Vocabulary Trickling Filters Biomass A mass or clump of organic material consisting of living organisms feeding on the wastes in wastewater, dead organisms and other debris. Colloids Very small, finely divided solids (particles that do not dissolve) that remain dispersed in a liquid for a long time due to their small size and electrical charge. When most of the particles in the water have a negative electrical charge, they tend to repel each other. This repulsion prevents the particles from clumping together, becoming heavier, and settling out. Distributor The rotating mechanism that distributes the wastewater evenly over the surface of a trickling filter or other process unit. Fixed Spray Nozzle Cone-shaped spray nozzle used to distribute wastewater over the filter media, similar to a lawn sprinkling system. A deflector or steel ball is mounted within the cone to spread the flow of wastewater through the cone, thus causing a spraying action. Microorganisms Very small organisms that can be seen only through a microscope. Some microorganisms use the wastes in wastewater for food and thus remove or alter much of the undesirable matter. Nitrification An aerobic process in which bacteria change the ammonia and organic nitrogen in wastewater into oxidized nitrogen (usually nitrate). The second-stage BOD is sometimes referred to as the nitrogenous BOD (first-stage BOD is called carbonaceous BOD ). Ponding A condition occurring on trickling filters when the hollow spaces (voids) become plugged to the extent that water passage through the filter is inadequate. Ponding may be the result of excessive slime growths, trash, or media breakdown. Recirculation The return of part of the effluent from a treatment process to the incoming flow. - 26 -
Shock Load The arrival at a plant of a waste which is toxic to organisms in sufficient quantity or strength to cause operating problems. Possible problems include odors and sloughing off of the growth or slime on the trickling filter media. Organic or hydraulic overloads also can cause a shock load. Trickling Filter Media Rocks or other durable materials that make up the body of the filter. Synthetic (manufactured) media have been used successfully. Zoogleal Film A complex population of organisms that form a slime growth on the trickling filter media and break down the organic matter in wastewater. These slimes consist of living organisms feeding on the wastes in wastewater, dead organisms, silt and other debris. Slime growth is a more common term. Purpose of Trickling Filter To remove dissolved and suspended colloidal organic waste from wastewater. Process Description A typical trickling filter is a large diameter round tank containing a media on which organism can grow for the removal of dissolved and suspended organic waste. Wastewater is trickled over the top and is treated as the water makes its way downward. The zoogleal film on the trickling filter media uses the organic matter in the water for cellular reproduction. This process reduces the strength of the wastewater by reducing BOD. - 27 -
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Component Inlet pipe Distributor base Distributor bearings Distributor arm Outlet orifice Speed retarder orifice Splash plate Arm dump gate Filter media Support grill Underdrain system Underdrain channel Outlet box Outlet pipe Retaining wall Ventilation port Stay rod Turnbuckle Center well Splitter box Recirculation pump Types of Trickling Filters Purpose Transports wastewater to trickling filter Support rotating distributor arm Allows distributor arm to rotate Distributes wastewater evenly over media Controls flow to filter media and are adjustable Controls speed of distributor arm Assist in even wastewater distribution over media Drains distributor arm (used for flushing and fly control) Provides large surface area for biological slime growth Supports media and separates it from underdrain system Collects treated wastewater from under filter / allows air flow Transports wastewater to outlet box Collects filter effluent Transports filter effluent to next process Holds filter media in place Allows air circulation through media Supports distributor arm Allows adjustment and leveling of distributor arm Provides higher water head to ensure equal flow to all orifices Divides flow between recirculation and secondary clarifier Returns flow to trickling filter for further treatment Standard Rate Filter Hydraulic loading = 25 100 gal/day/ft 2 Organic Loading = 5 25 lb BOD/day/1,000 ft 3 Produce effluent BOD of 20 25 mg/l High Rate Filter Hydraulic loading = 100 2,000 gal/day/ft 2 Organic Loading = 25-300 lb BOD/day/1,000 ft 3 Produce effluent BOD of 20 50 mg/l Roughing Filter Hydraulic loading = 100 2,000 gal/day/ft 2 Organic Loading = 100-300 lb BOD/day/1,000 ft 3 Removes 50% - 70% BOD - 29 -
Controlling Process Under normal conditions, operate the filter at a constant hydraulic load by adjusting the recirculation rate. This will help to maintain adequate DO throughout the filter while preventing hydraulic shock, which could cause unwanted sloughing. Recirculation is used to accomplish three things: 1. Dilute incoming BOD load 2. Increase DO 3. Maintain hydraulic load on filter Possible Problems and Solutions Ponding 1. Flush the area of ponding with high pressure water or flood by stopping distributor arm over troubled area 2. Remove leaves or debris with rake 3. Dose filter with 5 mg/l clorine solution for several hours 4. Flood filter for 24 hours then carefully release to avoid permit violation 5. Shut off flow for several hours to dry slime growth and remove with rake Odors 1. Do all possible to maintain aerobic conditions in collection system 2. Pre-chlorinate or aerate if necessary 3. Ensure adequate ventilation in filter 4. Increase recirculation rate to increase DO Filter Flies 1. Increase recirculation rate to flush fly larvae 2. Keep orifice openings clear 3. Apply approved insecticides 4. Flood filter for 24 hours weekly (prevents completion of life cycle) 5. Dose filter with 1 mg/l chlorine for a few hours weekly 6. Minimize habitat with proper landscape maintenance Sloughing 1. Increase recirculation rate weekly to cause a regular controlled slough 2. Reduce distribution arm speed during this weekly flush period Poor Quality Effluent 1. Check influent BOD to determine if filter is overloaded High Plant Flow 1. Increase number of filters in operation 2. Reduce or stop filter recycle 3. Operate filters in parallel rather than series if possible - 30 -