ACKNOWLEDGEMENT

This study was supported by the NSF Engineering Research Center, ; the National Science Foundation EPSCOR project ; and the Ed & Harold Foreman Endowed Chair.

SELECTED RESULTS

Approach: Suitability of a self-flocculating strain, Coelastrella [COE], in enhancing the

settlability of a non-flocculating strain Chlorella Sorokiniana [CHL] grown in outdoor and indoor photo bioreactors is tested at various doses.

Settling studies were conducted in glass bottles with a culture volume of 20 ml. and percent settling was determined by measuring the OD data of settled material at different time intervals.

This study was performed at four different flocculating to non flocculating mixture ratios which are determined by cell counts using flow cam imaging analyzer.

ABSTRACTMicroalgae has been recognized as one of the most promising feed stocks for biofuel production. However, the economic viability of algal biomass-to-biofuel production is currently limited by the harvesting step, which accounts for 25% of the finished product cost due to the high energy requirements. Laboratory and field studies are being carried out at New Mexico State University to develop energy-efficient and cost-effective harvesting technologies for various strains. The focus of this study is to evaluate the energy free harvesting technology called bio flocculation and discuss its advantages over traditional and emerging methods

1Civil Engineering Department, New Mexico State University, Las Cruces, New Mexico, USA2 Energy Research Laboratory Molecular Biology Program, New Mexico State University, Las Cruces, New Mexico, USA

Harvesting Microalgae : Energetic comparison of current vs. Emerging technologiesC. Kukutla1, N. Nirmalakhandan1, Peter J. Lammers2

National Science Foundation for Energizing New Mexico and supporting a culture of

Innovation and entrepreneurship

BARRIERS TO HARVESTING

Current algal harvesting technologies are not energy-efficient to make biofuel production commercially viable. Major hurdles for efficient harvesting of microalgae include:

a) small size of algal cells and low density difference between algal cells and the growth medium prevent settling of biomass

b) low concentration of algal cells maintained in the cultivation system to ensure maximize light penetration renders cell separation energy-intensive

c) high capital costs and energy costs increase the overall harvesting cost

Ideal harvesting method desired for sustainable algal biofuel production: d) should be able to harvest large quantities reliably e) should meet down streaming processing requirements f) should demand minimal energy and material resources

OBJECTIVES OF THIS STUDY

The goal of this study was to conduct experiments on emerging technologies- bio flocculation and electrocoagulation/flotation to evaluate their performance in terms of removal efficiency (%) and energy consumption (kW-hr/cu m) and compare them against literature results on different harvesting methods.

MATERIALS AND METHODS

1) Bio flocculation: Bio flocculation involves the use of self-flocculating algal strains to enhance gravity settling of non-flocculant microalgae. As this approach does not use any flocculants or external input of energy, it is energy- and cost-efficient. Additionally, the settled biomass does not require any pre-treatment prior to oil extraction; and, the supernatant can be reused in the cultivation step.

Figure 1. Settling studies on Chlorella and Coelastrella

• Electrocoagulation flocculation has promise for flocculating and non-flocculating strains, achieving removals of 86-97% at low energy consumption (~7 kW-hr/ cu.m)

RESULTS

Figure 3. OriginOil electrocoagulation flocculation system

2) Electrocoagulation flocculation (ECF) vs. Electro flotation (EF):

Typical energy content of biomass

Figure 2. Bio flocculation at various Coelastrella and Chlorella mixtures

0 50 100 150 200 250 300 350 400 4500

2

4

6

8

10

12

80/20 ratio70/30 ratio60/40 ratio50/50 ratio

Time (min)C

on

ce

ntr

ati

on

Fa

cto

r (C

F)

CONCLUSIONSCompared to traditional harvesting technologies, emerging approaches consume less energy and achieve higher removal efficiencies in shorter time. • Bio flocculation has the potential for improving removal of the non-

flocculating strains such as Chlorella.• A concentration factor of nearly 5 at seven hours of gravity settling was

obtained under 80-20% ratio of Chlorella and Coelastrella• Concentration factor was high for high COE ratio, but the minimum CF

obtained in all ratios after 1 hour is 2.02) Electrocoagulation flocculation:

Electrocoagulation flocculation involves the use of sacrificial electrodes which release metal ions that induce coagulation of the algal biomass. The coagulated biomass is floated by the gases generated at the electrodes and skimmed.Approach: Commercially available electrocoagulation flocculation unit by OriginOil

was tested with Chlorella Sorokiniana and Coelastrella Power consumption and removal efficiencies were measured as a

function of feed rates, with and without electrocoagulation.

CONCLUSIONS

MethodRemoval

efficiency (%)Energy

consumed (kW-hr/cu. m)

Test species Source

Centrifuge > 90 0.3 – 8 Scenedesmus,Coelastrum proboscideum

Mohn et al. 1980

Air flotation 83 - 85 0.003 - 7.6 Primary Chlorella and Scenedesmus

Wiley et al. 2009

ECF > 90 0.14 - 0.9 Phaeodactylum,Dunaliella salina, Chlorella

E. Poelman 1996Dries vandamme et al. 2011

ECF + dispersed air flotation

98.9 0.235 Botryococcus braunii Ling Xu et al. 2010

ECF 86 - 97 6.8- 6.9 Chlorella Sorakaniana, Coelastrella

This Study

EF 94.6 5.85 Coelastrella This Study

Bioflocculation 21 - Coelestrella and Chlorella This Study

Centrifuge 99.2 8.13 Chlorella This Study

Comparison of removal efficiency and energy consumption:Current vs. emerging technologies

FUTURE IMPLICATIONS OF THIS STUDY• The work presented here has profound implications for future studies of

harvesting microalgae and making the biofuel production available in commercial scale.

• Bio flocculation proved to be a controlled and reliable pre concentration step in micro algal harvesting and more research has to be carried out to optimize the flocculating to non-flocculating ratios