Sludge Treatment in Reed Beds

WHAT THEY DO FOR YOU
Sludge Treatment in Reed Beds can help you with your disposal of sludge. They are a cost effective and environmentally friendly way of dewatering and treating surplus activated and digested sewage sludge from sewage treatment works, as well as some industrial wastes.

Sludge is loaded into the system, and is dewatered through filter layers. The drying is further aided by the reed plants (Phragmites australis) use of water for their growth. The systems consist of bed modules designed to give each bed a resting period between loads. During the sludge drying process, pathogens are lowered significantly and hazardous organic compounds are mineralised. The sludge residue becomes a Biosolid a valuable fertilizer that complies with the requirements of the safe-sludge-matrix for classification as an‘Enhanced Treated Product’ for use in agriculture.

After 10 years of operation, the mass of Biosolids will reach an approximate height of 1.2-1.5 metres with a dry solids content of 20-40%. The Biosolids are removed and spread on agricultural land. The reeds will regenerate quickly and a new cycle of loading sludge can commence.

In 2006, more than 140 systems were in operation in Denmark, treating 30% of the sludge produced.

MAJOR BENEFITS
The use of Sludge Treatment in Reed Beds over conventional sludge dewatering plant gives the following benefits:

1. Dewatering to 20-40% DS without chemicals of any description
2. Biosolids produced meet Safe Sludge Matrix criteria for ‘Enhanced Treated Product’ so disposal to agricultural land is possible
3. Significant mineralisation of solids
4. Very low maintenance cost and power consumption (just the feed pumps)
5. Low whole life costs
6. Robust and reliable method
7. Excellent quality return liquors (<10mg/l BOD and virtually solids-free)
8. Silent operation
9. Few odours
10. Excellent working environment

 

HOW BIG ARE THEY?
The sizing and design of the Sludge Treatment Reed Beds depends on the sludge production, sludge type, quality and regional climate. The sludge loading rate varies from 20-60 kg DS/m²/year. Loading cycles and resting periods are related to sludge type and quality and their ability to dewater and dry.

Usually between 8 and 18 bed modules are constructed, though larger systems with up to 30 beds are being designed.  As a ‘rule of thumb’ a land-take of around 0.5-1 m2 per head of population will give a rough idea for initial feasibility.

Systems with annual loading rates of up to 2,200 tonnes of dry solids equal to a 125,000 population have been installed, but larger throughputs can be easily accommodated.

HOW TO OPERATE THEM?
Little energy and no chemicals are used in the operation of sludge treatment reed beds. They require very little operator intervention and can be operated remotely.
Where there is insufficient land available on or near the works Sludge Treatment Reed Beds have been built where land is available some miles away and then pumped to this location.  A comprehensive SCADA system is established to keep full control of the loadings and drainage from the system. Thus, a weekly visit to site for a 30 minute visual inspection is all that is required as all controls for the system will be at the main works site or another suitable location.