Department of Civil Engineering, IIT Delhi (India) CVL722 (Sem1, ) (Dr. Arun Kumar;

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1 Department of Civil Engineering, IIT Delhi (India) CVL722 (Sem1, ) (Dr. Arun Kumar; Set 1 Do not submit. Please mention your assumptions explicitly. Q1. Say a raw wastewater sample from WWTP1 has 2000 mg/l 5-day BOD (due to carbon only) with reaction constant (k=0.23/day at 20 C). Calculate ultimate BOD; amounts of BOD exerted on 1- and 15- day and comment on observed differences between 1- and 15-day BOD values ( ) Q2. Qualitatively, arrange 5-day BOD values calculated using reaction rate constants (k) = 0.50, 0.23 and 0.30 values (unit: 1/day). (2 points) Q3. My student collected a raw wastewater sample from a community AA and reported me the presence of nitrogen and organic carbon in the sample using ammonia and TOC analysis (solution ph=5). To determine BOD of the sample, what type(s) of BOD she should consider and how are they related to each other? Also, what types of alkalinity you would expect in this sample? (6 points) Q4. Balance these equations, which are generally used to determine nitrogen-based BOD, to write the final balanced equation and also calculate number of moles of oxygen required for reacting with one mole of ammonia. - NH 3 +O 2 NO 2 + H + + H 2 O (1a) NO - 2 +O 2 + H + - NO 3 + H + (1b) Q5. In addition of using BOD, organic matter in wastewater is also expressed using chemical oxygen demand (COD; unit: mg/l) and total organic carbon (TOC; unit: mg/l). Given that in an untreated domestic wastewater, the BOD 5 /COD ratio varies between 0.4 and 0.8 and the BOD 5 /TOC ratio varies between 1 and 1.6. Using the BOD 5 (20 C) value from Q2, calculate ranges of COD and TOC for the WWTP1 raw wastewater? Q6. A settling column analysis is run on a type-i suspension. The settling column is 2 m tall and the initial concentration of the well-mixed sample is 650 mg/l. Results of the analysis are below: Time, min conc. remaining, mg/l What is the theoretical efficiency of the settling basin that receives this suspension if the loading rate is m/min? [5 points] Q7. Using the data from Q6, determine the theoretical efficiency of a settling basin with a surface area of 500 m 2 and m 3 /d? Given that v i = 0.04 x, where x is remaining fraction of suspended particles. [5 points] Q8. What is the basic difference between type-i and type-2 settling? Q9. What is the basic difference between settling of inert suspended particles and biological solids (i.e., biomass)? How would the settling pattern change if I have a sample with 100 mg/l inert suspended particles and 1

2 Q10. Suppose IIT Delhi water has suspended solids, organic matter, microorganisms, hardness, and dissolved CO 2, which are problematic constituents. Other dissolved constituents are below problem levels. Answer the following: (i) Draw a schematic diagram of a treatment plant that will render this water potable. Identify each unit and show points of chemical addition with their names. [5+5 = 10 points] (ii) Do you need coagulation unit process for the IIT Delhi water? If yes, which constituents do you want to remove using this process and why? [5+5 =10 points] Q11. Say IIT Delhi wastewater has 0.01 mm sand and 0.01 mm clay particles (total suspended solids=300 mg/l) and is passing through a tank of 0.5 m depth (water viscosity = Kg/ (m.sec); density = 1000 Kg/m 3 ). Which of these particles would settle first and why? [10 points] Q12. Draw a schematic of water treatment plant treating IIT Delhi canal water (suspended solids, organic matter, and fecal coliforms) to produce drinking water? Label different unit processes with appropriate sequence and provide brief reasons. [2+3=5 points] Q13. Calculate ultimate BOD for following water types with initial BOD=100 mg/l and compare these values? Water type Oxygen consumption rate (k) (1/day) Surface water 0.15 Weak municipal wastewater 0.35 Treated effluent 0.20 Q14. Calculate carboneous and nitrogenous oxygen demand in mg/l if the sample has 300 mg/l of acetic acid as well as glycine (CH 2 NH 2 COOH)? Q12. Balance the following equation and calculate number of moles of oxygen required for completely oxidizing 100 mg/l of benzene, 100 mg/l glucose solution? (Equation: C 6 H 6 +O 2 CO 2 + H 2 O ) ( points) 2

3 HW2-Coagulation Q1. Why solution ph is an important parameter in the coagulation-flocculation process and need to be maintained? Explain using alum water chemistry. [5 points] Q2. Suppose IIT Delhi water has suspended solids, organic matter, microorganisms, hardness, and dissolved CO 2, which are problematic constituents. Other dissolved constituents are below problem levels. Answer the following: (i) Draw a schematic diagram of a treatment plant that will render this water potable. Identify each unit and show points of chemical addition with their names. [5+5 = 10 points] (ii) Do you need coagulation unit process for the IIT Delhi water? If yes, which constituents do you want to remove using this process and why? [5+5 =10 points] Q3. Identify electrolytes useful for coagulating (i) negatively charged particles and (ii) charge neutral particles? Discuss role of metal type and valency. Q4. Alum reacts with alkalinity as per following equation. For removing 90% of 300 mg/l suspended solids, say 50 mg/l alum (for ph 8 solution) is required. If solution also has bicarbonate alkalinity ( 250 mg/l as CaCO 3 ), how much alum would be required for getting 90% removal of suspended solids? How much solid waste (in terms of aluminum hydroxide precipitate and settled suspended solids) would be produced? 3

4 HW: Ion Exchange, Softening, Adsorption, Disinfection-Part1 Q1. Draw schematic of a point-of-use system (POU) consisting of activated carbon-based adsorber, UV radiation unit and filtration unit (in correct order) for producing potable water. Why? [3 points] Q2. For a single-stage softening, following water (see characteristics below) is softening using the Limesoda ash process (ph =9). No magnesium removal is required here. [5+10 =15 points] Species Concentrations (milli-equivalents/l) Carbon dioxide 1.0 Ca Mg Na HCO SO Answer the following: (i) Write balanced equations for removing CO 2, calcium bicarbonate and calcium sulfate using the Lime-soda process. (ii) Calculate amount of CaO and Na 2 CO 3 required? (unit: milli-equivalents/l)? For a flow of 10,000 m 3 /day, calculate the daily chemical requirement and the mass of solids produced? Assume that the lime used is 90% pure and the soda ash is 80% pure. Q3. The AXX well water has bicarbonate hardness equal to 100 mg/l as CaCO 3. Calculate amounts of lime and soda ash required during the lime-soda ash process (Given: Daily flow rate: 10,000 m 3 /day). [10 points] Q4. Look at the following water quality data. Say one needs to treat this water using ion-exchange process (capacity: 90 Kg hardness/m 3 material at 0.4m/minute flow rate). For this material, regeneration is conducted using 10% NaCl solution which requires 100 Kg sodium chloride/m 3 resin. Answer the following: [7+3=10 points] (i) Calculate mass of resin required and chemical required for regeneration process? (ii) Can I use this ion-exchanger for removing anions from water? Provide reasons. Species Free CO 2 Ca 2+ Mg 2+ Na + - HCO 3 2- SO 4 Conc. (mequiv/l) Q5. Calculate the amount of lime-soda ash required for treating 1 MLD of water? How much solid waste is produced from this process? [5+5 =10 points] Free carbon dioxide 3 mg/l Mg mg/l Ca mg/l Na + 16 mg/l Alkalinity (HCO - 3 ) 122 mg/l Purity in lime 85% Purity in Soda 100% Q6. Calculate daily lime-soda ash requirement during softening of water (100 mg/l carbonate hardness (as CaCO 3 ) and 100 mg/l MgSO 4 ) (Given: Daily water production: 1000 m 3 /day; lime is 90% pure and soda ash is 80% pure). Q7. Draw a typical breakthrough curve for ion-exchanger unit and show different parameters on this curve. Discuss its importance in deciding regeneration frequency of an ion-exchanger unit. [2+2+6= 10 points] 4

5 Q8. Excess sodium intake can results in high blood pressure and inner ear problems for some people. The regulatory body recommends maximum allowable concentration to be 20 mg/l sodium in drinking water. Now sodium ions are used in ion exchange process. For reducing hardness from 6 to 1.5 meq/l in water, how much sodium ion is produced (mg/l) and if it poses any health risk based on given maximum concentration guideline. 5

6 Adsorption Q1. Groundwater contaminated with TCE is treated with powdered activated carbon by sorption. The adsorption of TCE on PAC follows a Freundlich isotherm model as per following equation Q eq = 129(C eq ) 0.73 where Qeq is mass of TCE adsorbed on PAC (mg/g PAC); C eq is concentration of dissolved TCE in water (mg/l). (i) Identify adsorbate and adsorbent in this scenarion. (ii) If TCE concentration in water is 1 mg/l (C 0 ), what mass of PAC must be used per volume of water (mg PAC/L water) to reduce TCE concentration to the allowed maximum contaminant level of mg/l? (iii) If the amount of PAC applied is only half of what is calculated in part (i), what is the equilibrium aqueous concentration of TCE? Q2. Differentiate between kinetic and equilibrium studies. Q3. What is the difference between Langmuir and Freundlich adsorption isotherm mechanisms? What do these models indicate about adsorption capacities of adsorbent? Can these models provide information on homogeneity or heterogeneity of adsorption sites? Q4. Untreated drinking water has 0.02 mg/l of geosmin, which gives earthy odor. How much removal can be achieved by adding 10 mg/l powdered activated carbon (PAC) in water? Assume geosmin adsorption on PAC is defined by Freundlich adsorption Q eq = K f (C eq ) 1/n where Qeq is mass of geosmin adsorbed on PAC (µg) per mg of PAC; C eq is concentration of dissolved geosmin in water (µg/l), and K f = 0.5 (µg/mg)(l/ µg) (1/n) and (1/n)=1.08. Q5. How does drawing a breakthrough curve help in deciding time for changing of activated carbon packed in activated carbon-based absorber? Q6. Draw a breakthrough curve and label all important information one can obtain from this curve. Can this curve be used in setting time for changing adsorbent in absorber? Q7. Fit Langmuir and Freundlich adsorption isotherm model for adsorption data of Sand_110 (initial arsenic concentration = 1mg/L). Calculate values of Qmax (mg/g) and (b) (L/mg) and coefficient of determination (R2) for this model fitting and comment on model effective of explaining this data? Media Ceq Qt Ceq/Qeq Ceq g/l ug/l mg/g g/l mg/l

7 Q8. Compare arsenic adsorption isotherm patterns for Fig (a) high concentration range in distilled ionized water and for Fig (b) low concentration range in distilled ionized water? Q9. Comment on effect of adsorbent concentration and contact time on removal of adsorbate. 7

8 Q10. Comment on effect of contact time on adsorption isotherm. Also, for a given contact time of 72 h, describe adsorption isotherm. What does Freundlich model fitting tell about adsorption of arsenate on Windsor soil? Q11. Fit kinetic models (from table given below) to following data for adsorption of arsenate on Sand_110 (initial arsenic concentration = 1mg/L; X=10g/L). Calculate model parameters and coefficient of determination (R 2 ) for determining the best model? time (h) %reduction in arsenate concentration % % 2 80% 20 85% % 8

9 Disinfection Q1. Calculate the quantity of chlorine consumed/day for 3-log removal of rotaviruses from secondary effluent (ph7), where free chlorine residual is 2 mg/l, the first-order decay rate of chlorine is 0.2/h and flow rate is 1000m 3 /day. Given that Ct value is 243 for ph7.0. [15 points] Q2. Name three disinfection kinetics models generally used to model disinfection process. Can CT concept be applied to all three kinetic models? Why or why not? [10 points] Q3. For wastewater consists of ammonia, organic matter and microorganisms), use following information: Chlorine dosage (mg/l) Chlorine residual (mg/l) (i) Discuss the significance of different regions. [8 points] (ii) Calculate chlorine dose to achieve 0.75 mg/l free available chlorine? [4 points] Q4. Look at the following relationship between concentration of free residual chlorine and contact time required for 99% kill (Watson s Law: C 0.86 t p = λ (constant) for different pathogens). Pathogen type Adenovirus 3 E.coli Coxsackievirus A2 λ (constant) For given chlorine dose, how long would you like to disinfect to achieve maximum removal of all pathogens? Explain the result. [6+4=10 points] Q5. Comment on decay of adenovirus using low pressure (LP) and medium pressure (MP) UV rays. Calculate dosages of LP rays for getting at least 99.9% removal? [5+5=10 points] +++extra questions 9

10 Q1. Define Ct concept; ionic layer compression; alum coagulation versus ferric chloride coagulation. [ =10 points] 10