Updated: July 2002

1. Abstract

Hitachi Zosen's membrane separation-type septic tank system is able to remove SS (Suspended Solids), BOD (Biochemical Oxygen Demand) and even N (Nitrogen) and P(Phosphorus) from domestic wastewater . Its most important feature is recycling, and it is also able to recycle phosphorus, treated water and sludge.
Phosphorus can be recovered in the form of valuables (sodium phosphate) that are recycled as a soil improvement agent. Treated water is recycled as toilet flush water and sludge is recycled as fertilizer by processing it into compost.
For environmental protection, recycling needs are increasing. Hitachi Zosen is the first company to establish a system to recover phosphorus from domestic wastewater.

2. Features

(1) First with phosphorus recycling: Phosphorus can be recovered as Sodium phosphate effectively.
(2) Recycling of treated water: the membrane can remove SS (Suspended Solids) and coliform.
(3) Recycling of generated sludge: No use of coagulating agent makes sludge recycling possible.
(4) Low generation of sludge: Generated sludge volume is about one third the amount of conventional systems.
(5) Compact equipment: Operation with high-density activated sludge makes installation space about half compared with conventional systems.
(6) Stable activated sludge for long continuous operation: This system can prevent clogging of membrane.
(7) Stable treatment for long continuous operation of de-nitrification: Biological treatment can remove total nitrogen effectively.

We installed pilot plant with treatment capacity for 60 persons (12m³/d) at a sewage treatment facility in Taimeicho, Tamana-gun, Kumamoto prefecture and performed a pilot test lasting 17 months. We have confirmed the performance stated at the left.
Hitachi Zosen's membrane separation-type septic tank system has been approved as a"septic tank having de-nitrogen and de-phosphorus capacity within the range of 51 to 10,000 persons"in a performance evaluation for night soil septic tanks by The Building Center of Japan, and has obtained general approval by the Ministry of Construction.

Block Flow

HZ Membrane Separation Type Septic Tank-Sketch