TABLE 1.
Characteristics of some of the STW included in the survey
| Measurement | Result | Median; range |
|---|---|---|
| No. of STW samplede | 40 | |
| No. of STW for which information was obtained | 34a | |
| Mean no. of PE served by STW (n = 34) | 38,900 | 9,650; 50-440,300 |
| No. of STW (% of 34) serving 50-900 PE (group 1); (mean PE) | 9 (26.5); (320) | 280; 50-600 |
| No. of STW (% of 34) serving 1,000-9,900 PE (group 2); (mean PE) | 8 (23.5); (3,850) | 3,200; 1,300-9,300 |
| No. of STW (% of 34) serving over 10,000 PE (group 3); (mean PE) | 17 (50); (75,760) | 45,000; 10,000-440300b |
| Mean daily influent vol, in m3 (n = 28)c | 28,600 | 5,000; 40-300,000 |
| Mean daily influent vol, in m3, for group 1 (n = 6c) | 100 | 75; 40-200 |
| Mean daily influent vol, in m3, for group 2 (n = 6c) | 1,500 | 1,000; 200-3,300 |
| Mean daily influent vol, in m3, for group 3 (n = 16c) | 49,500 | 24,600; 2,000-300,000 |
| Total (% of 32c) no. of STW with significant input from animal sources (e.g., abattoirs, veterinary establishments, etc.) in group 1 (n = 8c), group 2 (n = 7c), and group 3 (n = 17) | 9 (28) (group 1, 0; group 2, 2; group 3, 7) | |
| Treatment | ||
| Total no. of STW (% of 32c) in group 1 (n = 8c), group 2 (n = 7c), and group 3 (n = 17) with only primary mechanical treatment (straining/sand/fat removal/primary settlement) | 13 (41) (group 1, 4; group 2, 3; group 3, 6) | |
| Total no. of STW (% of 32c) in group 1 (n = 8c), group 2 (n = 7c), and group 3 (n = 17) with primary mechanical treatment and chemical treatment followed by flocculation/settlement | 17 (53) (group 1, 4; group 2, 4; group 3, 9) | |
| Total no. of STW (% of 32c) in group 1 (n = 8c), group 2 (n = 7c), and group 3 (n = 17) with biological treatments (e.g., activated sludge) | 15 (48) (group 1, 4; group 2, 5; group 3, 7) | |
| Total no. of STW (% of 31c) in group 1 (n = 8c), group 2 (n = 7c), and group 3 (n = 17) with tertiary treatments (filtration, nitrogen removal, disinfection) | 3 (10) (group 1, 0; group 2, 0; group 3, 3d) | |
| Sewage discharge | ||
| No. of STW discharging by location (n = 28c) | Sea, 15; lake, 6; river, 7 |
Questionnaires were returned from 32 STW, although many omitted to answer, or were unable to answer, various questions. Information on two STW was obtained via the Internet and other sources.
Only two STW served a PE greater than 100,000.
Relevant information was not available from all questionnaires.
Two STW had nitrogen removal, one had UV treatment of effluent.
Sample collection was intended to be completed in March 2004. Twenty samples were collected in March, nine in April, four in May, two in June, and two in July 2004. For those STW which were sampled over time, results from a sample within this period were selected at random for comparison purposes, apart from one STW which had terminated sample collection. For this STW, results from a sample from the previous October were included in the comparisons.