Constructed wetland

Wetlands are overgrown with plants plants in which waste water by the interaction of plants, microorganisms, waste constituents, and - is also cleaned the filter substrate - in soil filtration.

There are a wide variety of different wetlands. The various systems can be prepared by the reference system (aquatic - terrestrial) members. So you come from planted soil bodies on retention soil filter Hangverrieselung, overflowed wetlands finally where an open water surface is present at floating islands without soil passage. Affiliated to the method according to practice - probation, be covered horizontal and vertical filter according to DWA A 262 have proven for years in large number and conform to generally accepted rules of technology. Two-stage vertical filter with Rohabwasserbeschickung have (usually about 1000 plants for about 500 - 2000 people) for years in France in large numbers proven. Other types of plant ( Multilayer vertical filter, retention soil filter, Sewage sludge, Hangverrieselung, floating islands, marsh plants roofs overflowed, wetlands) are more or less common, but sometimes also correspond to the prior art. In planted soil filter (. Called root zone treatment plant), the waste water is cleaned within a wetland body ( the root zone ), the - purpose ( goal: highest possible cleaning performance of the discharged wastewater ) - mostly with reed (Phragmites australis ), supported by marsh or reposition such as cattails, rushes or sedges, is planted. The plant roots serve as a habitat for microorganisms that contribute to the reduction of wastewater constituents, as well as continue to entry of atmospheric oxygen, which also improves the cleaning performance of the constructed wetland. Wetlands are scientifically recognized, as long as they can keep the boundary parameters, since they correspond to the recognized rules of technology. A wetland may be the most water constituents degrade naturally.

This is mainly due to an interaction of filter material ( mechanical), by absorbing or degrading the contaminants by bacteria and organic processes ( biological), adsorption to soil particles ( physically ) and by precipitation reactions between the roots of ( chemical).

The wastewater flows through the wetland either vertically from top to bottom or horizontally from the inlet to the outlet backdrop backdrop. In the bottom body laid drainage pipes to catch the treated wastewater and direct it into a manhole. After this shaft, the purified water is discharged into water bodies, seeps, or is stored for further use.

For vertical, intermittent operation, the best method for this cleaning services ( carbon degradation and nitrification) can be achieved.

The structure of a plant

Constructed wetlands consist of:

• A mechanical separation of the solid components. This can be done in three ways:

• The plant bed, usually a overgrown with reeds filled with gravel and sand basin ( sediment ). The waste water is introduced either via a slope or a pump ( usually at intervals ) from the collecting chute to the phyto-treatment plant. Abwasserverteilanlagen, running on the surface and drainage pipes that run in from the top down -flow systems on the Beetsohle, bring the water to be purified in the soil body and pull it from the. It also be built along flowed through systems in which the effluent is fed to one side of the vegetable basin and removed on the other side. Possibly several stages ( plant basins ) can be connected in series. Basically, vertical -flow constructed wetlands are characterized by high nitrification and denitrification rates low, whereas horizontal flow constructed wetlands are good denitrifying and nitrifying bacteria but mostly worse. Of course, with horizontal flow open water wetlands are similar occurring wetlands, but they have the major disadvantage that they create ideal breeding conditions for mosquitoes.
• Before the purified water leaves the wetland, it passes through a checkpoint. The required water quality ( BOD5, COD, nitrogen, phosphorus) can be measured.

End and control shaft

The inspection chamber is the last stop before the water leaves the wetland cleaned. The water quality must be analyzed on the basis of wastewater parameters (important, the scope of investigation is usually prescribed in the approval of the system by the Authority and may consist of the self to be carried out by the operator self-monitoring and to be carried out by an independent investigation institute of foreign monitoring).

The inspection chamber has except the direct control of water quality, also has the function to regulate the internal water level. In some cases, it is realized from here a water recycle. Here, the power of the treated wastewater is halved and a half passed back to the first or second compartment of the septic tank ( primary treatment ). This leads to a suppression of the formation of hydrogen sulfide in the primary treatment of sludge reduction, a " revival " of the wastewater already in the first stage - and expected to improve the flow values. In systems which are fed by gravity, so a wastewater recycling can only happen with a pump. In PCA, which are fed via a pump, which waste water recirculation on the gravity can be effected.

The impounding of the bed takes place in some PKA - types only in the start (about 3 months); other types are permanently impounded. The better flow values ​​brings the not accumulated operation because it is rich in oxygen.

Functioning of the wetland

The cleaning performance of a constructed wetland is accomplished by the interaction of various processes. Each process causes several functions. This is a very complex and semi-natural cleaning process.

The water contents are firstly absorbed by the plants to meet the nutritional needs of plants growing. In addition, the roots of the reeds get the permeability of the soil ( oxygen supply ), which is reduced when entering or by deposits in operation. On the other hand, most of the cleaning is done by microorganisms or bacteria that live in the soil body. Both processes purify the water "organic", that is, by biochemical reactions.

The microorganisms live and clean either:

• In an aerobic environment ( oxygen-rich zone)

Many marsh and aquatic plants have adapted during evolution to a particularly low-oxygen environment and trained aerenchymatisches tissue. This fabric provides a particularly effective transport of the oxygen recovered in photosynthesis through the entire plant, to the roots. Here, the oxygen diffusion to the water is released near the roots and so favored autotrophic microorganisms that perform the first purification step, the nitrification.

• In the anoxic environment ( oxygen-poor zone)

The oxygen is chemically bound only before, such as the Nitrifikationsprodukt nitrate. This nitrate is converted by microorganisms that prefer a low-oxygen air as part of their metabolism in elemental gaseous nitrogen, which can then escape into the air. This second step, denitrification is performed by heterotrophic microorganisms and, therefore, does require a low oxygen environment as a condition containing a carbon source.

• Anaerobically ( without oxygen zone)

Is the absence of oxygen, a mostly for reasons of odor undesired process, but which is used in special cases in the anaerobic wastewater treatment.

In addition to other biogeochemical cycles, such as the phosphorus cycle or the sulfur cycle, the nitrogen cycle occupies a prime importance as the large number of wetlands of purified waters are polluted by nitrogen compounds. The main types of entries wastewater, are particulate entry, ammonification and fixation of atmospheric nitrogen. Particulate entry is made in the form of suspended particles in the water that are filtered through the substrate in which the plants live physically out of the water and eventually be added by metabolism in the form of microbial biomass to the system. In addition, ammonification also affect the nitrogen balance. This organic nitrogen from bacterial biomass or plant remains in an equilibrium reaction is mineralized into inorganic nitrogen. In addition, dissolved in small amounts of atmospheric nitrogen in the water and then added to the system. The main Austragsarten from a wetland are denitrification, ammonia volatilization, and anaerobic ammonia oxidation ( anammox ). In addition to denitrification as the main cleaning effect of nitrogen is discharged through ammonia volatilization. Ammonia is in equilibrium in ionized and non- ionized, while the non-ionized ammonia version is relatively volatile and can be gas discharged from the system. Especially in wastewaters with low chemical oxygen demand, the anammox process by ammonia metabolized microbially without an intermediate step to atmospheric nitrogen, will make a significant contribution to the cleaning performance of a constructed wetland. Apart from these inputs and effluents represent precipitation, ion exchange and degradation of nitrogen addition to a storage depots dar. by precipitation, nitrogen is accumulated together also based on the principle of the ion exchanger, especially in clay minerals. In addition, nitrogen is also stored by degradation (dead plant residues ) in the system because poorly degradable nitrogen compounds are microbially not fully processed in plant residues by ammonification. Outstanding importance to affect the nitrogen cycle, the pH and the temperature in the wetland. In addition, phosphorus is a vital plant nutrient and can occur both as a custodian as well as discharge. In case of regular removal of plant biomass can be removed via this route phosphorus from the system, otherwise remain parts of the phosphorus contained in the plant remains in the system as a custodian.

Water quality can be determined using the so-called sum parameters or individual parameters such as nitrogen and phosphorus content. The carbon load of the wastewater, for example, by the sum of parameters

• BOD5 (ATH ) ( inhibited biological oxygen demand. Within five days by microorganisms oxygen consumed Inhibition by allyl thiourea ( ATH) is necessary because otherwise, an evaluation would not be possible, because additionally a more or less complete nitrogen oxidation would also measured. ),
• COD ( Chemical Oxygen Demand by catalytic chemical conversions (oxidation ) of oxygen consumed ) and
• TOC (total organic carbon )

Determined.

Many sewage treatment plants use, where appropriate, ferric chloride, ferric sulfate or aluminum chloride to remove when a surplus of phosphate this out of the water. This is done by the "iron" or "aluminum", the phosphate is converted to a non-soluble in water compound, in the secondary clarifier to the ground which is then " covered " ( therefore, the technical term precipitation). In a wetland, these precipitation reactions take place due to the presence in the soil body iron salt or other minerals. In addition, phosphorus is taken up in the context of plant physiology as a nutrient and can be removed from the water so. However, this operation can only proceed unless the increased plant biomass is removed regularly, otherwise the phosphorus is returned to in the course of decomposition of the water. In contrast to nitrogen, phosphorus may not be deposited in a gaseous form, which means the further that constructed wetlands can take a finite amount of phosphorus.

Overall, the treated water can be used from the endpoints and control slot again to higher-value uses in compliance with the sanitary and technical regulations. This means a closed cycle and re-use, and is especially for water management in countries where water shortages, useful.

Furthermore, there is a development in which is deliberately on the ground body. The plants stand on their own roots. The cleaning is done here essentially by the plants themselves and by the microorganisms in their roots. Benefits include a lower overall weight and better flow, thus an increase in performance and a possible use on roofs.

Planning

The purchase price varies, it is due to the cost of planning and construction, as well as through the acquisition of certain elements or materials as necessary a settling pit, at different heights. Important to what extent is ( connected EW) it was planned. Apart from still incurring lower costs, they result largely through continued maintenance, by the disposal of the solids ( about once a year ), as well as the control of water parameters.

Wetlands must be carefully planned according to DWA A 262, which is necessary to ensure a functioning system. The planning costs are dependent on the expansion size. A wetland is always designed for a population equivalent or to the population equivalent ( pe or EEC). The minimum size is 4EW.

To avoid ecological consequences that flow levels should be monitored regularly. This monitoring is done according to the regulatory requirements in most cases annually by an authorized company. Construction and Release into a water or groundwater is subject to approval by the relevant regulations ( in Germany the Water Resources Act WHG and the respective laws of the state or in Austria the Water Act WRG).

Conclusion

In most municipalities is mandatory connection to public sanitation. So one is forced to connect to the municipal sewer system, even with the existence of our own plant. In Central Europe, the use of small wastewater treatment plants such as sewage treatment plants is therefore limited to the undeveloped areas. However, constructed wetlands can also be used for disposal of wastewater smaller towns and thus be used in place of other purification processes.

Other fields of obstacles could also be the space required (4 to 5 m / EW ) or more extensive cleaning requirements (very high, secured nutrient removal ). Further negative features are not known. This can be noted that the cleaning is going odorless (because usually no standing water surfaces and anaerobic zones form ). The possible technical lifetime of wetlands is difficult to determine, as most plants are still operational (the first created around 1980 ). But a new planting, possibly a renewal of the filter material and a loosening of the soil compaction is useful to obtain the desired effluent quality.

The wetland is an alternative to wastewater treatment plant using the activated sludge process or a trickling filter. A body of water is beneficial to the outlet of the plant, which can hold the purified water ( outfall ). Or the purified water is supplied to the ground or possibly re-used. However, the introduction into groundwater in some cases for the sake of ensuring the pollution of groundwater water not economically desirable (hygiene, residual stress with non-degradable substances).

It is noteworthy that constructed wetlands do not freeze because of the running processes, when properly executed, in winter and (except for any pumps for waste water added) are mechanically robust because of the relative absence of aggregates. They are also, as the degrading bacteria are "anchored" in the soil matrix, not the settling behavior of the activated sludge dependent ( see Operating Problems / bulking the activated sludge process ). This robustness of the process is a positive aspect when used in circumstances in which an intensive, daily maintenance can not be guaranteed.