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The ability of free water surface constructed wetland system to treat high strength domestic wastewater: A case study for the Mediterranean
Ecological Engineering 44 (2012) 278–284
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Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
The ability of free water surface constructed wetland system to treat high strength domestic wastewater: A case study for the Mediterranean Kemal Gunes a,∗ , Bilal Tuncsiper b , Selma Ayaz a , Aleksandra Drizo c a
TUBITAK Marmara Research Center, Environment Institute, P.O. Box 21, Gebze 41470, Kocaeli, Turkey Ni˘gde University, Faculty of Engineering-Architecture, Environmental Engineering Department, Ni˘gde, Turkey c University of Vermont, College of Agriculture and Life Sciences, Department of Plant and Soil Science, 63 Jeffords Building, Burlington 05405 VT, USA b
a r t i c l e
i n f o
Article history: Received 7 November 2011 Received in revised form 22 March 2012 Accepted 2 April 2012 Available online 3 May 2012 Keywords: Constructed wetlands Natural wastewater treatment Domestic wastewater treatment Catchment management
a b s t r a c t This study evaluates a full-scale free water surface flow-constructed wetland (FWS-CW) system that was developed in 2005 to treat high strength wastewater in Garip village near Lake E˘girdir in the Mediterranean (Turkey). This FWS-CW was the one of the first full-scale wastewater treatment systems of this type in Turkey and the Mediterranean, and as such represents an important reference for the application of CW systems in other regions with similar climates. This FWS-CW system consists of two stages, the first one being comprised of a 3-compartment septic system with the second one comprised of the FWS CW. The treatment efficiency of the system was found to be significantly affected by the pollutant loading rates, hydraulic retention time and temperature. Long term monitoring revealed that the system removed approximately 86%, 92%, 56% and 43% of the total suspended solids (TSS), biochemical oxygen demand (BOD), total nitrogen (TN), and total phosphorus (TP) from the high strength domestic wastewater, respectively. Therefore, this type of FWS can be applied as economical, environment-sensitive and very efficient for TSS and BOD for treating high strength domestic wastewaters. Alternative measures for improving TN and TP are discussed. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The Mediterranean Sea covers 2,500,000 km2 with the coastline extending 46,000 km running through 22 countries. Today about 82 million people live in coastal cities, with an estimated increase to 150–170 million by 2025 (Danovaro, 2003). The United Nations Environment Program estimated that 650 million tons of sewage and 36,000 tons of phosphates are discharged into the Mediterranean Sea each year, of which approximately 70% untreated (UNEP, 2007). Consequently, like in many other areas in the world, eutrophication of Mediterranean Sea has become a water quality issue of increasing concern (Gabrielides, 1995; Bianchia and Morri, 2000; Danovaro, 2003). Phosphorus (P) pollution and subsequent eutrophication of watercourses has been recognized as the one of the most pressing water quality issues worldwide, given the fact that addition of just 1 g of phosphate phosphorus (PO4 -P) promotes the growth of up to 100 g algae (Khan and Ansari, 2005; U.S. EPA, 2010; Putz, 2008). The critical concentrations for incipient eutrophication are about
∗ Corresponding author. Tel.: +90 262 677 29 55; fax: +90 262 641 23 09. E-mail addresses: [email protected], [email protected] (K. Gunes). 0925-8574/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecoleng.2012.04.008
0.1–0.2 mg l−1 PO4-P in running water and 0.005–0.01 mg l−1 PO4 P in still water (Khan and Ansari, 2005; Putz, 2008). Thus, in view of the potential hazard to surface waters, the EU Directive 91/271/EEC established limit values for the discharge of phosphate compounds for municipal sewage treatment plants into receiving waters 20 years ago (1991), and has been revisited and amended in 2003 and 2008. Depending on the size of the sewage treatment plant, the specific limit values are currently set at 2 mg l−1 TP (10,000–100,000 PE) and 1 mg l−1 TP (>100,000 PE) (UWWT Directive, 2012). With the global population expansion, the need for finding new, low cost and maintenance, energy efficient domestic wastewater treatment solutions for rural communities has become emerging priority among wastewater engineers and scientist. Over the past 20 years, constructed wetlands (CW) have been developed and accepted as a wastewater management practice for treatment of variety of wastewater effluents across the globe (Kadlec and Knight, 1996; Vymazal, 2010). 1.1. Constructed wetlands development in Turkey To date, most studies evaluating the use of CW for wastewater treatment in Turkey have been pilot-scale. The first experimental studies were the CWsystems established in TUBITAK Marmara Research Center (MRC) campus, located in Gebze-Kocaeli in 1995.
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Fig. 1. Studied area (lake Egirdir and its basin).
In 2003, a collaborative program developed between the Istanbul Technical University (ITU) and TUBITAK MRC enabled the establishment of 3 pilot facilities (PF) in Pasakoy Waste Water Treatment Facility belonging to Istanbul Water Sewerage Administration (ISKI). The PFs were fed by tertiary effluents, each having a surface ∼100 m2 . The first PF employed subsurface flow (SSF) and was vegetated with Cyperus. The second PF, was a floating system vegetated with Lemma minor while the third PF was built as free water surface (FWS) system and also vegetated with Cyperus (Ayaz and Akc¸a, 2000). Another pilot scale CW was constructed for treatment of domestic wastewater at the campus of Middle East Technical University (METU). This CW consisted of two CW units with vertical flow (each covering surface area of 30 m2 ) connected in series (Korkusuz et al., 2005). Following these pilot scale CW investigations, several fullscale CW were built since 2004. Turkish General Directorate of Rural Affairs initiated the campaign of founding natural treatment sewage treatment facilities in which resulted in construction of CWs in Ankara–Haymana–Dikilitas village and in Muratbagi village of Kovancilar county; The Turkish Ministry of Agriculture and Rural Affairs established the “Natural Treatment Project” in Korucuk village, Izmir region; and the Governorship of Afyon for the improvement of Akarcay funded the CW system which was built in Afyon. More recent full scale CWs include a newly developed, the first of its kind, combined natural wastewater treatment system in the Village of Ileydagi (population of 313) situated in the reservoir of Lake Egirdir which is the second largest fresh water lake in Turkey (Gunes and Tuncsiper, 2009). The system described in this paper represents the first full scale FWS CW built in Turkey for treatment of high strength domestic wastewater. Because this is the first system of its type in the region, this study was conducted to determine if such systems provide an economical and environment-friendly solution for the treatment of wastewater in Turkey.
Therefore, the main objective of this study was to investigate economic viability and sewage treatment efficiency of a free surface flow constructed wetland (FWS CW) system and its potential applications in other Mediterranean regions. Another objective of the study was to investigate the effects of various pollutant loading rates on the system treatment performance. The results of this study revealed that this type of CW have a potential to be used as the base for the future operational and design optimization of the FWS-CWs in the areas with similar climates. 2. Material and methods 2.1. Description of the study area Garip village is located at the Lake E˘girdir, the second largest freshwater lake in Turkey, situated in the Mediteeranean region. Since 2000, 5 projects were carried out to mitigate point and nonpoint sources of pollution within the Lake E˘girdir catchment area. The village has an existing population of approximately 625 that is expected to reach 868 by 2030 (Fig. 1). The climate in Lake Egirdir basin, is between the Mediterranean and the Middle Anatolian territorial climate (Ugurlu et al., 1999). Therefore, the winters are severe and rainy while the summers are hot and partly dry. In addition, the region is under the influence of the northern and southern winds nearly all year round (Ugurlu et al., 1999). The average annual precipitation is 581 mm, the average temperature is 12 ◦ C, the average humidity is 61%, and the average evaporation is 1222 mm (Gunes et al., 2001). 2.2. Sampling and analysis According to the waste water flow measurement of the settlement unit used in this system, the amount of wastewater being
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Fig. 2. Schematic layout of the experimental system.
treated was approximately 74 l/person/day resulting in the total wastewater daily flow of 462 m3 d−1 . Samples were collected from 3 different points including the septic system inlet, septic system outlet and the constructed wetland outlet over a period of 12 months. All samples were fixed and then stored at 4 ◦ C until being transported to the laboratory. All analyses were performed according to the Standard Methods (APHA, 1998).
Table 1 Characteristics of raw wastewater.
2.3. FWS-CW system design The FWS-CW system is comprised of a 3-compartment septic system and 3-stage FWS (Fig. 2). The septic system is 9.0 m × 3.0 m × 3.0 m (L × W × H) with an effective volume of 67.5 m3 , resulting in the hydraulic residence time (HRT) of the septic system of 1.4 days. This system was designed to decrease the solid material load entering the constructed wetland. Treatment area needed per person of the FWS system for future population is 3.2 m2 /person, however the current treatment area is 4.5 m2 /person. The system consists of 3 stages covering total surface area of 2840 m2 . The first stage (22.1 m × 52.4 m, L × W) was built to provide the sedimentation and flocculation functions (USEPA, 2000). The second stage (10.0 m × 52.4 m), is an open water surface algae system, however, submerged macrophytes were also planted to provide aeration (or oxygen) to the water column and increase nitrification. The third stage (22.1 m × 52.4 m, L × W) was designed as macrophytes (Typha latifolia L.) to further remove pathogens, metals and suspended solid materials through sedimentation and denitrification. The first and the third stages both have a depth of 0.75 m and are vegetated with T. latifolia L [Such design resulted in a total HRT of 29.1 days. The FWS-CW described in this study was designed based on the most up to date CW guidelines, and constructed in the field as a full scale treatment system with the objective to treat highly concentrated wastewater from a
Parameter
Mean
Standard deviation
Range
a Temperature (◦ C) pH Dissolved oxygen (mg l−1 ) TSS (mg l−1 ) BOD (mg l−1 ) COD (mg l−1 ) TN (mg l−1 ) TP (mg l−1 )
11.8 6.4 13.8 222 352 728 42.2 7.6
5.9 0.3 4.9 50 23 92 4.6 1.5
4.2–23.5 5.8–6.7 7.2–23.5 124–310 318–397 596–786 35.5–50.6 5.0–10.5
a
Temperature (◦ C) is 7.2 in winter, and 15.5 in summer as average.
village population. For this reason, a parallel study was not performed for control or comparison. The system comprises actual data from the full scale system like other studies (Reilly et al., 1999; Song et al., 2006; Zhang et al., 2010)]. 2.4. Wastewater characteristics According to the typical composition of the domestic wastewaters (Tchobanoglous and Burton, 1991) the wastewater treated in the FWS system is high strength domestic wastewater (Table 1). This is because the wastewater contains partial wastewaters from stock farming in addition to the domestic wastewaters generated by the village population. Characteristics of raw wastewater are given in Table 1. 3. Results and discussion 3.1. FWS-CW treatment performance The results of the twelve months water quality monitoring, including influent and effluent pollutant concentrations and
Table 2 The FWS average influent and effluent concentrations and percentage reductions achieved. Water quality parameters
Septic S. influent
Septic S. effluent e.g. FWS influent wetland influent
FWS effluent
Septic S. red effluent (%)
FWS red effluent (%)
Total system effluent (%)
TSS (mg l−1 ) COD (mg l−1 ) BOD (mg l−1 ) TN (mg l−1 ) TP (mg l−1 )
222 728 352 42 7.6
92 616 292 36 6.6
31 61 30 18 4.3
58.6 15.4 17.0 14.3 13.2
66.30 90.10 89.7 50.0 34.8
86.0 91.6 91.5 57.1 43.4
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Fig. 3. Change in septic and FWS-CW system performances during the summer and winter periods.
reduction efficiencies achieved by each FWS treatment system stage are presented in Table 2. The septic system alone achieved 60% reduction in TSS, however its performance in reducing other pollutants was poor, ranging from 13.6% (TP) to 17% (BOD). The FWS system alone achieved an average TSS reduction of 66%, very high efficiency in both COD and BOD reduction (about 90%), while its performance in nutrients removal was poor (50% for TN and 34.8% for TP). However, the combined septic system and FWS CW system achieved 86% reduction in TSS, and 91% reduction in BOD and COD (Table 2). In addition it achieved an average of 57% TN and 43% of TP, with removed load ranging between
0.17–0.34 g N m−2 d−1 and 0.02–0.06 g P m−2 d−1 , respectively. The combined wetland systems with pretreatment conducting partial nitrification and partial denitrification will be more effective in summer, leading to less ammonia and less nitrate in the warmer months (Kadlec and Wallace, 2009). The results suggest that in this study, TN removal was achieved through denitrification in septic system and mostly nitrification and partial denitrification in FWS system. In addition, nitrogen reduction could have also been associated with the vegetation and microbial uptake which are well established mechanisms of N removal in CW (Kadlec and Wallace, 2009).
Fig. 4. Average pollutant reductions achieved for different hydraulic residence times (HRT) employed.
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Fig. 5. Removal rates (in g m−2 d−1 ) versus loading rates of CW system.
Treatment efficiencies found in this system are in accordance with the TSS, BOD, TN and TP single-stage CW systems reductions reported by other researchers (Kadlec and Knight, 1996; Meahlum and Stalnacke, 1999; Vymazal, 2005, 2010). It has been well established that considerably high TSS and BOD reductions are achievable by CW, while TN and TP are significantly lower and highly variable. Vymazal (2005) reported that depending on inflow loading, TN and TP could be removed in the range of 40–50%, and 40–60%, respectively, with removed load ranging between 0.68–1.72 g N m−2 d−1 and 0.12–0.20 g P m−2 d−1 . Although the regulatory framework currently does not require P reduction from domestic residential wastewaters neither in the EU nor in the US (Bird and Drizo, 2010; Johansson Westholm et al., 2010; Drizo, 2012), given the extent of eutrophication across the world, improving CW TP removal efficiencies remains one of the major scientific and research questions among CW scientists (IWA, 2010). Since early 1990s, numerous natural and industrial by products have been tested as potential P adsorbing materials in laboratories across the world (e.g. Drizo et al., 2002; Johansson Westholm, 2006; Vohlaa et al., 2011), however to date, very few full scale systems have been implemented (Johansson Westholm et al., 2010). Following research on adsorbing materials, Brix (2007) and co-researchers suggested traditional chemical P-precipitation in sedimentation tank as the way to enhance P removal in CW. Following over 15 years of research, Drizo and Picard (2010) recently developed PhosphoReducTM custom designed systems capable of removing TP to over 90%, consisting of one or more filter units filled with iron and/or calcium based filtration materials, that can be easily incorporated as an add on units to CW and other onsite filtration systems (Drizo and Picard, 2010; Drizo, 2012).
3.2. Statistical analysis In order to determine the distribution analyses of the average removal percentages of systems in summer and winter periods, a K–S (Kolmogorov–Smirnov) Test was conducted. Test results demonstrated a normal distribution at p < 0.05 significance level for all of the investigated water quality parameters (Fig. 3). TP change intervals were higher and less homogenous compared to other pollutants. The variance analysis (ANOVA one-way) revealed that all pollutants were affected by the temperature. F values varied between 400 and 2000 for TSS, BOD and TN, while p values vary between 6 × 10−27 and 6 × 10−18 . The fact that F value obtained for P was so close to Fc (critical F value) value and that the p value almost approached 0.05 significance value suggests that temperature had lesser effect on TP removal compared to other investigated pollutants (F = 14, Fc = 4.2, p = 0.0003). With the exception of TP, the average removal efficiency was found to be higher during the summer periods, with the removal efficiency of BOD and TN being approximately 3% higher on average, and the TSS removal being 10% higher in the septic system during this period. However, TP removal in septic system was higher during winter than in summer months, which can be attributed to the fact that phosphorus loading was significantly lower during winter months. The findings from our study are in agreement with Kadlec and Knight (1996) and Meahlum and Stalnacke (1999) who have reported that the differences between CW removal efficiencies during summer and winter seasons are very low (<10). The ability of the wetland system evaluated in this study to remove TP was nearly the same (about 34%) during summer and winter seasons. Conversely, the TSS, BOD, and TN removal efficiencies were approximately
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4% higher during summer compared to winter performance. Such differences may have occurred as a result of different biological activities of the microorganisms in response to different temperatures. It has been well established that the biological activity decreases during cold seasons, whereas the activity increases in response to increasing temperature and biomass, which results in a higher removal of organic material and nitrogen (Steinmann et al., 2003).
3.3. The effects of hydraulic residence time (HRT) Hydraulic residence times (HRTs) measured in this study were higher that the optimum hydraulic retention times of 4–15 days reported for the FWS-CWs (Tchobanoglous and Burton, 1991; Knight et al., 1993; ITRC, 2003). The FWS performance was evaluated in response to 4 different hydraulic retention times (25, 28, 31 and 35 days). We selected higher HRTs in order to test the effects of longer HRT on organic matter and Nitrogen removal efficiencies. The results showed that the optimal removal efficiencies were achieved at 30 days HRT of 30 days without further increase in the removal efficiency above this HRT (Fig. 4). After a period of 30 days, change intervals of average removal increased while the homogeneity decreased. Statistical analyses revealed that there were significant differences between TSS, BOD and TN removal efficiencies achieved at different HRTs, (F > Fc and p < 0.05 for TSS, BOD and TN; F = 4.59 < Fc = 4.2) with the exception of P, which did not seem to be affected by the difference in HRTs investigated in this study (p = 0.063 > 0.05). These results are similar to those that have been reported in previous studies (Tunc¸siper, 2007; Tunc¸siper et al., 2005, 2006).
3.4. The effects of pollutants loading rates Variance analyses showed significant relations between the influent and the effluent pollutants loading rates. TN and TP had higher F (>150) and lower p (<0.05) values compared to TSS and BOD, suggesting that influent loading rates had greater effect on these pollutants removal efficiencies compared to TSS and BOD (Fig. 5). Overall, the average BOD and TSS removal rates increased linearly with the increase in loading rates (R2 > 0.92) (Fig. 5). It has been shown that the best relationship between TN removal rate and loading rate is a 2nd degree polynomial relationship (R2 : 0.98). These relationships are in accordance with other data reported in the literature (Kadlec and Wallace, 2009). The median net period-of-record removal rate for 116 FWS systems receiving more than 5 mg l−1 was reported as 0.354 g m2 d−1 (129 g m2 yr−1 ) while in this study, the median removal rate of FWS system was 0.311 g m2 d−1 (Kadlec and Wallace, 2009). TN removal rates increased linearly until a 0.6 g m−2 d−1 TN loading rate was attained, with the further TN addition resulting in removal efficiency decrease. The relationship between the TP influent loading and FWS removal rates were generally poor, exhibiting logarithmic trend. The results of this study are in accordance with the previous studies conducted to evaluate changes in TN and TP removal efficiencies in response to different loading rates (Kadlec and Knight, 1996; Headley et al., 2000; Coveney et al., 2000). In addition, the analyses of variance conducted here revealed that there is a significant relationship between loading rates and removal rates (p < 0.05), with the best relationship being found for TN (F: 203.5 > Fc: 4.17).
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4. Conclusions • The average removal efficiencies of a FWS CW system consisting of a septic system and a free surface CW were high for TSS and BOD (approximately 86% and 92%, respectively) and low for TN and TP (56% and 43%, respectively, confirming the need for further improvements in CW design in order to achieve higher TP reductions. • The results of this study provide further evidence that the most important factors to be considered in designing CW for high strength sewage effluents treatment are pollutant loading rates, hydraulic residence times and temperature. • Phosphorus removal efficiencies can be further increased by incorporation of phosphorus adsorbing materials either as a CW substrate or as independent treatment unit (Drizo and Picard, 2010). • We suggest that the number of large-scale systems in regions with similar climates should be implemented and a data network established. The implementation of large-scale systems especially designed to achieve high P reductions from high strength effluents would provide a baseline for a comprehensive nutrients reduction assessment via innovative designs in Turkey and across Mediterranean region. Acknowledgements The authors would like to thank to TUBITAK Marmara Research Center and the Governorship of Isparta for their financial support and encouragement. References APHA, 1998. Standard Methods for the Examination of Water and Wastewater, 20th ed. APHA, Washington, USA. Ayaz, C¸.S., Akc¸a, L., 2000. Treatment of wastewater by constructed wetland in small settlements. Water Sci. Technol. 41, 69–72. Bianchia, C.N., Morri, C., 2000. Marine biodiversity of the Mediterranean Sea: situation, problems and prospects for future research. Mar. Pollut. Bull. 40 (5), 367–376. Bird, S., Drizo, A., 2010. EAF steel slag filters for phosphorus removal from milk parlor effluent: the effects of solids loading, alternate feeding regimes and in-series design. Water 2 (3), 484–499, http://dx.doi.org/10.3390/w2030484. Brix, H., 2007. Types and applications of constructed wetland systems – recent developments. In: Proceedings of the SmallWat 2007, 2nd International Congress on Wastewater Treatment in Small Communities, held in Seville, Spain, November 11–15th. Coveney, M.F., Lowe, E.F., Battoe, L.E., 2000. Performance of a recirculating wetland filter designed to remove particulate phosphorus for restoration of lake Apopka (Florida, USA). In: Proceedings of 7th International Conference on Wetland systems for Water Pollution Control, Florida, USA. Danovaro, R., 2003. Pollution treats in the Mediterranean Sea: an overview. Chem. Ecol. 19 (1), 15–32. Drizo, A., Forget, C., Chapuis, R.P., Comeau, Y., 2002. Phosphorus removal by EAF steel slag – a parameter for the estimation of the longevity of constructed wetland systems. Environ. Sci. Technol. 36, 4642–4648. Drizo, A., Picard, H., 2010. Systems and methods for removing phosphorus from wastewaters. Filling date 8/30/2010 (U.S. serial number 12/807, 177). Drizo, A. 2012. Innovative Phosphorus Removal Technologies. Australian online journal A to Z of Clean technologies, Azo Cleantech: http://www.azocleantech.com/article.aspx?ArticleId=226. Gabrielides, G.P., 1995. Pollution of the Mediterranean Sea. Water Sci. Technol. 32 (9–10), 1–10. Gunes, K., Tuncsiper, B., 2009. A serially connected sand filtration and constructed wetland system for small community wastewater treatment. Ecol. Eng. 35, 1208–1215. Gunes, K., Tufekci, H., Karakas, D., Morkoc, E., Tufekci, V., Okay, O., Tolun, L., Karakoc, F.T., 2001. Monitoring of Lake Egirdir Surface Waters Quality. Tubitak MRC, Energy Systems and Environmental Research Institute, Gebze (Kocaeli), Turkey. Headley, T.R., Huett, D.D., Davison, L., 2000. The removal of nutrients from plant irrigation runoff in subsurface horizontal-flow wetlands. In: Proceedings of 7th International Conference on Wetland systems for Water Pollution Control, Florida, USA. Interstate Technology Regulatory Council (ITRC), 2003. Technical and Regulatory Guidance Document for Constructed Treatment Wetlands. Mitigation Wetlands Team, Washington, DC, USA.
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Contents lists available at SciVerse ScienceDirect
Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
The ability of free water surface constructed wetland system to treat high strength domestic wastewater: A case study for the Mediterranean Kemal Gunes a,∗ , Bilal Tuncsiper b , Selma Ayaz a , Aleksandra Drizo c a
TUBITAK Marmara Research Center, Environment Institute, P.O. Box 21, Gebze 41470, Kocaeli, Turkey Ni˘gde University, Faculty of Engineering-Architecture, Environmental Engineering Department, Ni˘gde, Turkey c University of Vermont, College of Agriculture and Life Sciences, Department of Plant and Soil Science, 63 Jeffords Building, Burlington 05405 VT, USA b
a r t i c l e
i n f o
Article history: Received 7 November 2011 Received in revised form 22 March 2012 Accepted 2 April 2012 Available online 3 May 2012 Keywords: Constructed wetlands Natural wastewater treatment Domestic wastewater treatment Catchment management
a b s t r a c t This study evaluates a full-scale free water surface flow-constructed wetland (FWS-CW) system that was developed in 2005 to treat high strength wastewater in Garip village near Lake E˘girdir in the Mediterranean (Turkey). This FWS-CW was the one of the first full-scale wastewater treatment systems of this type in Turkey and the Mediterranean, and as such represents an important reference for the application of CW systems in other regions with similar climates. This FWS-CW system consists of two stages, the first one being comprised of a 3-compartment septic system with the second one comprised of the FWS CW. The treatment efficiency of the system was found to be significantly affected by the pollutant loading rates, hydraulic retention time and temperature. Long term monitoring revealed that the system removed approximately 86%, 92%, 56% and 43% of the total suspended solids (TSS), biochemical oxygen demand (BOD), total nitrogen (TN), and total phosphorus (TP) from the high strength domestic wastewater, respectively. Therefore, this type of FWS can be applied as economical, environment-sensitive and very efficient for TSS and BOD for treating high strength domestic wastewaters. Alternative measures for improving TN and TP are discussed. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The Mediterranean Sea covers 2,500,000 km2 with the coastline extending 46,000 km running through 22 countries. Today about 82 million people live in coastal cities, with an estimated increase to 150–170 million by 2025 (Danovaro, 2003). The United Nations Environment Program estimated that 650 million tons of sewage and 36,000 tons of phosphates are discharged into the Mediterranean Sea each year, of which approximately 70% untreated (UNEP, 2007). Consequently, like in many other areas in the world, eutrophication of Mediterranean Sea has become a water quality issue of increasing concern (Gabrielides, 1995; Bianchia and Morri, 2000; Danovaro, 2003). Phosphorus (P) pollution and subsequent eutrophication of watercourses has been recognized as the one of the most pressing water quality issues worldwide, given the fact that addition of just 1 g of phosphate phosphorus (PO4 -P) promotes the growth of up to 100 g algae (Khan and Ansari, 2005; U.S. EPA, 2010; Putz, 2008). The critical concentrations for incipient eutrophication are about
∗ Corresponding author. Tel.: +90 262 677 29 55; fax: +90 262 641 23 09. E-mail addresses: [email protected], [email protected] (K. Gunes). 0925-8574/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecoleng.2012.04.008
0.1–0.2 mg l−1 PO4-P in running water and 0.005–0.01 mg l−1 PO4 P in still water (Khan and Ansari, 2005; Putz, 2008). Thus, in view of the potential hazard to surface waters, the EU Directive 91/271/EEC established limit values for the discharge of phosphate compounds for municipal sewage treatment plants into receiving waters 20 years ago (1991), and has been revisited and amended in 2003 and 2008. Depending on the size of the sewage treatment plant, the specific limit values are currently set at 2 mg l−1 TP (10,000–100,000 PE) and 1 mg l−1 TP (>100,000 PE) (UWWT Directive, 2012). With the global population expansion, the need for finding new, low cost and maintenance, energy efficient domestic wastewater treatment solutions for rural communities has become emerging priority among wastewater engineers and scientist. Over the past 20 years, constructed wetlands (CW) have been developed and accepted as a wastewater management practice for treatment of variety of wastewater effluents across the globe (Kadlec and Knight, 1996; Vymazal, 2010). 1.1. Constructed wetlands development in Turkey To date, most studies evaluating the use of CW for wastewater treatment in Turkey have been pilot-scale. The first experimental studies were the CWsystems established in TUBITAK Marmara Research Center (MRC) campus, located in Gebze-Kocaeli in 1995.
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Fig. 1. Studied area (lake Egirdir and its basin).
In 2003, a collaborative program developed between the Istanbul Technical University (ITU) and TUBITAK MRC enabled the establishment of 3 pilot facilities (PF) in Pasakoy Waste Water Treatment Facility belonging to Istanbul Water Sewerage Administration (ISKI). The PFs were fed by tertiary effluents, each having a surface ∼100 m2 . The first PF employed subsurface flow (SSF) and was vegetated with Cyperus. The second PF, was a floating system vegetated with Lemma minor while the third PF was built as free water surface (FWS) system and also vegetated with Cyperus (Ayaz and Akc¸a, 2000). Another pilot scale CW was constructed for treatment of domestic wastewater at the campus of Middle East Technical University (METU). This CW consisted of two CW units with vertical flow (each covering surface area of 30 m2 ) connected in series (Korkusuz et al., 2005). Following these pilot scale CW investigations, several fullscale CW were built since 2004. Turkish General Directorate of Rural Affairs initiated the campaign of founding natural treatment sewage treatment facilities in which resulted in construction of CWs in Ankara–Haymana–Dikilitas village and in Muratbagi village of Kovancilar county; The Turkish Ministry of Agriculture and Rural Affairs established the “Natural Treatment Project” in Korucuk village, Izmir region; and the Governorship of Afyon for the improvement of Akarcay funded the CW system which was built in Afyon. More recent full scale CWs include a newly developed, the first of its kind, combined natural wastewater treatment system in the Village of Ileydagi (population of 313) situated in the reservoir of Lake Egirdir which is the second largest fresh water lake in Turkey (Gunes and Tuncsiper, 2009). The system described in this paper represents the first full scale FWS CW built in Turkey for treatment of high strength domestic wastewater. Because this is the first system of its type in the region, this study was conducted to determine if such systems provide an economical and environment-friendly solution for the treatment of wastewater in Turkey.
Therefore, the main objective of this study was to investigate economic viability and sewage treatment efficiency of a free surface flow constructed wetland (FWS CW) system and its potential applications in other Mediterranean regions. Another objective of the study was to investigate the effects of various pollutant loading rates on the system treatment performance. The results of this study revealed that this type of CW have a potential to be used as the base for the future operational and design optimization of the FWS-CWs in the areas with similar climates. 2. Material and methods 2.1. Description of the study area Garip village is located at the Lake E˘girdir, the second largest freshwater lake in Turkey, situated in the Mediteeranean region. Since 2000, 5 projects were carried out to mitigate point and nonpoint sources of pollution within the Lake E˘girdir catchment area. The village has an existing population of approximately 625 that is expected to reach 868 by 2030 (Fig. 1). The climate in Lake Egirdir basin, is between the Mediterranean and the Middle Anatolian territorial climate (Ugurlu et al., 1999). Therefore, the winters are severe and rainy while the summers are hot and partly dry. In addition, the region is under the influence of the northern and southern winds nearly all year round (Ugurlu et al., 1999). The average annual precipitation is 581 mm, the average temperature is 12 ◦ C, the average humidity is 61%, and the average evaporation is 1222 mm (Gunes et al., 2001). 2.2. Sampling and analysis According to the waste water flow measurement of the settlement unit used in this system, the amount of wastewater being
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Fig. 2. Schematic layout of the experimental system.
treated was approximately 74 l/person/day resulting in the total wastewater daily flow of 462 m3 d−1 . Samples were collected from 3 different points including the septic system inlet, septic system outlet and the constructed wetland outlet over a period of 12 months. All samples were fixed and then stored at 4 ◦ C until being transported to the laboratory. All analyses were performed according to the Standard Methods (APHA, 1998).
Table 1 Characteristics of raw wastewater.
2.3. FWS-CW system design The FWS-CW system is comprised of a 3-compartment septic system and 3-stage FWS (Fig. 2). The septic system is 9.0 m × 3.0 m × 3.0 m (L × W × H) with an effective volume of 67.5 m3 , resulting in the hydraulic residence time (HRT) of the septic system of 1.4 days. This system was designed to decrease the solid material load entering the constructed wetland. Treatment area needed per person of the FWS system for future population is 3.2 m2 /person, however the current treatment area is 4.5 m2 /person. The system consists of 3 stages covering total surface area of 2840 m2 . The first stage (22.1 m × 52.4 m, L × W) was built to provide the sedimentation and flocculation functions (USEPA, 2000). The second stage (10.0 m × 52.4 m), is an open water surface algae system, however, submerged macrophytes were also planted to provide aeration (or oxygen) to the water column and increase nitrification. The third stage (22.1 m × 52.4 m, L × W) was designed as macrophytes (Typha latifolia L.) to further remove pathogens, metals and suspended solid materials through sedimentation and denitrification. The first and the third stages both have a depth of 0.75 m and are vegetated with T. latifolia L [Such design resulted in a total HRT of 29.1 days. The FWS-CW described in this study was designed based on the most up to date CW guidelines, and constructed in the field as a full scale treatment system with the objective to treat highly concentrated wastewater from a
Parameter
Mean
Standard deviation
Range
a Temperature (◦ C) pH Dissolved oxygen (mg l−1 ) TSS (mg l−1 ) BOD (mg l−1 ) COD (mg l−1 ) TN (mg l−1 ) TP (mg l−1 )
11.8 6.4 13.8 222 352 728 42.2 7.6
5.9 0.3 4.9 50 23 92 4.6 1.5
4.2–23.5 5.8–6.7 7.2–23.5 124–310 318–397 596–786 35.5–50.6 5.0–10.5
a
Temperature (◦ C) is 7.2 in winter, and 15.5 in summer as average.
village population. For this reason, a parallel study was not performed for control or comparison. The system comprises actual data from the full scale system like other studies (Reilly et al., 1999; Song et al., 2006; Zhang et al., 2010)]. 2.4. Wastewater characteristics According to the typical composition of the domestic wastewaters (Tchobanoglous and Burton, 1991) the wastewater treated in the FWS system is high strength domestic wastewater (Table 1). This is because the wastewater contains partial wastewaters from stock farming in addition to the domestic wastewaters generated by the village population. Characteristics of raw wastewater are given in Table 1. 3. Results and discussion 3.1. FWS-CW treatment performance The results of the twelve months water quality monitoring, including influent and effluent pollutant concentrations and
Table 2 The FWS average influent and effluent concentrations and percentage reductions achieved. Water quality parameters
Septic S. influent
Septic S. effluent e.g. FWS influent wetland influent
FWS effluent
Septic S. red effluent (%)
FWS red effluent (%)
Total system effluent (%)
TSS (mg l−1 ) COD (mg l−1 ) BOD (mg l−1 ) TN (mg l−1 ) TP (mg l−1 )
222 728 352 42 7.6
92 616 292 36 6.6
31 61 30 18 4.3
58.6 15.4 17.0 14.3 13.2
66.30 90.10 89.7 50.0 34.8
86.0 91.6 91.5 57.1 43.4
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Fig. 3. Change in septic and FWS-CW system performances during the summer and winter periods.
reduction efficiencies achieved by each FWS treatment system stage are presented in Table 2. The septic system alone achieved 60% reduction in TSS, however its performance in reducing other pollutants was poor, ranging from 13.6% (TP) to 17% (BOD). The FWS system alone achieved an average TSS reduction of 66%, very high efficiency in both COD and BOD reduction (about 90%), while its performance in nutrients removal was poor (50% for TN and 34.8% for TP). However, the combined septic system and FWS CW system achieved 86% reduction in TSS, and 91% reduction in BOD and COD (Table 2). In addition it achieved an average of 57% TN and 43% of TP, with removed load ranging between
0.17–0.34 g N m−2 d−1 and 0.02–0.06 g P m−2 d−1 , respectively. The combined wetland systems with pretreatment conducting partial nitrification and partial denitrification will be more effective in summer, leading to less ammonia and less nitrate in the warmer months (Kadlec and Wallace, 2009). The results suggest that in this study, TN removal was achieved through denitrification in septic system and mostly nitrification and partial denitrification in FWS system. In addition, nitrogen reduction could have also been associated with the vegetation and microbial uptake which are well established mechanisms of N removal in CW (Kadlec and Wallace, 2009).
Fig. 4. Average pollutant reductions achieved for different hydraulic residence times (HRT) employed.
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Fig. 5. Removal rates (in g m−2 d−1 ) versus loading rates of CW system.
Treatment efficiencies found in this system are in accordance with the TSS, BOD, TN and TP single-stage CW systems reductions reported by other researchers (Kadlec and Knight, 1996; Meahlum and Stalnacke, 1999; Vymazal, 2005, 2010). It has been well established that considerably high TSS and BOD reductions are achievable by CW, while TN and TP are significantly lower and highly variable. Vymazal (2005) reported that depending on inflow loading, TN and TP could be removed in the range of 40–50%, and 40–60%, respectively, with removed load ranging between 0.68–1.72 g N m−2 d−1 and 0.12–0.20 g P m−2 d−1 . Although the regulatory framework currently does not require P reduction from domestic residential wastewaters neither in the EU nor in the US (Bird and Drizo, 2010; Johansson Westholm et al., 2010; Drizo, 2012), given the extent of eutrophication across the world, improving CW TP removal efficiencies remains one of the major scientific and research questions among CW scientists (IWA, 2010). Since early 1990s, numerous natural and industrial by products have been tested as potential P adsorbing materials in laboratories across the world (e.g. Drizo et al., 2002; Johansson Westholm, 2006; Vohlaa et al., 2011), however to date, very few full scale systems have been implemented (Johansson Westholm et al., 2010). Following research on adsorbing materials, Brix (2007) and co-researchers suggested traditional chemical P-precipitation in sedimentation tank as the way to enhance P removal in CW. Following over 15 years of research, Drizo and Picard (2010) recently developed PhosphoReducTM custom designed systems capable of removing TP to over 90%, consisting of one or more filter units filled with iron and/or calcium based filtration materials, that can be easily incorporated as an add on units to CW and other onsite filtration systems (Drizo and Picard, 2010; Drizo, 2012).
3.2. Statistical analysis In order to determine the distribution analyses of the average removal percentages of systems in summer and winter periods, a K–S (Kolmogorov–Smirnov) Test was conducted. Test results demonstrated a normal distribution at p < 0.05 significance level for all of the investigated water quality parameters (Fig. 3). TP change intervals were higher and less homogenous compared to other pollutants. The variance analysis (ANOVA one-way) revealed that all pollutants were affected by the temperature. F values varied between 400 and 2000 for TSS, BOD and TN, while p values vary between 6 × 10−27 and 6 × 10−18 . The fact that F value obtained for P was so close to Fc (critical F value) value and that the p value almost approached 0.05 significance value suggests that temperature had lesser effect on TP removal compared to other investigated pollutants (F = 14, Fc = 4.2, p = 0.0003). With the exception of TP, the average removal efficiency was found to be higher during the summer periods, with the removal efficiency of BOD and TN being approximately 3% higher on average, and the TSS removal being 10% higher in the septic system during this period. However, TP removal in septic system was higher during winter than in summer months, which can be attributed to the fact that phosphorus loading was significantly lower during winter months. The findings from our study are in agreement with Kadlec and Knight (1996) and Meahlum and Stalnacke (1999) who have reported that the differences between CW removal efficiencies during summer and winter seasons are very low (<10). The ability of the wetland system evaluated in this study to remove TP was nearly the same (about 34%) during summer and winter seasons. Conversely, the TSS, BOD, and TN removal efficiencies were approximately
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4% higher during summer compared to winter performance. Such differences may have occurred as a result of different biological activities of the microorganisms in response to different temperatures. It has been well established that the biological activity decreases during cold seasons, whereas the activity increases in response to increasing temperature and biomass, which results in a higher removal of organic material and nitrogen (Steinmann et al., 2003).
3.3. The effects of hydraulic residence time (HRT) Hydraulic residence times (HRTs) measured in this study were higher that the optimum hydraulic retention times of 4–15 days reported for the FWS-CWs (Tchobanoglous and Burton, 1991; Knight et al., 1993; ITRC, 2003). The FWS performance was evaluated in response to 4 different hydraulic retention times (25, 28, 31 and 35 days). We selected higher HRTs in order to test the effects of longer HRT on organic matter and Nitrogen removal efficiencies. The results showed that the optimal removal efficiencies were achieved at 30 days HRT of 30 days without further increase in the removal efficiency above this HRT (Fig. 4). After a period of 30 days, change intervals of average removal increased while the homogeneity decreased. Statistical analyses revealed that there were significant differences between TSS, BOD and TN removal efficiencies achieved at different HRTs, (F > Fc and p < 0.05 for TSS, BOD and TN; F = 4.59 < Fc = 4.2) with the exception of P, which did not seem to be affected by the difference in HRTs investigated in this study (p = 0.063 > 0.05). These results are similar to those that have been reported in previous studies (Tunc¸siper, 2007; Tunc¸siper et al., 2005, 2006).
3.4. The effects of pollutants loading rates Variance analyses showed significant relations between the influent and the effluent pollutants loading rates. TN and TP had higher F (>150) and lower p (<0.05) values compared to TSS and BOD, suggesting that influent loading rates had greater effect on these pollutants removal efficiencies compared to TSS and BOD (Fig. 5). Overall, the average BOD and TSS removal rates increased linearly with the increase in loading rates (R2 > 0.92) (Fig. 5). It has been shown that the best relationship between TN removal rate and loading rate is a 2nd degree polynomial relationship (R2 : 0.98). These relationships are in accordance with other data reported in the literature (Kadlec and Wallace, 2009). The median net period-of-record removal rate for 116 FWS systems receiving more than 5 mg l−1 was reported as 0.354 g m2 d−1 (129 g m2 yr−1 ) while in this study, the median removal rate of FWS system was 0.311 g m2 d−1 (Kadlec and Wallace, 2009). TN removal rates increased linearly until a 0.6 g m−2 d−1 TN loading rate was attained, with the further TN addition resulting in removal efficiency decrease. The relationship between the TP influent loading and FWS removal rates were generally poor, exhibiting logarithmic trend. The results of this study are in accordance with the previous studies conducted to evaluate changes in TN and TP removal efficiencies in response to different loading rates (Kadlec and Knight, 1996; Headley et al., 2000; Coveney et al., 2000). In addition, the analyses of variance conducted here revealed that there is a significant relationship between loading rates and removal rates (p < 0.05), with the best relationship being found for TN (F: 203.5 > Fc: 4.17).
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4. Conclusions • The average removal efficiencies of a FWS CW system consisting of a septic system and a free surface CW were high for TSS and BOD (approximately 86% and 92%, respectively) and low for TN and TP (56% and 43%, respectively, confirming the need for further improvements in CW design in order to achieve higher TP reductions. • The results of this study provide further evidence that the most important factors to be considered in designing CW for high strength sewage effluents treatment are pollutant loading rates, hydraulic residence times and temperature. • Phosphorus removal efficiencies can be further increased by incorporation of phosphorus adsorbing materials either as a CW substrate or as independent treatment unit (Drizo and Picard, 2010). • We suggest that the number of large-scale systems in regions with similar climates should be implemented and a data network established. The implementation of large-scale systems especially designed to achieve high P reductions from high strength effluents would provide a baseline for a comprehensive nutrients reduction assessment via innovative designs in Turkey and across Mediterranean region. Acknowledgements The authors would like to thank to TUBITAK Marmara Research Center and the Governorship of Isparta for their financial support and encouragement. References APHA, 1998. Standard Methods for the Examination of Water and Wastewater, 20th ed. APHA, Washington, USA. Ayaz, C¸.S., Akc¸a, L., 2000. Treatment of wastewater by constructed wetland in small settlements. Water Sci. Technol. 41, 69–72. Bianchia, C.N., Morri, C., 2000. Marine biodiversity of the Mediterranean Sea: situation, problems and prospects for future research. Mar. Pollut. Bull. 40 (5), 367–376. Bird, S., Drizo, A., 2010. EAF steel slag filters for phosphorus removal from milk parlor effluent: the effects of solids loading, alternate feeding regimes and in-series design. Water 2 (3), 484–499, http://dx.doi.org/10.3390/w2030484. Brix, H., 2007. Types and applications of constructed wetland systems – recent developments. In: Proceedings of the SmallWat 2007, 2nd International Congress on Wastewater Treatment in Small Communities, held in Seville, Spain, November 11–15th. Coveney, M.F., Lowe, E.F., Battoe, L.E., 2000. Performance of a recirculating wetland filter designed to remove particulate phosphorus for restoration of lake Apopka (Florida, USA). In: Proceedings of 7th International Conference on Wetland systems for Water Pollution Control, Florida, USA. Danovaro, R., 2003. Pollution treats in the Mediterranean Sea: an overview. Chem. Ecol. 19 (1), 15–32. Drizo, A., Forget, C., Chapuis, R.P., Comeau, Y., 2002. Phosphorus removal by EAF steel slag – a parameter for the estimation of the longevity of constructed wetland systems. Environ. Sci. Technol. 36, 4642–4648. Drizo, A., Picard, H., 2010. Systems and methods for removing phosphorus from wastewaters. Filling date 8/30/2010 (U.S. serial number 12/807, 177). Drizo, A. 2012. Innovative Phosphorus Removal Technologies. Australian online journal A to Z of Clean technologies, Azo Cleantech: http://www.azocleantech.com/article.aspx?ArticleId=226. Gabrielides, G.P., 1995. Pollution of the Mediterranean Sea. Water Sci. Technol. 32 (9–10), 1–10. Gunes, K., Tuncsiper, B., 2009. A serially connected sand filtration and constructed wetland system for small community wastewater treatment. Ecol. Eng. 35, 1208–1215. Gunes, K., Tufekci, H., Karakas, D., Morkoc, E., Tufekci, V., Okay, O., Tolun, L., Karakoc, F.T., 2001. Monitoring of Lake Egirdir Surface Waters Quality. Tubitak MRC, Energy Systems and Environmental Research Institute, Gebze (Kocaeli), Turkey. Headley, T.R., Huett, D.D., Davison, L., 2000. The removal of nutrients from plant irrigation runoff in subsurface horizontal-flow wetlands. In: Proceedings of 7th International Conference on Wetland systems for Water Pollution Control, Florida, USA. Interstate Technology Regulatory Council (ITRC), 2003. Technical and Regulatory Guidance Document for Constructed Treatment Wetlands. Mitigation Wetlands Team, Washington, DC, USA.
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