Printer Friendly

Performance of a Surface Flow Constructed Wetland System Used to Treat Secondary Effluent and Filter Backwash Water.

Byline: JUAN A. VIDALES-CONTRERAS - Email juan.vidalescn@uanl.edu.mx, CHARLES P. GERBA, MARTIN M. KARPISCAK, HUMBERTO RODRIGUEZ FUENTES, JESUS JAIME HERNANDEZ ESCARENO AND CRISTOBAL CHAIDEZ-QUIROZ

ABSTRACT

The performance of a surface flow wetland used to treat activated sludge effluent and filter backwash water from a tertiary treatment facility was evaluated. Samples were collected before and after vegetation removal from the wetland system, which consisted of two densely vegetated settling basins (0.35 ha), an artificial stream and a 3-ha surface flow wetland. Bulrush (Scripus spp.) and cattail (Typha domingensis) were the dominant plant species. The average inflow of chlorinated secondary effluent during the first two months of the actual study was 1.84 m3 min-1, while the inflow for backwash water treatment ranged from 0.21 to 0.42 m3 min-1.

The system was able to reduce TSS and BOD5 to tertiary effluent standards; however, monitoring of chloride concentrations revealed that wetland evapotranspiration is probably enriching pollutant concentrations in the wetland outflow. Coliphage removal from the filter backwash was 97 and 35% during 1999 and 2000, respectively. However, when secondary effluent entered te system, coliphage removal averaged 65%. After vegetation removal, pH and coliphage density increased significantly (pless than0.05) at the outlet of the wetland. This study showed that surface flow wetlands are an alternative technology for TSS, BOD5 and turbidity removal from both secondary or backwash water. However, growth of bacterial populations or recovery of injured bacteria may occur. (c) 2010 Friends Science Publishers

Key Words: Wetlands; Backwash water; Secondary effluent; BOD5; TSS; Turbidity

INTRODUCTION

In conventional wastewater or drinking water treatment plants, backwash water results from periodic backwashing of single or mixed media filters used for removing organic matter, enteric pathogens, and other particulate matter from raw drinking water or activated sludge secondary effluent (Persson et al., 2005; Khan and Subramania, 2007; Horan and Lowe, 2007). Consequently, backwash water without efficient treatment or recycling in treatment facilities may represent a public health risk (Koivunen et al., 2003). In order to protect public health, environmental protection agencies have regulated its recycling in conventional drinking water treatment plants to control disinfection resistant microbial pathogens and consequently waterborne diseases (USEPA, 2002). In the wastewater treatment industry, constructed wetlands are considered an attractive technology to treat low strength domestic sewage and secondary wastewater effluents.

Wetland technology has also offered an innovative approach for reduction, with different degrees of success, of a wide range of chemical pollutants (Kara and Kara, 2005; Grove and Stein, 2005; Abou EL-Kheir et al., 2007; Matamoros et al., 2007; Troesch et al., 2009) and microbial indicators (Mendez et al., 2009; Von Sperling et al., 2010). However, until recently, few or not data existed on the efficacy of constructed wetland systems to treat backwash water; even though, one of the most common methods to treat backwash water has been settling in lagoon facilities (Montgomery, 1985). In 1997, two wetland systems were constructed at the Sweetwater Recharge Facility to treat backwash water from a tertiary wastewater treatment plant in Tucson AZ, USA. After soil aquifer treatment, wastewater is recovered from the aquifer at 1.6 x 107 m3 year-1 extraction rates to be deliver in golf course facilities, parks, schools and residential sites.

The objective of the actual study was to assess wastewater quality performance in the wetland system before aquifer recharge. Hence, physical, chemical and microbial indicators for wastewater quality were evaluated

To cite this paper: Vidales-Contreras, J.A., C.P. Gerba, M.M. Karpiscak, H.R. Fuentes, J.J.H. Escareno and C. Chaidez-Quiroz, 2010. Performance of a surface flow constructed wetland system used to treat secondary effluent and filter backwash water. Int. J. Agric. Biol., 12: 821-827 in the wetland during secondary effluent and backwash water treatment from February to September 1999 and 2000. The actual paper presents the results of this monitoring study.

MATERIALS AND METHODS

Research site and sampling: The research was conducted at the Sweetwater Wetland and Recharge Facility (SWRF) in Tucson, AZ. In this site (Fig. 1), two polishing wetland systems referred to as East and West were designed in about 12.46 ha to reclaim backwash water from the City of Tucson Reclamation Plant. At this site, residual chlorine in secondary effluent at the pressure mixed media filters was on average 1 mg L-1. After backwashing mixed media filters, the backwash effluent was kept free of chlorine additions.

At the wetland facility, both the East or West polishing systems consist of a 3-ha wetland cell and a pair of settling basins vegetated with bulrush species (Scirpus spp.) and cattail (Typha domingenses). However, in the East Polishing System (EPS), wastewater flows briefly through an artificial stream before entering the 3-ha wetland cell for additional wastewater treatment. A sequence of islands of different sizes, shallow vegetated zones and 1.2-m deep open water areas is the geometric configurtion of the wetland to provide tertiary treated wastewater. After wetland treatment, polishing wastewater goes by gravity to four recharge basins, located at the vicinity area of The Santa Cruz River, for soil aquifer treatment.

Eventually, drilling wells pump reclaimed water from the aquifer to the Pima County Roger Road Wastewater Treatment Facility (RRWTF) for chlorine disinfection and deliver in parks, schools and golf course fields. In spite of both polishing systems were designed to treat backwash water, chlornated secondary effluent from RRWTF was introduced for starting wetland operation in October 1997; on April 1998, the polishing wetland systems began to treat backwash water. In the winter 1999, wetland vegetation was harvested from the EPS; however, by the end of Spring a new complete plant canopy had taken its place.

From February to September of 1999 and 2000, water samples were collected monthly from the EPS at the backwash splitter box (1), outlet of the south settling basin (2), both ends of the stream (3 and 4) and outlet of the wetland cell (5). Concurrently, measurements of water temperature (T), biochemical oxygen demand (BOD5), total suspended solids (TSS), SO4-2, Cl-, total and free chlorine (Cl2), turbidity, pHnative coliphages (NC) and total (TC) and fecal coliforms (FC) were conducted.

Physical and chemical analysis: The 5-days incubation method (APHA/AWWA/WEF, 1998) was used for BOD5 analysis. Determination of TSS was conducted by filtering a known volume of sample through a pre-cleaned and pre-weighed glass fiber filter. TSS concentration was estimated reweighing the filter after a 24-h drying period at 100oC. Sulfate was assessed by adding BaCl2 to a known volume of sample measuring the absorbance at 420 nm in a HACH DR/2000 spectrophotometer (Loveland, CO).

Chloride was quantified by a chloride-specific electrode and turbidity with a portable turbidimeter (HACH, model 2100P, Loveland, CO) reading as Nephelometric Units (NTU). A pH meter (model 8005, West Chester, PA) quantified water pH whereas the DPD (N, N-diethyl-p-phenylenediamine) indicator method (HACH Spectrophotometer, model DR/2000, Loveland, CO) was chosen for total and free chlorine (Cl2) determination.

Coliforms and coliphages: Total and fecal coliforms were analyzed within 4 h of sampling by membrane filtration using mEndo Agar Les and mFC culture media (DIFCO, Detroit, MI), respectively. The membrane filters were 47 mm diameter with a 0.45-mm pore size (Millipore, Molsheim, France). Sample volumes of 0.1, 1 and 10 mL were assayed and incubated at 37oC for total coliforms and 44.5oC for fecal coliforms, results are reported as colony forming units (CFU). Native coliphages were quantified by the double layer agar method described by Adams (1959). A 1-mL aliquot from Escherichia coli ATCC 15597 (ATCC) culture, previously incubated at 37oC for 24 h in trypticase soy broth (DIFCO, MI), was combined with one mL of sample in a test tube containing molten overlay agar. This suspension was poured onto a layer of tripticase soy agar (DIFCO, MI) and incubated at 37oC for 18 h in order to enumerate the coliphage as plaque forming units (PFU). This method detects both somatic and male specific coliphages.

Statistical analysis: The statistical analysis was conducted using the Statistical Package for Social Science 12 (SPSS Inc., Chicago ILL). Tests to determine significant differences between sampling periods and monitoring sites were conducted by two way ANOVA analysis. Because of extreme concentration values and high variability into microbial data sets, ANOVA analysis was conducted transforming microbial concentrations to base 10 logarithmic units (log10) for backwash water operation. The geometric mean was used as a centrality measure for observed microbial indicator distributions. Extent of data dispersion was represented by geometric coefficient of variation, (10^ (s) - 1) x 100, where s is the standard deviation of log10 microbial concentration values. The physical/chemical data sets were analyzed without transformation.

RESULTS

Hydrologic conditions: An actual hydraulic residence time of 7.2 days was estimated by a tracer study in the East wetland cell. During this study, February 12 to March 18, 1999, the wetland was receiving chlorinated secondary effluent at an average rate of 1.84 m3 min-1. From March 19 to 22, a mixture of chlorinated secondary effluent and backwash water was introduced into the East and West system changing to 100% backwash water at 0.42-m3 min-1 flow rate, on March 23.

This hydraulic condition was changed to 0.25 m3 min-1 on June 30 and was held until September 21, when the EPS started to be drained for vegetation harvesting in the winter of 1999. The EPS returned to normal operation in February 2000 at an average inflow rate of about 0.32 m3 min-1 of backwash water (Tucson Water, 1999 and 2000).

Sampling of chlorinated secondary effluent: Two water samples were collected per sampling site during February and March, 1999. Influent BOD5 and TSS concentrations were 29 and 21.5 mg L-1, respectively decreasing about 69% at sampling location 2 (Table I). Turbidity reduction was very similar to BOD5 and TSS performance with a 56% decrement from location 1 to 2. At sampling site 2, a significant increase of indicator bacteria was observed; in fact, TC inflow concentration increased by a forty five-fold factor, approximately, at this sampling site.

In contrast, the East wetland cell noticeably removed TC, FC, and NC reaching reductions about 91, 81 and 72%, respectively from end to end of the 3-ha wetland. Chloride was practically constant in the wetland system showing the lowest concentration at site 5. Sulfate revealed a greater variability than Cl- ranging its concentration between 122.5 and 144.5 mg L-1. For pH, the lowest value was observed in the settling basin and the highest at splitter box. An averaetemperature of 22.7oC was recorded at site 1 decreasing to 10.5oC at wetland outlet, 3.66oC below the average temperature for February and March 1999 recorded at the Tucson Meteorological Station (The Arizona

Meteorological Network, AZMET, 2008). On February 19, total and free Cl2 concentrations were 1.19 and 0.14 mg L-1, respectively in the splitter box water. Both concentrations were below the method detection limit thereafter. On March 20, Cl2 was undetected at any sampling point in the EPS.

Sampling of Backwash Effluent

Indicator microorganisms: Geometric mean concentrations for total coliforms, fecal coliforms and coliphage observed at monitoring sites during backwash water study are presented in Fig. 2. It can be clearly seen that TC and FC average concentrations increased in the settling basin. The remaining wetland treatment units resulted in further bacterial removal. At the system outflow, inflow NC concentrations decreased by about 97 and 35% in 1999 and 2000, respectively. Table II illustrates the high variability observed in microbial concentrations particularly in the first sampling period when geometric coefficient of variation (CV) ranged between 90 and 633% for TC and from 120 to 526% for FC. The ANOVA analysis revealed a significant difference for microbial indicator concentrations between sampling sites (pless than0.05) but not for sampling periods (pgreater than0.05).

BOD5, TSS, temperature and turbidity: Table III shows BOD5, TSS and turbidity descriptive statistics for 1999 and 2000 backwash water treatment. The CV values for those water quality parameters varied from 14.33 to 127.66%; however, CV estimates during 2000 ranged between 19 to 76.10% for all the sampling sites. In contrast to the artificial stream and wetland cell, the settling basins were efficient for backwash water treatment. At this site, the average TSS, BOD5 and turbidity were significantly (pless than0.05) reduced to 91-93%, 60-74% and 65-78%, respectively. These results are fairly lower than the estimates for the entire polishing system during both sampling periods, 90-96% for TSS; 84- 89% for BOD5 and 77-79% for turbidity, suggesting that TSS are more efficiently removed than BOD5 and turbidity. Cl-, SO4-2 and pH: From April to September 1999, ANOVA analysis indicated that Cl-average influent concentration was 141 mg L-1 increasing significantly

Table I: Two-sample average concentrations for parameters analyzed in the Sweetwater wetlands during secondary effluent operation study, February-March 1999

Site Total coliforms Fecal###Coliphage###BOD5###TSS###Cl-###SO4-2###Turbidity###pH###Temperature

###coliforms###

###CFU/100 ml x 103###PFU/100 ml x###

###103###

###mg /L###NTU###-Log10 [H]###oC

1###0.36###0.064###4.89###29###21.5###126.0###128.5###17.9###8.17###22.7

2###16.21###8.51###7.24###9###6.5###125.0###133.0###7.8###7.22###20.2

3###11.74###4.26###7.94###7###8.0###122.5###127.0###7.6###8.15###19.0

4###6.48###1.17###6.02###7###5.0###127.0###144.5###6.3###7.95###18.0

5###0.58###0.22###1.69###8###5.0###116.5###122.5###2.8###7.49###10.5

Table II: Geometric coefficients of variation (CV) for coliform, fecal coliform and native coliphage concentrations observed at sampling sites in the East Polishing System during backwash water inflow

Indicator###Coefficient of variation (%)###

###1999###2000###

###Sampling site###Sampling site###

###1###2###3###4###5###1###2###3###4###5

TC###90###103###100###110###633###302###126###81.7###125###346

FC###120###410###182###188###526###145###119###122###107###468

NC###240###206###216###293###221###91###83###119###125###186

Table III: Descriptive statistics of TSS (mg L-1), BOD5 (mg L-1) and TUR (NTU) in samples collected from monitoring sites in the EPS during backwash water operation

Variable###Number of samples###Min###Max###Mean###Standard Error###CV (%)

###1999###2000###1999###2000###1999###2000###1999###2000###1999###2000###1999###2000

TSS (site 1)###6###7###98###7###380###278###190.66a###115.57a###40.76###37.24###127.66###69.17

TSS (site 2)###5###8###5###5###60###13###17.4b###7.87b###10.68###0.98###51.1###35.55

TSS (site 3)###6###8###5###5###30###16###10.33b###7.50b###5.38###1.30###37.2###49.37

TSS (site 4)###6###8###5###5###12###22###6.66b###10.37b###1.17###1.88###28.42###51.50

TSS (site 5)###6###8###5###5###10###30###7.0b###11.62b###1.00###3.12###14.33###76.10

Total Removal (%)###96.32###89.94###

BOD5 (site 1)###6###7###71###78###252###207###127.66a###144.71a###27.12###19.31###52.03###35.31

BOD5 (site 2)###4###8###10###25###136###46###51.5b###37.37b###28.58###2.52###111###19.07

BOD5 (site 3)###5###8###12###22###63###45###37.2b###36.87b###8.71###2.79###52.38###21.42

BOD5 (site 4)###6###8###10###19###42###42###28.42b###31.25b###7.39###2.85###58.29###25.81

BOD5 (site 5)###6###8###9###19###21###36###14.33b###23.62b###1.81###1.99###31.03###23.83

Total Removal (%)###88.77###83.67###

TUR* (site 1)###6###7###30.36###16.3###344###308###150.85a###142.62a###39.35###33.00###63.90###64.96

TUR (site 2)###6###8###13###17###70###105###32.81b###49.87b###8.10###11.20###60.49###63.53

TUR (site 3)###6###8###20###27.9###113###123###44.26b###57.9b###13.98###11.62###77.36###56.76

TUR (site 4)###6###8###14###31.2###68###129###37.93b###57.05b###10.45###11.11###67.48###55.08

TUR (site 5)###6###8###5.28###21.4###64###44.5###31.8b###32.9b###10.59###3.06###81.84###26.32

Total Removal (%)###78.91###76.93###

a,b Means within the same column and different letter for the same variable are significantly different (pless than0.05)###

*turbidity###

Table IV: Coefficients of variation, CV (%) for Cl- and SO42- observed at sampling sites in the East Polishing System during backwash influent operation

Indicator###1999 sampling site###2000 sampling site

###1###2###3###4###5###1###2###3###4###5###

Cl-###17.31###15.72###9.80###9.50###12.83###14.18###9.33###11.24###9.29###19.14###

SO42-###13.41###6.03###7.46###10.45###14.52###24.42###13.80###13.89###14.46###19.13

DISCUSSION

Physical/chemical water quality indicators: For secondary effluent treatment, outflow water in the wetland met on average the 10 mg L-1 tertiary standard required by the Arizona Department of Environmental Quality (ADEQ) for BOD5 and TSS. A significant increase of turbidity,

BOD5, and TSS occurred when secondary effluent was switched to backwash water at site 1. At the wetland outlet, removal of BOD5 was comparable to the 89% reduction reported by Vrhovsek et al. (1996) in a subsurface flow wetland operated at 962 mg L -1 BOD5 loading rate. Overall BOD5, and TSS removal in the East Polishing System was according to reported values for constructed wetlands operating across USA and other countries (Kadlec and Knight, 1996; Masi et al., 2010). In fact, the average TSS and BOD5 at the outlet end of the system were lower than the 30 mg L-1 secondary standard limit established by the ADEQ for wastewater treatment.

Chloride is considered highly stable in most terrestrial environments. In wetlands, its total mass is approximately constant (Kadlec and Knight, 1996), because its incorporation in plant tissues is negligible (Hayashi et al., 1998). Consequently, Cl- has been used as a conservative tracer to estimate evapotranspiration in wetland ecosystems (Hayashi et al., 1998). In the 3-ha polishing wetland, evapotranspiration may be a suitable mechanism for Cl-augmentation during both backwash sampling periods when water flow rate was below 0.42-m3 min-1. Concentrations of Cl- in the polishing wetland increased, from end to end, 25 and 19% during backwash operation, before and after vegetation removal, respectively. The ANOVA analysis indicated that only in 1999 was there a significant difference (pless than 0.05) between inflow and outflow concentration from the 3-ha wetland cell.

Sulfate is an essential nutrient for plants; thus, it can be retained by plant uptake in terrestrial environments; however, it is rarely a limiting facor for plant growth in wetlands (Kadlec and Knight, 1996). Its presence in high organic content environments induces production of hydrogen sulfide, because SO4-2 is an electron acceptor for sulfur-reducing bacteria (Maier, 2000). This microbiological mechanism probably was responsible for reduction of SO4 -2 in the settling basin, mainly observed during 1999 backwash water treatment. Similar to Cl-, an increase of SO4-2 concentration occurred at the outflow of the wetland. After vegetation removal, water pH statistically increased at the outflow of the wetland cell. Probably, vegetation removal allowed sun light penetration in the shallow areas promoting a water pH increase in the outflow of the wetland basin because alga proliferation (Kadlec and Knight, 1996).

Indicator microorganisms: Removal efficacies greater than 90% for FC in surface flow wetlands receiving 104-106 UFC/100 inlet concentration loads have been reported (Kadlec, 2005; Ghermandi et al., 2007). It appears that the amount of organic matter introduced into the settling basins is playing an important role for regrowth or recovery of injured coliform bacteria (Gerba, 2000; Bucklin et al., 2003; Bolster et al., 2005). Coliform bacteria such as Klebsiella,

Enterobacter and Citrobacter have shown ability to proliferate during wastewater treatment. For example, Klebsiella was found at high densities in the outflowing water from a treatment facility receiving municipal wastewater (Elmund et al., 1999) apparently, because of an increase of carbohydrates in the wastewater influent. F-specific RNA bacteriophages have been used as potential indicator for human enteroviruses instead of fecal coliforms and fecal streptococci (Stetler, 1984; Havelaar et al., 1993).

A 90% removal of coliphage has been previously observed in constructed wetlands (Gersberg et al., 1987; Chendorain et al., 1998); however, removals lower than 90% were reported by Karpiscak et al. (1995) in a duckweed (Lemna spp.) pond and by Gersberg et al. (1989) in non-vegetated wetland. The extent of somatic and F-specific RNA coliphage replication in water has been discussed by several researchers (Muniesa and Jofre, 2004; Jofre, 2009). Their findings suggest that coliphage replication is possible at host bacteria and virus concentrations uncommonly found in water environments.

However, threshold concentrations may emerge, because of bacterial growth. In the present study, coliphage removal in the settling basin, site 2, showed a decrease from 98 to 65% after vegetation harvesting in 1999. Probably, some mechanism associated to vegetation density or phage replication was responsible for undetectable coliphage removal from site 3 to 5 during the second backwash sampling period.

CONCLUSION

Settling basins are an acceptable facility for BOD5, TSS and turbidity removal from both secondary effluent and backwash water; however, growth of bacteria population or recovering of injured bacteria also may occur. The actual study has shown the complexity of a wetland environment, where biological, physical, and hydrological conditions may explain pollutant performance during wastewater treatment.

REFERENCES

Abou EL-Kheir, W., G. Ismail, F. Abou EL-Nour, T. Tawfik and D. Hammad, 2007. Assessment of the efficiency of Duckweed(Lemma gibba) in wastewater treatment. Int. J. Agric. Biol., 9: 681-687

Adams, M.H., 1959. Bacteriophage. Interscience Publishers, Inc., New York

APHA/AWWA/WEF, 1998. Standard Methods for the Examination of Water and Wastewater (1998), 20th edition, American Public Health Association/American Water Works Association/Water Environment Federation, Washington, DC

Bolster, C.H., J.M. Bromley and S.H. Jones, 2005. Recovery of chlorine-exposed Escherichia coli in estuarine microcosms. Environ. Sci. Technol., 36: 3083-3089

Bucklin, K.E., G.A. McFeters and A. Amirtharajah, 2003. Penetration of coliforms through municipal drinking water filters. Water Res., 25: 1013-1017

Chendorain, M., M. Yates and F. Villegas, 1998. The fate and transport of viruses through surface water constructed wetlands. J. Environ. Qual., 27: 1451-1458

Elmund, G.K., M.J. Allen and E.W. Rice, 1999. Comparison of Escherichia coli, total coliform populations as indicators of wastewater treatment efficiency. Water Environ. Res., 71: 332-339

Gerba, C.P., 2000. Indicator Microorganisms. In: Maier, R.M., I.L. Pepper and C.P. Gerba (eds.), Environmental Microbiology. Academic Press, Canada

ROLE OF WETLAND SYSTEM IN WASTEWATER TREATMENT / Int. J. Agric. Biol., Vol. 12, No. 6, 2010

Gersberg, R.M., R.A. Gearheart and M. Ives, 1989. Pathogen Removal in Constructed Wetlands. In: Hammer, D.A. (ed.), Constructed Wetlands for Wastewater Treatment. Lewis Publishers, Michigan

Gersberg, R.M., S.R. Lyon, R. Brenner and B.V. Elkins, 1987. Fate of viruses in artificial wetlands. Appl. Environ. Microbiol., 53: 731- 736

Ghermandi, A., D. Bixio, P. Traverso, I. Cersosimo and C. Thoeye, 2007. The removal of pathogens in surface-flow constructed wetlands and its implications for water reuse. Water Sci. Technol., 56: 207-216

Grove, J.K. and O.R. Stein, 2005. Polar organic solvent removal in microcosm constructed wetlands. Water Res., 39: 4040-4050

Havelaar, A.H., M. Olphen and Y.C. Drost, 1993. F-specific RNA bacteriophages are adequate model organisms for enteric viruses in fresh water. Appl. Environ. Microbiol., 59: 2956-2962

Hayashi, M., G. Kamp and D.L. Rudolph, 1998. Water and solute transfer between a prairie wetland and adjacent uplands, 2. Chloride cycle. J. Hydrol., 207: 56-67

Horan, N.J. and M. Lowe, 2007. Full-scale trials of recycled glass as tertiary filter medium for wastewater treatment. Water Res., 41: 253-259

Jofre, J., 2009. Is the replication of somatic coliphages in water environments significant. J. Appl. Microbiol., 106: 1059-1069

Kadlec, R.H. and R.L. Knight, 1996. Treatment Wetlands. Lewis Publishers, New York

Kadlec, R.H., 2005. Wetland to pond treatment gradients. Water Sci. Technol., 51: 291-298

Kara, Y. and I. Kara, 2005. Removal of cadmium from water using Duckweed (Lemma trisulca L.). Int. J. Agric. Biol., 7: 660-662

Karpiscak, M.M., C.P. Gerba, P.M. Watt, K.E. Foster and J.A. Falabi, 1995. Multi-species plant system for wastewater quality improvements and habitat enhancement. In: Angelakis, A., T. Asano, E. Diamadopoulos and G. Techobanoglous (eds.), Second International Symposium on Wastewater Reclamation and Reuse, pp: 37-42. IAWQ, Iraklio, Greece

Khan, E. and S. Subramania, 2007. Interferences contributed by leaching from filters on measurements of collective organic matter. Water Res., 41: 1841-1850

Koivunen, J., A. Siitonen and H. Heinonen-Tanski, 2003. Elimination of enteric bacteria in biological-chemical wastewater treatment and tertiary filtration units. Water Res., 37: 690-698

Maier, R.M., 2000. Biogeochemical cycling. In: Maier, R.M., I.L. Pepper and C.P. Gerba (eds.), Environmental Microbiology. Academic Press, Canada

Masi, F., B. El Hamouri, H.A. Shafi, A. Baban, A. Ghrabi and M. Regelsberger, 2010. Treatment of segregated black/grey domestic wastewater using constructed wetlands in the Mediterranean basin: the zero-m experience. Water Sci. Technol., 61: 97-105

Matamoros, V., J. Garcia and J.M. Bayona, 2007. Organic micropollutant removal in a full-scale surface flow constructed wetland fed with secondary effluent. Water Res., 41: 3337-3344

Mendez, H., P.M. Geary and R.H. Dunstan, 2009. Surface wetlands for the treatment of pathogens in storm water: three case studies at Lake Macquarie, New South Wales, Australia. Water Sci. Technol., 60: 1257-1263

Montgomery, J.M., 1985. Water Treatment Principles and Design. John Wiley and Sons. Inc. Toronto

Muniesa, M. and J. Jofre, 2004. Factors influencing the replication of somatic coliphages in the water environment. Antonie Van Leeuwenhoek, 86: 65-76

Persson, F., J. Langmork, G. Heinicke, T. Hedberg, J. Tobiason, T. Stenstron and M. Hermansson, 2005. Characterization of the behaviour of particles in biofilters for pre-treatment of drinking water. Water Res., 39: 3791-3800

Stetler, R.E., 1984. Coliphages as indicators of enteroviruses. Appl. Environ. Microbiol., 48: 668-670

The Arizona Meteorological Network/AZMET Monthly Summary, 1999. http://ag.arizona.edu /azmet/data/0199em.txt. (12 April 2008)

Troesch, S., A. Lienard, P. Molle, G. Merlin and D. Esser, 2009. Sludge drying reed beds: full-and pilot-scale study for activated sludge treatment. Water Sci. Technol., 60: 1145-1154

Tucson, W., 1999. Wetlands, Historical Data Information. Tucson Water, Tucson, Arizona

Tucson, W., 2000. Wetlands, Historical Data Information. Tucson Water, Tucson, Arizona

USEPA, 2002. Filter Backwash Recycling Rule, Technical Guidance Manual. United States Environmental Protection Agency, Washington, DC

Von Sperling, M., F.L. Dornelas, F.A.L. Assuncao, A.C. Paoli and O.A. Mabub, 2010. Comparison between polishing (maturation) ponds and subsurface flow constructed wetlands (planted and unplanted) for the post-treatment of the effluent from UASB reactors. Water Sci. Technol., 61: 1201-1209

Vrhovsek, D., V. Kukanja and T. Bulc, 1996. Constructed wetland for industrial waste water treatment. Water Res., 30: 2287-2292

(Received 13 April 2010; Accepted 11 June 2010)

Facultad de Agronomia, Universidad Autonoma de Nuevo Leon, Campus de Ciencias Agropecuarias, calle Francisco Villa al norte s/n, Exhacienda el Canada, Escobedo, Nuevo Leon, Mexico

Soil Water and Environmental Science Department, University of Arizona, Tucson Arizona, USA

Facultad de Medicina Veterinaria y Zootecnia, Universidad Autonoma de Nuevo Leon, Campus de Ciencias Agropecuarias, calle Francisco Villa al norte s/n, Exhacienda el Canada, Escobedo, Nuevo Leon, Mexico

Centro de Investigacion en Alimentacion y Desarrollo, Unidad Culiacan, Culiacan, Sinaloa, Mexico
COPYRIGHT 2010 Asianet-Pakistan
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2010 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Publication:International Journal of Agriculture and Biology
Article Type:Report
Geographic Code:1MEX
Date:Dec 31, 2010
Words:4600
Previous Article:Spatial and Temporal Variations of Physical-Chemical Water Quality and some Heavy Metals in Water, Sediments and Fish of the Mae Kuang River,...
Next Article:The Effect of Harvest Maturity Stage on ACC Synthase Activity and Total Proteins Profile in Kiwifruits during Normal and Controlled Atmosphere...
Topics:

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters