A success story: 10 years of HUBER Belt Dryer operation in Mooresville (North Carolina, USA)

This year we are celebrating 10 years of operation of the plant in Mooresville. The BT 20 belt dryer (formerly known as BT 5-2) serves the wastewater treatment plant with a maximum capacity of 28,400 m3/d (7.5 MGD). Since its commissioning in 2013, this dryer has made a significant contribution to efficient waste management and the sustainable utilisation of resources.

”Town brown”, the brown gold of Mooresville

The belt dryer is loaded with non-stabilised excess sludge from the sewage treatment plant. This is dewatered to 18% DR using a belt filter press. The dewatered sewage sludge is then dried to at least 90% solids content. This is passed on to local farmers for agricultural use. Among farmers in the region and in internal circles, the dried sewage sludge is also called ”town brown” – the ”brown from the town”, the "brown gold of Mooresville" – because of its colour and the place where it is dried. Heat is supplied to the plant by a hot water boiler fuelled by natural gas.

The dryer is designed for a water evaporation rate of 1,300 kg/h and offers the well-known and widely appreciated advantages of the HUBER belt dryer design:

• Sludge extruder for optimum feeding onto the dryer belt
• Minimised dust production
• Temperature control in the individual dryer modules

The tenth anniversary of the dryer operation was used as an opportunity to talk with the wastewater treatment plant manager, Jamie Levis, and the sludge treatment plant manager, Larry Hendren, about the operating experience and future plans. The lively exchange of information allowed a look behind the scenes of this historic project for HUBER.

Over 75,000 operating hours in total

In the course of this, the experience gained from 10 years of operation, during which more than 75,000 operating hours were accumulated, was discussed in great detail.
It was noted that it naturally takes some time to optimise the operation of such a system. This applies to the maintenance of the system as well as the special operating conditions of the individual system components. It also requires a machine operator who, as in most cases, should enjoy familiarising themselves with the machine technology and the subject matter.

Insights from the plant personnel

The plant personnel start their day with a daily inspection of the plant. According to Larry Hendren, this involves paying particular attention to the noises made by the individual components, which could indicate any developing susceptibility to faults. Smooth operation can be easily guaranteed with an appropriate stock of spare parts and proactive monitoring and maintenance work. In combination with stocking individual components, downtimes can be minimised and an average availability of the system of over 8,000 h/a can be guaranteed.

The following key points were mentioned:

• Operation of the hot water boiler: water quality control
• Fresh air supply to the dryer: seasonal check of the antifreeze content for heat recovery
• Sludge delivery pump: rotor and stator replacement required, mechanical seal is preferable to normal packing seal
• Motor bearings of blower drives
• Sludge feed extruder:

          + Perforated extruder plate
          + Cutter drive:                   

                    - Axle bearing
                    - Cutting knives

High satisfaction with plant operation

The sewage treatment plant staff are highly satisfied with the operation of the plant. This is also manifested in the fact that the staff regard the operation of the dryer as a personal matter when interested visitors come to see the plant. But it is also reflected in the large number of references that the Mooresville plant has provided for HUBER. This includes responding to enquiries from planning offices, through to personal visits to the plant, including answering questions relating to operation, maintenance and costs. The positive feedback from colleagues at the Mooresville wastewater treatment plant, especially Jamie Levis and Larry Hendren, regarding the belt dryer is certainly a major reason why the story of belt dryers in the USA has become a success story.

Further HUBER products in use

It should be mentioned in this context that other HUBER products are also in operation at the Mooresville WWTP:

• Tank-mounted HUBER Rotary Drum Fine Screen ROTAMAT^® Ro2 (1000, 6 mm)
• Third treatment stage for treatment plant effluent: Four HUBER Disc Filter RoDisc^® 18 units
• HUBER Multi-Rake Bar Screen RakeMax^® with Wash Press WAP^®, pumping station to the wastewater treatment plant

The Mooresville WWTP is also available for testing plants of HUBER Technology, Inc., the HUBER subsidiary in the USA. These include the Screw Press S-PRESS and the Sludgecleaner STRAINPRESS^®.

Firmly established in the region over the years

It should also be noted that the operation of the belt dryer has become firmly established in the region over the years. The final product of the drying process is gladly purchased by several agricultural businesses in order to return the nutrients to the cycle. Hay production or grass production are examples of this. The use of dried sewage sludge has also manifested itself in the figurative naming. Farmers can't get enough of ”town brown”, the brown gold of Mooresville.