Tofu is one of favourite daily meal in Indonesia. It is produced freshly in some small to large-scale industries, and generates a large volume of wastewater. Generally, untreated wastewater from tofu industries in Indonesia is still directly disposed to the environment that can cause severe pollution in water resources. Tofu wastewater contains very high organic compounds and nutrients, but it has an acidic pH. The possibility of utilizing tofu wastewater as a cultivation medium for microalgae is intriguing. The objective of this research was to utilize tofu wastewater as a cultivation medium for Chlorella vulgaris and Arthrospira platensis. Cultivation of microalgae was conducted for ten days using 3, 5, and 10 % of diluted tofu wastewater. For comparison, the tofu wastewater anaerobic digestion effluent (TW-ADE) was used as the medium. Walne medium was used as a positive control, and distilled water was used as a negative control. Both microalgae showed the highest biomass and protein production was in Walne medium (positive control), followed in 5% tofu wastewater medium for C. vulgaris, and 3 % tofu wastewater medium for A. platensis. The highest chlorophylls content of C. vulgaris and A. platensis was in 5 % tofu wastewater and Walne medium, respectively. The most top carotenoid content of C. vulgaris and A. platensis was in 5 % and 10 % tofu wastewater medium, respectively. On the other hand, biomass, chlorophylls, carotenoids, and protein content of both microalgae in TW-ADE medium had the lowest result. Cultivation of C. vulgaris and A. platensis in tofu waste medium offer a wide range of environmental and economic benefits, as a sustainable strategy to treat wastewater and produce high-value products from microalgae.

Liquid waste from tofu production can be treated by anaerobic digestion to produce biogas. The main components of biogas are CH4 (methane) and CO2 (carbon dioxide), but usually, biogas also contains water, H2S (hydrogen sulfide) or other sulfuric compounds, and other trace gases and impurities. Therefore, purification and upgrading the biogas are necessary to improve its quality as a fuel. One of the alternative methods of biogas purification is by reducing CO2 content using microalgae culture, which involves the ability of microalgae to use the CO2 in biogas for photosynthesis. In this research, Chlorella vulgaris and Arthrospira platensis were tested for their ability to grow under biogas produced from anaerobic digestion of tofu wastewater aeration in a batch system. The results indicated that Chlorella vulgaris could grow better than Arthrospira platensis on the same flow rate of input biogas. Despite the ability of Chlorella vulgaris to use CO2 in biogas, the cell numbers in culture aerated with biogas were lower than with air, which indicated an inhibition by biogas on Chlorella vulgaris growth.