a b s t r a c t   Clean and energy-efficient rotary drum vacuum filtration was selected to conduct algae-dewatering。 The dynamic formation of an algal cake-layer on the filter surface was modeled by correlating the cake-layer permeability to the physical parameters of algae and cake-layer。 The compressibility of algal cake-layer was taken into consideration in the modeling, and its effect on the algae-dewatering is   discussed。73071

The dewatering process was simulated to determine the process energy demand。 Process economics were assessed considering the dewatering cost, which includes capital investment and energy cost and also labor, installation, maintenance and infrastructure。 Optimal operating conditions and minimum dewatering cost were achieved by process optimization, and two cost-sensitive zones in operating the filtration were identified。 The techno-economics showed that the dewatering cost can be further reduced by scaling up the process。

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1。 Introduction Filtration is a mature technology for the removal of particulate matters from fluids。 It has found wide industrial applications in water treatment (e。g。 turbidity removal) [1–3], food processing (e。g。 clarification of beer and liquors) [4–6], air cleaning (e。g。 dust and  bacteria  removal),  etc。  [7]。  At  present,  various  filter  media

are available for the removal of these small particulates ranging from submicron to 100 lm [8–11]。 Filtration is based on size- exclusion, so it does not require large energy input。 A low pressure (e。g。 20–30 kPa) can generate a high flux through these well-tuned and highly porous filter media  [12]。

Microalgae, mostly in the range of 5–20 lm, are now playing a

key   role   in   the   ongoing   endeavors   to   sustain   energy      and

environment [13]。 Cultivation of  algae  consumes  large amounts of CO2, as a carbon source for algal biomass synthesis。 Because algae grow fast and possess high lipid contents, algae have been mass cultivated to provide renewable energy and at the same time mitigate CO2 emissions [14–16]。 The concentration of algae in a culture medium is usually 0。1 w/w%, and this concentration can be enhanced up to 20 w/w% through centrifugal harvesting。 The traditional method to dewater this 20 w/w% harvested algae is with thermal energy to evaporate most of the remaining 80% water content [17]。 Given the extremely high latent heat of water, algae- dewatering by evaporation requires a very large energy input。 Alternative approaches have good potential to improve the energy efficiency of  algae-dewatering。

One major objective of our algal biofuel project is to maximize the energy return to help better address energy sustainability。 Each operating unit of this process can benefit from use of energy-effi- cient  technology。 Energy-efficient filtration  with  the  rotary drum

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vacuum filter (RDVF) was selected to conduct algae-dewatering。 Continuous operation of filtration is favored by industry for its flex- ibility in process scale-up and for not needing extra storage space for intermediate product。 In addition, by using the vacuum opera- tion, the amount of filtrate water contained in the porous algal cake-layer can be minimized。 Consequently, much of the heating burden can be removed from the subsequent process for algae-dry- ing, which has been identified as one of the bottlenecks limiting the overall energy efficiency of algal biofuel technology   [18,19]。