Algae from Waste for Combined Biodiesel and Biogas Production (ALDIGA)

Project description

The main goal was to design and validate a new integrated concept of biowaste-to-energy based on algae and biogas production. The aim was to develop a process requiring minimal external energy involving efficient utilization of all sidestreams generated in addition to the main fuel streams, biodiesel and biomethane. New co-operation models relating to clean energy including various utilization of methane, service and utility providers for biodiesel production, opportunities for industrial waste utilization for renewable energy will be proposed and tested. 

Results generated at SYKE

The main task of SYKE was to examine the potential of growing different algal species in municipal wastewater, and we conducted different experiments in both treated and untreated municipal wastewater (originating from Suomenoja wastewater treatment plant).  

Screening in treated wastewater

Six different algal species were used in this test: Chlorella protothecoides, Chlorella pyrenoidosa, Euglena gracilis, Scenedesmus sp, Hematococcus sp and Nitzchia sp. The growth in wastewater was compared with growth in a reference medium, WC medium. The main results were that the algae grew as good as or better in the treated wastewater compared with the reference medium, and no inhibitory effect was observed. There were natural occurring algae in the treated wastewater that started to grow as well in the wastewater treatment. This natural community consisted of several difference species, mainly green algae and cyanobacteria. The growth of these algae was higher than some of the species introduced in the experiment, and we tested the characteristics of this natural community in further experiments.

Screening in untreated wastewater

For the screening of untreated wastewater, the wastewater was filtered through GF/D filters (1.5 µm) to remove particles and the natural community of algae. Three concentrations were used: 100% wastewater and dilutions with de-ionized water to concentrations of 10% and 50% wastewater. 18 different monocultures of algae were used. The growth of the algae was highly species specific. Some algae likeAnabaena cylindrica grew well in all concentrations of wastewater, whereas other species e.g. Cyclotella meneghiniana had clearly lower growth in the 100% wastewater treatment.

Nutrient concentrations in the wastewater were approximately 5 mg total phosphorus (TP) and 15 mg total nitrogen (TN) after filtration, and the N was mostly in the form of ammonium. Ammonium have toxic effects on algae at high concentration, and the species specific growth in the different wastewater concentration was most likely a reflection of different tolerance ammonium.

Testing community effect

After the initial screening of algal growth in untreated municipal wastewater, we carried out further experiments to test the effect of biodiversity on biomass growth and removal of nutrients. The experiment was set up with 12 individual species and random combinations of 3, 5 and 7 species. Accumulation of biomass and algal health was measured daily and inorganic nutrients weekly.

Our main hypothesis was the increasing biodiversity would increase the overall growth rate and nutrient uptake. Preliminary analysis of the data suggests that this is the case, strengthening our hypothesis. This would imply that a community of algae would function better as a biofilter, removing nutrients from wastewater, than a monoculture.

More information

Senior Research Scientist Kristian Spilling, Finnish Environment Institute SYKE, Phone: +358 400 148 526,

Published 2013-04-24 at 10:06, updated 2013-04-24 at 10:06