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A lava filter is a biological filter that uses lavastone pebbles as support material on which
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s can grow in a thin
biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular p ...
. This community of microorganisms, known as the
periphyton Periphyton is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. The related term Aufwuchs ( German "surface growth" or "overgrowth") refers to the co ...
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.


Method

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; # constantly submerged lava filters (for treatment ponds, combined treatment ponds/
irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has been develo ...
reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including control ...
s, ...) # not-submerged 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 (as ''
Iris pseudacorus ''Iris pseudacorus'', the yellow flag, yellow iris, or water flag, is a species of flowering plant in the family Iridaceae. It is native to Europe, western Asia and northwest Africa. Its specific epithet ''pseudacorus'' means "false acorus", ref ...
'' and '' Sparganium erectum)'' 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).Best Water Filter To Remove Calcium and Lime
/ref> 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 is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologi ...
and geographical location. Plants are usually chosen which are indigenous 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 is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well ...
, and shade are also added in ecologic water catchments,
ponds A pond is an area filled with water, either natural or artificial, that is smaller than a lake. Defining them to be less than in area, less than deep, and with less than 30% emergent vegetation helps in distinguishing their ecology from th ...
, ... This to allow a complete
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
to form. Finally, in addition to plants, locally grown bacteria and non-
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...
y fish are also added to eliminate pests. The bacteria are usually grown locally by submerging
straw Straw is an agricultural byproduct consisting of the dry stalks of cereal plants after the grain and chaff have been removed. It makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has a number ...
in water and allowing it to form bacteria (arriving from the surrounding
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
). The plants used (placed on an area 1/4 of the water mass) are divided in 4 separate water depth-zones; knowingly: # A water-depth zone from 0–20 cm;
Iris pseudacorus ''Iris pseudacorus'', the yellow flag, yellow iris, or water flag, is a species of flowering plant in the family Iridaceae. It is native to Europe, western Asia and northwest Africa. Its specific epithet ''pseudacorus'' means "false acorus", ref ...
, '' Sparganium erectum'', ... may be placed here (temperate climates) # A water-depth zone from 40–60 cm; ''
Stratiotes aloides ''Stratiotes aloides'', commonly known as water soldiers or water pineapple, is a submerged aquatic plant native to Europe and northwestern Asia. In Britain it was once common in East Anglia and still is in many places, particularly wet ditches ...
'', ''
Hydrocharis morsus-ranae ''Hydrocharis morsus-ranae'', frogbit, is a flowering plant belonging to the genus ''Hydrocharis'' in the family Hydrocharitaceae. In North America, it is referred to as common frogbit or European frog's-bit to distinguish it from the related Am ...
'', ... may be placed here (temperate climates) # A water-depth zone from 60–120 cm; Nymphea alba, ... may be placed here (temperate climates) # A submerged water-depth zone;
Myriophyllum spicatum ''Myriophyllum spicatum'' (Eurasian watermilfoil or spiked water-milfoil) is native to Europe, Asia, and north Africa, but has a wide geographic and climatic distribution among some 57 countries, extending from northern Canada to South Africa. It ...
, ... 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 The common dace (''Leuciscus leuciscus'') is a species of freshwater and brackish water ray-finned fish from the family Cyprinidae which is native to Europe but which has been introduced to other parts of the world. It is a quarry species for coa ...
'', ''
Leuciscus idus The ide (''Leuciscus idus''), or orfe, is a freshwater fish of the family Cyprinidae found in larger rivers, ponds, and lakes across Northern Europe and Asia. It has been introduced outside its native range into Europe, North America, and New Z ...
'', ''
Scardinius erythrophthalmus The common rudd (''Scardinius erythrophthalmus'') is a bentho-pelagic freshwater fish, widely spread in Europe and middle Asia, around the basins of the North, Baltic, Black, Caspian and Aral seas. Identification Morphologically, this speci ...
'' * Middle-swimmers: '' Rutilus rutilus'' * Bottom-swimming fish: '' Tinca tinca''


See also

*
Constructed wetland A constructed wetland is an artificial wetland to treat sewage, greywater, stormwater runoff or industrial wastewater. It may also be designed for land reclamation after mining, or as a mitigation step for natural areas lost to land development ...
* Treatment pond * Organisms used in water purification


References

{{reflist Water filters Appropriate technology Environmental soil science DIY culture