Mini-Biogas Digesters For Small Hog Raisers
If the government is really serious about its national organic agriculture program, the Department of Agriculture may as well encourage small hog producers (those with at least four sows with 25 piglets and fatteners) to put up their own mini-biogas digester, firstly for the production of sludge that would be used as a component in organic fertilizer production.
Secondly, the hog raisers would no longer need to spend for liquefied petroleum gas since a mini-digester can generate methane for their domestic use and several neighbors, according to Rommel N. Urgel, a mechanical engineer in Cebu who designs biogas digesters.
Thirdly, mini-biogas digesters would keep the integrity of the environment and safeguard the health of residents.
In our recent trip to Cebu, we visited a 10-cubic meter biogas digester in Sitio Cogon, San Miguel, Poblacion, Liloan. Set up by Rommel, the digester generates methane gas, which is used by six adjoining households for cooking. Each household saved about P600 for the purchase of a tank of LPG whose price is continuously increasing nowadays. That is already P3,600 of savings a month. If the neighbours pay P100 for the gas, for example, they would still have a lot of savings.
Rommel said the size of the biogas digesters would depend on the number of sows, piglets, and fatteners. As a rule of thumb, a 1 m3 digester can handle the waste of a sow and its piglets and fatteners. Thus, the size of the digester could be 4 m3, 6 m3, 8 m3or 10 m3.
According to Rommel, who improved the design of mini-biogas digesters when he was still a new employee of the Alternative Non-conventional Energy Center (ANEC), 1 m3 of digester generates 2 m3 of methane gas a day. Hog manure is fed into the digester by gravity. This means that as the pens are cleaned, the manure goes with the water into the digester. For more stable fermenting at 35°C, the digester is insulated so that variations in soil temperature will not affect the temperature inside.
Actually, before Rommel joined the center in 1987, ANEC technical men from a state college in Cavite constructed five units of 10 m3 digesters for a city abattoir. Unfortunately, the digesters did not work. Rommel said the technical men claimed to have gone through a lot of training on biogas digesters abroad but they were not sure of their application.
He added there are now more than 100 units of mini-biogas digesters in Cebu, as more and more hog raisers are becoming interested in the benefits derived from them.