Trickling Filter

A trickling filter (TF) is a non-submerged fixed bed reactor consisting of highly permeable packing media in which aerobic condition is maintained via diffusion, forced aeration, natural convection or splashing.

From: Journal of Water Process Engineering , 2016

Wastewater Handling and Reuse

J.R. Buchanan , in Comprehensive H2o Quality and Purification, 2014

3.13.5.iii.2.ane.ii Trickling filters

Trickling filters are like to the RMFs; however, trickling filters have far greater void space and porosity inside the media, which allows for a higher hydraulic loading. The higher loading charge per unit and an increased void volume promote a heavier biological growth on the media. This growth will periodically 'slough' off and travel with the effluent to a clarifier where it settles out. In larger municipal systems, clarifiers serving the trickling filters incorporate a sludge return to ship a portion of the settled biomass back to the trickling filter and with the remainder going to the terminal settling tank. Trickling filters are yet widely used in modest- to medium-sized communities throughout the globe to provide secondary treatment earlier surface water discharge. They have an reward over the suspended growth aerobic handling systems in terms of low maintenance requirements and resistance to upset from variations in wastewater volume and strength. The master disadvantage of trickling filters is that treatment is not as complete – there is a lower limit on the mass of oxygen demand that tin be removed and the open media does not provide effluent clarification. Trickling filters are bachelor in prepackaged units that can be easily placed at a decentralized wastewater treatment site.

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Wastewater Treatment Processes—Techniques, Technologies, Challenges Faced, and Alternative Solutions

Bahram Rezai , Ebrahim Allahkarami , in Soft Computing Techniques in Solid Waste and Wastewater Management, 2021

4.two.1 Trickling filters

Trickling filter is a bed with high specific surface surface area textile, such as shredded PVC bottles, crushed rocks, gravel, or special preformed plastic filter media to class a biofilm. Organisms abound in the biofilm over the surface of the media. They adsorb the organic load in the wastewater and stabilize it by aerobic metabolism to produce water and carbon dioxide, thereby removing oxygen-demanding substances. The wastewater is sprayed over the surface of media. Equally wastewater trickles down and puts in contact with filmy layers of microorganisms, it is further purified. They remove virtually 85% of organic matters from wastewater (2000). A schematic cross section of a trickling filter is shown in Fig. two.seven. Equally mentioned earlier, the removal of organic matters occurs past the use of the bacterial procedure. So, trickling filters are also chosen biofilters, or biological filters. Table 2.seven presents the advantages and disadvantages of trickling filters in wastewater treatment.

Figure ii.vii. Schematic cross section of a trickling filter.

 From Tilley, Lüthi, Morel, Zurbrügg, & Schertenleib, 2008

Table 2.seven. Advantages and disadvantages of trickling filters in wastewater treatment.

Advantages Disadvantages
Simple and reliable Need to additional treatment
Low power requirement Vector and odor bug
Demand to moderate level of technical expertise for managing the system Need to regular operator attention

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Environmental and Related Biotechnologies

D.Five. Vayenas , in Comprehensive Biotechnology (Third Edition), 2011

six.25.1.2 Attached Growth Bioreactors

Fixed film reactors accept high surface areas available for microbial growth. As well, these systems present a college potential for use than suspended growth biomass reactors since the former tin retain a higher concentration of biomass with higher metabolic activity when operated with continuous processes. Biofilm reactors take been constructed using different packing materials such equally granular activated carbon, polyurethane, kaolin, polystyrene, woods fries, soil sand, gravel, ceramic saddles, polyvinyl chloride, and polyethylene. eight Trickling filters and RBCs are the main types of attached growth bioreactors. In contempo years, hybrid systems such as moving bed biological reactors (MBBRs) and membrane bioreactors (MBRs) combine advantages of attached growth and activated sludge systems.

Biological filters specifically designed for water treatment take been adult since they combine biological pollutant oxidation, precipitate filtration, and biomass sloughing. Three chief filter types have been used for biological water treatment: pressurized, gravity, and trickling filters. 9

Pressurized filters are particularly designed to operate at high rates and use back up material of minor mean diameter, thus increasing the specific expanse available for biological oxidation. As a result, this blazon of filter exhibits high pollutant removal rates. On the other paw, the small size particles pb to small pores, which may become hands clogged due to bacterial growth and iron and manganese precipitate filtration. Consequently, very frequent backwashing is necessary. Finally, an external air supply is required, leading to increased operating cost.

Gravity filters are designed for plants where larger quantities of drinking h2o have to be treated. The flow rates are quite low compared to those in pressurized systems. The support cloth used is usually fine sand, which enables very good filtration and likewise needs frequent backwashing. The use of cascade aeration keeps the operating price low only the upper-case letter toll of these systems is relatively loftier.

Trickling filters are simple constructions and do not require an external air supply. To secure acceptable air circulation, the back up material is larger than that for pressurized systems. Filtration also takes place simultaneously with oxidation but a separate settling tank may be needed to ensure complete removal of fe and manganese precipitates. The menses rates in trickling filters lie between the high rates of pressurized systems and the low rates of gravity plants. Trickling filters provide both low uppercase and operating costs.

A short description of trickling filters is presented with some applications of fastened growth systems for potable water and wastewater.

6.25.1.2.1 Trickling Filters

Trickling filters provide a support medium for biofilm growth, thus allowing the possibility of maintaining bacteria at high hydraulic loadings. Wastewater treatment using biofilms grown on support media was the start continuous catamenia bioprocess employed by germ-free engineers most a century ago. Every bit the wastewater flows over the biofilm layer (0.1–0.2  mm), organic carbon, ammonia, and dissolved oxygen diffuse into the biofilm where they are metabolized by the leaner (Fig. ane). The essential processes are mass transport and bioconversion. As the microorganisms grow, the thickness of the biofilm layer increases and the diffused oxygen is consumed before it tin penetrate the total depth of the biofilm layer. Thus, an anaerobic environment is established near the surface of the media. Equally the biofilm layer increases in thickness, the adsorbed organic affair is metabolized earlier it can reach the microorganisms near the media face. Every bit a consequence of having no external organic source available for cell carbon, the microorganisms virtually the media face enter into an endogenous phase of growth and lose their power to cling to the media surface. The liquid and then washes the biofilm off the media, and a new biofilm layer starts to abound.

Effigy one. Schematic cross-section of a biofilm in a trickling filter.

In modern trickling filters, the hydraulic loading charge per unit is adjusted to maintain a biofilm layer of uniform thickness. An adequate air menstruation is besides of key importance for the successful performance of a trickling filter. The principal gene responsible for air flow is natural aeration, the driving forcefulness for airflow being the temperature deviation between air inside the filter and the surrounding air. two

The trickling filter is a nonsubmerged fixed film biological reactor using rock or plastic back up media. The depth of the back up media ranges from 0.nine to 2.5   m and averages 1.eight   m. Filter beds are commonly circular and the liquid wastewater is distributed over the elevation of the bed by a rotary distributor. Well-nigh, all new trickling filters are constructed with plastic media. Trickling filters that use plastic media have been built in round, square, and other shapes with depths varying from 4 to 12   grand. In add-on to the support media, other components of the trickling filter include a wastewater dosing or application organization, an underdrain, and a structure to comprise the media. Modern trickling filters that utilize plastic back up media tin can attain better performances but at a substantially higher cost than filters based on rock. ten

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Wastewater Treatment and Reuse

C.S. Butler , J.P. Boltz , in Comprehensive Water Quality and Purification, 2014

3.6.3.two.4 Trickling filter

Trickling filters have been in employ for more than than 50 years. Early filters distributed wastewater over a packed bed of either soil or rocks to oxidize carbon in the wastewater. Carbon oxidation occurs via a biofilm that is supported on the filter media, using oxygen in the form of air delivered from a ventilation space below the filter. Biomass, produced as part of the process, is released from the biofilm and transported with the effluent wastewater. Subsequent solids separation footstep is oftentimes needed to achieve effluent goals using a trickling filter. When solid separation is introduced to the treatment train, trickling filters are suitable for carbon oxidation, combined carbon oxidation and nitrification, or tertiary nitrification. Carbon oxidation in a trickling filter can accomplish effluents between 15 and 30  mg   fifty−i BOD and TSS. Ammonia concentrations less than three   mg NHiv +  N   50−1 and BOD less than 10   mg   l−1 have been observed with combined carbon oxidation and nitrification. Even lower ammonia concentrations tin can be reached, 0.5–3   mg NHiv +  N   50−1, when nitrification is the sole treatment objective (Metcalf and Eddy, 2003).

Instead of single treatment stream mixed within the reactor, wastewater influent is distributed across the height surface of the filter. Although stock-still distribution systems have been used in the past, the electric current convention uses rotary distribution. Another important consideration in the design of trickling filters is the selection of filter media. The media should have a high specific surface area, low cost, and high durability. Rocks are still used in many operating tricking filters, but newer systems are using plastic media. Plastic media offers more surface area, larger void space, and lower unit weight. The plastic media can be random, that is, drove of small carriers or structured, that is corrugated plastic sheets. The structured media can permit vertical flow or lx° crossflow (Harrison and Daigger, 1987). The selected media must have enough surface expanse to support the biomass that can accommodate the BOD loading for the reactor. The porosity should be large enough to let sufficient ventilation throughout the filter and discourage bottleneck.

Some other important component of trickling filter is the underdrain arrangement. The underdrain system provides a space below the trickling filter for the collection of treated wastewater and as well allows for ventilation, to supply air to the biofilm. Ventilation tin can be achieved naturally every bit a result of the temperature gradient between ambience air and air in the trickling filter. This method is ineffective when the temperature slope is not substantial enough to drive a suitable dose of oxygen to the filter. In this case, a mechanical ventilation technique is needed, such every bit a fan or forced air (Grady et al., 1999).

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Biological Filtration

Miklas Scholz , in Wetlands for Water Pollution Control (Second Edition), 2016

thirteen.3 Bones Ecology

Trickling filters are well known for their ecological multifariousness of life forms participating in the wastewater'south stabilization. These include prokaryotic and eukaryotic organisms likewise equally higher life forms such as rotifers, nematodes, annelid worms, snails, and many insect larvae.

The bacteria are agile in the uptake and deposition of soluble organic matter. Nitrifying leaner convert ammonia to nitrate. In a low-charge per unit trickling filter, there is a high nitrifier population and the effluent is well nitrified. In a high-charge per unit filter, in that location is more "sloughing" of the biomass due to college fluid shear, and so little or no nitrification takes place.

Fungi, which are also to exist institute in trickling filters, are active in the biofilm and are actively involved in waste material stabilization. These organisms tend to dominate at lower pH values, which are unremarkably associated with industrial waste matter handling. Algae are one time over again agile in the biofilm and produce oxygen during daylight hours. This helps to proceed the uppermost portion of the biofilm aerobic. Both the fungi and algae are important components of the biofilm in trickling filters.

Protozoa are unicellular prokaryotic organisms that feed on the bacteria within the biofilm. The continuous removal of bacteria by protozoa helps to maintain an active bacterial population and thus maintains a high decomposition charge per unit.

Rotifers are also present in the biofilm. One time again, these organisms predate on leaner, algae, and fungi. Most rotifers are taken to be indicative of a high caste of treatment efficiency and, when present, serve to reduce the effluent SS.

The major macroinvertebrates present in trickling filters are insect larvae (eastward.g., chironomids). These feed on the biofilm and help to control its thickness, thus avoiding clogging of the pores in the filter past microbial extrapolymeric substances. The larvae develop into adult insects (filter flies) in 2–iii weeks. These tin exist a nuisance to institute operators and local residents, peculiarly in summertime. Numbers as high as 3   ×   105/thousand2 have been reported. Insects are controlled by increasing the frequency of wetting of the filter surface (larvae only emerge on dry filters), by the use of insecticides, or by biological control using Bacillus thuringiensis var. israelensis. This pathogen contains a toxin that, when ingested past the insect, causes its death.

Other important controls on the ecology of the trickling filter include cold temperature and directly application of toxins. These ho-hum down or cease predator activity and thus increase the likelihood of clogging. This in turn may adversely affect the functioning of the humus tank, peculiarly in spring when predator activity usually resumes subsequently wintertime. Backlog biofilm from the jump sloughing is likely to overload the humus tank and causes high SS to exist discharged in the effluent. Nitrification is also reduced in winter every bit a effect of the depression average temperature.

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Energy from Wastewater Handling

S.Z. Ahammad , T.R. Sreekrishnan , in Bioremediation and Bioeconomy, 2016

11 Trickling Filter

Trickling filter is a widely used aerobic biological treatment system. Also chosen a biofilter, it is a downflow packed bed type of reactor. It consists of a fixed bed made up of unlike inert materials. Biofilm grows on the surface of the inert bed. Dissimilar cheap and porous materials such as rocks, lava, coke, gravel, slag, pumice stone, polyurethane foam, peat moss, ceramic, or plastic media can be used for making the porous bed. Wastewater enters from the summit of the fixed bed making apply of a rotating arm distributor or static nozzles fed with a variable head feed source. Microbial biofilm grown on the surface of the inert support helps to degrade the waste matter. Aerobic condition is accomplished by agile or passive aeration past using either a blower or fan (forced aeration) or natural convection of air due to the temperature departure between the water and ambience air. Depression strength wastewaters (COD  <   1000   mg   l−   1) such as sewage (domestic wastewater) can hands be treated using the organization and desired effluent quality can be accomplished by maintaining a typical HRT of 1 day. Clogging and channeling are two very common problems associated with its operation. Periodic cleaning of the bed (biomass removal) is required to get desired performance. A typical trickling filter used for treating sewage uses 0.22   kWh energy to remove ane   kg-COD (Evans et al., 2004).

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Wastewater Treatment Technologies

Iyyanki Five. Muralikrishna , Valli Manickam , in Environmental Direction, 2017

12.half dozen.3.2 Types of Filters

Trickling filters may be categorized equally depression rate, high rate, and super rate, primarily based on hydraulic and organic loading rates. Although at that place is no well-demarcated practice, some of import distinguishing design criteria and features for the iii types of filters are presented in Tabular array 12.4.

Table 12.iv. Blueprint Features for Trickling Filters

Due south.No. Pattern Feature Depression Charge per unit Filter High Rate Filter Super Rate or Roughing Filter
1 Hydraulic loading, kiii/m2·24-hour interval one.4 10–40 (including recirculation) 40–200 (including recirculation)
2 Organic loading, kg BOD5/1000three·day 0.08–0.32 0.32–one.0 (excluding recirculation) 0.8–half dozen.0 (excluding recirculation)
three Depth, m i.eight–3.0 0.9–two.five four.five–12
four Recirculation ratio 0 0.5–3.0 (domestic wastewater) up to eight or more than for strong industrial wastes one–4
5 Filter media Rock, gravel, slag etc. Rock, slag, synthetic materials Plastic media

The hydraulic loading rate is the full flow including recirculation applied on unit of measurement surface area of the filter in a mean solar day, while the organic loading rate is the 5-twenty-four hours 20°C BOD, excluding the BOD of the recirculant, applied per unit volume in a day. Much college organic loadings than indicated here accept been used in roughing filters. Recirculation is not mostly adopted in low rate filters and media depths for depression rate filters range from 1.8 to iii.0   thou. They require larger media volumes than loftier rate filters. However, they are piece of cake to operate and give consistently skillful quality of effluent and are preferred when found capacities are small, as in the case for institutions. In dissimilarity to the depression charge per unit filters, in high and super rate filters a part of the settled or filter effluent is recycled through the filter. Recirculation has the advantage of bringing the organic affair in the waste material in contact with the biological slime more than once, thus increasing the efficiency of the filters. It enables higher hydraulic loading and thereby reduces filter clogging and aids uniform distribution of organic load over the filter surface. It besides helps to dampen the variations in the forcefulness and the menstruum of sewage applied on the filter. The ratio of the sewage flow is known as the recirculation ratio. Recirculation ratios unremarkably range from 0.five to three, and values exceeding iii are considered to be uneconomical in the case of domestic sewage, but ratios of eight and above accept been used with industrial wastes and super-high rate filters, which may be unmarried stage or 2 stage. Media depths of 0.9–ii.5   m have been used for high rate filters with an optimum range of i.5–2.0   m for the first stage and 1–2   m for the 2nd-stage filters. Unmarried-stage units consist of a primary setting tank, the filter, secondary settling tank, and facilities for recirculation of the effluent.

Two-stage filters consist of two filters in series with a master settling tank, an intermediate settling tank, which may be omitted in certain cases, and a terminal settling tank. Recirculation facilities are provided for each stage. The effluent from the starting time-stage filter is applied on the second-phase filter either after settlement or without settlement. An intermediate clarifier is used for settling the first-stage effluent before it is applied to the second-phase filter, and the recirculation is only through the settling tanks. The intermediate settling is omitted, and their apportionment flows are settled. In the series-parallel arrangement, part of the settled raw sewage is applied straight to the second-stage filter, increasing the efficiency of that phase. Two-stage filtration will provide a higher degree of treatment than the single stage for the same total volume of media. 2-stage units are used for strong sewage when the effluent BOD has to be less than xxx   mg/L.

A well-operated low rate trickling filter in combination with secondary sedimentation tank may remove 75–90% BOD and produce highly nitrified effluent. It is suitable for handling of depression to medium strength domestic wastewaters. The high charge per unit trickling filter, single stage, and ii stage are recommended for medium to relatively high-strength domestic and industrial wastewaters. The BOD removal efficiency is effectually 75–xc%, merely the effluent is only partially nitrified. The super charge per unit or roughing filters find awarding for loftier-strength wastewaters. They have besides been used as roughing filters to reduce the BOD of high-strength wastewaters for further treatment. The effluent from these filters may be partially nitrified merely when low organic loadings are employed.

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Olive Processing Waste matter Management

In Waste Management Series, 2006

Trickling Filter

The trickling filter is a container filled completely with highly permeable filling material to which microorganisms are fastened. The wastewater is distributed by means of a rotary sprinkler on pinnacle of the material and then trickles through information technology. The filling material (e.m. stones, lava slag, or plastic bodies) serves equally a carrier. Biological growth and activity depend on a constant supply of dissolved oxygen. The effluent from the filter carries with it living and expressionless organisms and waste products of the biological reactions. Effluent sludge flocs are indicators of the efficient operation of the trickling filter and are separated from the water in settling banks. If the wastewater is non free of solid matter, information technology should be prescreened to reduce the risk of clogging ( Cortinovis D., 1975).

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Practical Ecology

Daniel A. Vallero PhD , in Ecology Biotechnology (Second Edition), 2016

Trickling Filter

The trickling filter is a time-tested, proven bioreactor system that has been widely used to treat municipal wastes and hazardous wastes. Every bit mentioned, the classic design of a trickling-filter arrangement illustrated in Figure 7.20 includes packed media (often rocks, but in that location are numerous materials onto which microbes tin attach) through which liquids contacting the organic matter move by gravity after being sprayed onto the surface. The large amount of area provides ample contact betwixt microbial populations and the liquid waste. That is, the microbes' biofilm comes into contact with an organic contaminant/food source. The concomitant microbial growth and metabolism event in degradation of the organic compounds, i.e., COtwo  +   H2O   +   microorganisms (+energy?).

Media bed depths can vary, but traditional trickling-filter beds take been between about one and 3   yard. The media size ranges from about 25 to 60   mm in diameter (e.g., circular gravel). All the same, diverse shapes and materials (e.g., polyvinyl chloride) take been used successfully. Waste matter is applied in a circular rotating manner to forbid pooling or uneven deposits. The interstices and openings betwixt the media allow for air penetration throughout the arrangement. In add-on, air tin exist supplied by blowers from the bottom of the reactor, migrating upward through the bed. This makes near of the trickling filter aerobic. The treated waste that moves downwardly through the bed later on enters a quiescent tank in which the microorganisms that are sloughed off of the rocks are settled, nerveless, and ultimately disposed of. Even though much of the surface surface area is aerobic, trickling filters are actually considered to exist mixed treatment systems because aerobic bacteria abound in the upper, higher oxygen layers of the media, whereas anaerobes grow in the lower, more than reduced regions lower in the system, specially if air is not pumped upward.

For especially strong and recalcitrant compounds, and when the organic loading increases with time, a multiple-filter system will be needed. For example, the first filter in a series may accept a high loading charge per unit of organic matter, followed by subsequent filters in which their media come up into contact with the partially treated waste material liquids that broke through the offset filter. Indeed, the process can be reversed so that the overloaded filter can recover from the loading (i.e., the second filter becomes the first filter, so that the original, first filter volition receive less organic loading).

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