Change effluent treatments of domestic and urban waste water
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Organic pollution occurs when treated sewage effluents containing organic compounds are discharged into rivers affecting plant growth and the number and diversity of insects. Riparian habitats are important for foraging bats and changes in water quality may have positive effects on foraging activity for some species, and negative effects for others (Vaughan et al. 1996, Kalcounis-Rüppell et al. 2007, Abbott et al. 2009).
We found evidence that filter sewage bed treatment works can provide foraging habitat for bats. However, the results should be treated with caution as a subsequent study found that insects above these filter beds were contaminated with endocrine disrupting chemicals that may have adverse effects on bats feeding on them (Park et al. 2009).
Abbott I.M., Sleeman D.P. & Harrison S. (2009) Bat activity affected by sewage effluent in Irish rivers. Biological Conservation, 142, 2904–2914.
Kalcounis-Rüppell M.C., Payne V., Huff S.R. & Boyko A. (2007) Effects of wastewater treatment plant effluent on bat foraging ecology in an urban stream system. Biological Conservation, 138, 120–130.
Park K.J., Müller C.T., Markman S., Swinscow-Hall O., Pascoe D. & Buchanan K.L. (2009) Detection of endocrine disrupting chemicals in aerial invertebrates at sewage treatment works. Chemosphere, 77, 1459–1464.
Vaughan N., Jones G. & Harris S. (1996) Effects of sewage effluent on the activity of bats (Chiroptera: Vespertilionidae) foraging along rivers. Biological Conservation, 78, 337–343.
Supporting evidence from individual studies
A replicated, site comparison study in 2003 at 30 sewage treatment works and in central and southern Scotland, UK (Park & Cristinacce 2006) found that percolating filter beds had higher activity of Pipistrellus spp. over them than activated sludge systems, and activity over filter beds was similar to that along nearby river banks. The number of Pipistrellus spp. bat passes recorded over percolating filter beds (54) was higher than over activated sludge systems (9). Activity of Pipistrellus spp. over filter beds (average 15 bat passes/site) was also similar to that along nearby river banks (23 bat passes/site), whereas activity over activated sludge sites (3 bat passes/site) was lower than along nearby river banks (18 bat passes/site). At filter beds, waste water is sprayed over inert filter material creating a microbial film which supports high insect numbers. In activated sludge systems, sewage and bacterial sludge are mixed creating an unfavourable habitat for insects. At each of 30 sites (18 filter bed, 12 activated sludge), bat activity was recorded with bat detectors at three points/site for 15 minutes each after dusk in June–August 2003. At each of 23 sites (15 filter bed, 8 activated sludge), recordings were also made at two points on the river bank 50 and 75 m upstream from the sewage treatment works.Study and other actions tested