Optimizing Photoperiodism, Growth Media Dilution, and Frequency of Inoculum Addition in Microalgae (Chlorella vulgaris) Culture Using Bi-oslurry (ADDMW) as Growth Media

Abstract

In biogas production using dairy manure, an anaerobic digestion process also produced a by product bioslurry, also known as Anaerobically Digested Dairy Manure Wastewater (ADDMW), which is rich in ammonium and ortophosphate. ADDMW is potentially to be used as growth media to grow autotrophic organism, including microalgae. Furthermore, microalgae potential-ly could reduce organic content in ADDMW, thus play a role as phycoremediator to organic wastewater. In this study we used ADDMW medium for the growth of microalgae, determining its growth kinetics and level of reduction in ammonium and or-thophosphate content in ADDMW. In addition, we also analysed protein content in microalgae biomass for potential use as animal feed. The experiment was conducted using some variations in photoperiodism, i.e., 16:8; 12:12; and 8:16 and medium dilution factor of 2.5 and 5 times. Furthermore, frequency of inoculum addition was also examined i.e., a) 80 mL on day 0 (once); b) 26.67 mL on day 0 to 2 (first 3 days); and c) 8 mL on days 0 to 9 (every day). The results showed that 16:8 photo-period and 5 times medium dilution produced the highest biomass growth and productivity kinetics. Variation in frequency of inoculum addition showed no significant effect to a decrease in ammonium levels but indicated some effect to orthophosphate level. It can be concluded that microalgae can be grown in ADDMW media and can reduce its ammonium and ortophosphate content, as a phycoremediator, before the wastewater is dumped to the river.