SICHUAN'S HOME-SCALE BIOGAS DIGESTERS

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

Furthermore, when the digested organic fertilizers were applied to existing fields (both the liquid effluent and dried sludge forms were used), crop yields rose noticeably, ranging from an average rice harvest increase of 7.8% to a 15.2% net gain in wheat production!

Perhaps even more significant, though-especially in view of the lack of information available in our own country on the subjectis the Chinese attitude toward human waste and its role in the ecological cycle. Naturally, owing to the fact that no less than 16 different pathogenic bacteria can be present in human excrement, the disposal of such material must be handled cautiously. The careless dispersal of raw sewage (and even of treated matter that hasn't had adequate time to "detoxify") often results in the spread of infectious disease.

However, if properly processed, human waste can be of great benefit to the soil ... and—in some regions of rural China, where sanitary facilities have generally been primitive, at best—a conscientious program of feces disposal in conjunction with biogas manufacture has proved to be the answer not only to energy and fertilizer shortages, but to many community health problems as well.

Sichuan scientists have proved repeatedly that a conglomerate of human and animal wastes contains, after a four-week or longer anaerobic digestion period, from 90 to 99% fewer parasite eggs than untreated manure does. A great number of harmful pathogens are destroyed in a matter of hours after the material enters the biogas pits, but the more tenacious parasites (including hookworms, tapeworms, and Schistosoma) endure for extended intervals . .. and it's only by means of the relatively high-temperature (85° to 104°F), airless environment of a methane generator that such undesirable organisms are eliminated, allowing the spent "slurry" material to be safely spread on fields used for the production of edibles.

HIGHLY FUNCTIONAL . . .

Naturally, no one specific biogas plant plan is used throughout China . . . and, by the same token, even those of similar design must be modified to fit the terrain and soil type of the area in which they're used. Whether the methane plant serves a rural household of several people or a commune of several hundred, it is constructed with a number of important criteria in mind.

First, the plant is invariably located in the ground, which [1] saves valuable farmland, [2] provides thermal insulation both to promote digestion of the manure substrate and to discourage the cracking that can result from swings in temperature, [3] allows the substratum soil to serve as a structural aid, and [4] takes advantage of gravity to assure trouble-free feeding.

Site selection is also carefully considered. Ideally, a pit is located near a family's living quarters (especially in the case of the household-sized digester) so the latrine can be situated fairly close to the house . . . but at the same time, the unit should also be near—or in some cases under—the pigsty, to provide convenient manure loading. (The floors of such stalls typically slope into a trough that leads directly to the digester inlet, permitting the waste to be washed downward daily.)

RSS | Comments | E-mail | Print