Effect of temperature on algal biomass production and nutrient removal in synthetic biogas slurry

The effluent of anaerobic reactors (biogas slurry), which is widespread today, contains a significant amount of nutrients. The compounds C, N and P in the biogas sludge composition should be removed because they are not desired in the receiving environment. The known biological processes for nitrogen removal in waters is very expensive and complicated. Investigations are increasing day by day for the use of algal reactors which are thought to be less energy and easier to operation. This study was conducted to investigate the effect of temperature on nutrient removal and the growth of mixed culture algae in synthetic biogas sludge. The study was carried out in triplicated parallel reactor at white light (12 hour light / 12 hour dark, light intensity: 37.1 ± 5.2 µmol/m-2.s-1) and 15°C, 25°C and 35°C of temperature under laboratory conditions. Studies continued until biomass production continued in batch reactors inoculated with mixed culture algae. Although the amount of COD, NH4-N and PO4-P removal and algal biomass productivity in the biogas slurry for all three temperatures were very close, the incubation times for temperatures of 15°C, 25°C and 35°C were determined as 131 days, 78 days and 38 days. In kinetic studies, COD, NH4-N, PO4-P removal and biomass concentration increase rates were found to be more appropriate to 0th degree. The effect of temperature on kinetic coefficients was also determined. The temperature correction coefficient (Ɵ) was found to be 1.065, 1.048, 1.056 and 1.067 for COD, NH4-N, PO4-P and biomass growth, respectively. The study showed that significant COD was also removed in addition to N and P removal from biogas slurry. As a result, it was determined that temperature is an important factor in nutrient removal with mixed culture algae from biogas slurry.