Effect of sedimentation time on methane generation rate of compressed water hyacinth juice

Author(s): Anas Hijazi
Email (s): hijazianas@soka.gr.jp
Institution or organization of origin: Soka University
Country: Japan


Water hyacinth (WH) (Eichhornia crassipes) is a widespread aquatic weed threatening waterbodies and dependent life-forms by clogging streams and causing fishing interference. Anaerobic digestion (AD) is a low-cost and eco-friendly method that uses high-moisture waste like WH to generate biogas. However, a pre-treatment is required to significantly improve the overall AD process. Compression is a simple pre-treatment where the substrate is separated into a solid and liquid fraction. The liquid fraction contains soluble compounds that create an easily degradable substrate for AD. However, compression causes suspended solids (SS) to enter the liquid fraction leading to reactor instability, especially in an up-flow anaerobic sludge blanket reactor. Sedimentation is a simple pre-treatment which removes indigestible SS from WH juice (WHJ). Therefore, this study aims to understand the effect of sedimentation pre-treatment on methane recovery potential of WHJ. WH was shredded, compressed into WHJ then allowed to sediment for 0.5, 2, 8 and 24 hours. The supernatant was used as a substrate for AD. Sedimentation resulted in effective decrease in SS concentration with removal efficiency of 37%, 67%, 75% and 76% for 0.5, 2, 8 and 24 hours respectively. Sedimentation for 0.5 h led to an increase of methane yield (555 mL/g-VS) compared to untreated WHJ (495 mL/g-VS). Further, the total carbon content decreased (7.2 to 5.0 g-TC/L) with increase in sedimentation time (2 h) reducing the methane yield. Thus, sedimentation pre-treatment of WHJ (0.5 h) can be a promising alternative for biogas recovery while (2 h) is better when prioritizing treatment performance.

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