Efficient Energy Generation through Microalgae with Co-Digestion

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 7, Issue 2, February 2017)

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Efficient Energy Generation through Microalgae with

Co-Digestion

Animesh Patel

1

, Archana Paranjpe

2

1_{M.Tech Scholar,}2_{Prof. Dept. of EX, Takshshila Institute of Engg. & Tech. Jabalpur, India}

Abstract-- The present paper focuses on microalgae as the third generation bio energy feedstock. Microalgae can convert to biogas, bio oil, biodiesel and bio ethanol. Through the description of the microalgae characteristics and compilation with other biomass feedstock, Microalgae has high lipid contents, fast growing and less land use superiorities. For getting biogas from microalgae, microalgae energy production process was studied, which includes microalgae cultivation, harvesting & oil extraction and energy conversion parts. The technology readiness level and production difficulties of microalgae energy are shown from the introduction of different techniques of different production processes. The climate condition, water resource, carbon dioxide condition, land and nutrients are five requirements of large scale production in environmental concern which need to be meet. Furthermore, how to decrease the investment cost and production cost are the economic challenges have to be solved. In combination with all of the environmental requirements and economic concerns, an ideal microalgae energy production plant was imagined. Microalgae as renewable energy resource, the sustainability of microalgae must to be estimated.

Keywords: - Biogas, Micro Algae, Co-digestion.

I. INTRODUCTION

The simultaneous growth of the human population and the dependence on energy and fuels has increased the need for research into alternative energy resources. Coupled with the increasing threat of climate changes, an effective energy source is greatly desired. Many sources of alternative energies come from natural resources. Solar energy, hydroelectricity, geothermal power, and wind power can all generate energy using natural occurrences when coupled with technology. One of the many types of renewable energy that has been developed is the use of converting biological materials into usable fuels. This bio energy can come in many forms. Resources such as char, bio-oil, or gas can be obtained through gasification and pyrolysis. A useful energy material is Biogas. Biogas is a carbon-based gas primarily made from biological reactions. The reactions take place with microorganisms in the absence of oxygen in a process called anaerobic digestion.

Anaerobic digestion takes place when the simultaneous growth of the human population and the dependence on energy and fuels has increased the need for research into alternative energy resources. Coupled with the increasing threat of climate changes, an effective energy source is greatly desired [1].

1.1 Microalgae

Microalgae refer to small size algae which shape can only be seen under the microscope. Microalgae are the main primary producers in the aquatic ecosystem . Chlorella, spirulina and Nitzschia as the main microalgae sources are usually used to produce biofuel. They are sort of single primitive cell organism with high photosynthesis capability. The growth period is short, and the cell doubling time of microalgae is only 1-4 days. Microalgae which contain at least 30% lipids in the microalgae cell have possible to be used to convent biofuel. Through photosynthesis, microalgae can absorb large amounts of CO2 to produce sugars and oxygen. The photosynthesis reaction equation as follow:

6CO2 + 6H2O + sunlight energy →C6H12O6 (sugars) + 6O2

Then sugars can convert to lipids, proteins and carbohydrates, which are as the materials can be converted to the biofuel.

To sum up, the advantages of microalgae in energy production can be found in the following points:

1.Microalgae have chlorophyll and other photosynthetic organs, which can do photosynthesis. So microalgae use the sunlight, H2O which contain in the microalgae cell and CO2 from the air to convert organic compounds which can be produced to the biofuel [2].

2.The reproduction of microalgae is generally split type breeding, the cell cycle is relatively short, so it is easy to carry out large scale cultivation.

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1.2 Harvesting of Microalgae

The harvesting methods are not only depending on the microalgae species and microalgae cell density, but also rely on the different cultivate conditions. The cultivation conditions relate to climate. The cultivate conditions relate to climate condition, Microalgae can be harvested by some feasible methods, such as centrifugation, membrane filtration, flocculation and froth flotation. Centrifugation and flocculation as two most commonly used methods.

Centrifugation is a process by using centrifuge to sediment mixture by centrifugal force. Currently, centrifugation is the most widely used harvesting method in microalgae production. Moreover, the results have shown that recovery rate of microalgae is relate to settling character of microalgae, residence time and depth of settlement. In the suitable conditions, the recovery rate can be up to 95%.

Sometimes, cationic coagulants are also suggested to add into the microalgae on account of the microalgae cell surface take negative charges. The high production cost of this technique lead to unable to large scale application.

However, until now, there is not a significant method that have been used in the middle or large scale production, and where both economic and technologic conditions can be satisfied at the same time.

[image:2.612.48.288.454.568.2]

Therefore, harvesting process of microalgae needs to be improved and developed in future.

Fig. 1: Energy conversion processes for biofuel production from microalgae [1]

1.3 Biogas production through anaerobic digestion

A simpler method of energy recovery may be facilitated by anaerobic digestion of algal biomass providing a promising source of bio-energy in the form of biogas. The process was considered a potential source of useful energy recovery from algal cultivation near the start of modern research [3]. Anaerobic digestion is a process that has been used for hundreds of years to provide a source of energy from low value organic matter with minor energetic inputs [4].

In the case of algal biomass, all the carbohydrates, proteins and fats can be converted into Biogas and carbon dioxide, although some components provide greater Biogas yields than others [5]. It follows therefore that there is slightly less necessity to cultivate particular strains of algae for increased yields.

1.4 Where do Algae Grow? - Algae Growth Environments

Algae are some of the most robust organisms on earth, able to grow in a wide range of conditions.

Algae are usually found in damp places or bodies of water and thus are common in terrestrial as well as aquatic environments. However, terrestrial algae are usually rather inconspicuous and far more common in moist, tropical regions than dry ones, because algae lack vascular tissues and other adaptions to live on land As mentioned above, algea grow in almost every habitat in every part of the world. The following are examples of non-marine habitats.

 Animals: Reported substrates include turtles, snails, rotifers, worms, crustacean, alligators, three-toed sloths, aquatic ferns, freshwater sponges and some other animals.

 Aquatic plants: Algae grow on and inside water plants (including other algae)

 Artificial substrates: Wooden posts and fences, cans and bottles etc. all provide algal habitats.

 Billabongs & lagoons: Rich microalgal habitats, particularly for desmids.

 Bogs, marshes & swamps

 Farm Dams

 Hot springs

 Lakes

1.5 Algal Chemical Composition

Algae are made up of prokaryatic as well as eukaryotic cells. These are cells with nuclei and organelles. All algae have plastids, the bodies with chlorophyll that carry out photosynthesis. But the various lines of algae have different combinations of chlorophyll molecules. Some have only Chlorophyll A, some A and B, while other lines, A and C.

II. METHODOLOGY

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Unlike other renewable sources, it does not suffer from intermittency of supply and it is carbon-neutral. Consequently, an appreciable number of research efforts have been directed towards algal biomass as a potential source of renewable biofuel. These efforts have primarily focused on the production of biofuels through lipid extraction, which involves high temperature and high pressure, resulting in an energy intensive process. This research explores the potential of algal Biogas gas via anaerobic digestion (AD) as a carbon-neutral energy source. In particular, the research investigates Biogas production from the anaerobic co-digestion of the microalgae with wastewater sludge.

2.1 Algae substrate for anaerobic Digestion

Algae cultivation Fresh water was collected from gwarighat in March (early spring/late winter). The water was used immediately in the experiment, without any preservation or storage. A batch experiment was set up with two 10 litre airtight container each containing about 7

litre algae waste and other mix waste. The containers were placed in a climate chamber with consistent light at 30-40 oC.

2.1 Digester Setup

The experimental setup consisted of 2 reactors, each with approximate working volumes of 10 litre. The digesters were constructed of clear airtight Plastic container with 0.5 inch plastic tube for carry the biogas and 2 litre plastic bottle for gas collection. A threaded PVC fitting was used on the top of each reactor, with a threaded PVC plug sealing the reactor. M. seal was used to seal all fitting on the reactor, not including the top threading, allowing for opening. Sealing compound putty was used in the threaded connection to prevent gasleaks from the pressure inside the reactors.

The digester caps were drilled to allow for outlets. The top was drilled for two outlets; one consisted to allow for sample feeding, while a second outlet used a tube connection to transfer gas into the connected gas collector. All fittings were sealed using a thread sealant tape to prevent leakage.

Gas collectors were built as 2 litre airtight plastic containers used for gas collection. Tube connections on both ends were measured to be 0.5 inch in diameter on the top and bottom of the collectors.

The digesters were sealed from the atmosphere and any biogas produced displaced water into the measuring jar allowing for gas measurements.

After several days, when the water levels of the collectors neared empty, gas samples were taken to release pressure as the overhead carboy refilled the collectors to repeat the process. . A space heater was used to maintain a temperature of 35° C in the room.

2.2 Experimental setup

The experimental setup stabilized in the college campus at mesophilic temperature (35-40oC) in month of May for 35 days.

Picture 1: Experimental Setup of Algae with co digestion Cow manure in two different Ratio

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Picture 3: Experimental Setup of Algae with co digestion Cow manure (50%:50%) subtract

III. RESULTS AND DISCUSSION

Initial analysis shows high volatile solids content in algae, and manure demonstrating the spent microbial activity from the original process. Algae and anaerobic sludge showed fairly similar moisture contents. For the proper functioning of anaerobic digesters, the physical and chemical characteristics of the substrate are important as they affect the biogas production and the stability of the process. The parameters that were of interest are number of washings required to decrease the salinity of the algae, pH, VFA, COD, VS, TS and biogas production.

3.1 Effects of feeding composition on co-digestion performance

The C/N ratio is an important parameter to take into account when investigating different substrates and substrate mixtures for anaerobic digestion. Several reports suggest that optimum C/N ratios in anaerobic digesters are between 50 and 50.

Except for Algae alone, C/N ratios in the CM were outside the ideal range. In set-up 2, Two substrates in D2 had a C/N ratio of 25:1, which is within the range required for a correctly operating digester, and they all had significantly higher cumulative biogas production than from single digestion. In addition, co-digestions in D2, where Algae and Cow manure showed higher biogas and Biogas potentials, as well as VS removal rates, than for digestion of Algae alone.

3.2 Effects of the C/N ratio on co-digestion performance

In set-up 2 the roles of optimized feeding composition in improving biogas and Biogas production were investigated in set-up 1. However, due to the importance of the C/N ratio in anaerobic digestion, it is essential to optimize it in co-digestion of multiple substrates to achieve higher efficiency. As shown in C/N ratios of 25:1 and 30:1 had similar highest cumulative biogas production, about threefold higher than that from only algae with a C/N ratio of 15:1. With the increase in C/N ratio, the biogas and Biogas potential both initially increased to a peak at a C/N ratio of 30:1 and then declined. However, the highest VS removal rate was found at a C/N ratio of 25:1. A lower C/N ratio causes ammonia accumulation and pH values exceeding 8.5, which is toxic to methanogenic bacteria treatments with C/N ratios at 25:1 and 30:1 had stable pH values around 7.0. However, a C/N ratio of 15:1 had a higher pH range from 7.5 to 8.0 from day 15 and material with a C/N ratio of 20:1 also finally reached 7.5. When the C/N ratio rose to 35:1, the pH value was lower at around 6.5. It has been reported that methanogenic activity occurs at pH values between 6.2 and 8, but with an optimum range between 7.0 and 7.2 , which is supported by the results of this study.

3.3 Daily Biogas Production

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International Journal of Emerging Technology and Advanced Engineering

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Fig. 2 Cumulative biogas production rate from batch reactor (ml/g) [3]

IV. CONCLUSION

The combination of Algae and cow manure showed positive effect on biogas production. Studies on the performance of the reactor showed that the two substrates are biodegradable and can complement each other when they were used in co-digestion. The cow manure and algae can balance C/N ratio and can increase the cellulose activity and this enhances the biogas production. It can be concluded that a synergetic effect at mesophilic conditions formed in the reactor at the time of co-digestion of cow Manure is responsible for the enhanced biogas production by balancing the nutrient composition and C/N ratio in the reactor. Experimental studies could assess the co digestion required for maximizing the rate of production of biogas. Investigations to locate the optimum proportion of substrates in the feed mixture to attain maximum biogas yield are in progress.

The experiment was conducted within the pH range for optimum Biogas production and there was little temperature variation throughout the experiment. Accordingly, there was a negligible temperature variation effect on biogas production. The results in shows that, there was no Biogas production in the first day in both experimental setup, this may be the methanogenic bacteria which act upon the organic material within the digester were inactive within this period due to the formation of organic acid which decreases the pH value below 6.

This study investigated the feasibility of biogas production from the co digestion of algae with cow manure. The results from the codigestion experiment of algae with cow Manure is maximum biogas generation is 60.60 ml/day and cumulative biogas production is 2121.2 ml/kg compare to single subtract digestion biogas generation is 38.90 ml/day and cumulative biogas production is 1362.9 ml/kg This work is yet to investigate the seasonal availability of algae based on which together with the findings so far, the choice of the type of algae for co-digestion with cattle manure can be determined

At the conclusion of the experiment, it was found that biogas production increased when algae with co digestion cow manure was added to the digester. This shows that the presence of cow manure with algae increases the overall Biogas production. The effects of carbon balancing for the carbon-to-nitrogen ratio also showed that overall, mixtures balanced at 25:1 carbon-to-nitrogen yielded more biogas. The exception is the normal algae mixture, in which the optimal ratio was 20:1. In conclusion, the anaerobic co-digestion of cattle manure with algae, when balanced for carbon and nitrogen, can severely increase Biogas production rates.

REFERENCES

[1] Paul, L. Melville, and M. Sulu,” Anaerobic Digestion of Micro and Macro Algae, Pre-treatment and Co-Digestion-Biomass — A Review for a Better Practice” International Journal of Environmental Science and Develospment, Vol. 7, No. 9, September 2016 doi: 10.18178/ijesd.2016.7.9.855.

[2] Federica Barontini , Enrico Biaginia, Federico Dragonib,” Microalgae Residues for Biogas Production”, ISBN 978-88-95608-41-9; ISSN 2283-9216, Copyright © 2016, AIDIC Servizi S.r.l. [3] Enrica UggettiFabiana Passos,Maria Solé,” Recent Achievements in

the Production of Biogas from Microalgae” 08 June 2016 ,DOI: 10.1007/s12649-016-9604-3.

[4] David U. Santos-Ballardo, Sergio Rossi, Cuauhtémoc Reyes-Moren,” Microalgae potential as a biogas source: current status, restraints and future trends”, 05 March 2016, DOI 10.1007/s11157-016-9392-z.