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a Percolation of primary or secondary effluent through 5 ft (1.5 m) of soil.

^Percolation of primary or secondary effluent through 15 ft (4.5 m) of soil.

cRunoff of comminuted municipal wastewater over about 150 ft (45 m) of slope.

Source: Process Design Manual for Land Treatment of Municipal Wastewater, U.S. EPA,

a Percolation of primary or secondary effluent through 5 ft (1.5 m) of soil.

^Percolation of primary or secondary effluent through 15 ft (4.5 m) of soil.

cRunoff of comminuted municipal wastewater over about 150 ft (45 m) of slope.

Source: Process Design Manual for Land Treatment of Municipal Wastewater, U.S. EPA,

should be less than 20 percent on cultivated land and 40 percent on noncultivated land. Soil permeability should be moderately slow to moderately rapid* and the depth to groundwater a minimum of 2 to 3 feet, although 5 feet is preferred. High-rate spray irrigation rates are 4 to 40 and up to 120 inches per week. Soil permeability for high-rate systems should be rapid with a permeable soil depth of 15 feet or more. Nitrogen and phosphorus removal is usually not complete in high-rates systems.

Ridge-and-furrow ditch systems are typically 100 to 1,500 feet in length, with depth and spacing varying depending on the type of crop and the soil's ability to transmit water laterally. Border strips are 30 to 60 feet long.62 Application rates for ridge-and-furrow (gpm/100ft) and border strip irrigation are similar to those for spray irrigation and will vary with soil permeability, spacing, and slope of the furrow.

Overland Flow Overland flow is a treatment process in which wastewater is treated as it flows down a series of vegetated terraces. Application to the top of a grassed, slightly permeable slope (2 to 8 percent) as sheet flow allows for both physical (grass filtration and sedimentation) and chemical-biological (oxidation) treatment. Treated runoff is collected in ditches and discharged to a watercourse. Surface runoff may be 50 percent or more. Grasses, which have high nitrogen uptake capacity,^ are usually chosen for cover vegetation. Viruses and bacteria are not removed. Overland flow treatment is more effective during warm weather.

*0.2 to 6.0 or more inches per hour permeability corresponding roughly to a soil percolation rate of 1 inch in 45 minutes to less than 10 minutes.

+Bent grass, Bermuda grass, Reed Canary grass, Sorghum-Sudan, Vetch; also Alfalfa, Clover, Orchard grass, Broome grass, and Timothy.

Natural or Constructed Wetlands Secondary wastewater effluent can be applied to either existing or artificial wetlands. Wetlands include inundated areas having water depths of less that 2 feet, which support emergent plants such as bulrush, reeds, hyacinths, or sedges. These plants provide surfaces to which bacterial films can attach, aid in the filtration and adsorption of wastewater constituents, and add oxygen to the water column. Natural wetlands include marshes, bogs, peat lands, and swamps. Constructed wetlands include both free water surface systems and subsurface flow systems.

Free water surface systems are generally composed of a series of parallel shallow basins from 0.3 to 2 feet in depth, which have relatively impermeable bottom soil and emergent vegetation. Wastewater is treated in these systems as it flows through the stems and roots of the emergent vegetation. Subsurface flow systems are composed of beds or channels filled with gravel, sand, or similar permeable material in which emergent plants have been planted. Wastewater is treated in these systems as it flows horizontally through the media-plant filter.

Advanced Wastewater Treatment

Advanced (tertiary) wastewater treatment may be needed in some instances to protect the water quality of the receiving surface and groundwaters from undesirable nutrients, toxic chemicals, or pathogenic organisms, which are not removed by conventional secondary treatment. For example, nitrogen and phosphorus in plant effluent may promote the growth of plankton; toxic organic and inorganic chemicals may endanger fish and other aquatic life and endanger sources of water supply, recreation, and shellfish growing; and pathogens, such as the infectious hepatitis virus and giardia, that are not removed by conventional sewage treatment increase the probability of waterborne disease outbreaks. Figure 3.13 shows wastewater treatment unit process including advanced or tertiary treatment.

Advanced wastewater treatment may include combinations of the following unit processes depending on the water quality objectives to be met. This list is meant to be illustrative and should not be considered all-inclusive.

For Nitrogen Removal

Breakpoint chlorination—to reduce ammonia nitrogen levels (nitrate and organic are not affected).

Ion exchange, after filtration pretreatment—to reduce nitrate nitrogen and ammonium levels using selective resin for each; phosphate also reduced.

Nitrification followed by dentrification, ammonia (if present) removed or converted to nitrate and then to nitrogen gas—ammonia stripping* (degasi-fying) to remove ammonia nitrogen, or biological oxidation of ammonia

* Wastewater pH is raised to 10.0 to 10.5 or above, usually by the addition of lime or sodium hydroxide, at which pH the nitrogen is mostly in the form of ammonia, which can be readily removed by adequate aeration, but pH adjustment of the effluent will be needed to meet stream standards. Organic or nitrate nitrogen are not removed. Ammonia stripping equipment includes tray towers, cascade aerators, step aerators, and packed columns.

Primary treatment

(Solids separation)

i Secondary treatment

Teritiary treatment

(Nutrient removal including biological nitrification-denitrification and phosphorus precipitation, residual solids and orga_nic matter removal)

Disinfection

(Inactivation of virus and bacteria)_

Grinder

Grit Primary removal sedimentat

Aeration Secondary on tank sedimentat

Nitrification on

Metallic salt

Final sedimentation

Denitrification Post 0 .. ... aeration

Sedimentation supplementary , Metallic salt

Carbon adsorption

Grinder

Grit Primary removal sedimentat

Aeration Secondary on tank sedimentat on

Metallic salt

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Return sludge

Return sludge

Return sludger

Mechanically I cleaned screen!

Aux bar screen

Primary sludge

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carbon feed^j coagu^t^

Filtration rx

Return sludge

Combined chemical and waste biological sludges

Return sludge

Return sludger

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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