Project for conversion of waterworks sludge into soil conditioner
12 November 2004, News release from GOLDCREST CHEMICALS LTD
At present, most of the (UK) potable waterworks sludge produced as a waste by-product in the production of potable water is disposed of to landfill.
The purpose of this work is to develop value added products from waterworks sludge which will provide huge savings for the water companies, by diverting the waste from landfill and providing a soil conditioner with beneficial properties for application to agricultural land.
This project was partially funded by the European Union European Regional Development Fund through the Support For Growth funding agreement between Business Link South Yorkshire and Goldcrest Chemicals Limited.
It has been estimated that in the UK there are over 200,000 tonnes/annum of waterworks sludge produced (on a dry weight basis). The sludge produced at works where there is dewatering plant rarely has a solids content of more than 40% which means there is over 500,000 tonnes / annum of sludge to dispose of.
The most common methods of dewatering sludge's are centrifugation which typically produces solids content of approximately 15%, filter pressing which can give solids content of 15 to 25% and membrane pressing which can achieve 40% solids. The waterworks sludge results mainly from the treatment of surface waters such as reservoir water or direct abstraction of river water to produce potable water.
For the purification process coagulants are used to remove impurities and these are generally one of two types, aluminium based coagulants such as aluminium sulphate or polyaluminium chloride and iron based coagulants such as ferric sulphate or ferric chloride.
The quality of the raw water varies widely with geographical area ranging from hard water areas to soft water areas and from highly coloured waters to high turbidity waters.
Clearly with combinations of these variations the nature of the resulting sludge can vary widely from one works to another but all tend to be sticky and difficult to handle, and often have an unpleasant odour dependant upon their source.
This project was aimed at evaluating the conversion of as wide a range of sludge's as possible into value added soil conditioner in an easily handle-able form with minimal odour.
Much work has been reported on the re-use of biological wastes such as sewage sludge for agricultural application but little on the re-use of waterworks sludge apart from the use as a constituent in brick making and ceramics.
Some works are able to spray sludge which hasn't been dewatered onto neighbouring land at certain times of the year, and others pump it to a local sewage treatment plant which only transfers the problem of disposal to the waste water treatment plant. In general however most dewatered sludge still goes to landfill at considerable expense, but it has been reported (Yorkshire Post 21.04.04 by Eric Barkas, City Editor) that there are probably just 12 years of landfill left for the UK's rubbish.
There is also much concern about deterioration of soils according to a report by the Environmental Agency as reported in Cutting Edge June 2004 and WET News July/August 2004.
An additional problem of great concern is the pollution of water sources by agriculture caused by run off of nitrates and phosphates. Agriculture covers 76% of England and research shows agriculture is responsible for around 70% of nitrate and 40% of phosphate entering English waters (WET News July/August 2004).
It is intended that by conversion of waterworks sludge into a value added soil conditioner that the following benefits could be achieved:
1. Cost savings to Water Companies for sludge disposal.
2. Divert sludge from landfill.
3. Improve soil condition and workability.
4. Increase aeration to roots
5. Reduce drainage and loss of nitrates and phosphates into water courses.
6. Retain nutrients in the root zone for the benefit of the crops.
7. Increase yield and quality of crops.
8. Replace peat for horticultural applications.
9. Reduce irrigation requirements.
10. Produce a solution with universal applicability.
SUMMARY OF FINDINGS.
The principal objective of finding a one fit solution to convert all types of sludge cake into a stable and handle-able product suitable for use as a soil conditioner was achieved.
It was demonstrated that all types of waterworks sludge could be converted into a value added product suitable for application to land and capable of providing significant cost savings to the water companies for sludge disposal to landfill.
For further information please email GOLDCREST CHEMICALS LTD