munities and products. This concept has been passed down over generations and still exists in the modern expression of “local production for local consumption.”

In the Edo era, night soil and ash from urban areas were effectively used to fertilize the soil in farmland and to grow vegetables. These wastes were not only accepted by farmers but also traded and bartered for money or vegetables. As well as helping suburban farmers fertilize their farm soil, such practices even fostered the development of SMC blocks between cities and the surrounding farm vil-

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# Safe and sanitary night soil reservoirs in Japan

Rice cultivation was introduced to Japan from China during the Yayoi era. Initially, cultivation technologies were developed under the technical guidance of settlers from the Korean Peninsula. However, original irrigation technologies and farming methods, more suitable for the climate and the natural features of Japan, were also developed by the Japanese people themselves. In the early years of rice cultivation, fertilizer was available in the form of young leaves and weeds or ash from slash-and-burn agriculture. As the population grew and paddy fields expanded, farmers began using cow and horse manure. Later, when the double-cropping of rice and wheat began, during the Heian era, people also began using night soil as fertilizer.

However, there is a problem associated with handling night soil in that it can harm the living environment and has a bad odor if left untreated. If any live pathogenic bacteria or parasitic worm eggs are present, night soil can even spread infectious diseases. Another problem is that, if used as fertilizer without any treatment first, night soil may damage plant roots because it generates heat and releases hazardous gases such as ammonia during decomposition.

Hence, before being used as a fertilizer, night soil needs to be chemically or biochemically stabilized in order to prevent decomposition and it must be processed to ensure sanitary safety and prevent infectious diseases spreading throughout society. The key question here is how people, long ago, were able to stabilize night soil and make it safe to use.

The answer is the night soil reservoir. Night soil reservoirs are facilities to ferment night soil and convert it into fertilizer. These facilities could be as simple as a hole dug beside a field and covered with a lid.

Farmers mixed rice straw into the night soil inside the reservoir. When night soil, which is a mixture of carbohydrate, fat, nitrogen compounds and many other organic substances, is stored in an airtight chamber with the lid closed (under anaerobic conditions) and with rice straw added, it then decomposes into substances with a relatively simple structure (such as organic acids, fatty acids and amino acids) as a result of the metabolic activities of various anaerobic bacteria. Subsequently, methane bacteria then generate gases such as carbon dioxide, methane, hydrogen, nitrogen, ammonia and hydrogen sulfide. Eventually, night soil is stabilized and rendered free of almost all round-worms, which are killed by the heat generated during the fermentation process.

In the Edo era, the shogunate government ordered all citizens to install a large cesspool with each toilet, in order to efficiently store all night soil. This led to the installation of cesspools in rural and urban houses alike. The night soil stored in these tanks underwent partial anaerobic decomposition before being collected and transported to suburban farms by boat or by horse or ox-drawn wagons. This night soil was then stored in night soil reservoirs for stabilization and sanitation before being spread on the fields as fertilizer.

During the Edo era, Japan therefore had a true SMC Society in which night soil was sanitarily treated for effective use without affecting the living environment, thereby making the best possible use of the limited resources available. People today, who no longer make use of night soil, can learn a great deal from the sanitary recycling of night soil in the Edo era. It is important that Japan should share the benefits of its experience with developing countries, especially from the perspective of hygiene education and village development.

[Sanitary use of the night soil reservoir]

Source: Ministry of the Environment