Carbon capture and consumption

 

Could it Eliminate the Need for Wastewater Aeration?

Algal blooms have always proved a challenge for the water industry. Yet could this organic matter,with the help of wastewater nutrients, be turned into a biofuel and help alleviate fossil fuel shortages? Tom Freyberg investigates the European funded All-Gas project.

First generation biofuels from crops never really bloomed into a fruitful harvest. Opponents criticized using up valuable land to grow crops and fuel the cars of the rich, instead of filling the stomachs of the poor. Second generation biofuels – made from biomass - have proved a lot harder to extract the required fuel and fully crack.

And then along came algae. Unlike first generation biofuels, algae can be grown using land and water not suitable for plant and food production.

Consuming solar energy and reproducing itself, algae generates a type of oil that has a similar molecular structure to petroleum products produced today. As if this wasn't enough – algae growth also consumes carbon dioxide, a known major greenhouse gas (GHG).

As a result of the apparent benefits the race is on to commercialize second and now third generation biofuels, in the case of algae. Continents and companies are putting money where their mouths are to find out how what we thought was simply a green weed growing in the sea could be the answer to inevitable fossil fuel shortages.

Algal culture ponds are used to grow and harvest micro-algae using nutrients contained in wastewater

Earlier this year US President Barack Obama announced that the Department of Energy would make $14 million available to support research and development into biofuels from algae. The Department has suggested that up to 17% of the US' imported oil for transportation could be replaced with biofuels derived from the substance.

Meanwhile Europe is going even further and mandating the gradual replacement of fossil fuels to biofuels. An EU Directive stipulates that by 2020 a total of 20% of energy needs should be produced by renewable fuels. A further requirement is that 10% of biofuels need to be met through transport related activities.

Even UK government backed agency the Carbon Trust has forecast that by 2030, algae-based biofuels could replace more than 70 billion litres of fossil fuels used every year around the world in road transportation and aviation.

Nutrients: burden or blessing?

So far, so good. Yet while algae derived biofuels sound like an answer to inevitable fossil fuel shortages, two challenges remain: space and nutrients. The first challenge will be addressed later but on the topic of nutrients, phosphorous and ammonia are required alongside sun light and carbon dioxide to "feed" the algae. And with up to 30% of operating costs at algae farms attributed to buying and adding in such nutrients, it's a notable expense.

It is in response to this particular challenge where the wastewater sector could play its part, with untreated effluent being a known source of phosphorous and other nutrients. An EU funded project aims to bring together the challenge and solution and link the water and biofuel industries together.

The €12 million, five-year project is starting at water management company aqualia's wastewater treatment plant in Chiclana, Southern Spain and is backed by the European Union as part of its FP7 program – supporting energy-related projects - with six partners.

Called All-Gas, which translates into algae in Spanish, the project will see "algal culture ponds" being used to grow micro-algae using nutrients contained in wastewater, such as phosphorous. A 10-hectare site will eventually be needed for the project. Frank Rogalla, head of R&D at aqualia, says nutrients are abundant in wastewater, so it makes sense to incorporate the two industries.

Traditionally aeration processes at wastewater treatment plants are heavy energy users, accounting for up to 30% of a facility's operating costs. In the US, according to the Environmental Protection Agency, drinking water and wastewater systems account for between 3% and 4% of national energy consumption alone.

However, Rogalla later told Water & Wastewater International magazine (WWi) that growing algae with wastewater can eliminate the need for aeration, thus reducing energy use.

He said: "We have converted our treatment to anaeraobic pre-treatment, meaning we will generate biogas from the start instead of destroying organic matter, so no aeration will be needed. From the 0.5 kWh [kilowatt-hour] per m³ which you generally spend for aeration, that will be completely gone. We will have a net output of energy from algae conversion either to oils or to gas. So that's why you get this positive output of 0.4 kWh per m³ of wastewater treated."

Rogalla added: "It will not cost more than traditional wastewater treatment, which costs about 0.2 Euros per cubic metre. We think we will use the same operational costs but instead of consuming energy we will produce additional benefit, meaning we generate about 0.2 Euros per cubic metre in additional profit from the fuel. Our aim is to be cost neutral."

So the question has to be asked of how, technically, can the proposed treatment eliminate the need for wastewater aeration? The answer, as Rogalla later tells WWi, is through the initial conversion to biogas.

Compared to nitrification and dentrification to eliminate nutrients in conventional wastewater treatment, a process Rogalla says consumes about 5 kWh/kg Nitrogen during aeration, All-Gas will use an alternative conversion. Firstly anaerobic pre-treatment will convert most organic matter into biogas (CH4 and CO₂). Algae will then take up the nitrogen and phosphorous.

Productive: instead of using traditional nitrification and dentrification processes, organic matter will instead be converted into biogas

As the algae will transform most nutrients into biomass, they will also produce O2 in the process, as CO₂ is taken up and oxygen released in their metabolic process. As a result, according to Rogalla, aeration is not necessary. Most organic carbon is transformed into energy (via biogas), nutrients are incorporated into algae, which produce oxygen for any polishing action necessary.

An overview of aqualia's wastewater treatment plant in Chiclana, Southern Spain

"It only seems logical to use the wastewater nutrients to grow algae biomass; on the one hand saving the aeration energy, on the other hand the algae fertilizer and cleaning wastewater without the occurrence of useless sludge, but producing biofuels and added value instead," Rogalla adds.

CROATIAN CENTER of RENEWABLE ENERGY SOURCES (CCRES)

  special thanks to U.S. Department of Energy | USA.gov

  and WaterWorld, Industrial WaterWorld

Space challenges

Addressing the second challenge of space requirements to harness algae ponds, for a commercial scale operation it's estimated that a 10 hectare site is required (roughly 10 football pitches). Yet when compared to the oil yields of other crops, algae still proves favourable.

Data from US-based National Renewable Energy Laboratory (NREL) show that oil yields from soybeans work out at 400 litres/hectare/year, which compares to 6,000 for palm oil and theoretically, a potential 60,000 for microalgae. For barrels/hectare/year, the same comparison yields 2.5 for soybeans, 36 for palm oil and a minimum of 360 for microalgae.

As predictions go, the production of 60,000 litres of biofuel from only one hectare of algae is optimistic compared aqualia's aims for the Europe project. If a target set by the EU is reached, then each hectare should produce 20,000 litres of biodiesel. This, the firm says, compares to 5000 litres of biofuel per hectare per year for biofuels such as alcohol from sugar cane or biodiesel from palm oil.

The Spanish project also hopes to use produced biogas from the anaerobic pre-treatment and raw wastewater organic matter as car fuel, with each hectare touted to treat about 400 m³ per day.

Statistics to one side, the challenge of space remains. Booming urban populations are expanding closer to rural wastewater treatment plants but at the same communities insist on an 'out of sight, out of mind' rule when it comes to infrastructure that treats their waste. Rogalla does not think the land issue could impede the development of algae ponds to the majority of wastewater treatment plants. "Algae ponds of course can be put on marginal lands, or even on rooftops," he adds. "In rural areas extensive oxidation ponds for wastewater treatment are not uncommon, not to mention the often unused land areas as buffer zones around wastewater treatment plants.

Biogas generated from wastewater could mean the 0.5 kWh per m3 usually spent on aeration won't be required

"As we do not claim that all fuel can be made from biofuel on land, but only where possible wastewater should be turned into biofuel (excluding mostly big cities), the land issue seems secondary."

Carbon capture and consumption

One further benefit that has made algae growth attractive compared to other fuels is its consumption of Greenhouse Gases (GHG), namely CO₂, in order to grow. While captured carbon consumed by algae will inevitably be released later when used as a fuel in cars, it could still be a step in the right direction in reducing the impact of a world still firmly grasping CO₂ emitting fuel sources.

An article entitled Algal Biofuels: The Process from NREL in a Society for Biological Engineering journal suggests that over two billion tons of CO₂ could be captured by growing algae on the space equivalent to the entire U.S. soybean crop of 63.3 million acres.

Power plants and cement kilns appear to be an ideal match for algae growth, then. Yet, in order for All-Gas to attract seven million Euros worth of funding for its project, the CO₂ had to come from renewable sources. Any fossil fuel burning plants were not permitted, as Denise Green, manager of biofuels across Europe and Africa from Hart Energy Consulting tells WWi.

"This particular call was restricted to projects in which the carbon dioxide supply for the algae cultivation was provided by renewable applications, excluding carbon dioxide from fossil fuel installations," she says.

"However I see no reason why future funding for algae projects could not be provided for research into algae as part of the solution for CO₂ capture for zero emission power generation. If there are objections to using algae from fossil fuel installations for transportation fuels, there are other industries for which algae can be used where this may not be an issue."

Project roll out and commercialisation

The project will be implemented in two stages, with a prototype facility being used to confirm the scale of the full-size plant during the first two years. Once the concept has been proven in full-scale ponds, a 10 hectare site will be developed and operated at commercial scale during the next three years.

Rogalla suggests the project could be rolled out among aqualia's existing facilities along the Mediterranean belt, including Italy, Portugal, Egypt and even South America, all of which have "favourable conditions, meaning the climate is advantageous and the land is available".

Clearly, the conversion of algae to fuel is possible and has been demonstrated on a laboratory scale. It could hold the potential to turn a new leaf for biofuels haunted by their unsuccessful and much criticized first generation brothers. The real interest for the water sector should be the pipe dream of the project to eliminate aeration and turn existing wastewater treatment facilities into biofuel production centres.

The pivotal outcome of the project will be cost. This was proved in the well documented closure of the US Department of Energy's algae research programme in 1996 after nearly 20 years of work. At the time it was estimated that the $40-60/bbl cost of producing algal oil just couldn't compete with petroleum for the foreseeable future.

However, it is the additional methane extracted from raw wastewater and algae residue that differentiates this project. It's not just reliant upon biodiesel produced from the algae. All-Gas has the chance to spearhead Europe into proving that algae biofuel, through the help of wastewater, could eventually be more competitive on a per barrel price with traditional oil.

CCRES ALGAE PROJECT 

part of 

Croatian Center of Renewable Energy Sources (CCRES)