Wastewater algae to biocrude oil

In November, the New Zealand Minister for Energy and Resources, Hon Gerry Brownlee, opened what is claimed to be the largest wastewater algae to biocrude oil demonstration project in the world.

The biocrude from wastewater algae system is a technology for the future. It enables renewable fuel production while achieving low-cost, energy-efficient wastewater treatment, nutrient recovery and greenhouse gas abatement.

The project combines NIWA’s scientific expertise on advanced wastewater treatment and algal production pond technology with Solray’s biocrude oil conversion technology and is hosted by Christchurch City Council at the Christchurch Wastewater Treatment Plant.

“The reality is that no one in the world has done anything on this scale. Our trial aims to show that this complete process can be cost effective and efficient,” says pioneering NIWA Algal Pond Scientist Dr Rupert Craggs.

The process creates value at every step - it treats wastewater, recovers wastewater nutrients as fertiliser, removes carbon dioxide from flue gas and creates biofuel.

The Christchurch wastewater treatment plant has 230 hectares of polishing ponds that are currently used to provide disinfection of the treated wastewater prior to discharge.

It is in one of these ponds that five hectares have been cordoned off by NIWA and converted into a series of specially designed high rate algal ponds (HRAPs) with carbon dioxide (CO₂) addition.

“Adding CO₂ into the ponds enhances wastewater treatment and doubles algal production - biofuel production could be a great co-benefit for the community from its wastewater treatment,” says Dr Craggs.

Another advantage of HRAPs is that the algae growing in these systems can be easily harvested by simple gravity settling - the harvested algal biomass can then be used as either a fertiliser or feed for livestock and aquaculture, or, as in this case with this demonstration, be converted to biofuel and the residue used as fertiliser.

The algae is collected from the harvesters and pumped to Solray’s specially designed ‘Super Critical Water Reactor’ where pressure and heat convert it to biocrude oil. The biocrude, like fossil crude oil, can then be refined into LPG, petrol, kerosene, diesel, bitumen, and other oil-based products.

“This process is essentially the same as nature used many millions of years ago to create the oilfields of the world we are currently rapidly depleting,” says Chris Bathurst, Solray Energy Ltd.

The Foundation for Research Science and Technology-funded three-year trial is in its first year and may, in time, generate fuel that the Christchurch City Council can use to power facilities in the city.

The aim of the project is for NIWA to produce between 150 and 300 tonnes of algae per year from the 5 hectares of wastewater treatment HRAPs. After harvesting and dewatering, these algae could potentially be converted into 45,000-90,000 L (275-550 barrels) of biocrude oil by Solray.

This biocrude oil would normally be converted into a variety of products such as LPG, petrol, kerosene, diesel and bitumen, but if this amount were completely converted to petrol, it would power between 22 and 45 cars per year.

Christchurch City Council’s Unit Manager City Water and Waste, Mark Christison, says, “The City Council is very interested in the project, both in terms of how the high rate algal ponds can remove nutrients from the wastewater and the energy efficiency of super critical water reactor conversion of algal biomass into biocrude oil.”

This trial is the culmination of over 12 years of research into HRAP wastewater treatment by NIWA and will demonstrate the commercial feasibility of algal biofuel production from these advanced wastewater treatment ponds, which are a cost-effective way to upgrade the oxidation ponds currently used to treat the wastewater from many New Zealand communities.