While researching meat consumption and production in China last month, I visited two farms that have installed large-scale biogas digesters. These intriguing, bulbous contraptions capture animal waste, prevent pollution, make use of a renewable source of energy (methane), and transform the icky stuff into a rich fertilizer for crops. Biogas digestion has not been widely used by farmers in the U.S. (for reasons I’m still trying to understand) but has long been part of China’s rural energy strategy: the government estimates that today some 35 million small farmers have small-scale digesters installed in their backyards, a figure reflecting decades of work to distribute them. China has been called “biogas capital of the world” and now is making another big push to encourage large-scale farms, which are a key part of the government’s agricultural intensification strategy, to install them too.
How does it work? Well, biogas is a byproduct of the fermentation of waste. Micro-organisms go to work in anaerobic conditions, though I understand some digesters operate under aerobic conditions. As the bacteria work their way through the waste, they kill off the pathogens, and release a mixture of gas heavy on methane with a touch of carbon dioxide. That gas can then be used to power a stove, a farm, and can even go back into the grid if there’s enough of it and the transmission lines are set up.
In my conversations with Chinese farmers and even officials from the Ministry of Agriculture it was difficult to get a handle on exactly how many biogas digesters are in use on industrial-scale farms in China. This is an important question as small farms are increasingly replaced by big farms and farmers grapple with mounting piles of waste that can pollute waterways and contribute to dead zones in the ocean. (According to the Ministry of Agriculture, the volume of livestock and poultry manure increased from 3.8 billion tons in 2000 to 4.8 billion tons in 2008 and is responsible for much of the phosphorus and nitrogen discharges into waterways.) But an article recently published in China Daily cites a discouragingly low number: less than one percent of the 4.2 million large-scale farms for pigs, cattle and chicken use biogas digesters to dispose of livestock waste. I learned that some provincial governments are offering a number of incentives and subsidies — up to 50 percent of the cost of installation in some places — but apparently this coupled with the myriad environmental benefits of using the digester is not enough to lure most farmers.