Trickling filter - AbsoluteAstronomy.com

A trickling filter consists of a fixed bed of rock

Rock (geology)

In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

s, lava

Lava

Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

, coke

Coke

Coke may refer to:* Coca-Cola, a soft drink originally based on coca leaf extract** The Coca-Cola Company, makers of this drink** Cola, any soft drink similar to Coca-Cola** Soft drink, any non-alcoholic carbonated beverage* Coca, a plant...

, gravel

Gravel

Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...

, slag

Slag

Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and metal atoms in the elemental form...

, polyurethane

Polyurethane

A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...

foam

Foam

-Definition:A foam is a substance that is formed by trapping gas in a liquid or solid in a divided form, i.e. by forming gas regions inside liquid regions, leading to different kinds of dispersed media...

, sphagnum peat moss, ceramic, or plastic media over which sewage

Sewage

Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community. Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains...

or other wastewater

Wastewater

Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...

flows downward and causes a layer of microbial slime (biofilm

Biofilm

A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...

) to grow, covering the bed of media. Aerobic conditions are maintained by splashing, diffusion, and either by forced air flowing through the bed or natural convection of air if the filter medium is porous.

The terms trickle filter, trickling biofilter, biofilter, biological filter and biological trickling filter are often used to refer to a trickling filter. These systems have also been described as roughing filters, intermittent filters, packed media bed filters, alternative septic systems, percolating filters, attached growth processes, and fixed film processes.

Operation

The removal of pollutants

Pollution

Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

from the wastewater stream involves both absorption and adsorption

Adsorption

Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...

of organic compounds by the layer of microbial biofilm

Biofilm

. The filter media is typically chosen to provide a very high surface area to volume. Typical materials are often porous and have considerable internal surface area in addition to the external surface of the medium. Passage of the wastewater over the media furnishes dissolved air, the oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

which the slime layer requires for the biochemical oxidation of the organic compounds and releases carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

gas, water and other oxidized end products. As the biofilm layer thickens, it eventually sloughs off into the treated effluent

Effluent

Effluent is an outflowing of water or gas from a natural body of water, or from a human-made structure.Effluent is defined by the United States Environmental Protection Agency as “wastewater - treated or untreated - that flows out of a treatment plant, sewer, or industrial outfall. Generally refers...

and subsequently forms part of the secondary sludge. Typically, a trickling filter is followed by a clarifier or sedimentation tank for the separation and removal of the sloughing. Other filters utilizing higher-density media such as sand, foam and peat moss do not produce a sludge that must be removed, but require forced air blowers and backwashing or an enclosed anaerobic environment.

The treatment of sewage or other wastewater with trickling filters is among the oldest and most well characterized treatment technologies.

Types

The three basic types of trickle filters are used for:

the treatment of small individual residential or rural sewage
large centralized systems for treatment of municipal sewage
systems applied to the treatment of industrial wastewater.

Septic system leach field

This is the simplest form of waste liquid disposal system, typically using pipes buried in loose sand or gravel to dissipate the liquid outflow from a septic tank

Septic tank

A septic tank is a key component of the septic system, a small-scale sewage treatment system common in areas with no connection to main sewage pipes provided by local governments or private corporations...

. Liquid purification is performed by a biofilm

Biofilm

which naturally forms as a coating on the sand and gravel in the absorption field and feeds on the dissolved nutrients in the waste stream.

Due to the system being completely buried and generally isolated from the surface environment, the process of waste breakdown is slow and requires a relatively large surface area to absorb and process liquid wastes. If too much liquid wastes enter the field too quickly, the wastes may pass out of the biofilm before waste consumption can occur, leading to pollution of groundwater.

In order to prolong the life of a leaching field, one method of construction is to build two fields of piping side-by-side, and use a rotating flow valve to direct waste into one field at a time, switching between fields every year or two. This allows a period of rest to let the microorganisms have time to break down the wastes built up in the gravel bed.

In areas where the ground is insufficiently absorptive (fails the percolation test) a homeowner may be required to construct a mound system

Mound system

A mound system is an alternative to the traditional rural septic system leach field. The mound system is an engineered leaching field used in areas where septic systems are more prone to failure due to having extremely slow or extremely fast permeable soils, soil with shallow cover over porous...

which is a special engineered waste disposal bed of sand and gravel mounded on the surface of the ground with poor liquids absorption.

Leach field dosing

Generally it is better if the biofilm is permitted a period of time to rest between liquid influxes and for the liquids to be evenly distributed through the leaching bed to promote biofilm growth throughout the pipe network. Typically flows from septic systems are either small surges (handwashing) or very large surges (clothes washer emptying), resulting in highly erratic liquid outflow into the field and uneven biofilm growth concentrating primarily around the field inlet and dropping off in the outer reaches of the piping system.

For this reason it is common for engineered mound systems to include an electrically powered dosing system which consists of a large capacity underground storage tank and lift pump after the septic tank. When the tank fills to a predetermined level, it is emptied into the leaching field.

The storage tank collects small outflows such as from handwashing and saves them for dosing when the tank fills from other sources. During this fill period the field is able to rest continuously. When full, the discharge dose fills out the entire field completely to the same degree of flow, every time, promoting an even biofilm growth throughout the system.

Dosing systems have maintenance requirements over traditional non-powered surge systems. The pump and float system can break down and require replacement, and the dosing system also needs electricity. However, the system can be designed so that in the event of power failure the storage tank overflows to the field operating in the traditional surge-flow manner until power is restored or repairs can be done.

Soil Compaction issues

The biofilm is most productive if the absorption field is loosely packed, to permit easy air infiltration down into the biofilm bed. Consequently the land over the leaching field is often a restricted area where large vehicles cannot be allowed to drive, because the heavy weight will compact the bed, and potentially cause system failure due to hindering of biofilm growth.

One method to help prevent compaction of the field is to place a U-shaped cover over gravel trenches in the bed, with a dosing pipe suspended above the bed by the cover. Any weight from above is passed to the sides of the trench keeping the bed directly under the cover free from compaction.

Sewage treatment trickle filters

Onsite sewage facilities (OSSF) are recognized as viable, low-cost, long-term, decentralized approaches to sewage treatment if they are planned, designed, installed, operated and maintained properly (USEPA, 1997).

Sewage trickling filters are used in areas not serviced by municipal wastewater treatment plants (WWTP). They are typically installed in areas where the traditional septic tank

Septic tank

system are failing, cannot be installed due to site limitations, or where improved levels of treatment are required for environmental benefits such as preventing contamination of ground water or surface water

Surface water

Surface water is water collecting on the ground or in a stream, river, lake, wetland, or ocean; it is related to water collecting as groundwater or atmospheric water....

.

Sites with a high water table

Water table

The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...

, high bedrock

Bedrock

In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...

, heavy clay

Clay

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

, small land area, or which require minimal site destruction (for example, tree removal) are ideally suited for trickling filters.

All varieties of sewage trickling filters have a low and sometimes intermittent power consumption. They can be somewhat more expensive than traditional septic tank-leach field systems, however their use allows for better treatment, a reduction in size of disposal area, less excavation, and higher density land development.

Configurations and components

All sewage trickling filter systems share the same fundamental components:

a septic tank for fermentation and primary settling of solids
a filter medium upon which beneficial microbes (biomass, biofilm
Biofilm
A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...

) are promoted and developed
a container which houses the filter medium
a distribution system for applying wastewater to be treated to the filter medium
a distribution system for disposal of the treated effluent or percolation ponds.

By treating septic tank effluent before it is distributed into the ground, higher treatment levels are obtained and smaller disposal means such as leach field, shallow pressure trench or area beds are required.

Systems can be configured for single-pass use where the treated water is applied to the trickling filter once before being disposed of, or for multi-pass use where a portion of the treated water is cycled back to the septic tank and re-treated via a closed-loop. Multi-pass systems result in higher treatment quality and assist in removing Total Nitrogen (TN) levels by promoting nitrification

Nitrification

Nitrification is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitrites into nitrates. Degradation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil...

in the aerobic media bed and denitrification

Denitrification

Denitrification is a microbially facilitated process of nitrate reduction that may ultimately produce molecular nitrogen through a series of intermediate gaseous nitrogen oxide products....

in the anaerobic septic tank.

Trickling filters differ primarily in the type of filter media used to house the microbial colonies. Types of media most commonly used include plastic matrix material, open-cell polyurethane

Polyurethane

foam

Foam

, sphagnum peat moss, recycled tires, clinker, gravel, sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

and geotextiles. Ideal filter medium optimizes surface area

Surface area

Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...

for microbial attachment, wastewater retention time, allows air flow, resists plugging and does not degrade. Some residential systems require forced aeration units which will increase maintenance and operational costs.

Regulatory approvals

Third-party verification

Third party verification is a process of getting an independent party to confirm that the customer is actually requesting a change or ordering a new service or product...

of trickling filters has proven them to be a reliable alternative to septic systems with increased levels of treatment performance and nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

removal. Typical effluent

Effluent

quality parameters are Biochemical Oxygen Demand

Biochemical oxygen demand

Biochemical oxygen demand or B.O.D. is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. The term also refers to a chemical procedure for...

(BOD), Total suspended solids

Total suspended solids

Total suspended solids is a water quality measurement usually abbreviated TSS. It is listed as a conventional pollutant in the U.S. Clean Water Act. This parameter was at one time called non-filterable residue , a term that refers to the identical measurement: the dry-weight of particles trapped...

(TSS), Total Kjeldahl Nitrogen

Total Kjeldahl Nitrogen

Total Kjeldahl Nitrogen or TKN is the sum of organic nitrogen, ammonia , and ammonium in the chemical analysis of soil, water, or wastewater...

(TKN), and fecal coliforms

Fecal coliforms

A fecal coliform is a facultatively-anaerobic, rod-shaped, gram-negative, non-sporulating bacterium. Fecal coliforms are capable of growth in the presence of bile salts or similar surface agents, are oxidase negative, and produce acid and gas from lactose within 48 hours at 44 ± 0.5°C.Coliform...

.

The leading testing facility in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

is the Massachusetts

Massachusetts

The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...

Alternative Septic System Test Center, a program of the Buzzards Bay National Estuary Program. Testing conducted here includes the stringent Environmental Technology Initiative (ETI) where systems are tested in triplicate over two years, and the Environmental Technology Verification (ETV) program which is funded by the U.S. Environmental Protection Agency (EPA) and includes stress testing as well as evaluation of nitrogen

Nitrogen

removal over 14 months. Systems are approved for installation by local, state and federal regulations and controls.

Industrial wastewater treatment trickle filters

Wastewaters from a variety of industrial processes have been treated in trickling filters. Such industrial wastewater trickling filters consist of two types:

Large tanks or concrete enclosures filled with plastic packing or other media.

Vertical towers filled with plastic packing or other media.

The availability of inexpensive plastic tower packings has led to their use as trickling filter beds in tall towers, some as high as 20 meters. As early as the 1960s, such towers were in use at: the Great Northern Oil's Pine Bend Refinery

Pine Bend Refinery

The Pine Bend Refinery is the largest oil refinery in Minnesota, located in the Twin Cities suburbs of Rosemount and Inver Grove Heights next to southern split of U.S. Highway 52 and Minnesota State Highway 55. The refinery is notable for being the largest in the United States to be located in a...

in Minnesota

Minnesota

Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...

; the Cities Service Oil Company Trafalgar Refinery in Oakville, Ontario

Oakville, Ontario

Oakville is a town in Halton Region, on Lake Ontario in Southern Ontario, Canada, and is part of the Greater Toronto Area. As of the 2006 census the population was 165,613.-History:In 1793, Dundas Street was surveyed for a military road...

and at a kraft paper mill.

The treated water effluent from industrial wastewater trickling filters is very often subsequently processed in a clarifier-settler to remove the sludge that sloughs off the microbial slime layer attached to the trickling filter media (see Image 1 above).

Currently, some of the latest trickle filter technology involves aerated biofilters which are essentially trickle filters consisting of plastic media in vessels using blowers to inject air at the bottom of the vessels, with either downflow or upflow of the wastewater.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Operation

Types

Septic system leach field

Leach field dosing

Soil Compaction issues

Sewage treatment trickle filters

Configurations and components

Regulatory approvals

Industrial wastewater treatment trickle filters

See also

External links