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Environmental and technical evaluation of the dual use of microalgae for municipal wastewater bioremediation and sustainable biofuel production
* Dr. Taurai Mutanda & Prof Faizal Bux Institute for Water and Wastewater Technology,
Durban University of Technology, P O Box 1334, Durban, 4000
E-mail : [email protected]
Presentation Outline
Why microalgal biofuels? Pros and cons Wastewater as a cultivation medium Characteristics of wastewater vs. BG11 medium Benefits of microalgal cultivation using wastewater Indigenous microalgal species Results Conclusions and recommendations Current work Acknowledgements
Published Technical Paper
Why Microalgal Biofuels? Microalgae have faster growth rates Greater photosynthetic efficiencies Microalgal lipid productivities can be twenty times that of
oilseed crops Lipid content 20-40%/g DCW Flue gas CO2 fixing via photosynthesis Supplementary food and feed products Bioremediation of wastewaters Synthesis of a wide array of primary and secondary
metabolites Biotechnological and pharmaceutical applications
Pros and Cons
Cons
Pros
Wastewater as a cultivation medium Large scale microalgal cultivation requires large amounts of N and P.
chemical or organic up to 50% of the energy use and GHG emissions associated with chemical fertilizer
production Ammonia N and phosphates in readily available secondary-treated
20-40 mg.L-1 N 10 mgL-1 P
Coupling wastewater treatment with biofuels production is a very
attractive option for energy, freshwater and fertilizer reduction
showed that wastewater serves as a complete medium equivalent to chemical media from a kinetics standpoint. Wastewater treatment with the production of microalgae for biofuels significantly improves the economics of biomass production as secondary and tertiary wastewaters contain nitrates and phosphates. This reduces the cost of treatment that would normally be incurred for nutrient removal by conventional methods (Lam and Lee, 2011, Zhou, et al., 2011).
Characteristics of Wastewater vs. BG11 Medium
Parameter Wastewater Media Unit Nitrates 4.5 200-1500 mg/l Phosphates 5 40 mg/l Free chlorine 0.2 36 mg/l Salinity 0.68 ppt Ammonia as N 23.9 - mg/l Calcium as Ca 18 36 mg/l Magnesium as Mg 11.7 75 mg/l Total Nitrogen as N 25 mg/l Potassium as K 15.2 40 mg/l Sulphate as SO4 51 75 mg/l Iron as Fe 0.25 6 mg/l Manganese as Mn 0.178 0.00181 mg/l Sodium 72 20 mg/l Sulphide <0.1 - mg/l Zinc as Zn <0.015 0.0022 mg/l Molybdenum <0.026 0.00391 mg/l Cadmium <0.008 - mg/l Selenium <0.00153 - mg/l Lead <0.02 - mg/l Mercury <0.00034 - mg/l Copper 0.017 0.000079 mg/l
Benefits of Microalgal Cultivation using Wastewater
Improvement of economics Wastewater replaces artificial media Media use for large scale application not cost effective Wastewater meets discharge standards
Potential for mixotrophic growth More efficient Net Energy Ratio Higher lipid productivity
Tertiary treatment of Wastewater Removal of residual N & P COD removal Protection of surface water in receiving streams
Indigenous Microalgal Species
A lipid producing microalgal strain was isolated, purified, and cultured in post-chlorinated wastewater
Laboratory scale under batch mode. 16:8 Light: Dark Cycle Plant grow light @ 120 umol.m-2s-1
Biomass concentration 1g/L Lipid yields of 18-35% Pre and post-chlorinated tested
Media Supplemented Post-chlorinated ww
Figure 1: Microalgal accretion in BG-11 medium supplemented with post-chlorinated municipal domestic wastewater. The BG-11 strength was diluted with wastewater as follows: 100 % BG-11 to 0% pure post chlorinated wastewater. The data points are means of duplicate experiments.
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Figure 2: Chlorella accretion in post-chlorinated wastewater supplemented with sodium nitrate. The values reported are means of duplicate experiments.
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Figure 3. Lipid and biomass yield of Chlorella in post-chlorinated wastewater supplemented with different concentrations of NaNO3 (0 to 40 mM). The values reported are means of duplicate experiments.
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Biomass (mg/L)
Lipid Yield (mg/L)
Effects of Chlorine
Figure 4. Effect of chorine dosage on the growth of Chlorella sp under batch conditions. The initial chlorine dosage (0.2 mg/L) in post-chlorinated wastewater was serially diluted to 0.04 mg/L and chlorella growth was monitored spectrophometrically at 600 nm. The reported values are means of a duplicate experiment.
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Figure 5. Effect of free chlorine dosage on microalgal growth in post-chlorinated wastewater. The reported values are means of a duplicate determination.
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Nutrient Removal Efficiency
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Time(days)
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N
Figure 6 Depletion of phosphates and nitrates during growth of Chlorella spp. on post-chlorinated wastewater. The data points are means of triplicate experimental runs.
Conclusions and Recommendations
Supplemented wastewater enhanced biomass and lipid productivity
hypochlorite solution enhances microalgal growth at threshold value of 0.4 mg/L.
feasible to use post-chlorinated wastewater for microalgal growth for biomass and lipid production
Need for experimentation using partially treated wastewater
Need for large scale experimentation
Current Work Optimisation of wastewater for algal growth and lipid
production Adaptation Supplementation Wastewater characteristic monitoring
Commissioning of 300 000 L raceway pond Bioprospecting for high CO2 sequestering microalgae Assessment of microalgae for high value products
Acknowledgement
The author would like to acknowledge: National Research Foundation Claude Leon Foundation Institute for Water and Wastewater Technology Durban University of Technology EThekwini Municipality
Thank You!!!
Tel: +27 31 373 2346 Fax: +27 31 373 2777 Email: [email protected] Email: [email protected] Web: http://www.dut.ac.za/iwwt
