Protecting the Environment by Separating Mixtures Sewage treatment Protecting the Environment by Separating Mixtures

The mixture of water and waste you flush down the sink or toilet Sewage treatment Sewage: The mixture of water and waste you flush down the sink or toilet

What happens after you flush? Passes through drain to sewage treatment plant Primary Treatment Secondary Treatment Tertiary Treatment

Primary treatment Half the solids in the sewage are removed from the mixture First: sewage passes through a metal grid Filters out objects that don’t easily decompose (Example- fabric or plastic)

Primary treatment [cont’d] Second: sewage poured into large pool and allowed to settle for several hours Most solids settle to the bottom; floating parts (Ex., oil and grease) rise to the top Third: solids removed, treated; used as fertilizer, burned, or sent to landfill

Secondary treatment First: remaining dirty water passes through tanks containing bacteria Bacteria break down any remaining human waste and plant material Second: water allowed to settle again Third: bacteria settle to the bottom and are removed

Tertiary treatment First: pollutants like phosphorous and nitrogen removed Second: water may also pass through filters, have ozone bubbled through it, or be exposed to ultraviolet radiation Finally: chlorine is added to the water to kill any remaining organisms

Then what? Water is clean enough to be returned to the ocean, lake, or river

Keeping our water clean Contaminants in the water: Sewage Waste produced by manufacturing or processing factories Fertilizers, pesticides, or salt from farms, golf courses, or roads Accidental spills and leaks

Petroleum (oil) and water Petroleum/petroleum products are shipped around the world An oil spill from a sinking or leaking cargo ship is difficult to clean up/difficult to separate Some parts of the petroleum float and spread across the surface affecting wildlife Other substances in the petroleum sink and contaminate the lake or sea bed