AIRSprinklerFEED PIPETRICKLING FILTER0.9-3.5mDiameter30 t! "0 m 0.#-0.$ mmOrganic present in wastewater is degraded by a population of microbes attached to the flter media. 1. Organics will be adsorbed onto the biological slimy layer (0.1-0.2 mm thick) 2. the organics gets degraded by aerobic microorganism s.. !hickness of slime layer increases as the organisms grow in number". O#ygen will be consumed before it can penetrate full depth$ anaerobic situation will grow$ and anaerobes grow.%. &urther growth of slimy layer shall limit the penetration of food. &ood will get e#hausted before it can go to the anaerobes'. (naerobes then die and no longer can cling to the media surface. !he whole slimy layer breaks out and comes out with the treated wastewater. !his is called )loughing. )loughing is a function of organic and hydraulic loading of the flterATTAC%ED GR&'T% PR&CESS*astewater trickles through a bed of highly permeable porous media of plastic or rock containing microbes and treated water gets collected at the bottom. +t resembles like a flter bed but operationally it is much di,erent.-ecirculation of wastewater is not for the same reason as (cti.ated sludge process. +t does not help to increase the e/ciency of the system.-ecirculation is done only to ensure a low-strength in0uent and constant hydraulic loading rate to maintain a thin layer of bioflm on the media and a.oiding the periodic sloughing of the microbes. -ecirculation helps to maintain a minimum wetting ratio so that they do not run dry at certain points inside the flter at any particular point of time.!ypes of )ystems1artial 2O3 remo.alInterme(iate- an( %i)*-Rate Filter+-ecirculation of the flter e4uent or fnal e4uent permits higher organic loadings$ pro.ides higher dosing rates on the flter to impro.e the li5uid distribution and better control of the slime layer thickness$ pro.ides more o#ygen in the in0uent wastewater 0ow$ and returns .iable organisms. -ecirculation also helps to pre.ent ponding in the flter and to reduce the nuisance from odors and 0ies.L!,-Rate Filter+ 3osing tanks are small$ usually with only a 2-min detention time based on twice the a.erage design 0ow$ so that intermittent dosing is minimi6ed. 7.en so$ at small plants$ low night-time 0ows may result in intermittent dosing and recirculation may be necessary to keep the packing moist. +f the inter.al between dosing is longer than 1 or 2 h$ the e/ciency of the process deteriorates because the character of the biological slime is altered by a lack of moisture. Di+tri-.ti!n S/+tem+ 8learance of 1%0 to 22% mm should be allowed between the bottom of the distributor arm and the top of the bed. !he clearance permits the wastewater streams from the no66les to spread out and co.er the bed uniformly. !he ma#imum diameter is '0 m. 9ence the designer should consider this fact while f#ing the si6e of the trickling flter units.:o66les are spaced une.enly so that greater 0ow per unit of length is achie.ed near the periphery of the flter than at the center. 9eadloss through the distributor is in the range of 0.' to 1.% m. !he underdrain system for a rock flter usually has precast blocks of .itrifed clay or fberglass grating laid on a reinforced-concrete sub0oor 0n(er(rain+!he 0oor and underdrains must ha.e su/cient strength to support the packing$ slime growth$ and the wastewater andshould slope to a central or peripheral drainage channel at a 1 to % percent grade.!he e4uent channels are si6ed to produce a minimum .elocity of 0.' m;s at the a.erage daily 0owrate. 7 *+!9-78+-87 11rimary 8larifer)econdary 8larifer)econdary 8larifer!*O-)!(>7 *+!9-78+-87 2?r?$ )i?$ )Pr!2e++ De+i)n F!r Tri2klin) FilterF!r Tri2klin) Filter+ ,it* R!2k 3e(ia 4NRC E5.ati!n6 Sin)le Sta)e7@ e/ciency of 2O3 remo.al in the flter*@ 2O3 loading to the &ilter$ kg;dayA@ .olume of the flter media$ m

&@ -ecirculation &actor-@ -ecirculation ratio F!r Tri2klin) Filter+ ,it* R!2k 3e(ia 4NRC E5.ati!n6 T,! Sta)e721@ e/ciency of 2O3 remo.al inthe frst flter of two stage process*21@ 2O3 loading to the &ilter1 of 2 stage process$ kg;dayA21@ .olume of the flter media$ m

&@ -ecirculation &actor-21@ -ecirculation ratio in flter 1 of 2 stage fltration VFWE44 . 0 1100+=2) 10 / 1 (1R RF++=QQr=21 21212144 . 0 1100F VWE+=22 22222122144 . 01100F VWEE+=F!r Tri2klin) Filter 3a(e !7 Pla+ti2 3e(ia7ckenfelderBs 75uation>ermainBs 75uation)@ 2O3% of the settled e4uent$ mg;=)0@ !otal 2O3% of wastewater in0uent to the flter$ mg;=3 @ 3epth of the flter. C?. @ ?;((@ surface area of the flter)a @ )pecifc surface area of the flter$ @ surface area; .olume.D@ obser.ed reaction rate constant$ m;dk20$3@ treatability constant for a flter with a specifc depth 3n@ e#perimental constant$ usually 0.%#@ 0.% for .ertical and rock media flters@0. for cross-0ow plastic media flters!emperature correction for k is same as that of 2O3$ but E@ 1.0% (not 1.0"F)] ) ( exp[nvmaiQ D KSSS =] ) ( exp[, 20nv DiQ D kSS =xD DDDk k=211 , 20 2 , 203esign a trickling flter using rock media to treat wastewater with 0owrate ".% million liters per day. 2O3 of the raw sewage 2%0 mg;=.2O3 remo.ed in the primary clarifer is 2%G. !he treated wastewater needs to discharged to a surface water body where the regulatory limit for 2O3% is 0 mg;=. !he 0uctuation in the wastewater 0owrate can be controlled by keeping a recirculation ratio of 1.".+n0uent 2O3% @ F%G of 2%0 mg;= @1HF.% mg;=74uent 2O3%@ 0 mg;=7/ciency$ 7 @*@ 2O3 loading to the &ilter$ kg;day@".%I10'I1HF.%;10'

@H".F% kg;day(ssume a depth of 1.% m% 84 100 *5 . 18730 5 . 187=VFWE44 . 0 1100+=2) 10 / 4 . 1 1 (4 . 1 1++= F846 . 1 =846 . 1 *75 . 84344 . 0 110084V+=3m 96 . 2438 = Vm 5 . 455 . 196 . 2438 4 4= = = HVDia+t is proposed to use a two stage plant instead of the single stage plant in the pre.ious e#ample. !he total .olume of flter media remains the same and gets e5ually di.ided$ (i.e each flter is to contain half of the flter media as earlier).