Friday, May 7, 2010

Research and publications: Waste to bioenergy bioprocessing, a circular system

In our studies, I have been working on converting biowaste to value-added products. Using biological agent like algae such as microalga Chlorella vulgaris, or C. protothecoides have shown very interesting outcome. In these publications (Journal of Microbial Biochemical Technology-US base journal, and Indian journal of Science and Technology, we showed that a digestion-fermenter side by side symbiosis system is likely possible for the follwing bioproducts:

Biomethane was produced at 74% content, digestate residue was cleaned and feed to Chlorella vulgaris which showed optimum growth performance (high algal yield biomass, later we designed feeding mechanism that improved algal oil content/yield that was used for making biodiesel.
The residue digestates as semi solid were assessd as biofertilizer and found of high value for crop production. A backyard eco-farm can be sufficiently supported that feeds agro-waste to the digester for biomethane (the cycle)

Briefly, the study was recommendable becuase the biowaste processing-digester-fermenter (alga cultivation) system was new concept that can be easily produced even at family unit. The family housewhole or backyard farm watse,livestock waste can be converted into more useful energy feedstocks(biomethane,algal oil. The big picture here was algae commercialization involving the population, in other words, algae can be produced and be sold to the processor that makes range of biofuel (biodiesel,bioethnaol,biomethane,biobuthanol). In this way, algae becomes a 'cash crop' for many. Thus the algae 2020 plan (USA) can be easily achieved involing people from the bottom up.

Finally, the use of digested waste in microalgae cultivation using different modes of nutrition (dark/light) conditions proved interesting an art. Cellular lipid content and yield were easily increased with carbon source addition at later state of growth. The circular system proofed feasible.

The two abstracts are pasted here:

Abstract 1
Poultry manure (PM) was decomposed under high and low aeration-agitations and the digestates were supplemented in mixotrophic cultivation of microalga Chlorella vulgaris. High aerobic decomposition was recommended for faster mineralization. The study was conducted to find out the effect of poultry manure digestate (PMD) on cell biomass and lipid yield in C. vulagris. The cultivation were conducted ‘with’ (single and two-stage feeding strategy) and ‘without’ PMD feeding. Cultivation ‘without’ PMD at 120 h, dry cell weight (DCW) of 8.2g/L was reached, by 180 h, lipid yield of 2.1 g/L (45%) was reached. In single-stage of adding varied PMD, at 120 h, DCWs of 8.48, 9.39 and 10.45 g/L were achieved for PMD of 20, 30 and 40 ml/L, respectively. By 180 h, lipid contents were 45, 43 and 40% giving yields of 2.4, 2 and 1.8 g/L, respectively. In two-stage feeding (0-120 h and 120-180 h), at 120 h, DCWs were similar to single-stage but improved when supplementing with 2 g/L glucose reaching DCW of 12.6, 13.14 and 14 g/L achieving lipid yields of 2.9, 3.8 and 4.9 g/L, respectively, after 180 h. The addition of glucose seems to assist nitrogen depletion which in turn resulted in rapid increase in cellular lipid. It was obvious that addition of glucose at stationary phase maybe a novel method to improve lipid yields. The algal biomass PMD dependent accumulation showed that PM is an attractive waste which means that PM is potential waste for algae biofuels.

Keywords: aeration; digestion; digestate; Chlorella vulgaris; poultry manure

Abstract 2:
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 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 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. We filtered the digestate and used in algal supplemental feed and also found that glucose depletion was linearly depleted (as sufficiently 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 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. 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.

Keywords: poultry manure, biomethane, biogas, biofertilizer, Chlorella vulgaris, alga biodiesel