PERFORMANCE EVALUATION OF THREE METHODS OF TERTIARY TREATMENT ON SMALL AND MEDIUM SIZED WASTEWATER TREATMENT WORKS

摘要

The performance of three systems of tertiary treatment applied at waste waterrnfacilities serving populations of up to 15,000 were compared by analysis of regulatoryrndata from groups of sites in the UK and of water utility data from a small subset ofrnthose sites.rnDistributions of means for 21 sites using sand filters, 42 sites using grass plots and 35rnsites using subsurface flow reed beds were compared for TSS, BOD5, NH4N and totalrnoxidised nitrogen (TON). The data set was also used to tabulate overall means and 95rnpercentiles for the three systems. The facilities with reed bed systems clearlyrnproduced higher quality effluents than those with grass plots or sand filters in terms ofrnSS, BOD5 and TON. The distribution of results for NH4N was much closer for all threernsystems and both the reed bed and grass plot data sets were influenced by thernperformance of facilities which had not been required to nitrify. BOD5 concentrationsrnwere lower for sites with grass plots than those with sand filters despite the betterrnperformance in terms of TSS at the latter.rnComparison of influent and effluent data for the three systems was conditioned by anrnimbalance in data collection for the systems but it supported the conclusion drawnrnfrom the regulatory data. Confirmation was given of the additional biological treatmentrnprovided by reed beds and grass plots used for tertiary treatment. Sand filters providedrneffective solids straining and a consistent removal of about 0.3 to 1 mg/L of NH4N.rnNeither sand filters nor grass plots removed TON but SSF reed beds removed up torn33 % of the influent concentration.