aerial view of sewage treatment plant in winter in Poland aerial view of sewage treatment plant in winter in Poland Close-up female hand applying detergent to remove severe stains in clothes aerial top view of round water settlers for sewage recycling. modern wastewater treatment plant Waste water treatment, purification plant at a wastewater treatment plan in usa Modern urban wastewater treatment plant Modern urban wastewater treatment plant Wastewater treatment plant in operation holding cleaning products and tools on bucket, close up Modern urban wastewater treatment plant.