Treatment Performance of Domestic Wastewater in a TropicalConstructed Wetland: Efficiency and Reuse PotentialJonah S Butle...
environments and populaces. In tropical climates, constructed wetlands provide effectivewastewater treatment and the abili...
This study assessed the performance efficiency of a hybrid-constructed wetland, treatingdomestic wastewater from a fisherm...
with distilled water. All samples were analyzed within 1-12 hours of sampling, ifsamples were not analyzed within two hour...
enumeration; flourogenic and chromogenic reactions in 96 wells was used to quantify themost probable number (MPN) of colon...
Physical parameters. Significant changes occurred in pH, DO, TSS and BOD5, in thesystem as a whole and per cell (Table 1 &...
efficiency of BOD5 removal; supporting that higher BOD5 removal rates can occur intropical climates (Steer et al., 2002; Z...
has been obtained with similar design and similar media selection; the use of sand is adescription of media but is very br...
nitrification than denitrification. This trend was to be expected since nitrification isfavorable in aerobic conditions (D...
with a higher HLR (240mm/d). Due to the concentrated nature of E. coli and totalcoliform in influent water, relatively hig...
The need for further reduction of pathogen indicators in effluent water being reused,became apparent when education of the...
for fodder and soil amendments, and as potential biofuel sources are some exampleswhere wetland plants have been utilized ...
ReferencesAPHA-AWWA-WEF. (1999). Standard Methods for the Examination of Water and Wastewater, 20th Ed.,APHA-AWWA-WEF, Was...
Greenway, M. (2006). The Role of Macrophytes in Nutrient Removal Using Constructed Wetlands.In: Environmental Bioremediati...
Muga, H. E., & Mihelcic, J. R. (2008). Sustainability of wastewater treatment technologies. Journ.Environ. Manag., 88, 437...
Sub-Surface Flow. Environmental Pollution 14. Springer New York, New York.Vymazal, J. & Kröpfelová, L. (2009). Removal of ...
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Treatment Performance of Domestic Wastewater in a Tropical Constructed Wetland: Efficiency and Reuse Potential


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

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Treatment Performance of Domestic Wastewater in a Tropical Constructed Wetland: Efficiency and Reuse Potential

  1. 1. Treatment Performance of Domestic Wastewater in a TropicalConstructed Wetland: Efficiency and Reuse PotentialJonah S Butler**Fulbright Scholar, DILG-GTZ Affiliate in Philippines: For Environmental Science Study on WastewaterTreatment.(Email: 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; sustainabilityINTRODUCTIONAffordable and efficient methods of wastewater treatment and effluent recycling areessential to the sustainable growth of developing countries and conservation of naturalwater resources; constructed wetlands provide an effective method of treatment that havemany sustainable characteristics. It is estimated that over 1 billion people do not haveaccess 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, isresponsible for approximately 3.575 million deaths annually, of which about ~2 millionare mortalities of children (Bartlett, 2003; Prüss-Üstün et al., 2008). The Philippines hassome of the highest population growth in SE Asia, while less than 1% of all cities andtowns have any type of wastewater treatment (Ancheta et al., 2003; UN, 2009;). There isa great need for efficient wastewater treatment to safeguard the health of local
  2. 2. environments and populaces. In tropical climates, constructed wetlands provide effectivewastewater treatment and the ability to generate valuable biomass year round; the lowoverall cost and energy demand, and the reuse potential for irrigation make this techniquea sustainable option for developing countries.Constructed treatment wetlands (CWs) have one primary purpose: to improve waterquality. The processes that occur in constructed wetlands are similar to those in naturalwetlands; these include solar driven plant growth, evapotranspiration, UV degradationand complex systems involving biological, microbial, biochemical, chemical and physicalinteractions 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 ahigher pollutant removal efficiency than natural wetlands per unit of area (Kadlec &Knight, 1996). These engineered natural ecosystems have certain ideal characteristicsover conventional treatment methods; passive treatment techniques lowers the treatmentcost 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 constructedwetlands; 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 tropicalregions have been built, studied and shown effectiveness, though the research available islimited. (Greenway, 2005; Konnerup et al., 2009; Yeh & Wu, 2009). Tropical climatesincrease plant and microbial growth and with higher temperatures greater enzymaticactivity is possible; these factors have shown to increase certain removal efficiencies(Kadlec, 1999; Mitsch & Gosselink, 2007; Katsenovich et al., 2009; Caselles-Osorio etal., 2011).Effluent waters from constructed wetlands have shown biological oxygen demand(BOD), total suspended solids (TSS), and pathogens to be more efficiently removed thannitrogen or phosphorous (Rousseau et al., 2004; Chen et al., 2006; Zhang et al., 2009).Incomplete nitrification and denitrification, along with media that has poor phosphoroussorption capabilities can limit removal efficiency; other processes such as volatilizationand plant uptake do effect the removal but not as significantly (Brix & Arias, 2005;Vymazal, 2007; Tuncsiper, 2009). The remaining nutrient value of effluent waterprovides a potential source of irrigation and fertilizer for agricultural applications(Lipkow & Münch, 2010). Pathogens and bacteria that remain in effluent water can posea threat to the health of farmers and consumers; this increases the need for propermonitoring and education of the farmers/gardeners in safe handling methods and correctapplication technique (WHO, 2006). The land requirements of CWs are greater thanconventional mechanical systems; in many developing areas land prices are relativelylow, while consistent supplies of energy, highly skilled labor, and replacement parts forcomplex mechanical systems are less available, supporting the use of low tech options(Massoud et al., 2009). Constructed wetlands provide a low cost option for wastewatertreatment, while providing a closed loop irrigation and fertilizer source for its users.
  3. 3. This study assessed the performance efficiency of a hybrid-constructed wetland, treatingdomestic wastewater from a fisherman resettlement village, and the potential of effluentreuse in local gardens. Both cells in the constructed wetland were studied: the verticalflow cell, and the horizontal flow cell. Efficiency was assessed by measuring the averagechange of biological, physical and chemical parameters, in each cell and as a wholesystem. The study examines the effectiveness of a hybrid-constructed wetland in atropical setting and the capacity of effluent reuse as a potentially hazardous but valuablefertilizing irrigation resource for the local community gardeners.MATERIALS AND METHODSSite locationThis research was conducted in Bayawan City (9° 21′ 49″ N, 122° 48′ 4″ E) on the islandprovince of Negros Oriental in the Philippines, from December 2008- May 2009. Theclimate is tropical and has an average temperature of 28° Celsius, a high relativehumidity and an average annual rainfall of 187cm. The site of study was a fishermanresettlement 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 enterslocalized septic tanks, and then flows to a centralized settling tank. After settling, a 2hpcentrifugal-pump moves the wastewater to four elevated holding tanks (each with aholding capacity of 15M3). The influent is gravity fed to the wetland once each dayduring the evening. The wetland has been in operation since September 2006.Wetland DesignThe hybrid wetland design consisted two wetland cells: a vertical flow cell (VF) (~1770m2) and a horizontal flow cell (HF) (~880 m2). During the evening time the influent wasgravity fed through twelve perforated pipes to the VF cell (Figure 1). The water thenflowed to a midway holding area, then distributed to the HF cell and finally collected inthe effluent holding tank (Figure 1). Both cells were planted with Phragmites karka,locally know as tambo (Lipkow & Münch, 2010). The cells were constructed of concreteand the total depth of substrate was 0.75 meters; the substrate was composed of 0.6meters of sand, 0.05 pea sized gravel, and 0.1 meters of gravel. The average dailytreatment was 60 m3. The hydraulic loading rate was calculated to be 226mm d-1. Astudy 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 ~72hours. The effluent was either pumped to an elevated header tank where the watergravity fed to the garden irrigation system, or overflowed to an outlet to the sea.Water SamplingGrab samples were taken in 3 places, the elevated header tank of the untreatedwastewater 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 werecollected in sterile disposable Whirl Bags. All water samples used for chemical andphysical analysis were collected in Nalgene 500ml bottles. Prior to sampling these weresoak-washed with non-ionic, anti-bacterial soap, acid washed and finally triple rinsed
  4. 4. with distilled water. All samples were analyzed within 1-12 hours of sampling, ifsamples 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 Bayawanengineering department figure.Water AnalysisAll physical and chemical analytical methods were performed directly from the Hach(Loveland, CO, USA) Water Analysis Handbook 5th Edition and following standardtechniques for wastewater analysis (APHA, 1999). The biological analyses wereperformed according to Blue Water Biosciences (Mississauga, ON, Canada) methods forE. coli and Total Coliform enumeration. BOD, DO, and pH were measured using, theHach HQ40D multi-meter in conjunction with the corresponding probe. pH analysisused Hach calibration standards and the pHC30101 probe. DO and BOD analysis used300mL 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 bufferpillows. BOD samples, chemicals reagents and standards were all stored in the WTW TS606-6/2i refrigerator at 20°C. The TSS was analyzed using Sartorius Stedim BiotechGlass-Microfiber Discs 55mm for filter media, a 55mm buchner funnel, and a Nalgenehand vacuum pump. Filter media was dried in a Binder oven at 105°C for 3 hours. Thebalance used for all mass analysis was the Denver Instrument SI-234.All chemical analysis was performed with Hach reagents and standards. Standards wereused 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 andchromotrophic acid method), total phosphorous (Total P) (heated acid persulfatedigestion 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 ofE. coli and total coliform. The technique used for enumeration analysis was the BlueWater Biosciences Coliplate 400. Coliplate is a defined substrate technology (DST)method using x-gal and 4-methylumbelliferyl -D-glucuronide (MUG) substrate for
  5. 5. enumeration; flourogenic and chromogenic reactions in 96 wells was used to quantify themost probable number (MPN) of colony forming-units (cfu) per 100mL sample. Sampleswere diluted as necessary using serial dilution techniques and then transferred into thewells of the plates and incubated for 24-28 hours at 35°C. Total Coliform was analyzedunder natural light, while E. coli samples were analyzed under UV light.Biologically active slow sand filter constructionA small biologically active slow sand filter was constructed to test for effectiveness ofadditional bacterial removal from effluent water. A 200 liter plastic drum (15mm pipewith attached spigot installed at 5 cm above base) was layered with the followingmaterials (starting from base to top): 5 cm of ~15mm gravel, 5 cm of ~10mm gravel, 5cm of ~5mm gravel, and 65cm of beach sand. All materials were triple washed witheffluent water. Filter was “inoculated” by watering filter with effluent water, for onemonth as needed to keep media moist but not saturated. After one month, 15L of effluentwater was treated and analyzed for pathogen indicators, pre and post bio-sand filtration.StatisticsAn independent statistician analyzed all statistics. Analysis of variance (ANOVA) andStudent-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 allanalyses. SAS software (SAS Institute, Cary, NC, USA) was used to perform statisticalanalysis.3. RESULTS AND DISCUSSIONSample analysisDuring the 6-month sample period the wetland’s performance was analyzed on a weeklybasis. This report gives the analysis of the data averages for the given time span. Thegoal was to have the most accurate representation of wetland performance with the timeand resources available. Only two parameters were not sampled for the entire 6-monthperiod; bacteria analysis was sampled over four months, while TSS was sampled for onlya two-month period. The bacterial analysis period should provide a sufficient amount oftime to give an accurate representation of the wetland performance. The TSS should beused as a reference point to give a small range of where the Total Suspended Solidsconcentrations lie. Overall the system performance has shown significant difference ofall parameters from cell to cell and from influent to effluent; the only exception was NO3-N removal from mid to effluent.Parameter Concentrations & Removal efficiencyOverview. The system has show high efficiency in removal of key parameters andsignificant removal of all parameters, except for NO2-N and NO3-N where increasesoccurred (Table 1). Removal efficiency relates to the percentage of concentration levelreduction, relative to parameter (mgL-1 or cfu mpn /100mL). Total nutrient removalefficiency was less substantial than removal of biological and physical parameters, butwas still significant (Figure 2). On average the removal rates were 60% or greater.
  6. 6. Physical parameters. Significant changes occurred in pH, DO, TSS and BOD5, in thesystem as a whole and per cell (Table 1 & 2). The pH changed from slightly basic in theinfluent to slightly acidic in the effluent. The dissolved oxygen increased 777% frominfluent to effluent. Total suspended solids were reduced 96.8% from influent (Figure 2& 3). The remaining TSS concentrations of effluent water were well within thePhilippine DENR effluent discharge standards 50 mgL-1 for TSS in recreational andfishery water class (DENR 34 & 35, 1990).Table 1. Average (± SD) concentrations of wastewater in wetland cells and removal efficiency of totalsystemFigure 2. Average (± SE) concentration of parameters for influent, mid, and effluent sampling locationsBiological 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 inmany constructed wetland systems in temperate climates, though comparable to otherwetlands systems in other tropical settings (Solano et al., 2004; Vymazal, 2005; Dan etal., 2010). Lowered biological activity in colder seasons has been shown to decrease
  7. 7. efficiency of BOD5 removal; supporting that higher BOD5 removal rates can occur intropical climates (Steer et al., 2002; Zhang et al., 2009). The high efficiency of the BOD5removal of this system puts the effluent quality well within the DENR effluent dischargeregulation of 30 mgL-1 (DENR 35, 1990).Nutrients. Total nutrient removal was lowest of all parameters on average; though thistrend was to be expected (Table 1, figure 3-5). Ammonia (NH3-N) removal was greatestof all nutrients removed, with 99.5% removed from influent to effluent (Table 1). Thisvery 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 averagetemperature, the large ratio of sand to gravel, and relative oxygen content (oxygentransfer capacity) of the vertical cell are all likely factors that contributed to the highNH3-N removal efficiency; these aspects increase the favorability of nitrification to occur(Tunc,siper, 2009; Vymazal & Kröpfelová, 2011). Nitrite (NO2-N) levels increasedsignificantly in each sector, and Nitrate (NO3-N) increased significantly from influent tomid 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 percentdecrease of any parameter that underwent removal in the system. Reviewed literature hasshown similar results for this removal efficiency (Brix et al. 2003). Low total nitrogenremoval 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%. Theremoval efficiency is comparable to wetland performance in reviewed literature(Rousseau et al., 2004; Weedon, 2010). In certain wetlands higher phosphorous removal
  8. 8. has been obtained with similar design and similar media selection; the use of sand is adescription of media but is very broad since different sand types have shown significantlydifferent sorption and removal capacities and may be a reason for high variation in total premoval 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 ispossible that phosphorous removal efficiency will decrease as the media sorptioncapacity decreases due to saturation. A multi-year study would be needed to show thechanges in wetland media sorption capacity, and optimal timeframe for mediareplacement. 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 VFperformance and Mid- Final displays HF PerformanceCell ComparisonVertical subsurface flow cell. The vertical cell had the greatest efficiency for removingtotal nitrogen; on average 49.1% of total nitrogen was removed in this cell. NH3-N madeup 88.7% of the total N. The majority of all nitrification occurred in this cell; 90.9% ofthe 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 thatthe removal mechanism for the total nitrogen was through nitrification-denitrificationprocesses; subtracting the NO3-N produced from the NH3-N removed results in 91.8% ofthe total N removed in this cell. Figure 5 displays the decreasing trend of NH3-N andtotal N while N03-N increases within this cell; a similar trend was observed in literaturereview of Kadlec (1999), which sugguest that conditions were more favorable towards
  9. 9. nitrification than denitrification. This trend was to be expected since nitrification isfavorable in aerobic conditions (DO increased 590%), where denitrification occurs morereadily in anoxic or anaerobic environments (Vymazal, 2007). Total P and P04-3 removalwas 54.7% and 53.2% respectively; the percent removal between cells was notsignificantly different. Removal of BOD accounted for 88.1% of total BOD in thesystem. Reduction of indicator bacterial was significantly less efficient in the VF cellthan the HF cell, 0.8 log (87.72%) vs. 2 log (99.05%) respectively (Table 2). Percentremoval of TSS was not significantly different between cells. Overall this cell removedthe gross concentration of parameters analyzed (Figure 3 & 4).Horizontal subsurface flow cell. Relative percent removal of BOD was higher in this cellthan the VF, with a 94.9% efficiency (Figure 4). Initial (Mid) NH3-N concentrations wererelatively low in the HF cell 12.3 (± 5.9) mgL-1 though removal was considerablyefficient (95%). Percent removal of total nitrogen was the lowest any parameter thatunderwent removal in the in the HF cell, only 21.5% was removed. The minimumamount of organic matter or C:N ratio (measured by BOD and total N), lack of anaerobicconditions (measured by DO), and high removal of NH3-N, gives evidence that this celldid not have optimal conditions important for denitrification processes (Vymazal &Kröpfelová, 2008). In future designs, if higher denitrification is required, a trench filledwith waste shredded or carbonized wood material, coconut shells, rice hull or otherlocally available organic matter could be installed directly after the vertical cell; researchhas shown that high denitrification can occur in organic-carbon based media beds whichprovide more suitable environmental conditions for denitrification of nitrates (Cameron& Schipper, 2010; Moorman et al., 2010). An immediate option for increaseddenitrification 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 afavorable environment for denitrification (Arias et al., 2005).Pathogen removal. Removal rates of pathogen indicator bacteria were highest of allparameters. 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 inreviewed 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 mayprovide higher bacterial removal, as the loading rates were also significantly higher thanin the current study. HF cells may be more effective in pathogen removal as the HF cellin 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 growthrates in cells as a result of the warmer tropical climate (Thurston et al. 2001; Zdragas etal., 2002). Higher treatment efficiency of indicator bacteria may be possible with theselection of smaller sand particle sizes and lower HLR. Sleytr et al. (2007) observed 4.35log 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 wassignificantly reduced (>2.5 log removal) when larger sand particles (1-4mm) were used
  10. 10. with a higher HLR (240mm/d). Due to the concentrated nature of E. coli and totalcoliform in influent water, relatively high effluent concentrations were observed, eventhough removal efficiencies were very high. The remaining effluent concentrations oftotal coliform was significantly lower than DENR standards (3x106 MPN/100mL) foreffluent discharge into receiving waters (DENR 35, 1990).Reuse potential and human-risk exposure mitigationThe reuse of wastewater effluent provides the ability for a closed loop agriculturalsystem; the main problem with effluent reuse is the safety concerning farmer’s andconsumer’s health. Effluent standards for pathogen indicator concentrations are not set instone; this makes data interpretation a challenge when assessing the optimal applicationfor reuse. The DENR standards for irrigation of fruit and vegetable crops that may beeaten raw, is < 500 cfu/100mL fecal coliforms, placing the E. coli effluent concentrationin this study, significantly (1.3 log) above this reuse standard (DENR 35, 1990). TheWHO (2006) described a variation of effluent guidelines for irrigation with wastewatereffluents; the total acceptable removal depended on: the crop being irrigated, the methodof irrigation (e.g. drip irrigation), the farming practices being used and theimplementation and proper education of farmers and consumers using safe handlingtechniques (e.g. proper hand and vegetable washing). Salgot et al. (2006) indicated moresolidified ranges of standards for various applications of wastewater effluent reuse; forirrigation 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 andCryptosporidium oocysts were removed effectively (87.8% & 64.2& respectively) but notcompletely in HF CWs. This evidence, coupled with the variation in wetlandperformance (assessed by standard deviation of E. coli in effluent), furthers the need forproper precautionary measures when reusing domestic wastewater effluent. Education ofboth farmers and consumers on proper handling, irrigation, and washing techniques tominimize exposure is important to the success of safe reuse. If the education process isdifficult to perform effectively, further treatment may be necessary to ensure the propersafety of effluent reuse.Figure 6. Average (±SD) indicator bacteria removal in wetland cells and biosand filter.Biologically active slow sand filter
  11. 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 takeeffect. A low cost, low energy, and simple to operate method of filtration wasinvestigated. Slow sand filtration is a passive filtration method that has been effective inremoving pathogens from contaminated drinking water; minimal technical inputs wererequired to bring water quality within acceptable WHO drinking standards (Mahmood etal., 2011). It was hypothesized that effective additional pathogen removal in wastewatereffluent could be observed through utilization of this low technology treatment method.A preliminary experiment was conducted to investigate the efficacy of bio-sand filtrationon wastewater effluents. The removal of total coliform and E coli in this precursory trialwas significant (n=5), 99.39% & 99.93% respectively (Figure 6). These removal ratesare comparable the slow sand filters reviewed in literature (Eliot et al., 2008). The finalconcentration of E. coli was <30 mpn cfu/100mL while total coliforms were <100 mpncfu/100mL, well within the range of all reviewed irrigation guidelines for raw-consumedcrops. More comprehensive pilot-scale and full-scale examinations should be conductedto prove the effectiveness of this pathogen removal method over a longer term and with ahigher treatment volume.Sustainability: costs, energy, increasing productivity and community educationCost and energy use. Economics heavily impact the decision-making process and usuallyaffect the viability and long-term sustainability of treatment systems in developingcountries. The per-house cost of capital construction was estimated at 340-195USD; GTZestimated the total cost was 230,000 USD (including consultancy) while the Bayawangovernment estimated the cost at 132,000 USD (no consultancy costs) (Lipkow &Münch, 2010). Annual operation, maintenance and energy costs were 5,500 USD (4,400USD for O&M, 1,100 USD for energy); due to the cost of local labor this wasconsiderably low as there were 3, 8-hour watch duties daily. The annual operational costsper house were 8.5 USD. Total annual energy consumption for operating two pumps wasestimated at 6,900 kWh or 115 kWh /treated m3 year-1. The annual per houseconsumption is 10.2 kWh; a current day comparison of this energy use is ~8 times lessthan running a wireless internet router continuously for 1 year. The energy usage for thiswetland is estimated to be about 10 times less than with the energy consumed for aconventional wastewater treatment system (1179 kWh / treated m3 year-1) reported inMiddlebrooks & Middlebrooks (1979). The low capital, O&M and energy costs makethis treatment option considerably less than conventional methods, and support theapplication of sustainable treatment systems in developing countries (Muga & Mehelcic,2008).Increased productivity. Increased productivity and cost recovery is important whenusable plant based materials can be harvested and utilized effectively; this potential isgreater in areas where local labor costs are lower. Ideal plant candidates for constructedwetlands 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 ofapplication and value; building materials for native handicrafts, agricultural applications
  12. 12. for fodder and soil amendments, and as potential biofuel sources are some exampleswhere 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-roundgrowth in tropical settings increases the potential for the removal of various parameters;the ability for substantial removal of can increase with multiple harvests of biomassannually (Koottatep & Polprasert, 1997; Vymazal, 2005; Greenway, 2006; Katsenovichet al. 2009; Konnerup et al., 2009). Continued research on optimization of plant selectionand design types in tropical settings is important to fully utilize the potential of thesesystems as a treatment method that can produce usable plant materials, water forirrigation and improve water quality.CONCLUSIONSRapidly increasing population combined with lack of proper wastewater treatment indeveloping countries is leading to many health problems and ecosystem degradation;there is a great need for efficient and affordable methods of wastewater treatment andwater recycling. This study has shown the hybrid constructed wetland provided aneffective option for wastewater treatment in a tropical setting. Reuse of effluent water isfeasible when proper education, irrigation and crop selection is employed. The bacterialstate of the effluent water indicates that irrigation would be ideal for non-raw consumedcrops, tree nurseries, and landscaping. Additional research is needed to prove full-scaleand long-term efficacy of biologically active slow sand filtration as a means of furtherpathogen removal for irrigation with domestic wastewater effluent ; however thepreliminary study did show promising results of a low-tech method for further reducingpathogen indicators. Efficient removal of various parameters, coupled with low-cost andlow energy use, makes this system a sustainable option for wastewater treatment indeveloping countries. Future studies are needed to identify plant species that provideefficient removal combined with a high production of valuable biomass in constructedwetlands; cost recovery and increased productivity will play an important role to increasethe sustainability of engineered natural ecosystem treatment methods.ACKNOWLEDGEMENTSI would like to thank the following organizations for their support in this study: FulbrightFoundation for fuding, DILG-GTZ for affiliation, and logistical assistance, Bayawanwater department for use of laboratory and lab assistance, CENRO for technical wetlandassistance, Bayawan City Government & Engineering Department for support and use offacilities. My deepest appreciation goes to the following individuals for their support andassistance 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 havebeen possible.
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