Although immobilised microalgae culture is structurally feasible for scaled growth systems, a mixture of selected bio-composite gelling agents is not price competitive with conventional microalgae culture systems in water. Results show that the costs of production are almost threefold greater than the production incomes per cycle, using an alginate concentration of 2%. Conversely however, an immobilised production system could have merits as a higher value biochemical production platform. This research has demonstrated the ability of the pectin and alginate hydrogels to both capture and retain microalgae nutrients, as evaluated by lack of incremental increase in ion detection within the hydrating de-ionised water over the duration of the experiment. It has also been demonstrated that lack of buoyancy is a functional constraint to enteric system development.
Typically biomimetics has been successfully applied to structural and applied mechanical engineered products, as well as pharmaceutical and biotechnology products. Examples include the hydrodynamic and aerodynamic exterior surfaces of transportation vehicles. Biomimetics has been less effectively applied to engineer the living environment of microorganisms destined for biofuel technologies. A controlled replication event of a marine foam or an algae bloom
which could be simultaneously be harvested for an end product for human appropriation could possibly be a way to grow algae on a massive scale.
Mimicking the natural world is not the only way to facilitate this process though it is an effective delivery strategy. This could have a profound impact on the scalable development of this technology from laboratory to commercialisation.
Coupling fast growth rates of microalgae with a mechanism for optimisation of containment is necessary to ensure the viability of scalable development of microalgae for biofuels. The close association of microalgae with gels is of particular interest for investigation, considering the natural exopolysaccharide secretions from both microalgae and macroalgae into their surrounding environment. In order to achieve a scalable production process of microalgae using gelation technology, it is necessary to ensure that the structure can withstand torsion and tension forces. The proposition for implementation of this technology would be to grow the structure in a marine environment where there would be limiting conflicting business activities, land or sea utilisation. This investigation has demonstrated an objective test methodology for quantitative measurement of structural forces in biopolymer pectin-alginate hydrogel disks.
This could align with the geotextile puncture resistance test if the displacement delivery is 50 +/- 10 mm per minute rather than a hand cranked delivery action.
This research has demonstrated the ability of 300 ml gel disks to support between 30 and 60 N breaking strain force. This is considered to be in the range sufficient to tolerate physical forces from the natural environment including wind, waves and birds. The plasticity of the structure will allow further deformation and memory stresses which would otherwise cause shear tearing within the structure. The use of natural fibres such as coconut increases the composite nature of the gel matrix material to further increase multi-directional strength (Yao, Hu and Lu, 2012). Air bubbles were primarily included as an investigative potential means for increased structural flotation, but they could also be used as a strategy for increased gas delivery at higher cell densities and light intensities, if the structure can achieve cost-effective flotation. In terms of the application for usage of coir fibre together with microalgae, marine diatoms have an obligatory requirement for silica (Anderson, 2006), and therefore association with the silica nodules on the
longitudinal surface of coir fibres could have implications for commensal association in conjunction with alginate. However, growth of microalgae irrespective of their type was considerably less of a problem than achievement of flotation. The algae grew, but the structure did not float. As such, more pertinence was given to try to make the structure float than to try to grow the algae within the composite which was already achieved with ease.
The chronological daily detection of ions in the hydrating “de-ionised” water surrounding the gel disks evaluated the potential for the gels to adequately encapsulate the nutrient media. This is of interest because of the batch cultivation process which provides the entire nutrient requirements for the remainder of the growth and harvest cycle up until 14 days. Alternatively, if the growth priority was for lower value smaller scaled high value biochemical production, the algae could be drip fed with nutrients rather than batch culture. Varying nutrient growth media compositions could feasibly have been used as there was demonstrably no leakage of nutrient ions into the incubating de-ionised water. This research has demonstrated the ability of the pectin and alginate hydrogels to both capture and retain microalgae nutrients, as evaluated by lack of incremental increase in ion detection within the hydrating de-ionised water over the duration of the experiment. Nitrate and phosphate, both present in the nutrient media, were not even detected in the incubating de-ionised water which suggests that the gel has good capability for nutrient capture and retention. Optimisation of nutrient resource acquisition during the growth lifecycle will allow effective nutrient delivery without incurring nutrient wastage once microalgae cells have grown to the maximum cell densities.
Engineering products by aligning their construct with design structures of the natural environment is an effective strategy to novel product development.
Advanced generation biofuels utilise micro-organisms as scalable converting platforms of waste nutrients into valued outputs. Industrial development of third generation biofuel technologies will rely on a versatile re-enactment of traditional engineering practices on account of the fluid characteristics of the habitat of these microorganisms. In particular, microalgae are more efficient than terrestrial plants
in converting sunlight to biochemical energy (Stephenson et al., 2011). This facet, together with microalgae being able to be grown on land or water bodies unsuitable for conventional agricultural production deems microalgae pertinent for third generation biofuel research.
Culturing microalgae in liquid water as opposed to gelled water has inherent issues with downstream processing including harvesting, drying and the associated high energetic and economic costs of such procedures. It may be that control over containment of microalgae is one of the most critical factors in successful amplification of scale from the laboratory to commercial production.
Attached microalgae cultivation can either happen as a biofilm or within an enclosed matrix. When grown as a biofilm, a significant production constraint is the shading of high density cells in close proximity to each other which acts to alter spectral composition, reduce gas exchange and nutrient acquisition. Unlike liquid water, the addition of ionotropic gelation agents to water at ambient conditions can increase the viscosity of water to form a gel, an intermediary state between solid and liquid matter. Such gels have been demonstrated to allow the successful growth of microalgae and entrapment of the required nutrients for batch culture (Hameed & Ebrahim, 2007). Enclosed matrix immobilised microalgae growth is also advantageous because cellular growth occurs in uniform proximity, therefore avoiding issues of light attenuation and nutrient acquisition aforementioned. Ionotropic gelation agents are refined to various levels of purity for commercial processes, typically reducing the phenolic content, therefore improving transparency and light transmission. These processes increase commercial production costs as described in the final chapter, yet the raw materials for gelation are of comparable value with other tradable raw commodities such as sugar beet and citrus fruit pectin and seaweed alginates.
Food grade standard product refinement is not a pre-requisite for the manufacture of a gel required to culture microalgae. Gel composite structure costs can further be reduced using bio-composites of other lower value gelling products such as terrestrial pectins from agriculture and by-products from fast growing tropical traded commodities including coir fibre.