Improved Algal Harvesting Using Suspended Air Flotation

Abstract

Current methods to remove algae from a liquid medium are energy intensive and expensive. This study characterized algae contained within a wastewater oxidation pond and sought to identify a more efficient harvesting technique. Analysis of oxidation pond wastewater revealed that algae, consisting primarily of Chlorella and Scenedesmus, composed approximately 80% of the solids inventory during the study period. Results demonstrated that suspended air flotation (SAF) could harvest algae with a lower air:solids (A/S) ratio, lower energy requirements, and higher loading rates compared to dissolved air flotation (DAF) (P , 0.001). Identification of a more efficient algal harvesting system may benefit wastewater treatment plants by enabling cost effective means to reduce solids content of the final effluent. Furthermore, use of SAF to harvest commercially grown Chlorella and Scenedesmus may reduce manufacturing costs of algal-based products such as fuel, fertilizer, and fish food. Water Environ. Res., 81, 702 (2009).

Harvesting of microalgae within a biorefinery approach: A review of the developments and case studies from pilot-plants

“…This water is then released into a flotation tank at atmospheric pressure. The dissolved air precipitates out of the water forming small bubbles (10-100 μm), which adhere to the suspended matter carrying them to the surface, given the lower combined specific gravity than that of water [52,90,98]. The biomass forms a layer at the top of the flotation tank which is continuously skimmed into a collection tank [99].…”

Algae-Derived Biomass for Sustainable and Renewable Biofuel Production

“…13 (Munir et al 2013;Srivastava and Prasad 2000). The flotation process is achieved using bubble production method, dispersed air flotation method, dissolved air flotation, and suspended air flotation methods (Vandamme 2013;Wiley et al 2009). In dispersed air flotation method, air is bubbled into a flotation cell forming foam with the aid of a surfaceactive chemical in the cells.…”

“…Dispersed air flotation method is similar to dissolved air flotation, but in the case of the later, air-supersaturated water is pumped under pressure into the floating cells (Hanotu et al 2012). Suspended air flotation is designed to correct the shortcoming of dispersed and dissolved air flotation methods towards depending on compressor and air-water saturator, but rather employed the use of cationic surfactant to create electrically charged small bubbles with excellent float stability (Vandamme 2013;Wiley et al 2009). …”

Effective C–N–P ratio for growth and nutrient removal efficiency of Scenedesmus obliquus in sugar mill effluent

“…Though microalgae normally grow in either fresh water and/or seawater depending upon the kind of species, effluent discharges such as municipal, industrial and agricultural wastewaters also offer suitable source of nutrientrich water, making their cultivation less expensive (Becker 1994;Dalrymple et al 2013). Nevertheless, mass cultivation of microalgae is still considered expensive than certain traditional crop production due to significant energy requirement especially at the harvesting stage (Bare et al 1975;Wiley et al 2009). The major nutritional requirement for microalgal growth is nitrogen, phosphorous and potassium (NPK) and certain trace elements such as magnesium and iron (Becker 1994;Mulbry et al 2005;Dalrymple et al 2013), and they take up these nutrients along with CO 2 during photosynthesis to convert into biomass.…”