INNOVATIVE USE OF ALGAL-BACTERIAL TREATMENT
Wastewater is most frequently treated by bacteria using an aerobic process. Organic substances that come with the wastewater are consumed by bacteria, which need a lot of oxygen in this process. We supply oxygen with aeration. Optimally, the process is designed in such a way that bacteria convert these organic substances into CO2 that is released to the atmosphere; some of the organics are inevitably built into the biomass which is removed and called wastewater sludge.
When we add algae to such system, they can consume the CO2 produced by bacteria and convert it into their own biomass using solar light (photosynthesis). A side product of this process is oxygen; its availability replaces the need for aeration. Algal-bacterial process thus not only eliminates the energy requirement of aeration, but also partially embodies the energy contained in the wastewater into the biomass which can then be used for other purposes or to recover energy into biogas. As result, the treatment is much cheaper due to the reduced costs of aeration, CO2 is recycled rather than contributing to the climate change, and biomass can be further utilized (and sold). To put this in perspective of some figures: a cubic metre of typical municipal wastewater contains up to 7 kWh in dissolved organics, conventionally we have to spend additional 0,5 kWh for aeration; using algal-bacterial process we recover significant part of this energy and at the same time recycle CO2 that would otherwise be released to the atmosphere.
Compared to conventional wastewater treatment, algal bacterial treatment produces significantly more biomass and several project consortia members are working on exploitation of such algal biomass.
DESIGN OF 3 DEMO SITES FOR WASTEWATER TREATMENT OF F&B INDUSTRY
Three demo sites are being constructed (Italy, Slovenia and Israel).
The demo sites are all based on existing infrastructure that will be converted and extended to allow treatment of salty wastewater. Archimede Ricerche (Camporosso, Italy) will use their existing high performance ponds to treat water from the milk industry, KOTO and Algen (Ljubljana, Slovenia) will use existing pond, built within the AlgaeBioGas project, to treat the water from hide warehouse (representative of tannery wastewater), and Arava (Hazeva, Israel) will use water from the fish farming by algae that can be used for food.
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FINDING THE MOST EFFICIENT ALGAE AND BACTERIA THAT WILL TREAT WASTEWATER WITH HIGH SALINITY
One of the main premises of the Saltgae project is the fact that there are many more (known) algal species tolerating high salinity than there are (known) bacterial
species. Algal bacterial treatment of such water thus seems to be the technology of choice. In the first year of the project, we have been studying algal bacterial community used for wastewater treatment. A detailed genetic microbial community analysis has been done by Parco Technologico Padano (Lodi, Italy) to study the algal bacterial communities present in algal bacterial wastewater ponds of Algen and KOTO (Ljubljana, Slovenia). The observed ecological diversity was a big surprise: genome sequencing revealed many more species that were known from the microscopic observations. This may explain the robustness and adaptability of such communities for the wastewater treatment. Algal bacterial communities represent complex
interconnected systems with only limited modelling done so far. Both, a good verified model and assignment of ecological diversity into such model will enable us to control the complex processes to be stable and perform well thus not only reducing the organic content of the water, but also ammonia, nitrates and phosphates that are – if released with the wastewater – a burden to the environment.
DEVELOPMENT OF A SALT-TOLERANT ANAEROBIC DIGESTION
Converting organic matter to energy is best achieved by the methanogenic archea as used in many biogas installations. Archea are known to be salt sensitive and they cannot survive elevated salinity levels. To overcome this problem, three measures are used. Results from laboratory testing of anaerobic digestion enable us to design pilot scale equipment that will be used at the demo sites.