1. CLEANING UP THE RIVERS 4.11

2.  For many years our rivers were used to carry wastewater away from the cities.  The industrial revolution and the invention of the w.c. (water closet) increased the river’s load of wastes.  The rivers smelled of sewage and water-borne diseases: diseases cause by organisms in the water were common

3. Thames River-London, England  In the mid 1800’s – 25000 people living near the river died of cholera  Caused by Vibrio cholerae bacteria in wastes in the water.  Sewers were built to take the waste out to the sea – did not solve problem only moved the problem  Sewage plants were built in1960’s and river is clean again.

4. America’s Rivers  America’s rivers were once like the Thames.  The first sewers were constructed in NYC during 18 th century. They carried untreated sewage and dumped in rivers.  During 1970’s, 290 million gallons of raw sewage flowed into the Hudson and East Rivers.  Now the city has 14 sewage treatment plants

5.  Charles River of Boston is still polluted by raw sewage and storm water runoff but it is steadily improving.  In 1950, the Delaware River had a DO of zero. Fish either died or migrated back to ocean. States along the river have issued fish consumption advisories because of fish contaminated with toxins.

6. Fishable & Swimmable Rivers  No river is too small or too polluted that it is not worth saving.  Water in ALL rivers should be fishable and swimmable.  Thus the 1972 Clean Water Act was passed – Requires cities to treat their sewage before dumping it into rivers and streams.

7. The 2000 National Water Quality Inventory reports that: 40% of streams 45% of lakes 50% of estuaries were not clean enough to support fishing and swimming.

8. Sewage Treatment Plants 1. As sewage enters, it flows through a vertical bar screen that removes rags, sticks, and other large solids. The trash is scraped from bars and taken to a landfill 2. Primary Treatment: physical separation of liquids and solids. 1/3 rd of the suspended solids (organic matter) settles out to the bottom of the tank and called sludge. Floating grease and oils are skimmed off the surface of the water. The sludge and the effluent, the partially treated wastewater, are piped to separate tanks for further treatment.

10. 3. Secondary Treatment: a biological process that increases the oxygen in the wastewater and allows time for organisms to remove organic matter. 2 Processes for this: 1. Activated sludge process-air is pumped into the tank which supplies bacteria with the oxygen they need to break down the organic matter. Then pumped to a second tank where remaining solids settle out.

11.  2. Trickling filters - a tank filled with a rock-like or grid system that is coated with slime, which contains algae, bacteria, and other pollutant tolerant organisms. The effluent is sprayed over the tank and as it trickles over the organisms, they remove most of the organic matter and nutrients from the wastewater. Primary and Secondary treatment can remove 85% of the organic matter and nutrients from the sewage.

12. 4. Digesters- sludge from the primary and secondary settling tanks is piped to large tanks that re heated to 95F. Sludge held 15-20 days so anaerobic bacteria in waste can digest more organic material. Natural gas or methane is a waste product. Some is burned to provide heat for digesters and also heat for buildings nearby.

13. BIOSOLIDS  Sludge = biosolids WHAT DO WE DO WITH IT? 1. EPA approved sites off the coast 2. Farmers can use as fertilizers but must be tested for disease-causing agents and nutrient content (N P K) 3. Used to make compost

14. Pretreatment  Industries must pretreat wastewater before dumping it into the sewers to reduce the levels of heavy metals.  Required to pretreat wastewater so toxic wastes don’t interfere with the treatment process.

15. Chlorination  After secondary treatment, wastewater is disinfected through an outfall pipe into a body of water nearby.  Chlorination – sodium hypochlorite is added to kill any disease-causing bacteria that might remain in the water.  Disadvantage – chlorine reacts with organic compounds to form trihalomethanes, a carcinogenic. Chlorine is also toxic to some aquatic organisms.

16. Chlorination (cont.)  Before the water is released thru the outfall pipe into the river,  Sulfer dioxide is added to burn off the chlorine to minimize effects on fish and other aquatic organisms

17. Combined Sewers  Carry both sewage and storm water.  During average rainfalls the volume of water is 5-15 times greater than normal.  Sewage treatment plants are not designed to process this massive volume of water.  During storms, untreated sewage and storm water may flow directly into river. Ex. Potomac River, Washington D.C.

18. Lagoons & Aquaculture  Another method for primary and secondary treatment that requires large amounts of land and less expensive to build/maintain.  A lagoon is a shallow pond where sewage is held for 20-30 days.  In warm climates, algae and bacteria in a series of lagoons provide acceptable primary and secondary sewage treatment.

19. Lagoons  In warmer climates, Hyacinths are added to lagoons to control odors, they use nitrates and phosphates, and roots filter the water.  In cooler climates, duckweed, watercress or cattails are used.  To control mosquitoes, fish that eat the larvae and bats that eat the adults are introduced.

20. On-site Sewage Treatment  Septic Tank – a large tank buried in the ground to treat sewage from an individual home or business. Solids settle to the bottom, bacteria break down organic matter, and the effluent flows through piles into the soil absorption field (drain field).

21. Septic Tanks  Bacteria normally digest about 50% of the solids that remain in the tank. The remainder will accumulated in the bottom as sludge.  The mixture of fluids and solids pumped from the tank is called septage. Septage contains disease- causing organisms. It us usually disposed as spray on farmland.

22.  Livestock do not feed on crops sprayed with septage for at least 60 days.  Septage should not be used on home gardens or commercial production of food that will be eaten raw.  Septage applied on dairy farms must be plowed down before crops are planted.

23.  Effective wastewater treatment is essential for human health.  Effective treatment of wastewater and proper disposal of sludge is essential to meet the goal of “fishable, swimmable” waters.