“All existence is born from the earth and is a circle that returns to the earth,” says architect Tono Mirai, who has embodied this belief in his latest project, Toiletowa. A closed-loop flush bio-toilet, this project is a part of the Santome Konjaku Mura (Santome Past and Present Village), an ecological theme park developed by Ishizaka Sangyo in Miyoshi City, Japan. The park houses the recycling plant for industrial waste and educates people on sustainability in a playful, natural setting. Spread across 2.5 square kilometres, the campus mainly runs on geothermal energy and purchases renewable energy from other companies to meet its needs. The park has numerous interventions for visitors to engage in learning – a craft centre, recreational areas for children, multiple food options and day camping provisions, with the recycling plant and the educational facility at the centre of it.

“Santome Konjaku Mura is Satoyama, which means located halfway between pristine nature and the city and is an area consisting of settlements and secondary forests surrounding them, mixed with farmland, reservoirs, and grasslands. This area was once a garbage satoyama where illegal dumping was repeated. This initiative led by Ishizaka Sangyo, an industrial waste disposal company involves leasing the devastated woodland around the factory and managing it through activities like cutting down and regenerating trees, thereby improving biodiversity and reviving the beautiful satoyama of Musashino. It has been certified by the Japan Ecosystem Association's JHEP,” the Japanese architect tells STIR, highlighting the positive impact of the park and its initiative.

Toiletowa is nestled in a grove of trees, northeast of Ishizaka’s recycling plant. Two semicircular walls displaced along the central axis create a gentle movement within the forest. The entire building acts as a well of light, connecting heaven and earth through the skylights. The circular main building, with its elegant strokes of warm neutrals, displays 27 layers of rammed earth architecture. The building’s foundation is made from crushed stones and wooden stakes to minimise the environmental impact. Due to the lack of compressive strength, the soil is mixed with slaked lime and applied over a handcrafted wooden framework. The same mixture is used as plaster for the partition walls and the hard-packed earthen floor.

The architects meticulously developed this public architecture project from January 2021 to March 2023, with a detailed focus on the NS-10 reconstructed soil created by Ishizaka Sangyo and IS Engineering, to ensure its suitability for the project. The company’s factory brought gypsum boards and soil from demolished buildings to create recycled products through separating and processing. To expand the limited use of recycled soil as a roadbed for pavements, Mirai devised a way to use it as an essential building material.

Based in Karuizawa of the Nagano Prefecture, architect Tono Mirai designs sustainable structures with a modern flare, using traditional building techniques and embracing both wood and stone architecture. He composes gentle organic forms, believing that materials bring relief and joy to the stressful modern life.

Skylights illuminate the interiors and highlight the textured landscaping of the bathroom furnishings which are made from waterproof wood chips. These chips are also used for the sidewalk along with lava stones. Crushed Japanese roof tiles are set over laminated wood panels and galvalume steel roofing, and crushed recycled stone is used to catch the rain. The waste from the toilets is sent to a nearby shed for processing, which purifies the water for further use with the added benefit of making the toilets odourless.

The fermentation shed of the project consists of the fermentation layer, synthesis layer and the catalyst tank which are arranged in an arc on raised beds, creating a three-dimensional vegetable garden while preserving trees on site. The subtle 2/10 slope of the galvalume steel roof, the short walls, and the circular design of the courtyard create an inviting space for visitors to observe the process. The exterior walls of the shed are made of locally produced cedar boards in different sizes which are arranged in varying gaps in between to blend with the local forest landscape. Every board is coated with Wood Long Eco, a wood protectant created from natural materials which changes its colour randomly from its exposure to UV rays.

The wastewater is treated using a biotechnology called combined fermentation (EMBC), developed by Dr. Yasuhide Takashima, the representative director of Takashima Development Engineering Research Institute, who studies and develops the decomposition of various persistent and radioactive substances. Inspired by the fermentation process of Japanese Sake, aerobic and anaerobic bacteria work together to make the wastewater odourless and pure enough to drink. The impurities completely break down within 48 hours, and the resulting enzyme water activates the soil to improve crop productivity.

The sustainable architecture project is on a mission to revitalise the weakened soil of the land and surrounding forest, inspired by the traditional farming practices in the local region. Plants and plant-based materials from the site such as fallen leaves, branches, bamboo, and charcoal, are buried in the soil to create water veins.

Speaking of the regeneration process, Mirai adds, “There is an adjacent farm. There, the ‘leaf compost farming method’ has been used since the Edo period and 50 types of "fixed species" vegetables are rooted in the local climate to the present day. Regenerative agriculture for the future weaves together the soil, techniques, and blessings of our ancestors.”

When asked about the most challenging aspects of this project, the Japanese architect concludes, “This is not just a toilet, but a system showcase of the ecosystem by water circulation.” The wastewater and forest activation were among the most difficult things to execute. Reactivating the underground ecosystem clears the hard and poorly drained soil from the puddles, regenerating the forest vegetation. Thus, using the principle of circulation, the intervention creates an everlasting cycle of vitality.

By opening their recycling plant and Santome Park to the public, the Ishizaka Sangyo corporation aims to inspire visitors to view waste as a valuable resource and adopt sustainable design practices in their daily lives. Toiletowa is an initiative that bridges society with nature and technology, fostering a strong sense of community. Santome, also known as Satoyama, embodies the Japanese concept of natural environments with human settlements, farmlands and wild biomes. In their coexistence and interdependence, these elements exemplify a resource-circulation model for the future; a waste-free, recycling-centric and sustainable society that thrives in harmony with nature.

Project Details

Name: Toiletowa
Location: Miyoshi City, Saitama, Japan
Client: Ishizaka Sangyo
Architect: Tono Mirai Architects
Building and Floor Area: 9.9 sqm
Maximum Building Height: 2.68 m
Eaves Height: 2.22 m
Foundation: Clasher run – Burned wood pile
Design Term: January 2021 to March 2023
Construction Term: March to August 2023
Supervision: Tono Mirai Architects
Landscape: WAKUWORKS
Building Construction: Terashima Corp.
Equipment: GEN JAPAN, Marunaka Equipments
Combined fermentation: Takashima Development Engineering
Naming Design: TSDO Taku Sato

(Text by Bansari Paghdar, intern at STIR)