Chapter 9 · MCQ Read Mode

Wastewater Treatment Technology

The chemical oxygen demand of a wastewater is always greater than its five-day biochemical oxygen demand because COD

A wastewater with a BOD5 to COD ratio of 0.15 is best treated by

Volatile suspended solids are determined as the fraction of suspended solids lost on ignition at

For a town of 10 000 people the Harmon peaking factor is approximately

The hydraulic elements of a treatment plant — channels, weirs and pumps — are sized on the

The chief disadvantage of a combined sewerage system is that

The volume of sewage generated is commonly taken as what proportion of the water supplied?

The principal purpose of preliminary treatment is to

Nitrogen and phosphorus removal belongs to which stage of treatment?

The hydraulic profile of a treatment plant is drawn

A wastewater treatment plant should preferably be located

The ultimate BOD of a sewage with BOD5 of 220 mg/L, taking BOD5 as 0.68 of the ultimate, is approximately

Effluent discharged into a public sewer is permitted at a weaker quality than effluent discharged to a river because

In a circular sewer the velocity of flow is a maximum when the depth of flow is about

The discharge carried by a circular sewer is a maximum at a depth of flow of about

When a circular sewer flows exactly half full, the velocity compared with the full-bore velocity is

The minimum self-cleansing velocity normally specified for a sanitary sewer is

For a circular pipe flowing full, the hydraulic radius is equal to

A 300 mm concrete sewer (n = 0.013) laid at a slope of 1 in 400 flows full at a velocity of approximately

Sanitary sewers are normally designed to flow only half to three-quarters full at peak flow in order to

The egg-shaped sewer was adopted for combined systems because its narrow invert

Crown corrosion of a concrete sewer is caused by

Sewer pipes are laid starting from the downstream end with the sockets facing upstream because

The minimum diameter normally permitted for a public sanitary sewer is

Where a sewer and a water main cross, the sewer must be laid

Compared with a concrete sewer, a PVC sewer of the same size and gradient will carry

The parameter that governs the removal of discrete particles in a sedimentation tank is the

Primary sedimentation removes about 60 per cent of suspended solids but only about 30 per cent of BOD because

The horizontal velocity in a grit chamber is held at about 0.3 m/s in order to

A proportional flow (Sutro) weir is placed at the outlet of a horizontal grit chamber in order to

An aerated grit chamber is insensitive to variations in the rate of flow because separation is governed by

The detention time normally provided in a horizontal flow grit chamber is

The volume of a flow equalization tank is obtained from the cumulative inflow mass diagram as

An in-line equalization tank is preferred to a side-line arrangement where it is important to

Head loss through a clogged bar screen, with a velocity through the openings of 0.9 m/s and an approach velocity of 0.6 m/s, is approximately

The approach velocity in the channel ahead of a bar screen is kept above about 0.4 m/s so that

A town produces 8000 m³/d of sewage. At a surface overflow rate of 40 m³/m²·d the primary tank surface area required is

Short-circuiting in a sedimentation tank means that

Grit is removed ahead of the biological stage principally because it

An anoxic process is correctly defined as one in which

The controlling design parameter of every suspended growth biological process is the

Nitrification fails in winter at a plant that nitrifies successfully in summer chiefly because

In the Monod equation the half-saturation constant Ks is the substrate concentration at which

The yield coefficient for anaerobic treatment is only about one-tenth that for aerobic treatment, which means that anaerobic processes

A reactor of 2000 m³ holding 2500 mg/L MLVSS receives 5000 m³/d of sewage at 200 mg/L BOD. The F/M ratio is

A high food to microorganism ratio produces a sludge that is

Compared with a plug-flow reactor, a completely mixed reactor is preferred for a variable industrial wastewater because it

Tapered aeration is used in a plug-flow aeration tank because

The rate-limiting step in the anaerobic digestion of a particulate substrate such as sewage sludge is

A digester becomes sour when the methanogens are inhibited, and the standard early warning of this condition is a rise in

Excessive growth of filamentous organisms in activated sludge is commonly caused by

The nutrient ratio commonly specified for aerobic biological treatment is BOD to nitrogen to phosphorus of

The return of settled sludge to the aeration tank is essential to the activated sludge process because it

A mixed liquor of 3000 mg/L MLSS settles to 300 mL/L in thirty minutes. The sludge volume index is

Rising sludge in a secondary clarifier, in which settled sludge floats to the surface in clumps, is caused by

Extended aeration differs from conventional activated sludge chiefly in using

A trickling filter is misnamed because it actually works by

Recirculation around a high-rate trickling filter is practised in order to

The principal operating advantage of a moving bed biofilm reactor over activated sludge is that it

A facultative stabilization pond functions through the symbiosis in which

Treatment in a horizontal subsurface flow constructed wetland is achieved principally by

The oxygen required for nitrification is

Nitrification of 30 mg/L of ammonia nitrogen destroys alkalinity as calcium carbonate amounting to

The anoxic zone is placed ahead of the aerobic zone in the Modified Ludzack-Ettinger arrangement principally in order to

The key feature that allows a UASB reactor to treat sewage at a hydraulic retention time of only six to twelve hours is

A septic tank is correctly described as treatment

A septic tank should never be completely emptied and washed out during desludging because

The minimum distance normally required between a soak pit and a drinking water well is

Thickening a sludge from 1 per cent to 4 per cent solids reduces its volume to

Waste activated sludge is far more difficult to thicken by gravity than primary sludge, so its design solids loading rate is

Mesophilic anaerobic digestion of sludge is normally carried out at

A plant produces 1000 kg/d of dry solids with 70 per cent volatile matter, of which half is destroyed in digestion. The volatile solids destroyed amount to

The principal advantage of a high-rate digester over a standard-rate digester is that being heated and completely mixed it

Sludge drying beds are particularly suited to Nepali conditions outside the monsoon because they

The usual reason for refusing to apply a stabilised sludge to agricultural land is its

Lime stabilization of sludge differs from digestion in that it

Incineration of sewage sludge achieves the greatest volume reduction but

Faecal sludge emptied from septic tanks by tanker should be