Biogas – not just cow power - it is renewable natural gas

Many of us consider biogas as just gobar gas or poo power. We can extract many times more energy from other biodegradable wastes than that from cow dung. For example, 1 kg of food waste when decomposed in an anaerobic environment yields 160 litres of biogas whereas non-edible oil seed cake produces 242 litres and bagasse gives 330 litres in the place of 40 litres of cooking gas with same weight of cow dung under similar conditions.

Biogas has vast potential as a sustainable renewable energy source.  Biogas is poised to lead the biofuel race owing to its advantages over the others.  When other biofuels require specific energy crops which may seize food crops or agricultural land, biogas can be generated from different biomass available – municipal waste being the most attractive option. After producing biogas, the anaerobic bacteria provide us a very good fertilizer whereas some other biofuel generation processes discharge toxic wastes. Utilisation of agricultural & other wastes as a resource and the value of the bio-fertiliser are significant for a country whose economy is depended on agriculture. Moreover, the energy content of biogas is higher than that of other biofuels extracted from biomass grown on a unit area. Some studies show that the average ethanol production from cereals and sugar cane crops is 2,400 litre of oil equivalent per hectare. Under the same conditions biogas delivers 4,500 litre of oil equivalent.  

Biogas consists mainly of methane along with carbon-dioxide and hydrogen-sulphide.  Purified biogas or biomethane being very similar to natural gas, it can be mixed with or substituted for the latter (called bio Natural Gas) in vehicles or other applications. In other words, biomethane can directly utilize the natural gas infrastructure.  In countries like Germany, biomethane is already being injected into their natural gas grids.

Biomethane is the cleanest fuel after hydrogen produced from water using solar or wind power.  Hydrogen to be used in fuel cells can be produced from methane also. But the recent technological developments allow the direct use natural gas or biomethane in the fuel cells with reduced cost of operation. Fuel cells, being more energy efficient, reliable and less polluting than other electricity generation methods, can be used in distributed power generation or in vehicles.

The transmission loss, cost of energy storage and transmission are very less for biomethane even compared to electricity as a long distance energy carrier.  The cost of building up natural gas/biomethane pipelines is said to be half that required to build electric transmission lines for the same quantity of energy transmitted. Biogas production at source of biomass will be convenient rather than transporting the biomass elsewhere for generating electricity. Besides all these, if waste heat from decentralised power generators can also be used, we could utilise up to 85% energy of the source compared to 30% energy reaching the users in the case of coal based power plants.

It is projected that by 2050 global primary energy demand will be 1014 EJ (Exa Joules) whereas the total biomass alone has an energy potential of 1,135 EJ without affecting food production.  Sweden is already using biogas to meet 25% of its energy requirement with majority being used for heating and as vehicle fuel including that for trains.

Our tropical climate is favourable for the bacteria in anaerobic decomposition of biomass and for the growth of energy crops or other biomass. Governments should create a natural gas infrastructure and promote biogas on a big way.  Even if they are not interested in helping the common man, it can bring about reduction in imports of petroleum (for fuel and fertiliser) to save the ‘poor’ oil marketing companies from their ‘under recoveries burden’.

Super plants – a solution to food-water-energy shortage

According to some U.N. estimates, by 2030, a rapidly growing population in the world will need at least 50 percent more food, 45 percent more energy and 30 percent more water. Small aquatic plants are promising a way out in this context.

Tiny water plants like duckweed and azolla are characterised by their tremendous growth. Under favourable conditions, they can double their mass in 1-3 days absorbing carbon dioxide from air through photosynthesis. These little plants can fix the greenhouse gas far better than other plants besides offering solutions to many other burning issues. Some 49 million years ago, azolla is believed to have reversed the greenhouse effect which is known as the azolla event.

Growing them

Various species of duckweed and azolla can be grown in shallow ponds or even in trays with water height less than 10cm or 4inch. These free-floating plants do not require full sunlight, a 50% shade is necessary for their optimum growth. Places getting heavy sunlight allow growing them in between other crops or on multileveled trays/channels with top level for drying harvested plants. The diluted slurry from biogas digesters is found to be a good medium for their growth.  Vivekananda Kendra-Natural Resources Development Project (VK- NARDEP) in Kanyakumari, Tamil Nadu promotes growing of azolla on silpauline lined pits in the backyards or terraces to reduce the production cost of the small plant to less than 30paise per kg harvested.

Azolla & duckweed

Duckweeds grow by taking up nutrients like nitrogen, phosphorus & potassium from water and some of their species can tolerate salinity to an extent.  Azolla can fix nitrogen directly from the atmosphere with the help of blue-green algae called Anabaena azollae, which lives symbiotically in the leaf cavities of the fern plant. These little plants can rejuvenate biologically dead water bodies.

Azolla in agriculture

Rice farmers in China and Vietnam have been using azolla for centuries in their wetland fields. Azolla is allowed to grow on rice fields before the rice plants are transplanted. Azolla forms a thick mat over the water surface making it difficult for weeds and mosquitos to grow. Studies by Tamil Nadu Agricultural University shows that azolla can contribute, besides other nutrients, 40-60 kg N/ha per rice crop. Use of urea/nitrogen fertiliser and other fertilisers can be reduced if azolla is used as bio-fertiliser. Azolla has been used as green manure for other crops also. Because they are grown locally, it reduces the use of petroleum products otherwise needed for the processing & transportation of fertilisers giving savings to the nation.

As a feed

Duckweed and azolla contains about 30% protein on dry weight basis. They can produce more than 9 tonnes of protein per hectare per year. Farmers around the world use them as a feed supplement for cattle, poultry and fish.

Trials carried out by the VK- NARDEP, with azolla as a feed supplement for diary animals, shows an increase of milk yield when azolla was combined with regular feed and shows that azolla feeding improves the quality of milk and the health & longevity of livestock.

Poultry and fish supplemented with azolla or duckweed were also reported to have reduced the cost of feeds and at the same time shown increased productivity for the farmers.  Besides providing healthy food through its use in agriculture, they being rich in proteins, essential amino acids, vitamins & minerals, the small plants themselves are healthy and nutritious food for humans.

In water purification

Various aquatic plants, mainly duckweed, have been used for treating domestic and industrial wastewaters. These plants grow by absorbing the impurities in the wastewater, thereby enabling us to recover the nutrients from the wastewater and allow reuse of the precious resource. Punjab State Council for Science & Technology is one of the promoters for the duckweed based wastewater treatment system in India.

Biomass to energy

Dwindling petroleum reserves have prompted us to search for alternative sources of energy and biomass is one of the promising routes to the future energy utilisation. Lot of money is being spent on the research to bring out biofuels from biomass.  Some of the edible crops such as soybean and corn were diverted for use in biofuel extraction, which resulted in the rise of food prices. Even larger aquatic plants like water hyacinth are now considered as a resource and not as a menace, owing to their biomass potential. According to VK- NARDEP, the biomass yield of Azolla is 1000 MT/ hectare/year. On controlled environments with extended day light (using artificial lighting), with increased carbon dioxide presence and optimal nutrient availability in water we could achieve more biomass yield.

Biogas, which consists mainly of methane, can be generated easily from biomass using simple household biogas plants or using sophisticated plants that can convert any organic waste to pure methane and that can release it into a pipelined grid or bottled similar to LPG. Diluted slurry from biogas plants may be used for growing these water plants which make a closed loop of growth and utilisation of these aquatic plants. Biogas will help the houses, restaurants & canteens to reduce the use of costly LPG when cooking. Scientists foresee the future of renewable energy in bio-methane because it is equivalent to natural gas.

Pacific Domes, an US company, grows duckweed along with fish and vegetables in ponds covered with domes maintaining consistent natural sunlight. Duckweeds are hand harvested, dried and fed into generator. A 24 foot dome placed in the backyard is sufficient to generate optimally 5kW electricity (along with 4-7 kg of food daily) at the same price as coal which is significantly cheaper than renewable sources like wind or solar. Carbon dioxide generated in the process here is offset by the growth of duckweed. They also claim that a 60 foot commercial unit optimally generates about 200 kilowatts of electricity besides purifying about 20,000 litres of grey-water per day. With multiple commercial units, it could be possible to generate many Giga Watts of power from the area occupied by typical thermal, hydro or nuclear power stations as they occupy thousands of hectares.

To summarise, the tiny plants can be seen as a

* cheap substitute for imported chemical fertilisers which also gives higher crop yields

* solution to reduce cost of feed for cattle, poultry & fish along with increased productivity

* healthy food for humans

* key for decreasing water pollution and recovery of nutrients from waste water

* carbon neutral renewable energy source, an alternative to the petroleum products.

In other words, the super plants can reduce the cost and increase the availability of food, water & fuels. Governments shall promote the use of the ‘green gold’ by providing kits and training to the farmers, housewives & the unemployed and shall make sure that no land is left uncultivated. Decentralised units for generating electricity or biogas may be setup for utilising excess biomass grown by farmers or wastewater treatment systems. 

Biofuel: Duckweed Vs Soybean

Soybean and other edible crop produce being diverted to bio fuel projects are of great concern for the people around the world as the food prices are rocketing. In this context, it will be worth considering different species of weeds commonly called duckweeds, as they show great potential in this regard as replacement for soybean.

Duckweeds are small, fragile, free floating aquatic plants that grow ubiquitously on fresh or polluted water throughout the world. When conditions are ideal, it’s biomass can double every 1-2 days. The diluted slurry from biogas digesters was found to be a good medium for the growth of duckweed. Duckweeds were also being used by some farmers as a protein rich food supplement for cattle, poultry and fish. In aquaculture, it can assist in controlling the algae growth, which denies oxygen for fishes. Duckweed is eaten by people also, mainly in Thailand. Some of their species are being used for medicine is countries like China.

Advantages of duckweed compared to soybean

* Duckweeds are as good as or better than soybean as cattle, poultry, aquaculture feed.

* Duckweeds give many times more protein yield per hectare compared to soybean.

* Duckweed protein has higher concentrations of the essential amino acids, lysine and methionine, than most plant proteins and more closely resembles animal protein in that respect.

* Duckweeds can be grown in wastewater and can be harvested daily.


Another important use for duckweed is in waste processing. Duckweeds are being used in water treatment plants as they have the potential to purify both domestic and industrial wastewater that too at minimal cost of operation. They also help in recovering mineral nutrients which would otherwise be lost with the wastewater.

There is widespread research interest on generating bio-fuels from duckweeds. We have made advances in production of biogas from aquatic plants like water hyacinth and duckweeds can be easily harvested compared to algae or other aquatic plants. Until better techniques are developed for generating ethanol or biodiesel from duckweeds, generating biogas from duckweed will be the attractive utilisation (in fact biogas is being used in buses, cars and trains in Linköping, Sweden)

So I am envisioning decentralised waste treatment plants in which wastes (organic wastes & wastewater) are being fed into a biogas plant where the wastes are subjected to anaerobic decomposition resulting in odour free, germ free slurry plus of course methane gas. This slurry shall be fed to ponds where duckweeds are grown may be along with fish. Duckweeds should be harvested daily from the pond and shall be fed into biogas plant after pre-treatment.

References:

http://en.wikipedia.org/wiki/Duckweed
http://www.fao.org/ag/againfo/resources/documents/DW/Dw2.htm
http://www.cpcb.nic.in/News%20Letters/Archives/R&D%20for2003/pollutioncontrol.html
http://www.mobot.org/jwcross/duckweed/practical_duckweed.htm
http://www.naturia.per.sg/buloh/plants/duckweed.htm
http://www.herbvideos.com/globald.htm#Duckweed
http://www.carbon-connections.org/downloads/Biofuel%20from%20duckweed%20case%20study.pdf


Picture from http://www.fractalnature.com/duckweed.html

Reusing waste plastics as fuel

Plastics are so adaptable in use that their impacts on the ecosystem are far-reaching. Irresponsible dumping of plastic bags block drains, obstructs the permeability of the soil and causes problems for groundwater recharge. Plastic upsets the soil microbe activity, and once eaten, can kill animals. The estimated quantity of municipal sold waste generated in India every day is 131,000 tonnes or 48 million tonnes annually (2003). Plastics constitute at least seven per cent of this waste or 9,200 tonnes daily. Unlike other wastes, plastics do not degrade easily and is usually advised not to burn them as it emanates poisonous gases during its burning in open air at temperatures less than 400 degree Celsius. It is generally estimated that our households contribute major share of plastic wastes in urban areas in the form of used carry bags, bottles, packets of milk, etc. Packaging constitutes 52% of plastics consumption. The tendency of people in urban areas is to throw these plastics along the roads, as they cannot process them or recycle them in their compounds and it becomes a ‘burning’ problem for Municipalities & Corporations.

Recycling plastics
Most people think that all of their waste plastics can be recycled, but that's not true. Plastics in category 1 (Polyethylene Terephthalate) and category 2 (High Density Polyethylene) are mainly recycled. It is usually called down-cycling because the waste plastics are converted into low-grade plastics. The cost of conversion is also high making the down cycling less attractive and also the conversion process cannot be repeated forever. Plastic categories 4 through 7 -- such as lids, sheets of plastic and wrappers -- traditionally are discarded at recycling centres. But they are of value because they generate heat when burned. Plastics, being derived from petroleum, have the energy content similar to petroleum fuels. The main concern about burning plastics is when type 3 plastics (mainly PVC) are incinerated, because of the chlorinated compounds they contain. There have been attempts in India to use waste plastics in developing road surfaces with it. This does not dispose of the toxins but simply spreads it around, much like in the case of landfills.

Plastics as fuel
James W. Garthe of the Pennsylvania State University has developed a process in 1995 to convert all types of dirty plastics into fuel nuggets. The intent of the nugget process was to direct used plastics into a new raw material stream for energy recovery, either co-fired with coal in community and agricultural boilers or burned directly. The process was developed for waste agricultural plastics, yet it works with plastics found in all sectors of society. Both film and rigid thermoplastics can be accommodated.

The 'plastofuel', as Garthe calls it, overcomes most major impediments in plastic waste management. The Garthe machine is a hydraulic compactor with a heated die. Roughly shred and cleaned waste is fed into the hopper, from where a ram pushes it into the heated die. At exit of the die, the extrudate is sliced by a hot-knife into nuggets. The nuggets may then be stored forever and transported economically. These nuggets can be used as a high-energy fuel supplement for coal-fired applications. In such applications, it is found that plastics will not adversely affect emissions levels as the plastics are burned at very high temperatures. At more than 1,200 degree Celsius, plastics burn completely without leaving out toxic solids and without black, toxic smoke usually associated with burning plastics at the backyards.

A blessing in disguise
In the Garthe machine, the die is heated just enough to fuse the outer skin of the nugget. The energy required for this is minimal. It is in fact a compaction process, readying the waste for storage and transportation. The calorific value in the plastic waste remains trapped. Thus, the energy gained from nuggets is more than what was put in to create them. Cottage level entrepreneurs (similar to Kudumbashree units in Kerala) can generate income by using such a machine, after collecting the waste plastics directly from the source (like the households).

Commercial utilisation of waste plastics
1. GR Technology Company, Ltd. of Seoul, Korea
A new technology, developed by GR Technology Company, Ltd. of Seoul, Korea, burns plastic pellets made from waste plastics of all sorts, initially from agricultural sources. William Bang of GRT arranged to ship one of these burner units to Penn State for testing. It was installed to heat a high tunnel and a greenhouse at the Penn State Horticulture Research Farm. Eventually the burner/boiler system was modified to burn plastofuel nuggets, which were significantly larger than the pea-sized pellets. Testing of the 120,000 kcal/hr heater unit in Korea showed the system meets US EPA emissions standards.

2. Whitehall Cement Plant of Lafarge North America
Lafarge North America, which has begun fuelling the kilns at its Whitehall Township cement plant in part by burning the scraps of non-recyclable plastic. Lafarge says burning plastic could keep more than 10,000 tons of the substance out of landfills each year, while also cutting the amount of coal used by the Whitehall cement plant. The plant, which has burned used tires for several years, now can derive up to 45 percent of its power from tires and plastic. Plastic also costs less than coal, which means the new power source will cut Lafarge's fuel bills. The state Department of Environmental Protection approved the plastic plan after a five-year review, ruling it would not exceed standards for chemical release.

3. Unique Plastic Waste Management & Research Co Pvt Ltd, Nagpur, India
Prof. Mrs. Alka Umesh Zadgaonkar, Head of Department of Applied Chemistry at the Nagpur based G. H. Raisoni College of Engineering invented an Environment friendly catalytic process for disposal of waste plastic. The invented process involves degradation waste plastic using `catalytic-additive’ and is different from the generally existing pyrolytic processes. The laboratory scale set-up was developed in batch mode in which individual as well as mixed plastics were successfully converted in to fuels. The products obtained in the process are Liquid hydrocarbons, Gas and residual Coke. Prof Alka & Dr. Umesh Zadgaonkar started a company named Unique Plastic Waste Management & Research Co Pvt Ltd, which is converting plastic wastes into fuels equivalent to petrol and LPG on a commercial basis.

Summary
This commercial utilisation of waste plastics give great scope for people engaged in waste collection to earn more income, saves more fossil fuel, keeps our neighbourhoods clean and saves landfill space. Policy makers should take into consideration the failure of attempts to ban plastics of various thicknesses.

Read also:
PSU team turning waste plastic to fuel
Waste plastic technology
Burning plastic for fuel a win-win situation
Alka Zadgaonkar wrings plastic waste for profit
Plastic to Petrol: Conversion of waste plastic to energy