The WWTP of the City of Schweinfurt is designed for a total population of 250,000. Its actual load is only 150,000 to 170,000, with peaks of 220,000. About 200,000 m³ of waste activated sludge are thickened per year. Excessive operation, maintenance and repair costs of the existing thickening centrifuges were the reason for the plant’s management search for a more efficient thickening technology. After discussions with the operation staff, belt thickening was identified as a good solution. But first an on-site trial with a mobile HUBER Drainbelt unit was performed. The testing went well and showed the following results:
- Power consumption is lower
- Polymer consumption can be reduced
- Solids capture rate is improved
After a restricted tendering process, we received an order for the supply of a single Draibelt 1.0 unit with a belt width of 1 m. Its capacity is sufficient to process the entire surplus sludge. One of the old centrifuges was kept in place for redundancy, but has not been used since November 2007, when our Drainbelt was started-up.
In addition to the Drainbelt machine, we supplied the following components: polymer station, feed pumps, controls and control panel as well as connecting pipelines. Our customer also ordered the following extra features: filtrate recycling for belt cleaning (no wash water costs), stainless steel cover and ventilation pipeline with blower (no emission of hazardous aerosols, no manual access during operation for operator safety), automated spray nozzle cleaning (frequent nozzle cleaning to prevent decreasing washing effectiveness), solids concentration sensor in the thin sludge feed line (automated control of polymer dosing depending on the solids freight; reduced polymer consumption and improved thickening).
Our Drainbelt units are very cost-effective: they need little polymer, power, wash water, operator attention and maintenance. They are available in four sizes, with a maximum sludge feeding capacity of about 100 m³/h. Their advantages are the result of the following design features:
- thin sludge is continuously fed through a flocculation reactor wherein large and strong flocs are generated,
- flocculated sludge is gently and evenly distributed over the entire width of the belt by means of a chute,
- the belt is horizontally moved by a drive roller and maintained straight by a tensioning roller,
- a sensor detects belt rupture or too low belt tension,
- flexible plows ride on the belt and generate open drainage areas in their wake,
- a discharge ramp generates a rolling sludge movement and increases the thickening degree,
- clear filtrate and soiled wash water are collected in separated pans thus permitting reuse of filtrate as spray water.
The operators are very happy with our Drainbelt’s operation and performance. They are also very content with its low power and polymer consumption. And they like the ease of operation and maintenance. In comparison to their old centrifuges, operation costs are far lower and the solids capture rate much better. The plant superintendent Klaus Theobald stated: “the HUBER belt thickener has even exceeded our boldest expectations; the thickener operates without failures and exceeds the guaranteed performance; our cooperation with HUBER is smooth, they are very responsive.”
The following are average operational parameters of this Drainbelt installation:
- Feed solids concentration: 1 %DS
- Thickened sludge solids concentration: 5.5 %DS
- Feed capacity: 23 m3/h
- Operation time: 24 hours per day and 7 days per week
- Polymer consumption: 2.3 g/KgDS
- Nominal power: 0.75 kW