104
Evaluation of an ecological wastewater treatment system based on constructed
wetlands for small rural communities
M. L. Merino, E. Villegas, J. De Anda, A. López
Environmental technology unit, Centro de Investigación y Asistencia en Tecnología y Diseño
del Estado de Jalisco, A. C. Normalistas 800, 44270 Guadalajara, Jalisco, Mexico
,
Abstract
This work evaluates the performance of a municipal wastewater treatment pilot system
integrated by an upflow anaerobic filter (UAF) followed by a horizontal subsurface
constructed wetland (HSSCW). Both systems were filled with tezontle as biofilm support
while the HSSCW was planted with two ornamental plants species,
Canna hybrids
and
Strelitzia reginae
. This sequence allows reducing the dimensions and clogging problems in
the HSSCW. The experiment evaluated sequentially three hydraulic resident times (HRTs)
during four months each one in order to analyze the results by means of a nested design
with a crossover factor. The results for HSSCW established the best efficiencies in short
HRTs of 3 and 4 days to remove nutrients. As expected the UAF was responsible for
removing most of the organic matter and the HSSCW of nutrients. The global efficiencies
ranges found were: 82 and 85% for chemical oxygen demand (COD), 80 and 90% for
biochemical oxygen demand of five days (BOD), 30 and 36% for total nitrogen (N
tot
), and
27 and 46% for total phosphorous (P
tot
).
Keywords:
constructed wetlands, upflow anaerobic filter, organic matter removal, nutrient
removal, ornamental plants
Introduction
The untreated wastewater coming from cities and small rural communities, enriched with
nutrients, is an environmental issue that alters lakes and streams, since it accelerates the
eutrophication process changing the quality of freshwater bodies. A good ecological
alternative that fits perfectly with the small rural communities is to treat the municipal
wastewater through constructed wetlands.
The horizontal subsurface flow constructed wetland (HSSCW) is characterized because the
water flows beneath of the permeable bed surface, between the granular media, the
rhizomes and emergent plant roots. Its construction includes the placement of a cover
membrane for groundwater protection and adequate inlet and outlet hydraulic structures to
control water level (Knight and Wallace 2009; U.S. EPA 2000). They are commonly used
for secondary treatment; nevertheless the CWs need a large land area. In order to reduce
this requirement, and to complete an integral and ecological wastewater treatment, it is
necessary to add a pre-treatment. The upflow anaerobic filter (UAF) is capable of treating
wastewater with different strengths and is used specially for small rural communities with
moderate climate reaching a desired quality; also, the anaerobic digesters are the pre-
