prepared by Jonah S Butler* *Fulbright Scholar, DILG-GTZ Affiliate in Philippines: For Environmental Science Study on Wastewater Treatment. (Email: Jonahsbutler@gmail.com) for Urban Environments in Asia, 25-28 May 2011, Manila, Philippines. organized by International Water Association (IWA).

1. Treatment Performance of Domestic Wastewater in a Tropical
Constructed Wetland: Efficiency and Reuse Potential
Jonah S Butler*
*Fulbright Scholar, DILG-GTZ Affiliate in Philippines: For Environmental Science Study on Wastewater
Treatment.
(Email: Jonahsbutler@gmail.com)
Abstract
This paper assesses performance efficiency of a tropical hybrid-constructed wetland
and discusses the potential for reuse of the treated water in an agricultural setting. The
facility treated wastewater from 3,500 inhabitants (677 houses) of a resettled fishing
community in the Philippines. The system consisted of a vertical (1,770 m2) and a
horizontal (880 m2) subsurface flow cell. Both cells were planted exclusively with a
local variety of Phragmites karka. Samples were collected from the influent, the mid-
point (between the two cells) and the final effluent. The average E. coli and total
coliform reduction was 99.88% or 2.8 log units. On average BOD was reduced
99.4%. Total phosphorous was reduced 77.4%. Total nitrogen reduction was 60%,
which was lowest removal efficiency observed. Effluent bacteria levels were
significantly higher than various irrigation standards for certain crops; potentially
jeopardizing the safety of reuse for gardeners and consumers of those crops. A
preliminary study using a biologically-active sand media filter was assessed for
further bacterial polishing, which showed an average of 99.87% or an additional 2.5
log reduction in E. coli concentrations. Post treatment of bio-sand filtration, final
concentrations of indicator bacteria fell within acceptable ranges of standards for
irrigation waters of all crops. The remaining nutrients in the effluent provided an
inexpensive organic fertilizing irrigation source for the local garden. Rapidly
increasing population combined with lack of proper wastewater treatment in
developing countries is leading to ecosystem degradation and many health problems.
This method of wastewater treatment has shown to be very effective in this climate
and setting; relatively low amounts of energy or maintenance are needed to keep a
consistent performance of treatment.
Keywords
Tropical constructed wetlands; decentralized low-cost wastewater treatment,
wastewater effluent reuse; sustainability
INTRODUCTION
Affordable and efficient methods of wastewater treatment and effluent recycling are
essential to the sustainable growth of developing countries and conservation of natural
water resources; constructed wetlands provide an effective method of treatment that have
many sustainable characteristics. It is estimated that over 1 billion people do not have
access to safe drinking water and over 2.5 billion people do not have adequate sanitation;
this worldwide lack of access to proper sanitation and to safe-drinking water, is
responsible for approximately 3.575 million deaths annually, of which about ~2 million
are mortalities of children (Bartlett, 2003; Prüss-Üstün et al., 2008). The Philippines has
some of the highest population growth in SE Asia, while less than 1% of all cities and
towns have any type of wastewater treatment (Ancheta et al., 2003; UN, 2009;). There is
a great need for efficient wastewater treatment to safeguard the health of local

2. environments and populaces. In tropical climates, constructed wetlands provide effective
wastewater treatment and the ability to generate valuable biomass year round; the low
overall cost and energy demand, and the reuse potential for irrigation make this technique
a sustainable option for developing countries.
Constructed treatment wetlands (CWs) have one primary purpose: to improve water
quality. The processes that occur in constructed wetlands are similar to those in natural
wetlands; these include solar driven plant growth, evapotranspiration, UV degradation
and complex systems involving biological, microbial, biochemical, chemical and physical
interactions taking place within the media, rhizosphere and plants (Vymazal et al., 2006;
Mitsch & Gosselink, 2007). The ability to regulate flow rate, retention time,
plants/planting schemes, along with media types and depths, give constructed wetlands a
higher pollutant removal efficiency than natural wetlands per unit of area (Kadlec &
Knight, 1996). These engineered natural ecosystems have certain ideal characteristics
over conventional treatment methods; passive treatment techniques lowers the treatment
cost through decreased needs for capital, energy, operation and maintenance (Haverson,
2004). The ability to cost effectively and efficiently treat wastewater in many locations,
applications and time spans throughout the world has been proven using constructed
wetlands; the majority of this research has been in the United States and Europe (Kadlec
& Wallace, 2009; Vazmayal, 2011). More recently, CWs in sub-tropical and tropical
regions have been built, studied and shown effectiveness, though the research available is
limited. (Greenway, 2005; Konnerup et al., 2009; Yeh & Wu, 2009). Tropical climates
increase plant and microbial growth and with higher temperatures greater enzymatic
activity is possible; these factors have shown to increase certain removal efficiencies
(Kadlec, 1999; Mitsch & Gosselink, 2007; Katsenovich et al., 2009; Caselles-Osorio et
al., 2011).
Effluent waters from constructed wetlands have shown biological oxygen demand
(BOD), total suspended solids (TSS), and pathogens to be more efficiently removed than
nitrogen or phosphorous (Rousseau et al., 2004; Chen et al., 2006; Zhang et al., 2009).
Incomplete nitrification and denitrification, along with media that has poor phosphorous
sorption capabilities can limit removal efficiency; other processes such as volatilization
and plant uptake do effect the removal but not as significantly (Brix & Arias, 2005;
Vymazal, 2007; Tuncsiper, 2009). The remaining nutrient value of effluent water
provides a potential source of irrigation and fertilizer for agricultural applications
(Lipkow & Münch, 2010). Pathogens and bacteria that remain in effluent water can pose
a threat to the health of farmers and consumers; this increases the need for proper
monitoring and education of the farmers/gardeners in safe handling methods and correct
application technique (WHO, 2006). The land requirements of CWs are greater than
conventional mechanical systems; in many developing areas land prices are relatively
low, while consistent supplies of energy, highly skilled labor, and replacement parts for
complex mechanical systems are less available, supporting the use of low tech options
(Massoud et al., 2009). Constructed wetlands provide a low cost option for wastewater
treatment, while providing a closed loop irrigation and fertilizer source for its users.

3. This study assessed the performance efficiency of a hybrid-constructed wetland, treating
domestic wastewater from a fisherman resettlement village, and the potential of effluent
reuse in local gardens. Both cells in the constructed wetland were studied: the vertical
flow cell, and the horizontal flow cell. Efficiency was assessed by measuring the average
change of biological, physical and chemical parameters, in each cell and as a whole
system. The study examines the effectiveness of a hybrid-constructed wetland in a
tropical setting and the capacity of effluent reuse as a potentially hazardous but valuable
fertilizing irrigation resource for the local community gardeners.
MATERIALS AND METHODS
Site location
This research was conducted in Bayawan City (9° 21′ 49″ N, 122° 48′ 4″ E) on the island
province of Negros Oriental in the Philippines, from December 2008- May 2009. The
climate is tropical and has an average temperature of 28° Celsius, a high relative
humidity and an average annual rainfall of 187cm. The site of study was a fisherman
resettlement village composed of 670 densely clustered homes (in a 7.4 hectare area),
with a population of ~3500 inhabitants. The wastewater of this village first enters
localized septic tanks, and then flows to a centralized settling tank. After settling, a 2hp
centrifugal-pump moves the wastewater to four elevated holding tanks (each with a
holding capacity of 15M3). The influent is gravity fed to the wetland once each day
during the evening. The wetland has been in operation since September 2006.
Wetland Design
The hybrid wetland design consisted two wetland cells: a vertical flow cell (VF) (~1770
m2) and a horizontal flow cell (HF) (~880 m2). During the evening time the influent was
gravity fed through twelve perforated pipes to the VF cell (Figure 1). The water then
flowed to a midway holding area, then distributed to the HF cell and finally collected in
the effluent holding tank (Figure 1). Both cells were planted with Phragmites karka,
locally know as tambo (Lipkow & Münch, 2010). The cells were constructed of concrete
and the total depth of substrate was 0.75 meters; the substrate was composed of 0.6
meters of sand, 0.05 pea sized gravel, and 0.1 meters of gravel. The average daily
treatment was 60 m3. The hydraulic loading rate was calculated to be 226mm d-1. A
study using a fluorescent water tracing dye to determine the total hydraulic retention time
(HRT) was conducted by a local university, and found the retention time to be ~72
hours. The effluent was either pumped to an elevated header tank where the water
gravity fed to the garden irrigation system, or overflowed to an outlet to the sea.
Water Sampling
Grab samples were taken in 3 places, the elevated header tank of the untreated
wastewater influent, the midway point between the vertical flow and horizontal flow cell,
and the final effluent after the horizontal cell (Figure 1). All bacteria samples were
collected in sterile disposable Whirl Bags. All water samples used for chemical and
physical analysis were collected in Nalgene 500ml bottles. Prior to sampling these were
soak-washed with non-ionic, anti-bacterial soap, acid washed and finally triple rinsed

4. with distilled water. All samples were analyzed within 1-12 hours of sampling, if
samples were not analyzed within two hours of sampling they were stored at 4°C.
Figure 1. Arial diagram of wetland: water flow in cells, media and sample points. Adapted from Bayawan
engineering department figure.
Water Analysis
All physical and chemical analytical methods were performed directly from the Hach
(Loveland, CO, USA) Water Analysis Handbook 5th Edition and following standard
techniques for wastewater analysis (APHA, 1999). The biological analyses were
performed according to Blue Water Biosciences (Mississauga, ON, Canada) methods for
E. coli and Total Coliform enumeration. BOD, DO, and pH were measured using, the
Hach HQ40D multi-meter in conjunction with the corresponding probe. pH analysis
used Hach calibration standards and the pHC30101 probe. DO and BOD analysis used
300mL Wheaton glass BOD bottles and the HACH LBOD101 luminescent DO probe.
The biological oxygen demand (BOD5) was analyzed using a 5-day dilution method;
samples were buffered with a solution of distilled water and Hach BOD nutrient buffer
pillows. BOD samples, chemicals reagents and standards were all stored in the WTW TS
606-6/2i refrigerator at 20°C. The TSS was analyzed using Sartorius Stedim Biotech
Glass-Microfiber Discs 55mm for filter media, a 55mm buchner funnel, and a Nalgene
hand vacuum pump. Filter media was dried in a Binder oven at 105°C for 3 hours. The
balance used for all mass analysis was the Denver Instrument SI-234.
All chemical analysis was performed with Hach reagents and standards. Standards were
used with ammonia, total nitrogen, total phosphorous, orthophosphate, nitrate and BOD,
to ensure proper calibration of equipment, and accuracy of methods. Ammonia (NH3-N)
(salicylate method), nitrate (NO3-N) (chromotrophic acid method), nitrite (NO2-N)
(diazotization method), total nitrogen (Total N) ( heated acid persulfate digestion and
chromotrophic acid method), total phosphorous (Total P) (heated acid persulfate
digestion and ascorbic acid method) and orthophosphate (PO43-) (ascorbic acid method)
were all colorimetric methods analyzed with the Hach DR 2800 spectrophotometer.
Pathogen concentrations were determined by examining the indicator bacterial levels of
E. coli and total coliform. The technique used for enumeration analysis was the Blue
Water Biosciences Coliplate 400. Coliplate is a defined substrate technology (DST)
method using x-gal and 4-methylumbelliferyl -D-glucuronide (MUG) substrate for

5. enumeration; flourogenic and chromogenic reactions in 96 wells was used to quantify the
most probable number (MPN) of colony forming-units (cfu) per 100mL sample. Samples
were diluted as necessary using serial dilution techniques and then transferred into the
wells of the plates and incubated for 24-28 hours at 35°C. Total Coliform was analyzed
under natural light, while E. coli samples were analyzed under UV light.
Biologically active slow sand filter construction
A small biologically active slow sand filter was constructed to test for effectiveness of
additional bacterial removal from effluent water. A 200 liter plastic drum (15mm pipe
with attached spigot installed at 5 cm above base) was layered with the following
materials (starting from base to top): 5 cm of ~15mm gravel, 5 cm of ~10mm gravel, 5
cm of ~5mm gravel, and 65cm of beach sand. All materials were triple washed with
effluent water. Filter was “inoculated” by watering filter with effluent water, for one
month as needed to keep media moist but not saturated. After one month, 15L of effluent
water was treated and analyzed for pathogen indicators, pre and post bio-sand filtration.
Statistics
An independent statistician analyzed all statistics. Analysis of variance (ANOVA) and
Student-Newman-Keuls Test was used to determine if the removal between groups
(parameters and cells) was statistically significant; P-values <0.05 were used in all
analyses. SAS software (SAS Institute, Cary, NC, USA) was used to perform statistical
analysis.
3. RESULTS AND DISCUSSION
Sample analysis
During the 6-month sample period the wetland’s performance was analyzed on a weekly
basis. This report gives the analysis of the data averages for the given time span. The
goal was to have the most accurate representation of wetland performance with the time
and resources available. Only two parameters were not sampled for the entire 6-month
period; bacteria analysis was sampled over four months, while TSS was sampled for only
a two-month period. The bacterial analysis period should provide a sufficient amount of
time to give an accurate representation of the wetland performance. The TSS should be
used as a reference point to give a small range of where the Total Suspended Solids
concentrations lie. Overall the system performance has shown significant difference of
all parameters from cell to cell and from influent to effluent; the only exception was NO3-
N removal from mid to effluent.
Parameter Concentrations & Removal efficiency
Overview. The system has show high efficiency in removal of key parameters and
significant removal of all parameters, except for NO2-N and NO3-N where increases
occurred (Table 1). Removal efficiency relates to the percentage of concentration level
reduction, relative to parameter (mgL-1 or cfu mpn /100mL). Total nutrient removal
efficiency was less substantial than removal of biological and physical parameters, but
was still significant (Figure 2). On average the removal rates were 60% or greater.

6. Physical parameters. Significant changes occurred in pH, DO, TSS and BOD5, in the
system as a whole and per cell (Table 1 & 2). The pH changed from slightly basic in the
influent to slightly acidic in the effluent. The dissolved oxygen increased 777% from
influent to effluent. Total suspended solids were reduced 96.8% from influent (Figure 2
& 3). The remaining TSS concentrations of effluent water were well within the
Philippine DENR effluent discharge standards 50 mgL-1 for TSS in recreational and
fishery water class (DENR 34 & 35, 1990).
Table 1. Average (± SD) concentrations of wastewater in wetland cells and removal efficiency of total
system
Figure 2. Average (± SE) concentration of parameters for influent, mid, and effluent sampling locations
Biological oxygen demand. Removal of BOD5 was reduced 99.4% removal (Table 1,
Figure 2 & 3). The high removal efficiency is greater than reported removal rates in
many constructed wetland systems in temperate climates, though comparable to other
wetlands systems in other tropical settings (Solano et al., 2004; Vymazal, 2005; Dan et
al., 2010). Lowered biological activity in colder seasons has been shown to decrease

7. efficiency of BOD5 removal; supporting that higher BOD5 removal rates can occur in
tropical climates (Steer et al., 2002; Zhang et al., 2009). The high efficiency of the BOD5
removal of this system puts the effluent quality well within the DENR effluent discharge
regulation of 30 mgL-1 (DENR 35, 1990).
Nutrients. Total nutrient removal was lowest of all parameters on average; though this
trend was to be expected (Table 1, figure 3-5). Ammonia (NH3-N) removal was greatest
of all nutrients removed, with 99.5% removed from influent to effluent (Table 1). This
very high removal efficiency is greater than the majority of CWs reviewed in literature
(Vymazal et al., 2006; Masi & Martinuzzi 2007; Zhang et al., 2009). The high average
temperature, the large ratio of sand to gravel, and relative oxygen content (oxygen
transfer capacity) of the vertical cell are all likely factors that contributed to the high
NH3-N removal efficiency; these aspects increase the favorability of nitrification to occur
(Tunc,siper, 2009; Vymazal & Kröpfelová, 2011). Nitrite (NO2-N) levels increased
significantly in each sector, and Nitrate (NO3-N) increased significantly from influent to
mid though no significant change was observed from mid to effluent (Table 1 & 2).
Total nitrogen decreased 60% from the influent to effluent; this was the lowest percent
decrease of any parameter that underwent removal in the system. Reviewed literature has
shown similar results for this removal efficiency (Brix et al. 2003). Low total nitrogen
removal is common in many wetlands and is mainly due to incomplete nitrification-
denitrification; this system had excellent nitrification but incomplete denitrification
(Vymazal, 2007).
Table 2. Average changes in parameters from cell to cell and the wetland as a whole. (* denotes increase)
Ortho phosphate (PO4-3) was 78.4%, while total phosphorous removal was 77.4%. The
removal efficiency is comparable to wetland performance in reviewed literature
(Rousseau et al., 2004; Weedon, 2010). In certain wetlands higher phosphorous removal

8. has been obtained with similar design and similar media selection; the use of sand is a
description of media but is very broad since different sand types have shown significantly
different sorption and removal capacities and may be a reason for high variation in total p
removal in various wetlands reviewed in literature (Arias et al., 2001; Dan et al., 2010).
Various media options can be utilized if increased phosphorous removal is necessary
(Park, 2009). During the time of this study the wetland had been in use for 2.5 years, it is
possible that phosphorous removal efficiency will decrease as the media sorption
capacity decreases due to saturation. A multi-year study would be needed to show the
changes in wetland media sorption capacity, and optimal timeframe for media
replacement.
Figure 3. Average removal efficiency of Figure 4. Average removal of parameter in each
parameters: displaying the relative percent wetland cell, % removal refers to specific cell’s
removal of each cell in terms of total % of peformance (VF % =In:Mid ; HF %= Mid-Eff).
concentration per parameter.
Figure 5. Average nitrogen species concentration in sampling points. Influent-Mid displays VF
performance and Mid- Final displays HF Performance
Cell Comparison
Vertical subsurface flow cell. The vertical cell had the greatest efficiency for removing
total nitrogen; on average 49.1% of total nitrogen was removed in this cell. NH3-N made
up 88.7% of the total N. The majority of all nitrification occurred in this cell; 90.9% of
the total NH3-N was removed or transformed and the majority of NO3-N was produced.
Similar trends were observed in reviewed literature that took place in tropical settings.
(Konnerup et al., 2009; Konnerup et al., 2011). There is strong evidence to support that
the removal mechanism for the total nitrogen was through nitrification-denitrification
processes; subtracting the NO3-N produced from the NH3-N removed results in 91.8% of
the total N removed in this cell. Figure 5 displays the decreasing trend of NH3-N and
total N while N03-N increases within this cell; a similar trend was observed in literature
review of Kadlec (1999), which sugguest that conditions were more favorable towards

9. nitrification than denitrification. This trend was to be expected since nitrification is
favorable in aerobic conditions (DO increased 590%), where denitrification occurs more
readily in anoxic or anaerobic environments (Vymazal, 2007). Total P and P04-3 removal
was 54.7% and 53.2% respectively; the percent removal between cells was not
significantly different. Removal of BOD accounted for 88.1% of total BOD in the
system. Reduction of indicator bacterial was significantly less efficient in the VF cell
than the HF cell, 0.8 log (87.72%) vs. 2 log (99.05%) respectively (Table 2). Percent
removal of TSS was not significantly different between cells. Overall this cell removed
the gross concentration of parameters analyzed (Figure 3 & 4).
Horizontal subsurface flow cell. Relative percent removal of BOD was higher in this cell
than the VF, with a 94.9% efficiency (Figure 4). Initial (Mid) NH3-N concentrations were
relatively low in the HF cell 12.3 (± 5.9) mgL-1 though removal was considerably
efficient (95%). Percent removal of total nitrogen was the lowest any parameter that
underwent removal in the in the HF cell, only 21.5% was removed. The minimum
amount of organic matter or C:N ratio (measured by BOD and total N), lack of anaerobic
conditions (measured by DO), and high removal of NH3-N, gives evidence that this cell
did not have optimal conditions important for denitrification processes (Vymazal &
Kröpfelová, 2008). In future designs, if higher denitrification is required, a trench filled
with waste shredded or carbonized wood material, coconut shells, rice hull or other
locally available organic matter could be installed directly after the vertical cell; research
has shown that high denitrification can occur in organic-carbon based media beds which
provide more suitable environmental conditions for denitrification of nitrates (Cameron
& Schipper, 2010; Moorman et al., 2010). An immediate option for increased
denitrification in this wetland, would be recycling the effluent back to the main sump;
recycling of nitrate-rich effluent water back to a septic tank has shown to produce a
favorable environment for denitrification (Arias et al., 2005).
Pathogen removal. Removal rates of pathogen indicator bacteria were highest of all
parameters. E. coli and total coliform had a 2.8 log reduction or 99.88% (Table 1;
Figure 6 ). These removal rates are comparable to other constructed wetlands in
reviewed literature (Laber et al, 1999; Thurston et al., 2001; Steer et. al., 2002;
Ghermandi et al., 2007; Barros et al., 2008). Two studies, Masi & Martinuzzi (2007) &
Laber et al. (1999), showed significantly higher removal rates of 99.93%-99.99% (<3log)
for indicator bacteria of a hybrid wetland with a HF-VF design; the HF-VF design may
provide higher bacterial removal, as the loading rates were also significantly higher than
in the current study. HF cells may be more effective in pathogen removal as the HF cell
in this study showed significantly higher removal efficiency than the VF cell (2 log vs.
0.8 log respectively). The lower bacterial removal efficiency of the CW in this study,
when compared to studies with greater efficacy, could be due to higher bacteria growth
rates in cells as a result of the warmer tropical climate (Thurston et al. 2001; Zdragas et
al., 2002). Higher treatment efficiency of indicator bacteria may be possible with the
selection of smaller sand particle sizes and lower HLR. Sleytr et al. (2007) observed 4.35
log removal of E. coli when using small sand sizes (.006mm-4mm) and a low HLR
(60mm/d) of similar bacterial concentrations in pilot scale VF wetlands; efficiency was
significantly reduced (>2.5 log removal) when larger sand particles (1-4mm) were used

10. with a higher HLR (240mm/d). Due to the concentrated nature of E. coli and total
coliform in influent water, relatively high effluent concentrations were observed, even
though removal efficiencies were very high. The remaining effluent concentrations of
total coliform was significantly lower than DENR standards (3x106 MPN/100mL) for
effluent discharge into receiving waters (DENR 35, 1990).
Reuse potential and human-risk exposure mitigation
The reuse of wastewater effluent provides the ability for a closed loop agricultural
system; the main problem with effluent reuse is the safety concerning farmer’s and
consumer’s health. Effluent standards for pathogen indicator concentrations are not set in
stone; this makes data interpretation a challenge when assessing the optimal application
for reuse. The DENR standards for irrigation of fruit and vegetable crops that may be
eaten raw, is < 500 cfu/100mL fecal coliforms, placing the E. coli effluent concentration
in this study, significantly (1.3 log) above this reuse standard (DENR 35, 1990). The
WHO (2006) described a variation of effluent guidelines for irrigation with wastewater
effluents; the total acceptable removal depended on: the crop being irrigated, the method
of irrigation (e.g. drip irrigation), the farming practices being used and the
implementation and proper education of farmers and consumers using safe handling
techniques (e.g. proper hand and vegetable washing). Salgot et al. (2006) indicated more
solidified ranges of standards for various applications of wastewater effluent reuse; for
irrigation of raw-consumed crops, E. coli should be <1,000 cfu/100mL while not raw-
consumed crops, pastureland, or tree nurseries should have E. coli <10,000 cfu/100mL.
Using any of these standards would clearly indicate that the use of this effluent for raw-
consumed crops is not advisable. Thurston et al. (2001) found that Giardia cysts and
Cryptosporidium oocysts were removed effectively (87.8% & 64.2& respectively) but not
completely in HF CWs. This evidence, coupled with the variation in wetland
performance (assessed by standard deviation of E. coli in effluent), furthers the need for
proper precautionary measures when reusing domestic wastewater effluent. Education of
both farmers and consumers on proper handling, irrigation, and washing techniques to
minimize exposure is important to the success of safe reuse. If the education process is
difficult to perform effectively, further treatment may be necessary to ensure the proper
safety of effluent reuse.
Figure 6. Average (±SD) indicator bacteria removal in wetland cells and biosand filter.
Biologically active slow sand filter

11. The need for further reduction of pathogen indicators in effluent water being reused,
became apparent when education of the community was slow to implement and take
effect. A low cost, low energy, and simple to operate method of filtration was
investigated. Slow sand filtration is a passive filtration method that has been effective in
removing pathogens from contaminated drinking water; minimal technical inputs were
required to bring water quality within acceptable WHO drinking standards (Mahmood et
al., 2011). It was hypothesized that effective additional pathogen removal in wastewater
effluent could be observed through utilization of this low technology treatment method.
A preliminary experiment was conducted to investigate the efficacy of bio-sand filtration
on wastewater effluents. The removal of total coliform and E coli in this precursory trial
was significant (n=5), 99.39% & 99.93% respectively (Figure 6). These removal rates
are comparable the slow sand filters reviewed in literature (Eliot et al., 2008). The final
concentration of E. coli was <30 mpn cfu/100mL while total coliforms were <100 mpn
cfu/100mL, well within the range of all reviewed irrigation guidelines for raw-consumed
crops. More comprehensive pilot-scale and full-scale examinations should be conducted
to prove the effectiveness of this pathogen removal method over a longer term and with a
higher treatment volume.
Sustainability: costs, energy, increasing productivity and community education
Cost and energy use. Economics heavily impact the decision-making process and usually
affect the viability and long-term sustainability of treatment systems in developing
countries. The per-house cost of capital construction was estimated at 340-195USD; GTZ
estimated the total cost was 230,000 USD (including consultancy) while the Bayawan
government estimated the cost at 132,000 USD (no consultancy costs) (Lipkow &
Münch, 2010). Annual operation, maintenance and energy costs were 5,500 USD (4,400
USD for O&M, 1,100 USD for energy); due to the cost of local labor this was
considerably low as there were 3, 8-hour watch duties daily. The annual operational costs
per house were 8.5 USD. Total annual energy consumption for operating two pumps was
estimated at 6,900 kWh or 115 kWh /treated m3 year-1. The annual per house
consumption is 10.2 kWh; a current day comparison of this energy use is ~8 times less
than running a wireless internet router continuously for 1 year. The energy usage for this
wetland is estimated to be about 10 times less than with the energy consumed for a
conventional wastewater treatment system (1179 kWh / treated m3 year-1) reported in
Middlebrooks & Middlebrooks (1979). The low capital, O&M and energy costs make
this treatment option considerably less than conventional methods, and support the
application of sustainable treatment systems in developing countries (Muga & Mehelcic,
2008).
Increased productivity. Increased productivity and cost recovery is important when
usable plant based materials can be harvested and utilized effectively; this potential is
greater in areas where local labor costs are lower. Ideal plant candidates for constructed
wetlands are those that have great production of biomass; selection of tropical plants,
that’s biomass is a valuable material resource, increases the potential for cost recovery.
Sustainable materials produced from wetland plants have a considerable range of
application and value; building materials for native handicrafts, agricultural applications

12. for fodder and soil amendments, and as potential biofuel sources are some examples
where wetland plants have been utilized ( Verma et al., 2007; Koonerup et al., 2009;
Zwane et al., 2011). Optimal selection of macrophytes coupled with the year-round
growth in tropical settings increases the potential for the removal of various parameters;
the ability for substantial removal of can increase with multiple harvests of biomass
annually (Koottatep & Polprasert, 1997; Vymazal, 2005; Greenway, 2006; Katsenovich
et al. 2009; Konnerup et al., 2009). Continued research on optimization of plant selection
and design types in tropical settings is important to fully utilize the potential of these
systems as a treatment method that can produce usable plant materials, water for
irrigation and improve water quality.
CONCLUSIONS
Rapidly increasing population combined with lack of proper wastewater treatment in
developing countries is leading to many health problems and ecosystem degradation;
there is a great need for efficient and affordable methods of wastewater treatment and
water recycling. This study has shown the hybrid constructed wetland provided an
effective option for wastewater treatment in a tropical setting. Reuse of effluent water is
feasible when proper education, irrigation and crop selection is employed. The bacterial
state of the effluent water indicates that irrigation would be ideal for non-raw consumed
crops, tree nurseries, and landscaping. Additional research is needed to prove full-scale
and long-term efficacy of biologically active slow sand filtration as a means of further
pathogen removal for irrigation with domestic wastewater effluent ; however the
preliminary study did show promising results of a low-tech method for further reducing
pathogen indicators. Efficient removal of various parameters, coupled with low-cost and
low energy use, makes this system a sustainable option for wastewater treatment in
developing countries. Future studies are needed to identify plant species that provide
efficient removal combined with a high production of valuable biomass in constructed
wetlands; cost recovery and increased productivity will play an important role to increase
the sustainability of engineered natural ecosystem treatment methods.
ACKNOWLEDGEMENTS
I would like to thank the following organizations for their support in this study: Fulbright
Foundation for fuding, DILG-GTZ for affiliation, and logistical assistance, Bayawan
water department for use of laboratory and lab assistance, CENRO for technical wetland
assistance, Bayawan City Government & Engineering Department for support and use of
facilities. My deepest appreciation goes to the following individuals for their support and
assistance with this project and my academic research : Ulrike Lipkow, Jouke Boorsma,
Dr. Margaret Greenway, Alma Alabastro, Dr. Robert Knight, Dr. Sandra Gilchrist, Dr.
Lee Newman, and Dr. Aaron Ellison. Without their assistance this study would not have
been possible.

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