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Sustainable Bioenergy Bioprocessing: Biomethane Production, Digestate as Biofertilizer and as Supplemental Feed in Algae Cultivation to Promote Algae Biofuel Commercialization

Author(s): Gene Drekeke Iyovo | Guocheng Du | Jian Chen

Journal: Journal of Microbial & Biochemical Technology
ISSN 1948-5948

Volume: 02;
Issue: 04;
Start page: 100;
Date: 2010;
Original page

Keywords: Poultry manure | Biomethane | Biogas | Biofertilizer | Chlorella vulgaris | Alga biodiese

In this study we developed and tested a sustainable system that produces high-yield outputs of biomethane,biofertilizer and biodiesel. These were achieved by blending of poultry manure (PM), paper pulp and algae waste sludgein co-digestion producing biomethane, digestate fi ltrated to get semi-solid and aqueous, the former as biofertilizerand latter was used in algal cultivation to enhance algal biomass for biodiesel production. The varied blending of thesubstrates resulted in carbon/nitrogen ratios (C/N) of 26, 30, 31, 34 and 37 which were assessed for biomethane. C/N26 resulted in 1045 ml/L/d (74% biomethane content) which was highest yield comparing to other C/N, C/N 30 achievedin similar (1010 ml/L/d) making the C/N range for optimum biomethane for these substrates to range between C/N 26 to30. In comparison, C/N 31 to 37 achieved lower biomethane yields indicating. Pretreatments of the digestate improvethe yields of biomethane in C/N 26 and 30 signifi cantly. We assessed all the digestates from each of the C/N 26,30,31,34and 37 based on nitrogen mineralization and found C/N 26 to 31 as being nutrients-rich. We fi ltered the digestate andused in algal supplemental feed and also found that glucose depletion was linearly depleted (as suffi ciently used incell growth) lowest with the nutrients-rich that is C/N 26 to 30.As expected, digestates from C/N 34 and 37 in singleadditionfailed to yield comparable algal yields then yields from C/N 26, 30 and 31 digestates at 120 h that achieveddry cell weight (DCW) of 7.72, 7.8 and 7.12 g/L respectively. To improve alga biomass yield and enhance cellular lipidcontent and its fi nal yield, we investigated two-stage supplemental feeding strategy using digestates from C/N 26 and30. Based on cultivation ‘without’ digestate that showed growth phases, we added digestate at lag-exponential (0-120h) and stationary (120-180 h) phases. The supplemental feeding resulted in rapid glucose depletion achieving 9 g/L at120 and reaching lipid yield 3.77 g/L after 180 h. Based on this study, it is conceivable that a circular system using thebiowastes discussed or those of the similar nature can develop and constitute a self-supporting sustainable system fromwaste treatment, biogas to algal biofuel opportunities. The simple approach taken in algal cultivation under the conditionstudied further showed that microalgae biofuel can be easily promoted and commercialized as a revenue generatingback-yard entity for housewhole. The way-forward for microalgae biofuel is to attract and make more population as afun art.
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