Building ServicesSedimentation

Submitted By:Group C

Sedimentation:Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration, or electromagnetism.

Sedimentation is a physical water treatment process using gravity to remove suspended solids from water. Solid particles entrained by the turbulence of moving water may be removed naturally by sedimentation in the still water of lakes and oceans.

Sedimentation-Contact Bed-Intermittent Sand Filters-Trickling Filter-Miscellaneous Filter

1. Contact BedIn this type of wastewater filtration, the sewage applied on the contact material is allowed to stand undisturbed for some time before, being emptied and an interval is allowed before recharging the contact beds. During the 'contact period', when the filter is standing full, the fine suspended particles of sewage are deposited on the contact material and worked over by the anaerobic organisms. During the 'empty period' that follows next, the deposited matter is oxidized by the aerobic bacteria. It is then washed off the contact material and carried out with the sludge effluent on the next emptying of the tank.

Construction

Contact beds are watertight tanks with masonry walls and very much similar in construction to an intermittent sand filter. The contact material is made of broken stone called ballast and is of 2.5 - 7.5 cm gauge. The tank is filled with the sewage over a period of an hour; allowed to stand full over a period of two hours, then emptied through underdrains. This process takes another hour. The tank is now left empty for 3 to 4 hours before admitting the next charge. (Thus with a total working period in a shift of 8 hours, the contact bed can be worked in three shifts daily). The organic loading in this case is about the same i.e., 1.1 million liters per hectare per day.

Use

The contact beds method is now only of historical interest and not commonly used. This is mainly because of the loss of efficiency brought about by the exclusion of air when the tank is standing full. For an efficient biological action, it is imperative that the aeration should be through the mass of sewage. It has therefore, been superseded by more efficient biological wastewater treatment process, as in the case of trickling filter wastewater treatment method and activated sludge plants. However, the contact beds have some merit when compared to the trickling filters as:(i) Lesser operating head required (ii) Freedom from filter (psychoda) flies (iii) Lesser nuisance due to odor

Intermittent Sand Filter • They are a viable alternative to conventional methods when

soil conditions are not conducive for proper treatment and disposal of wastewater through percolative beds/trenches.

• Sand filters can be used in sites that have shallow soil cover, inadequate permeability, high groundwater, and limited land area.

• Treatment is accomplished through physical and chemical means, but mainly by microorganisms attached to the filter media.

• The treated wastewater is collected in under drains at the bottom of the sand filter and is then transported to a line for further treatment or disposal.

Types of Intermittent Sand Filter

Gravity Discharge ISFs

• The gravity discharge ISF, is usually located on a hillside with the long axis perpendicular to the slope to minimize the excavation required.

• The effluent leaving the sand filter flows out by gravity, the bottom of the sand filter must be several feet higher than the drain field area.

• To achieve that difference in elevations, a sand filter may be constructed partially above ground.

Bottomless ISFs

• A third type of buried sand filter has no impermeable liner and does not discharge to a drain field, but rather directly to the soil below the sand.

Pumped Discharge ISFs

• The pumped discharge sand filter, is usually sited on level ground.

• Its location in relation to the drain field is not critical since a pump located within the sand filter bed allows effluent to be pumped to a drain field at any location or elevation.

• Discharge piping goes over—not through—the sand filter liner, so the integrity of the liner is protected.

Advantages of Using Intermittent Sand Filter• ISFs produce a high quality effluent that can be used for drip irrigation

or can be surface discharged after disinfection.

• Drain fields can be small and shallow.

• ISFs have low energy requirements.

• ISFs are easily accessible for monitoring and do not require skilled personnel to operate.

• No chemicals are required.

• If sand is not feasible, other suitable media could be substituted that may be found locally.

• Construction costs for ISFs are moderately low, and the labour is mostly manual.

• The treatment capacity can be expanded through modular design.

• ISFs can be installed to blend into the surrounding landscape.

• The soil cover prevents odours.

Disadvantages of Using Intermittent Sand Filter

• The land area required may be a limiting factor.

• Regular (but minimal) maintenance is required.

• Odour problems could result from open filter configurations and may require buffer zones from inhabited areas.

• If appropriate filter media are not available locally, costs could be higher.

• Clogging of the filter media is possible.

• ISFs could be sensitive to extremely cold temperatures.

• ISFs may require an NPDES Permit when the effluent is surface discharged.

Trickling FilterA trickling filter, also called trickling biofilter, biofilter, biological filter and biological trickling filter, is a fixed-bed, biological reactor that operates under (mostly) aerobic conditions. Pre-settled wastewater is continuously ‘trickled’ or sprayed over the filter. As the water migrates through the pores of the filter, organics are aerobically degraded by the biofilm covering the filter material.

It is used in the secondary treatment. A trickling filter consists of a fixed bed of rocks, lava, gravel, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime (biofilm) to grow, covering the bed of media. 12

Aerobic conditions are maintained by splashing, diffusion, and either by forced air flowing through the bed or natural convection of air if the filter medium is porous.

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Miscellaneous Filters

Water Distillation (Water Distillers)- Water Distillation involves heating the water to boiling point and condensing the steam. Pollutants with a boiling point near that of water are hard to remove, but generally the distilled water is of very high quality. The major drawback to this method is that it requires a large amount of energy. Some people will also complain that the distilled water tastes flat (this is due to less dissolved oxygen).

Water Distillers

Reverse Osmosis (Hyper-filtration)- In water filter terms, reverse osmosis (or hyper-filtration) is the process of filtering water under pressure through a semi-permeable membrane, allowing water to pass through but rejecting other particles such as bacteria, toxins, salts, and anything bigger than around 150 Daltons.

Activated Carbon (AC) Water Filters- Activated Carbon Filtration is an established technology that works through absorption of the problematic compounds, primarily to remove taste and odour but systems will also remove some harmful contaminants. AC is a highly porous material with a very large surface area. Chemical pollutants are attracted to and held by AC's surface. These water filters are best suited for the removal of organic compounds.

UV Filters- UV filters are able to kill the majority of bacteria and viruses in the water which passes through them, However, they won't remove chemical pollutants from the water. Since the treatment is ineffective outside the treatment area, water should be used immediately after it is treated.

Eaton's BECO INTEGRA® PLATE system offers an enclosed filter system for sophisticated filtration tasks. The product channels of the filter elements are sealed via the depth filter sheet and ensures that only the filter element and the filter sheet are in contact with the product. For added protection, an additional circumferential gasket hermetically seals the filter packet.  Eaton's BECO INTEGRA PLATE system can  be used for sheet filtration, precoat filtration or step filtration

Enclosed Filtration

BIOFILTRATION-Biological filters can be used in the treatment of screened raw sewage or settled wastewater from primary settlement (sedimentation) tanks. The filter plant consists of a bed of random or modular plastic media through which the effluent percolates.