Mono Munchers make their mark in Massachusetts

A pair of Series ‘A’ Munchers from NOV Mono have helped reduce maintenance intervals and improve capacity at a major wastewater treatment plant in Massachusetts, USA. The special construction of the Mono units - and their ability to handle over 41 million litres per day - has also helped reduce the risk of overflows during storm periods.

Operated by the Lynn Wastewater Treatment Plant, the Humphrey Street facility in Swampscott, MA, had previously been using a single large grinder unit to process wastewater. However, the unit’s 127 cm-tall cutter stack and single 25 cm-diameter drum were struggling to cope with the excessively high flows experienced during intense rain storms, and the cost of replacing it with a similar alternative was prohibitive.

Given their sizeable handling capacity, two Mono CA215 units were selected as a replacement solution. The Swampscott station receives roughly 7.5 million litres per day of inflow, but the Mono units can accommodate almost 21 million litres per day each. Combined with an initial filter installed upstream to limit any extreme flow, this virtually eliminates any risk of overflow, even during major storms.

The Mono units have been built on 1.8 m extended shafts and fitted with extra-high sides to mitigate the risk of the flow going over the top of the inlet channel. Both units are located in the channel and during normal flow levels they are used alternately, on a monthly basis. This extends the intervals between repairs and always allows one unit to be in operation while the other is being maintained.

“The Mono units have made a tremendous difference to our Humphrey Street operation,” said Al Watt, project manager, Lynn Wastewater Treatment Facility. “Our levels can rise dramatically during a storm and it’s reassuring to know that we can now handle that sort of event without any concern about overflows.”

The Mono Muncher is a twin-shaft, slow-speed, high-torque grinder offering a solution for the maceration of sludge and solids within a flow. The twin shafts have a series of interleaved cutters and spacers which create a powerful ‘positive displacement’ grinding action. Once solids are trapped in the slowly revolving cutters, the differential speed of the cutter stacks pulls apart fibrous material, crops and shears plastic and crushes brittle materials, while the low cutter-tip speeds reduce wear rates by minimising any impact loading.

Suitable for either pipeline or channel installations, the Series ‘A’ Muncher eliminates the need for manual handling of screening debris and the associated transport costs. It can be installed into an existing concrete channel or in a fabricated frame, complete with guide rails, into an existing submersible pump station as a simple and quick retrofit.

The Munchers are suitable for high-volume grinding applications and offer rugged protection for pumps and other downstream process equipment. They are supplied with a programmable logic controller to protect the machine against damage and overloads. An optional Profibus data capture system is available to record operational information.