• International Journal of Technology (IJTech)
  • Vol 12, No 2 (2021)

Algal-Bacterial Synergy for Lipid Production and Nutrient Removal in Tofu Liquid Waste

Algal-Bacterial Synergy for Lipid Production and Nutrient Removal in Tofu Liquid Waste

Title: Algal-Bacterial Synergy for Lipid Production and Nutrient Removal in Tofu Liquid Waste
Shinta Elystia, Lely Rahmawati Saragih, Sri Rezeki Muria

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Cite this article as:
Elystia, S., Saragih, L.R., Muria, S.R., 2021. Algal-Bacterial Synergy for Lipid Production and Nutrient Removal in Tofu Liquid Waste. International Journal of Technology. Volume 12(2), pp. 287-297

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Shinta Elystia Department of Environmental Engineering, Faculty of Engineering, Riau University, Indonesia, 28293, Panam, Pekanbaru, Indonesia
Lely Rahmawati Saragih Department of Environmental Engineering, Faculty of Engineering, Riau University, Indonesia, 28293, Panam, Pekanbaru, Indonesia
Sri Rezeki Muria Department of Chemical Engineering, Faculty of Engineering, Riau University, Indonesia, 28293, Panam, Pekanbaru, Indonesia
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Abstract
Algal-Bacterial Synergy for Lipid Production and Nutrient Removal in Tofu Liquid Waste

Energy diversification using microalgae biomass offers a solution to the fossil fuel crisis, which has become a global issue. Chlorella sp. is a microalga that can produce lipids and reduce chemical oxygen demand (COD) in liquid waste. In this research, we used Chlorella sp. to produce lipids and reduce COD in tofu liquid waste. This research aimed to identify the interaction between a complex microorganism, as a decomposer agent, with the addition of the photosynthetic microalgae Chlorella sp. as an oxygen producer to reduce COD in tofu liquid waste. Moreover, we aimed to determine the interaction between Chlorella sp. and a bacterial consortium for microalgae growth and lipid production. This study was conducted in batches with the addition of bacteria at five different concentrations (% v/v): 0 (no addition), up to 0.25, 0.50, 0.75, and 1. Cultivation was conducted for 13 days with solar irradiation in a photobioreactor. As a result, the highest density and the highest growth rate were obtained from the treatment with 1% bacteria, achieving as many as 5.65´106 cell/mL and 0.21/day. The 1% treatment was able to produce lipids and COD removal efficiencies of 20.93% and 96.30% at the best-removing detention times, which both occurred on the 13th day of cultivation.

Bacteria; Chlorella sp.; COD; Lipid; Tofu liquid waste

Introduction

The energy crisis and fossil fuels present environmental problems that have become a global issue. The availability of fossil fuels, which are increasingly depleting, accompanies ever-increasing consumption levels. Indonesia’s reserves and production of petroleum (fossil) fuels have decreased by 10% each year, and the country’s average oil consumption level has increased by 6% per year. In addition to this limited availability, the fossil-fuel burning process also produces greenhouse gas emissions, such as carbon dioxide (CO2), which certainly harm the environment (Kuncahyo et al., 2013).

        Energy diversification through the creation of renewable energy sources, such as biodiesel, offers a solution to the fossil fuel crisis. Microalgae are believed to be a good renewable energy source because of their rapid growth rate and ability to be cultivated in wastewater. Alga lipids could serve as an ideal feedstock for high-energy-density transportation fuels, such as biodiesel (Jegathese and Farid, 2014). Microalgae can produce high enough lipids (±65% in dry weight) to be converted into biodiesel (Skill, 2007).

During the microalgae cultivation process, growth rates can be increased by adding bacteria to growth media. Bacteria, as a promoting agent, can increase microalgae biomass  during cultivation. Increased biomass in algal cultivation increases lipid levels from these microalgae. In bacteria-algae symbiosis systems, bacteria can release CO2, which benefits algal growth. Meanwhile, microalgae can provide O2 via photosynthesis and produce nutrients for bacterial growth (Sayre, 2010). Ferro et al. (2019) reported that some bacteria can achieve high efficiency in removing pollutants from wastewater and promote algal biomass production through metabolic complementarity.

        The microalgae cultivation system requires a medium with sufficient nutrients for growth. One growing medium that can be used to cultivate microalgae is tofu liquid waste (Jayanudin and Syaichurrozi, 2016). Elystia et al. (2020) reported that the cultivation of microalgae in tofu liquid waste under sterile conditions can produce algae cells of 8´105 cells/mL with a lipid content of 27.12%, reducing the COD levels with 73.91% efficiency. Nugroho et al. (2016) reported that the cultivation of Chlorella Vulgaris with the addition of Azospirillum in tofu liquid waste can produce algae cells of 5.56´106 cells/mL, while cultivation without the addition of these bacteria can only produce algae cells of 3.07´106 cells/mL. Restuhadi et al. (2017) also reported that the use of a symbiosis of Chlorella sp. and a bacterial consortium reduced COD in palm oil mill effluent (POME) with an 82.7% removal efficiency. These studies have shown that the addition of bacteria into microalgae growing media can support algal growth and reduce pollutants in wastewater media. The current research observed a reduction of pollutants and algal growth in tofu liquid waste, as well as the effects of adding a bacterial consortium containing Lactobacillus sp., Actinomycetes, and nitrifying bacteria on lipid levels produced by microalgae grown in tofu liquid waste. As growth-promoting agents and decomposers, bacteria help grow microalgae and reduce pollutants. In the processes of lipid production and pollutant reduction, microalgae and bacteria conduct symbiosis that allows bacteria to use the O2 produced by microalgae, in turn producing CO2 and growth-promoting substances as a by-product of their respiratory metabolism that microalgae can use to grow (Siregar, 2012).

Conclusion

    This study has demonstrated that bacteria and algae interact with each other to significantly reduce COD in tofu liquid waste, which can promote algal growth. Meanwhile, COD removal and algal growth with a lower bacteria addition (control) performed no better than treatments adding bacteria. The higher microalgae’s higher biomass, the more lipids are produced. The produced lipids could serve as a biodiesel feedstock to overcome the fossil fuel crisis. The optimal conditions for COD-value reduction, growth, and lipid levels of the microalgae Chlorella sp. were attained with a treatment that added a 1% bacterial consortium. The study’s COD-value removal efficiency and lipid content of microalgae under optimal conditions stood at 96.30% and 20.93%, respectively.

Acknowledgement

    The authors would like to express their gratitude to the Alga Research Centre Laboratory at the Faculty of Fisheries and Marine Sciences and the Laboratory of Control and Prevention of Environmental Pollution at the Faculty of Engineering—both at the University of Riau—for their support in this research.

Supplementary Material
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