How does a pig farm end up producing a power station?
A new model of circular economy at a Pengshui nucleus breeding pig farm: pig manure produces biogas and even generates electricity, and the biogas slurry is a "super nutrient solution" for crops
Before our eyes are two huge gas storage tanks and a miniature power station, making it hard to believe that we are standing in a pig farm.
"I'd only ever heard that water and coal can generate electricity. I never imagined that stinking pig manure could end up 'conjuring up' electricity!" said villager Yang Longzhi, who lives next to the pig farm, with emotion yesterday.
A "big fellow" in a small mountain village
This is a small mountain hollow in Baojia Town, Pengshui Autonomous County, where 7 households of villagers live scattered about.
In May last year, the Jiyuan Livestock Pengshui Nucleus Breeding Pig Farm, with a total investment of 21 million yuan, officially went into operation here.
"In addition to the nucleus breeding pig farm, which keeps 500 grandparent sows year-round, there is also a secondary multiplication farm keeping 450 foreign two-way crossbred sows year-round, as well as a fattening farm for foreign three-way crossbred commercial pigs with an annual output of 10,000 head," introduced Xie Xingrong, general manager of Jiyuan Company.
It is reported that the breeding farm has introduced the newest and best breeding pig breeds, including the new English line, new American line and Canadian line, and can provide 4,000 fine purebred grandparent breeding pigs and 6,000 two-way crossbred sows to the southeastern Chongqing area every year.
This large-scale breeding farm produces more than 10 tons of fresh pig manure and over 100 cubic meters of wastewater every day.
However, a large-scale biogas project with a total investment of 4.5 million yuan completely solved this pollution problem.
Stinking pig manure "turns into" electricity
"According to the different raw materials, a two-stage anaerobic fermentation process is used, effectively solving the problem of treating the farm's manure and sewage," introduced technician Ju Jian. "The biogas produced in the fermentation tank is purified and then stored in the gas storage tanks."
Beside the two huge gas storage tanks is a miniature power station.
"The biogas project treats 12.5 tons of fresh manure and 125 cubic meters of sewage per day, and produces 464 cubic meters of biogas per day," Ju Jian introduced. This biogas is supplied free of charge for the office and domestic gas use of the breeding pig farm and the domestic gas use of the surrounding 7 farming households, yet at most only 50 cubic meters are needed each day.
The remaining roughly 90 percent of the biogas is sent to the miniature power station to generate electricity.
The electricity generated is also transmitted through lines to every corner of the breeding pig farm and to the 7 farming households.
"My refrigerator, washing machine and rice cooker all use biogas electricity for free," Yang Longzhi said with a chuckle.
"If the power station runs at full load, it can generate 1,000 kWh per day," Xie Xingrong said, but in reality the breeding pig farm and the farming households simply cannot use that much.
"At most only one third of the biogas is actually put to use," Xie Xingrong said with some regret. "The surplus can only be released for now."
A better approach would be to pipe the surplus biogas to Baojia Town, two kilometers away.
"But the one-time investment is relatively high, and a booster station would be needed, so it hasn't been built yet," Xie Xingrong said.
Discarded biogas slurry becomes "super fertilizer"
According to Zeng Linfang, director of the Pengshui Science and Technology Commission, this biogas project at the breeding pig farm is "extremely high in technological content."
Standing beside the biogas tank, one can hardly smell the slightest stench.
"By using the waste heat of a 50 kW biogas generator set, the temperature of the two-stage biogas tank is kept at around 35 degrees, allowing the pig manure to ferment quickly and fully," Zeng Linfang introduced.
With sufficient biogas, the breeding pig farm has put to use equipment such as high-power stoves, large rice cookers and water heaters; nearby farming households not only use biogas for cooking and stir-frying, but also use biogas to cook pig feed, so they no longer need to burn firewood.
"What makes me happiest is still the biogas slurry discarded by the biogas project," Yang Longzhi said.
Since the biogas project was put into use in October 2009, he, like the surrounding farming households, began using this free biogas slurry to irrigate crops, and has never spent money on a single grain of chemical fertilizer again.
"The breeding farm produces 45,600 tons of biogas slurry every year, and can also produce 1,368 tons of pollution-free organic fertilizer," Xie Xingrong introduced. At present, the surrounding villagers have used only a very small part of it.
In order to make full use of the biogas slurry and organic fertilizer, the breeding farm is currently working with the local area to build a 1,000-mu pollution-free vegetable base. The vegetable base is located only about 100 meters from the biogas tank, and the pipeline network has now been laid.