Trickling Filter | Environmental Engineering - Civil Engineering (CE) PDF Download

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 | Environmental Engineering - Civil Engineering (CE)

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 | Environmental Engineering - Civil Engineering (CE) (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 | Environmental Engineering - Civil Engineering (CE) (4.4.2)

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

   Trickling Filter | Environmental Engineering - Civil Engineering (CE)  (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 | Environmental Engineering - Civil Engineering (CE)              (4.3.4) 

Trickling Filter | Environmental Engineering - Civil Engineering (CE) (4.3.5) 

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

Trickling Filter | Environmental Engineering - Civil Engineering (CE) (4.3.6) 

Trickling Filter | Environmental Engineering - Civil Engineering (CE)  (4.3.7) 

 

[D] Eckenfelder equation (Plastic media) 

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

Trickling Filter | Environmental Engineering - Civil Engineering (CE) (4.3.8) 

Trickling Filter | Environmental Engineering - Civil Engineering (CE)


Trickling Filter | Environmental Engineering - Civil Engineering (CE)

Trickling Filter | Environmental Engineering - Civil Engineering (CE)
Trickling Filter | Environmental Engineering - Civil Engineering (CE)
Trickling Filter | Environmental Engineering - Civil Engineering (CE)
Trickling Filter | Environmental Engineering - Civil Engineering (CE)

From Eckenfelder equation, 

Trickling Filter | Environmental Engineering - Civil Engineering (CE)

The document Trickling Filter | Environmental Engineering - Civil Engineering (CE) is a part of the Civil Engineering (CE) Course Environmental Engineering.
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FAQs on Trickling Filter - Environmental Engineering - Civil Engineering (CE)

1. What is a trickling filter?
Ans. A trickling filter is a biological wastewater treatment system that uses a bed of rock or plastic media to support the growth of microorganisms. The wastewater is sprayed or trickled over the media, allowing the microorganisms to break down organic matter and remove pollutants.
2. How does a trickling filter work?
Ans. In a trickling filter, wastewater is distributed over the media bed using rotating arms or spray nozzles. As the wastewater trickles down through the media, a biofilm of microorganisms forms on the surfaces. These microorganisms digest the organic matter present in the wastewater, converting it into carbon dioxide, water, and biomass.
3. What are the advantages of using a trickling filter?
Ans. Some advantages of using a trickling filter for wastewater treatment include its simplicity, low energy requirements, and ability to handle variations in flow and load. Trickling filters also have a smaller footprint compared to other treatment systems and can be easily retrofitted into existing facilities.
4. Are trickling filters effective in treating wastewater?
Ans. Yes, trickling filters are effective in treating wastewater. They are particularly suitable for removing organic pollutants and reducing biochemical oxygen demand (BOD). However, they may not be as effective in removing nutrients such as nitrogen and phosphorus, which may require additional treatment processes.
5. How do you maintain a trickling filter?
Ans. Regular maintenance is essential for the proper functioning of a trickling filter. This includes monitoring the media condition, ensuring proper distribution of wastewater, and periodically cleaning the media to remove any accumulated solids. It is also important to monitor the performance of the trickling filter through regular sampling and testing to ensure its efficiency in treating wastewater.
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