Interview Questions.

Question 1. What Is Waste Water? How Is It Generated?

Answer :

Waste water is the water that emerges after fresh water is utilized by human beings for domestic, business and commercial use. This report will limit itself handiest to the waste water generated because of domestic use.

By and massive,it's miles sparkling water this is used for a diffusion of home uses such as washing, bathing & flushing lavatories. Washing entails the bathing of utensils utilized in cooking, washing greens and different meals gadgets, bathing, washing arms, washing clothes.

The water that emerges after those uses contains, vegetable matter, oils utilized in cooking, oil in hair, detergents, dust from floors that have been washed , cleaning soap utilized in bathing along side oils/greases washed from the human body. This water is known as “ Grey Water” or sullage.Water used to flush bathrooms to evacuate human excreta is called “ Black Water” or Sewage.

Grey water is simpler to purify as compared to black water, i.E sewage. However, the exercise predominantly observed in India is to mix those two wastes to discharge into a public sewer or right into a sewage treatment plant in a residential network/ building that has no get entry to to a public sewer.

Question 2. How Much Waste Water Is Generated In A Residential Complex?

Answer :

As in step with standards laid down with the aid of the CPHEEO (Central Public Health Environmental & Engineering Organisation), the fresh water intake in line with day per character need to be between a hundred thirty five to a hundred and fifty litres in step with day. It is officially expressed as “litres according to capita every day” (lpcd). By and massive public water supply and sewerage bodies/authorities all across the u . S . A . Use the previous parent to work out probable water consumption.

Waste era in a residential complicated:
When water is consumed through people dwelling in a residential complex without get entry to to an underground sewerage/drainage device , the amount fed on is estimated to be 135 lpcd. The general amount (No. Of residents X a hundred thirty five litres) comes right into a sewage remedy plant(STP) in the premises, and , this general quantity must be handled by using the STP.

In a huge majority of instances, the real waste generated exceeds this figure effortlessly leading to overloading of the STP. This takes place robotically due to the fact almost all residential complexes do now not deploy water meters or similar water extent and glide size gadgets to keep tune of water consumption in a residential complex/ gated network.

Consequently, while a tool is hooked up and readings monitored, consumption has been discovered to be double and a few instances triple the suggested parent of 135 lpcd. 

Waste era in a business complex:
Human profession of this kind of constructing is best throughout “duty hours”,i..E for approximately 8 to ten hours in keeping with shift if there's greater than a single shift. In this case water intake is considered as 50 lpcd in keeping with person in keeping with shift.

Civil Engineering Interview Questions
Question 3. What Are The Constituents Of Waste Water (sewage) ?

Answer :

Waste water contains all the dissolved minerals gift within the sparkling water that turned into used and which became waste water as well as all of the different contaminants noted above. These are proteins, carbohydrates, oils & fats. These contaminants are degradable and expend oxygen within the degradation process.

Therefore, those are measured in phrases of their demand for oxygen which may be installed through positive checks in a laboratory. This is known as Biodegradable Oxygen demand(BOD). Some chemicals which additionally contaminate the water all through the technique of domestic use also degrade and use oxygen and the test accomplished to establish this call for that's referred to as Chemical Oxygen call for (COD).

Typically a home sewage could contain about 300 to 450 mg/litre of BOD and COD on a mean. Sewage additionally includes coliform bacteria (e coli) that's dangerous to human beings if water containing such micro organism is ate up(under the influence of alcohol). E coli is bacteria that prospers in the intestines of warm blooded creatures inclusive of people, animals and birds.

Another feature of sewage is the excessive stage of Total Suspended Solids (TSS). This is what offers the sewage a black coloration ,therefore the name “ black water”. If sewage is permitted to show septic, it then additionally has a strong, unpleasant odour.

Question 4. Why Treat Waste Water ?

Answer :

Much of the water used for domestic purposes does now not require potable ( appropriate for consuming) water high-quality. For instance, water used for flushing lavatories or for laundry flooring, yards or roads & gardening does now not require to be potable. In a scenario wherein fresh water is getting an increasing number of scarce and whilst good sized volumes of sewage generated in the us of a aren't being dealt with ,however goes unchecked to pollute fresh water from lakes, rivers and the ground water desk, it must be handled.

Discharging untreated sewage into any drains apart from an underground sewerage system, or into open land , is an offence and invitations prosecution below the laws of all Pollution Control Boards in the u . S ..

Sewage need to necessarily be dealt with effectively after which re-used/re-cycled for numerous uses that don't want potable water first-rate. Recycling/reusing treated sewage can lessen sparkling water necessities range extensively, through almost 50-60%.In a state of affairs where fresh water availability itself is increasingly doubtful that is vital.

Question 5. How Can Treated Sewage Be Re-used/recycled?

Answer :

This calls for plumbing to be laid for you to serve two sets of garage tanks at the roofs of any residential/industrial constructing. One set of garage tanks may be used to receive and shop fresh water with a view to waft via plumbing laid to take it to toilets and kitchens where it may be used for consuming, cooking, washing & bathing.

The second set of tanks will get hold of handled sewage so one can be related with the aid of plumbing to all of the flush tanks in lavatories and to other points wherein the water may be used for washing yards, floors and additionally for gardening.

Civil Service Interview Questions
Question 6. How Is Waste Water Treated ?

Answer :

Sullage (grey water) which is cited above, if collected in a garage tank one by one can be treated by way of aerating it to prevent it from turning septic, after which dosed with a coagulant, chlorinated and then subjected to filtration through strain sand filtration followed with the aid of activated carbon filtration and saved in a separate overhead tank or tanks from which it is able to be used for flushing bathrooms and other uses where sparkling or potable water is not required.

However, the modern exercise is to combine sullage and sewage (black water) and treat the aggregate in an STP (Sewage treatment plant). This exercise has are available in predominantly to reduce the value of construction of two separate flowers and because area is now at a top rate in any building.

Question 7. Why Not Consider Grey Water Treatment Seriously In Spite Of The Extra Space It Requires ?

Answer :

From the point of view of a resident it's far well worth considering because it complements the water protection of the resident. A builder’s priority is definitely one-of-a-kind, seeing that the gap taken up by the treatment machine can not be ‘offered’ to a purchaser, he'll just no longer take into account it, as a substitute the builder will integrate gray water with sewage in an STP. This permits the builder to save fees.

However if checked out from the citizens’ view factor, a separate grey water treatment gadget being less complicated to operate provides a facility to ‘fall back on’ when the STP fails.

Rain Water Harvesting Interview Questions
Question eight. What Are The Problems That Can Be Expected With An Installed Stp?

Answer :

The maximum not unusual issues encountered are indexed below and are based totally on an informal survey of STPs (along with Water Treatment flowers also) done over the past 4 years.

Initial Start up of an STP failing to treat sewage: An STP is typically designed for the overall sewage that can be expected when a building or premises is fully occupied. Full career in most instances generally takes up to a yr or more. During this era while occupancy can be as little as 30% or so and regularly will increase over a year or extra, consequently the sewage that is available in first of all does now not offer the minimum load wished for high-quality operation of an STP. It outcomes in a scenario that may simplest be called “sewage in sewage out”. Many STPs which face this example take a long time to stabilize and provide dealt with sewage, very frequently, because of poor or incorrect operation, STPs do no longer stabilize.

Poor design/under layout of the STP : Often STPs which to begin with ‘conflict’ to conquer the first hassle defined above also can't function due to the fact

the balancing tank is undersized

aeration tank is undersized or clarifier is improperly designed
the full inflow of sewage is better than the extent the STP became designed to address.
The tanks cited in 1) & 2) above are part of the primary and secondary remedy portions of an ASP machine.Consistent mal-operation of the STP : Another very not unusual feature is that a majority of plant working employees employed by using agencies that take on Operation & Maintenance(O&M) contracts are illiterate, un skilled and supervised by people with little or no knowledge of what O&M includes. Such organizations generally rate O&M charges that residents’ associations consider lower priced. Companies with well skilled operation personnel and experienced supervisory staff fee for services an quantity that mirror their ability and expertise which residents’ Associations are reluctant to pay and thereby lose out on a well run/operated water infrastructure. They often do now not understand that even the charges which they remember as inexpensive/lower are going to waste if the sewage is simplest partly treated.

Strong smell/odour from the STP: This is a very common criticism from numerous housing communities and even business homes that have an STP in operation. The odor is regularly very robust and pretty frequently unbearable. It is because of any individual or all of the troubles indexed above. 

Very high noise ranges from the STP: Quite frequently residents of an apartment building have sought help from professionals to minimize the very high noise ranges from their STP which they discover insufferable throughout the day and more so at night time, thereby stopping the citizens from drowsing in peace.

Question 9. How Can Common Problems In Stp Be Avoided And/or Resolved?

Answer :

Modern designs for STPs which can be modular are available from reputed companies which are within the discipline of water and waste water treatment. Such corporations have standardized designs in which,for example an STP to address 150 KLD ( a hundred and fifty,000 Litres per day) of sewage can be made up of three modular STPs every of 50KLD capability. Such an installation would be capable of deal with the preliminary decrease load of sewage with one module in operation with last modules being commissioned/started up because the sewage volume will increase. Such a modular approach also makes it feasible to address sewage in the case of a spoil-down of the STP as it is extremely uncommon for all modules to interrupt-down collectively. In short, there may be a stand-by way of always to be had. For several years now some corporations have been presenting microbial agents that may help conquer those issues if these microbial dealers are added to the incoming sewage. Go in for Modular STPs & use microbial dealers often.

 It is similarly critical to realize and be able to manipulate the extent of clean water used in a network so that it does now not exceed the design potential of an STP. This includes installing water meters in any respect critical factors to measure water glide (intake) & thereafter taking movement to curb extra intake of sparkling water to save you overloading the STP. Control extra consumption of fresh water and thereby save you overloading of the STP

Builders are not expected to be specialists in water or sewage treatment plant layout, manufacture and so on. They can however have tie-americawith reputed environmental engineering groups with sound technical enjoy and a validated song file, to make up for their lack of knowledge. This seldom happens seeing that a builder’s interest ends with selling a completed project after which turning in the project to the Resident’s Association as soon as feasible, regularly without even demonstrating real, successful operation of the water infrastructure. Most builders link up with small, difficult to understand nearby agencies with insufficient information and information in waste and water treatment,however will put up some thing for an exceptionally low fee. The result is terrible/ wrong operation of an STP main to untreated sewage and unsightly odours from it. Ensure deliver of an STP from a reputed provider and entrust operation & preservation to a well trained professional team.

One of the fundamental motives for STPs no longer operating nicely is the fluctuations in enter loads. Flow of sewage in a residential community is in no way uniform. It varies with top flows inside the morning (residents on the point of visit paintings), very low or nearly no flows later within the day with some other top in the nighttime. Raw sewage is accrued in a sewage balancing tank(cited above) which need to be sized to hold at the least 6 to 8 hours float of sewage. This guarantees that the sewage gathered in the balancing tank is homogenized, thereby heading off enter fluctuations in enter load at the STP. Do not compromise on the size of a uncooked sewage balancing tank.

High noise degrees from an STP are because of the operation of electrical motor driven system consisting of pumps, air blowers, air compressors, and so on. Old designs/makes of pumps, blowers , compressors , and many others are still available at very low costs inside the marketplace and these are used in most of the STPs which have been placed up. The noise levels of such device may be very excessive in comparison to fashionable, world class pumps and rotary motor driven system now to be had in India. These present day makes are almost noiseless and extraordinarily green. The antique designs are also the reason of high power intake in addition to very excessive noise degrees. As per the legal guidelines in force in India, the noise degree accepted in a residential location is 55 dB (dB= decibels of sound) at some stage in day time,i.E from 6:00 am to ten:00 pm and forty five dB during night time(10:00pm to six:00 am).As compared to these limits, the actual noise degrees are possibly to be as excessive as 75 dB or better. To lessen noise levels and excessive power intake, it will likely be necessary to replace maximum of the crucial rotary motor pushed gadget with the contemporary noiseless high performance device. Here it's miles beneficial to select a reputed enterprise with a longtime popularity in sewage/waste water treatment to buy an STP. Such corporations have continuously progressed their designs to lessen the foot prints (space occupied) in their equipment and reduction in the strength consumption of energy by using a completely appreciable amount. Unfortunately, citizens haven't any say in this as they face up to this essential fact whilst it's far too overdue because the STP has been ordered likely even earlier than the citizens sold a home inside the property.

Watershed Interview Questions
Question 10. What About The Operating Costs For An Stp?

Answer :

The working prices, together with upkeep for:

STP of 75 KLD ability and above :  1.2 paise per litre of sewage handled.
STP of 50 KLD and below : 1.5 paise per litre of sewage handled.
These expenses do not include the cost of plant running personnel. If O&M is provided by a reputed corporation which could use well skilled operators with one operator per shift and one supervisor at some stage in fashionable shift, they would fee approximately Rs.60,000. In keeping with month. Other difficult to understand groups who tackle O&M contracts could rate approximately Rs.20,000.00 to 30,000.00 for providing the same wide variety of employees, however without the important education.

Question eleven. What Can A Resident’s Association Do If It Needs Expert Help To Sort Out Problems With Sewage Treatment?

Answer :

Go to the “Ask the Expert” service and you may locate that there are numerous folks with the vital know-how based in specific towns in India. Contact them and ask if they may help and the terms on which they'll do so if it involves traveling your vicinity. You will get considered one of them to clearly offer to help.

Question 12. Why Should An Stp Not Be In A Basement ?

Answer :

Something that is extremely critical however by no means completed till it will become too past due. A citizens’ affiliation ought to insist at the builder furnishing the affiliation with all documentation of what the property has hooked up on it, eg, As constructed drawings with criteria used for designing/selecting, in addition to specified technical specs for the electric installations, strength generation device, entire water infrastructure, piping for sparkling water and sewage with drawings displaying the routings and this need to include the piping for the waste water to and from the STP.

Details of all the pumps and other motor pushed rotary gadget as established with facts on how these had been selected, as, this may have a essential bearing on the strength consumption inside the community. Proper documentation is a need to for all of the engineering incorporated in a assets Here, lack of information is not bliss,it's far an unmitigated catastrophe! Without this, protection/maintenance can emerge as a prime problem because of sheer loss of records on all of the device which is required to undertake deliberate preservation.

Civil Engineering Interview Questions