Microbial diversity and community composition in recirculating vertical flow constructed wetlands.

Microorganisms constitute a central component of constructed wetlands (CWs), playing a major role in these systems' capacity for treating wastewater. The aim of this study was to determine the diversity and composition of the microbial community found in a recirculating vertical flow CW (RVFCW) bed fed with primarily settled domestic wastewater and its response to the presence of plants, season and location in the bed. The RVFCW removed 90-95% of TSS and BOD(5) to below 10 mg L(-1). The effluent quality was not significantly affected by seasonal temperature or the existence of plants in the bed. None of these factors had discernible effects on bacterial diversity, e.g. in the planted RVFCW, the richness (S') and Shannon-Weiner diversity (H') indices were 18.3 (±3.5) and 2.49 (±0.15), respectively, which are similar to the values of 19.4 (±3.5) and 2.57 (±0.18) in the unplanted RVFCW. However, there were indications that the structure of the microbial community underwent changes that were uncorrelated with the environmental factors tested and that did not affect the overall performance. The consistency in diversity and composition/structure of the bacterial community in the face of temporal and environmental influences possibly contributes to the robustness and high treatment capacity of the RVFCW system.

Small scale recirculating vertical flow constructed wetland (RVFCW) for the treatment and reuse of wastewater.

The quantity of freshwater available worldwide is declining, revealing a pressing need for its more efficient use. Moreover, in many developing countries and lightly populated areas, raw wastewater is discarded into the environment posing serious ecological and health problems. Unfortunately, this situation will persist unless low-cost, effective and simple technologies are brought in. The aim of this study is to present such a treatment method, a novel setup which is termed recirculating vertical flow constructed wetland (RVFCW). The RVFCW is composed of two components: (i) a three-layer bed consisting of planted organic soil over an upper layer of filtering media (i.e. tuff or beads) and a lower layer of limestone pebbles, and (ii) a reservoir located beneath the bed. Wastewater flows directly into the plant root zone and trickles down through the three-layer bed into the reservoir, allowing passive aeration. From the reservoir the water is recirculated back to the bed, several times, until the desired purification is achieved. The results obtained show that the RVFCW is an effective and convenient strategy to treat (domestic, grey and agro) wastewater for re-use in irrigation. The system performance is expected to be further improved once current optimization experiments and mathematical modeling studies are concluded.