Two weeks ago we published an article describing the open sewage systems in Puducherry, a Union territory in South India. In these systems, wastewater from businesses and homes is simply released into the environment with little to no treatment. This release poses a threat to public health and local water quality.

The conventional method of wastewater treatment requires a network of pipes and sewer lines that feed into a centralized wastewater treatment plant. After treatment, the water is expelled to a nearby body of water or used as reclaimed water. The conventional method often requires a central authority (e.g. a city government) to organize construction of sewer lines and connect users to the public system. After that, the authority must ensure that the treatment plant continues to operate correctly.

It is challenging to build and maintain a functioning wastewater treatment plant. In the United States we often take the operation of wastewater treatment plants for granted –the US has a strong regulatory system which ensures that municipalities and governments keep their services running as promised. In countries with less accountability in government (a consequence of corruption, holes in public policy, civil unrest, economic problems, a weak judicial system, etc.), centralized disposal systems are difficult to implement successfully. In Ghana, for instance, many wastewater treatment plants are constructed and then abandoned after just a few years of operation.

One alternative to utilizing a centrally controlled conventional treatments system is utilizing a decentralized array of smaller treatment systems. According to Small & Decentralized Wastewater Management Systems, decentralized wastewater management may be defined as the collection, disposal, or reuse of wastewater from individual homes, clusters of homes, isolated communities, or parts of existing communities at or near the point of wastewater generation. By having an array of decentralized treatment systems, regions are less susceptible to a total failure of wastewater treatment. The failure of one centralized system will stop treatment on a large scale. The failure of one decentralized system will only affect a small group of people.

Japan’s Miniature Wastewater Treatment Plants: Johkasou

The Puducherry Pollution Control Committee has decided to adopt a solid waste management scheme similar to Japan’s model. In the realm of wastewater treatment, the PPCC should also consider one of Japan’s approaches to decentralized wastewater treatment: the “johkasou.”

A johkasou is a wastewater treatment tank. It looks like a septic tank, but it behaves like a miniature wastewater treatment plant. The technology that engineers have fit into these small tanks is impressive –a small-scale johkasou for an individual house might sport an anaerobic filter tank, contact aeration tank, sedimentation tank, and disinfection tank. All of these treatment tanks can be held in a main tank as small as 4 cubic meters, and once water undergoes johkasou treatment it can be used for non-potable applications or released directly to the environment.

According to the Japan Sanitation Consortium, johkasou require electric energy comparable to the energy needed to light a room (a system designed for 5 people will consume about 37 kWh per month –the same amount of energy consumed by a 60 W lightbulb kept on for 26 days straight). Johkasou are intended for areas with limited access to centralized sewage systems. Because the tanks require electricity to operate, they cannot be used in areas that lack reliable electricity supply.

Installing a johkasou typically requires one week of construction work. The cost to purchase and install a 5-person johkasou is about ¥860,000, or nearly $10,000. Depending on the region, the Japanese government has subsidized between 40% to 90% of this cost for homeowners and businesses interested in having a johkasou.

Why would the Japanese government subsidize up to 90% the cost for a small-scale system? Release of untreated wastewater into the environment can threaten the fishing industry and increase water treatment costs downstream. Also, threats to public health increase healthcare expenditures and can hinder productivity (sick people are less productive). The economic benefits of decentralized wastewater treatment coupled with a cultural desire to protect Japan’s environment make it appealing for the government to subsidize johkasou programs.

Is a conventional wastewater treatment system feasible in Puducherry? In 2007, only about 30% of the urban area had sewage service. The other 70% discharged wastewater to the environment via exposed channels or septic tanks.

The costs associated with the conventional system and the johkasou decentralized systems are high. One must study the Puducherry hydrology, its political climate, its economic system, and its culture before a decision can be made. Centralized systems? Or decentralized systems? Or both?

In 2005, 35 million people in Japan (about 27% of the country’s population) used johkasou tanks. The technology is widely used, and it may offer regions like Puducherry a way to clean its wastewater without centralized treatment systems. Other cheaper alternatives to the johkasou include natural treatment systems like treatment wetlands and ponds. Unlike a johkasou, however, a natural treatment system often requires more land area than highly urbanized areas can provide.

To learn more about johkasou use in Japan, visit the Japan Education Center of Environmental Sanitation website here.

Tags: Japan, johkasou, Puducherry, wastewater
Posted in Waste Management, Water Treatment | 1 Comment »

One Response to “Decentralized Wastewater Treatment, Puducherry, and Japan’s Johkasou”

1. Saravana Balaji says:

   May 25, 2011 at 4:45 am

   Hi,
   I am interested in knowing more about the decentralised water treatment system.I am planning to impliment the same for my House at Trichy.Will the system be efficient for individual houses of population less than five?How much would it cost(including civil)approx?
   Thanks
   J.Saravana Balaji

   Reply