Sludge Dewatering "Sack Drain"

Sludge dewatering with filter bags - a real alternative to sludge drying beds and mechanical processes

The costs for the treatment of waste water are a significant cost factor in the municipal as well as in the commercial and industrial sectors. The fact that there is considerable potential for savings here is often not recognized. However, the use of methods that are not optimally suitable can result in considerable additional costs for disposal, which could be avoided.

Technologies that were originally developed for high throughput rates and adapted to the lower requirements are often used, particularly with smaller quantities. As a result, such processes are often technically excessive, correspondingly expensive to invest and complex to operate. In many areas of application, however, simple processing methods would meet the requirements. This also applies in particular to the technologies for dewatering the sludge that is unavoidable in wastewater treatment.

Although the use of filter bags would be very versatile, regardless of the type of wastewater treatment, this often goes unnoticed. This may also be due to the fact that there is hardly any specialist literature on this simple and inexpensive process.

The effectiveness of filter bags in terms of throughput and drying results that can be achieved is often underestimated. However, because of the extremely low investment and operating costs and the simple handling, this process should definitely be considered, especially for smaller quantities of sludge.

This cost-effective type of sludge dewatering is used wherever small amounts of sludge accumulate and a high dry matter content is required. So for sewage treatment plants between 5 - 1,000 PE.

Functional description

The excess sludge is sucked out of the sludge storage tank with the self-priming pump. At the same time, a dosing pump is used to add the right amount of flocculant in order to achieve optimal dewatering. The mixture is pumped to the actual sack drainage, where geotextile filter sacks are installed in the basic module.

Due to the locking options in the distribution line, the bags can be loaded in series or at the same time.

It is not possible to overfill the sacks, as a pressure relief valve with a return is provided. The flocculated excess sludge now remains in the bags and is statically dewatered. The cloudy water is collected in the trough located under the grate and returned to the inflow area of ​​the sewage treatment plan


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After a few hours of dewatering, the bags can be removed and placed on a shelf to dry. The special properties of the bag material allow further moisture release through evaporation. With sufficiently long storage times, solids contents are achieved that are not inferior to those of mechanical sludge dewatering.

After a while, the sacks with the dried mud can be disposed of cheaply, or used as flower fertilizer, for example.

A reduction in volume and weight of over 95% is possible at any time with this method.

Customer References

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