World-first wastewater algal bio-crude oil demonstration

The world’s largest wastewater treatment High Rate Algal Pond (HRAP) system with conversion of harvested algal biomass to biofuel has been constructed at the Christchurch (Chch) Wastewater Treatment Plant and will be operated over two years to demonstrate wastewater treatment performance. This paper describes HRAP wastewater treatment technology and the associated co-benefits, discusses the design, construction and operation of the Chch HRAP system and presents preliminary data on wastewater treatment efficiency and algal productivity from the first summer of operation. The 5 ha HRAP demonstration system was constructed within an existing oxidation pond. Four adjoining 1.25 ha single loop raceway HRAPs were formed by earthwork and the bottom of the HRAP was left unlined to demonstrate cost-effective construction and self-sealing. Each HRAP included a paddlewheel, CO2 addition sump, and had an algal harvester with inflow pump and harvested algae pump. Preliminary results from the first summer of operation without CO2 addition showed that the four replicate demonstration HRAPs had similar wastewater treatment efficiency (~66% removal BOD5; ~86% removal of fBOD5; ~76% removal ammoniacal-N removal and ~35% removal of DRP); algal species composition and productivity (equivalent to >30 t ha -1.y). Harvested algal biomass had a solids content of ~1% volatile solids. These preliminary results show reasonable replication of treatment performance and algal productivity between the four demonstration HRAP and were similar to previous results for pilot-scale HRAP with CO2 addition during NZ summer conditions; and further indicate the potential for energy efficient and effective tertiary-level wastewater treatment using HRAP.