A lava filter is a biological filter that uses lavastone pebbles as support material on which microorganism

Microorganism

A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...

s can grow in a thin biofilm. This community of microorganisms, known as the periphyton

Periphyton

Periphyton are a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that are attached to submerged surfaces in most aquatic ecosystems. It serves as an important food source for invertebrates, tadpoles, and some fish. It can also absorb contaminants; removing them from...

 break down the odor components in the air, such as hydrogen sulfide. The biodegradation processes that occurs is provided by the bacteria themselves. In order for this to work, sufficient oxygen as well as water and nutrients (for cell growth) is to be supplied.

Contaminated air enters the system at the bottom of the filter and passes in an upward direction through the filter. Water is supplied through the surface of the biofilter and trickles down over the lava rock to the bottom, where it is collected. Constant water provisioning at the surface prevents dry-out of the active bacteria in the biofilm and ensures a constant pH value in the filter. It also functions to make nutrients available to the bacteria.

Percolating water collected at the filter bottom contains odour components as well as sulfuric acid from the biological oxidation of hydrogen sulfide. Depending on the process design the collected water is recirculated or subjected to further treatment.

Types of systems

At present: 2 types of systems are used;

1. constantly-submerged
   Submerged
   Submerged is an action film, released in 2005. The film stars Steven Seagal, Christine Adams, William Hope, Gary Daniels, Alison King and Vinnie Jones. The film was directed by British director Anthony Hickox.- Plot :...
   
    lava filters (for treatment pond
   Treatment pond
   A treatment pond treats water fouled by anaerobic bacteria. It is used mainly by tree nurseries, dairy farms and other agricultural companies near horse or cattle sheds or barns...
   
   s, combined treatment pond
   Treatment pond
   A treatment pond treats water fouled by anaerobic bacteria. It is used mainly by tree nurseries, dairy farms and other agricultural companies near horse or cattle sheds or barns...
   
   s/irrigation
   Irrigation
   Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...
   
    reservoir
   Reservoir
   A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...
   
   s, ...)
2. not-sumerged lava filters (for wastewater treatment; wastewater is simply sprayed on the pebbles with this system)

Constantly submerged lavafilters

These are constructed out of 2 layers of lava pebbles and a top layer of nutrient-free soil (only at the plants roots) . On top, water-purifying plants

Helophyte

A helophyte or limnodophyte is the phytosociologic definition of a biennial or herbaceous plant of which only the buds survive a harsh period, such as winter, e.g. sweet flag or bulrush ....

 (as Iris pseudacorus

Iris pseudacorus

Iris pseudacorus is a species of Iris, native to Europe, western Asia and northwest Africa. Common names include yellow iris and yellow flag...

and Sparganium erectum

Sparganium

Sparganium is a genus of flowering plants, containing about 20 species in temperate regions of both the Northern and Southern Hemispheres. It was previously placed alone in the family Sparganiaceae...

) are placed. Usually, around 1/4 of the dimension of lavastone is required to purify the water and just like slow sand filters, a series of herringbone drains are placed (with lava filters these are placed at the bottom layer).

The water-purifying plants used with constantly-submerged, planted, lavafilters (e.g. treatment ponds, self-purifying irrigation reservoirs, ...) include a wide variety of plants, depending on the local climate

Climate

Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

 and geoographical location. Plants are usually chosen which are indigenous

Indigenous (ecology)

In biogeography, a species is defined as native to a given region or ecosystem if its presence in that region is the result of only natural processes, with no human intervention. Every natural organism has its own natural range of distribution in which it is regarded as native...

 in that location for environmental reasons and optimum workings of the system. In addition to water-purifying (de-nutrifying) plants, plants that supply 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...

, and shade

Shade

Shade is the blocking of sunlight by any object, and also the shadow created by that object. Shade also consists of the colors grey, black, white, etc...

 are also added in ecologic water catchments

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

, ponds, ... This to allow a complete ecosystem

Ecosystem

An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

 to form. Finally, in addition to plants, locally grown bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 and non-predatory fish are also added to eliminate pests. The bacteria are usually grown locally by submerging straw

Straw

Straw is an agricultural by-product, the dry stalks of cereal plants, after the grain and chaff have been removed. Straw makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has many uses, including fuel, livestock bedding and fodder, thatching and...

 in water and allowing it to form bacteria (arriving from the surrounding atmosphere

Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

). The plants used (placed on an area 1/4 of the water mass) are divided in 4 separate water depth-zones; knowingly:

1. A water-depth zone from 0–20 cm; Iris pseudacorus
   Iris pseudacorus
   Iris pseudacorus is a species of Iris, native to Europe, western Asia and northwest Africa. Common names include yellow iris and yellow flag...
   
   , Sparganium erectum
   Sparganium
   Sparganium is a genus of flowering plants, containing about 20 species in temperate regions of both the Northern and Southern Hemispheres. It was previously placed alone in the family Sparganiaceae...
   
   , ... may be placed here (temperate climates)
2. A water-depth zone from 40–60 cm; Stratiotes aloides
   Stratiotes
   Stratiotes is a genus of submerged aquatic plant commonly known as water soldiers. A characteristic of the genus is the habit of the plants rising to the surface at flowering time.-Description:...
   
   , Hydrocharis morsus-ranae
   Hydrocharis
   Hydrocharis is a genus of aquatic plants within the family Hydrocharitaceae.The best known species is Hydrocharis morsus-ranae, commonly called common or European frogbit, and occasionally water-poppy. The name "American frogbit" refers to another aquatic plant, Limnobium spongia....
   
   , ... may be placed here (temperate climates)
3. A water-depth zone from 60–120 cm; Nymphea alba
   Nymphaea
   Nymphaea is a genus of aquatic plants in the family Nymphaeaceae. There are about 50 species in the genus, which has a cosmopolitan distribution.-Name:The common name, shared with some other genera in the same family, is Water Lily....
   
   , ... my be placed here (temperate climates)
4. A submerged water-depth zone; Myriophyllum spicatum
   Myriophyllum
   Myriophyllum is a genus of about 69 species of freshwater aquatic plants, with a cosmopolitan distribution. The center of diversity for Myriophyllum is Australia with 43 recognized species...
   
   , ... may be placed here (temperate climates)

Finally, three types of (non-predatory) fish (surface; bottom and ground-swimmers) are chosen. This of course to ensure that the fish may 'get along'. Examples of the three types of fish (for temperate climates) are:

• Surface swimming fish: Leuciscus leuciscus, Leuciscus idus, Scardinius erythrophthalmus
• Middle-swimmers: Rutilus rutilus
• Bottom-swimming fish: Tinca tinca