Journal of Microbial & Biochemical Technology

Abstract

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

Gene Drekeke Iyovo, Guocheng Du and Jian Chen

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