The Purpose Of Sewage Treatment Biology Essay

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Municipal waste water is collected through sewage system. The purpose of sewage treatment is to produce such a effluent which is dispose with out causing harmful effect on surrounding environment. Different experiment were conduct like an-aerobic, aerobic mechanical chemical and thermal by different scientist to treat municipal waste water results were designed in term of organic content removal, pollutant removal and ask removal etc. these result proved that activated sludge process (aerobic- an aerobic) is much more efficient for waste water treatment.

Municipal waste water comprises the domestic water in urban areas. It is collected through sewage system. It has high BoD content and different contaminants like waste oil heavy metals, chemicals, detergents and chloro fluoro- carlions (Kadlec, 1996). Evidence is sought. From number of sources that hazardous xenobiotic compounds are also present in waste water and pose serious health rick (Slack et al, 2005). Different studies were conducted to treat waste water in terms of green house gas emission (Batool and Chaudhry, 2009).

Mechanical biological treatment was performed in order to check mass reduction, biostability of biologically treated water and emission reduction. The experimental results showed a 46.2% dry matter reduction (Bayard et al, 2010). The pre mechanical treatment was modified in this experiment by introducing sieves which are designed to reduce hair and fibrous materials. The efficiency of the removal is determined in terms of suspended solids uptill now. But in future, different parameters will influence the experiment (Frenchen et al, 2008).

ii) Anaerobic Treatments:

An experimental set up was held at thermophilic temp. (55°C) in a wet digester system organic fractions were co-digested with manure, keeping the conc. Of organic fractions high. Organic fractions conc. Was increased over a period of 8 weeks. Recirculated process liquid put a beneficial stability effect and value of pH raised to 8. Biogas production increased and volatile solids reduced upto 69 74% (Hartmann and Ahring, 2005). Greater amount of volatile solids in total solids leads to greater biodegradability. Three reactors contained total solids about 16%, 13.5%, 11% and volatile solids 26.1%, 35.8%, 41.8% respectively then the methane production was 273, 283, 3144kg vs in these reactors respectively (Dong et al, 2010).

The stabilization of municipal waste is modified by combining the upflow anaerobic sludge blanket and a waste stabilization pond. This system achieved 30 - 35% organic pollutant reduction and nutrient reduction upto 30 - 80% along with feacal reduction upto 97 - 99% (Ghosh et al, 1999). The feasibility of digestion and stabilization of activated sludge was examined in mesophilic conditions (37°C) in three laboratory digesters. Results indicated that reduction of mixing had a pronounced effect on the stabilization of unstable digester (stroot et al, 2000). By using two stage anaerobic membrane treatment at different loading rates and hydraulic retention time over 200 days, CoD) level reduced upto 90% (Trzcinski and Stuckey, 2009). Water shredding effect on the anaerobic treatment was studied in three anaerobic bioreactors, which were loaded with raw waste, shredded waste and compact waste. Methane production was higher in shredded reactor. So shredding reduces waste quantity, bio-degradation time and organic content (sponsza and Agdag, 2005). Anaerobic treatment was also performed on two different wastes obtained from university cafeteria and from a municipal treatment plant. Discontinuous operations were performed at (55°C). At the end high level of methan production approx 25 30L was achieved along with high degradation rate (Carneiro et al, 2008).

iii) Aerobic Treatment:

The experiment showed that sample sludge was completely retained in a submerged hollow. Fiber membrane having a pore size of 0.2 mm. the performance during treatment was very stable even at very high level. The results indicated that CoD was reduced upto 95% and nitrification was completed upto the 82% (Rosenberger et al, 2002).

iv) Chemical Treatment:

In order to prevent the hazards effects caused by waste water, different chemicals were used for water purification. Samples were pre treated with Al2 (So4)8H2O and then with H2O2 / UV. About 93% turbidity reduction was observed (Bhatia et al, 2010).. Anodizing aluminium waste was used as coagulant for the treatment of waste water. It gave positive results and final turbidity and pollutant level was reduced upto 85% (Correia et al, 2005). Different alkali chemicals were added in waste water sample like Na2Co3, NaHCo3 and NaOH and a sample reactor with out any chemical. The reactors containing as much alkali contents gave much better removal efficiencies like 92.21% for Na2CO3, 92.74 for NaHCO3 than reactor without alkali which gave 90.56 (Jun et al, 2009).

v) Thermal Treatment:

The melting treatment made incinerator residues, fly ash, bottom ash stable and non toxic and for re-useable. After melting residues were decomposed at a temp of approx 1400 °C in a furnance (Sakai and Hiraoka, 2000). Ash obtained after melting is of different types like scrubber ash, bottom ash and contained diff. metals like Cd and Pb in higher concentration X ray diffraction showed that large amount of glass is also present in ash above 1400°C or still repaired in ash white Cd, Pb were removed (Lin and Chang, 2006). Continuous sintering behavior proved very efficient for ash removal. It was investigated that the water washing before the sintering is very effective for detoxifying fly ash (Wey et al, 2006). By mixing the one unit weight of bottom ash and 2 unit volume of H2O for about 15 mins, the level of total organic carbon was greately minimized. So water washing is an effective step for the removal of odourous substances (Lin et all, 2011). Hydrothermal process was performed for subcritical H2O for the treatment of rabbit food. Reactors were set at temp. range of 473 - 623K. Organic components and ash content ware greatly reduced at these temp. ranges (Goto et al, 2004).

Conclusion: -

Above researchers which have been done in the field of municipal waste water treatment showed that a large no of treatment processes are applied. Every category has it's own advantages and disadvantage. Comparatively activated sludge process (aerobic- an aerobic) is much more advantageous because it is simple, cheaper and pollutant removal is much greater.