MICROBIOLOGICAL EFFICIENCY OF WATER TREATMENT: MICROBlOLOGICAL
MONITORING OF FULL SCALE WATER TREATMENT PROCESSES
Report No FR0282

March 1992

SUMMARY

I OBJECTIVES

To develop methods to examine 10 to 100 litre volumes of water for a range of micro-organisms and to use these methods at two treatment works to investigate the efficiency of water treatment processes at removing micro-organisms. To use the results obtained from this study to assess the adequacy of current bacteriological monitoring (ie the absence of E Coli in 100 ml of water) by examining 100 litre volumes of finished water for a range of micro-organisms.

II REASONS

Recent outbreaks of Cryptosporidiosis have demonstrated the vulnerability of certain aspects of some treatment strategies. The previous progress report (Denny, 1991) highlighted shortcomings in current bacteriological monitoring to ensure that water supplies were free of viruses and cysts. The use of alternative microbial indicators were proposed by several authors (Berg 1978, 1983; Payment et al 1979; Havelaar 1987).

III CONCLUSIONS

1. The large volume membrane filtration techniques which have been developed, provide a simple, low cost method for increasing the sensitivity

   Large volume analysis techniques for enteric viruses are currently too inefficient and of variable precision to be of real value in routine monitoring applications.

2. Of the 100 litres finished water samples analysed, 25% were found to contain indicators of faecal pollution at levels which would have gone undetected by conventional bacteriological monitoring (ie the absence of thermotolerant coliforms (ThTC) in 100 ml of water).

3. Two-stage treatment by rapid and slow sand filtration removed 99% of ThTC, faecal streptococci, Cl. perfringens and coliphages.

4. Two-stage treatment by rapid and slow sand filtration plus post chlorination removed >99.99 % of ThTC, faecal streptococci, Cl. perfringens and coliphages.

5. Treatment by pre-chlorination, coagulation, sedimentation, rapid sand filtration and post chlorination removed >99.99 % of ThTC, faecal streptococci, Cl. perfringens and coliphages.

6. Cl. perfringens and coliphages were found to be more resistant to chlorine. The presence of Cl. perfringens and coliphages in samples of chlorinated water in the absence of ThTC suggests that these organisms could be better indicators of treatment works performance at removing disinfectant resistant pathogens.

IV RECOMMENDATIONS

1. Further evaluation of the relative performance of Cl. perfringens and ThTC as indicators of treatment works performance.

2. Current bacteriological monitoring of finished water examines 100 ml volumes, the analysis of larger volumes would increase the chance of detecting possible faecal pollution.

3. Future work in this project area should involve :-

   • Pilot scale studies on the filtration efficiency of rapid sand filters.

   • Studies to investigate the microbial loading of backwash waters and sludges.

   • Investigations into the effect of granular activated carbon filtration on water quality.

   • Further studies to improve the efficiency and consistency of viral analysis techniques.

V RESUME OF CONTENTS

This is a progress report in connection with the FWR contract Microbial Hazards in Water Supplies F-1401. The report describes methods developed to examine 10 to 100 litre volumes of water for a range of micro-organisms. These methods were used at two treatment works to investigate the efficiency of water treatment processes at removing micro-organisms. The results have been used to assess the adequacy of current bacteriological monitoring.

Copies of the Report are available from FWR, price £15.00 less 20% to FWR Members