independent of price fluctuations for other protein supplements (soybean or cottonseed meal). Other studies report improved animal health/resilience and consumer benefits, as microalgae also provide a mixture of other nutrients that may be beneficial to cattle production and beef products. Most microalgae are high in vitamins and antioxidants and many also contain omega-3 fatty acids. The main focus of this project was to develop ways to cheaply produce algal protein, preferably on-property, to supplement cattle. Algae had previously been evaluated for intake, digestion and live weight gain responses with positive results.

New, low-cost technology has been developed to significantly reduce the cost of algal biomass production. Major technology advances throughout the project included (1) the selection and adaptation of fast-growing, protein-rich, easy-to-harvest, saline- and heat-tolerant microalgae collected from cattle farms in the NT, (2) a new hydrodynamic pond design that cuts the cost of mixing cultures by half, (3) a new airlift design for efficient culture mixing and CO2 supply to ensure rapid growth of healthy cultures, (4) a new, low-cost harvesting process that uses gravity for induced settling instead of costly centrifugation, (5) a low-cost solar dryer. All of the above needed to be incorporated in a single large-scale demonstration farm. After substantial testing using smaller pilot facilities, a 250,000 L Algae Energy Farm was constructed at the University of Queensland, Pinjarra Hills. Production of protein-rich cattle feed supplement has been tested and further optimised in routine operation towards low costs and high yields. For more than 1 year, regular yield data have been collected from high-frequency harvesting of microalga Scenedesmus dimorphus NT8c (local NT strain with high protein yields), Lemna (a miniature aquatic floating plant) and more recently, Limnothrix planctonica (an easy-to-harvest, highly-productive filamentous summer strain). For NT8c, consistent yields have been 54 DM/ha/year (15 g DM/m2/day) with cell densities of 0.7-1.2 g DM/L. Yields at moderate temperatures around 25ºC during spring and autumn reached 72 t DM/ha/year, but at high water temperatures, ammonium-mediated grazer control restricted further yield increases. Lemna biomass production was only half  that of NT8c (25 t DM/ha/year or 7 g DM/m2/day), but clear advantages exist for this floating species as harvesting is simple. Summer strain Limnothrix showed average yields of 72 t DM/ha/year (19.8 g DM/m2/day), but up to 110 t DM/ha/year were recorded.

Cost reductions have been achieved by (1) increasing the harvesting frequency to three harvests/week, (2) growth without CO2 or improved CO2 dissolving, and (3) the use of low-cost fertiliser combinations that are amenable to grazer control and harvesting by settling. Further cost reductions have been achieved by streamlining standard operating procedures, resulting in a reduction in labour costs. The option of not using externally supplied CO2 in combination with the specially designed airlift approximately halved the yields, but reduced operation costs.
Average yield data from routine production showed that 55 t DM per ha growing area is realistic. To supply protein supplement for 1000, 250 kg weaner steers with 3.5 g DM alga supplement per kg W per day over a period of 3 months would require 79 t algae DM. A 2 ha algae farm should therefore be sufficient to provide protein supplement for 1000 weaner steers, although this can vary depending on the specific requirements for supplementation.

A full techno-economic analysis has been performed and applied to a 10 ha farm with 8 ha pond surface area (annual production capacity > 400 t DM pa). Taken all into account (including costs for operation, maintenance/repair, labour and amortisation of CAPEX), conservatively and without assumption of improvements or at scale operation, the costs were $2,289/t DM for NT8c. The cost of Lemna production was $781/t DM and $2,219/t DM for Limnothrix. Costs for NT8c and Limnothrix production can be cut by >50% if a free CO2 source is available. Additional technological improvements and cost savings are to be expected from the learning curve of this new farming system over the next few years and the economy of scale from on-farm operations. Suggestions are made on processes how costs can be further reduced to reach competitive production.

Benefits to industry

Benefits for cattle farmers include convenient on-farm protein-rich supplement supply all-year-round, making them less dependent on price fluctuations and availability of conventional soybean or cottonseed meal. The increased weight gain of weaners can lead to higher farm profitability and potentially a meat product with increased nutritional benefits for the consumer.