A Novel Approach to treat Bio Wastes Using Biodigesters and

Microorganisms Employed to Increase Plastic Degradation

 

Thangavel S.*, Sujin David Rajan S., Kevin B.C.

Department of Bio-technology, Udaya School of Engineering, Kanyakumari.

 

ABSTRACT:

Introducing newly Designed biodigesters for domestic and industrial use to process biosolids (organic wastes) by microbes to rapid the process. Digester gas (60% to 65% methane), ammonia and manure (boil) are the byproduct of  this process. With proper treatment, this methane can be used in an internal combustion engine to drive a generator and make electricity. Also it can be used for cooking and heating purposes in rural areas. Biol consists of a mix of manure and water that has fermented in the biodigester. Biol is a liquid fertilizer that can completely replace chemical fertilizer. It can be sprayed on crops as a foliar fertilizer, or can be placed directly on the soil or into irrigation canals. Producers report an increase in crop production from 30% to 50%. In addition, biol protects against insects and helps plants recover from damage by frost. Ammonia released from this can be used for garden plants  to grow. The microbes such as Pseudozyma spp. yeasts , Strains of P.antarctica , etc has more degradation activity which can degrade bioplastics . The Microbial Fuel Cell can be Installed within this digester to promote considerable amount of electricity. The purpose of this study is to determine the technical and economic feasibility of generating energy from the methane using these kind of biodigesters.

 

INTRODUCTION:

Biodigester is a system that promotes decomposition of organic matter. Biogas gas is produced by the conversion of green waste by a process called anaerobic digestion. It is a stabilization process, reducing odor, pathogens and mass eduction. Anaerobic Digestion (AD) is a natural process where plant and animal materials (biomass) are broken down by micro-organisms in the absence of air.

 

The AD process begins when biomass is put inside a sealed tank or digester. Naturally occurring micro-organisms digest the biomass, which releases methane-rich gas (biogas) that can be used to generate renewable heat and power; this helps cut fossil fuel use and reduce greenhouse gas emissions. The remaining material (digestate) is rich in nutrients, so it can be used as a fertilizer.

 

Many forms of biomass are suitable for AD; including food waste, slurry and manure, as well as crops and crop residues. However, woody biomass cannot be used in AD because the micro-organisms can't breakdown the lignin, the compound that gives wood its strength. The products of AD are referred to as biogas and digestate. Biogas is a mixture of 60% methane, 40% carbon dioxide and traces of other contaminant gases. The exact composition of biogas depends on the type of feedstock being digested. Biogas can be combusted to provide heat, electricity or both. Alternatively, the biogas can be 'upgraded' to pure methane, often called biomethane, by removing other gases. This pure stream of biomethane can then be injected it into the mains gas grid or used as a road fuel. Digestate is made from left over indigestible material and dead micro-organisms. It contains valuable plant nutrients like nitrogen and potassium. It can be used as a fertiliser and soil conditioner.

 

The Process of Biodigestion:

·        Liquefaction

·        Acidogenisis

·        Acetogenisis

·        Methanogenisis:

 

 

 

Common Design of Biodigester:

In a batch system biomass is added to the reactor at the start of the process. The reactor is then sealed for the duration of the process.

 

In its simplest form batch processing needs inoculation with already processed material to start the anaerobic digestion. In a typical scenario, biogas production will be formed with a normal distribution pattern over time. Operators can use this fact to determine when they believe the process of digestion of the organic matter has completed. There can be severe odour issues if a batch reactor is opened and emptied before the process is well completed.

 

A more advanced type of batch approach has limited the odour issues by integrating anaerobic digestion with in-vessel composting. In this approach inoculation takes place through the use of re-circulated degasified percolate. After anaerobic digestion has completed, the biomass is kept in the reactor which is then used for in-vessel composting  before it is opened. 

 

As the batch digestion is simple and requires less equipment and lower levels of design work, it is typically a cheaper form of digestion. Using more than one batch reactor at a plant can ensure constant production of biogas.

 

In continuous digestion processes, organic matter is constantly added (continuous complete mixed) or added in stages to the reactor (continuous plug flow; first in – first out). Here, the end products are constantly or periodically removed, resulting in constant production of biogas. A single or multiple digesters in sequence may be used. Examples of this form of anaerobic digestion include continuous stirred tank reactors, upflow anaerobic sludge blanket, expanded granular sludge beds and internal circulation reactors.

 

Theoretically Designed Biodigester

 

Construction:

The digester tank is fitted with the inlet for dumping the organic waste. The digester is built deeply within the ground.  There is no leakage should be allowed within the tank. It may be sealed with concrete or metal. At the top, two holes is left for installing electrodes. The electrodes are connected to the external circuit. They are separated by the permeable membrane for electron diffusion. There is two more inlets for watering and pressure maintenance. One outlet for Biogas which is connected to the generator via a control chamber. In this control chamber, the unwanted gases are removed from the mixture to obtain more methane. There is an outlet for transferring sludge to the vermicomposting ditch. Where the sludge is further composed to manure by vermicomposting. Nearby the tank, a bioplastic degrading chamber is set over the composting ditches, which are interconnected with each other. An opening valve is set between this interconnection. The bioplastic chamber should be suitable for the faster degrading yeast.

 

Working:

The organic waste is fed through the inlet tube. The microbes for anaerobic digestion are encouraged within the tank. Hyrolysis is enhanced by watering through the appropriate inlet.  The microbes for the MFC are allowed to grow within the chamber. After 60 to 90 days, the accumulation of gases increases. Simultaneously, the generation of electricity is started by MFC. It can be utilized for the domestic purposes. After the required amount of gas gets accumulated, it is allowed to enter the control chamber in which it is processed to remove maximum amount of methane by Separation process. The separated methane allowed to pass through the generator for the electricity production.  After a particular consumption of sludge, it is transferred to composting ditch. Then by the process of vermicomposting it is converted to manure. The bioplastics are dumped in the chamber over the composting ditch. After 90 days, the decomposed bioplastic waste is allowed into the compost ditch such that its toxicity is further reduced. Then, it is excavated to the environment. Finally, the electricity is supplies domestic purposes.

 

For Degrading Bioplastic:

Biodegradable plastics are composed of esterified organic acids that are solid at room temperature. From the phyllosphere, we isolated various species of Pseudozyma yeasts that degraded PBS and PBSA films. Pseudozyma spp. strains, which were easily isolated from the leaves and husks of paddy rice (Oryza sativa) and vegetables, secreted biodegradable plastic-degrading enzymes that degraded poly-butylene succinate (PBS) or poly-butylene succinate-co-adipate (PBSA) film to a greater extent than other microorganisms.

 

·        GB-1 Smooth C. flavus

·        Wrinkled P. antarctica

·        GB-5S Smooth C. rajasthanensis

 

1&2- Waste Inlet; 3-Cathode; 4-Anode ; 5-Proton Exchange Membrane; 6- Vermicomposting  ditch; 7- Bioplastic degrading chamber;  8-Watering Inlet; 9-Pressure controller 10- Control Chamber; 11-Generator ; 12-Electricity Production

 

Micro turbines for electricity generation using Biogas:

The digester gas can be used as fuel in reciprocating engines or in a micro turbine. Each of these prime movers can power a generator to create electricity.

 

DIGESTER GAS à TREATMENT &COMPRESSION SKID à RECIPROCATING ENGINE GENERATOR

 

ELECTRICITY

 

Separation Process:

(Based on the experiment given by Pual Harris, University of Agricultural Management)

 

A syringe body fitted with flexible tube and dilute sodium hydroxide (NaOH) or potassium hydroxide (KOH) solution can be used to quickly estimate carbon dioxide percentage for field purposes, as NaOH absorbs CO2 but not methane. This is not exact as there may be some CO2 remaining in the gas phase.

 

Vermicomposting:

Vermicompost is the product or process of composting using various worms, usually red wrigglers, white worms and other earth worms to create a heterogenous  mixture of decomposing vegetable or food waste, bedding materials, and vermicast. Vermicast, also called worm castings, worm humus or worm manure, is the end-product of the breakdown of organic mannure by an earthworm. These castings have been shown to contain reduced levels of contaminants and a higher saturation of nutrients than do organic materials before vermicomposting. Containing water-soluble nutrients, vermicompost is an excellent, nutrient-rich organic fertilizer and soil conditioner. This process of producing vermicompost is called vermicomposting.

 

Microbial Fuel cell:

Bacteria have such a rich diversity that it can handle almost any waste organic compound in their daily diet.  Metal reducing species such as Geobacteria sulfurreducens, Alteromonas sp. Shewanella spp. and Desulfuromonaceae, Alteromonadacea families are suggested for MFC’s and commonly employed. Metal reducing species have the special ability to act as self mediators, transferring electrons to the anode through physical contact. These organisms have an outer membrane cytochrome oxidase type c protein that allows transfer of electrons from the interior of the bacteria cell membrane to the exterior of the cell membrane. These bacteria which have pili on their external membrane are able to transfer the electron via these pili.

 

 

RESULT AND DISCUSSIONS:

Based on the survey conducted by Thomas E. Vik, P.E. DEE:

McMahon Associates, Inc. in the Grafton village digester.

Primary Sludge to Digester 2,580 lb/day

Secondary Sludge to Digester 1,193 lb/day

Total 3,773 lb/day

Assume Volatiles are 75%

Volatile Solids(vss) to Digestion = 3,773 lb/day x 0.75  = 2,829 lb/day

Assume 15-C.F. of digester gas produced per pound of volatile solids destroyed.

Gas Production = 1,415 lb/day VSS destroyed x 15 C.F./lb  = 21,225 C.F./day

Gas Production (cfm) = 21,225 C.F./day 

24 hr/day x 60 min/hr = 14.7 cfm

Each microturbine will generate 30 KW at a digester gas feed rate of 13.13 cfm.

KW Generation Potential = 14.7 cfm x 30KW  13.13 cfm  = 34KW

 

In the Sludge, Anaerobic digestion only removes organics, and the main mineral material and almost all nutrients remain in the bottom sludge.

•           Phosphorus: almost 100 %  

•           Nitrogen (ammonium):  and 50 to 70 %

 

The ammonium released can be directed to the plants for its growth.

 

In the case of Microbial fuel cell, Lab estimates that a MFCs operated wastewater treatment plant serving 100,000 people or a large industrial plant could produce around 0.8 megawatts, which is enough to power about 500 homes.

 

CONCLUSIONS:

The amount of biogas depends on the waste itself and design of the digester. Some digesters can yield 20 liters of biogas per kilogram of waste up to 800 liters per kilogram. Moreover the microbial fuel cell acts as boosting factor to reduce the liquid waste. Employment of yeast to degrade the bioplastic will decrease the accumulation to some extent. Though the biodigester is an old technique of digesting the organic waste, we are in a critical situation to deal with the increasing wastes. Daily the accumulation of waste is keep on increasing, if this continuous the world will be in threaten with these dumps.  Although there are many advantages and limited disadvantages, the researches are going on to rectify it, soon it will be implemented all over the world. Hope for the healthy world with green environment.

 

REFERENCES:

1.       Chaudhuri, S. K. and Lovley, D. R. (2003) Electricity generation by direct oxidation of glucose in mediatorless microbial fuel cells.

2.       Willy Verstraete1, Microbial Fuel Cells: Recent Advances, Bacterial Communities and Application Beyond Electricity Generation, Department of Environmental Science and Engineering.

3.       Park, H. S. and Kim, H. J. (2003) Operational parameters affecting the performance of a mediator-less microbial fuel cell.

4.       Roller, S. D., Bennetto, H. P., Delaney, G. M., Mason, J. R., Stirling, J. L. and Thurston, C. F. (1984) Electron transfer coupling in microbial fuel-. J. Chem. Technol. Biotechnol. B- Biotechnology vol. 34

5.       Comparison of redox-mediator reduction rates and Respiratory rates of bacteria. BPO (2006): Support Project to the Biogas Programme for the Animal Husbandry Sector in some Provinces of Vietnam. BP I Final report. Hanoi: Biogas Project Office (BPO) Hanoi.

6.       Bunny, H., Besselink, I. (n.y.): The National Biodigester Programme in Cambodia. In Relation to the Clean Development Mechanism. National Biogidgester PRobramme and NV Netherlands Development Organisation.

7.       FAO (1996): Biogas Technology - A Training Manual for Extension. Consolidated Management Services Nepal (P) Ltd. and Food and Agriculture Organization of the United Nations (FAO).

8.       GTZ (2009): Biogas sanitation for black water or brown water, or excreta treatment and reuse in developing countries. Draft Version.(=Technology review). Eschborn: German Agency for Technical Cooperation  GmbH (GTZ) and Sustainable Sanitation Alliance (SuSanA).

9.       ISAT/GTZ (1999): Biogas Basics. (=Biogas Digest, Volume I). Information and Advisory Services on Appropriate Technology (ISAT) and German Agency for Technical Cooperation GmbH (GTZ).

10.     Joensson, H., Richert A., Vinneraas, B., Salomon, E. (2004): Guidelines on the Use of Urine and Faeces in Crop Production. (EcoSanRes Publication Series, Report No. 2004-2). Stockholm: Stockholm Environment Institute (SEI)

11.     MANG, H.-P., (2005): Biogas Sanitation Systems. (=Ecological sanitation course, Norway, 15.-20. August 2005). Beijing: Chinese Academy of Agricultural Engineering.

12.     Mes, T.Z.D. de, Stams, A.J.M, Reith, J.H., Zeeman, G. (2003): Chapter 4. Methane production by anaerobic digestion of wastewater and solid wastes.  In: Reith, J.H., Wijffels, R.H., Barten, H.(Eds.) (2003): Biomethane and Biohydrogen. Status and perspectives of biological methane and hydrogen production. Dutch Biological Hydrogen Foundation and the Netherlands Agency for Energy and the Environment.

13.     Mueller, C. (2007): Anaerobic Digestion of Biodegradable Solid Waste in Low- and Middle-Income Countries. Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC)

14.     Muench, E. (2008): Overview of anaerobic treatment options for sustainable sanitation systems. In: BGR Symposium „Coupling Sustainable Sanitation and Groundwater Protection“ 14 – 17 Oct 2008, Hannover, Germany. Eschborn: German Agency for Technical Cooperation (GTZ) GmbH.

15.     Nijaguna, B. T. (2002): Biogas Technology. New Delhi: New Age International (P) Ltd.

16.     Pipoli, T. (2005): Feasibility of Biomass-based Fuel Cells for Manned Space Exploration. In: Proceedings of the Seventh Eurpean Space Power Conference, Stresa, Italy. 9 to 13 May 2005.

17.     Sasse, L. (1988): Biogas Plants. German Appropriate Technology Exchange (GATE) and German Agency for Technical Cooperation (GTZ) GmbH    Available at: http://www.borda-net.org/modules/wfdownloads/viewcat.php?cid=5  [Accessed: 25.04.2010]

18.     Well (n.y.): Using Human Waste. (=Well Technical Briefs, No. 63)  Loughborough: Water and Environmental health at London and Loughborough (Well)    Available at: http://www.lboro.ac. uk/well/resources/technical-briefs/technical-briefs.htm  [Accessed: 26.04.2010]

19.     Werner, U. Stoehr, U., Hees, N. (1998): Biogas Plants in Animal Husbandry. German Appropriate Technology Exchange (GATE) and German Agency for Technical Cooperation (GTZ) GmbH    Available at: http://www.scribd.com/doc/27434211/Biogas-Plant-in-Animal-Husbandry [Accessed: 25.04.2010]

20.     Yadava, L. S., Hesse, P. R. (1981): The Development and Use of Biogas Technology in Rural Areas of Asia (A Status Report 1981). Improving Soil Fertility through Organic Recycling. (=Project Field Document No. Food and Agriculture Organization (FAO) and United Nations Development Programme (UNEP)

 

 

Received on 29.08.2013                             Accepted on 01.09.2013        

©A&V Publications all right reserved