Production of lipid-containing algal-bacterial polyculture in wastewater and biomethanation of lipid extracted residues: Enhancing methane yield through hydrothermal pretreatment and relieving solvent toxicity through co-digestion.

Journal: The Science of the total environment
Published Date: Nov 6, 2018

Abstract

The feasibility of generating a lipid-containing algal-bacterial polyculture biomass in municipal primary wastewater and enhancing biomethanation of lipid-extracted algal residues (LEA) through hydrothermal pretreatment and co-digestion with sewage sludge (SS) was investigated. In high-rate algal ponds, the polyculture of native algal and bacteria species demonstrated a monthly average net and gross biomass productivity of 30 ± 3 and 36 ± 3 g m day (summer season). The algal community was dominated by Micractinium sp. followed by Scenedesmus sp., Chlorella sp., pennate diatoms and Chlamydomonas sp. The polyculture metabolic activities resulted in average reductions of wastewater volatile suspended solids (VSS), carbonaceous soluble biochemical oxygen demand (csBOD) and total nitrogen (N) of 63 ± 18%, 98 ± 1% and 76 ± 21%, respectively. Harvested biomass contained nearly 23% lipid content and an extracted blend of fatty acid methyl esters satisfied the ASTM D6751 standard for biodiesel. Anaerobic digestion of lipid extracted algal residues (LEA) demonstrated long lag-phase in methane production of 17 days and ultimate methane yield of 296 ± 2 mL/gVS (or ~50% of theoretical), likely because to its limited biodegradability and toxicity due to presence of the residual solvent (hexane). Hydrothermal pretreatment increased the ultimate methane yield and production rate by 15-30% but did not mitigate solvent toxicity effects completely leading to less substantial improvement in energy output of 5-20% and diminished Net Energy Ratio (NER < 1). In contrast, co-digestion of LEA with sewage sludge (10% to 90% ratio) was found to minimize solvent toxicity and improve methane yield enhancing the energy output ~4-fold, compared to using LEA as a single substrate, and advancing NER to 4.2.

Authors

  • Pavlo Bohutskyi
    Biological Sciences Division, Pacific Northwest National Laboratory, 3300 Stevens Dr., Richland, WA 99354, USA. Electronic address: pavlo.bohutskyi@pnnl.gov.
  • Duc Phan
    Department of Environmental Health and Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218-2686, USA; Department of Civil and Environmental Engineering, The University of Texas at San Antonio, 1 UTSA Cir San Antonio, TX 78249, USA.
  • Ruth E Spierling
    Civil and Environmental Engineering Department, California Polytechnic State University, 1 Grand Ave., San Luis Obispo, CA 93407, USA; MicroBio Engineering Inc, PO Box 15821, San Luis Obispo, CA 93406, USA.
  • Anatoliy M Kopachevsky
    Department of Water Supply and Sanitary Engineering, Academy of Construction and Architecture of V.I. Vernadsky Crimean Federal University, 4 Prospekt Vernadskogo, Simferopol 295007, Republic of Crimea; Water Technologies Research and Production Company, 7 Petropavlovskaya street, Simferopol 295000, Republic of Crimea; Water of the Crimea State Unitary Enterprise of the Republic of Crimea, 1а Kievskaya street, Simferopol 295053, Republic of Crimea.
  • Edward J Bouwer
    Department of Environmental Health and Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218-2686, USA.
  • Trygve J Lundquist
    Civil and Environmental Engineering Department, California Polytechnic State University, 1 Grand Ave., San Luis Obispo, CA 93407, USA; MicroBio Engineering Inc, PO Box 15821, San Luis Obispo, CA 93406, USA.
  • Michael J Betenbaugh
    Department of Chemical & Biomolecular Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218-2686, USA.

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