Abstract
This study contributes to the enhancement of nitrogen removal, as well as to the understanding of internal nitrogen transformation processes in horizontal subsurface flow constructed wetlands. Constructed wetlands of this type are able to efficiently remove polluting organic materials, total suspended solids and pathogens from sewage, but nitrogen removal is usually of relatively low efficiency. However, constructed wetlands are a competitive sustainable alternative for conventional wastewater treatment technologies. The primary objective was to evaluate the influence of plants and anaerobic ammonium oxidation (anammox) bacteria on the treatment performance of the wetlands in order to improve the management of these systems. Laboratory-scale horizontal subsurface flow wetland mesocosms were set up in the specialized reactors. The experimental system consisted of three planted fixed bed reactors with a volume of 19.5 L and a surface area of 0.040 m 2 each. Two of the reactors were planted with Juncus effusus and one was kept unplanted. All systems were fed with synthetic wastewater containing ammonium (NH 4 + )as a main contaminant. Hydraulic loading rate was fixed at 45 mm d -1 . In accordance with the varying operational conditions, the total experimental period was divided into three phases. During the last phase of the experimental period one of the planted reactors was inoculated with an enrichment culture of anammox bacteria. In summary, experimental results have shown that prompting of anammox process by inoculation of externally enriched biomass could be of tremendous importance for increasing the effectiveness of nitrogen removal in horizontal subsurface flow constructed wetlands.
Highlights
Scientific research on the use of wetland plants for wastewater treatment started in the early 1950s in Germany
Horizontal subsurface flow (HSSF) constructed wetlands (CWs) are one of the most popular, reliable and efficient near-natural wastewater treatment systems applied around the world
In order to evaluate the effect of anammox bacteria on nitrogen transformations and to enhance nitrogen removal in horizontal subsurface flow constructed wetlands, one of the planted reactors after nine months of operation was inoculated with an enrichment culture of anammox bacteria
Summary
Scientific research on the use of wetland plants for wastewater treatment started in the early 1950s in Germany. Already in the late 1960s the first full scale constructed wetlands (CWs) were built. Since these systems have widely spread all over the world as a low cost, energy efficient and easy to operate engineered systems for sustainable wastewater treatment. Horizontal subsurface flow (HSSF) CWs are one of the most popular, reliable and efficient near-natural wastewater treatment systems applied around the world. HSSF CWs are able to efficiently remove polluting organic materials, total suspended solids and pathogens from sewage, but nitrogen removal is usually of relatively low efficiency and has been reported in long term studies between 20 % and 70 % [6,7,8]. It is important to investigate internal nitrogen transformation mechanisms in constructed wetlands in order to provide better management of these treatment systems and water quality improvement
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