Trickling Filter Computer Science Engineering (CSE) Notes | EduRev

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Computer Science Engineering (CSE) : Trickling Filter Computer Science Engineering (CSE) Notes | EduRev

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TRICKLING FILTER 

  • Trickling filter is an attached-growth type of process in which microorganisms attached to a medium are used for removing organic matter from wastewater. that utilizes 
  • This type of system is common to a number of technologies such as rotating biological contactors (RBCs) and packed bed reactors (biotowers). These reactors are also called as non-submerged fixed film biological reactors. 


COMPONENTS OF TRICKLING FILTER 

Trickling Filter Computer Science Engineering (CSE) Notes | EduRev

Figure 4.4.1 Trickling filter 

[A] Packing

  • Trickling filter uses packing medium composed of crushed stone, slag, rock or plastic over which wastewater is distributed continuously (Figure 4.4.1). 
  • The ideal medium should have the following properties: high specific surface area, high void space, light weight, biological inertness, chemical resistance, mechanical durability, and low cost. 
     The important characteristics of medium includes-
     a) Porosity: It is a measure of the void space available for passage of the wastewater and air and for ventilation of product gases.
     b) Specific surface area: It refers to the amount of surface area of the media that is available for biofilms growth.
     c) Size of the medium ranges from 50-100 mm having specific surface area in the range of 50-65 m2/m3 with porosities of 40-50 %.

[B] Wastewater dosing 

  • Influent wastewater is normally applied from the top of the trickling filter. · Under a hydraulic head of about 1.0 m, jet action through the nozzles is sufficient to power the rotor.
  • As the flow is intermittent, there is enough air circulation through the pores between dosing. 
  • The distributer arm distributes the wastewater continuously over the medium, which trickles down through the bed.

[C] Under-drain 

  • It is used in trickling filters to support the filter medium, collect the treated effluent and the sloughed biological solids, and circulate the air through the filter.  
  • The liquid flow in under-drains and collection channels should not be more than half full for adequate air flows. 


PROCESS DESCRIPTION OF TRICKLING FILTER 

  • A rotary or stationary distribution mechanism distributes wastewater from the top of the filter percolating it through the interstices of the film-covered medium . 
  • As the wastewater moves through the filter, the organic matter is adsorbed onto the film and degraded by a mixed population of aerobic microorganisms. 
  • The oxygen required for organic degradation is supplied by air circulating through the filter induced by natural draft or ventilation.  
  • As the biological film continues to grow, the microorganisms near 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 by the under-drain system and transported to a clarifier for removal from the wastewater.
  • Microorganisms used
    • The microorganisms used are mainly facultative bacteria that decompose the organic material in the wastewater along with aerobic and anaerobic bacteria. 
    • It includes Achromobacter, Flavobacterium, Psudomonas, and alcaligenes. 
    • In the lower reaches of the filter, the nitrifying bacteria are usually present. 


FACTORS AFFECTING THE OPERATION OF TRICKLING FILTER  

[A] Organic loading

  • A high organic loading rate results in a rapid growth of biomass.
  • Excessive growth may result in plugging of pores and subsequent flooding of portions of the medium. 

[B] Hydraulic flow rates 

  • Increasing the hydraulic loading rate increases sloughing and helps to keep the bed open. Range of hydraulic and organic loading rates for trickling filters are shown in table 1. 

 

[C] Relative temperature of wastewater and ambient air

  • Cool water absorbs heat from air, and the cooled air falls towards toward the bottom of the filter in a concurrent fashion with the water. · Warm water heats the air, causing it to rise through the underdrain and up through the medium. 
  • At temperature differentials of less than about 3 to 40C, relatively little air movement results, and stagnant conditions prevent good ventilation. 
  • Extreme cold may result in icing and destruction of the biofilms. 


 DESIGN EQUATIONS FOR TRICKLING FILTER 

[A] Tentative method of ten states of USA 

The equation is given as follows: 

Trickling Filter Computer Science Engineering (CSE) Notes | EduRev (4.4.1) 
 where, Q is the flow rate, R is the recycle flow rate and E is the efficiency. 

a) Loading rate 

(Raws ettleddomesticsludge)<102kg BOD/(dm3 )

b) R/Q should be such that 

BOD entering filter (including recirculat ion) ≤ 3 x BOD expected in effluents

 

[B] Velz equation 

The following equation is used for a single-stage system and in the first stage of a two-stage system: 

Trickling Filter Computer Science Engineering (CSE) Notes | EduRev (4.4.2)

The following equation is used for the second stage of a two-stage system: 

   Trickling Filter Computer Science Engineering (CSE) Notes | EduRev  (4.4.3) 

 Where, Se is the effluent BOD from the filter (mg/l), Si is the influent BOD (mg/l), r is the ratio of recirculated flow to wastewater flow, D is the filter depth (m), A is the filter plan area (m2), Q is the wastewater flow (m3/min), T is the wastewater temperature (oC), k and n are empirical coefficients (for municipal wastewaters, k = 0.02 and n = 0.5) and subscript i (i = 1, 2) repressent the stage number. 

 

[C] NRC equations

The following equation is used for a single-stage system and the first stage of a two-stage system: 

Trickling Filter Computer Science Engineering (CSE) Notes | EduRev              (4.3.4) 

Trickling Filter Computer Science Engineering (CSE) Notes | EduRev (4.3.5) 

The following equation is used for the second stage of a two-stage system: 

Trickling Filter Computer Science Engineering (CSE) Notes | EduRev (4.3.6) 

Trickling Filter Computer Science Engineering (CSE) Notes | EduRev  (4.3.7) 

 

[D] Eckenfelder equation (Plastic media) 

The Eckenfelder equation used for plastic media is as follows: ..

Trickling Filter Computer Science Engineering (CSE) Notes | EduRev (4.3.8) 

Trickling Filter Computer Science Engineering (CSE) Notes | EduRev


Trickling Filter Computer Science Engineering (CSE) Notes | EduRev

Trickling Filter Computer Science Engineering (CSE) Notes | EduRev
Trickling Filter Computer Science Engineering (CSE) Notes | EduRev
Trickling Filter Computer Science Engineering (CSE) Notes | EduRev
Trickling Filter Computer Science Engineering (CSE) Notes | EduRev

From Eckenfelder equation, 

Trickling Filter Computer Science Engineering (CSE) Notes | EduRev

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