A STUDY ON MAIN FERMEMTING CONDITIONS DURING WINTER FOR RURAL BIOGAS PITS IN NORTH CHINA AND TECHNIQUES FOR MAINTAINING AND INCREASING THEIR TEMPERATURE

Five years's experiment and study has shown that Iow temperature is the key factor restricting the production of biogas during winter in North China. The lowest biogas pit temperature should not be under 13℃; the adequate fermenting concentration is between 12%—16%; and the proper proportions of raw materials are 50% corn stalk, 20%pig manure, 20% night soil, 10% horse shit, and 0.3% nitrogen fertilizer. Measures for keeping and increasing temperature consist of digging cold protection ditches, building indigenous hot houses, piling up high temperature compost on the biogas pit, erecting wind preventing walls, etc.with these comprehensive measures, inside and outside the pit,the pit temperature can be raised more than7℃ and the daily average rate of gas produuction can reach 0.165m³/m³ liquid material per dag, this practically solving the technical problem of failing to produce biogas during winter in North China.