Pacific Rim BioEnergy

Fuel from Algae

Heterotrophic vs. Photoautotrophic Algae Cultures

Posted on | February 25, 2011 | 3 Comments

In a follow-up to my last post it is my belief that the Canadian government will be much more responsive in assisting the alternative fuels industry based on a climate change approach as opposed to that of energy security. That being said what is the greenest approach to cultivating algae in British Columbia? I put some quick flow charts together outlining the different issues and benefits of these two leading agricultural processes.

Photoautotrophic System
Photobioreactor Environmental Flowchart

Environmental Benefits

  • Recycled industrial CO2 emissions offers algae productivity
  • Decreased land requirements due to increase algae productivity
  • Minimized impact on natural habitats
  • Designed in scalable modules, limited only by CO2 capital/operational costs and land availability
  • Continuous/cascading production allows the cultivation process to continue with less frequent systme shut-downs for cleaning and inoculation

Environmental Concerns

  • Efficient light delivery and distribution are principle obstacles to scale-up
  • Energy demand may be a challenge in bringing this to commercial scale
  • Requires a continuous input of carbon dioxide (energy drain and concentration of heavy metals)
  • Exotic and potentially invasive algal species could threaten the integrity of local and regional ecosystmes, e.g., if escaped through released waste water

Environmental Unknowns

  • Implications of energy demand
  • Very few large-scale closed photobioreactor systems have been implemented, so the feasibility is difficult to ascertain
  • Algae to overcome challenges of efficient cultivation

Heterotrophic System

Environmental Benefits

  • Minimized water usage and management
  • Minimized energy inputs due to high cell densities, low water content, and exclusion of light
  • Reduced landfill by use of cellulosic “wastes” that result in methane emissions
  • Applicable in most climates and regions with limited impact on land use or adjacent ecosystems
  • Scalability is based on a group of feedstock types that are locally available

Environmental Concerns

  • Indirect water burden if feedstock is derived from an irrigated crop
  • Potential for organic substrates on arable land
  • Feedstock could be limited by seasonal availability
  • Organic material processed by energy-intensive hydrolysis before use as a feedstock

Environmental Unknowns

  • The energy imbalance, including inputs
  • Direct and indirect water use data is limited and changes from region to region
  • Potential environmental costs and benefits associated with other green technologies competing for those same waist feed-stocks
  • Some feedstock sources may be more sustainable than others

Environmental Summary


Clearly the most significant environmental concern for a Canadian / British Columbian based photobioreactor will be the electrical drain of utilizing a hybrid, solar / artificial illumination system. What is the energy return for the creation of a liquid fuel? Fortunately here in British Columbia we are one of the cleanest provincial / state environments in North America. A significant amount of our electrical energy comes from renewable sources. With the large volumes of CO2 that algae can consume it would be interesting to see just how much this process could further bring down our carbon footprint.


It can be assumed that the electrical consumption of processing the cellulosic waist and maintaining the fermentors will be less than that of the PBRs. The difficulty comes in analyzing the indirect impact associated with the algae feedstock. We know that the CO2 consumed and processed by this feedstock is significantly less than would have been processed directly from the algae in a photobioreactor, but this is not the best way to measure the reduction in greenhouse gas emissions. If this cellulosic waist is left to rot, it will emit methane gas. Methane is believed to be several times more potent than CO2 when it comes to climate change. The difficulty is there is significant debate over how potent it actually is.


There are many other ‘cellulosic waist to energy’ solutions that compete for fermentation feedstock and the key here is big picture environmental reform. Without running both techniques side by side within a specific regional economy it will be difficult to definitively gauge wether one technique has a better environmental benefit to concern ratio over the other. That being said, utilizing PBR technology is going to visibly appear to have much more dramatic environmental benefits because you are redirecting unsightly emissions into algae production. Because alternative fuels need both public and governmental support, if both techniques turn out to be equally financially viable, PBRs definitely have a significant marketing edge. In some upcoming posts I will be conducting an analysis of the economics of Heterotrophic vs. Photoautotrophic Algae Cultivation.


3 Responses to “Heterotrophic vs. Photoautotrophic Algae Cultures”

  1. Climate Change could spark an alternative revolution in Canada : Pacific Rim BioEnergy
    February 25th, 2011 @ 8:32 pm

    […] What I would like to focus on is Canadian’s genuine concern for our environment which I believe will kickstart the algae biofuel industry. I believe that the political motivation is there for making dramatic environmental changes that will reduce greenhouse gas emissions in British Columbia. So the question is, “All things being equal, which technique of growing algae in Canada is going to offer us the biggest reduction in our carbon foot print?” Check out my next post where I will be squaring off these two techniques to see if one of them stands out as the environmental technique of choice. […]

  2. Fermentation or Photosynthesis – Continuation : Pacific Rim BioEnergy
    March 6th, 2011 @ 8:54 pm

    […] } This is a follow up on a previous post regarding the environmental benefits of Heterotrophic vs. Photoautotrophic Cultures. Before moving ahead with an algae solution, you need to make a determination as to what would be […]

  3. David
    July 8th, 2011 @ 3:57 pm

    Great summary. Hope Canada considers the most environmentally, sustainable, modular, and durable photobioreactor solution: closed-loop glass tubing systems :

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