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Urban Waste Water Treatment Industry
Waste waters are produced by medium and large scale settlements such as provinces, districts, towns and villages. Such municipal (domestic) waste waters are to be treated. Processes in municipal waste water treatment plants vary depending on their area of use since they contain domestic and partially industrial waste waters and rain waters.

While the plants vary depending on the project in general they are designed to include stages such as coarse grid, fine grid, sand arrestor, oil catcher, lifting station, nitrogen phosphor elimination tank (biophosphor), aeration tanks, settlement tanks, distribution structures, sludge concentration units, digesters, sludge dewatering units, disinfection unit and odor elimination units.

HAUS turbo blowers are employed in sand arrestor, aeration tank, sludge tanks and stabilization tanks of treatment plants. Nearly 50-60% of the overall power consumption of a treatment plant is used by blowers. Therefore, blowers are among the most significant and technological equipment pieces in a waste water treatment plant and they impact the plant operating costs significantly.

HAUS decanters and screw presses are employed in sludge concentration and/or dewatering stage which is generally the final stage of waste water treatment plants and used for solid and liquid separation. Elimination of sludge has critical importance for ensuring continuity of the plant. Sludge elimination constitutes nearly 25-30% of waste water treatment plant investment and 45-60% of the operating costs. Selection of adequate dewatering equipment and process optimization are very important for minimization of costs.

Urban Waste Water Treatment Process
HAUS Centrifuge Technologies employs decanters and screw presses for primary sludge (PS), activates sludge (WAS), extended aeration advanced activated sludge, aerobic / anaerobic digested sludge, MBR sludge produced in municipal waste water treatment plants.

Concentration Process: It is used for increasing the solid matter content of the sludge which is approximately 1-3% to the levels of 6-8%. Concentrated sludge is then fed to dewatering decanter or digester.

Dewatering Process: Decanter or screw press is used for dewatering of primary or secondary sludge.

HAUS Centrifuge Technologies turbo blowers are used for supplying air needed in sand arrestor, aeration tank, sludge tanks and stabilization tanks with a polytrophic efficiency up to 84% and an extensive operating range.

It is generally the sludge output from primary (pre-) sedimentation and has a grey color and slimy structure. It generally has a very strong smell. Digestion and dewatering of such sludges is easier than biological sludges.

Presedimentation tank contains settling / separable coarse particles.
Has an average solid matter content of 2-4% and volatile solid matter content of ̴ 80%. Feeding of sludge to the dewatering equipment is performed from sludge conditioning and storage tank.
The matter output from the final sedimentation is usually brown and flocculated. If a darker color is observed this is generally considered as occurrence of septic conditions. If the color is lighter, it is expected to have low settlement characteristics due to lesser aeration. It is generally aimed to produce a sludge with an earthy smell.

WAS is produced through growth of heterotrophic microorganisms in the activated sludge process.
It has an average solid matter content of 1.0-1.5%. It has a volatile solid matter content of ~75%. Feeding of sludge to the dewatering equipment is performed from concentration tank. Turbo blowers are used for supplying the needed air to the biological aeration tanks.
Waste water is retained in the aeration tank for a longer period than other processes to ensure stabilization and digestion of sludge. Carbon (C) and nitrogen (N) elimination can be performed in the same tank in case of extended aeration activated sludge processes. Sludge age is high and it is the most commonly used advanced treatment process.

No sufficient substrate is present for microorganisms due to extended retention period of the waste water. Therefore, microorganisms enter into endogenous respiration by competent each other and consume their own cells. This causes increase in effluent quality. An oxygen concentration lower than 1 mg/L inhibits the nitrification bacteria. optimum pH range is 8-9 for growth of nitrification bacteria. Mineral acidity is produced during oxidization of ammonia to nitrate. pH value of the system is decreased in case of insufficient alkalinity. Optimum dose shall be determined and lime shall be added to keep pH value constant. Extended aeration process is equivalent to aerobic digestion process.
Anaerobic treatment is a biological treatment technology which allows recovery of energy from waste and produces less waste that requires ultimate disposal. It is a digestion method frequently preferred in waste waters with high pollution load. It is more frequently applied in cities where industrialization is high.

When anaerobic conditions are satisfied biogas can be produced from the organic matter content of the waste water. These plants can also generate electrical energy.

Separation of organic matter content of waste water in anaerobic environment consists of two stages. Acid bacteria of organic matters are converted into organic acids, alcohol and CO2 through hydrolysis and acid fermentation.

It includes transformation of the products generated through reaction of acid bacteria to methane, CO2 and water by methanogens. High calorie methane gas is generated with the process and it can be used as an energy source.
In aerobic activated sludge process organic wastes etc are digested through synthesis and oxidization. Used for biological stabilization of organic sludges.

Aerobic digestion is used in stabilization of treatment sludges with low solid matter content. Nearly 40-50% volatile solid matter elimination is realized in the period of 15-20 days in sludge digestion.

When supply of feed stuff (organic waste-substrate) is ceased in the final digestion stage of the process, microorganisms consume each other to survive causing decrease in solid matter content in the sludge and accordingly, water, CO2 and ammonia is produced. Ammonia is oxidized to nitrate in the later phase of the reaction.


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