Long term outdoor operation of a tubular airlift pilot photobioreactor and a high rate algal pond as tertiary treatment of urban wastewater

Abstract

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit:

Microalgal biofuel revisited: An informatics-based analysis of developments to date and future prospects

“…However, low culture density, low biomass productivity, contamination, susceptibility to weather events such as rainfall, and high evaporative losses in open ponds are major drawbacks hindering commercialization of this approach [45,46]. PBRs are closed to the atmosphere and have several advantages over ponds: (1) the risk of contamination is reduced; (2) the growth parameters (e.g., temperature) can be better controlled; (3) they have higher volumetric productivities and cell concentrations due to a higher surface-to-volume (S/V) ratio; and (4) these closed systems eliminate or strongly reduce evaporation and thus conserve water [47,48]. Although few PBR designs have been explored at the pilot level, the high capital and operating costs of PBRs are the major hurdles for their large-scale implementation for biofuel production and they still await evaluation at real scale [18].…”

Outdoor production of microalgae

“…The presence of a larger dark zone resulted in reduced performance due to increased respiration losses and/or unfavourable light/dark cycling as discussed above. The values obtained in this study for the open raceway pond are similar to values reported in literature, which were obtained on locations with higher PFD or in shallower systems [57][58][59][60]. Areal productivities for the HT during turbidostat operation were lower than areal productivities obtained during chemostat operation in a previous study.…”

“…When comparing the different systems it is important to note that configuration and mixing are completely different [57,79,80]. Slower mixing along the light gradient in the ORP therefore could explain the bigger impact of high biomass concentration on productivity in comparison to the VT and HT.…”

“…If the dilution rate is too high the biomass concentration is low and photo inhibition could occur. If the dilution rate is too low the biomass concentration can become so high that the dark zone in the reactor is so large that a significant amount of biomass production is lost due to endogenous respiration [31,48,57]. Operation of photobioreactors with a fixed biomass concentration (turbidostat mode) can prevent culture washouts as dilution of the culture only takes place when growth occurs.…”

Current Status and Outlook in the Application of Microalgae in Biodiesel Production and Environmental Protection

“…The main advantages and limitation of open ponds and PBRs are summarized in Table 3 (Singh et al, 2011b;Pires et al, 2012;Arbib et al, 2013). Compared to open ponds, PBRs have several advantages (Moazami et al, 2012;Arbib et al, 2013): (1) PBRs are closed to the atmosphere and protect the cultivated alga to some extent (note that by being closed, PBR are less prone, but not immune, to contamination); (2) growth parameters (e.g., temperature) can be better controlled; (3) due to a higher surface-to-volume (S/V) ratio, PBRs allow to reach higher volumetric productivities and cell concentrations; (4) closed systems eliminate or strongly reduce evaporation; (5) since PBRs have not been engineered to the extent of other bioreactors in commercial use, there are rooms for improvement. Although many different PBR designs have been proposed for biofuel production, few of them have been tested at pilot scale, none developed at the (large) scale necessary for a complete and correct evaluation because of high cost and reduced scalability.…”