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Providing evidence to improve practice

Action: Change effluent treatments of domestic and urban waste water Bat Conservation

Key messages

Read our guidance on Key messages before continuing

  • One study evaluated the effects of different sewage treatments on the activity of foraging bats. The study was in the UK. We found no studies that evaluated the effects of changing effluent treatments of domestic and urban waste water discharged into rivers on bat populations.



  • Abundance (1 study): One replicated, site comparison study in the UK found higher activity (relative abundance) of foraging bats over filter bed sewage treatment works than over active sludge systems.


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 together 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.

Referenced papers

Please cite as:

Berthinussen, A., Richardson O.C. and Altringham J.D. (2019) Bat Conservation. Pages 67-140 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.