CSG water as a medium to grow marine microalgae for biofuel production

Harrington, Daniel (2011) CSG water as a medium to grow marine microalgae for biofuel production. [USQ Project]

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Abstract

Over the next decade, the expanding Coal Seam Gas (CSG) industry in the Bowen and Surat Basins is expected to produce between 50 to 300 GL of CSG water per year as a by-product of its methane extraction processes. CSG water is high in sodium, salts, carbon in the form of bicarbonates and other undesirable substances making it unfit for direct use.

Typically CSG water has been considered as a waste product, and is currently discharged in large evaporation ponds. The QLD Government has recently introduced policy encouraging the beneficial utilization of this water. Due to its high bicarbonate concentration, CSG water has the potential to be used as a medium for growing microalgae for the production of biofuel.

Microalgae derived biofuel is one of the more promising alternate green energy fuel sources to emerge in recent years. This method is superior to traditional crop based biofuels as it requires substantially less water and land area to yield equivalent oil volumes. Furthermore, it has the additional potential of cleansing nutrient rich waste waters.

Hence, the aim of this dissertation was to assess the potential of using CSG water as a medium for growing microalgae to produce biofuel. Additionally, investigation was made of the carbon sequestration and nutrient removal capacity of this process. Three sets of batch experiments
were conducted using a 3.5 L batch bio-reactor. In all trials, DO, pH and temperature were monitored in real time, along with daily sampling of carbon, nitrogen and phosphorous to calculate the depletion rates. Furthermore, algal growth was documented by measuring suspended solids concentrations, and by optical density measurement using a spectrophotometer.

A preliminary set of trials were completed to validate the growth and monitoring capacity of the bio-reactor. The trials inoculated microalgae Chlorella vulgaris in a controlled MBL media. A florescent light source, compressed air and a CO2 feed were provided to facilitate algal growth.
The pH was set within the range 7.5±0.6. Trial results generally validated monitoring and growth capacity using the installed bio-reactors.

Trials were then conducted using the microalgae Dunaliella tertiolecta in a CSG water medium. All trials were run for 5 days. The reactor was filled with 3L CSG water, inoculated with 250ml Dunaliella tertiolecta, and 5ml/L of F2 concentrate was added to provide a nutrient source. The bicarbonate level in the CSG water was increased to a mean concentration level (216 C mg/L), through the addition of sodium bicarbonate (NaHCO3). The pH was controlled at a set point 7.6±0.5. A fluorescent light source was provided, and assessment was made of the effect of aeration on algal growth and carbon stripping. Poor growth was recorded for non-aeration and aeration scenarios, with initial growth rates of 0.0292 g SS/L/d and 0.0303 g SS/L/d, respectively. Over the five day trial periods, algal carbon sequestration quantities of up to 90.9mg/L were achieved, and aeration was found to cause carbon stripping of up to 81.52 mg/L.
Nitrogen and phosphorous removal rates were 0.818mg N/L/d and 0.362 mg P/L/d for the nonaeration trial, and 1.523 mg N/L/d and 0.381 mg P/L/d for the aeration trial. Nutrient depletion P:N ratios of 1:2 to 1:4 were observed.

Due to the poor growth performance, identification was made of the optimal salinity level for growth of Dunaliella Tertiolecta in CSG water (10 mg NaCl/L), trials were then repeated. Results found high growth in the non-aeration and aeration trials, with growth rates of 0.0935 g SS/L/d and 0.0808 g SS/L/d, respectively. Growth performance suggested no overall benefit in adopting aeration for algal growth facilitation. Furthermore, carbon sequestration levels of up to 82.2mg/L were achieved, and carbon aeration was found to cause carbon stripping of up to 72.4 mg/L. Nitrogen and phosphorous removal rates were 2.335 mg N/L/d and 1.156 mg P/L/d for the non-aeration trial, and 2.808 mg N/L/d and 0.959 mg/L/d for the aeration trial. Nutrient depletion P:N ratios of 1:2 to 1:3 were observed. The algal dry mass and total lipid content of the trials were 0.39 g and 24% for the non-aeration, and 0.41 g and 20% for the aeration trial.

The research suggest that the microalgae Dunaliella Tertiolecta has the potential to be grown in CSG water, in an open pond settings, for biofuel production purposes. Trials found that the microalgae Dunaliella Tertiolecta would grow in the CSG media, however increased salinity
levels of about 10 g/L were required to achieve optimal growth. This suggests that if the CSG water is subjected to reverse osmosis treatment, then the resulting brine having a high concentrated salinity could be used as an ideal medium to grow the desired algal strand. Further
analysis would be required to determine the economic viability of this process.

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Item Type:	USQ Project
Refereed:	No
Item Status:	Live Archive
Faculty/School / Institute/Centre:	Historic - Faculty of Engineering and Surveying - Department of Agricultural, Civil and Environmental Engineering (Up to 30 Jun 2013)
Supervisors:	Aravinthan, Vasanthadevi
Date Deposited:	17 Sep 2012 02:54
Last Modified:	03 Jul 2013 01:29
Uncontrolled Keywords:	microalgae derived biofuel
Fields of Research (2008):	09 Engineering > 0902 Automotive Engineering > 090201 Automotive Combustion and Fuel Engineering (incl. Alternative/Renewable Fuels) 09 Engineering > 0902 Automotive Engineering > 090202 Automotive Engineering Materials
Fields of Research (2020):	40 ENGINEERING > 4002 Automotive engineering > 400201 Automotive combustion and fuel engineering 40 ENGINEERING > 4002 Automotive engineering > 400202 Automotive engineering materials
URI:	https://sear.unisq.edu.au/id/eprint/21946

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