Algae Cultivation: Worse Carbon Footprint Than Corn

You can use or misuse every idea or technology. Some algae might be interesting for nutrition because of their vitamins and minerals, othere might be a source of energy. Perhaps some could be used to clean water and gain some energy at the same time. May be their footprint is not that bad. We have to find out. Silly is to expect one idea or one technology to be the only possible solution for a whole problem.

But thinking of solar energy, I contradict myself with a dream. If we succeed in storing energy much better, we won’t have to produce energy at all. Even the worst performance photo voltaic device might do, because there is a lot of Energy, the sun sends us daily. Imagine a worldwide power grid and collecting stations wherever possible. We even might have few need to store energy, because the lightened part of the globe could supply the dark. But then, where will you all go to, all the ones who try to sell us your produced energy?

Yes, biofuels production emit CO2 (greenhouse gas) as do most biological processes, but it’s the carbon taken out of the current environment being recycled by these biological processes, which is a whole lot different than the release of the sequestered carbon in fossil fuels from millions of years ago being released into the current environment. You have to look at the net current impacts, not just that an amount of CO2 is emitted from the production/utilization process. This same bad accounting has been used to undermine biofuels progress since the 70’s.

No CO2 is best, recycling current CO2 is next best, releasing CO2 from millions of years ago resulting in a net increase is not so good. Most biofuels solutions are feasible now. While we’re waiting for best, next best is better than not so good. As the old saying goes, what solution does the current energy industry favor, which ever one is just 5 years away.

The conclusions of this report are misleading, in my opinion. I have read the supporting material freely accessible (I did not buy access to the full paper). First, I was surprised at the number of errors found, e.g. missing decimal points. (For example, algae productivity in table S8 is off by a factor of 100, and on page S18 the number of paddles is 10/ha, or 1 per 100m2, but there are 10,000m2 in a ha.)

One nice feature of this study is using a Functional Unit (FU) of the per capita (per person) energy use in the US—317GJ and indicating the area, water, and energy in this unit system.

Another important point is that the units compared are HHV values of the biomass, not converted biofuel or even burned biomass to generate energy (a fraction of the LHV). Unfortunately, the supporting material also has problems with missing units. For corn ethanol or switchgrass, substantially more energy is required to create ethanol biofuel—in fact most of the energy is used in this conversion, not agriculture.

The crux the problem with high water and energy use is the water and energy (MJ) assigned to inputs to the algae ponds. In the supporting material, the details are hidden for how the totals are arrived, but there are some hints that partly explain the water/energy for algae. A great deal of explanation covers water that needs to be replenished as part of extraction, and energy of operations, but totals for these are omitted. But extraction and evaporation are 470 and 144 m3/ha-y compared to 2350 rainfall in San Diego. (Rainfall is much greater than water usage of operations.) It is difficult to check energy of operations due to errors in the supporting material, but the equation supplied assumes that operating energy (electricity) is 3% of algae energy. Enough energy of operations could be obtained from solar panels covering the paddlewheels (or could be placed along the dikes separating raceways). So operations water is less than rainfall, and operational electricity is less than extra space available for possible solar panels—not a problem in water or energy.

According to the supporting material, water and energy (supposedly more than the algae energy) are associated with CO2 infusion, fertilizer (urea and phosphate), and alum flocculant.  The amount assumed for alum is not specified. But most of the water and energy is assigned to the CO2 added to the algae.  Per FU (energy/person) 198GJ of 317 (64% overhead) is the cost of CO2 provided—but no benefit of electricity generated is assumed. Also, 51,496m3 of water is used to generate this (maybe from cooling towers?). This alone is 2 orders of magnitude more than the water used for operations. The water and CO2 is bogus—this could be nearly free if CO2 is provided by biogas digesters, etc. Only the cost of bubbling the CO2 would apply.

A high cost is also assigned to urea & phosphates added as fertilizer—25% overhead in energy (71+10/317GJ) and 4562+2756m3 of water per FU. Note that only 7m3 of water is used in the algae itself. Fertilizer is a high cost for corn, etc., but it is hard to compare because the inputs are not itemized, and because the cost of conversion into usable fuel is not included. So algae looks bad and corn looks good.

Also not detailed in the supporting material is the indirect cost to separate algae from water with flocculants. Alum is assumed and the energy+water per kg of alum is specified, but not kg/ha (or kg per Mg algae extracted). With current technology, the cost of algae biodiesel is very high. But many startup companies are developing advances in technology that can lower cost of growing and extracting algae. For biodiesel to be practical, a low-energy cost effective means of extraction still needs to be developed. If such a method is found, the analysis in the Clarens report is wrong. (I could not check even current assumptions because of missing information in the supporting material.)

If a process to separate oil from algae is developed, the oil contains no N or P, so the remnants after separation could be returned to the algae ponds for recycling the N and P. Bacteria can convert waste matter into CO2, N and, P to feed algae. So assumptions about algae production with oil extraction could be fundamentally changed.

One aspect of this report is the possibility for using wastewater as feedstock for algae ponds. The DOE/NREL Aquatic Species Program report from 1996 summarizes current algae production and mentions the Sunnyvale, CA (where I live) wastewater treatment plant with a 180ha algae pond. The sewage treatment plant uses landfill and digester biogas to generate electricity. The CO2 from this would supply about 100ha of algae ponds at rates assumed in the Clarens report. The fertilizer in sewage could be used in lieu of energy intensive additives. Garden waste in Sunnyvale is sent to San Jose where a biogas digester is to be built (the Zanker facility), so additional possible source of energy and CO2.