Temperature Influence and Heat Management Requirements of Microalgae Cultivation inPhotobioreactors. Thomas Hagen MehlitzMicroalgae are considered one of the most promising feedstocks for biofuel production for the future. The most efficient way to produce vast amounts of algal biomass is the use of closed tubular photobioreactors (PBR). The heat requirement for a given system is a major concern since the best algae growth rates are obtained between 25-30 °C, depending on the specific strain. A procedure to determine temperature influence on algal growth rates was developed for a lab-scale PBR system using the species Chlorella. A maximum growth rate of 1.44 doublings per day at 29 °C (optimal temperature) was determined. In addition, a dynamic mathematical model was developed to simulate heating and cooling energy requirements of tubular PBRs for any desired location. Operating the model with hourly weather data as input, heating and cooling loads can be calculated early in the planning stage of a project. Furthermore, the model makes it possible to compare the operation inside a greenhouse to the outdoor operations, and consequently provides fundamental information for an economic feasibility study.The best configuration for a specific location can be evaluated easily. The model was exemplary tested for a hypothetical 100,000 l photobioreactor located in San Luis Obispo, California, U.S.A. Average algae productivity rates of 23% and 67% for outdoor and indoor PBR operations, respectively, were obtained. Actual energy loads (heating and cooling) needed to maintain the PBR at optimal temperature were determined and v compared. Sensitivity analyses had been performed for abrupt temperature and solar radiation steps, PBR row distances, ground reflectivities, and ventilation rates of the greenhouse. An optimal row distance of 0.75 m was determined for the specific PBR.The least amount of energy was needed for a ground reflectivity of 20%. The ventilation rate had no major influence on the productivity rate of the system. Results demonstrated the importance of a simulation model as well as the economic impact of a sophisticated heat management system. Energy savings due to an optimized heat management system will eventually increase proficiency of the systems, which will support a new sustainable industry and future developmental potential.

This chapter first presents and discusses a dynamic mathematical model which is developed to simulate a tubular photobioreactor (PBR) and microalgae growth within at any desired location. The model has options to evaluate the effects of location, time of the year, orientation, shading and night curtains, heating and cooling systems, and indoor and outdoor operating conditions. Then the chapter focuses on the algal growth kinetics of microalgae cultivated with coal-fired flue gas, and presents two algal strains, Chlorella vulgaris and Tetraselmis sp. cultivated in lab-scale PBRs to assess the feasibility of using flue gas as a carbon source. And then, the chapter presents an economic feasibility analysis for manufacturing biodiesel from algae using a PBR. The chapter then introduces a mathematical model to investigate the thermal effects on algae population in growth in both fluid and porous media. The study reveals the potential feedback between hydrodynamic and local demographic processes in microorganism populations in the context of the influence of climate change on natural ecological systems. Finally, the chapter discusses the relationship dynamics between algae and nutrient or herbivore and algae using the predator-prey approach based on classical Lotka-Volterra system.

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In addition to the labor, energy and water consumption are the two main cost drivers in current greenhouse systems. Consequently, considerable effort is expended to conserve energy and water, and look for alternative energy sources, especially environmentally friendly renewable energy sources and technologies. Greenhouses in hot and arid regions also require large quantities of water for irrigation. Using proper technologies and environmental management systems can significantly change the energy and moisture dynamics of greenhouse production systems. This study aims to focus on reducing natural gas, electricity, and water consumption in semi-arid California greenhouses introducing renewable energy heat pump technologies to both open and confined greenhouses in California. The confined system has no external aeration and has no need for further water supply. It has a great potential to reduce the demand for natural gas, the load on the power grid, and the demand for irrigation water in greenhouse operations. It also allows plant protection without using chemical insecticides and the accumulation of carbon dioxide without aeration losses.

In addition to the labor, energy and water consumption are the two main cost drivers in current greenhouse systems. Consequently, considerable effort is expended to conserve energy and water, and look for alternative energy sources. Greenhouses in hot and arid regions also require large quantities of water for irrigation. Proper environmental management systems can significantly change the energy and moisture dynamics of greenhouse production systems. This study aims to focus on reducing energy and water consumption in semi-arid California greenhouses. Influences of mulch (having different reflectivities) on energy and water conservation were investigated. The reflectivity of mulch used as a floor cover affects the radiation distribution within the canopy stand, eventually affecting the overall energy and water consumption. A dynamic computer simulation model was used to compare different mulch reflectivities, plant heights, and leaf dimensions to draw a conclusion about energy and water conservation. The results showed that using mulch with less reflectivity (for instance, 20% instead of 80%) reduced energy consumption by as much as 4.2%. With a decrease in reflectivity, the absorptivity of the mulch increases consequently. A high absorptivity results in higher rates of solar energy being absorbed during the day, and released during the night. The mulch functions as a collection device, while the floor itself being the thermal mass. By increasing the reflectivity from 20% to 80%, water savings of up to 8.6% occurred. The savings in energy consumption, therefore, always have to be seen in conjunction with the water consumption. Also, the effect of reflective mulch fades away as shade from canopy stand increases. A complete system analysis is necessary to obtain a complete energy and water balance and to be able to make a viable conclusion.