Plant to use advanced wastewater system

MHI-MS’ method increases treatment capacity and greatly reduces excess sludge from the treatment process

May 2015

Mitsubishi Heavy Industries Mechatronics Systems Ltd (MHI-MS), a group company of Mitsubishi Heavy Industries, has received an order for wastewater treatment facilities employing its proprietary two-phase activated sludge system, an advanced wastewater treatment technology, for installation at Mitsubishi Chemical Corporation’s Yokkaichi Plant in Mie Prefecture.

Compared to conventional technologies, MHI-MS’s two-phase activated sludge system achieves up to twice the wastewater treatment capacity by dividing the biological treatment tank (aeration tank) – where organics in wastewater are decomposed by microorganisms – into two parts, a configuration that enables an 80 per cent reduction in excess sludge produced from the wastewater treatment process.

The system ordered by Mitsubishi Chemical offers an unprecedented wastewater treatment capacity of up to 9,000 m3/day, vis-a-vis 7,500 m3 with conventional systems. Delivery of the system is scheduled for the first half of 2017.

The new system will be installed in conjunction with renovation of the Yokkaichi Plant’s superannuated wastewater treatment system. In addition to providing increased treatment capacity within the plant’s existing space limitations, the new system is expected to contribute significantly to sludge reduction.

In the conventional activated sludge process incorporating a single aeration tank, bacteria (suspended bacteria) that decompose and assimilate organics contained in wastewater share the tank with animalcules (protists and small metazoa) that feed on this bacteria. In MHI-MS’s two-phase activated sludge system, the aeration tank is divided into two parts and the wastewater is treated progressively.

As the speed of treatment within the first (carrier) tank containing the bacteria is considerably faster than that in the second (activated sludge) tank that contains the animalcules that feed on the bacteria, the two-tank configuration not only enables maximised biodegradation and treatment capacity for both bacteria and animalcules, the scale of equipment can also be optimised according to the two tanks’ treatment capacities, enabling savings in installation space.


The latest order is the second received for the system to be installed at Mitsubishi Chemical. MHI-MS developed the two-phase activated sludge system in 2009, and to date the company has received substantial orders from clients including the major chemicals firms, Mitsubishi Chemical among them, and food production plants.

Going forward the company will continue to provide finely tuned responses to a diverse range of user needs in the organic wastewater treatment markets of Japan and nations worldwide, with systems for increasing the capacity of existing facilities, new installations for use within limited space parameters, and systems for reducing excess sludge production volumes.

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