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 H2o Process Engineering , 2016

Wastewater Treatment and Reuse

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

3.thirteen.v.3.2.1.2 Trickling filters

Trickling filters are like to the RMFs; even so, trickling filters have far greater void space and porosity inside the media, which allows for a college hydraulic loading. The college loading rate 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 render to ship a portion of the settled biomass back to the trickling filter and with the remainder going to the final settling tank. Trickling filters are yet widely used in small- to medium-sized communities throughout the earth to provide secondary treatment before surface water discharge. They have an reward over the suspended growth aerobic treatment systems in terms of low maintenance requirements and resistance to upset from variations in wastewater volume and strength. The principal disadvantage of trickling filters is that treatment is non as consummate – at that place is a lower limit on the mass of oxygen demand that can exist removed and the open up media does not provide effluent clarification. Trickling filters are available in prepackaged units that tin be easily placed at a decentralized wastewater handling site.

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

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

4.2.1 Trickling filters

Trickling filter is a bed with high specific surface area material, such as shredded PVC bottles, crushed rocks, gravel, or special preformed plastic filter media to grade a biofilm. Organisms abound in the biofilm over the surface of the media. They adsorb the organic load in the wastewater and stabilize information technology by aerobic metabolism to produce water and carbon dioxide, thereby removing oxygen-demanding substances. The wastewater is sprayed over the surface of media. Every bit wastewater trickles down and puts in contact with filmy layers of microorganisms, information technology is further purified. They remove almost 85% of organic matters from wastewater (2000). A schematic cross department of a trickling filter is shown in Fig. 2.seven. As mentioned earlier, the removal of organic matters occurs past the apply of the bacterial process. Then, trickling filters are too called biofilters, or biological filters. Table 2.7 presents the advantages and disadvantages of trickling filters in wastewater handling.

Figure 2.7. Schematic cross section of a trickling filter.

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

Table 2.7. Advantages and disadvantages of trickling filters in wastewater treatment.

Advantages Disadvantages
Simple and reliable Need to additional treatment
Low power requirement Vector and smell problems
Need to moderate level of technical expertise for managing the arrangement Need to regular operator attention

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Ecology and Related Biotechnologies

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

6.25.1.2 Attached Growth Bioreactors

Fixed film reactors have high surface areas available for microbial growth. As well, these systems present a higher potential for utilise than suspended growth biomass reactors since the old can retain a higher concentration of biomass with college metabolic activity when operated with continuous processes. Biofilm reactors accept been synthetic using different packing materials such as granular activated carbon, polyurethane, kaolin, polystyrene, wood chips, soil sand, gravel, ceramic saddles, polyvinyl chloride, and polyethylene. 8 Trickling filters and RBCs are the principal types of attached growth bioreactors. In recent years, hybrid systems such equally 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 have been developed since they combine biological pollutant oxidation, precipitate filtration, and biomass sloughing. 3 master filter types have been used for biological water treatment: pressurized, gravity, and trickling filters. nine

Pressurized filters are peculiarly designed to operate at high rates and use back up material of pocket-size mean diameter, thus increasing the specific surface area available for biological oxidation. As a result, this type of filter exhibits high pollutant removal rates. On the other manus, the small size particles lead to minor pores, which may get 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 water have to exist treated. The catamenia rates are quite low compared to those in pressurized systems. The support material used is usually fine sand, which enables very practiced filtration and also needs frequent backwashing. The apply of cascade aeration keeps the operating cost depression but the capital letter toll of these systems is relatively loftier.

Trickling filters are simple constructions and practice not require an external air supply. To secure adequate air circulation, the support 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 iron and manganese precipitates. The catamenia rates in trickling filters prevarication betwixt the high rates of pressurized systems and the low rates of gravity plants. Trickling filters provide both low capital and operating costs.

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

6.25.one.two.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 back up media was the commencement continuous flow bioprocess employed by germ-free engineers virtually a century ago. Equally 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 bacteria (Fig. i). The essential processes are mass transport and bioconversion. Equally the microorganisms grow, the thickness of the biofilm layer increases and the diffused oxygen is consumed before it can penetrate the full depth of the biofilm layer. Thus, an anaerobic surround is established near the surface of the media. Equally the biofilm layer increases in thickness, the adsorbed organic thing is metabolized before it tin achieve the microorganisms most the media confront. Every bit a result of having no external organic source available for cell carbon, the microorganisms near the media confront enter into an endogenous stage of growth and lose their ability to cling to the media surface. The liquid then washes the biofilm off the media, and a new biofilm layer starts to grow.

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

In modern trickling filters, the hydraulic loading rate is adjusted to maintain a biofilm layer of uniform thickness. An acceptable air menstruation is also of fundamental importance for the successful operation of a trickling filter. The principal factor responsible for air flow is natural aeration, the driving strength for airflow existence the temperature departure betwixt air inside the filter and the surrounding air. 2

The trickling filter is a nonsubmerged fixed film biological reactor using rock or plastic support media. The depth of the support media ranges from 0.9 to 2.5   grand and averages 1.eight   thou. Filter beds are usually circular and the liquid wastewater is distributed over the top of the bed by a rotary distributor. Virtually, all new trickling filters are constructed with plastic media. Trickling filters that employ plastic media have been built in round, square, and other shapes with depths varying from four to 12   m. In addition to the support media, other components of the trickling filter include a wastewater dosing or application organisation, an underdrain, and a construction to contain the media. Modern trickling filters that use plastic back up media tin can attain ameliorate performances only at a substantially higher cost than filters based on stone. 10

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Wastewater Treatment and Reuse

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

3.half dozen.3.2.4 Trickling filter

Trickling filters accept been in use for more than l 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 infinite below the filter. Biomass, produced as function of the process, is released from the biofilm and transported with the effluent wastewater. Subsequent solids separation step is oft needed to achieve effluent goals using a trickling filter. When solid separation is introduced to the treatment railroad train, trickling filters are suitable for carbon oxidation, combined carbon oxidation and nitrification, or tertiary nitrification. Carbon oxidation in a trickling filter can achieve effluents betwixt 15 and xxx  mg   l−1 BOD and TSS. Ammonia concentrations less than three   mg NH4 +  N   fifty−1 and BOD less than 10   mg   l−1 take been observed with combined carbon oxidation and nitrification. Fifty-fifty lower ammonia concentrations can be reached, 0.5–3   mg NH4 +  N   50−i, when nitrification is the sole treatment objective (Metcalf and Boil, 2003).

Instead of single treatment stream mixed within the reactor, wastewater influent is distributed beyond the top surface of the filter. Although fixed distribution systems have been used in the past, the 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 immovability. Rocks are withal 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 tin be random, that is, drove of small-scale carriers or structured, that is corrugated plastic sheets. The structured media tin can allow vertical flow or 60° crossflow (Harrison and Daigger, 1987). The selected media must have enough surface area to support the biomass that can arrange the BOD loading for the reactor. The porosity should be big enough to allow sufficient ventilation throughout the filter and discourage clogging.

Another important component of trickling filter is the underdrain system. The underdrain arrangement provides a infinite below the trickling filter for the collection of treated wastewater and also allows for ventilation, to supply air to the biofilm. Ventilation can be achieved naturally as a upshot of the temperature gradient betwixt ambient air and air in the trickling filter. This method is ineffective when the temperature gradient is not substantial enough to bulldoze 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 Command (Second Edition), 2016

13.3 Basic Ecology

Trickling filters are well known for their ecological variety of life forms participating in the wastewater'southward stabilization. These include prokaryotic and eukaryotic organisms also equally college 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 thing. Nitrifying bacteria convert ammonia to nitrate. In a low-rate trickling filter, there is a loftier nitrifier population and the effluent is well nitrified. In a loftier-charge per unit filter, there is more "sloughing" of the biomass due to higher fluid shear, and and so little or no nitrification takes identify.

Fungi, which are likewise to be institute in trickling filters, are active in the biofilm and are actively involved in waste product stabilization. These organisms tend to dominate at lower pH values, which are ordinarily associated with industrial waste material handling. Algae are once again agile in the biofilm and produce oxygen during daylight hours. This helps to keep 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 inside the biofilm. The continuous removal of bacteria by protozoa helps to maintain an agile bacterial population and thus maintains a high decomposition rate.

Rotifers are also present in the biofilm. Once over again, these organisms predate on bacteria, algae, and fungi. Most rotifers are taken to exist indicative of a high degree of treatment efficiency and, when nowadays, serve to reduce the effluent SS.

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

Other important controls on the ecology of the trickling filter include cold temperature and direct application of toxins. These boring down or stop predator action and thus increase the likelihood of clogging. This in turn may adversely bear upon the performance of the humus tank, specially in leap when predator activity unremarkably resumes after winter. Excess biofilm from the spring sloughing is likely to overload the humus tank and causes high SS to be discharged in the effluent. Nitrification is also reduced in winter as a effect of the low average temperature.

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Energy from Wastewater Treatment

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

xi Trickling Filter

Trickling filter is a widely used aerobic biological handling system. Also called a biofilter, it is a downflow packed bed type of reactor. It consists of a fixed bed made up of different inert materials. Biofilm grows on the surface of the inert bed. Dissimilar inexpensive and porous materials such as rocks, lava, coke, gravel, slag, pumice stone, polyurethane foam, peat moss, ceramic, or plastic media tin exist used for making the porous bed. Wastewater enters from the top of the fixed bed making employ of a rotating arm distributor or static nozzles fed with a variable head feed source. Microbial biofilm grown on the surface of the inert back up helps to dethrone the waste material. Aerobic condition is achieved by active or passive aeration by using either a blower or fan (forced aeration) or natural convection of air due to the temperature departure between the water and ambient air. Depression strength wastewaters (COD  <   1000   mg   l−   1) such as sewage (domestic wastewater) can easily be treated using the system and desired effluent quality can be achieved by maintaining a typical HRT of 1 24-hour interval. Bottleneck and channeling are ii very mutual 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 1   kg-COD (Evans et al., 2004).

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Wastewater Treatment Technologies

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

12.six.3.2 Types of Filters

Trickling filters may be categorized equally low rate, high charge per unit, and super charge per unit, primarily based on hydraulic and organic loading rates. Although there is no well-demarcated exercise, some important distinguishing pattern criteria and features for the three types of filters are presented in Tabular array 12.4.

Table 12.iv. Pattern Features for Trickling Filters

S.No. Design Feature Depression Rate Filter Loftier Charge per unit Filter Super Rate or Roughing Filter
1 Hydraulic loading, yard3/kii·day 1.4 10–twoscore (including recirculation) forty–200 (including recirculation)
ii Organic loading, kg BOD5/gthree·twenty-four hours 0.08–0.32 0.32–1.0 (excluding recirculation) 0.8–six.0 (excluding recirculation)
iii Depth, m 1.8–iii.0 0.9–2.5 four.five–12
4 Recirculation ratio 0 0.5–3.0 (domestic wastewater) up to eight or more for strong industrial wastes 1–four
5 Filter media Rock, gravel, slag etc. Stone, slag, synthetic materials Plastic media

The hydraulic loading charge per unit is the full flow including recirculation applied on unit of measurement expanse of the filter in a 24-hour interval, while the organic loading rate is the v-day 20°C BOD, excluding the BOD of the recirculant, applied per unit volume in a day. Much higher organic loadings than indicated here accept been used in roughing filters. Recirculation is not generally adopted in depression rate filters and media depths for low rate filters range from i.viii to three.0   1000. They crave larger media volumes than high charge per unit filters. However, they are easy to operate and give consistently good quality of effluent and are preferred when plant capacities are small-scale, as in the case for institutions. In contrast to the low rate 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 matter in the waste material in contact with the biological slime more than once, thus increasing the efficiency of the filters. Information technology enables college hydraulic loading and thereby reduces filter clogging and aids uniform distribution of organic load over the filter surface. It also helps to dampen the variations in the forcefulness and the flow of sewage applied on the filter. The ratio of the sewage menstruation is known as the recirculation ratio. Recirculation ratios unremarkably range from 0.five to three, and values exceeding 3 are considered to be uneconomical in the case of domestic sewage, but ratios of 8 and above take been used with industrial wastes and super-loftier charge per unit filters, which may be unmarried stage or 2 stage. Media depths of 0.ix–2.5   thousand take been used for high rate filters with an optimum range of ane.v–ii.0   k for the first stage and 1–2   m for the second-phase filters. Single-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 principal settling tank, an intermediate settling tank, which may be omitted in certain cases, and a concluding settling tank. Recirculation facilities are provided for each stage. The effluent from the beginning-stage filter is practical on the second-stage 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-stage 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 system, office of the settled raw sewage is applied directly to the 2nd-stage filter, increasing the efficiency of that stage. Two-stage filtration will provide a higher degree of treatment than the single stage for the same total book of media. Two-stage units are used for strong sewage when the effluent BOD has to be less than 30   mg/L.

A well-operated depression rate trickling filter in combination with secondary sedimentation tank may remove 75–90% BOD and produce highly nitrified effluent. Information technology is suitable for treatment of low to medium strength domestic wastewaters. The loftier rate trickling filter, unmarried stage, and 2 stage are recommended for medium to relatively loftier-force domestic and industrial wastewaters. The BOD removal efficiency is effectually 75–90%, just the effluent is only partially nitrified. The super rate or roughing filters detect application for high-strength wastewaters. They accept besides been used as roughing filters to reduce the BOD of high-strength wastewaters for farther handling. The effluent from these filters may be partially nitrified only when low organic loadings are employed.

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Olive Processing Waste Management

In Waste Direction Serial, 2006

Trickling Filter

The trickling filter is a container filled completely with highly permeable filling material to which microorganisms are attached. The wastewater is distributed by means of a rotary sprinkler on top of the material and then trickles through information technology. The filling material (eastward.g. stones, lava slag, or plastic bodies) serves every bit a carrier. Biological growth and activity depend on a constant supply of dissolved oxygen. The effluent from the filter carries with information technology living and dead organisms and waste products of the biological reactions. Effluent sludge flocs are indicators of the efficient functioning of the trickling filter and are separated from the water in settling banks. If the wastewater is not free of solid matter, it should exist prescreened to reduce the run a risk of bottleneck ( Cortinovis D., 1975).

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Applied Ecology

Daniel A. Vallero PhD , in Ecology Biotechnology (2d Edition), 2016

Trickling Filter

The trickling filter is a time-tested, proven bioreactor organization that has been widely used to care for municipal wastes and hazardous wastes. Equally mentioned, the archetype design of a trickling-filter system illustrated in Figure vii.20 includes packed media (often rocks, just there are numerous materials onto which microbes can adhere) through which liquids contacting the organic matter motion by gravity after being sprayed onto the surface. The big amount of surface expanse provides ample contact betwixt microbial populations and the liquid waste product. That is, the microbes' biofilm comes into contact with an organic contaminant/food source. The concomitant microbial growth and metabolism result in degradation of the organic compounds, i.e., CO2  +   HiiO   +   microorganisms (+energy?).

Media bed depths can vary, just traditional trickling-filter beds accept been between about ane and three   m. The media size ranges from almost 25 to 60   mm in diameter (east.m., round gravel). However, various shapes and materials (eastward.yard., polyvinyl chloride) take been used successfully. Waste is applied in a circular rotating manner to prevent pooling or uneven deposits. The interstices and openings between the media allow for air penetration throughout the organisation. In add-on, air can be supplied by blowers from the bottom of the reactor, migrating upward through the bed. This makes nearly of the trickling filter aerobic. The treated waste that moves downward through the bed after 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 expanse is aerobic, trickling filters are actually considered to be mixed treatment systems because aerobic bacteria abound in the upper, higher oxygen layers of the media, whereas anaerobes abound in the lower, more reduced regions lower in the system, particularly if air is not pumped upward.

For particularly strong and recalcitrant compounds, and when the organic loading increases with fourth dimension, a multiple-filter system will be needed. For example, the get-go filter in a serial may accept a high loading rate of organic matter, followed by subsequent filters in which their media come into contact with the partially treated waste liquids that broke through the first filter. Indeed, the procedure can be reversed and then that the overloaded filter can recover from the loading (i.eastward., the second filter becomes the first filter, so that the original, first filter will receive less organic loading).

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