Project report on waste water treatment gas 87 89 93


Oxygen present in the sample oxidize in divalent mass generation its higher valency with precipitates as a brown hydrates, oxides after addition of NaOH and KI upon acidifica­tion manganese reverts to divalent state and liberate iodine from KI equivalent to DO con­tent of the sample which is titrated against 1 standard N/80 solution of sodium thiosulphate using starch as an indicator.

However, it has been observed that about 70 – 80% of the total B.O.D. is exerted in first 5 days. The sample is therefore incubated for 5 days at 20°C and the B.O.D. values determined are reported as B.O.D. A polluted sample may power per kwh consume more oxygen in 5 days than present in water (nearly 9 mg/1 at 20°C). Hence before analysis it is diluted with a specially prepared “Dilution Water”.

The dilution water is prepared by passing air in distilled water for 1 – 2 days so as to make it saturated by dissolved oxygen. In one liter of this 1 ml each of phosphate buffer MgCl 2, CaCl 2 and FeCl 3 are mixed. The sample so diluted is taken in two bottles. The D.O. of one is determined immediately and that of the other after 5 days incubation. The B.O.D. of the sample is then calculated by

Measurement of D.O. content of the sample before or after in combustion at 20°C for 5 days or glutonic BOD at 27°C for 3 days. If the sample does not contain any oxygen, it is supplied with oxygen and the depletion caused is calculated as the B.O.D. measurement. Microbial organisms or seed may also have to provided B.O.D. is expressed in mg/1. iii. Chemical Oxygen Demand (C.O.D.):

The quantity of solids removed by screening depends on screen-opening size. Screened solid are coated with organic material of a very objectionable nature and should be promptly disposed-off to prevent a health hazard and/or nuisance condition. Disposal in a sanitary land fill, grinding and returning to the waste water flow, and incineration electricity symbols are the most com­mon disposal practices.

As mentioned above screenings are sometimes shredded and returned to the waste wa­ter flow. A hammer mill device is most often used for this purpose. Most often; a shredding device called a comminutor is located across the flow path and intercepted the coarse solids and shreds them to approx. 0.8 mm in size. These solids remain in the waste water.

Shredding devices should be located ahead of pumping facilities at the treatment plant. Grit removal ahead of the shredder will save wear on the cutting head. Usually, however, grit chambers are located at or above ground level to facilitate grit handling, and pumps may be necessary to lift the sewage to them. In this case, shredding is done ahead of the pumps and cutter wear must be tolerated.

Municipal waste water contains a wide assortment of inorganic solids such as pebbles r gasquet tennis, sand, silt, egg shells, glass and metal fragments. Operations to remove these inorganics will also remove some of the larger, heavier organics such as bone chips, seeds etc. Together, these comprise the material known as grit in waste water treatment systems.

Grit removal facilities basically consist of an enlarged channel area where reduced flow velocities allow grit to settle out. Many configurations of grit tanks are available. At-least two separate chambers should be provided, one to take care of low flow and the electricity symbols ks2 worksheet other for the high flow. A period of detention of 1 minute is commonly employed. Grit chambers are cleaned by hand, mechanically or hydraulically.

Hand clearing is done only in the case of smaller plants, is less hygienic and odour free though somewhat easier for disposing of the removed material than in the case of mechanical cleaning. In hydraulic-cleaning, the depos­ited material is flushed out under fire-streams directed from a central point and removed through pipes in the side-walls or bottom of the chamber.

In this step, the settleable solid are removed by gravitational settling under quiescent conditions. The sludge formed at the bottom of the tank is removed as under flow either by vacuum suction or by raking it to a discharge point at the bottom of the tank for withdrawal. The clear liquid produced is known as the overflow and it should contain gas 101 no readily settle- able matter.

In rectangular tanks, feed is introduced at one end along with the width of the tank and the overflow is collected at the surfaces, either across the other end or at different point along the length of the tank. An endless conveyor scrapes the floating material into a screen through which it also pushes the settled solids into a sludge hopper.

Flotation may be used in place of sedimentation, primarily for treating industrial waste water containing finely divided suspended solids and oily matter. Flotation technique is used in paper industry to recover fine fibres from the screened effluent and in the oil industry for the classification of oil bearing waste. It is also used for treating effluents from tanner­ies, metal finishing, cold-rolling and pharmaceutical industries.

This has the effect for increasing the buoyancy of the particles as a result; the par­ticles float to surface from where they can be readily removed. To aid in the flotation process, chemical coagulants such as aluminium and ferric salts or polymer coagulant-aids are often used. These chemicals increase the flocculent structure of the floated particles so that they can easily entrap the air bubbles.

In the activated sludge system, the national gas average 2012 waste water is brought into contact with a diverse group of micro-organisms in the form of a flocculent suspension in an aerated tank, whereas in the biological film system, also known as trickling filters, the waste water is brought into contact with a mixed microbial population in the form of a film of slime attached to the surface of a solid support system. In both cases the organic matter is metabolized to more stable inorganic forms.

The effluent from the aeration tank containing the flocculent microbial mass, known as sludge, is separated in a settling tank sometimes called a secondary settler of a clarifier. In the settling tank the separated sludge exits without contact with the organic matter and becomes activated to the aeration tank as a seed; the rest is wasted.

If all the activated sludge is recycled, then the bacterial mass would keep increasing to the stage where the system gets clogged with solids. It is therefore, necessary to ‘waste’ some of the micro-organisms, and this wasted sludge is the one which electricity 101 is processed and disposed of. The process flow diagram for a typical activated sludge plant is given in Fig. 7.11.

The influent is sprinkled over the bed packing (See Fig. 7.12) which is coated with a biological slime. As the liquid trickles over the packing, oxygen and the dissolved organic matter diffuse into the film to be metabolized by the micro-organism in this slime gas monkey live layer. End products such as NO 3, CO 2 etc. diffuse back out of the film and appear in the filter effluent.

The concentration of solids in the primary sewage sludge is about 5 percent; the activated sludge contains less than 1 percent solids; from trickling filters has about 2 percent solids. The common unit operation of sludge treatment and disposal involve concentration or thicken­ing, digestion, conditioning, dewatering, oxidation and safe disposal.

This technique is used extensively for concentration and separation of metal ion from large volumes of natural and waste waters. The total free metal q gastrobar leblon ion content of a water sample is determined by passing the sample through H+ – cation exchanges and titrating the acid liberated with a standard alkali solution. Another aliquot may be titrated with EDTA to estimate the total hardness of water.

Ion exchange chromatography provides an excellent method for concentration and sepa­ration of ions from waste water. The ions are first concentrated on a suitable ion exchange column and then selectively eluted to be measured polarograhically, spectrophotometrically, radio metrically etc. Ion exchange membranes are also useful for separation and concentra­tion of metal ions prior to analysis.

In this way size of particles is increased, improving rates of sedi­mentation. A plant to be designed for an effluent or water having a consistent suspended solids content and flow velocity. Sludge is usually continuously removed to maintain the blanket consistency. This type of plant is often called a sludge contact clariflre. It has very reduced free surface area.