Providing evidence to improve practice

Action: Change effluent treatments of domestic and urban waste water

Key messages

  • We found no evidence for the effects on bats of changing effluent treatments of domestic and urban waste water discharged into rivers. One replicated, site comparison study in the UK found that foraging activity over filter bed sewage treatment works was higher than activity over active sludge systems.

'No evidence' for an action means we have not yet found any studies that directly and quantitatively tested this action during our systematic journal and report searches. Therefore we have been unable to assess whether or not the action is effective or has any harmful impacts. Please get in touch if you know of such a study for this action.


Supporting evidence from individual studies


In a replicated, site comparison study between June and August 2003 at 30 sewage treatment works in central and southern Scotland, UK (Park & Cristinacce 2006) significantly higher activity of Pipistrellus spp. was recorded over percolating filter beds than over activated sludge systems (average 15 vs. 4 bat passes/15 min respectively). Foraging activity of Pipistrellus spp. over filter beds was comparable to that at nearby foraging habitat along river banks, whereas foraging activity over activated sludge sites was lower. 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. Insect biomass was found to be significantly higher at filter beds. Bat activity was recorded with bat detectors at three points per site for 15 minutes each after dusk, and insects were assessed using suction traps for two hours after dusk at each site. Myotis spp. were also detected at both types of treatment works but numbers were too low for analysis.

Referenced papers

Please cite as:

Berthinussen, A., Richardson, O.C., Smith, R.K., Altringham, J.D. & Sutherland, W.J. (2017) Bat Conservation. Pages 67-93 in: W.J. Sutherland, L.V. Dicks, N. Ockendon & R.K. Smith (eds) What Works in Conservation 2017. Open Book Publishers, Cambridge, UK.