Here Comes A Portable Biogas Generator
It is true that one man’s junk is another man’s treasure. In agriculture, farm wastes such as rice straw, bio-solids, from vegetables, grasses, biodegradable feedstock, and manure are not immediately dispose as these could he alternative sources of fuel energy.
These agricultural wastes are converted into biogas fuel through an anaerobic process. Biogas, which is comprised primarily of methane and carbon dioxide, could be used as fuel for generating electricity at homes and farms particularly in remote areas where electricity is limited. These could be burned directly for cooking, heating, lighting and process heat, and absorption refrigeration.
But how will we generate biogas fuel from these agricultural wastes? This is possible with the Portable Biogas Generator or Portagas.
INTRODUCING THE PORTAGAS
Portagas was developed by a group of researchers from the Bureau of Soils and Water Management (BSWM) led by Dr. Rogelio Concepcion and Dr. Gina Nilo with Alan Anida, Carlos Serrano, Leonora de Leon, and Victorcito Babiera. Its feasibility and development were undertaken from 2001 to 2006.
According to Dr. Nilo, all common biogas generators have two main parts: the digester, where the slurry is mixed and fermented to produce the gas; and the gas holder, where the gas is collected and connected to a burner for cooking or lamp for lighting.
Prior to the development of the portagas, BSWM developed four biogas generators. The first ever model is an integrated batch type generator developed in 2000. It is called “integrated batch type” because the gas holder is not separated from the digester. In 2001, it was modified into a split-batch type (digester and gas holder are separated) and was referred to as PortaGas Model-1 or Pm-1. It has a floating gas holder attached to a Bunsen burner for cooking.
Using a surplus burner from a non-functional auto-ignition LPG stove, the previous model was further developed in 2002 and it was called Pm-2. Then a more refined model called Pm-3 was developed in 2003. It has a pre-fabricated cast-iron manual gas stove and simplified gas holder fittings.
Finally, the most simplified model, Pm4, was developed. This is the upshot of the Portagas.
Recycled drums fixed with necessary fittings were used as the digesters and gas holders for Portagas. A unit consists of 10-drum digesters and two sets of gas holders. Each gas holder is made up of two drums, one for the water and another for the gas. According to Dr. Nilo, this floating type gas holder, which serves as the pressure regulator, is the “heart” of this generator.
DERIVING BIOGAS FROM AGRICULTURAL WASTE
While the floating gas holder serves as the “heart” of the generator from which the gas is being accumulated, agricultural wastes serve as the “nub” or the meat of the generator wherein the biogas will come from.
For the portagas, BSWM utilized farm wastes (fresh rice straw and animal manure) and urban wastes (vegetables and fruits refused, grasses and ornamental plant trimmings) to convert into biogas.
These wastes are collected and loaded into the drums, making up two-thirds of the loaded drum. After which, the animal manure and water are mixed into the container. The drum is then compressed with a concrete hollow block, which serves as weight on top of the mixture. The drum is sealed and left for several days to digest and ferment.
Gas was discharged from the collectors after 14 days. On the 15th day, a burner may be attached for the initial flame test. It is advised not to conduct flame test directly from the gas collectors’ nozzle to avoid accident. A secondary hose must be inserted from the gas collector’s nozzle onto the burner before conducting flame test.
The agricultural wastes inside the drums are to be unloaded after three months.
After the trial, it was found that the wastes charged into the Portagas were able to produce 25 cubic meter of biogas fuel or one cylinder of LPG (11kg), which is the approximate fuel consumption of a typical Filipino family for two and a half months.
Results also showed that biogas emission consistently increases within the first three weeks and fluctuates within the next five weeks. Emission of biogas dwindles after the fifth week due to the declining amount of carbon in the substrate.
THE “ZERO WASTE” FACTOR Developing the portagas is said to be a “zero waste” endeavor because the digested agricultural waste, which is unloaded from the drums, now becomes byproducts, which will serve as compost for soil fertility enhancement.
In the study trial conducted, among the byproducts collected were 98.5 kg of compost and 750 liters of organic liquid fertilizer. Results showed that the nitrogen (N) content of the compost increased from 0.6% in fresh rice straw to 1.5%.
According to Dr. Nilo, this is equivalent to two bags of organic fertilizer. In addition, the digested compost from biogas generation contributed greatly in crop production and in mitigating the methane gas greenhouse effect. Benefit-cost analysis of the portagas showed that return of investment starts after the 12th cycle.