Environmental Engineering CIVL 241 Fundamentals

Environmental Engineering What is your definition of Environmental Engineering? “ Take care of garbage “ “ keep the air and water clean so we can use it “ “ take care of pollution “

Environmental Engineering Environmental Engineers protect the health by minimizing the release and impact of pollutants into the air, land, and water. They work each day to design control and treatment systems that reduce or limit the negative effects that human have on the many ecosystems of the world.

Environmental Engineering Dimensions and Units.

Fundamental Dimension : quantitative description for basic characteristics, such as force (F), mass (M), length (L), and time (T). Derived Dimensions : calculated by an arethmatic manipulation of one or more fundamental dimensions. Velocity has dimensions of length per time (L/T) and volume is L3. Dimensions are descriptive but not numerical. They cannot describe how much, they simply describe what. Length described in units as a meter or yard.

Engineering Dimensions and Units Density : is mass divided by unit volume Where : ρ : density M: mass V: volume In SI unit density is kg/m3 while in American system is Ib/ft3 Water density is 1000 kg/m3 or 62.4 Ib/ft3

Engineering Dimensions and Units Concentration: is the mass of material A in a unit volume consisting of material A and some other material B. The concentration of A in a mixture of A and B is: Where: CA: concentration of A MA: mass of material A VA : volume of material A VB: volume of material B

In many environmental aqueous systems, its appropriate to assume that 1mg/l equal to ppm, provided that the fluid is primarily water so the density of the solution is 1g/ml

Engineering Dimensions and Units Flow Rate: can be either mass or volumetric flow rate. Mass flow rate unit is kg/s or Ib/s, and volumetric flow rate is in m3/s or ft3/s. So mass (M) of material passing a point in a flow line during a unit time is related to the volume (V) of that material. Mass =Density x Volume Volumetric flow rate can convert to mass flow rate : QM = QV x ρ (1)

Engineering Dimensions and Units The relationship between mass flow of some component A, concentration of A, and the total volume flow (A+B) is QMA = CA x QV(A+B) (2) The difference between Equ.1 and 2 is that at 1 applicable to only one material in a flow stream while at 2 relates to two different materials in a flow stream.

Retention Time: is the time required to fill the container, and the average time the fluid spends in a reactor or control volume. Retention time also called detention time, or residence time. if the volume of container such as large tank is V (L3), and the flow rate into the tanks is Q (L3/t). Then the residence time is: The average retention time can be increase by reducing the flow rate or increasing the volume.

Example 1 plastic beads with a volume of 0.04 m3 and a mass of 0.48 kg are placed into a container, and 100 liters of water poured into the container. What is the concentration of plastic beads, in mg/L? Solution

Example 2 A wastewater sludge has a solids concentration of 10,000 ppm. Express this in percent solids (mass basis), assuming that the density of the solids is 1 kg/cm3. solution

Example 3 A wastewater treatment plant discharge a flow of 1.5 m3/s (water plus solids) at a solids concentration of 20 mg/L, how much solids is the plant discharge each day? Solution

Quiz A water treatment plant has 6 settling tanks that operate in parallel. And each tank has a volume of 40 m3. if the flow to the plant is 35 m3/s. what is the retention time in each of the settling tank? If the entire flow goes first through one tank then the second and so on, what would be the retention time in each tank?

Home work1 consider a rectangular wastewater treatment cell having a length of 30 m, width of 7 m, and depth of 7 m. if the flow into the cell is 1400 L/min. calculate the residence time of the treatment cell.

a circular water treatment separator with diameter of 60 cm and depth of 1.2 m. the water depth is 26 cm. calculate the detention time for the following flow rates. Q (m3/s) 1x10-5 2 X 10-5 3 X 10-5 4 X 10-5 t(day) 23.5 47 7.8 94

Environmental Engineering Material Balances

Outline material balance around a "black box" unit operation is introduced first. In all cases the flow is assumed to be at steady state, that is, not changing with time. Initially, these black boxes have nothing going on inside them that affects the materials flow. Then it is presumed that material quantities are produced or consumed within the box.

3.1 MATERIAL BALANCES WITH A SINGLE MATERIAL Figure 3.1&3.2 shows a black box into which some material is flowing. All flows into the box are called influents and represented by the letter X. If no processes are going on inside the box that will either make more of the material or destroy some of it and if the flow is assumed not to vary with time (that is, to be at steady, state). [ mass per unit time] = [ mass per unit time] IN OUT [X0]= [ X1]+ [ X2 ] generally convenient to use the volume balance for liquids and the mass balance for solids.

3.1.1 Splitting Single-Material Flow Streams Previous figure illustrates that under steady state conditions and no material being produced or destroyed then the material balance : [ X0]= [ X1]+ [ X2 ] The material X can, of course, be separated into more than two fractions, so the material balance can be: where there are n exit streams, or effluents.

Splitting Single-Material Flow Streams EX.3.1 A city generates 102 tons/day of refuse, all of which goes to a transfer station. At the transfer station the refuse is split into four flow streams headed for three incinerators and one landfill. If the capacity of the incinerators is 20, 50, and 22 tons/day, how much refuse must go to the landfill? Solution The input stream is the solid waste delivered to the transfer station. Four output stream , three for incinerators and one for landfills.

Splitting Single-Material Flow Streams

3.1.2 Combining Single-Material Flow Streams A black box can also receive numerous influents and discharge one effluent. as shown in Figure 3.4. If the influents are labeled X1, X2, . . . , X„„ the material balance would yield steady state condition is remaining for combining single material flow streams .

Combining Single-Material Flow Streams EX.2 A trunk sewer, shown in Figure 3.5, has a flow capacity of 4.0 m3/s. If the flow to the sewer is exceeded, it will not be able to transmit all the sewage through the pipe, and backups will occur. Currently, three neighborhoods contribute to the sewer, and their maximum (peak) flows are 1.0, 0.5, and 2.7 m3/s. A builder wants to construct a development that will contribute a maximum flow of 0.7 m3/s to the trunk sewer. Would this cause the sewer to exceed its capacity?

Combining Single-Material Flow Streams Solution

Ex 3) A stream flowing at 10 m3/s has a tributary feeding into it with a flow of 5 m3/s. the stream's concentration of chloride upstream of the junction is 20 mg/L, and the tributary chloride concentration is 40 mg/L. find the downstream chloride concentration. **Tributary : a river or stream that flows into a larger river or a lake Solution Outline black box for problem under study. So the black box is the stream and concentration plus flow rates feeding into the black box from stream and tributary. while the effluent is chloride concentration and stream discharges

Ex 4) 18,925 m3/d of wastewater, with a concentration of 10 mg/L of a conservative pollutant is released into a stream having an upstream flow of 37,850 m3/d and pollutant concentration of 3 mg/L. what is the concentration in ppm just downstream? ** conservative : pollutant which doesn’t growth up or consumed inside the stream meaning no reaction coming out due to such pollutant. Solution Upstream and downstream are black box boundary parameters for current problem. So the influent is coming from upstream and effluent out off the black box at downstream.

Ex 5) A river with a 400 ppm of salts ( conservative substance) and an upstream flow of 25 m3/s receives an agriculture discharge of 5 m3/s carrying 200 mg/l of salts. The salts quickly become uniformly distributed in the river. A municipality just down -stream withdraws water and mixes it with enough pure water (no salt) from another source to deliever water having no more than 500 ppm salts to its customers. What would be the mixture ratio of pure water to river water?

Ex 6) A lagoon with volume of 1200 m3 has been receiving a steady flow of conservative waste at a rate of 100 m3/day for a long time to assume the steady state conditions apply. The waste entering the lagoon has a concentration of 10 mg/l. assuming completely mixed condition. a) What would be the concentration of pollutant in the effluent leaving the lagoon? b) If the input waste concentration suddenly increased to 100 mg/l, what would be the concentration in the effluent?

Home work 2 a) A stream flowing at 471 m3 /hr and 20 mg/L suspended solids, receives wastewater from three separate sources : What are the flow and suspended solids concentration downstream at sampling point ? Source Quantity m3/hr Solid conc. Mg/L A 314 200 B 942 50 C 157

Home work 2 b) A manhole receives inflows from two sewer laterals and has one outflow as seen in the diagram below. The flow rates and suspended solids (ss) concentrations in each of the flow streams are given on the same diagram. Determine the unknown flow and suspended solids concentration

Environmental Engineering Energy Balance

Energy Balance Energy balance must be performed when dealing with thermal pollution from coal fired power plants and nuclear reactors. Potential climate changes resulting from the discharge of greenhouse gasses and combustion of fossil fuel ( coal, natural gas and gasoline) to produce energy.

Energy Balance Thermodynamics : is the study of energy changes resulting from physical and chemical processes. Changes in energy associated with biological and chemical processes are very important in environmental engineering.

Energy Balance Enrgy : the capacity for doing work. Many forms of energy such as, chemical, electrical, kinetic, potential, and thermal(heat). Heat and work are related forms of energy. Thermal energy can be converted into work and work can be converted into heat energy. Various units are used for measuring energy such as: BTU, Cal, J,

Energy Balance British Thermal Unit (BTU) is energy required to raise the temperature of one pound of water one degree Fahrenheit oF. The Calorie: is the amount of energy required to raise the temperature of one gram of water by one degree Celsius. Celsius = 1.8 Fahrenheit 1 BTU= 252 calories. Joule : the amount of work done by a force of one newton to raise an object one meter.

Energy Balance Work : is transferring energy to an object by applying force and causing motion. (N.m) Power: the rate of doing work. So has unit of energy per unit of time. Watt (W)= 1 J/s and = 3.412 BTU/h Therefore, Chemical energy is a form of internal Energy(U), Kinetic Energy (KE) can produce electricity through windmills or water flowing through turbines. Potential Energy(PE) results from change in elevation a

Energy Balance Total Energy (E) is the sum of internal , kinetic, and potential energies E= U+KE+PE So the first law of thermodynamic states that the energy cant be created or destroyed (excluding nuclear reactors). Only the form of energy will change. So similar to material and mass balance. [energy accumulated]= [energy input]-[energy output] +[energy generated].

Energy Balance Energy generated is usually comprised two terms: [energy generated]= [energy produced]-[energy consumed] During energy conversion some loss of useful energy will occurs, normally through waste heat. Second law of thermodynamics states that there will always be some waste heat released during energy conversions.

Energy Balance Heat is a form of internal energy expressed as the thermodynamic property enthalpy (H), which is function of temperature, pressure, and volume. H=U+PV Where: U= the internal energy of the substance P= pressure of the system V= volume of the system

Energy Balance When a process occurs without a change in volume, the change in internal energy can be calculated as follow: ΔU= mcv ΔT Where: m: mass of the substance Cv: specific heat or heat capacity of the substance at constant volume ΔT: Temperature change

Energy Balance For constant pressure systems, thermal or heat energy changes can be estimated by using the following equation: ΔH= mcp ΔT Where: ΔH: change in enthalpy or thermal (heat) energy m: mass of the substance Cp: specific heat or heat capacity of the substance at constant Pressure

Energy Balance For incompressible substances, such as solids and most liquids. Cv and cp are nearly the same and they replaced with c. therefore, ΔU= ΔH and this yield to: ΔU= mc ΔT Where: c: specific heat or heat capacity of the substance

Energy Balance For most environmental applications, we are concerned with the rate of energy change. [the rate of change in stored energy]= mc ΔT And m here account for the mass flow rate . At 15oC the specific heat of water is 4.18kJ/kg. oC, 1.0 kcal/kgoC or 1.0 BTU/ib. Of. The density of the water also equal to 1000 kg/m3 under the same Temp.

Energy Balance In any water plant the output Energy over the plant efficiency will equal to the input energy. Enrgy heat = EnergyIN – consumed Energy

Energy Balance EX1Calculate the minimum rate at which 15°C make-up water from a river must be pumped to evaporative cooling towers for a 1000 MW nuclear power plant. The efficiency of the plant is 32% and all of the waste heat is assumed to be dissipated through evaporative cooling with no direct heat lost to the atmosphere.

Energy Balance Ex2 : An industrial WWTP discharges approximately 9000 cubic meter per day of treated effluent to the river at an average Temperature of 27 o C. If the temperature and flow rate of the river upstream of the discharge are 10 o C and 2 cubic meter per second respectively. Determine the temperature in the river downstream of the industrial discharge.