ANOR Newsletter
A mini-digester network:----------------A strategy for manure disposal
Recently, animal husbandry in China has
been developing very rapidly and contributed
greatly to the improvement of life standard ofChinese people. The distribution of thefarms has a distinguish tendency ofintensification and centralization around large
cities because of the economic concern. The
concomitant production of manure once
caused a great environmental issue in thecorresponding areas. Presently, the disposal
has to undergo a standard treatment
technology such as anaerobic digestion, A/O
process, to meet the rigid national standard forthe discharge of the wastewater and solidwastes. However, a way of animal raising,typically pigs, which probably occurs in otherdeveloping countries, has a difficulty in waste
disposal.
In many areas, the animal farms are notoperated in a large scale; farms each having
several ten heads of animals are quite popular,
and distributed scatteredly in land with a smallarea. Two decades ago, manure, in this case,was used as an important nutrient resource andplayed a crucial role in better cropping.
However, the importance of manure as anutrient resource has declined with thereduction of fertilizer cost and the increase oflabor and transport cost, and therefore, farmers
are reluctant to use manure as “organicfertilizer”. Furthermore, the large quantity ofmanure produced, due to the increase ofanimals in number, in a relative small area
exceeds the loading capacity of the landaround the farms. On the other hand, it isobvious that farmers are not able to establish astandard manure treatment plant individually
because of the high cost. Of the limited
technologies available for manure treatment,anaerobic digestion seems to be a proper way
for manure treatment, which supplies farmers
with biogas for energy and residues fornutrient purpose with low operation cost.
However, the collection facility for manure isalso prohibitively expensive for the farmers.
Each farm can only build a digester small inscale. This small-sized anaerobic digester
was widely adopted in China in 70s andproved unsuccessful in many places. The
main problems it encountered were:Ø relatively high cost in that time;Ø poor liability in biogas production.
Now, farmers do not have an economic
problem in building the small-sized digester asshown in Fig 1; but the liability of biogas
production hampered yet the wide acceptanceof the way of manure treatment. An aerobic
digestion network, which is indicatedschematically in Fig 2, is established byconnecting these “mini-digesters” with biogas
pipe system, and proved very successful inbiogas supply.
The biogas produced is“buffered” by the pipe system and thus an
individual biogas consumer uses the biogasthat probably comes from all the nearby“min-digester”, avoiding the temporary biogasshortage. Experience shows a stable supplyof biogas in four seasons. The liquid manure
following digestion can be used for
fertilization purpose since the most of thecarbonaceous materials have been removed.
Field experiment shows that this kind ofnutrient resource is better for cropping,especially for product quality.
(March, from Zhejiang University, China)

Fig 1. Mini-anaerobic digester.

Fig 2. A mini-digester network.
: Pipe system;: Biogas supply to farmers;: An individual mini-digester.