Microalgae dewatering is a major obstruction to industrial-scale processing of microalgae for biofuel prodn. The dil. nature of harvested microalgal cultures creates a huge operational cost during dewatering, thereby, rendering algae-based fuels less economically attractive. Currently there is no superior method of dewatering microalgae. A technique that may result in a greater algal biomass may have drawbacks such as a high capital cost or high energy consumption. The choice of which harvesting technique to apply will depend on the species of microalgae and the final product desired. Algal properties such as a large cell size and the capability of the microalgae to autoflocculate can simplify the dewatering process. This article reviews and addresses the various technologies currently used for dewatering microalgal cultures along with a comparative study of the performances of the different technologies.

Dewatering of microalgal cultures : a major bottleneck to algae-based fuels

Catalytic deoxygenation of microalgae oil to green hydrocarbons

Microalgae have been promoted as the next frontier of green biotechnology and gained widespread attention as desirable feedstocks for biofuels. Using conservative assumptions for microalgal growth rates (15 g m− 2 d− 1) and total lipid content (25%), the entire “pond-to-pump” lifecycle of algal biofuels for 1000 bbl d− 1 of crude algae oil production is modeled with approximately 4875 ha of raceway ponds for solar collection and cultivation and 1463 MLD (385 MGD) of water handling capacity in the current analysis. Technoeconomic analysis based on an array of 6000 modular 0.8 ha (2 acre) paddlewheel-driven ponds in New Mexico identified several cost barriers and resources challenges (i.e., nutrient and water resources). For 10- and 20-year capital return scenarios, the cost of algal oil production – $4.10 L− 1 ($15.52 gal− 1) and $3.21 L− 1 ($12.14 gal− 1), respectively – requires substantial capital and facility maintenance investments with principal cost sensitivities attributed to extraction efficiency and lipid content. Baseline conditions result in an energy return on investment (EROI) of 2.73. Uncertainty in energy requirements for paddlewheels as well as water supply and circulation significantly affect the EROI and operating costs. Alternative strategies to address the major cost barriers are needed for algal biofuels to realize their full potential.

A critical analysis of paddlewheel-driven raceway ponds for algal biofuel production at commercial scales

Algal technology has potential to combat the global energy crisis, malnutrition, and production of several value added products useful for the mankind. The cost effective cultivation system is the basis to realize this goal. Microalgal production in raceway ponds seems to be most promising, especially in the large scale. Several environmental (location of the cultivation system, rainfall, solar radiation, etc.), engineering (pond depth, CO 2 delivery system, methods of mixing, power consumption, etc.), and biological (light, pH, oxygen accumulation, salinity, Algal predators etc.) parameters affect the biomass productivity in the open pond system. Vertical mixing is an important criteria influencing the algal growth compared to axial mixing as it determines the frequency by which cell will travel from bottom (dark zone) to surface (light zone) of the open pond. Therefore, different research works on the various designs of raceway ponds were mostly focused towards enhancing the vertical mixing (e.g. Design of bend and surface geometry, engineering flow field, etc.) and CO 2 residence time (e.g. Closed, sump, airlift driven raceway ponds etc.). The present study summarizes the current state of knowledge for the biomass production in raceway ponds.

Recent trends in the mass cultivation of algae in raceway ponds

Biowaste-to-bioenergy using biological methods – A mini-review

First test flights using blends with algae oil are already carried out and expectations by the aviation and other industries are high. On the other hand technical data about performance of cultivation systems, downstream processing, and suitability of algae oil as fuel are still limited. The existing microalgae growing industry mainly produces for the food and feed market. Energy efficiency is so far out of scope but needs to be taken into account if the product changes to biofuel. Energy and CO2 balances are used to estimate the potential of algae oil to fulfil the EU sustainability criteria for biofuels. The analysis is supported by lab tests as well as data gained by a pilot scale demonstrator combined with published data for well-known established processes. The algae oil composition is indicator of suitability as fuel as well as for economic viability. Approaches attaining high value fractions are therefore of great importance and will be discussed in order to determine the most intended market.

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Composition of Algal Oil and Its Potential as Biofuel

Present geothermal power cycle for low enthalpy geothermal fields (utilizing brine not steam) attain electrical efficiencies far from the ideal carnot factor and therefore are not well utilizing the expensive geothermal wells. This is to a large part due to excessively high exergy losses in heat transfer from the geothermal water to the steam of the turbine process, sometimes visible in a drastically reduced temperature reaching the turbine entrance. These exergy losses could be widely reduced by methods which have long been applied in other heat recovery processes for electricity. Also a new power cycle is presented, which minimizes these losses. These measures are presented in order to stimulate the awareness for thermodynamics and the development of such improved power systems. Furthermore this would contribute to the reduction of electricity cost.

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Pascal Schlagermann

Papers

Composition of Algal Oil and Its Potential as Biofuel

New Concepts for Power Generation Necessary