How To Design A Trickling Filter
Lesson 24:
Trickling Filter Calculations
Objective
In this lesson we will learn the following calculations:
- Hydraulic Loading Charge per unit
- Organic Loading Rate
- BOD and SS Removal
- Recirculation Ratio
Lecture
Trickling Filters
Trickling filters are used to remove organic matter from wastewater. This type of treatment process utilizes microorganisms attached to a medium to remove organic matter from wastewater. This type of system is common to a number of technologies, such as rotating biological contactors (RBCs), which nosotros will cover in the side by side lesson. These systems are known as attached-growth processes. In dissimilarity, systems in which microorganisms are sustained in a liquid are known as suspended-growth processes.
Trickling filters enable organic material in the wastewater to be adsorbed past a population of microorganisms , including aerobic, anaerobic, and facultative leaner as well as fungi, algae and protozoa, that is attached to the medium as a biological moving-picture show or slime layer (approximately 0.1 to 0.2 mm thick). As the wastewater passes over this slime, the slime adsorbs the organic (nutrient) thing. This organic matter is used for nutrient past the microbes. At the same time, air moving through the open spaces in the filter transfers oxygen to the wastewater. This oxygen is and so transferred to the slime to continue the outer layer aerobic. As the microbes use the food and oxygen, they produce more organisms, carbon dioxide, sulfates, nitrates, and other stable byproducts
As the layer thickens through microbial growth, oxygen cannot penetrate the medium confront, and anaerobic organisms develop. As the biological moving-picture show continues to grow, the microorganisms about the surface lose their ability to cling to the medium, and a portion of the slime layer falls off the filter. This process is known as sloughing. The sloughed solids are picked up past the underdrain system and transported to a clarifier for removal from the wastewater.
Allow's watch a video that shows how trickling filters and RBCs can exist used to care for wastewater. This video explains how to keep the trickling filters operating properly.
Trickling Filter Process Calculations
Several calculations are useful in the operation of trickling filters: these include hydraulic loading, organic loading, and biochemical oxygen demand (BOD) and suspended solids (SS) removal. Each type of trickling filter is designed to operate with specific loading levels. These levels profoundly depend on the filter nomenclature. To operate the filter properly, filter loading must be within the specified levels. The three master loading parameters for the trickling filter are hydraulic loading, organic loading, and recirculation ratio.
Hydraulic Loading Charge per unit
Calculating the hydraulic loading rate is of import to account for both the main effluent as well as the recirculated trickling filter effluent. These quantities are combined earlier being applied to the filter surface. The hydraulic loading rate is calculated based on filter surface area.
Trickling Filter System Overview
Cross-Section of a Trickling Filter
The normal hydraulic loading rate ranges for standard rate and high rate trickling filters are:
- Standard charge per unit: 25 - 100 gpd/fttwo
- High rate: 100 - 1000 gpd/ft2
If the hydraulic loading rate for a detail trickling filter is likewise low, septic atmospheric condition will brainstorm to develop.
The hydraulic loading rate for a trickling filter can be determined with the following equation:
Instance:
A trickling filter that is 60 ft in diameter is operated with a master effluent of 0.785 MGD and a recirculated effluent flow charge per unit of 0.824 MGD. Calculate the hydraulic loading charge per unit on the filter, in gpd/ft2.
Since the main effluent and the recirculated flow are both applied together across the surface of the filter you need to take both into account for the total menses:
0.785 MGD + 0.824 MGD = ane.609 MGD
The question wants the loading rate in gpd/ft2, so we need to convert the MGD period to gpd:
1.609 MGD ten (ane,000,000 gal/ane MG) = 1,609,000 gpd
Next, decide the area of the filter:
Circular surface expanse = 0.785 x Diametertwo
Circular expanse = 0.785 10 (60 ft)2
Circular expanse = 2826 ft2
Now that nosotros have all the components of the equation, permit's determine the hydraulic loading charge per unit on the filter:
Sometimes the plant wants the results recorded in cubic meters instead of gallons. Allow's have a await at 1 of these types of bug. You will want to look at your common conversions listed at the lesser of the formula sail for the grade to run across the equivalencies to utilize. The formula from the formula sheet that needs to be used is:
Case:
A trickling filter that is sixty ft in diameter treats a main effluent flow of 625,000 gpd. If the recirculated catamenia to the clarifier is 0.3 MGD, what is the hydraulic loading on the trickling filter, in m3/twenty-four hour period/m2?
For this i, it's worked the same manner, you will simply demand to do a few extra conversions (which is why it's handy to have your formula canvas at all times). Let's become step by step:
We already know the circular expanse of a sixty ft bore trickling filter. We calculated information technology in the previous example. So the area of the circular trickling filter is 2826 ftii. According to the question, we need this in square meters, not square anxiety, and then let'south do the correct conversion:
We know that ane ft = 0.305 thou, then that ways that 1 ftii = (.305 m)2 or 0.093 kii
That's i conversion. Now let's work on getting the flow from gallons to cubic meters.
First, determine the total flow in gpd, remember to include the recirculated flow (and convert it to gpd from MGD in the process):
625,000 gpd + 300,000 gpd = 925,000 gpd
According to the formula sheet, i cubic meter equals 264 gallons, so allow's convert gpd to m3/twenty-four hour period:
At present that we have all the measurements in the correct units, permit's "plug and play":
Organic Loading Rate
Trickling filters are sometimes classified by the organic loading rate applied. The organic loading rate is expressed every bit the amount of BOD (food) practical to a certain book of media. In other words, the organic loading is defined equally the pounds of BOD practical per day per 1000 cubic feet of media. It is basically a measure of the corporeality of food beingness applied to the filter slime. To summate the organic loading on the trickling filter, two things must be known:
- the pounds of BOD (or COD) beingness practical to the filter media per day
- the volume of the filter media in units of 1000 cubic feet.
The BOD and COD contribution of the recirculated menstruation is non included in the organic loading calculation. The organic loading rate for a trickling filter tin can be determined by using the following equation:
It is VERY important to realize that the unit of measurement is 1000 ftthree. That means that if the volume is 30,000 ftthree, that means y'all would enter it into the equation equally xxx (1000 ftthree). "30" volition exist the simply number used in your adding because "1000 ft3" is the unit only.
Let's lookout man a video showing how to solve for organic loading of a trickling filter.
Example:
A trickling filter receives a flow of 2.24 MGD. The primary effluent BOD concentration is 95 mg/Fifty. Calculate the organic loading to this plant, in lb/day/grand ftthree, if the trickling filter has a bore of 145 ft and a media depth of vi ft.
There are some pre-processing calculations that demand to be done outset, like converting BOD mg/Fifty to lb/day to determine the organic load, so let'due south start with that, using the "pounds" formula:
Concentration, mg/L x Menses, MGD 10 eight.34 lb/gal
95 mg/L 10 2.24 MGD 10 eight.34 lb/gal = 1774.75 lb/day
Side by side, determine the volume of the trickling filter:
Surface area = 0.785 10 Diameterii
Surface area = 0.785 x (145 ft)2
Surface area = 16,504.63 ft2
Volume = Area 10 Depth
Book = 16,504.63 ft2 x 6 ft
Volume = 99,027.75 ft3
Remember, the volume needs to take the unit "yard ft3". To determine what to enter for the volume amount simply carve up the book determined above by thousand, giving y'all 99.03( yard ftiii), which is what you will enter into the organic loading calculation. Go along in listen that you volition just apply "99.03" in the calculation. The "1000 ftthree" is a Unit of measurement Only.
Sometimes the institute may want the results recorded in kg BOD per solar day per cubic meter. Allow's take a await at ane of these types of problems. Y'all will want to wait at your common conversions listed at the bottom of the formula canvas for the class to encounter the equivalencies to use. The formula from the formula sheet that needs to be used is:
Example:
A trickling filter receives a catamenia of ane.85 MGD. The main effluent BOD concentration is 89 mg/Fifty. Calculate the organic loading to this establish, in kg/24-hour interval/1000iii, if the trickling filter has a bore of 145 ft and a media depth of 4 ft.
Notice the diameter is aforementioned in this example, and then that'southward 1 less measurement to summate. We can become straight to volume:
Surface expanse = sixteen,504.63 ft2
Volume = Area x Depth
Volume = 16,504.63 ft2 ten iv ft
Volume = 66,018.52 ft3
We need the volume in cubic meters instead of cubic anxiety, so look at the formula sheet conversion factors to see that 1 ft = 0.305 m. Allow'southward catechumen the volume from cubic anxiety to cubic meters using this conversion factor:
Notice that nosotros used the conversion factor of "1 ft = 0.305 one thousand" iii times. We did this because we needed to cancel the cubic anxiety from the equation. That means yous needed to utilise it 3 times because ft 10 ft x ft = ftiii. That is how the answer becomes cubic meters: one thousand ten grand ten g = m3. The answer would be determined by 66,018.52 x 0.305 thousand x 0.305 m ten 0.305 k = 1873.12 kiii.
That's i conversion. Now let'southward determine the BOD load using the pounds formula offset:
Concentration, mg/L x Flow, MGD x viii.34 lb/gal
89 mg/L 10 1.85 MGD x 8.34 lb/gal = 1373.18 lb/day
The question wants the load given in kg/twenty-four hours instead of lb/24-hour interval. Look on the formula sheet at the conversion factors and detect that 1 lb = 0.454 kg. You volition use this conversion gene:
Now you have all the units in the proper format, and then all you need to do is plug the values into the formula:
BOD and Suspended Solids Removal
In order to determine the amount of BOD and suspended solids removed past a trickling filter, you must know the mg/50 of BOD and suspended solids removed also as the constitute catamenia rate.
Case:
A trickling filter has an influent flow of 2.8 MGD with a BOD content of 195 mg/L. If the trickling filter effluent has a BOD content of 75 mg/L, how many pounds of BOD are removed daily?
First make up one's mind the mg/L of BOD removed daily. The influent has a measurement of 195 mg/L and the effluent has a measurement of 75 mg/50:
BOD removed, mg/L = 195 mg/L - 75 mg/Fifty = 120 mg/L
Now all you need to do is use the "pounds" formula to determine how many pounds of BOD are removed daily:
Concentration, mg/L x Menstruum, MGD 10 eight.34 lb/gal
120 mg/Fifty 10 2.8 MGD x eight.34 lb/gal = 2802.24 lb/day
Recirculation Ratio
Recirculation in trickling filters involves the return of filter effluent back to the caput of the trickling filter. Information technology can level flow variations and help in solving operational problems, such as ponding, filter flies, and odors. The operator must check the rate of recirculation to ensure that it is inside pattern specifications. Rates in a higher place design specifications point hydraulic overloading, while rates under the specifications indicate hydraulic underloading. The trickling filter recirculation ratio is the ratio of the recirculated filter flow to the master effluent flow. This ratio may range from 0.5:ane (0.5) to v:1 (5); however, the ratio is often constitute to be one:1 or ii:i.
The recirculation ratio for a trickling filter can be determined past using the equation:
Case:
A trickling filter receives a menses of 1.92 MGD. If the trickling filter effluent is recirculated at the rate of two.25 MGD, what is the recirculation ratio?
Since both flows are in the aforementioned units, it'south but a matter of plugging in the values:
Instance:
A trickling filter receives a flow of 0.855 MGD. If the trickling filter effluent is recirculated at the charge per unit of 925,000 gpd, what is the recirculation ratio?
Since the flows are not in the same unit, we will demand to catechumen one or the other. Let's convert the recirculated menstruation rate of 925,000 gpd to MGD:
(925,000 gal/mean solar day) x (1 MG/1,000,000 gal) = 0.925 MGD
At present you can plug the values into the formula:
Summary
Trickling filters enable organic material in the wastewater to exist adsorbed past a population of microorganisms , including aerobic, anaerobic, and facultative bacteria likewise as fungi, algae and protozoa, that is attached to the medium as a biological film or slime layer (approximately 0.1 to 0.two mm thick). As the wastewater passes over this slime, the slime adsorbs the organic (food) thing. This organic thing is used for nutrient by the microbes. At the same time, air moving through the open spaces in the filter transfers oxygen to the wastewater. This oxygen is then transferred to the slime to keep the outer layer aerobic. Equally the microbes utilize the nutrient and oxygen, they produce more organisms, carbon dioxide, sulfates, nitrates, and other stable byproducts
Equally the layer thickens through microbial growth, oxygen cannot penetrate the medium face, and anaerobic organisms develop. As the biological flick continues to abound, the microorganisms well-nigh the surface lose their ability to cling to the medium, and a portion of the slime layer falls off the filter. This procedure is known equally sloughing. The sloughed solids are picked up by the underdrain system and transported to a clarifier for removal from the wastewater. Each type of trickling filter is designed to operate with specific loading levels. These levels greatly depend on the filter nomenclature. To operate the filter properly, filter loading must be within the specified levels. The three main loading parameters for the trickling filter are hydraulic loading, organic loading, and recirculation ratio. Calculating the hydraulic loading charge per unit is important to account for both the principal effluent also every bit the recirculated trickling filter effluent. These quantities are combined before being applied to the filter surface. The hydraulic loading rate is calculated based on filter surface area. The normal hydraulic loading rate ranges for standard rate and high rate trickling filters are: Standard rate: 25 - 100 gpd/ftii and High charge per unit: 100 - 1000 gpd/fttwo.
Trickling filters are sometimes classified by the organic loading rate applied. The organic loading rate is expressed every bit the corporeality of BOD (nutrient) applied to a sure volume of media. In other words, the organic loading is defined as the pounds of BOD practical per twenty-four hours per 1000 cubic anxiety of media. Information technology is basically a measure of the amount of food being applied to the filter slime. To calculate the organic loading on the trickling filter, two things must be known: the pounds of BOD (or COD) being applied to the filter media per mean solar day and the book of the filter media in units of 1000 cubic feet.
Recirculation in trickling filters involves the return of filter effluent dorsum to the head of the trickling filter. It can level flow variations and help in solving operational problems, such as ponding, filter flies, and odors. The operator must bank check the rate of recirculation to ensure that it is within blueprint specifications. Rates above design specifications indicate hydraulic overloading, while rates nether the specifications indicate hydraulic underloading. The trickling filter recirculation ratio is the ratio of the recirculated filter catamenia to the primary effluent flow. This ratio is often establish to be ane:ane or two:1.
Assignment
Complete the math worksheet for this lesson and render to instructor via email, fax or mail.
How To Design A Trickling Filter,
Source: https://water.mecc.edu/courses/ENV148/lesson24b.htm
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