Case study – Kujalan Komposti Oy
The concept of integrating microalgal cultivation into a biowaste management
center was assessed using Kujalan Komposti Oy’s process as a case study. The
study included a scenario in which the algae would utilize spill heat and CO2 from
the composting plant and the residual microalgal biomass after lipid extraction
would be utilized as a biogas co-substrate Fig. 5). The area allocated for algal
cultivation was 2.2 ha (Fig. 6). The feasibility study was done using results from
laboratory scale tests (algal growth rates and removal of nutrients originating from
organic waste streams). Due to restricted resources, the role of illumination, CO2,
nutrients and heat variation were not examinedThe case study assessed the reserved area’s (Fig. 6) potential for three scenarios:
a worst-case (low harvesting density of 0.6 g/l per 6 d, an average of the lowest
values found in the literature), a moderate case (3.0 g/l per 6 d, (literature and
project result average) and an optimal case (5.0 g/l per 6 d, an average of the
maximum values found in the literature). The scenarios modelled the biomass
productivity and determined the area and water requirements in the three situations.
This gave a range and understanding of the minimum and maximum capacity of
the cultivation facility area.
The results showed that with the algal production rates presented, the reserved
area in Kujala (2.2 ha) was far too small for the targeted biomass production
60 000 t/a, (Kujalan Komposti Oy 2011). In addition the corresponding water consumption
would be 14 700–44 100 m3 per year of raw waste water, meaning significant
pumping and treatment costs (Järvelin 2011).