Report No FR0428
TREATMENT AND DISPOSAL OF WATERWORKS SLUDGE IN SELECTED EUROPEAN COUNTRIES
- Current awareness of the pressures which are influencing treatment and disposal practices for waterworks sludge in other countries and which may have implications for corresponding practices in the UK.
- Providing the FWR Members with information on alternative ways of disposing of waterworks sludge, particularly to respond to further restrictions on disposal to landfill.
To review the current and future pressures affecting treatment and disposal practices for waterworks sludge in France, Germany, the Netherlands and Switzerland and to relate these to existing policy and practices in the UK.
To examine the current and future treatment and disposal practices for waterworks sludge in France, Germany, the Netherlands and Switzerland and to identify possible alternatives for disposal of waterworks sludge which could be adopted in the UK.
The operations involved in handling and disposing of waterworks sludge have received increased attention in the last 15 to 20 years. Attention has focused on the quality of waterworks sludge in relation to the standards required for the traditional ultimate disposal to receiving waters or to land. At the same time, volumes of drinking water produced have increased and thus so have volumes of sludge. There are increasing pressures on the disposal routes traditionally used for waterworks sludge and emphasis has been put on waste avoidance, so that opportunities for recycling or utilising this by-product of potable water treatment need to be considered.
- There is no European Community legislation specifically concerned with waterworks sludge and it is unlikely to be classified as hazardous waste under the EC Directive on Hazardous Waste. Consequently it is also unlikely to be affected by the proposed ban on co-disposal.
- WHO Guidelines on Drinking Water Quality now include a guideline value of 0.5 µg l-1 for acrylamide and 0.4 µg l-1 (provisional) for epichlorohydrin; these are minor contaminants of polyacrylamide and polyamine polyelectrolytes, respectively.
- Similarly to the UK, chemicals used for water treatment are subject to approval or authorisation in all four countries (France, Germany, Netherlands and Switzerland).
- Controls on the discharges of wastes to surface waters include a limit of
30 mg l-1 for total suspended solids, except in Switzerland where the limit is 20 mg l-1. It is likely that the UK-NRA will require compliance with 100 mg l-1 suspended solids in the receiving water.
- Disposal of waterworks sludge to sewer is usually permitted with the agreement of the sewerage authority, but there may be limits for certain parameters in the discharge, making it necessary to pretreat the sludge.
- Disposal of waterworks sludge to landfill is under increasing pressure in France (will be phased out by 2002), Germany (organic contents must be less than 1% TOC or 3% ignition loss for Class I landfills and less than 3% TOC or 5% ignition loss for Class II landfills), and the Netherlands (controls on leaching characteristics, density and shear stress).
- Central softening of drinking water supplies is being introduced in the Netherlands; this is expected to produce 80000 t y-1 of carbonate residues by 1997.
- The potential for beneficial utilisation of softening sludges is high because of their high quality. In the Netherlands pelletisation has enabled utilisation as soil conditioner and chicken feed. Several other potential applications have been identified in Germany.
- Groundwaters and some surface waters in the Netherlands have sufficiently high levels of arsenic to cause the sludge produced during treatment to be classified as chemical waste.
- Waterworks sludge production, treatment and disposal is being reviewed at individual plant level in Germany; the objective is to avoid the production of sludge where possible, to encourage utilisation and to ensure the safe disposal of unavoidable residues.
- Potential methods of reducing the volume of waterworks sludge produced include the adoption of techniques such as membrane filtration which avoid the addition of chemical coagulants.
- Waterworks sludge may have beneficial applications in wastewater treatment, including the suppression of hydrogen sulphide formation and the removal of phosphates from solution.
- There is renewed interest in the beneficial use of waterworks sludge in agriculture or forestry, although there are potential drawbacks in the fixation of phosphorus and leaching of contaminants into the soil.
- Successful utilisation of waterworks sludges has been reported; for ferric sludges in the cement and brick industry, for softening sludges as soil conditioner, animal feed, dispersion dye and filler material.
- Research into sludge utilisation is in progress in Germany and The Netherlands.
Although there is no current or proposed EC legislation directly relating to waterworks sludge, there are increasing pressures on waste disposal in general. The most promising routes of disposal or usage of waterworks sludge, as indicated from this study, appear to be: disposal to sewage works (this may have beneficial effects on sewage treatment); coagulant recovery and re-use in sewage treatment; and application to land, possibly involving co-disposal with sewage sludge to improve the beneficial effect. A number of other, potentially useful applications have been identified for different types of sludges; these include soil and lake conditioning, cement and brick production, dispersion dye and filler material, and animal feed (softening sludges).
For most uses there is inadequate information concerning the beneficial aspects and potential problems, though research is being carried out in Germany and The Netherlands. It would be advisable to examine different disposal/usage options in detail, including carrying out cost/benefit evaluations.
VI RESUME OF CONTENTS
Legislative constraints affecting the production and disposal of waterworks sludge are summarised. Existing and recently proposed treatment and waterworks sludge disposal practices are described to highlight beneficial alternatives for waterworks sludge disposal. The findings are discussed in the main report, and further details are provided in Annexes A (European legislation) and B to E (information on individual countries).
Copies of the report are available from FWR, price £35.00, less 20% to FWR Members.