Upping use of algae in feed may reduce global warming rate

A group of researchers with the International Institute for Applied Systems Analysis (IIASA) evaluated potential outcomes for the climate system stemming from the use of microalgae biomass as animal feed and alternative fuel along with carbon capture and sequestration (CCS).

“It’s critical, if we think about arable land as a scare resource, that we take care of this resource,”​ said lead researcher Brian Walsh, scholar with IIASA.

The project and analysis came about as an exploration of what could be achieved with large-scale algae production after examining small scale efforts, he told FeedNavigator. Currently, there are already systems that can produce up to 150 dry tons of algae per hectare per year.

Using algae to make animal feed helps decouple bioenergy production from food prices, he said, and eliminates competition between the two systems for the same arable land.

“We have demonstrated the theoretical and technological potential of microalgal feedstock to relieve land scarcity, allowing arable land to be leveraged to produce cleaner energy while addressing the threats of climate change, deforestation, eutrophication, and food and water scarcity,” ​said researchers. “In recognition of the fact that these systems can be engineered to produce biomass without generating a commensurate burden on critical ecosystems cycles and services, algacultural systems have already been established at some experimental farms to overcome biomass shortages in dry seasons.”​

Walsh said the next step for the research is evaluation and work to turn the project into a white paper where it could be offered to policy circles: “The goal is to join the conversation."​​

Why algae?​

To slow the increases in mean global surface temperatures to less than two degrees, the net anthropogenic carbon emissions need to be eliminated, said researchers.

“Livestock production currently accounts for roughly one fifth of total anthropogenic greenhouse gas emissions, a footprint which must be expected to grow as meat demand scales with the size and affluence of global populations,” ​they said. “Given a dwindling global carbon budget, a carbon-negative energy sector stands out as an obvious target for offsetting sustained or growing emissions from other sectors.”​

Photosynthesis is the least expensive and most efficient solution to the need for carbon-sequestering technologies, said researchers. But, large-scale biomass generation for energy uses could change land use or raise food prices.

Mass algae-culture could be used to create biomass for energy production that would not offer some of the same risks, noted the team. “More promisingly, however, microalgae can also be exploited as a source of animal feedstock, offsetting anticipated growth in demand for meat and dairy while allowing vast areas of agricultural land to be repurposed for biomass production or habitat restoration,”​ added the authors.

“Algacultural production systems can be constructed on degraded or otherwise unproductive land unsuitable for conventional feedstocks, mitigating competition for arable land as well as tradeoffs between bioenergy production and food security,” ​they said. ​

Algae also can filter nitrogen and phosphorus from wastewater or manure, they said, and the necessary CO2 can be drawn from the atmosphere or added with flue gas.

“Relative to conventional feeds, field studies have established neutral-to-positive effects on feed palatability, overall livestock growth and mortality rates, and meat taste for diets containing up to 10, 33, and 45% microalgae for poultry, pigs, and ruminants, respectively,”​ said the researchers. “As a result, microalgae represents a potential replacement for soy, fishmeal, and other conventional sources of protein.”​

Much of the focus on using microalgae has been on its inclusion in biofuels, said Walsh. However, it offers more promise as a feed ingredient.

Scenarios and results ​

The researchers ran a set of simulations to model future land use and emissions. The situations tested included a business-as-usual (BAU) model where production continues along current trends; a bioenergy system with expanded bioenergy and renewable energy production; an Alg-Fuel situation where algae was produced for energy; and an Alg-Feed scenario where it was used as a feedstock.

In the algae production systems, on-shore generation is considered to use non-arable land, recycled fresh or brackish water and gain nutrients from wastewater, agricultural runoff or manure. “In these scenarios [Alg-Fuel and Alg-Feed], we impose exogenously the construction of 25-50 Mha of algaculture at a constant rate between 2015 and 2060,”​ they added.

In the feed scenario the output met up to 40% of the global feed demand, they said. Agro-biomass was able to expand production using former pasture or feed crop land – the swap would reduce fossil fuel use to less than 20% of the primary energy supply.

“Significant expansion of renewable energies combines with avoided land use change emissions in the Alg-Feed scenario to achieve an emissions pathway between RCPs [representative concentration pathways] 2.6 and 4.5,” ​they said. “Even before additional potential emissions benefits from CCS, this strategy is expected to reduce global temperature change 0.7​∘C relative to BAU by 2100.”​

Replacing 10% of feed ingredients with algae would reduce atmospheric carbon concentration and reduce warming to below 2 degrees a year by 2100 if other steps were also taken, said researchers. If 40% of feed is replaced, then net zero emissions would be reached if 25% of emissions from the energy sector are sequestered.

“Microalgal feedstock does not need to be maximized in order to contribute to the decarbonization of the energy and land use sectors,” ​they said. “On any scale, algaculture creates the possibility of freeing large areas of arable land for biomass production. While the magnitude of the resulting carbon sink varies, microalgal feedstock holds significantly more promise than marginal improvements including conventional methods of agricultural intensification and algal biofuels, and is much closer to reality than other potentially transformational alternatives.”​

Source: Carbon Balance and Management

Title: New feed sources key to ambitious climate targets

DOI: 10.1186/s13021-015-0040-7​

Authors: Brian Walsh, Felicjan Rydzak, Amanda Palazzo, Florian Kraxner, Mario Herrero, Peer Schenk, Philippe Ciais, Ivan Janssens, Josep Peñuelas, Anneliese Niederl-Schmidinger and Michael Obersteiner