The first household biogas plants were installed by well-off families in the forties. However, biogas was not propagated or promoted extensively until around 1970. After a phase of massive campaigns some million biogas plants were constructed, but these only functioned to a minor extent due to technical defects. The focal point of biogas dissemination was the province of Sichuan, and here especially the area around Mienyang. Due to climatic conditions, biogas only played a less significant role in Northern China. Biogas plants spread most rapidly in areas where politicians particularly devoted themselves to this task and in areas whose traffic infrastructure was well developed and which and were not, in fact, among the poorest of regions.
The interaction of the three levels, state, cooperative and household was a favourable atmosphere for the dissemination of biogas in periods of a strongly socialist tendency. The state provided the skeleton conditions, the cooperatives or communes provided material and paid for the labour for the otherwise private biogas plants. On the user side also there was hardly any coalition of interests between communes and cooperatives. This very interesting interaction of varying levels has ceased since the introduction of privatisation. For example, since privatisation straw is far less frequently used in the biogas plants as emptying of the plants involving a high work input no longer becomes necessary because the digested straw no longer has to be provided for use on communal fields as it had to be during times of communal management.
Since 1982 obligatory standards have been prescribed and applied in the construction of biogas plants. At the same time, the aggressive dissemination strategy has been cut back, scientific research has been intensified and direct subsidies have been reduced. Since subsidies were abolished the number of plants built annually has slumped. In Sichuan, in 1992 there were around 1.7 million biogas plants in operation.
Biogas dissemination is integrated into the administration structure of the Ministry for Agriculture. Local biogas offices are the reference points for farmers. It is here where they receive advice and where they commission the biogas plant. Technicians supervise the construction of the plant which is carried out by private companies which, in some cases have specialised in biogas plants. Costs for labour and material are borne by the farmers. The gas appliances are purchased against payment in the biogas offices.
Direct subsidies have been abolished but in some individual cases the farmer receives allowances from an Agricultural Supporting Fund or from state enterprises which have taken over sponsorship of biogas plants or which employ owners of plants.
In the biogas offices four sizes of standardised plants are offered; the most frequently built are plants with 6 m3 digester volume. These are fixed-dome plants which are either concreted or are fixed domes built of bricks according to the availability of materials locally. The pipe connected to the compensation chamber is at medium height. Such details and similar matters have been scientifically investigated over many years and finally standardised.
According to high-level biogas officials, the strategy of biogas dissemination is based on the recognition that biogas plants are important in saving energy, in improving agriculture and in the protection of the environment. However, it is assumed that these overriding objectives are of little significance for the potential owner of the plant in his decision to invest. It is for this reason that an increase in income, by intelligently integrating the biogas plant in the production process, is emphasised as the incentive for investment. The greater role here is played by the utilisation of slurry. Consequently, production processes involving the use of the slurry for the cultivation of edible fungi, for fish farming, pest control or as pig food are propagated which thus increase the value of the subsequent products. The use of human nightsoil as substrate is, of course, a condition of this, and in fact, it is practised in 80% of all cases.
A summary on the technical development is given by Cao Guo-Quiang (Overview on Biodigester Development in China, BIOGAS FORUM No. 48). An interesting case study by Hu Qichin on the rural district of Xindu (published by AIT Bangkok, 1991) describes, in addition to many details, the drastic decline in demand in recent years.