Chopper pump mixing system solves solids build-up at Hokkaido biogas plant

A farm-based biogas plant in a remote part of Hokkaido, the northernmost of Japan's main islands, has replaced its original digester mixers after they struggled to process high-solids manure and agricultural feedstock.

The previous mixers could not cope with the heavy particles typical of farm waste, and retrieving them for maintenance or repair required draining the digester entirely – an expensive and labour-intensive process.

The replacement is an externally mounted GasMix system from Landia, which uses the company's Chopper Pump, first invented in 1950, to continuously break down heavy solids before they can cause blockages.

The system uses two floor-mounted Landia Chopper Pumps, each rated at 18.5kW and running for just 15 minutes per hour, together with venturi nozzles. Sludge is recirculated, homogenised and injected back into the digester, increasing the active surface area available to anaerobic bacteria through combined vertical and horizontal mixing. Because there are no moving or wearing parts inside the digester itself, all servicing can be carried out externally, without downtime.

Fergus Clark, from Landia (Asia/Pacific), said: "In such a remote, rural area, reliable equipment is essential. Many mixers are just fine in other, gentler applications, but at a biogas plant, unless they are designed for purpose, cannot deal properly with the grit, straw and solids that you always have to contend with in an agricultural feedstock."

He added: "Now, with an efficient and highly dependable mixing system, the farmer has a perfectly healthy biogas plant that can utilise the much-needed excess heat for his cow sheds in Hokkaido's very cold winters – and sell excess renewable energy to the grid."