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treatment technology most used with constructed wetlands (Barros et al. 2008; Ruiz et al.
2010; Manariotis et al. 2008).
Therefore, the aim of this study is to evaluate the performance of an ecological wastewater
treatment system conformed by an upflow anaerobic filter (UAF) followed by a horizontal
subsurface constructed wetland (HSSCW) considering the influence of the hydraulic
retention time (HRT) in the depletion of organic matter and nutrients.
Methodology
The pilot-scale treatment system was built in the installations of the municipal wastewater
treatment plant of Chapala, Jalisco, located in the vicinity of Chapala Lake, the biggest lake
of Mexico. The ecological wastewater treatment system was working with an operation
water flow between 0.05 and 0.1 L/s and it was made up of an UAF followed by a HSSCW.
Both, the UAF and the HSSCW use tezontle as biofilm support. This material has high
porosity and is inexpensive, since it is abundant in this part of México (Zurita et al. 2009).
Moreover, the HSSCW was sown with two plant species; the first half with
Canna hybrids
and the second half with
Strelitzia reginae
at a density of 3 plants/m
2
. Although these
species are not common in this type system, they give a pleasing appearance and it is
reported that they have a good acclimatization and development (Konnerup et al. 2009;
Zurita et al. 2009).
The monitoring time had a duration of 12 months divided in four-month periods in order to
test consecutively three hydraulic resident times (HRTs) of 2, 3 and 4 days, according to
the HSSCW, considering a depth of 0.6m. The samples were taken every week from four
monitoring points along the treatment system: influent (M1), oulet UAF/inlet HSSCW
(M2), middle part of HSSCW (M3) and effluent (M4). The water quality laboratory
parameters carried out were: biochemical oxygen demand of five days (BOD), chemical
oxygen demand (COD), total nitrogen (N
tot
), ammonia nitrogen (NH
3
-N), nitrite (NO
2
),
nitrate (NO
3
) and total phosphorous (P
tot
). Moreover, some parameters were monitored in
situ: pH, temperature, relative humidity and dissolved oxygen (DO). The experiment with
all data was evaluated by means of a nested design with a crossover factor using
Statgraphics Centurion XVI ® with a confidence level of 95%.
Results
The organic matter in terms of BOD and COD (figure 1) had a similar behavior with a
concentration logarithmic decrease. The majority of organic matter was eliminated in the
UAF process (p≤0.05). In addition, it was possible to observe significantly lower values of
DO and pH in sampling point M2 due to anaerobic conditions predominating in the UAF
process. The lowest variations were found between the sample points 3 and 4, due to the
fact that the HSSCW process is represented by both points. The complete ecological
treatment system carried out removals higher than 80% in shorts HRTs.
Nitrogen is incorporated into the system (influent) mainly as N
Org
and NH
3
-N in order to be
incorporated in the nitrogen cycle. The N
Org
in the wastewater is biologically converted to
NH
3
-N by ammonification in aerobic or anaerobic conditions; therefore, in the sample point
