moist Influent wastewater is normally applied at the top of the packing through distributor arms that extend across the trickling filter inner diameter and have variable openings to provide a uniform application rate per unit area. The distributor arms are rotated by the force of the water exiting through their opening or by the use of electric drives. The electric drive designs provide more control flexibility and a wider range of distributor rotational speeds than possible by the simple hydraulic designs. In some cases, especially for square or rectangular filters, fixed flat-spray nozzles have been used Primary clarification is necessary before rock trickling filters, and generally used also before trickling filters with plastic packing, though fine screens(smaller than 3mm openings) have been used successfully with plastic packing. With increases in plastic and rubber floatable materials in wastewater, screening of these materials is important to reduce fouling of the packing. In some installations a wire-mesh screen is olaced over the top of plastic packing to collect debris that can be vacuumed off periodically a slime layer develops on the rock or plastic packing in the trickling filters and contains the microorganisms for biodegradation of the substrates to be removed from the liquid flowing over the packing. The biological community in the filter includes aerobic and facultative bacteria, fungi, algae, and protozoans. Higher animals, such as worms, insect larvae, and snails, are also present Facultative bacteria are the predominating organisms in trickling filters, and decompose the organic material in the wastewater along with aerobic and anaerobic bacteria Achromobacter Flavobacterium Pseudomonas, and Alcaligenes are among the bacterial species commonly associated with the trickling filter. Within the slime layer, where adverse conditions prevail with respect to growth, the filamentous forms Sphaerotilus natans and Beggiatoa will be found. In the lower reaches of the filter, the nitrifying bacteria will be present. The fungi present are also responsible for waste stabilization, but their role is usually important only under low-pH conditions or with certain industrial wastes. At times, fungi growth can be so rapid that the filter clogs and ventilation becomes restricted. Among the fungi species that have been identified are Fusarium, Mucor: Penicillium, Geotrichum, Sporatichum, and various yeasts Algae can grow only in the upper reaches of the filter where sunlight is available Phormidium, chlorella and Ulothrix are among the algae species commonly found in trickling filters. Generally, algae do not wastewater.From an operational standpoint, the algae may be troublesome because they can cau o take a direct part in waste degradation, but during the daylight hours they add oxygen to the percolating logging of the filter surface. The protozoa in the filter are predominantly of the ciliate group, including Vorticella, Opercularia, and Epistylis. Their function is to feed on the biological films and, as a result, effluent turbidity decreases and the biofilm is maintained in a higher growth state. The higher animals, such as worms, snails, and insects, feed on the biological film. Snails are especially troublesome in trickling filters used mainly for nitrification, where they have been known to consume enough of the nitrifying bacteria to significantly reduce treatment efficiency The slime layer thickness can reach depths as much as 10 mm. Organic material from the liquid is sorbed onto the biological film or slime layer In the outer portions of the biological slime layer(0. 1 to 0.2 mm), the organic material is degraded by aerobic microorganisms. As the microorganisms grow and the slime layer thickness increases, oxygen is consumed before it can penetrate the full depth, and an anaerobic environment is established near the surface of the packing. As the slime layer increases in Bacteria in the slime layer enter an endogenous respiration state and lose their ability to cling to the packing surface. The liquid then washes the slime off the packing, and a new slime layer starts to grow. The phenomenon of losing the slime layer is called sloughing and is primarily a function of the organic and hydraulic loading on the filter. The hydraulic loading accounts for shear velocities, and the organic loading accounts for the rate of metabolism in the slime layer. Hydraulic loading and trickling filter sloughing can be controlled by using a wastewater distributor with an electric motor drive to vary The mechanisms of biological film loss in plastic and rock packing are different. Continuous, small-scale sloughing of the film occurs in high-rate plastic filters due to hydraulic shear, while large-scale, spring-time sloughing occurs in rock filters located in temperate zones. Sloughing is due to the activity of insect larvae, which become active in the warmer spring temperatures and consume and mechanically dislodge thick biofilms that accumulate over the winter. when a rock filter sloughs. the effluent before settling will contain higher amounts of BOD and TSS than the applied wastewater Trickling Filter Classification and Applications Trickling filter applications and loadings, based on historical terminology developed originally for rock filter designs. are summarized in Table 8-18-3 moist. Influent wastewater is normally applied at the top of the packing through distributor arms that extend across the trickling filter inner diameter and have variable openings to provide a uniform application rate per unit area. The distributor arms are rotated by the force of the water exiting through their opening or by the use of electric drives. The electric drive designs provide more control flexibility and a wider range of distributor rotational speeds than possible by the simple hydraulic designs. In some cases, especially for square or rectangular filters, fixed flat-spray nozzles have been used. Primary clarification is necessary before rock trickling filters, and generally used also before trickling filters with plastic packing, though fine screens (smaller than 3mm openings) have been used successfully with plastic packing. With increases in plastic and rubber floatable materials in wastewater, screening of these materials is important to reduce fouling of the packing. In some installations a wire-mesh screen is placed over the top of plastic packing to collect debris that can be vacuumed off periodically. A slime layer develops on the rock or plastic packing in the trickling filters and contains the microorganisms for biodegradation of the substrates to be removed from the liquid flowing over the packing. The biological community in the filter includes aerobic and facultative bacteria, fungi, algae, and protozoans. Higher animals, such as worms, insect larvae, and snails, are also present. Facultative bacteria are the predominating organisms in trickling filters, and decompose the organic material in the wastewater along with aerobic and anaerobic bacteria Achromobacter, Flavobacterium, Pseudomonas, and Alcaligenes are among the bacterial species commonly associated with the trickling filter. Within the slime layer, where adverse conditions prevail with respect to growth, the filamentous forms Sphaerotilus natans and Beggiatoa will be found. In the lower reaches of the filter, the nitrifying bacteria will be present. The fungi present are also responsible for waste stabilization, but their role is usually important only under low-pH conditions or with certain industrial wastes. At times, fungi growth can be so rapid that the filter clogs and ventilation becomes restricted. Among the fungi species that have been identified are Fusarium, Mucor, Penicillium, Geotrichum, Sporatichum, and various yeasts. Algae can grow only in the upper reaches of the filter where sunlight is available Phormidiun, Chlorella and Ulothrix are among the algae species commonly found in trickling filters . Generally, algae do not take a direct part in waste degradation, but during the daylight hours they add oxygen to the percolating wastewater. From an operational standpoint, the algae may be troublesome because they can cause clogging of the filter surface. The protozoa in the filter are predominantly of the ciliate group, including Vorticella, Opercularia, and Epistylis. Their function is to feed on the biological films and, as a result, effluent turbidity decreases and the biofilm is maintained in a higher growth state. The higher animals, such as worms, snails, and insects, feed on the biological film. Snails are especially troublesome in trickling filters used mainly for nitrification, where they have been known to consume enough of the nitrifying bacteria to significantly reduce treatment efficiency. The slime layer thickness can reach depths as much as 10 mm. Organic material from the liquid is adsorbed onto the biological film or slime layer. In the outer portions of the biological slime layer (0.1 to 0.2 mm), the organic material is degraded by aerobic microorganisms. As the microorganisms grow and the slime layer thickness increases, oxygen is consumed before it can penetrate the full depth, and an anaerobic environment is established near the surface of the packing. As the slime layer increases in thickness, the substrate in the wastewater is used before it can penetrate the inner depths of the biofilm. Bacteria in the slime layer enter an endogenous respiration state and lose their ability to cling to the packing surface. The liquid then washes the slime off the packing, and a new slime layer starts to grow. The phenomenon of losing the slime layer is called sloughing and is primarily a function of the organic and hydraulic loading on the filter. The hydraulic loading accounts for shear velocities, and the organic loading accounts for the rate of metabolism in the slime layer. Hydraulic loading and trickling filter sloughing can be controlled by using a wastewater distributor with an electric motor drive to vary rotational speed. The mechanisms of biological film loss in plastic and rock packing are different. Continuous, small-scale sloughing of the film occurs in high-rate plastic filters due to hydraulic shear, while large-scale, spring-time sloughing occurs in rock filters located in temperate zones. Sloughing is due to the activity of insect larvae, which become active in the warmer spring temperatures and consume and mechanically dislodge thick biofilms that accumulate over the winter. When a rock filter sloughs, the effluent before settling will contain higher amounts of BOD and TSS than the applied wastewater. Trickling Filter Classification and Applications Trickling filter applications and loadings, based on historical terminology developed originally for rock filter designs, are summarized in Table 8-1