What Is Sewage

  What is sewage? Sewage is waste water generated in carrying out daily activities and include discharges from kitchens, toilets laundry, washing of floor etc. In broad terms discharges other than those generated from any industrial process     Why sewage does needs treatment? Requirement of law mandate it mainly because it pollutes the ecosystem or other resources in which it is introducedwithout treatment. For e.g. Sewage without treatment seeps into groundwater pollutes.   What is a sewage treatment plant (S.T.P)? Sewage Treatment Plant is a set of equipments which treat the raw effluent to bring its characteristics to levels that will not disturb the environment when discharged into it.
S.T.P. includes package type units of small capacities such as few thousand kilo liters per dayto mega treatment units of capacities enough to complete cities.
In this booklet we are specifically concerned about S.T.P. of sizes upto 1000 kl/day.
    Who needs an S.T.P.? All establishments whether industrial, commercial or residential where waste water is generated due to daily domestic chores need S.T.P. to treat sewage before its disposal. The list below is indicative one:

•Residential Colonies & Apartments
• Hospitals
• Malls/Multiplexes
• Hotels
• Restaurants & Clubs
• Schools, Colleges & Hostels
• Industrial Units
• Institutional Buildings
    What are common technologies used for S.T.P.? For capacities of S.T.P under consideration the common technologies used are mostly Aerobic (with air) Treatment based. Though for higher capacities Anaerobic (withoutair) Technologies are used.
Under Aerobic Treatment broad classification can be made between:
• Suspended Growth Based Treatment
• Attached Growth Based Treatment
One thing common between all technologies is that they are all combination of Physico-Biological Processes i.e. no chemicals are used for treatment, except for nutrients for seeding (sometimes) or for disinfection before disposal.
     What is suspended growth or attached growth based technologies? All S.T.P. come with a Bio-Reactor which is the heart of the complete unit.
Bio-reactor is where the process of treatment with help of microbes occurs and reduction in key characteristics is achieved. Growth of these microbes may take place in suspended form in water inside the reactor or they may grow attached to some media(plastic or else) provided inside the reactor. This is where the key difference between suspended and Attached Growth Processes lies.
Suspended Growth process requires recirculation of microbial mass to maintain key parameters inside the reactor for treatment, where as it is not needed in Attached Growth Process.
Main Suspended Growth Processes commonly used are:
• Activated Sludge Process (A.S.P)or Extended Aeration(E.A)
Main Attached Growth Processes commonly used are:
• Submerged Aerobic Fixed Film (S.A.F.F)
• Moving Biological Bed
    Which one to choose among suspended growth or attached growth based technologies? It is not a choice between different technologies because one is better than other. Generally speaking all of the before mentioned processes, if used properly, produceadequate results. All processes have their positives and negatives. Choice is based mainly on suitability of a process to user’s needs. Hence they have to be evaluated on a case to case basis rather than adopting a “one fits all” approach.
    What are misconceptions about S.T.P.? There are certain misconceptions prevalent about S.T.P. among the user groups which are:
BRAND IS BETTER
Truth:Proper designing and execution at site only make a S.T.P. produce
results, not just brand of the supplier.
FIT & FORGET
Truth: A S.T.P. is a combination of equipments which need as much care & maintainace as any other machine you use, that too on continuous basis.
SMALLER IS BETTER & CONVERSLY BETTER TECHNOLOGY MEANS SMALLER UNIT
Truth: Designing of S.T.P. determines size, no...