Johkasou Sewage Treatment Plant

Usafi Comfort: Johkasou Sewage Treatment Plant

The Johkasou is a prefabricated, five-chamber onsite sewage treatment plant manufactured by Daiki Axis Co. Ltd. of Japan and distributed exclusively in East Africa by Usafi Comfort Ltd. Unlike conventional septic tanks that merely separate solids and discharge partially treated effluent into the ground, the Johkasou processes both black and grey water through a complete biological treatment cycle within a single FRP (fibre-reinforced plastic) unit, producing effluent clean enough for landscape irrigation or safe sub-surface discharge. Over 10 million Johkasou units have been installed worldwide across 30 years in Japan, Kenya, the USA, Australia, Indonesia, China, India, Algeria, Nigeria, and other markets. The system is soil-type agnostic, performing reliably on black cotton soil, in high water table conditions, and in flood-prone areas, making it suited to the full range of Kenyan terrain and ground conditions. Usafi Comfort provides engineering, procurement, and construction services for each installation, with on-site supervision by their engineers and a 10-year warranty on treated wastewater quality.

Technical specifications

• Five-chamber treatment process: (1) Sedimentation, separating bulk solids and grease; (2) Anaerobic Filtration, where organisms on fixed-film media digest waste and perform denitrification; (3) Aerobic Contact Filtration, invigorating aerobic bacteria to reduce BOD; (4) Storage/Sedimentation, with air-lift pump recirculating flow for further denitrification; (5) Disinfection via chlorine tablet chlorinator
• Treated effluent quality: BOD reduced from 300 to 20 mg/L or less, COD from 400 to 50 mg/L, SS from 240 to 30 mg/L, Oil and Grease from 40 to 10 mg/L, Coliforms to 3,000 MPN/100 mL
• Performance standards: BOD of 20 mg/L or less, T-N of 20 mg/L or less, SS of 20 mg/L or less, COD of 30 mg/L or less
• Capacity range: 1 m3 to 2,000 m3 per day (1,000 to 2,000,000 litres per day), covering single-family homes (1 to 10 m3/day), multi-family and community systems (10 to 100 m3/day), and commercial and institutional installations (100 to 2,000 m3/day)
• Tank material: FRP (fibre-reinforced plastic), stronger than steel or concrete, with modular design allowing phased capacity expansion over time
• Safety factor of 2.5 built into the design for loading variations
• Installation: above ground or underground; plug-and-play for both new builds and existing buildings
• Operating noise level: 56 dB
• Desludging required only once per year
• Delivery timeline: 12 to 14 weeks from order placement; installation, testing, and commissioning: 2 to 3 weeks; total project duration: 15 to 17 weeks
• Shipped in 40 ft open-top or 40 ft dry container
• Manufactured in an ISO-certified factory and tested and certified by three Japanese government agencies
• Listed with the National Environment Management Authority (NEMA) in Kenya (Reference: NEMA/2017/WQ/TECH/041, dated 24 July 2017)
• Warranty: 10-year warranty on treated wastewater quality; 3-year warranty on the plant itself

Sustainability features

• Treats both black and grey water on-site in a single unit, eliminating the need for centralised sewer infrastructure and conventional septic-and-soakaway systems that risk groundwater contamination
• Uses half the electricity of competing treatment systems and can be powered by solar energy
• Delivers 50 to 75% savings on energy and chemical costs compared to alternative onsite systems
• Enables 25 to 50% savings on water costs through treated effluent reuse for irrigation and non-potable applications
• Achieves 98%+ savings on exhauster/desludging costs, with desludging required only once annually versus multiple times per year for conventional septic tanks
• Soil-type and terrain agnostic: performs on black cotton soil, rocky ground, hilly terrain, high water table areas, flood-prone zones, and earthquake-prone regions
• No pumps in standard operation; no smell; no underground seepage
• Modular design supports phased build-out, allowing developers to match treatment capacity to occupancy as a project fills
• Biological treatment process with chlorine disinfection only at the final stage
• After-sales support includes quarterly maintenance visits, staff training, and a maintenance manual