Wastewater treatment advanced processes and technologies

Depending on the mode of discharge of the waste and the nature of the constituents present in it, most of the treatments are based on conventional technologies, for example, equalization

Wastewater Treatment

Advanced Processes and Technologies

Tai Lieu Chat Luong

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Wastewater Treatment

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Preface viiContributors xi

1 Introduction 1

D G Rao, R Senthilkumar, J A Byrne, and S Feroz

2 Solar Photo-Fenton as Advanced Oxidation Technology

for Water Reclamation 11

Sixto Malato Rodríguez, Nikolaus Klamerth, Isabel Oller Alberola,

and Ana Zapata Sierra

11 Removal of Lower-Molecular-Weight Substances from Water

and Wastewater: Challenges and Solutions 275

V Jegatheesan, J Virkutyte, L Shu, J Allen, Y Wang, E Searston,

Z P Xu, J Naylor, S Pinchon, C Teil, D Navaratna, and H K Shon

The.importance.of.wastewater.treatment.in.the.modern.industrial.world.is.very.high.in.view.of.the.fact.that.more.than.97%,.dormant.in.polar.regions,.of.the.available.water.is.saline.(in.seas.and.oceans).and.2%.of.the.freshwater.is.unavailable.for.human.consumption Thus,.very.little.quantity.of.water

is available for human consumption The world population is increasing,.and.the.per.capita.water.consumption.is.also.increasing.day.by.day,.which.lays a heavy burden on science, technology, and engineering to meet the.challenges.of.water.treatment.and.supply.in.the.future Economic.and.social.growth.cannot.be.ensured.without.industrialization,.which.is.in.turn.a.cul-prit.in.spoiling.the.available.water.resources.due.to.the.generation.of.large.quantities.of.wastewater It.is.paradoxical.but.true To.add.another.dimen-sion.to.the.existing.problem.is.the.increased.day-by-day.legislative.restric-tions.that.are.being.imposed.by.various.governments.all.over.the.world.in.view of the safety and health concerns of the citizens Urbanization with.overconcern.for.hygiene.also.generates.huge.quantities.of.wastewater.that

is.known.as graywater It.comes.from.household.kitchens,

toilets,.and.res-taurants The.graywater.from.kitchens.and.restaurants.is.not.toxic.but.is.not.suitable.for.human.consumption In.the.present.complex.scenario,.the.only.alternative.is.to.treat.the.available.wastewater.to.make.it.as.clean.as.possible The.treated.water.may.not.be.exactly.suitable.for.potable.purpose,.but.can.at.least.be.used.for.various.other.purposes,.viz.,.recycling.partly.for.industrial.purposes,.steam.generation,.or.gardening.and.agriculture

The.treatment.of.wastewater.is.complicated.because.of.the.heterogeneous.nature.of.the.water.streams.coming.from.the.various.domestic.and.indus-trial sources The industrial sources are as diverse as drugs and pharma-ceutics, pesticides, food processing, fermentation, vaccines manufacturing.nuclear.processing,.and.metallurgical.and.animal.processing.industries The.pollutants.generated.can.be.physical,.chemical,.and.biological.in.nature,.and.they.can.be.toxic.or.nontoxic Hence,.the.treatment.methods.are.also.varied.in.nature.in.order.to.process.the.diverse.effluent.wastewaters.coming.from.various.sources

This book is an honest attempt to present important concepts, gies,.and.issues.in.this.direction.by.various.experts.in.the.field.of.wastewater.treatment The.treatment.methods.cover.various.process.industries.and.uti-lize.various.technologies.for.the.purpose Chapters.2–4.deal.with.advanced.oxidation.processes.including.processes.based.on.Fenton.and.photo-Fenton,.ozonolysis,.photocatalysis,.and.sonolysis Various.types.of.reactors.used.in.wastewater.treatment.are.dealt.with.in.Chapters.5,.9,.and.13 Microbial.treat-ment.methods,.in.general,.for.wastewater.treatment.are.described.in.Chapter.6,.whereas.those.used.in.various.process.industries.are.covered.in.Chapter.8

technolo-Effluent.treatment.methods,.usually.practiced.in.food.processing.industries,.are.comprehensively.dealt.with.in.Chapter.10 Removal of.low-molecular-weight.substances.from.wastewater.is.a.challenging.task,.and.hence.special.methods.for.their.removal.are.needed,.which.are.all.described.in.Chapter.11 Seaweeds.are.good.adsorbents.and.may.be.applied.in.wastewater.treatment.for.the.removal.of.toxic.substances.(Chapter.7) The.treatment.of.graywater.needs a special attention in view of its increasing magnitude Chapter 12.describes.such.treatment.methods.with.a.case.study.of.the.Muscat.munici-pality A.special.concept.of.central.effluent.treatment.plants.(CETPs).is.gain-ing.prominence.in.the.treatment.and.release.of.wastewater.from.small-scale.processing.units.into.municipal.water.lines,.after.meeting.the.stringent.leg-islative.requirements It.is.dealt.with.in.the.introductory.chapter.(Chapter.1).All.efforts.have.been.made.by.the.editors.and.authors.to.judiciously.blend.most of the treatment processes and technologies in one single book in.order.to.make.the.diverse.subject.matter.as.comprehensible.as.possible It.is, indeed, difficult to make it concise with the whole gamut of advanced.processes and technologies in a single book of this nature; hence, enthu-siastic readers are advised to consult the original references for complete.understanding.of.any.process.or.technology This.book.is.ideally.suited.for.researchers.and.professionals.working.in.the.area.of.wastewater.treatment Each.chapter.is.specific.in.its.own.way.and,.hence,.may.cater.to.the.require-ments.of.professionals.interested.in.that.area The.bibliography.given.at.the.end.of.each.chapter.would.act.as.a.guide.for.comprehensive.information.in.that.particular.area Hence,.most.of.the.chapters.end.with.a.comprehensive.list.of.literature.references.

At.the.very.outset,.we.would.like.to.thank.all.our.contributing.authors,.who have done an excellent job in drafting and delivering the chapters The.success.of.this.publication.is.largely.due.to.them We.would.also.like.to.extend.our.sincere.thanks.to.the.staff.of.the.editorial.and.publication.depart-ment.of.CRC.Press,.who.have.been.very.helpful.and.cooperative.throughout.the preparation of this material and have been largely responsible for the.book.in.its.present.form We.thank.all.the.authors,.publishers,.and.industries.whose.works.have.been.referred.to.and.who.have.extended.the.copyright.permissions.to.utilize.their.published.information.in.this.book.in.some.form.or.the.other We.would.like.to.extend.our.sincere.thanks.to.the.executives.and.management.of.Caledonian.College.of.Engineering,.Muscat.(Sultanate.of.Oman),.and.to.the.staff.of.the.University.of.Ulster.(United.Kingdom),.for.their.encouragement.and.support.for.this.work We.also.thank.our.families,.who.had.largely.extended.their.moral.support.during.the.last.2.years.while.preparing.(editing).this.book

This.publication.is.a.sincere.effort.made.by.us.to.put.in.a.nutshell.the.vast.subject.matter.of.wastewater.treatment,.which.is.so.vital.in.the.twenty-first.century We.are.aware.of.the.fact.that.this.book.may.not.be.holistic.in.its.approach;.but.still.we.feel.we.are.richly.rewarded.if.the.publication.meets

at least partly the requirements of researchers, professionals, and young

D G Rao

R Senthilkumar

J Anthony Byrne

S Feroz

Department.of.Civil.and

Architectural.EngineeringSultan.Qaboos.UniversityAl-Khod,.Muscat,

Sultanate.of.Oman

J A Byrne

Nanotechnology.and.Integrated.BioEngineering.CentreUniversity.of.UlsterNorthern.Ireland,.UK

P Fernández-Ibáñez

Plataforma.Solar.de.AlmeríaCarretera.Senés

Tabernas,.Spain

S Feroz

Caledonian.College.of.EngineeringMuscat,.Sultanate.of.Oman

V Jegatheesan

School.of.EngineeringDeakin.UniversityGeelong,.Australiaand

School.of.Engineering.and.Physical.Sciences

James.Cook.UniversityTownsville,.Australia

Sri.Venkateswara.College.of

EngineeringSriperumbudur,.Chennai,.India

S Pinchon

School.of.EngineeringDeakin.UniversityGeelong,.Australia

P B Punjabi

Department.of.ChemistryM.L Sukhadia.UniversityUdaipur,.India

D G Rao

Caledonian.College.of.EngineeringMuscat,.Sultanate.of.Oman

Sixto Malato Rodríguez

Plataforma.Solar.de.AlmeríaCarretera.Senés

Tabernas,.Spain

E Searston

School.of.EngineeringDeakin.UniversityGeelong,.Australia

R Senthilkumar

Caledonian.College.of.EngineeringMuscat,.Sultanate.of.Oman

H K Shon

Faculty.of.EngineeringUniversity.of.Technology.SydneyBroadway,.Australia

Environmental.EngineeringKarlsruhe.Institute.of.TechnologyKarlsruhe,.Germany

andSingapore-Delft.Water.AllianceNational.University.of.SingaporeSingapore

J Virkutyte

Pegasus.Technical.Services.Inc.Cincinnati,.Ohio,.USA

Y Wang

School.of.EngineeringDeakin.UniversityGeelong,.Australia

Z P Xu

ARC.Centre.of.Excellence.for.Functional.NanomaterialsAustralian.Institute.for

BioEngineering.and

NanotechnologyThe.University.of.QueenslandBrisbane,.Australia

Introduction

D G Rao, R Senthilkumar, J A Byrne, and S Feroz

One of the greatest challenges of the twenty-first century would be to have

an incessant supply of safe drinking water and clean air to breathe for the millions of living things all over the world The major concern in this is not the depletion of air and water but the indiscriminate damage that is being done to them under the guise of industrial development The day is not far off when they will become rare commodities The problem being addressed

in this book is concerned with the wastewater treatment

The worldwide concern for the depletion of global water sources is ing day by day It is more than just the depletion of sources; with the ever-increasing population and growing economy, demands for water are also continuously growing Water sources, however, are not as abundant as they seem at first, since only in a very limited number of situations can available water be used without any treatment A casual observation of the world map would suggest that the supply of water is endless since it covers over 80% of the earth’s surface Unfortunately, however, we cannot use it directly since 97% is in the salty seas and oceans, 2% is tied up in the polar ice caps, and most of the remainder is beneath the earth’s surface When a huge amount of water is required for different industrial processes, only

ris-a smris-all frris-action of the sris-ame is incorporris-ated into their products ris-and lost

by evaporation; the rest finds its way into the water courses as ter Wastewaters are those waters that emanate from (i) domestic sources, (ii) restaurants and establishments, and (iii) factories and industries Of them, industries are the main polluters of natural bodies of water Newer technologies lead to newer and more toxic wastes; these wastes take lon-ger periods of time for decomposition, and most of the time, toxic wastes are deeply buried in the ocean or land But this is far from a permanent solution as it degrades the earth Newer technologies are being researched every day, but much less development has occurred in the field of waste treatment The world depends on earth for disposal, but what will happen

wastewa-to earth Little thought has been given wastewa-to this Recently, the world saw a major disaster in the Mexican Gulf, where BP (M/s British Petroleum) lost

an oil well, creating an oil slick of millions of gallons and deeply gering marine and human life nearby

endan-Anthropogenic activities include rapidly growing industrialization, series

of new constructions, manyfold increases in transportation, aerospace movements, development and enhancement in technologies, that is, nuclear power, pharmaceutical, pesticides, herbicides, agriculture, etc All of these are most desirable activities for human development and welfare but they also lead to the generation and release of objectionable materials into the environment Thus, they pollute the whole environment, making our life

on this beautiful earth quite miserable The situation, if not controlled in a timely manner, could become a malignant problem for the survival of man-kind on the earth To have a neat, clean, healthy, and green environment, there is an urgent need to search for such an approach, which may be appli-cable at room temperature, safe to handle, economic, eco-friendly, and above all, the main requirement is that it should not be harmful to the environment

in any manner

There are many sources of water pollution, but two general categories exist: direct and indirect contaminant sources Direct sources include effluent outfalls from industries, refineries, waste treatment plants, etc Indirect sources include contaminants that enter the water supply from soils/groundwater systems and from atmosphere via rain water Soils and groundwater contain residues of human agricultural practices (fertilizers, pesticides, etc.) and atmospheric contaminants that come from various human practices (such as gaseous emissions from automobiles, factories, etc.) Pollutants in water include a wide spectrum of chemicals and patho-gens, with different physical chemistries or sensory changes There are a number of ways to treat wastewaters based on the type of contaminants These various treatment methods can be conveniently classified into the following:

1 Direct disposal of wastes into streams without any treatment

2 Discharge of wastes into municipal sewers for combined treatment

3 Separate treatment of industrial wastes before discharging into water bodies

The selection of a particular process depends on the self-purification capacity of streams, permissible levels of pollutants in water bodies, and the economic interests of both the municipalities and the industries Depending

on the mode of discharge of the waste and the nature of the constituents present in it, most of the treatments are based on conventional technologies, for example, equalization, neutralization, physical treatment, chemical treat-ment, and biological treatment

A number of water treatment technologies are desired to at least tially cleanse the water to serve the following purposes even though it is certain that the treated water cannot be as safe and pure as freshwater for potable purposes:

1 The treated water may be used for some other beneficial purposes

2 The effluents do not mix directly with streams, lakes, and beaches and cause them to become polluted

3 The treated water may be used for agricultural purposes

4 In small quantities, the treated water may be used for raising kitchen gardens, horticultural crops, etc

Most wastewater treatment processes cannot effectively respond to nal, seasonal, or long-term variations in the composition of wastewater

diur-A treatment process that may be effective in treating wastewater during one time of the year may not be as effective at treating wastewater during another time of the year Some of the major concerns of treated water for reuse are as follows:

1 How reliable are the treatment methods so that the treated water may be reused for the intended purpose, if not directly for the pota-ble purpose for human consumption?

2 How safe is the water for protecting public health?

3 To what extent does the treated water gain public acceptance?

Nowadays, much attention is given to the treatment of industrial wastes, due to their growing pollution potential arising out of the rapid industri-alization Streams can assimilate certain amounts of waste before they are polluted, and a municipal sewage treatment plant can be designed to handle any kind of industrial waste

In addition to the treatment by municipalities, there is also an approach

known as common effluent treatment plants (cetps), which is mostly in vogue

in most of the industrial estates in India to treat the industrial wastewaters These treatment plants are established in industrial areas Effluents from some of the small-scale processing plants are transported to the CETP where they are treated to safe limits based on the following:

1 Composition of effluents

2 Type of processing plant

3 Time of delivery from processing plant

The CETPs are a wonderful concept in wastewater treatment and are cially helpful to small and medium industries that cannot afford to have a treatment plant of their own (Rao 2010, p 410) However, such treatment plants can meet the requirements of a particular group of processing indus-tries, namely pharmaceutical industries, textile industries, food process-ing industries, etc They obviously may not be able to treat a wide range of effluent waters But the effluents can be classified in terms of their pollutant constituents on the basis of some physicochemical parameters such as flow rate, pH, TSS (total soluble solids), COD (chemical oxygen demand), BOD (biological oxygen demand), etc One such treatment plant in operation in India is in Vatva Industrial Estate (in Gujarat state), where the processing industries include dyes, dye intermediates, bulk drugs and pharmaceuti-cals, fine chemicals, and textiles The characteristics of the effluents were consolidated by M/s Sudarshan Chemicals, Pune, based on which the design for CETP was made by M/s Advent Corporation, USA (Figure 1.1) The extended aeration technique in biological treatment process is the main criterion for treatment in this unit

espe-A similar kind of effluent treatment plant, operating in the Industrial estate

in Pattancheru (Hyderabad, India) and catering to the needs of local bulk drug and pharmaceutical manufacturing units, is Enviro-Tech Ltd The unit works on the dissolved air floatation principle and was supplied by M/s Krofta Engineering (Krofta Technologies Corporation, USA) A coagulant (alum) is used along with a small dosage of a polyelectrolyte to coagulate the suspended solids (Rao 2010, p 410) A special decanter is used to scoop the floated material (sludge) with the help of a patented “Krofta spiral scooper” and push it to the stationary central section from where it is discharged (Figure 1.2)

FIGURE 1.1 (See color insert)

Common Effluent Treatment Plant in Vatva Industrial Estate in Gujarat (India).

Major industries have their own wastewater and effluent treatment plants Most of the chemical processing units release wastewaters in some form or the other Some of the major categories of processing industries releasing effluents are summarized in Table 1.1 The contaminants in wastewaters released from any of the above-mentioned processing industries can be broadly classified as follows:

• Proteins and proteinaceous materials

• Soluble vitamins and micronutrients

• Toxins and vaccines

• Microorganisms, bacteria, virus, etc

Hence, the treatments for them are also varied The various treatment els are as follows:

lev-FIGURE 1.2 (See color insert)

Krofta spiral scooper.

TABLE 1.1

Various Processing Industries with Possible Contaminants

S No Processing Industry

Possible Contaminants in

suspended particles, toxins Physical, chemical, and biological methods, BOD

Physical, chemical, and biological methods, neutralization

processes Organic matter, soluble and suspended particles Physical, chemical, and biological methods, BOD

reduction

industries Organic matter, soluble and suspended particles Physical, chemical, and biological methods, BOD

reduction (see Chapters 8, 9, and 11)

industries Organic matter, soluble and suspended particles Physical, chemical, and biological methods, BOD

reduction

and flavors Organic matter, soluble and suspended particles,

chemical contaminants

Physical, chemical, and biological methods, BOD reduction

and petrochemicals Chemical contaminants, oils, fats, and greases Physical and chemical methods (see Chapter 8)

molasses-based industries Organic matter, soluble and suspended particles Physical, chemical, and biological methods, BOD

reduction

soluble and suspended particles

Physical and chemical methods

manufacturing units Organic matter, soluble and suspended particles Physical, chemical, and biological methods, BOD

reduction

oils, fats, and greases Physical and chemical methods

• Primary

• Secondary

• Tertiary

• Advanced tertiary processes

All these treatment methods utilize a number of separation processes

that are classically known as unit operations (UOs) UOs are a set of physical

separation processes that all can be broken down into a number of simple mathematical expressions that, on integration, will unify all of the process-ing operations Various UOs are shown in the Table 1.2 for various combina-tions of phases (Rao 2010, p 362) The information in the table is more general

in nature and is particularly applicable to bioprocessing

Heavy metal ions present in the wastewaters of various chemical tries (listed in Table 1.1) have been noticed to have adverse effects on the performance of treatment methods, and hence their impact on the receiv-ing environment needs careful consideration Reckless and uncontrolled discharge of wastewaters containing heavy metals into the environment will pose detrimental effects to humans, animals, and plants As a result, removal and recovery of heavy metals from industrial wastewaters before subjecting them to biological treatment have gained significant attention

indus-in recent years to protect the environment Lead, mercury, chromium, mium, copper, zinc, nickel, and cobalt are the most frequently found heavy

cad-TABLE 1.2

Various Unit Operations for the Treatment of Suspended and Soluble

Particulates in Wastewater Treatment

Ultrafiltration a Reverse osmosis

Sedimentation Decanting

Sedimentation Centrifugation Liquid–

liquid–solid MiscibleImmiscible Air floatation, foamingAdsorption Centrifugation

Sedimentation Decanting

Source: Rao, D.G., Introduction to Biochemical Engineering, 2nd edn, Tata McGraw

Hill Education Pvt Ltd, New Delhi, 2010 With permission.

metals in industrial wastewaters Methods used for removing heavy als from wastewaters are also based on physical, chemical, and biological methods Physicochemical methods such as precipitation, adsorption, ion exchange, and solvent extraction require high capital and operating costs and may produce large volumes of solid wastes, so these methods are often restricted because of technical and/or economic constraints Among the

13

processes (AOPs) Photo-Fenton AOPs for wastewater reclamation; overview of photo-Fenton processes 2 and 4

processes Solar collectors and concentrators were described Semiconductor photocatalysis was described to

produce reactive O 2 species for the destruction

of organic contaminants and inactivation of microorganisms.

8

in food processing

industries

A general review on wastewater treatment in

various biological methods, biosorption has emerged as a cost-effective and efficient alternative treatment technology for heavy metals Biosorption is the process of uptake of heavy metal ions and radio nuclides from aque-ous solutions by biological materials Different types of biomass in nonliving form are found to be suitable for the uptake of heavy metals Bacteria, fungi, algae, plant leaves, and root tissues are used as biosorbents for the recovery

of metals from industrial discharges (Chapters 6 and 7) Among these ferent types of biomass, seaweeds are extensively used for metal biosorption due to their high uptake capacities

dif-In addition to the above classical physical and biological processes, we may also use membrane separation processes, reverse osmosis (RO), and ultra-filtration processes However, their application in wastewater treatment is usually discouraged in view of their prohibitive costs and large quantities of wastewater to be handled These processes are time-consuming and can be used at a small-scale level as in the case of downstream processing steps in chemical or bioprocessing industries There are some advanced techniques,

such as photocatalytic and photo-Fenton processes, which are being

increas-ingly tried upon for wastewater treatments The application of solar energy either in the form of photovoltaic effect or in a concentrated form is another emerging area used for wastewater treatments (see Chapters 2–4) The appli-cation of nanotechnology and nanoparticles for wastewater treatment is another fascinating area and has been attracting the attention of researchers

in the recent years in wastewater treatment

Thus, wastewater treatment has many facets that need to be attended to

in order to cleanse the wastewaters and make them as pure as possible The benchmark is to make them fully potable If not, they at least should

be used for agricultural purposes and various other non-potable purposes The approach (cleaning process) protects the environment from the contami-nants of wastewaters This book addresses some of these issues covering a wide range of wastewaters produced from different processing industries

by utilizing a variety of treatment methods Some are traditional methods, while others are advanced processes The treatment methods also use a wide variety of equipment for various UOs, solar panels, solar heaters, and photo-Fenton processes, while others use a wide variety of biochemical reactors for the biological treatment of wastewaters They are all summarized in a nutshell in Table 1.3

Reference

Rao, D.G 2010 Introduction to Biochemical Engineering, 2nd edn New Delhi: Tata

McGraw Hill Education Pvt Ltd., pp 362, 410.

of 2008, the European Commission approved a new Directive (2008/105/EC)

on environmental quality standards in the field of water policy The new directive considers the identification of the causes of chemical pollution of surface waters and the dealing with emissions at the sources, in the most

CONTENTS

2.1 Introduction 112.2 Solar Photo-Fenton 142.2.1 Fenton and Photo-Fenton 142.2.2 Solar Photocatalysis Hardware 172.2.2.1 Compound Parabolic Concentrators 192.3 Experimental Setup 212.3.1 Solar Pilot Plant 212.3.2 Reagents 222.3.3 Analytical Measurements 252.3.4 Experimental Procedures 262.4 Results and Discussion 26Acknowledgment 33References 33

economically and environmentally effective manner as a matter of priority Concerning the 33 priority substances and priority hazardous substances (alachlor, anthracene, atrazine, benzene, and so on), Directive 2008/105/EC expresses the environmental quality regulations in terms of annual aver-ages, providing protection against long-term exposure and maximum per-missible concentrations for short-term exposure.

Apart from the priority pollutants with established risk, there are hardly any studies on most of the organic compounds, and there are no environ-mental quality criteria for them yet Current developments in analytical techniques, such as gas chromatography–mass spectrometry (GC-MS or GC-MS/MS) and liquid chromatography–mass spectrometry (LC-MS or LC-MS/MS), have made the detection and analysis of many of these new organic compounds in the environment, the analysis of which was hith-erto difficult, possible (Petrovic and Barceló 2006; Hogenboom et al 2009; Pietrogrande and Basaglia 2007; Gómez et al 2009) “Emerging contami-nants” (ECs) are defined as a group of unregulated substances that could

be candidates for future regulation, depending on the findings of research

on their effects on human health and aquatic biota and surveillance data

on the frequency of their presence in the environment A wide range of compounds, for example, detergents, pharmaceuticals, personal hygiene products, flame retardants, antiseptics, industrial additives, steroids, and hormones, have recently been found to be particularly relevant The main characteristic of these pollutants is that they do not need to be persistent

to cause negative effects, because their rates of removal are compensated

by their constant introduction into the environment The increasing use of these substances directly increases their concentration in treated and other waters (Fono et al 2006; Jackson and Sutton 2008; Nakada et al 2008), as con-ventional wastewater treatment plants are not able to remove them entirely (Göbel et al 2007; Teske and Arnold 2008) As most of these ECs have xeno-biotic, endocrine-disrupting, nonbiodegradable, toxic, or persistent prop-erties, they must be degraded and removed prior to their release into the environment This is even more important if the water is reused for irriga-tion, as these contaminants could accumulate in soil and crops (Radjenović

et al 2007; Muñoz et al 2009; Snow et al 2007)

Traditionally, wastewater treatment has focused on pollution abatement, public health protection, and environmental protection by removing biode-gradable materials, nutrients, and pathogens (Levine and Asano 2004) At present, wastewater reclamation is one of the tools available to better manage the water resources diverted from the natural water cycle to the anthropic cycle The way water is reused should always be linked to health protection, public acceptance, and its perceived value in the community The main objec-tive of wastewater reclamation and reuse projects is to produce water of suf-ficient quality for all nonpotable uses (uses that do not require the standards

of drinking water) Using reclaimed water for these applications would save significant volumes of freshwater that would otherwise be wasted (Sala and

Serra 2004) Reusable water should be free of these persistent, toxic, disrupting, or nonbiodegradable substances (Radjenović et al 2007; Teske and Arnold 2008); hence, an effective tertiary treatment method is required

endocrine-to remove these substances completely Conventional municipal wastewater treatment plants (MWTPs), typically based on biological processes, are capa-ble of removing some substances, but nonbiodegradable compounds may escape the treatment and be released into the environment (Carballa et al 2004; Ternes et al 2007) Antibiotic drugs have been identified as a particular category of trace chemical contaminants (Le-Minh et al 2010) Much of the concern regarding the presence of antibiotics in wastewater and their persis-tence through wastewater treatment processes is related to the concern that they may contribute to the prevalence of resistance to antibiotics in bacterial species in wastewater effluents and surface water near wastewater treatment plants (Auerbach et al 2007; Jury et al in press) ECs and priority substances have been found in the MWTP effluents at mean concentrations ranging from 0.1 to 20 μg/L (Martínez Bueno et al 2007; Richardson 2007; Zhao

et al 2009) Concern about the growing problem of the continuously rising concentrations of these compounds must be emphasized, and therefore, the application of more thorough wastewater treatment protocols, including the use of new and improved technologies, is a necessary task Conventional secondary wastewater treatment processes appear to be highly variable in their ability to remove most of these compounds, with their performance apparently dependent upon specific operational conditions, such as the spe-cific retention time (SRT) Accordingly, tertiary and advanced treatment pro-cesses may be necessary to provide a further reduction of these compounds,

in order to minimize environmental and human exposure

Among the advanced processes that can degrade these ECs, advanced dation processes (AOPs) are a particularly attractive option (Westerhoff et al 2009; Klavarioti et al 2009) Although there are different reacting systems (see http://www.jaots.net/), all of them are characterized by the same chemi-cal feature: production of hydroxyl radicals (∙OH), which can oxidize and mineralize almost any organic molecule, yielding CO2 and inorganic ions

oxi-Rate constants (kOH) for the formation of ∙OH radicals by the rate expression

(r  = kOH [∙OH] C) for most reactions involving hydroxyl radicals in aqueous solution are usually of the order of 106−109 M−1/s They are also character-ized by their nonselective attack, which is a useful attribute for wastewa-ter treatment to solve pollution problems The versatility of AOPs is also enhanced by the fact that there are different ways of producing hydroxyl radicals, facilitating compliance with the specific treatment requirements Methods based on UV, H2O2/UV, O3/UV, and H2O2/O3/UV combinations use the photolysis of H2O2 and ozone to produce the hydroxyl radicals Heterogeneous photocatalysis and homogeneous photo-Fenton are based

on the use of a wide-bandgap semiconductor and the addition of H2O2 to dissolved iron salts, respectively, and the irradiation with UVA-visible light (Pignatello et al 2006; Comninellis et al 2008; Shannon et al 2008)

Some of the disadvantages associated with AOPs are their high ing costs depending on the specific process: (i) high electricity demand (e.g., ozone and UV-based AOPs), (ii) relatively large amounts of oxidants and/or catalysts consumed (e.g., ozone, hydrogen peroxide, and iron-based AOPs) and slow kinetics (photocatalysis with TiO2), and (iii) the pH required (e.g., Fenton and photo-Fenton) By using solar energy as a light source, optimiz-ing the pH, and optimizing the amounts of oxidant/catalyst, processes such

operat-as photo-Fenton may be used for commercial applications

AOP efficiency in the removal of ECs has typically been studied in eralized water at bench scale in the initial concentration range of few milli-grams to grams This may not be realistic compared with the concentrations detected in real water and wastewaters Hence, this work focused on solar photo-Fenton degradation of ECs typically found in the effluents of MWTPs, leaving the treated wastewater suitable for reuse Moreover, to make the pro-cess suitable for practical applications, high iron concentrations (mM range) and excessive amounts of H2O2 were avoided The results presented were obtained

demin-in a pilot-scale solar photo-Fenton treatment plant run with startdemin-ing tions of 5 mg/L Fe and 50 mg/L H2O2 Real effluent wastewaters (REs) to which

concentra-a mixture of 15 ECs concentra-at low concentrconcentra-ations, consisting of phconcentra-armconcentra-aceuticconcentra-als, cides, and personal-care products, selected from a list of 80 compounds found

pesti-in MWTP effluents pesti-in previous studies (Martínez Bueno et al 2007), was added (100 μg/L or 5 μg/L each were tested in this study) RE without spiking with any

EC was also tested and evaluated by LC-MS Water reuse is required to deal not only with ECs but also with the potential problems of pathogens Therefore, the preliminary results of the removal of pathogens are also presented

of the application of the photo-Fenton process for the treatment of ter were published by the groups of Pignatello, Lipcznska-Kochany, Kiwi, Pulgarín, and Bauer (Pignatello et al 2006) Much of the literature that deals with the photo-Fenton process takes into account the possibility of driving the process with solar radiation This is due to the fact that a priori the photo-Fenton process seems to be the most apt of all AOPs to be driven by sunlight, because soluble iron hydroxide (and especially iron–organic acid complexes)

wastewa-absorbs even part of the visible light spectrum (Malato et al 2009) Though several excellent and comprehensive reviews on the process exist (Neyens and Baeyens 2003; Pignatello et al 2006), we will give a short summary of the principles of reactions that occur in the photo-Fenton system for the sake of completeness and clarity of the following discussion.

Hydrogen peroxide is decomposed into water and oxygen in the presence

of iron ions in an aqueous solution in the Fenton reaction, Equation 2.1, which was first reported by Fenton (1894) A mixture of ferrous iron and hydrogen

peroxide is called Fenton's reagent If ferrous is replaced by ferric iron, then

the mixture is called Fenton-like reagent Equations 2.1 through 2.7 show the reactions of ferrous iron, ferric iron, and hydrogen peroxide in the absence

of other interfering ions and organic substances The regeneration of ferrous iron from ferric iron, shown in Equations 2.4 through 2.6, is the rate limiting step in the catalytic iron cycle, if iron is added in small amounts

Fe3 O Fe2 O

2 ++ •− 2 → ++ , (2.6)

OH•+H O2 2→H O HO2 + • 2 (2.7)Furthermore, radical–radical reactions (Equations 2.8 through 2.10) have to

be taken into account:

2OH•→H O2 2, (2.8)2HO2 •→H O2 2+O2, (2.9)

HO2 •+OH•→H O O2 + 2 (2.10)

If organic substances (such as quenchers, scavengers, and pollutants in the case of wastewater treatment) are present in the system Fe2+/Fe3+/H2O2, they

react in many ways with the generated hydroxyl radicals Yet, in all cases, the oxidative attack is electrophilic and the rate constants are close to the diffusion-controlled limit The following reactions with organic substrates have been reported (Legrini et al 1993): hydrogen abstraction from aliphatic carbon atoms (Equation 2.11), electrophilic addition to double bonds or aro-matic rings (Equation 2.12), and electron transfer reactions (Equation 2.13).

OH•+RH→R•+H O2 , (2.11)

R CH CH− = 2+OH•→ −R C H CH OH• − 2

, (2.12)

OH•+RX→RX•++OH− (2.13)The generated organic radicals continue reacting, prolonging the chain reaction, and thereby contribute to reduce the consumption of oxidants in wastewater treatment by Fenton and photo-Fenton methods In the case of aromatic pollutants, the ring system is usually hydroxylated before it is bro-ken up during the oxidation process Substances containing quinone and hydroquinone structures are typical intermediate degradation products Anyway, sooner or later, ring-opening reactions occur, which further carry on the mineralization of the molecules (Chen and Pignatello 1997) But there is one major setback of the Fenton method: especially when the treatment goal

is the total mineralization of organic pollutants, the carboxylic intermediates cannot be further degraded Carboxylic and dicarboxylic (L: monocarboxylic and dicarboxylic acids) acids are known to form stable iron complexes, which inhibit the reaction with peroxide (Kavitha and Palanivelu 2004) Hence, the catalytic iron cycle reaches a standstill before total mineralization is accom-plished, as shown in Equation 2.14

Fe3 + nL FeL + H O , dark 2 2 no further reaction

+ →[ n]x → (2.14)

In the photo-Fenton system, the primary step in the photoreduction of dissolved ferric iron is a ligand-to-metal charge-transfer (LMCT) reaction Subsequently, the intermediate complexes dissociate as shown in reaction 2.15 The ligand can be any Lewis base that is able to form a complex with ferric iron (OH−, H2O, HO2−, Cl−, R–COO−, R–OH, R–NH2, etc.) Depending on the reacting ligand, the product may be a hydroxyl radical, such as the ones shown in reactions 2.16 and 2.17, or another radical derived from the ligand The direct oxidation of an organic ligand as well is possible, as shown in reaction 2.18, for carboxylic acids

Fe L3 + h Fe L3 + * Fe2 + L•[ ]+ ν→[ ] → + , (2.15)

a reaction shows an initial lag phase, until intermediates are formed, which can regenerate ferrous iron from ferric iron more efficiently by accelerating the process This behavior is observed in most of the degradation results shown in the following sections.

Fe(III) complexes present in mildly acidic solutions, such as Fe(OH)2+, absorb light appreciably in the UV and visible regions The quantum yield for Fe2+formation in reaction 2.17 is dependent on the wavelength It is 0.14–0.19 at

313 nm and 0.017 at 360 nm (Faust and Hoigne 1990) Fe(III) may also complex with certain contaminants or their organic by-products These organic com-plexes typically have higher molar absorption coefficients in the near-UV and visible regions than the aquo complexes Polychromatic quantum efficiencies

in the UV/visible range from 0.05 to 0.95 are common (Pignatello et al 2006) This is why the photo-Fenton process is apt to be driven by sunlight

2.2.2  Solar Photocatalysis Hardware

For many of the solar detoxification system components (Blanco and Malato 2003), the equipment used is identical to that used for other types of water treatment, and the construction materials for such treatments are commer-cially available Most piping may be made of polyethylene or polypropylene, avoiding the use of metallic or composite materials that could be degraded

by the oxidation conditions of the photocatalytic process The materials must

not be reactive and must not interfere with the photocatalytic process All materials used must be inert to degradation by UV solar light, in order to be compatible with the minimum required lifetime of the system Photocatalytic reactors must transmit UV light efficiently because of the process require-ments With regard to the reflecting/concentrating materials, aluminum is the best option because of its low cost and high reflectivity in the solar UV spectrum on the earth's surface The reflectivity (reflected radiation/incident radiation) of traditional silver-coated mirrors is very low (between 300 and

400 nm) and, therefore, aluminum-coated mirrors are the best option in this case Aluminum-coated surface is the only metal surface that is highly reflec-tive throughout the ultraviolet spectrum For aluminum, the reflectivity ranges from 92.3% at 280 nm to 92.5% at 385 nm, while the reflectivity values for silver are 25.2% and 92.8%, respectively

The photocatalytic reactor must be transparent to UV radiation The choice

of materials that are both transmissive to UV light and resistant to its tive effects is limited Common materials that meet these requirements are fluoropolymers, acrylic polymers, and several types of glass Quartz has excellent UV transmission as well as good temperature and chemical resistance, but high costs make it completely unfeasible for photocatalytic applications Fluoropolymers are a good choice of plastic for photoreac-tors because of their good UV transmittance, excellent ultraviolet stability, and chemical inertness But one of their greatest disadvantages is that, in order to achieve a desired minimum pressure resistance, the wall thickness

destruc-of a fluoropolymer tube has to be increased, which in turn will lower its

UV transmittance Acrylics could also be potentially used, but they are very brittle Other low-cost polymeric materials are significantly more susceptible

to attack by ∙OH radicals Standard glass, used as a protective surface, is not satisfactory because it absorbs part of the incident UV radiation due to its iron content Borosilicate glass has good transmissive properties in the solar range with a cutoff of about 285 nm (Blanco et al 2000) Therefore, such a low-iron-content glass would seem to be the most adequate one Therefore, both fluoropolymers and glasses are valid photoreactive materials

The original solar photoreactor designs (Goswami 1995) for cal applications were based on line-focus parabolic-trough concentrators (PTCs) In part, this was a logical extension of the historical emphasis on trough units for solar thermal applications Furthermore, PTC technology was relatively mature, and the existing hardware could be easily modified for photochemical processes The main disadvantages are that these collec-tors (i) use only direct radiation, (ii) are expensive, and (iii) have low optical efficiencies On the other hand, one-sun (nonconcentrating) collectors have

photochemi-no moving parts or solar tracking devices They do photochemi-not concentrate the tion So, efficiency is not reduced by the factors associated with concentration and solar tracking As there is no concentrating system (with its inherent reflectivity), the optical efficiency of these collectors is higher as compared with PTCs They are able to utilize both the diffuse and direct portions of

radia-the solar UV-A An extensive effort in radia-the design of small nontracking lectors has resulted in the testing of several different nonconcentrating solar reactors (Blanco-Galvez et al 2007) Although one-sun collector designs pos-sess important advantages, the design of a robust one-sun photoreactor is not trivial, due to the need for weather-resistant and chemically inert UV transmitting reactors In addition, nonconcentrating systems require signifi-cantly more photoreactor area than concentrating photoreactors Hence, as a consequence, full-scale systems must be designed to withstand the operat-ing pressures of fluid circulation.

col-2.2.2.1  Compound Parabolic Concentrators

To design a solar collector for photocatalytic purposes, there is a set of main constraints for performing the optimization: (1) collection of UV radiation, (2) working temperatures as close as possible to ambient temperature, and (3) quantum efficiency Finally, its construction must be economical and should be efficient, with a low pressure drop As a consequence, the use

of tubular photoreactors has a decisive advantage because of the inherent structural efficiency of the tubing The tubing is also available in a large variety of materials and sizes and is a natural choice for a pressurized fluid system There is a category of low-concentration collectors called compound parabolic concentrators that are used in thermal applications They are an interesting option between parabolic concentrators and static flat systems Thus, they also constitute a good option for solar photochemical applica-tions (Ajona and Vidal 2000) Compound parabolic collectors (CPCs) are static collectors with reflective surfaces designed to be ideal in the sense of nonimaging optics and can be designed for any given reactor shape They

do so, illuminating the complete perimeter of the receiver, rather than just the “front” of it, as in conventional flat plates These concentrating devices have ideal optics, thus maintaining the advantages of both the PTCs and the

static systems (Colina-Márquez et al 2009) The concentration factor (RC) of

a two-dimensional CPC collector is given by Equation 2.19 and is defined in

Figure 2.1, where A is the aperture of the solar collector.

around the tubular receiver so that almost the entire circumference of the receiver tube is illuminated CPCs have the advantages of both technologies (PTCs and nonconcentrating collectors) and none of the disadvantages, so they seem to be the best option for photocatalytic processes based on the use

of solar radiation They can make highly efficient use of both direct and fuse solar radiations, without the need for solar tracking

dif-One important factor related to the photoreactor design is its diameter It seems obvious that a uniform flow must be maintained at all times in the reac-tor, since a nonuniform flow causes nonuniform residence times, which can lower the efficiency when compared with the ideal As already commented,

Photoreactor Photoreactor Photoreactor

r r

r

A A

the Fenton reactant consists of an aqueous solution of hydrogen peroxide and ferrous ions providing hydroxyl radicals When the process is complemented

with UV/visible radiation, it is called photo-Fenton In this case, the process

becomes catalytic Fe3+ (related species and organic complexes) absorbs solar photons as a function of its absorptivity This effect must be considered when determining the optimum load as a function of light-path length in the pho-toreactor The optimum concentrations of 0.2–0.5 mM Fe as a function of the photoreactor diameter have been proposed after many experiments with dif-ferent photoreactors under sunlight at the Plataforma Solar de Almeria (PSA) installation (Malato et al 2009) In the results shown in this chapter, attending

to the diameter of the photoreactor used, 0.35 mM mg/L of Fe has been used

2.3 Experimental Setup

2.3.1  Solar Pilot Plant

Experiments were performed in a pilot CPC solar plant designed at the Plataforma Solar de Almería for solar photocatalytic applications (Figure 2.2) This reactor is composed of two modules (11 L each) with 12 Pyrex glass tubes (30 mm O.D.) mounted on a fixed platform tilted to 37° (local lati-tude) The water flows (20 L/min) directly from one module to the other and finally to a reservoir tank (10 L) The material chosen for the piping and the valves (3 L) between the reactor and the tank is black high-density polyeth-ylene (HDPE) because it is highly resistant to chemicals, weather-proof, and opaque to avoid any photochemical effect outside of the collectors The total illuminated area is 3 m2 Polished aluminum is used as the reflective material because of its high UV reflectivity in the concerned UV range of 300–400 nm The total volume (two modules + reservoir tank + piping and valves) is 35 L

(VT), and the irradiated volume is 22 L (Vi) The incident solar ultraviolet ation (UV) was measured by a global UV radiometer (KIPP&ZONEN, model CUV 3) mounted on a platform tilted to 37° (the same as CPCs) The tem-perature inside the reactor was continuously recorded by a PT-100 inserted

radi-in the pipradi-ing With Equation 2.20, a combradi-ination of the data obtaradi-ined from several days’ experiments and their comparison with those obtained from

other photocatalytic experiments are possible, where t n is the tal time for each sample, UV is the average solar ultraviolet radiation (λ <

experimen-400 nm) measured between t n−1 and t n , and t30W is the “normalized tion time.” In this case, time refers to a constant solar UV power of 30 W/m2(typical solar UV power on a perfectly sunny day around noon)

2.3.2  Reagents

All reagents used for chromatographic analyses, namely acetonitrile, methanol, and ultrapure (Milli-Q) water, were of HPLC grade The ana-lytical standards for chromatography analyses were purchased from Sigma-Aldrich Table 2.1 lists the 15 compounds (pharmaceuticals, pesti-cides, and personal-care products) used Photo-Fenton experiments were performed using iron sulfate (FeSO4· 7H2O), reagent-grade hydrogen peroxide (30% w/v), and sulfuric acid, all provided by Panreac The fil-ters used were syringe-driven 0.2 μm Millex nylon membrane filters from Millipore RE were taken downstream of the Almería and El Ejido MWTP

T1

Sampling valve

OH O Antipyrine analgesic

N N

O N

OH O O F

(continued)

Progesterone steroid hormone

O OH

Sulfamethoxazole bacteriostatic

O

O H

O N

Flumequine broad-spectrum

antibiotic

N COOH

O

F

Triclosan antibacterial/antifungal agent

O OH

Cl

Cl

Cl

Hydroxybiphenyl biocide OH

secondary biological treatment (in the province of Almería, Spain) and used as received within the next 2 days Initial COD, DOC, and TIC were between 57–86 mg/L, 20–34 mg/L, and 100–126 mg/L, respectively.

2.3.3  Analytical Measurements

The dissolved organic carbon (DOC) and total inorganic carbon (TIC) were measured by the direct injection of samples filtered with 0.2 μm syringe-driven filters into a Shimadzu 5050A TOC analyzer Spectrophotometry for the determination of the iron and hydrogen peroxide concentrations was performed with a UNICAM 2 spectrophotometer The total iron con-centration was determined with 1,10-phenantroline according to ISO 6332 The hydrogen peroxide concentration was analyzed using titanium (IV) oxysulfate (DIN 38 402 H15 method), which allows the H2O2 concentration

to be determined immediately based on a yellow complex with maximum absorption at 410 nm formed during the reaction of H2O2 The perox-ide and iron concentrations are calculated using calibration curves The concentration profile of each compound during degradation was deter-mined by UPLC-UV (series 1200, Agilent Technologies, Palo Alto, CA) The analytes were separated using a reversed-phase C-18 analytical column (Agilent XDB-C18 1.8 μm, 4.6 × 50 mm) using acetonitrile (mobile phase A) and ultrapure water (25 mM formic acid, mobile phase B) at a flow rate of

1 mL/min A linear gradient progressed from 10% A (original conditions)

to 82% A in 12 min The reequilibration time was 3 min The limit of tification was between 1.5 and 10.0 μg/L, depending on the EC

quan-A 25 mL sample of RE spiked with 100 μg/L was filtered through a 0.2 μm syringe-driven filter, the filter was washed with 3 mL ACN, the two solu-tions were mixed, and an aliquot was injected into the UPLC-UV system

A 200 mL sample of RE spiked with 5 μg/L was extracted with solid-phase extraction (SPE) and recovered in 2 mL of acetonitrile/water (1/9), filtered through 0.2 μm syringe-driven filter, and injected into the UPLC-UV Under these conditions, the recovery factor was >80% This procedure was used also for RE (without any spiking) evaluation

The method for the analysis of the target compounds with HPLC-QTRAP-MS (Martínez Bueno et al 2007) was developed for the 3200 QTRAP-MS/MS sys-tem (Applied Biosystems, Concord, ON, Canada) The separation of the ana-lytes was performed using an HPLC (series 1100, Agilent Technologies, Palo Alto, CA) equipped with a reversed-phase C-18 analytical column (Zorbax SB, Agilent Technologies) of 5 μm particle size, 250 mm length, and 3.0 mm-i.d For the analysis in positive mode, the compounds were separated using acetoni-trile (mobile phase A) and HPLC-grade water with 0.1% formic acid (mobile phase B) at a flow rate of 0.2 mL/min A linear gradient progressed from 10%

A (initial conditions) to 100% A in 40 min, after which the mobile-phase position was maintained at 100% A for 10 min The reequilibration time was

com-15 min The compounds analyzed in the negative mode were separated using

acetonitrile (mobile phase A) and HPLC-grade water (mobile phase B) at a flow rate of 0.3 mL/min An LC gradient started with 30% mobile phase A and was linearly increased to 100%, in 7 min, after which the mobile-phase composition was maintained at 100% A for 8 min The reequilibration time was 10 min The injection volume was 20 μL in both modes.

2.3.4  Experimental Procedures

Three approaches were used: (i) spiking RE with 100 μg/L of each nant; (ii) spiking the RE with 5 μg/L of each contaminant as the typical EC concentrations in the effluent are in the 0.1–15.0 μg/L range, with an SPE follow-up (see below for details) in which the samples were preconcentrated 100-fold; and (iii) treating the RE and analyzing the EC devolvement with HPLC-QTRAP-MS after the same SPE preconcentration

contami-The mixture of the 15 compounds dissolved in methanol at 2.5 g/L (mother solution) was added directly into the pilot plant and well homogenized by turbulent recirculation for 30 min The pH in the RE was between 7.1 and 8.5, depending on the day when the water was collected, and the recirculation time for this process was usually from 60 to 120 min After stabilizing the desired pH, H2O2 at a concentration of 50 mg/L was added and homogenized

by recirculating for 15 min Finally, FeSO4· 7H2O was added (Fe2+= 5 mg/L) After recirculating for 15 min, during which the Fenton reaction started, the collectors were uncovered and the photo-Fenton process began The hydrogen peroxide and iron concentrations were measured in every sample taken The experiments normally lasted 3–4 h The peroxide was sometimes consumed completely and 10 mg/L more of it was added at a time during the tests

2.4 Results and Discussion

Figure 2.3 shows the photo-Fenton treatment of RE The initial DOC, TIC, and COD were 36 mg/L, 106 mg/L, and 60 mg/L, respectively In this case,

406 mg/L H2SO4 was added to reach <20 mg/L TIC, and the recirculation time

in the pilot plant, necessary to remove the carbonate species, was 30 min The spiked amount of 100 μg/L of each EC is high compared with that normally found in real wastewaters (<10 μg/L), but it is low enough to simulate real conditions and gain insight into the behavior of the photo-Fenton process.The residual concentrations of the contaminants at the end of the experi-

ments (t30W > 100 min) can be seen in Figure 2.3 Only atrazine remained at around 20% of the initial concentration The pH varied from the original 8.1

to 4.5 at the end, while the iron concentration varied from 5 g/L to 3.2 mg/L The overall amount of peroxide consumed was 29 mg/L It should be men-tioned, although not relevant to the purpose of the experiments, because