Constructed wetlands for domestic wastewater treatment in a Mediterranean climate region in Chile

Background: Constructed wetlands are a promising, cheap and effective wastewater treatment in small communities. The studies on these systems have been reported mainly from cold, tropical or subtropical climate regions. In this work we constructed a pilot plant with six horizontal subsurface flow constructed wetlands (HSSF CWs) with a surface area of 2 m² and a depth of 0.6 m each, planted with Typha latifolia or Scirpus sp., and filled with gravel (G) or fine gravel (FG) of 2.8 and 1.2 cm of diameter respectively, continuously fed with raw domestic wastewater. This experimental setup was evaluated over 280 days for the removal of organic matter and nutrients in a Mediterranean climate, near Valparaíso, Chile. The removal of total COD, NH4+-N and PO4-3-P was calculated, in order to assess by analysis of variance the effect of initial pollutants concentration, air temperature (season) and plant/support combination on the wetlands performance. Results: The Scirpus/FG combination showed the highest average removal of total COD of about 59%, and Typha/FG shows the highest removal of NH4+-N and PO4-3-P (49 and 32%, respectively). Furthermore, the removal of organic matter was independent of influent concentration, while mildly dependent of the season, unlike nutrients removal that was dependent on these two parameters. Media, plant and the plant/media combination influenced positively organic matter, ammonia and phosphorous removal, respectively. Conclusions: Overall, the results demonstrate the potential of wetlands in treatment of wastewater in Mediterranean regions and show how these can help to improve the quality of water in domestic zones without high-throughput technologies.

Improved sanitary landfill design using recirculation of anaerobically treated leachates: generation of advanced design criteria

In Latin America, the most accepted disposal systems for Municipal Solid Waste (MSW) are landfills, which nowadays have low rates of stabilization. The objective of this study was to develop design criteria for sanitary landfills which lead to a reduction in the stabilization times of MSW, based on experiment results obtain from a pre-pilot scale operation of two sanitary landfills (0.5 Ton), one with recirculation of leachates treated in an anaerobic digester and the other with recirculation of untreated leachates. This was complemented by another pilot scale sanitary landfill (1440 Ton) with recirculation of leaches treated in an anaerobic filter, and additionally by a computer simulation of leachate generation through the water balance of a theoretical cell of MSW (850 Ton), in which the initial humidity of the MSW and the type of final cover were evaluated. The results obtained on the pre-pilot scale indicate that recirculation of anaerobically treated leachates, when compared to the recirculation of untreated leachates, increased the rate of MSW stabilization, projecting a stabilization time reduction of 72 percent. In the pilot sanitary landfill an increase in the settling rate of around 200 percent was observed when operating with the recirculation of anaerobically treated leachates as opposed to operation without recirculation. The water balance carried out on the theoretical cell of MSW demonstrated the importance to leachate generation of both the initial landfill water saturation and the type of final barrier. From these results it may be stated that it is important for landfill design to maintain waste humidity close to its field capacity along with an adequate leachate application rate.