,ml~? , 7~ Vt. . X V.~

,ml~?--,--7~vT.-.-x-v.~

DESALINATION S

i"

'1

ELSEVIER

Desalination 152 (2002) 315-324

i

www.elsevier.com/locate/desal

Advanced treatment for municipal wastewater reuse in agriculture. UV disinfection: parasite removal and by-product formation Lorenzo LibertP*, Michele Notarnicola b, Domenico Petruzzelli b Department of Civil and Environmental Engineering, Polytechnic University of Bari, viale del Turismo 8, 74100 Taranto, ltaly °Tel. +39 (080) 5963-368; Fax +39 (080) 5963-282; email: [email protected] bTel. +39 (080) 5963-477; Fax +39 080 5963 635; emails: [email protected], [email protected] Received 30 March 2002; accepted 12 April 2002

Abstract

This paper reports the experimental results of a pilot-scale (100 mVh) investigation, carded out at the West Bari (S. Italy) municipal wastewater treatment plant, focused on parasite removal and disinfection by-product (DBP) formation during the UV disinfection of clarified (CL) and clarified-filtered (F) secondary municipal effluents at doses necessary for achieving the Italian microbial limit for unrestricted reuse ofwastewater in agriculture (2 CFU/ 100ml of total coliforms). The investigation demonstrated that parasites like Giardia lamblia cysts and Cryptosporidium parvum oocysts were both significantly affected by UV radiation and that potential UV-promoted formation of DBPs (nitro-phenols and N-nitroso-amines) did not occur according to GC/MS and LC/MS analytical evidences. O&M costs ranged from ~ 17.5 up to E 35/1000 m3for effluent F and CL respectively. Keywords: Cryptosporidium; Disinfection; Disinfection by-products; Giardia; Treatment costs; UV rays; Wastewater reuse

*Corresponding author. Presented at the EuroMed 2002 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and Alexandria University Desalination Studies and Technology Center, Sharm El Sheikh, Egypt, May 4-6, 2002. 0011-9164/02/$- See front matter © 2002 Elsevier Science B.V. All rights reserved PII: SOOl1-9164(02)01079-2

316

L. Liberti et al. /Desalination 152 (2002) 315-324

1. Introduction

Municipal wastewater contains a variety of pathogenic organisms of human origin. Diseases caused by these pathogens can occur as a result of ingestion of untreated or improperly treated water, ingestion of infected aquatic food species, skin contact with contaminated water and with improperly disinfected wastewater effluent in reuse application. Such diseases are more likely in countries characterised by scarce rainfall, lack of freshwater resources and high groundwater salinity as in the Mediterranean basin where agricultural reuse of municipal wastewater is becoming a compulsory choice for water resources manage-ment. Various schemes of advanced (or tertiary) treatment have been proposed in the last two decades with the so called "full Title 22" scheme [1 ], i.e. secondary effluent further submitted to clariflocculation, sand filtration and final disinfection, most often adopted so far. The increasing occurrence ofbio-resistant microorganisms and new pathogenic species, in particular, makes advanced disinfection a key-step for municipal wastewater reuse in agriculture [2]. Actually, municipal wastewater effluents are commonly disinfected by chlorination. However, protozoa like Cryptosporidium parvum and Giardia lamblia and helminths like Nematodes, of particular concern causing lethal diseases in immunocompromised populations, have demonstrated to be resistant to chlorine-based disinfection procedures [3,4]. Furthermore, chlorine is known to raise serious toxic effects on living organisms. In fact, it can react with organics contained in municipal wastewater to form various toxic chlorinated hydrocarbons, such as trihalomethanes and related disinfection by-products (DBP), known as animal carcinogen and suspected to be carcinogenic towards human being [5,6]. Accordingly, attempts are under way worldwide to address the effectiveness of safer alternative disinfectants able to meet the stringent microbial standards usually required for wastewater recla-

mation and reuse in agriculture [7]. In this context, a 3-year R&D project partially supported by the European Community within the framework of the Avicenne Iniziative was initiated in 1996 on various technical and health care aspects of advanced treatment for wastewater reuse. The Italian investigation, carded out by means of a 100 m3/h disinfection pilot plant purposely designed, built and operated at West Bail (S. Italy) municipal wastewater treatment plant (3000 m3/h), was specifically aimed at comparing pathogen removal, disinfection by-product formation and costs of 3 altemative disinfectants, namely UV rays, peracetic acid and ozone. For each disinfectant, the influence ofwastewater quality was investigated by disinfecting 3 different municipal effluents, namely secondary (II), following activated sludge oxidation and sedimentation, clarified (CL), following also post-precipitation with aluminum polychloride, clarified-filtered (F), further submitted to sand filtration. The general results of the investigation as well as those concerning peracetic acid and ozone disinfection have been already published [8-11]. Partial results of the UV investigation referring to bacterial inactivation effectiveness have been described in a previous note [12]. This paper reports further on UV disinfection of clarified and clarified-filtered municipal effluents. The investigation was carded out at the disinfecting doses necessary for achieving the Italian microbial standard for unrestricted agriculture reuse (2 CFU/100ml of total coliforms, based on the well known State of California Wastewater Reclamation Criteria, 1978) with specific objectives of: • evaluating the effect of UV disinfection towards selected parasitic pathogens often occurring in municipal wastewater (Nematodes eggs, Giardia lamblia cysts, Cryptosporidium parvum oocysts) • searching for eventual UV promoted DBP formation (i.e., nitro-phenols and N-nitrosoamines) • drawing economic estimates.

317

L. Liberti et al. / Desalination 152 (2002) 315-324

2. Materials and methods

The investigation was carried out by means of the 100 m3/h pilot plant (Fig. 1) with appropriate configuration for comparingthe performance of UV radiation on 2 different municipal wastewater effluents, namely clarified (CL), discharged directly from WBMP and clarified-filtered (F), obtained submitting CL to pressure sand filtration (MF) in the pilot plant. UV disinfection occurred in a non-contact apparatus (UVA), wherein the water flows inside Teflon tubes surrounded externally by low pressure Hg vapor lamps. The comparison was performed at UV doses required for meeting the Italian microbial standard (2 CFU/100ml of total coliforms) previously found to be 100 and 160 mWs/cm2 for feed F and CL respectively. On the contrary, the max dose achievable in the conditions investigated (430 mWs/cm2) was not enough to meet the standard with feed II, even if the total coliform value achieved (5 CFU/ 100 ml) was very close to the target. Further details on pilot plant, feed characteristics and main results of the previous part of the UV investigation may be found elsewhere [12].

For both feeds F and CL, about thirty cycles (i.e. a given feed submitted to a given dose) were replicated in the same conditions in order to check for selected pathogenic parasites (Nematodes eggs, Giardia lamblia cysts and Cryptosporidium parvum oocysts) before and after disinfection as well as for potential DBP formation (i.e., nitrophenols and N-nitroso-amines). Analytical procedures were according to Standard Methods [ 13] except as specified below: • Giardia lamblia cysts and Cryptosporidium parvum oocysts: the method (Standard Method No. 9711 B as modified by Portincasa [14]) involves pressure (4 atm) tangential ulaafiltmtion of a 10-1 sample through 142 mm diameter (1.2 ktm porosity) cellulose acetate membranes. The membranes were eluted wilh 0.1% Tween 80 solution using magnetic stirring and the eluate was centrifuged at 1500 rpm using plastic tubes. The centrate was purified by Percoll-sucrose gradient and identified by microscopy using immunofluorescent monoclonal antibodies. • Nematodes eggs: the method (not standardized yet) involves the filtration of a 2-1 sample, membrane elution and centrifugation as for

p2 ¸

~ 7

UVCP

,tl..-

t

UVA

V

Fig. 1. Pilot plant configurationduring UV disinfectionexperiments(MF, multilayerpressure filter; RV, 5 m3 fibre-glass vessel; UVA,non contactTeflonUV apparatus; UVCP,UV controlpanel;P, pumps;FM, flow meter;V, valve).

318

L. Liberti et al. / Desalination 152 (2002) 315-324

Giardia and Cryptosporidium. The centrate was identified by phase- and differential-interference-contrast optic microscopy. • Nitro-phenols: liquid-liquid extraction GC/MS method (Standard Method No. 6410 B) modified for extraction and concentration procedures: a 2-1 sample, previously filtered on 0.45-mm cellulose nitrate membrane, was acidified at pH 2 with sulphuric acid (1:1) and extracted by vacuum filtration on a previously conditionated polystyrene-divinil-benzene(SDVB) membrane. The membrane was eluted with methylene-chloride, the eluate was concentrated (up to 1 ml) under vacuum and analysed by GC/MS. Control o f extraction and concentration procedures was obtained with blanks and standard solutions. N-nitroso-amines: liquid-liquid extraction GC/MS method (Standard Method No. 64 10 B) modified for extraction and concentration procedures: a 2-1 sample was alkalinised to pH 11 with 10N NaOH, filtered on 0.45-ktm cellulose nitrate membrane and extracted by vacuum filtration on a previously conditionated C 18 membrane. The membrane was eluted with methylenechloride, the eluate was concentrated (up to 1 ml) under vacuum and analyzed by GC/MS. Control of extraction and concentration procedures was obtained with blanks and standard solutions.

The following analytical instruments were used: • tangential ultrafiltration apparatus mod. Sartocon 2 and mod. Sartocon Mini by Sartorius; • optic microscope (direct light, phase- and differential-interference-contrast)mod. Axioskop MC 80 by Zeiss; • fluorescence microscope mod. BH2 by Olympus; • gas chromatograph/mass spectrometer (GC/ MS) mod. Saturn 3 by Varian with purge and trap autosampler mod. 3000 by Tekmar; • vacuum concentration apparatus mod. AES 1000 by Savant;

•

liquid chromatograph/mass spectrometer (LC/ MS) mod. API 300 by Perkin Elmer.

3. Results and discussion

3.1. Parasite removal performance

As said, several cycles were run at UV dose of 100 and 160 mWs/cm 2 for F and CL feed respectively to evaluate UV effectiveness towards selected pathogenic parasites (Giardia lamblia cysts, C r y p t o s p o r i d i u m p a r v u m ocysts and Nematodes eggs) likely to occur in local wastewater and are reportedly resistant to chemical disinfectants. The occurrence of these pathogens in CL and F feed before and after UV disinfection is reported in Table 1 (average values). Nematodes eggs were never found in the feeds admitted to disinfection, confirming the effectiveness of clarification and filtration steps in removing consistently such large and heavy parasites [ 15], but not towards smaller ones like Giardia cysts and Cryptosporidium oocysts detected in appreciable number in feed CL and removed only in part by filtration, as expected [16]. In these conditions UV radiation was rather effective in both feeds towards both protozoan parasites with an average removal around 60 and 65% for Giardia and Cryptosporidium respectively. Table 1 Selected parasites before and after UV disinfection of clarified(CL) and clarified-filtered(F) feeds (UV dose: 160 and 100 mWs/cm2 respectively) Parasite Nematodes eggs (N/l) Giardia lamblia cysts (N/I) Cryptosporidium Parvum oocysts (N/I)

Feed In CL 0 F 0 CL 345 F 114 CL 23 F 6

Out 0 0 156 44 8 2

% removal --55 62 65 67

L. Liberti et al. / Desalination 152 (2002) 315-324

These results came not unexpected as protozoan cysts are resistant species, requiring higher UV doses than bacteria and viruses [17]. According to literature data, UV doses lower or similar to those investigated (around 60, 80 and 120180 mWs/cm 2) are claimed to produce 80, 90 and 99% inactivation of Giardia cysts [18-20] and Cryptosporidium oocysts [21,22] in drinking water. The multiple barrier concept involving clarification and filtration (plus eventually GAC adsorption) prior to UV disinfection undoubtedly appears the most effective approach for complete parasite removal in water and wastewater treatment [20]. It must be pointed out that the proved occurrence of some protozoa in the disinfected effluents does not cause restriction for their reuse in agriculture. In fact, according to the WHO guidelines [23], the only parasites of concern are intestinal nematodes (MAC < 1 egg/l), never found during this investigation. However, these latter are intended to serve as indicator organisms for all parasitic pathogens and it is implied that all helminth eggs and protozoan cysts should be removed to the same extent to avoid the risk of waterborne disease outbreaks. 3.2. Disinfection by-products formation

As for eventual formation of UV disinfection by-products during drinking water production, it is generally assumed that moderate ultraviolet irradiation (<50 mWs/cm z) affects the structure of organic compounds to a much lesser extent than chemical reagents like chlorine or ozone [ 17]. However, some results dealing with degradation of pesticides and other specific compounds in industrial wastewater under high UV doses (> 1000 roWs/ cm 2) indicated the need for further information about UV promoted transformation of organic compounds in municipal wastewaters [24,25]. On the basis of photochemistry fundamentals, in fact, it cannot be excluded that UV irradiation ofwastewater could affect the identity of the organic substances through either direct or indirect

319

interaction forming potentially toxic by-products [26, 27]. In the former case, a molecule known as a chromophore may be chemically modified as a result of direct radiation absorption. Indirect photolysis may occur when UV radiation acts on a species known as a photosensitiser which strongly absorbs the radiation energy and the resulting highly energetic species interacts with another molecule producing a chemical transformation [28,29]. Considering that amino- and phenolic-derivatives (chromophores) as well as nitrate/nitrite ions and humic materials (photosensitisers) are species commonly occurring in municipal wastewater and potentially capable of reacting [30], nitro-phenols and N-nitroso-amines were specifically searched for in this investigation as possible DBPs following UV irradiation. Figs. 2-5 show the corresponding GC/MS chromatograms ofF and CL feeds before and after UV disinfection (doses of 100 and 160 mWs/cm 2 respectively). The nearly total overlapping of all spectra seems to exclude the formation of both harmful N-derivatives above the instrumental detection limit (0.01 ppb) in the conditions investigated. A possible explanation could be the formation of non-volatile DBPs (NVDBP) which are not detected by GC/MS but only by LC/MS (or MS/MS) analytical technique. A special experiment was carefully planned to check this hypothesis at lab scale. In particular, in order to maximize the probability of detecting the eventual NVDBP formation, a 500-ml sample of CL feed was irradiated in a glassbatch-UV reactor using purposely an extremely high UV dose (25,000 mWs/cm2). Samples before and after the irradiation were concentrated 25 times by lyophilization and post-column injected into a LC-MS spectrometer. The obtained mass spectra reported in Fig. 6, once again, do not show any significant difference between irradiated and non-irradiated samples, excluding the eventual formation of NVDBPs even under the extreme irradiation adopted during the experiment.

320

L. Liberti et al, /'Desalination 152 (2002) 315-324

i

u

|

1200 Fig. 2. Nitro-phenols search: GC/MS spectra of F feed before and after LJV disinfection (100 mWs/cm~),

I fl~

16~1~

1200

2,400

20~

Fig. 3. N-nitroso-amines search: GC/MS spectra o f f feed before and after UV disinfection (100 mWs/cmZ).

!

9~

•

.h ,

!

t~9

°

I

t500

tfl(~

f

2186

Fig. 4, Nitro-phenols search: GC/MS spectra of CL feed before and after UV disinfection (160 mWs/cm2).

J

240~

321

L. Liberti et al. / Desalination 152 (2002) 315-324

, I

'

'

I

'

I

=

''

''

-

--

'

,,

|

|

'--

!

'

1600

:12,00

800

'

2400

2000

Fig. 5. N-nitroso-amines search: GC/MS spectra of CL feed before and after UV disinfection (160 mWs/crn2).

,1 5,416 4,Se6 $.6d

I

30~.1

2.7d" .8d g.otS, I 1"~o

2110

310

41o

490

5110

11,30

s~

~

TOO

|

GeS" 171,3 5t6"

~"

4elll, d

I ,

:'4S.3

z**

zlo

~io

4/0

m/I,

410

Tc~

,7*

Fig. 6. Post injection LC/MS spectra of iyophilizated samples of CL feed before and after UV irradiation (25,000 mWs/cm~).

The above evidences are in good agreement with the conclusions reported for similar investigation stating that UV-promoted transformation of chemical compounds, at least in clean waters, requires much higher doses than necessary for municipal wastewater disinfection [31-35].

3.3. Cost estimates

To assess the economic feasibility of UV disinfection treatment for wastewater reuse in agriculture, operation and maintenance (O&M) costs were preliminarily estimated on the basis of the experi-

322

L. Liberti et al. / Desalination 152 (2002) 315-324

mental results obtained by reference to the optimal UV dose for each feed that permitted the achievement of the target total coliforms standard of 2 CFU/100ml, i.e., 100 and 160 mWs/cm 2 for F and CL feeds respectively. The following assumptions were made: • O&M costs account essentially for electric power consumption and lamp replacement, including also maintenance requirements and miscellaneous equipment repair costs • power consumption of UV equipments is 3.1 kWh • average electricity cost is t~ 0.065/kWh • UV lamp (t~ 45 each) replacement is based on 8760 h of use. As shown in Table 2, O&M costs of UV advanced disinfection of the intermediate (clarified, CL) and the full tertiary treated feed (clarifiedfiltered, F) amounted to t~ 35 and t~ 17.5/1000 m 3 respectively. The above estimates do not include capital costs and can be influenced by variables such as feed quality, plant configuration, plant size (scale factor) and market situation. Cost effectiveness of UV advanced disinfection, in particular o f F feed, is evident considering that chlorination of municipal wastewater just for sea discharge in compliance with Italian regulations (20,000 CFU/100 ml for total coliforms) at West Bari treatment plant costs approximately ~ 5/ 1000 m 3. 4. Conclusions

The experimental results of a 9-month pilotscale (100 mVh) investigation, carried out at the West Bari (S. Italy) municipal wastewater treat-

ment plant, focused on parasite removal and disinfection by-product (DBP) formation during the UV disinfection of clarified (CL) and clarifiedfiltered (F) secondary effluents at doses (160 and 100 mWs/cm 2 respectively) necessary for achieving the total coliforms standard of 2 CFU/100 ml for unrestricted reuse of wastewater in agriculture, provided the following indications: 1. At the above doses, UV radiation was rather effective in both feeds towards protozoan parasites like Giardia lamblia cysts and Cryptosporidium parvum oocysts (approx. 60 and 65% removal respectively); Nematodes eggs were never found in the feeds admitted to disinfection because already removed by clarification and sedimentation; 2. The multiple barrier concept involving clarification and filtration prior to UV disinfection was confirmed to be the most effective approach for complete parasite removal in wastewater treatment; 3. None of the N-derivatives (i.e. nitro-phenols and N-nitroso-amines) searched for after UV disinfection of both feeds was detected by GC/MS analytical technique whilst LC/MS analyses excluded also the formation of non-volatile DBPs, suggesting the absence of detectable photochemical reactions at UV doses usually used in wastewater disinfection; 4. O&M costs of UV disinfection averaged t~ 17.5 and t~ 35/1000 m3for F and CL feed respectively. Further investigation is planned to assess UV effectiveness towards viruses, to exclude UV promotion of other DBPs, to prevent effluent recontamination (bacteria photoreactivation by cell repair and regrowth) and to evaluate possible

Table 2 Cost estimates for UV disinfection of CL and F feeds at West Bari pilot plant Feed F CL

UV dose, mWs/cm2

Total coliforms target achieved, CFU/100 ml

O&M costs, t~/1000 m 3 Electric power Lamp replacement

Total

100 160

I 1

6.7 13.5

17.3 34.8

10.6 21.3

L. Liberti et al. / Desalination 152 (2002) 315-324 synergy and/or catalytic effects o f UV radiation with long-acting chemical disinfectants such a s H20 2.

References [ ! ] State of California. Wastewater Reclamation Criteria. California Administrative Code, Title 22, Division 4, California Department of Health Services, Sanitary Engineering Section, Berkeley, CA, 1978. [2] T. Asano, Wastewater Reclamation and Reuse. Technomic, Lancaster, 1998. [3] A. Prost, Health risks stemming from wastewater reutilization, Wat. Quality Bull., 12 (1987) 73. [4] H.V. Smith, L.G. Robertson and J.E. Ongherth, Cryptosporidiosis and Giardiasis: the impact of waterborne transmission, J. Water SRT-AQUA, 44(4) (1995) 258. [5] J.J. Rook, Formation ofhaloforms during chlorination of natural waters, Wat. Treat. Examin., 23 (1974) 234. [6] R.A. Minear and G.L. Amy, Disinfection By-Products in Water Treatment, Lewis Publishers, New York, 1996. [7] V. Lazarova, P. Savoye, M.L. Janex, E.R. Blatchley III and M. Pommepuy, Advanced wastewater disinfection technologies: state of the art and perspectives, Wat. Sci. Technol., 40(4-5) (1999) 203. [8] L. Liberti and M. Notamicola, Advanced treatment and disinfection for municipal wastewater reuse in agriculture, War. Sci. Technol., 40(4-5) (1999) 235. [9] L. Liberti, A. Lopez and M. Notarnicola, Disinfection with peracetic acid for domestic sewage re-use in agriculture, J. Ch. Instn. Wat. Envir. Mangt., 13(4) (1999) 262. [10] L. Liberti, M. Notamicola and A. Lopez, Advanced treatment for municipal wastewater reuse in agriculture. III - Ozone disinfection, Ozone Sci. Eng., 22(2) (2000) 151. [11] L. Liberti, A. Lopez, M. Notarnicola, N. Bamea, R. Pedahzur and B. Fattal, Comparison of advanced disinfecting methods for municipal wastewater reuse in agriculture, Wat. Sci. Technol., 42(1-2) (2000) 215. [ 12] L. Liberti, M. Notamicola, A. Lopez and (2 Boghetich, Advanced treatment for municipal wastewater reuse in agriculture. UV disinfection: bacteria inactivation, J. Water SRT-AQUA, 50(5) (2001) 275. [13] Standard Methods for the Examination of Water and Wastewater. 19th ed., American Public Health Association/American Water Works Association/Water Environment Federation, Washington, DC, 1995.

323

[14] F. Portincasa, G. Torchietti, F. Donadio, D. Carnimeo, M.A. Panaro, S. Lisi, F. Maddalena and O. Brandonisio, Method for determination of Giardia cysts and Cryptosporidium oocysts in water, Igiene moderna, 107 (1997) 543 (in Italian). [15] D.C. Watson, M. Satchwell and C.E. Jones, A study of the prevalence of parasitic helminths eggs and cysts in sewage sludge disposed of to agricultural land, Wat. Poll. Control, 82 (1983) 285. [16] Z. Bukhari, H.V. Smith, N. Sykes, S.W. Humphreys, C.A. Paton, R.W.A. Girdwood and C.R. Fricker, Occurrence of Cryptosporidium spp oocysts and Giardia spp cysts in sewage influents and effluents from treatment plants in England, Wat. Sci. Technol., 35 (11-12) (1997) 385. [17] R.L. Wolfe, Ultraviolet disinfection of potable water, Environ. Sci. Technol., 24(6) (1990) 768. [18] E.W. Rice and J.C. Hoff, Inactivation of Giardia lamblia cysts by ultraviolet irradiation, Appl. Environ. Microbiol., 42 (1981) 546. [19] D.A. Carlson, R.W. Seabloom, F.B. DeWalle, T.F. Wetzler, J. Engeset, R. Butler, S. Wangsuphachart and S. Wang, Ultraviolet disinfection of water for small water supplies. Project summary. EPA/600/S2-85/092, Office of Research and Development, US Environmental Protection Agency, Cincinnati, OH, 1985. [20] P. Karanis, W.A. Maier, H.M. Seitz and D. Schoenen, UV sensitivity of protozoan parasites, J. Water SRTAQUA, 41(2) (1992) 95. [21] M.E. Ransome, T.N. Whitmore and E.G. Carrington, Effect of disinfectants on the viability of Cryptosporidium parvum, War. Suppl., 11 (1993)75. [22] A.T. Campbell, L.J. Robertson, M.R. Snowball and H.V. Smith, Inactivation of oocysts of Cryptosporidiumparvum by ultraviolet irradiation, Wat. Res., 29(11) (1995) 2583. [23] WHO. Health guidelines for the use ofwastewater in agriculture and aquaculture. Technical Report Series 778, World Health Organization, Geneva, Switzerland, 1989. [24] K. Nick, H.F. Scholer, G. Mark, T. Soylemez, M.S. Akhlaq, H.-P. Schuchmann and von C. Sonntag, Degradation of some triazine herbicides by UV radiation such as used in the UV disinfection of drinking water, J. Water SRT-AQUA, 41(2) (1992) 82. [25] M. Otaki and S. Ohgaki, Photochemical decomposition of organo-chiorine compounds by a medium pressure UV lamp. Proc. Water Quality International'94, IAWQ 17th Biennal International Conference, Budapest, Hungary, 1994, p. 110.

324

L. Liberti et al. / Desalination 152 (2002) 315-324

[26] B. Zoeteman, J. Hrubec, E. Greef and H.J. Kool, Mutagenic activity associated with by-products of drinking water disinfection by chlorine, chlorine dioxide, ozone and UV irradiation, Environ. Health Perspectives, 46 (1982) 197. [27] C. von Sonntag and H.-P. Schuchmann, UV disinfection of drinking water and by-product formation - - some basic considerations, J. Water SRT-AQUA, 41(2) (1992) 67. [28] R.W. Matthews, Environment: photochemical and photocatalytic processes. Degradation of organic compounds. In: Photochemical Conversion and Storage of Solar Energy. E. Pelizzetti and M. Schiavello, Eds., KluwerAcademic Publishers, The Netherlands, 1991. [29] J. Kopecky, Organic Photochemistry: A Visual Approach. VCH Publishers, New York, 1992. [30] R.P. Schwarzenbach, P.M. Gschwend and D.M. Imboden, Environmental Organic Chemistry. John Wiley & Sons, New York, 1993. [31] E. Lee, R.L. Joiley, M.S. Denton and J.E. Thompson, Ultraviolet irradiation of municipal wastewater: evaluation of effects on organic constituents,Environment International, 7 (1982) 403.

[32] J. Maarschalkerweerd, R. Murphy and G. Sakamoto, Ultraviolet disinfection in municipal wastewater treatment plants, Wat. Sci. Technol., 22(7-8) (1990) 145. [33] J.A. Oppenheimer, J.E. Hoagland, J.-M. Lain6, G. Jacangelo and A. Bhamrah, Microbial inactivation and characterization of toxicity and by-products occurring in reclaimed wastewater disinfected with UV radiation, WEF Specialty Conference Series: Planning, Design and Operation of Effluent Disinfection Systems, WaterEnvironment Federation,Alexandria, VA., 1993, p. 13. [34] Elsinore ValleyMunicipal WaterDistrict and National Water Research Institute. A Comparative Study of UV and Chlorine Disinfection for Wastewater Reclamation. Executive Summary. Montgomery Watson, Pasadena, CA, 1994. [35] K.G. Linden, G.S. Soriano and J.L. Darby, Investigation of disinfection by-product formation following low and medium pressure UV radiation ofwastewater. Proc. Disinfection'98 Specialty Conference, Water Environment Federation, Baltimore, Maryland, 1998, p. 137.