Sustainable microalgae biomass production integrated with wastewater treatment plant

Microalgae is a promising organism to produce biodiesel, high value products, fertilizer or industrial chemicals. Especially algal biofuel is very important for renewable and carbon neutral liquid transportation fuels production by using municipal wastewater as a nutrient source. Most of studies in literature about microalgae production with wastewater on optimizing environmental conditions or determinig capability of microalgae in short term experimental periods. The aim of this research was perfomed to evaluate the use of wastewater without sterilization and filtration to produce sustainable microalgae biomass in 90 days period. In this experiment, tertiary treatment effluent and centrate from dewatered anaerobically digested sludge from the wastewater treatment plant was used. The used wastewaster was fed to the lab scale 60 L reactor in order to cultivate Chlorella vulgaris biomass with the operating conditions given in current literature. In the preliminary phase of this research; the 23 days reactor operation was performed by providing a constant follow-up analysis along with short-term experimental reactor operation studies without a constant follow analysis. In this way, problems caused from environmental conditions were identified that may be seen during long-term operation. The identified problems are; the biomass precipitation within the reactor, the increasing or decreasing of culture temperature, the increase in the pH value due to algal anabolic activities, the decrease in the pH when CO2 was given to culture constantly, the necessity for time-controlled lighting, alkalinity requirement depending on ammonium removal. The reactor was designed to solve the identified problems and provide the long-term cultivation of algal biomass under optimum conditions. The reactor was developed by; the choosing of equipment to provide sufficient mixing, automatic temperature control system, automatic CO2 supply system according to set pH value, open and closed irradiation system in a determined time and alkalinity dosage equipment. In this way, the reactor system was designed to work automatically under optimum conditions. Lab scale raceway reactor was used in the experiment. In the trial operation stage, "Recirculated Sedimentation" system was developed to solve harvesting problem. During preliminary experimental period of this research, it has been understood that Recirculated Sedimentation system has a big potential to facilitate sustainable biomass production. In the phase of biomass production, other than the problems resulting from the environmental conditions, problems can be encountered from the biological process. Therefore to evaluate the effect of the Recirculated Sedimentation system on the biological-based problems, the experiment timeline of the research was performed in three stages. The specific acquirements from Recirculated Sedimentation system are as follows; • Contaminants were removed from the culture medium by passing all volume of culture through "Recirculated Sedimentation" by 5 times per day. • The formation of the biofilm could be seen in 3 days, this duration was observed to be 7 days when "Recirculated Sedimentation" was used. Thus, the rate of biofilm formation on the inner walls of the reactor was reduced. • The increase of the bacterial population within the culture medium was suppressed. • The predominating of the nitrifiers in the removal of the ammonium was prevented. • The suspended solids holding capacity of the open reactor was improved to a value of 770 mg L-1 from the maximum 500 mg L-1 accepted in the literature. • The ammonium removal rate was improved to about 30 mg L-1 d-1.