Samir Kumar Khanal

Publications (47) View all

• Article: Production of protein-rich fungal biomass in an airlift bioreactor using vinasse as substrate.

  Saoharit Nitayavardhana, Kerati Issarapayup, Prasert Pavasant, Samir Kumar Khanal
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  ABSTRACT: The potential for large-scale production of an edible fungus, Rhizopus oligosporus, on a liquid residue from sugar-to-ethanol production, vinasse, was investigated. An airlift bioreactor (2.5-L working volume) was used for cultivating the fungus on 75% (v/v) vinasse with nutrient supplementation (nitrogen and phosphorus) at 37°C and pH 5.0. Aeration rates were varied from 0.5, 1.0, 1.5 to 2.0volume(air)/volume(liquid)/min (vvm). The fungal biomass yield depended on the aeration rate, and the highest fungal biomass obtained was 8.04±0.80 (g(biomass increase)/g(initial biomass)) at 1.5vvm. The observed reductions in organic content by 80% (as soluble chemical oxygen demand) suggest the potential of recycling treated effluent as process water for in-plant use or for land applications. The fungal biomass contained ∼50% crude protein and the essential amino acids contents were comparable to commercial protein sources for aquatic feeds (fishmeal and soybean meal), with the exception of methionine and phenylalanine.
  Bioresource technology 01/2013; 133C:301-306. · 4.25 Impact Factor
• Article: Nitrogen transformations in intensive aquaculture system and its implication to climate change through nitrous oxide emission.

  Zhen Hu, Jae Woo Lee, Kartik Chandran, Sungpyo Kim, Keshab Sharma, Ariane Coelho Brotto, Samir Kumar Khanal
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  ABSTRACT: The rapid development of aquaculture could result in significant environmental concerns such as eutrophication and climate change. However, to date, very few studies have been conducted to investigate nitrogen transformations in aquaculture systems; and specifically the emission of nitrous oxide (N(2)O), which is an important greenhouse gas and ozone-depleting substance. In this study, nitrogen transformations in intensive laboratory-scale Chinese catfish (Clarias fuscus) aquaculture systems were investigated by identifying and quantifying N(2)O emissions. Results indicated that about 1.3% of the nitrogen input was emitted as N(2)O gas. Dissolved oxygen (DO) concentrations and feeding rates had significant effects on N(2)O emissions. Higher N(2)O emissions were obtained in aquaculture systems with lower DO concentrations and higher feeding rates. Both nitrification and denitrification appeared to be responsible for the emissions of N(2)O. Key factors which correlated with the N(2)O emission rate in aquaculture systems were NO(2)(-), DO and total ammonia nitrogen concentrations.
  Bioresource technology 12/2012; 130C:314-320. · 4.25 Impact Factor
• Article: Nitrous oxide (N2O) emission from aquaculture: a review.

  Zhen Hu, Jae Woo Lee, Kartik Chandran, Sungpyo Kim, Samir Kumar Khanal
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  ABSTRACT: Nitrous oxide (N(2)O) is an important greenhouse gas (GHG) which has a global warming potential 310 times that of carbon dioxide (CO(2)) over a hundred year lifespan. N(2)O is generated during microbial nitrification and denitrification, which are common in aquaculture systems. To date, few studies have been conducted to quantify N(2)O emission from aquaculture. Additionally, very little is known with respect to the microbial pathways through which N(2)O is formed in aquaculture systems. This review suggests that aquaculture can be an important anthropogenic source of N(2)O emission. The global N(2)O-N emission from aquaculture in 2009 is estimated to be 9.30 × 10(10) g, and will increase to 3.83 × 10(11)g which could account for 5.72% of anthropogenic N(2)O-N emission by 2030 if the aquaculture industry continues to increase at the present annual growth rate (about 7.10%). The possible mechanisms and various factors affecting N(2)O production are summarized, and two possible methods to minimize N(2)O emission, namely aquaponic and biofloc technology aquaculture, are also discussed. The paper concludes with future research directions.
  Environmental Science & Technology 05/2012; 46(12):6470-80. · 4.80 Impact Factor
• Article: Syngas fermentation to biofuel: Evaluation of carbon monoxide mass transfer and analytical modeling using a composite hollow fiber (CHF) membrane bioreactor.

  Pradeep Chaminda Munasinghe, Samir Kumar Khanal
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  ABSTRACT: In this study, the volumetric mass transfer coefficients (Ka) for CO were examined in a composite hollow fiber (CHF) membrane bioreactor. The mass transfer experiments were conducted at various inlet gas pressures (from 5 to 30psig (34.5-206.8kPa(g))) and recirculation flow rates (300, 600, 900, 1200 and 1500mL/min) through CHF module. The highest Ka value of 946.61/h was observed at a recirculation rate of 1500mL/min and at an inlet gas pressure of 30psig(206.8kPa(g)). The findings of this study confirm that the use of CHF membranes is effective and improves the efficiency CO mass transfer into the aqueous phase.
  Bioresource technology 03/2012; 122:130-6. · 4.25 Impact Factor
• Article: Biofuel Residues/Wastes: Ban or Boon?

  SAOHARIT NITAYAVARDHANA, SAMIR KUMAR KHANAL
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  ABSTRACT: Biofuel production generates significant amounts of low-value residues and wastes. This results in concern over the sustainability of the biofuel industry and its impact on the environment. Bioconversion offers opportunities for the economic utilization of biofuel residues and wastes with concomitant remediation of wastes. Due to their characteristics, these residues/wastes can serve as low-cost substrates for bioconversion to high-value products. Attempts have been made to produce several bio-based products, such as single-cell proteins, single-cell oil, enzymes, bioplastics, and organic acids. The authors review biofuel residues/wastes generation and their use in value-added processing. In addition, special attention is given to economic analyses of value-added processing of biofuel residues.
  Critical Reviews in Environmental Science and Technology 01/2012; 42(1):1-43. · 4.84 Impact Factor