POLYACRYLAMIDES IN DRINKING WATER TREATMENT AND RECYCLING OF SLUDGE
LIQUORS
Report No FR0119

Aug 1990

SUMMARY

I OBJECTIVES

To review the usage of polyacrylamide polyelectrolytes in the treatment of drinking water, including the treatment of waterworks sludge.

II REASONS

The Fifteenth Statement (March 1989) of the Committee on Chemicals and Materials of Construction for Use in Public Water Supply and Swimming Pools set a reduction in the maximum permitted content of free acrylamide monomer in polyacrylamide or acrylamide-acrylate copolymers and a reduction in the average dosage of the polymers. This regulation applies to the use of these polymers directly on the water being treated for supply. It was known that polymers of the same kind are also used in waterworks sludge treatment and that in some cases the water recovered from sludge treatment are returned to the main treatment processes. In such cases the concentration of acrylamide in the drinking water would be increased. The Committee had little information on polymer usage in sludge treatment and WRc were asked for such information.

III CONCLUSIONS

  1. The effect of the recent reduction in permitted limits has highlighted the Committee's concern about acrylamide but has not brought about any reduction in usage.
  2. The amount of polyacrylamide used in waterworks sludge treatment is significant compared with its use as a flocculant aid in clarification and the recycling of sludge liquors is commonplace.
  3. Most works' operations fall well within the permitted limits of polyacrylamide use, even when total doses are accounted and recycle is 100 percent.
  4. The works most affected are large and either new or recently uprated. They rely on polyacrylamide dosing to maintain output. There may be about 20 works in the UK which use a total of about or more than 0.25mg polymer per litre of water treated. They face additional expenditure, the amount of which will be affected by the terms of the Committee's next Statement.

IV RECOMMENDATIONS

  1. The time periods applicable to average and maximum doses should be specified.
  2. The Committee should take sludge treatment and recycle of sludge liquor into account in any future Statement.
  3. When the Statement is revised it would be helpful if it were to permit the treatment of liquors to remove acrylamide before recycling.
  4. Some practical research on chemical destruction of acrylamide is required. It may be that the normal process of sulphonation, where practised, has this effect.

V RESUME OF CONTENTS

The usage of polyacrylamide polyelectrolytes in drinking water treatment and waterworks sludge treatment is examined with particular consideration to the recycling of sludge liquors. Typical polymer dosages in water and sludge treatment are identified from results of an informal survey of a chance sample of 15 water treatment works. It is shown that the amount of polymer used in waterworks sludge treatment is significant compared with its use directly in water treatment.

The scope for the reduction in polymer usage and further reduction in monomer content is discussed. A list of possible methods for reducing polymer usage is given. The conclusions and recommendations reflect the subject of polymer usage and monomer content justifies further attention.

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