Assessment of Liquid and Solid Digestates from Anaerobic Digestion of Rice Husk as Potential Biofertilizer and Nutrient Source for Microalgae Cultivation

Abstract

The need to embrace a circular economy model for sustainable growth and development is increasing due to the rise in human population and the dwindling natural resources available to meet the demands for energy and food. In this study, anaerobic digestion of rice husk (RH) was carried out under mesophilic conditions to produce biogas and digestates. Two particle sizes (300 and 600 μm) and three dilution ratios (1:4, 1:6, and 1:8) were employed to determine the optimum conditions for biogas production. The best anaerobic digesters (300 μm/1:6 and 600 μm/1:4) in each of the categories produced a cumulative biogas of 3205 + 290 mL and 2310 + 320 mL, respectively. The digestates were separated into solid and liquid fractions and characterized to evaluate their potential as biofertilizers and nutrient sources for microalgae cultivation. The nitrogen and phosphorus contents of the solid fractions (1.00 ± 0.01 and 0.97 ± 0.04) were significantly higher (p < 0.05) than the liquid fractions whereas the liquid fractions had a higher potassium content than the solid fractions. The absence of heavy metals in the digestates confirmed their safety as biofertilizers. The pH values of 4.70 and 5.50 reported in this study for liquid digestates are appropriate for the cultivation of some strains of microalgae that thrive in an acidic medium. The ammonium nitrogen contents of the liquid digestates (0.03% + 0.00% and 0.04% ± 0.00%) were moderate and not as high as some values reported to inhibit the growth of some species of microalgae. However, the brownish color of the liquid digestates could impair microalgae growth; thus, there is a need for dilution to increase light penetration.

Assessment of Raisins Byproducts for Environmentally Sustainable Use and Value Addition

“…The availability of substrates at the early stages of AD could be a factor, and as AD progressed, the substrates on which the microorganisms could feed were depleted [46]. The patterns in average daily biogas production for each byproduct group were very similar to those reported by Olugbemide and Likozar [47].…”

Mini Review: Peran Biofertilizer Pada Pertanian Lahan Kering

“…Limbah pertanian ini dapat diolah menjadi kompos atau digunakan langsung sebagai bahan dalam proses fermentasi. Sisa-sisa tanaman, seperti jerami [6]- [8], sekam padi [9], [10], kulit buah [11], dan dedaunan [12], [13], dapat digunakan sebagai bahan baku untuk pembuatan biofertilizer. Limbah dari industri pangan, seperti ampas tebu [14], [15], limbah kopi [16], limbah sereal [17], dan limbah produk susu [18], dapat menjadi sumber biomassa yang baik untuk pembuatan biofertilizer.…”

Coupled Biogas and Fiber Production from Agricultural Residues and Energy Crops with Steam Explosion Treatment

“…Nevertheless, low DM concentration of the liquid phase would require a large reactor volume compared to an energy crop fed biogas plant with identic hydraulic retention time and methane production, which increases investment and operating costs. Therefore, dilution should be as low as possible to ensure the function of SE [43] and reduce the water input. Further research to optimize this parameter would be useful.…”