Water Treatment Plants

Removes pathogens and toxic elements to prepare water for use in homes and businesses Makes water potable (drinkable)

Steps for water treatment 1. Screen/filtration  source water is filtered to remove large organisms and trash (usually with screens)

2. Coagulation/flocculation  Alum or a ferric (iron) based compound is rapidly mixed in and forms sticky globs called flocs. Bacteria and other impurities stick to the flocs.

Over time the weight of the flocs increase and settle to the bottom of the basin  3. Sedimentation

4. Filtration  layers of sand, gravel and coal filter remaining impurities

5. Disinfection  add disinfectant (usually chlorine or ozone) to prevent bacterial growth Additional treatments  fluoride (dental health) lime (softens hard water) aeration (add O 2 ) – removes odors to improve taste pH adjustment Chlorine can form harmful byproducts (THMs)and has suspected links to stomach cancer and miscarriages. Many agencies now residually disinfect with Chloramine (chlorine/ammonia combo) to prevent formation of THMs.

Municipal Water Purification Plant

Wastewater (Sewage) Treatment Septic Tanks: typically treat small volumes of waste (e.g., from a single household, small commercial/industral) WasteWater Treatment Plants(WWTP) : typically treat larger volumes of municipal or industrial waste.

Septic Tanks Approx. 22 million systems in operation ( 30% of US population) Suitability determined by soil type, depth to water table, depth to bedrock and topography Commonly fail due to poor soil drainage Potential contaminants: bacteria, heavy metals, nutrients, synthetic organic chemicals (e.g. benzene)

WasteWater Treatment Plants

Sources –Domestic used water and toilet wastes –Rainwater –Industrial effluent ( Toxic industrial water is pretreated) –Livestock wastes

Steps for wastewater treatment Divided into three stages of treatment Primary Treatment – physical process Secondary Treatment – biological process Tertiary (advanced) Treatment – can be chemical or physical; expensive and rarely done; targets specific pollutants; varies based on needs of the community

1. Filtration  uses bar screens and grit chambers to filter out larger debris Primary Treatment

Grit chamber

2. 1 st settling tank (primary clarifier)  sewage sits to let smaller particles settle to bottom. Debris that settle to the bottom forms sewage sludge. Large arm skims the top to collect floating debris (grease/oil). *this process takes several hours*

Secondary Treatment 3. Aeration basin (tank)  activated sludge which includes microorganisms (bacteria and protozoans) and O 2 are added to feed on organic waste

4. 2 nd settling tank (secondary clarifier)  bacteria and remaining solid waste slowly settle to the bottom of the tank. Debris that settle to the bottom forms activated sludge. Samples are taken from the activated sludge and analyzed in the lab. If it is still usable it is recycled to the aeration basin.

5. Disinfection  uses ozone, UV light or chlorine to kill any remaining bacteria

All sludge ends up in an anaerobic digester where it is heated and dried  Biosolids High in NO 3 & PO 4 (unless removed by tertiary treatment)

Biosolids are sent to one of three places: Landfill Incinerator Agricultural fields – used as compost/fertilizer (most common practice)