Grantee Research Project Results
Final Report: Innovative in-situ Microwave-ultrasonic Reactor for Algal Biomass Harvesting and Biodiesel Production
EPA Grant Number: SU835519Title: Innovative in-situ Microwave-ultrasonic Reactor for Algal Biomass Harvesting and Biodiesel Production
Investigators: Gude, Veera Gnaneswar , Martinez-Guerra, Edith , Fast, Sara Ann , Kokabian, Bahareh
Institution: Mississippi State University
EPA Project Officer: Packard, Benjamin H
Phase: I
Project Period: August 15, 2013 through August 14, 2014
Project Amount: $14,999
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2013) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Air Quality , P3 Awards , Sustainable and Healthy Communities
Objective:
Algae represent a potential future energy source due to their high oil-yielding capacity, carbon neutrality and environmental friendliness. However, the major bottlenecks for current algal biodiesel production are harvesting/concentration, drying, and extraction steps due to their cost- and energy-intensive nature. For sustainable algal biodiesel production, energy-efficient technologies will need to be developed to increase the net energy gain and economic benefit.
This project develops an integrated process that includes an ultrasonic-biopolymer enhanced flocculation step for algal biomass harvesting followed by a microwave/ultrasonic single-pot extractive-transesterification step to improve the energy foot print of the overall algal biodiesel process.
Approach
Ultrasonics at high frequencies flocculate suspended algal cells and ultrasonics and microwaves together improve extraction of oils/lipids by diffusive and disruptive mechanisms and simultaneously transesterify the lipids/oils due to increased mass/heat transfer phenomena and thermal/specific non-thermal effects at molecular levels. Further, use of biodegradable polymers, chitosan, as flocculation agent eliminates toxic sludge problems. Recent research on microwaves and ultrasonics in various process chemistry applications has shown the potential to reduce process time, as well as reaction condition severities along with reduced chemical, energy and solvent consumption. The proposed process design can be considered sustainable because it utilizes high-oil yielding renewable feedstock, energy-efficient process techniques and reduces environmental pollution.
Expected Results
The proposed research design project addresses critical process issues of the harvesting, drying, and extraction stages of algal biofuel processes. The process operates under mild conditions, which eliminates the need for high pressure vessels and high processing costs. Central to this project is development of reactor design and process optimization techniques under microwave/ultrasonic mediated conditions. An in-situ microwave applicator with direct microwave and ultrasonic effect in a single process reactor will be developed. Understanding the effect of the two non-conventional technologies in the flocculation, extraction, and transesterification steps of algal biodiesel production will be beneficial for many other biofuel and chemical process related applications. Further, this design project is expected to produce results that promote energy independence through local algal biodiesel production (People), energy conservation by minimizing the process energy and cost requirements (Prosperity), and environmental pollution prevention by carbon-neutral algal biomass feedstock for biodiesel production (Planet).
Summary/Accomplishments (Outputs/Outcomes):
Fig. A. Overall Research Plan for MW/US algal biodiesel production
The research was conducted through two major process development and optimization stages: Phase I – Ultrasonic-biopolymer (chitosan enhanced algal cell harvesting; Phase II – Microwave/Ultrasonic extractive-transesterification. The overall research plan is as shown in Fig. A. The research started with analyzing the ultrasonic flocculation feasibility of chitosan for algal biomass harvesting and a comparison with the conventional rapid mixing process and evaluation of direct MW and ultrasound enhanced , process configuration validation and optimization. Process optimization studies were conducted to refine the individual process parameters. The data obtained from these tests were validated in triplicates to verify reproducibility and to confirm the reliability of the process techniques. We have completed four process design and optimization studies while some of the tasks are still in progress. The following research paragraphs describe the research findings from this project.
Algae harvesting by ultrasonication: In this study, an ultrasound-chitosan enhanced coagulation/flocculation process for treating algal suspensions was developed. The possibility of performing ultrasound mixing in lieu of conventional rapid mixing was evaluated. The effects of several process parameters such as chemical dosages, pH, ultrasound exposure time, concentration factors, and flocculation and sedimentation times were studied. Two comparative studies, i.e., a comparison between ultrasound-alum and ultrasound-chitosan flocculation of algal turbid waters as well as a comparison with conventional rapid mix and direct flocculation were conducted. The results from these studies reveal that ultrasound enhanced method can produce clear supernatant water with greater than 98% turbidity reduction. A power density of 0.1-0.25 W/mL was sufficient to provide adequate mixing for chemical distribution and pin-floc formation. The concentration factor for ultrasound-enhanced coagulation/flocculation was determined to be 30 with an optimum ultrasound exposure of 1 minute followed by a 20 minute flocculation process. This study confirms that ultrasound-chitosan enhanced flocculation process may provide additional benefits for algal cell harvesting compared to the conventional rapid mix method.
We evaluated the effect of the ultrasound-chitosan enhanced flocculation process for efficient removal of algal cells from low algal turbid waters and compared it with the conventional rapid mix process. The results show that the turbidity removal efficiencies for ultrasound-enhanced coagulation (97.8% - 99% removal) were comparable to the conventional rapid mix coagulation (96.8% - 99% removal) for alum and for chitosan (84.1% - 90.5% for RM and 84% - 97% for US). This study confers that ultrasound mixing can be performed instead of conventional rapid mixing to improve the algal cell removal efficacies from the low algal turbid waters.
Microwave and ultrasound enhanced algal biodiesel production: We investigated the effect of non-conventional methods, microwaves and ultrasound, for extractive-transesterification of algal lipids (Chlorella, sp.) using ethanol as a solvent. Microwaves and ultrasound possess unique enhancing (physical and electrical) mechanisms that can assist in successful extraction and transesterification of algal lipids in a very short reaction time. We performed a comparative study of microwave and ultrasound effects on the algal biodiesel production. The following conditions were determined as optimum through optimization studies: (1) microwaves – 1:12 algae to ethanol (wt./vol.) or 1:500 (molar) ratio; 2 wt.% catalyst; 5-6 minutes reaction time at 350 W microwave power; and (2) ultrasound – 1:6-9 algae to ethanol (wt./vol.) or 1:250-375 (molar) ratio; 2 wt.% catalyst; 6 minutes reaction time at 490 W ultrasound power. The highest fatty acid ethyl ester (FAEE) yields and conversions for microwave and ultrasound methods were 18.8%; 18.5% (yields) and 96.2%; 95.0% (conversions), respectively. In comparison, the ultrasound method resulted in higher FAEE yield and conversion at low solvent ratios while microwaves were able to produce better results at lower power levels compared to ultrasound. The two methods performed better than the conventional bench-top Bligh and Dyer method, which followed a two-step extraction and transesterification method with FAEE yields and conversions of 13.9% and 78.1%, respectively.
Conclusions:
The feasibility of the ultrasound-chitosan enhanced flocculation process was evaluated for algal cell harvesting. The results from this project suggest that ultrasound-chitosan enhanced flocculation process can provide comparable cell removal efficiencies when compared to rapid mixing method while reducing the chemical dosages as well as the sludge volumes. Further studies on process design and optimization may result in an environmentally friendly and sustainable alternative to the conventional rapid mixing-flocculation process, especially for low algal turbid waters. The use of chitosan as coagulant offers benefits such as environmental friendliness and small volumes of non-toxic sludge. Apart from initiating agglomeration of algal cells, ultrasound application may provide additional effects such as inactivation of algal cells, which results in efficient algal turbidity removal in water and wastewater treatment.
Extractive-transesterification of algal biomass under microwave and ultrasonic irradiations was performed. Both methods have resulted in improved lipid extraction and FAEE conversions compared to the conventional Bligh and Dyer method. Notable improvement in the two methods is that the extraction and transesterification reactions occur simultaneously with reduced solvent use and reaction times. The specific energy consumption for the microwave and ultrasound enhanced methods was lower than other conventional, supercritical methods of separate extraction and transesterification processes. The yields and conversion rates are observed to be higher in the extractive-transesterification because losses of reaction products are eliminated in single-pot conversion processes. This will result in chemical, energy, and economic savings in large-scale production provided the scalability and process design issues are resolved for these methods.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 5 publications | 3 publications in selected types | All 3 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
Fast S, Martinez-Guerra E. Ultrasound-chitosan enhanced flocculation of low algal turbid waters. JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY 2015;24:153-160. |
SU835519 (Final) |
Exit |
|
Martinez-Guerra E, Gude V. Synergistic effect of Simultaneous microwave and ultrasound irradiations on transesterification of waste vegetable oil. FUEL 2014;137:100-108. |
SU835519 (Final) |
Exit |
|
Martinez-Guerra E, Gude V. Assessment of Sustainability Indicators for Biodiesel Production. APPLIED SCIENCES 2017;7(9):869 |
SU835519 (Final) |
Exit |
Supplemental Keywords:
Non-conventional technologies, microwaves and ultrasonics, algal biomass, energy-efficiency, energy footprint, net energy balanceThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.