Open pond system
Open pond systems are typically built in circular or raceway configurations. The water is kept in motion, e.g. by paddle wheels. Open pond systems are seemingly inexpensive and easy to build. However, poor light utilization, danger of contamination and high water evaporation are main challenges, which lead to low biomass output per area and large water uptake. Some difficulties can be over-come by rooftops, however, increasing costs.
Closed systems are dominated by tubular and flat-plate reactors. Other options are bags, coils or domes. Flat plate systems have received a lot of attention due to their large illuminated surface area, but the technology suffers from heating problems and a strong tendency to build up biofilm formations on the inner walls. Tubular systems on the other hand reduce these drawbacks while maintaining the advantages of optimal light input and high productivity.
Therefore, closed, tubular glass PBRs, in particular glass tube PBRs with long lifetimes and easy cleanability, are very well suited for the highly reproducible cultivation of algae resulting in highest possible growth rates. As such, tubular glass PBRs are also best suited for providing high quality inoculum for open pond systems.
- Very low risk of contamination compared to open ponds, where other microorganisms or insects can have easy access
- No limitation regarding the algae species that can be grown, due to effective blocking against competing organisms
- Significantly higher productivity in terms of mass per area and day
- More efficient use of land
- Significantly higher concentration in terms of mass per liter
- More efficient harvesting procedure
- No evaporation within closed system compared in open ponds, which can lose significant water amounts, resulting in salt precipitation hazard
- Water loss is limited to external factors, such as cooling processes, use of green houses, tube diameter, target temperature etc.
- Biomass quality is highly reproducible due to excellent process control of tubular PBR systems
- High value products or high quality inoculum can be produced with optimum reliability
- Easy cleanability allows defined initial status any time, thus switching algae species is possible and secure
- GMO* is possible in closed reactor design whereas open ponds are very limited