The efficacy of low frequency dosing, and application of the insect growth regulator pyriproxyfen, for the control of sewage filter flies, was assessed. The low dosing frequency trials targeted primarily Sylvicola fenestralis, but also the chironomids Limnophyes minimus and Metriocnemus hygropetricus. The trials of pyriproxyfen targeted Psychoda altemata. Three trials, assessing the effect of a range of dosing frequencies (20 down to 6 doses h-1), on filters with 50mm and 75mm slag media were undertaken. Retention time studies demonstrated that an increased surge or pulse of the applied sewage passed rapidly through the filter when the dosing frequency was reduced below 10, and at or below 12 doses h-1, for filters with 50mm and 75mm media, respectively. A significant (P < 0.05) increase in the wash-out of S. fenestralis egg masses, and a highly significant (P < 0.01) reduction in S.fenestralis larval numbers and adult emergence was recorded, in filters with a dosing frequency below 10, and at or below 12 doses h-1, for filters with 50mm and 75mm media. S. fenestralis populations were positively correlated (P < 0.05) with dosing frequency and retention. Surface film accumulation was not appreciably reduced, but accumulation deeper into the filters was altered. Chironomid populations were significantly (P < 0.05) increased in filters with a reduced dosing frequency. Low frequency dosing did not effect the nondipteran fauna, or the long-term BOD purification efficiency of the filters. Two trials, assessing the efficacy of pyriproxyfen were undertaken. In the first, pyriproxyfen was applied as an aqueous suspension, at a concentration of 0.5mg 1-1. Significant (P < 0.05) reductions in the emergence of P. altemata adults were achieved for 22 days. Reductions ranged from 19% to 77%. In the second trial pyriproxyfen was applied as the granular formulation, Sumilarv®, at a dose rate of 77.4 g m-2 of filter area. Significant (P < 0.05) reductions in adult emergence were achieved for 28 days. Control ranged from 35% to 92%. No adverse effects on the non-dipteran filter fauna, the purification efficiency I or the invertebrates in the river receiving the works effluent, were detected.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:244876 |
| Date | January 1997 |
| Creators | Coombs, Robert |
| Publisher | University of Salford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://usir.salford.ac.uk/43033/ |
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