Sanitary Engineering

What do you mean by sanitation? How it is related with our human life? Why water-carriage system of sanitation is popular than conservancy system nowadays.

(a) Define "sanitation". Highlight the importance of wastewater management. [1+3] (b) You as a sanitary engineer are required to address recurring flood in Kathmandu valley, which type of sewerage system would you prefer from the perspective of wastewater flow, and why? [4] (c) Determine the size of combined circular sewer for a discharge of $1.6{\text{ m}}^3/\text{s}$ running half full. Assume a gradient of 1 in 2000 and manning's coefficient = 0.013 (constant for all flows). In the dry season if the flow drops to $0.60{\text{ m}}^3/\text{sec},does$ the flow maintain desired self-cleaning velocity of $0.6\text{ m/sec}$.

(a) Define sanitation system. Justify the importance of water-carriage sanitation system which is popular than the conservancy system. [4] (b) Why the wet weather flow and dry weather flow are considered as important parameters in designing a sewer line. [4] (c) Design a sewer running 0.6 times full at maximum discharge for a town provided with the separate system serving a population of 250,000 persons. Water is from the water-work at a rate of 200 lpcd. Take a constant value of $n=0.013$ at all depths of flow. The permissible slope is $1\text{ in }600$. Take peak factor of 2.25.

A storm sewer drains a catchment with inlet time (overland flow time) = 8 minutes; length of sewer line = 600m; velocity in sewer = $1.0\text{m/s}$. Calculate the total time of concentration to the outlet of the sewer. Interpret your answer.

Design a circular sewer running 0.70 full at maximum discharge for a town provided with the separate system serving a population of 100000 persons. Water is supplied from the water works at a rate of 200 liters per capita per day. Take a constant value of $n=0.013$ at all depths of flow. The permissible slope is 1 in 600. Take a peak factor of 2.25.

Why storm water regulators are commonly used as sewer appurtenance?

Write a short note on: (Any Two) [2x4] (a) Sewer appurtenances and its important (b) Solid waste disposal methods (c) Leaching cesspool

List the type of microorganism based on carbon source.

Explain bacterial metabolism processes highlighting the waste removal mechanism.

Interpret the higher and lower value of rate constant (K) in the BOD equation.

A factory produces an average of 250MLD of wastewater per day, with $BO{D}_5$ (at $20^{\circ }\text{C}$) of $1500\text{mg/L}$. Compute the BOD equivalent population given that the per capita $BO{D}_5$ (at $20^{\circ }\text{C}$) load is $80\text{ g/capita/day}$. Also, Interpret your answer.

A city discharges $1500\text{ L/s}$ of sewage into a stream whose minimum flow is $600\text{ L/s}$. The sewage $BO{D}_5$ is $240\text{ mg/L}$ and stream $BO{D}_5$ is $3\text{ mg/L}$. The temperature of both waters is $20^{\circ }\text{C}$. The DO content of the stream is 90% of saturation and sewage has zero DO. If the minimum DO in the stream must be $4\text{ mg/L},calculate$ the required degree of treatment. Use $K_1=0.1{\text{ day}}^{-1},K_2=0.3{\text{ day}}^{-1},and$ saturation DO at $20^{\circ }\text{C}=9.17\text{ mg/L}$. If required, the Streeter Phelps equation is provided below; $${\left[\frac{L_o}{f_s{D}_c}\right]}^{f_s-1}\Rightarrow [f_s(1-(f_s-1)\frac{D_o}{L_o})];f_s=R/K\text{ terms used in the equations have usual meaning.}$$Also set in 3 other sittings — see the exact wording of each<li class="back-only">2079 Jestha BackDetermine the degree of treatment required to reduce BOD containing in the sewage. The characteristics of raw sewage and a nearby river in which the sewage is discharge are as follows: (a) Sewage discharge = $1.7{\text{ m}}^3\text{/s}$ (b) ${\text{BOD}}_5$ at $20^{\circ }\text{C}$ of sewage = $230\text{ mg/l}$ (c) Minimum river discharge = $7.5{\text{ m}}^3\text{/s}$ (d) ${\text{BOD}}_5$ at $20^{\circ }$ of river water = $1.2\text{ mg/l}$ (e) Temperature of the river after mixing = $20^{\circ }\text{C}$ f) De-oxygenation constant = $0.1\text{/day}$ at $20^{\circ }\text{C}$ g) Re-oxygenation constant = $0.4\text{/day}$ at $20^{\circ }\text{C}$ h) Initial DO deficit just at mixing = $2.0\text{ mg/l}$\n(i) Critical DO deficit = $4.7\text{ mg/l}$

(a) Draw a block diagram highlighting various stages of waste water treatment train and describe the working and impurities removal of each unit. [3+5] (b) Design $a^n$ aeration tank of activated sludge process to treat a domestic waste water with following data Flow (Q) = 20 MLD ${\text{BOD}}_5$ of wastewater = $200\text{ mg/l}$ MLSS = $2500\text{ mg/l}$ $\text{MLVSS/MLSS}=0.8$ F/M ratio = $0.25/\text{day}$ SVI = $100\text{ ml/g}$. [8] (c) Define sewage filtration. Compare the intermittent sand filter and contact bed in terms of operation and construction procedure.

What are the steps involved at removing pollutant in Sequencing Batch Reactor (SBR)?

Identify the operational problems of the activated sludge process and provide possible solutions for each.

Describe the pollutant removal mechanism of an anaerobic baffled reactor.

Design a "Standard Rate Trickling Filter" to treat 5 MLD of sewage with a BOD of $240\text{ mg/L}$. The final effluent BOD should not exceed $35\text{ mg/L}$. Assume organic loading rate = $0.25{\text{ Kg-BOD/m}}^3\text{/day}$. Assume hydraulic loading rate = $2.5{\text{ m}}^3{\text{/m}}^2\text{/day}$.

Interpret the meaning of 10% sludge with $a^n$ example.

As an environmental engineer, how would you evaluate if an anaerobic sludge digestion process is functioning properly?

(a) A wastewater treatment plants treat 2 MLD in a PST, moving 60 % of suspended solids. Raw sludge has 97 % moisture, 70 % volatile solids. During digestion, 60 % of volatile solids are destroyed, leaving digested sludge at 84 % moisture. Fixed solids SG = 2.4, volatile solids SG = 1.0. Determine the volume of raw and digested sludge. [8] (b) Define onsite sanitation and provide suitable examples. Design a VIP latrine with neat sketch for 10 users.

Discuss in brief about the working mechanism of a septic tank with a neat sketch.

Determine the size of combined circular sewer for a discharge of $1.6{\text{ m}}^3/\text{s}$ running half full. Assume a gradient of 1 in 2000 and manning's coefficient = 0.013 (constant for all flows). In the dry season if the flow drops to $0.60{\text{ m}}^3/\text{sec}$, does the flow maintain desired self-cleaning velocity of $0.6\text{ m/sec}$.

Design the aeration tank for a conventional activated sludge treatment plant to treat domestic sewage with an average flow of 15 MLD considering the following data: BOD of settled sewage = $200\text{ mg/l}$; $F/M=0.25/\text{d}$; $MLSS=3000\text{ mg/l}$; $MLVSS/MLSS=0.8$ and $SVI=100\text{ ml/g}$

Why the wet weather flow and dry weather flow are considered as important parameters in designing a sewer line.

Define "sanitation". Highlight the importance of wastewater management.

(a) Describe about significance of BOD and COD. If $3\text{ days}$ $25^{\circ }\text{C}$ BOD of sewage sample is $250\text{ mg/l},what$ will be its $5\text{ days}$ BOD at $30^{\circ }\text{C}$? Assume $K_{20}=0.1\text{ per day}$. [2+2+4] (b) The wastewater generated from a newly established town is proposed to dispose in the nearby river. The characteristics of raw wastewater and that of river are as follows: Wastewater discharge = $300\text{ l/s}$; ${\text{BOD}}_5$ of wastewater at $20^{\circ }\text{C}=450\text{ mg/l}$; The sewage is in putrefied state; Minimum river discharge = $5.5{\text{ m}}^3/\text{s}$; ${\text{BOD}}_5$ of river at $20^{\circ }\text{C}=0\text{ mg/l}$; DO of river = $8.5\text{ mg/l}$; Temperature in the river after mixing = $20^{\circ }\text{C}$; De-oxygenation constant = $0.1/\text{day}$ (base10) at $20^{\circ }\text{C}$; Re-oxygenation constant = $0.4/\text{day}$ (base 10) at $20^{\circ }\text{C}$; Saturation DO of river at $20^{\circ }\text{C}=9.1\text{ mg/l}$; Allowable minimum DO deficit at d/s of disposal = $4.5\text{ mg/l}$. Is treatment necessary? If so, what will be the required degree of treatment?