Indian Journal of Science and Technology

Abstract

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 filtrated semi-solid and aqueous, the former as biofertilizer and latter 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 ranging between C/N 26 to 30. Pretreatments of the digestate improve the yields of biomethane in C/N 26 and 30 significantly. 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. Digestate in algal supplemental indicated glucose depletion linearly depleting, lowest with the nutrients-rich that is C/N 26 to 30. As expected, digestates from C/N 34 and 37 in single-addition 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 final 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. Conclusively, a circular system using the biowastes discussed or similar in nature can develop and constitute a self-supporting sustainable system opportunities.
Keywords: Poultry manure, biomethane, biogas, biofertilizer, Chlorella vulgaris, biodiesel.