The Typical Wastewater Treatment Biology Essay


As a result of the use and the need in industry, medical care, commercial goods and household activity, organic contaminants are growingly released into the environment. Regarding the limitation of conventional wastewater treatment technologies, effluents from biological wastewater treatment systems are still composed of a variety of soluble organic compounds, including residual degradable and non-biodegradable influent substrate, soluble microbial products, substrate byproducts and ultimate products, complex organic compounds formed through treatment reactions.

Usually, the degradation of organic compounds by direct UV photolysis at disinfection doses is restrained, so advanced oxidation processes (AOPs) present a potentially effective treatment alternative for effluent organic matters (EfOM). AOPs are based on fast and non-selective radical reactions, able to completely oxidize substances. They have great potential to eliminate non-biodegradable pollutants from municipal wastewater.

UV/H2O2 is often considered as an effective barrier against EfOM. The generated hydroxyl radicals (•OH ) by UV photolysis ensure the removal of a wide range of organic compounds. Numerous studies have been conducted on the removal efficiency of trace organic compounds via UV/H2O2 process, especially pharmaceuticals, personal care products (PPCPs) and natural organic matter (NOM). Apart from this, the inactivation effectiveness of pathogens, such as MS-2 phages, B.subtilis spores, E. coli and P. aeruginosa during UV/H2O2 has been reported by several research groups. This report will offer general information of the UV/H2O2 process performance on the removal of a diversity of soluble organic compounds and discuss the significant parameters associated with the system. It will also discuss the byproducts formation during UV/H2O2 process and the possibilities to employ the UV/H2O2 treatment with other technologies in order to enhance the overall wastewater treatment performance.

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Key words: municipal wastewater, UV/H2O2, effluent organic matter, pharmaceuticals, •OH scavenging, photodegradation, mineralization.


BOD-biochemical oxygen demand, TSS-total suspended solids, COD-chemical oxygen demand, TS-total solids, TDS-total dissolved solids, TOC-total organic carbon, NOM-natural organic matter, EfOM-Effluent Organic Matter, SOCs-synthetic organic compounds, DBPs-disinfection by-products generated, SMPs-soluble microbial products, BTSE-biologically treated sewage effluent, WWTP-wastewater treatment plant, EDCs-Endocrine-disrupting chemicals, PPCPs-pharmaceuticals and personal care products, AOPs-advanced oxidation processes, WWTP-wastewater treatment plant, DOC-dissolved organic carbon, DOM-dissolved organic matter, MBR-membrane bioreactor.

1. Overview

Recently, due to the rapid development of industrialization and population growth, clean water has been in increasingly urgent need. Because of this growing demand, a diversity of practical strategies and solutions has been applied to yield as many as viable water resources. Usually, some degree of municipal wastewater treatment plays an indispensable role in protecting the quality of limited freshwater resources and makes it possible for beneficial reclamation/reuse.

1.1. Typical wastewater treatment

Conventional wastewater treatment is composed of a treatment train, including physical, chemical, and biological operations, in order to remove a wide range of pollutants, such as particles, organic matters and pathogens from wastewater. General terms used to depict the increasing treatment degree are preliminary, primary, secondary, and tertiary and/or advanced wastewater treatment. Generally, preliminary treatment removes coarse solids and large materials with the size range of more than 0.01 mm in raw wastewater. Primary treatment removes the bulk of suspended organic and inorganic solids (35 μm to 0.1 mm) by sedimentation. Approximately 25 to 50% of the incoming biochemical oxygen demand (BOD5), about 70% of the total suspended solids (TSS), and 65% of the oil/grease can be removed during primary treatment. In the further step, secondary treatment removes the biodegradable dissolved and suspended organic matters. In the combination with primary treatment, 85% of the BOD5 and suspended solids, along with some heavy metals are removed from the raw wastewater. Tertiary and/or advanced wastewater treatment is employed to remove part of the remaining specific constituents in the wastewater which cannot be treated by secondary process. Disinfection is utilized to reduce the bacterial count, especially pathogenic microorganisms .

1.2. Properties of raw municipal wastewater

Municipal wastewater mainly consists of domestic wastewaters, industrial wastewaters, infiltration and inflow into sewer lines, and storm water runoffs . However, dependent on the population density, industrial distribution and other factors, for instance, degree of separation between storm water and sanitary wastes, the characteristics of municipal wastewater discharges vary from site to site.

The major source of the domestic section is the waste that people pour down the drain from the kitchen, bathroom and laundry . Sanitary wastewater consists of not only domestic wastewater but the discharge from commercial and institutional facilities. Industrial waste contains a large group of discharge from food industry, complex organic chemicals industry, iron and industry, etc. Storm water can be collected either together with domestic wastewater or separately by most new sewerage systems .

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Table 1 collects the general information of industrial wastewater characteristics. Except the pollutants listed in Table 1, thermal pollution and radioactive pollution can also be the representative characteristics of industrial wastewater.

Table 1 Properties of industrial wastewater


Physical properties

Solids content such as proteins, carbohydrates and fats

Dark grey or black

Offensive odor caused by chemical compounds such as hydrogen sulfide, indol, skatol etc.

7-18℃in cold regions while 13-24℃ in warm regions

Chemical properties

Heavy metals (chromium, cadmium, lead and mercury)

Organic chemicals (represented by BOD, COD and TOC)

Volatile organic carbons (benzene, toluene, xylenes, dichloromethane, trichloroethane and trichloroethylene)

Organic pollutants

Other inorganic pollutants (hydrogen sulphide, nitrite ion and sulfite ion)

Domestic wastewater properties vary from community to another due to the differences in the water use associated with food consumption and hygiene practices. Table 2 shows the influent characteristics of domestic wastewater.

Table 2 Common properties of domestic wastewater

Adapted from



Medium concentration (mg/L)

Total solids (TS)


Total dissolved solids (TDS)


Suspended solids (SS)


Settable solids


BOD5, 20℃


Total organic carbon (TOC)












Volatile organic compound


Contaminants in the wastewater can be classified by particulate size distribution, according to sedimentation, centrifugation, and filtration . Table 3 summaries four main molecular size fractions: settleable, supracolloidal, colloidal, and soluble.

Table 3 Composition of organic matters in wastewater

Adapted from






Size range (μm)





COD (% of total)





TOC (% of total)





Grease (% of total solids)





Protein (% of total solids)





Carbohydrates (% of total solids)





Biochemical oxidation rate-k (d−1, base 10)





1.3. Characteristics of biologically treated sewage effluent (BTSE) and effluent organic matter (EfOM)

Wastewater is processed by certain treatment units and then discharged to a receiving stream, from which is used by a downstream population. However, conventional wastewater treatment cannot remove all contaminants. Because of this, understanding of the chemical and biological composition of processed water is important. Effluents from biological wastewater treatment systems contain a complex matrix of organic compounds-effluent organic matter (EfOM), including natural organic matter (NOM) derived from drinking water sources; trace harmful synthetic organic compounds (SOCs) produced during domestic use and disinfection by-products generated (DBPs); and soluble microbial products (SMPs) generated during the biological treatment with the wastewater treatment plant (WWTP) and non-biodegradable organic matter .

Although the biological treatment contributes a 90% COD (of untreated water) elimination, most EfOM found in the treated water is soluble, taking up 86% of the COD . Normally organic materials consist of a combination of carbon, hydrogen, and oxygen, with nitrogen in some cases. Small quantities of organic components are present in different synthetic organic molecules, including surfactants, organic priority pollutants, volatile organic compounds, and agricultural pesticides .

During secondary treatment, biomass not only consumes organic material present in the wastewater, but produces soluble microbial products and extracellular polymeric substances during cell lysis . Several research groups successfully identified many individual compounds present in the effluents and their findings are summarized in Table 4. Further reports have identified several other compounds of microbial origin such as antibiotics, exocellular enzymes, siderophores, structural components of cells and products of energy metabolism .

Table 4 Percentage composition of soluble organics (w/w) in effluents from wastewater treatment systems

Adapted from


Trickling filter and activated sludge

Trickling filter

Sewage (dialysable fraction, MW<10 kDa)

Sewage (non-dialysable fraction, MW>10 kDa)

Ether extractables

<10 (65% strong acids)









Amino acids





Carbohydrates and polysaccharides

<5 (no simple sugars)




Tannins and lignins

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Alkyl benzene sulphonate





Anionic detergents





Non-ionic detergents





Humic, fulvic and hymathomelanic acids










Organo-chlorine compounds










Also identified in low (<50 mg/l) concentrations




glucose, fructose, sucrose, mannose, allulose, xylose, raffinose, formic acid, acetic acid, propionic acid, butyric acid, iso-butyric acid, iso-valeric acid, caproic acid, uric acid, pyrene, perylene, benzpyrenes, DDT, BHC, dieldrin, coprostanol and cholesterol

Another concern is endocrine-disrupting chemicals (EDCs), a class of toxic compounds in which an endogenous or exogenous chemical has the capability to mimic or block the natural action of estrogen, androgen and/or thyroid in animals . Apart from this, pharmaceuticals and personal care products (PPCPs) represent a group of emerging contaminants that can also be detected at nanograms per liter concentrations in wastewater. Most EDCs and PPCPs are quite polar and the majority has acidic or basic functional groups. Also usually EDCs and PPCPs occur at trace levels, being challenging for analytical detection and removal treatment .

Table 5 Country-wise occurrence of ANs and AIs in influents and effluents of WWTPs

Adapted from


WWTP influent (μg/L)

WWTP effluent (μg/L)

Representative country














Italy, France






Germany, South Korea




France, Italy, USA







Italy, France




South Korea

For example, 4-tert-octylphenol (OP) and n-butylparaben (BP) exert negative effect on animals and humans endocrine system . The latter one, butylparaben, can be applied as good antioxidant and preservative in personal care products, or as an additive in pharmaceuticals and food . Table 5 offers the contaminating levels of anti-inflammatory and analgesic drugs in WWTP influent and effluent within μg/L range, including diclofenac (DCF), ibuprofen (IBP), naproxen (NPX), ketoprofen (KTF), paracetamol (PCT).

1.4. Advanced oxidation processes (AOPs)

Because the previously existing chemicals and the new compounds derived from secondary treatment are not readily eliminated by the conventional treatment methods, a growing number of efficient wastewater treatment technologies have been applied in order to meet the ever-increasing requirements. Advanced oxidation processes (AOPs) are defined as the processes that generate hydroxyl radicals (•OH) in sufficient quantities to oxidize majority of the complex chemicals present in the effluent water .

Table 6 Commonly used AOPs for water and wastewater treatment

Adapted from

Advanced oxidation methods



UV oxidaiton





Ultrasound (US)


US/H2O2, US/O3


Wet-air oxidation

Photo-Fenton and Fenton-like systems


Photocatalytic oxidation (UV/TiO2)

Electrochemical oxidation

The first AOP is the Fenton reaction discovered by Fenton in 1894 where •OH radicals are produced from hydrogen peroxide under the addition of Fe(II) as a catalyst. It is accepted that AOPs are usually operated in synergism with other traditional processes. Theoretically, methods that are available for generating •OH radicals are divided into two groups: non-photochemical (e.g. O3/H2O2 and Fenton system) and photochemical methods (e.g. O3/UV, H2O2/UV and Fenton-like systems). Table 6 shows the most commonly used AOPs in the wastewater treatment plant.

H2O2 is a common and efficient oxidant from the viewpoint of stoichiometric and handling; however one of the disadvantages of H2O2 employment is the absorption coefficient is very low. Due to high oxidation potential (E0=2.80 V), the •OH radicals plays an important role for oxidation of compounds, reacting slowly with the chemical oxidizers. H2O2/UV application can overcome this disadvantage and completely mineralize any organic compound to carbon dioxide and water. To be specific, •OH radicals are produced from the photolytic dissociation of H2O2 in water by UV irradiation (200-280 nm) . The costs of UV treatment depend on the absorption properties of the compounds to be removed. Higher radical generation results from MP-UV lamps than LP-UV lamps, due to the greater H2O2 absorptivity at lower wavelengths .

2. Literature review

The ultimate aim of AOPs is to mineralize pollutants, converting them to carbon dioxide, water, nitrogen and other minerals. Molecularly, the structural diversity of contaminants induces variations in removal rates of AOPs; also, water matrix plays an important role in contaminants removal. Therefore, for an optimal organic pollutant control, H2O2/UV system has to be particularly operated in accordance with model predictions of the performance of AOP systems. Table 5 is a summary of recently published researches of the H2O2/UV application on EfOM control in the water and wastewater treatment.

Table 5 Recent studies of the H2O2/UV application on trace organic matter control


Aqueous matrices

Water matrices properties

H2O2/UV dose


Nagarnaik et al. 2011

WWTP effluent, WWTP influent and Hospital effluent

[DOC] 3.54 mg/L, 22.1 mg/L and 27.4 mg/L

600 μM/UV254 nm

Second order kinetic rate constant 1.1-1010 M-1s-1. 53%, 14.8% and 11.8% removal of NPEOs, 62.2%, 8.5% and 3.1% removal of OPEOs

Biń et al. 2012

Antibiotic wastewater

[COD] 18180 mg/L, [TOC] 9100 mg/L and [BOD5] 9090 mg/L

0.013 M/15 W (254 nm)

COD decay rate constant 7.6 - 10−4 s-1 (pH 8)

Felis et al. 2011

Distilled water

10 mg/L BPA

2.94 - 10-4 , 2.94 - 10-3 and 2.94 - 10-2 M/200W (255 to 579 nm)

BPA removal rate: 62%, 5 min, 40%, 2 min and 36%, 2 min; rate constant 3.3-109 M-1s-1

Katsoyiannis et al. 2011

Wastewater after membrane

bioreactor (MBR) treatment

Great amount of low molecular weight compounds

0.2 mM/15 W LP UV

[DOM] 3.9 mg/L, kOH,DOM 3.5-104 M-1s-1, Scavenging rate from DOM 13.7-104 s-1

(Table 5 Continued)

Yuan et al. 2011

Surface water (SW), drinking water treatment plant (DW), WWTP effluent

[DOC] 4.6, 3.7 and 5.0 mg/L; initial antibiotics concentration 5μM


Second order rate constants: Ciprofloxacin (CIP) 7.50-109M−1s−1, Oxytetracycline (OTC) 6.96-109M−1s−1, Doxycycline (DTC) 7.74-109M−1s−1

Rosario-Ortiz et al. 2010

Three tertiary wastewater treatment facilities (be less for PCFL, LVNV and RMCO)

[TOC] 6.6 and 10.3 mg/L, six pharmaceuticals

0, 2, 5, 10, 15, 20 mg/L/300, 500, and 700 mJ/cm2 LP UV

20 mg/L and 500 mJ/cm2, >89% removal of pharmaceuticals in LVNV

Vilhunen et al. 2010


creosote contaminated

3mM/24.4 mW/cm2 (254nm)

76% removal of TOC in 60 min; 85% removal of absorbance in 30min

Wu et al. 2010

Milli-Q water

7.4 mM parathion and 2.1 mM chlorpyrifos

0-50 mg/L/LP UV (254 nm)

Pesticide degradation follows pseudo-first-order kinetics

Baeza et al. 2011


[BACs] 4(±1) mM, [DOC] 7.3 mg/L

2, 6, and 10 mg/L/540 mJ cm-2 (LP)

second order rate constants 5-10-109 M-1s-1; 31-97% degradation at 6 mg/L H2O2

BŁedzka et al. 2010

Milli-Q water

4-tert-octylphenol (OP, 8-10-6-1.7-10-4 M) and n-butylparaben (BP, 5-10-6-4.4-10-5 M)

Most favorable dose of H2O2, about 0.01 M/11.8-44.4W/m2

As the pH increased from 5 to 12, dissociation degree of both OP and BP enhanced

Hu et al. 2010

Distilled water

4.0-10−3 mol/L 4-aminoantipyrine (4-AAP)

0 to 0.392 mol/L/15W LP UV

64.30% removal of COD after 80 min treatment

(Table 5 Continued)

Olmez-Hanci et al. 2011

Textile preparation process

Initial surfactant COD 300-900 mg/L [DOS] 200-600 mg/L, [ETHT] 155-464 mg/L and [NPEO] 147-441 mg/L

15-75mM/40W LP UV

The highest COD degradation rate coefficient was obtained for NPEO and after 60 min photochemical treatment

COD removal efficiencies were obtained as 66%, 61% and 77% for DOS, ETHT and NPEO

Pagano et al. 2008

De-ionized water and groundwater samples

14 mg/L and 1.4 mg/L each six alcohol ethoxylates and each four alkylphenol ethoxylates

3.2 mg/L and 5.3 mg/L/14W LP UV

Low COD and TOC removals (0-25 % and 0-18 %); total surfactants removal (98%)

Pereira et al. 2007a

Laboratory-grade water (LGW) and surface water (SW)

individual pharmaceutically active compounds (PhACs) 1 to 3 mM

10mg/L /40, 100, 300, 700, 1000, and 1700 mJ/cm2 MP UV

MP lamps increased clofibric acid and naproxen degradation by 30%, 50% UV/H2O2 degradation of the compounds in the SW

Benotti et al. 2009

River water

[TOC] 2.6 mg/L, 32 pharmaceuticals and EDCs

10 and 20 ppm

Followed pseudo-first-order kinetics, more efficient than UV/TiO2 photocatalysis

Kim et al. 2009

30 PPCPs spiked pure water (PW) and biologically treated water (TW)

For TW, [TOC] 50 μg/L and [DOC] 3.9 mg/L; 30 PPCPs initial concentration from 5 to 119 μg/L

8.2 and 6.1 mg/L

Direct UV photodegradation contributed by more than 50% to nine PPCPs degradation

(Table 5 Continued)

Tambosi et al. 2009

Capilano Reservoir surface water

[DOC]=[TOC] 2.2 mg/L

0, 5, 10, 15, and 20 mg/L/0 to 1400 mJ/cm2

No observed drop in TOC, larger NOM species degraded to smaller species

Li et al. 2011

Sewage treatment plant effluent (STP)

[DOC] 16.4 mg/L, [COD] 39 mg/L

H2O2 (30%, w/w)/ VUV lamp (10 W, 90% UV254 and 10% UV185

pseudo-first-order kinetic model;

Clofibric acid (CA) removal efficiency reached over 99% after 40 min

Felis et al. 2009

Distilled water

[Diclofenac], [naproxen] and [ibuprofen] 20 mg/L, urea (20 g/L) present and absent

1 g/L/200 W UV

Concentration below LOQ (0.25 mg/L) in 20 min; 31% TOC removed in 30 min

Klausen et al. 2010

Recycling water for fish industry

High UV254 absorbance, high color content, 281 mg HCO3-/L, 6-21 ng/L geosmin and 8-40 ng/L 2-methylisoborneol (MIB)

0.5 mmol/L/600 mJ/cm2

first order degradation constants for geosmin and MIB: 1.2±0.3 h-1 and 1.5±0.3 h-1

Olmez-Hanci et al. 2010

De-ionized water

100 mg/L diethyl phthalate (DEP)

0-50 mM/40W LP UVC

The optimum H2O2 amount for the removal of 100 mg/L DEP was 40 mM

Lekkerkerker et al. 2009

Pilot-scale on a pretreated river water

8 organic micropollutants with concentration of 3.0-5.3 and 0.6-1.7 μg/L at first and second phase

12 mg/L/2050 J/cm2

over 90% removal of all micropollutants except MTBE, the least probability of bromate formation

(Table 5 Continued)

Teksoy et al. 2011

Bottled water

Fulvic acid (0, 2, 6 mg/L), 106 CFU 100mL-1

0,5,10,25 and 50 mg/L/40 μW/cm2

Sensitivity of H2O2/UV:

E. coli>P. aeruginosa>B. subtilis

Cho et al. 2011

Milli-Q water

3-106 pfu/mL MS-2 phages or B.subtilis spores

0 to 0.6 mM/15W LP UV

3 log inactivation and model organic pollutants degradation

2.1. Trace organic matter control via H2O2/UV process

It was reported that H2O2/UV could be a promising method to degrade two subgroups (nonylphenol ethoxylates, NPEOs and octylphenol ethoxylates, OPEOs) of non-ionic surfactants, alkylphenol ethoxylates (APEOs), which are easily to be found in detergents, paints, dispersing agents, wetting products and pesticides . The result showed that the second order kinetic rate constant for both NPEOs and OPEOs with •OH radicals was 1.1-1010 M-1s-1, which were similar to the 107-1011 range for the reaction of organics with •OH . After 10 min of H2O2/UV reaction, APEOs removal was found greatest in tap water (not shown in Table 5) followed by the order of wastewater effluent, wastewater influent, and hospital effluent, indicating that the highest •OH radicals scavenging rate was for the hospital effluent and WWTP influent with greater [DOC] than any other water matrices.

Applying H2O2/UVC treatment process, photodegradation kinetics in terms of TOC and diethyl phthalate (DEP) abatement were studied . The destruction of DEP was observed in 20 min when adding at least 20 mM H2O2 while the complete mineralization of DEP was detected at initial H2O2 concentrations of 20 and 30 mM after 40 min. DEP abatement only appeared to steadily increase with increasing H2O2 amount from 5 to 40 mM. Further increase of H2O2 dose caused to decrease both the degradation rate and the mineralization of DEP. These observations were in well agreement with the results from . The second-order reaction rate constant of DEP was calculated as 2.33 ± 0.27-108 M-1 s-1, which was until then the first report of the •OH biomolecular reaction rate constant for DEP.

studied the photodegradation of three antibiotics in UV and UV/H2O2 process and also supported the fact that the higher value of DOC and other substances such as nitrate, sulfate and chloride, the more •OH radicals were scavenged, leading to lower•OH radical scavenging (ROH,UV). It was discovered that antibiotics oxidation was better for DW, followed by SW and WW, which corresponded to the trends observed for •OH radical scavenging. The similar trend was also found by , in which applying 20 mg/L H2O2 with a changing dose of UV (300, 500 and 700 mJ/cm2), the highest removals for pCBA was examined within the sample LVNV, indicating •OH exposure for the LVNV sample was higher than any other two samples, in agreement with the previous estimation according to the given scavenging rates.

By employing a CNT (carbon nanotubes) film-modified glassy carbon electrode, the photodegradation of 4-AAP was successfully monitored towards the electrochemical response . It was found that after 80 min treatment, 64.3% COD was removed from 4-AAP solution, which was less than the high degradation efficiency monitored via the electroanalytical method. The difference was caused by the fact that many 4-AAP molecules were transformed to intermediates rather than completely mineralized products under such UV/H2O2 treatment.

Not all pharmaceuticals can be removed by UV/H2O2 process. In one study done by , it was noticed that only dilantin oxidation occurred via photolysis, while atenolol, carbamazepine, meprobamate, primidone and trimethoprim could be oxidized by UV/H2O2 process and the removal rate increased as the H2O2 dose and UV fluence increased due to higher UV fluences required to promote greater •OH exposure.

did a comparing survey on the energy consumption of ozonation and two AOPs for transformation atrazine (ATR), sulfamethoxazole (SMX) and N-nitrosodimethylamine (NDMA). In the tested wastewater, the sum of high molecular compounds and humic substances contained only around 50% of the DOM, indicating the amount of low molecular weight compounds was high. The DOM decay rate constants for wastewater and three other surface waters varied from 2.0-104 to 3.5-104 M-1s-1, which were in agreement with the study conducted by , who investigated seven DOM isolates and found kOH,DOM ranged from 1.2-104 to 3.8-104 M-1 s-1. The result of DOM concentration along with DOM decay rate constant was supported by the observation that more polar lower molecular weight DOM from wastewater had higher values of kOH,DOM . It was also noted that the fluence-based transformation kinetics rate of SMX was only 5 times higher than that of NDMA, whereas it occurred 300 times higher by ozonation in one of the surface waters. This was agreed with , who calculated the transformation rate constant of NDMA increasing only by 26% after H2O2 was added to the UV treatment. As for the energy consumption, it highly depended on the •OH scavenging rates for micropollutant transformation. For 90% pCBA depletion, ozonation only required 0.035 kWh/m3, while UV/H2O2 process needed at least 0.2 kWh/m3 in the wastewater.

investigated different AOPs on the removal of the organic micropollutants. Compared with two pharmaceuticals diclofenac and carbamazepine as well as the pesticide isoproturon which could be very easily controlled by an O3 treatment alone with low O3 dose at 2 mg/L, other compounds such as atrazine or MTBE did not react efficiently with ozone, therefore H2O2/UV treatment was applied as a more powerful degrading method. Employing H2O2/UV treatment on both first and second phase, it was noticed that all organic micropollutants except MTBE could be removed by over 90%. For diclofenac, the combination of low dose UV and H2O2 was still able to achieve a removal of greater than 90%. determined the treatment efficacy of a photocatalytic reactor membrane pilot system for the degradation of 32 pharmaceuticals and endocrine disrupting compounds from river water. However, the applied UV/H2O2 system was not the same as the conventional one due to differences in reactor design. The result demonstrated that for the photolytic plus H2O2 treatment with 10 and 20 ppm H2O2, only tris (2-chloroethyl) phosphate (TCEP) was eliminated by highest level (39% and 25%, respectively of the initial amount). According to the evaluation of electrical energy per order (EEO), compared to photocatalytic reactor membrane mode which was effective to reduce 9 organic compounds concentrations, both photolytic plus H2O2 mode (10 ppm and 20 ppm H2O2) experiments were more efficient at contaminant destruction and it took UV photolytic mode a similar quantity of energy to decrease compound concentrations by one order of magnitude.

compared the antibiotic substances removal by UV, UV/H2O2 and O3 during wastewater treatment and described that higher COD decay within UV/H2O2 system occurred at 35℃ with pH 8 than that with pH 5. However, compared to UV-based processes, ozonation was found to be the most effective among the three AOPs with a detected COD decay rate constant of 2.0-10−3 s−1. The contaminants removal degree might be correlated with the reduction in UV254 absorbance in the treated wastewater samples . studied six biochemically active compounds (BACs) degradation in both UV and UV/H2O2 treatments. Sulfamethoxazole (SMX) and diclofenac (DCL) transformation in the UV/H2O2 was influenced by direct photolysis, conversely, slfamethazine (SMZ), sulfadiazine (SDZ), trimethoprim (TMP) and bisphenol A (BPA) transformation was dominated by •OH oxidation. BACs transformation efficiency was discovered as the order of DCL > SMX > SMZ > SDZ>BPA= TMP. For 90% transformation WWTPE, a H2O2 dose of 10 mg/L and at least 900 mJ/cm2 UV were required.

One study monitored the degradation of the selected PhACs (ketoprofen, naproxen, carbamazepine, ciprofloxacin, clofibric acid, and iohexol) using LP and MP-UV source in a UV/H2O2 batch reactor . The result showed that application of UV/H2O2 oxidation significantly decreased the UV fluences needed to achieve a target percent removal, especially for carbamazepine and naproxen, where for a 99% removal, when adding 10 mg/L H2O2, UV fluences dropped from 23026 to 1706 mJ/cm2 and from 1842 to 837 mJ/cm2. Apart from this, at the same light intensity, LP light source was noticed less efficient because of lower absorption of H2O2 at 254 nm than MP source. By applying LP and MP sources, the oxidation fluence-based rate constants for UV/H2O2 process obtained from the experiment were 1.7-10-3-6.4-10-3 cm2/mJ and 2.7-10-3-7.6-10-3 cm2/mJ, respectively. Further, the elimination of three analgesic drugs: diclofenac, naproxen and ibuprofen from the aquatic environment using UV photolysis and UV/H2O2 oxidation was surveyed by , in which the initial concentration of the test drugs in the water was controlled to be corresponded to that in human urine. The degradation rate of three drugs was estimated first by UV irradiation alone and the result showed that ibuprofen and naproxen shared similar decomposing behavior, in which after 20 min the removal rate of these two compounds reached the level of 63%. Comparably, diclofenac was the most receptive among the three to photochemical degradation since within 20 min above 80% of diclofenac was observed disappeared. The addition of 1 g/L H2O2 significantly enhanced the photochemical oxidation efficiency, in detail, within 1 min of the UV/H2O2 oxidation 45% of diclofenac, more than 33% of naproxen and about 41% of ibuprofen were found decayed. However, after adding 20 g/L urea, which equals 1.6 g C/L, within 60 min UV/H2O2 process the TOC removal was not significant and the pseudo-first-order rate constants for all investigated compounds decreased.

The target compound might be crucial to the application of H2O2/UV, from the standpoint of UV dose . The survey showed that two thirds of investigated PPCPs were degraded by more than 90% by H2O2/UV treatment in 30 min, where UV dose was 691 mJ/cm2. If employing UV dose of 890 mJ/cm2, the system would achieve 90% elimination of 6 PPCPs. However, for one PPCP, cyclophosphamide, showed the greatest resistance to UV irradiation.

The photochemical oxidation efficiency of commercially anionic (a dioctyl sulfosuccinate, DOS), cationic (a quaternary ammonium ethoxylate, ETHT) and nonionic (a nonyl phenol ethoxylate derivative, NPEO) surfactant types being frequently employed in the textile preparation (scouring, bleaching, mercerizing) activities was investigated by using a response surface methodology (RSM), which was a set of statistical and mathematical techniques that were usually applied in the development, improvement and optimization of certain processes . In order to identify the major experiment factors and the optimum ranges for the variables, the preliminary experiments were set up (initial [COD] 450 mg/L, pH 10.5 and [H2O2] 30 mM) and the result apparently showed that all test surfactant types via H2O2/UVC followed pseudo-first order kinetics. The surfactant decay rates were discovered in the decreasing order: NPEO (0.221 min-1) > ETHT (0.165 min-1) >DOS (0.081 min-1). Moreover, COD abatements also followed pseudo-first order kinetics and the coefficients were calculated in the order: ETHT (0.019 min-1)>DOS (0.021 min-1)>NPEO (0.026 min-1) and COD removal efficiencies for DOS, ETHT and NPEO were obtained 61%-77%. TOC abatements examination showed that the mineralization of DOS, ETHT and NPEO within 100 min treatment could achieve 93%-99%. Before this research, the oxidation of 10 nonionic surfactants (6 alcohol ethoxylates and 4 alkylphenol ethoxylates) was studied by employing H2O2/UV processes in different aqueous matrices . Both COD and TOC removals in the deionized water resulted very low (0-25 % and 0-18 %); while total surfactants removal (98%) was achieved in the groundwater. Further, the software also analyzed the behavior of the system within the experimental design according to different interactions of any independent variables. It was calculated that both initial COD values and initial H2O2 amount affected the COD abatements of all surfactant formulations.

The study about how UV/H2O2 impacts NOM was investigated by examining the effects of UV/H2O2 on NOM molecular weight (MW) distribution , in which the changes in MW distribution were reported to lead to DBP formation and biological regrowth potential . The results showed that the UV/H2O2 conditions applied did not lead to mineralization of NOM. Instead, great changes on NOM structure, particularly, a loss of aromatic and conjugated double bond structures took place. Applying high performance size exclusion chromatography (HPSEC), the oxidation of •OH preferentially happened on chromophoric NOM (CNOM) with larger molecular size, increasing lower molecular size CNOM. For example (Figure 1), at an initial H2O2 dose of 15 mg/L, when UV dose increased to 340 mJ/cm2, a significant decrease in higher MW CNOM was detected: 44%, 34%, and 19% reductions in F1, F2, and F3. Meanwhile, as the UV irradiation applied enhanced, the reduction percent became larger. On the other hand, smaller CNOM was observed increased in concentration: 19% and 24% increases for F5 and F6; whereas the degree of increasing among smaller CNOM was further improved as UV was controlled at 680 mJ/cm2. The tendency of MW change was similar to the discovery from , in which, the so-called depolymerization mechanism existed in the oxidation of CNOM.

Figure 1 Percent change in MW fractions during the UV/H2O2 treatment surface water at an initial H2O2 concentration of 15 mg/L

Taken from

2.2. Parameters that impact organic matter degradation via H2O2/UV process

2.2.1. H2O2

Different H2O2 doses may have significant influence on the organic compounds removal rate. For example, bisphenol A (BPA) is widely used in the plastics industry and manufacture of epoxy resins and classified as an endocrine disruptor . In the survey of , it was shown that high H2O2 dose (2.94-10-2 M) absorbed emitted photons from UVC, as a result, the photochemical decay of BPA from the solution may be limited. Meanwhile, excess H2O2 led to scavenging of •OH radicals, having an adverse impact on BPA control. found that antibiotics degradation rates in WW (with low •OH radical scavenging) did not increase greatly with the addition of H2O2, which indicated that under the same UV irradiation, more H2O2 was needed to promote higher •OH radical exposure and overcome the high scavenging capacity of the WW.

By employing RSM, investigated the optimum local conditions that influenced the removal of surfactants: DOS, ETHT and NPEO. Increasing the initial COD concentration of the surfactants resulted in the greatly retarded photochemical treatment. At initial [COD]>600 mg/L, increasing the amount of H2O2 was not helpful to improve the photochemical performance; what is more, the observed removal efficiencies dramatically dropped from 95% to only 25%. At low initial [COD] (<450 mg/L) of ETHT and NPEO, the optimum H2O2 concentration was around 50mM; initial [COD] above 450 mg/L adversely affected the performance because free radical scavenging effects took place as a result of H2O2 overdosing (initial [H2O2] >30mM for ETHT and initial [H2O2]>45mM for NPEO). In another similar study , removal rate of 10 nonionic surfactants was generally increased as increasingly dosing H2O2 when the initial mass concentration of surfactants was 14 mg/L. This may be caused by the greater •OH radicals formation. However, regarding the high H2O2 dose required for C18E10 H2O2/UV oxidation, it might be as a result of the surfactant micelles formation . Specifically, photolysis of H2O2 could be retarded in micellar solutions since a small amount of H2O2 in water partitioned into micellar pseudophase of surfactant, having decreased the photochemical reactivity.

However, for another study about the creosote contaminated groundwater, which contained PAH and mineral oil C10-C21, high removal rate (76%) of TOC was only achieved within 60 min by UV/H2O2 with the highest H2O2 dose (3 mM), in which pseudo-first-order reaction rate constant was 0.024 min-1. With a lower H2O2 dose (1.5 mM), pseudo-first-order reaction rate constant was found lower as 0.013 min-1 and some of the organic compounds were still found persistent towards UV/H2O2 process. Although it was possible for PAH to form harmful intermediates during UV/H2O2 process , the intermediates were thought to undergo further oxidation and convert to harmless low molecular end products as the treatment time increased. UV with 3mM H2O2 was discovered to remove the PAH content and mineral oils C10-C21 below detection limit (0.1 μg/L and (30 μg/L, respectively).

The effect of increasing H2O2 concentration was positive for the 4-AAP degradation at first since it was observed that the elimination efficiency for 4-AAP increased rapidly as H2O2 concentration gradually increased up to 0.196 mol/L . However, as large quantity of H2O2 was added and more •OH radicals were produced, •OH radicals reacted with H2O2 to form hydroperoxyl radicals (•HO2) which had lower oxidation capability than •OH radicals. As a result, the degradation efficiency of 4-AAP was monitored only slightly increased. Similar results were also found in the destruction of humic acid . What was interesting was that even there was not any UV irradiation, an unstable electroactive intermediate (the cation free radical AP-NH2•+) was formed because of the interaction between 4-AAP and H2O2 and converted immediately to its original form.

2.2.2. UV

Low-pressure UV and medium-pressure UV are commonly used in the UV disinfection and UV-based AOPs. The results from suggested that MP UV might be more effective to degrade the selected PhACs instead of LP UV. The PhAC decadic molar absorption coefficient of the targeted PhACs was measured in LGW covered by the normalized emission spectrum of the LP and MP-UV lamps, which was able to show the probability that a compound absorbed light at a peculiar wavelength . Take a specific example, at 100 mJ/cm2, applying LP-UV photodegradation, the removal of naproxen and clofibric acid was negligible and only 19%, respectively; however, under the employment of MP lamps, for both chemicals, degradation efficiency increased to approximately 36% and 50%, respectively. After adding 10 mg/L H2O2, the degradation of carbamazepine and naproxen in SW under 100 mJ/cm2 increased considerably, where increased to 13% from negligible for carbamazepine and to 52% from 36% for naproxen. Largely, at 100 mJ/cm2 for UV/H2O2 treatment, 50% elimination of the test compounds could be achieved in the SW, whereas greater than 90% removal could be obtained at 900 mJ/cm2 for some compounds, which was in agreement with the former result from .

On the other hand, it is worthy to note that Vacuum UV (VUV) light, combining 254 and 185 nm, is able to improve photolysis of organic compounds . compared the effectiveness of several photo-induced processes including UV/H2O2 and VUV/H2O2 for clofibric acid (CA) control in sewage treatment plant effluent and found that VUV/H2O2 was the most effective method among the investigated ways. The total CA removal by VUV/H2O2 only required about 40 min, compared with 80 min detected from UV/H2O2 treatment.

2.2.3. Specific components

Specific components such as some natural compounds as well as carbonate, bicarbonate and chloride ions, can act as antioxidants to negatively impact the contaminants control . For instance, the presence of HCO3- (1.80-10-4 M) in UV/H2O2 process decreased efficiency of BPA degradation since the concentration of BPA below the limit of quantification was found after 40 min . compared the effects of hydroxyl radicals and carbonate radicals on the photodegradation of two pesticides and discovered that despite carbonate radicals were able to somewhat degrade target pollutants, the reaction rate of parathion and chlorpyrifos via UV/H2O2 dropped 15% and 10% respectively with addition 0.5mM bicarbonate ions. In fact, carbonate radicals selectively react with organic compounds because reaction kinetics of organic compounds is different to carbonate radicals. The reaction rates can be substantial for aromatic or sulfur-containing molecules .

In another study , all 30 kinds of PPCPs investigated showed linear decrease in their concentrations when adding 8.2 mg/L and 6.1 mg/L for PW and TW UV experiments respectively. H2O2 addition was estimated to be more effective for PPCPs degradation than the efficiency obtained from in UV treatment experiment with low rate constant. By calculating, pseudo first order rate constants of ethenzamide, DEET theophylline and cyclophosphamide increased by a factor of 12-29 while 8.2 mg/L H2O2 was added in PW UV treatment; whereas adding 6.1 mg/L H2O2 did not change average rate constants of organic compounds significantly (only increased by a factor of 1-9), where by average pseudo first order rate constant went up from 2.1-10-3 s-1 to 2.8-10-3 s-1. This could be explained by the •OH radicals reacted by DOM and/or •OH radicals scavengers such as HCO3- and CO32- in tested biologically treated water . Similarly, BAC transformation rates were estimated to be slower in WWTPE than in buffered ultrapure water and generally the water matrix affected the •OH oxidation rate much more than the photolysis reaction . This discovery indicated that high amount of •OH scavengers (DOC, alkalinity, chloride, sulfate and nitrate) in WWTPE was the major factor impeding BAC removal rates.

studied the first order degradation constants of geosmin and MIB by UV/H2O2 and UV/O3 in full scale using real process water from a recirculated aquaculture system. The degradation rate obtained from UV/H2O2 process (1.2 ± 0.3 h-1 and 1.5 ± 0.3 h-1) for both geosmin and MIB was faster than the data from UV/O3 (0.6 ± 0.3 h-1 and 1.3 ± 0.2 h-1). Compared to previously reported degradation rate constants (11.9 h-1 and 5 h-1) of geosmin and MIB in controlled laboratory AOP experiments in demineralized water by , more insight into the impact of the water matrix on the chemicals degradation rate could be attained. In detail, the observed 40% decline of UV254 and 60% decline of color content showed that competitive processes to geosmin and MIB oxidation acted as a major contributor. Apart from this, it was highly probably that oxidation processes caused by inorganic radical scavengers (HCO3-) acted as another competitive contributor.

Except the appreciable levels of chloride ions in wastewater , bromide is another important scavenger of •OH. Bromination is of greater concern than chlorination for the reason that brominated compounds are more cyto- and genotoxic . It was reported that around 0.2 mM bromide gave rise to the maximum •OH scavenging and the maximum effect of bromide reduced 75% of degradation rate constant of the organic component, compared to solutions without any halide ions. However, the maximum scavenging happened when chloride was about 400 mM and the maximum effect reduced only 36% of degradation rate constant .

NOM present in the water matrices might influence the contaminants degradation greatly . Empirically, the fluence and time-based rate constants for the selected PhACs using an MP system in LGW were higher than those in SW, demonstrating that mostly the SW matrix competition for UV light and as a result reduced the UV photolysis rate constants. Based on the above, Figure 2 explains the expectable difference between UV/H2O2 degradation rate constants in LGW and SW, which was caused by a competition for the UV light from NOM present in SW, as well as by NOM scavenging of the •OH radicals generated by UV oxidation.

Figure 2 Fluence-based rate constants from MP-UV photodegradation and UV/H2O2 oxidation in LGW and SW

Taken from

2.2.4. pH

Moreover, the degradation rates of organic compounds might be influenced greatly by the solution pH. For example, the effect from pH was evaluated by . For TMP, the photolysis was negligible at both pH 3.6 and 7.85, while TMP degradation was observed to primarily happen via •OH oxidation. What is more, the oxidation rate of the cationic form (pH 3.6) was demonstrated to be greater and the second order rate constant for TMP and •OH reaction was pH dependent; specifically, the protonated form (pH 3.6) was noticed more readily than the neutral form (pH 7.85). This trend differs from that of TMP ozonation , while was consistent with TMP oxidation by potassium permanganate .

Apart from the above, the change of pH can affect the ionic formation of H2O2 . The degradation rate of 4-AAP went up to 86.63% with the increase of pH up to 6.80 because the formation of •OH radicals was improved; later it went down due to the further increase of pH, which can be explained by the formation of ionic H2O2 (HO2-) at high pH and the scavenging phenomenon caused by HO2-. Similar finding has been reported that the degradation rate of dimethyl phthalate enhanced with increasing pH only in the range of 2.5-4 but started to decrease when pH was going higher .

For BP and OP, it was reported that H2O2/UV process saved above 3 times less energy needed for 90% concentration reduction than indirect photolysis . Except from this, noticed that high oxidation rate for BP and OP was attained at the most favorable dose of H2O2, about 0.01 M. As pH increased, the decreasing of reaction rate for both substrates could be explained by the formation of anions of BP and OP and slower reaction between these molecules and •OH radicals. As for the influence of water components, humic acids and nitrate ions (present at the concentrations typical for natural waters) did not introduce any effect on the BP degradation.

2.2.5. Structure of organic compounds

The molecular structure also affects the degradation during UV/H2O2 process. For example, in the survey from , the complete degradation of NPEO and ETHT finished in 15-20 min and 30 min, respectively, whereas complete DOS degradation required a little longer treatment period, even though 90% was already eliminated after 20-25 min. The different rates for surfactants degradation were mainly due to the structural and charge differences between these three textile surfactant types . The primary step of NPEO degradation involved the hydrogen abstraction of the ethoxy moiety and the immediate cleavage of the ethoxylated chain . However, the attack from •OH occurred at two sites of DOS: the -CH3 groups located at the end of the ethoxy chain and the -CH2 groups in the intermediate position . As a result of the hydrogen abstraction reactions, alkyl radicals (•R) were formed within the oxidation of the anionic surfactants. Subsequently, low molecular weight degradation intermediates for example, alcohols, were considered to form in the reaction between •R radicals and •OH radicals . Therefore, based on the mentioned above, the observed retarding degradation for the anionic surfactant DOS could be explained by the formation of •R radicals and/or degradation intermediates with the •OH radicals.

2.3. Inactivation via H2O2/UV treatment

Recently, UV/H2O2 process has received attention on inactivation of microorganisms because application of the combined technologies has been shown to enhance the disinfection efficiency; in addition, synergistic lethal effects have been reported against both spores and vegetative cells by generation of •OH radicals . The principal targets of UV radiation are DNA or RNA, while chemical disinfectant, for example, H2O2, is thought to contain two primary mechanisms: first, oxidation and disruption of cell walls and membranes along with the disintegration of the whole cell; and second, diffusion of the disinfectant into the cell or particle with resulting enzymes inactivation, intracellular components damage, protein synthesis interference and transport systems destruction, etc. Therefore, the microbial repair mechanisms may become overloaded and lead to subsequent death .

reported that UV/H2O2 did not result in a significant decrease in the bacterial numbers associated with wild blueberry processing compared with the result from H2O2 alone. Also, reported that H2O2/UV disinfection only slightly reduced the pathogens in wastewater compared to UV alone and exhibited statistically significant antagonistic effects for E. faecalis and non-significant synergy for MS2 coliphage, in well agreement with the results from previous studies . The limited observed synergistic effect might be resulted from applying H2O2 at ambient temperature, where the generation of •OH radicals was low .

Inactivation of three indicator microorganisms, E. coli, P. aeruginosa and B. subtilis by UV/H2O2 process in humic waters with different concentrations was investigated . B. subtilis spores were the most resistant organism among the three test indicator microorganisms in all operation conditions. This resistance has been stated to stem from a protective outer proteinaceous layer (termed the spore coat) . As the concentrations of fulvic acid in the water went up, the required contact times for 3 log reduction were detected to increase for all microorganisms; however, compared with other two microorganisms, fulvic acid was effective in protecting E. coli from the UV/H2O2 processes. On the other hand, the increase of the H2O2 concentration did contribute to the inactivation of B. subtilis spores only in highly humic water, rather than moderately humic water, indicating that fulvic acid molecules were broken up and resulted in UV absorbance reduction .

Apart from this, it was revealed that a potential synergistic effect within UV/H2O2 disinfection process could be achieved on MS-2 phage and B. subtilis spores . H2O2 addition from 0.10 mM to 0.60 mM was linearly correlated with the •OH exposure degree, in particular, the •OH exposure and inactivation was found to be increased by a factor of six and four, respectively. This might be due to the enhanced oxidation of outer protein coat on MS-2 phage and cell disintegration of B. subtilis spores . At H2O2 concentration of 0.6 mM, in order to achieve a 3 log inactivation for MS-2 phage as well as B. subtilis spores, the required UV dose was 32 and 21 mJ/cm2, respectively, which were around 43% and 24% of the UV dose needed to have the same inactivation efficiency by the UV treatment only, revealing that the H2O2 addition effectively enhanced the inactivation kinetics for MS-2 phage and B. subtilis spores.

2.4. Byproducts formation during UV/H2O2 process

Complete mineralization of organic pollutants by UV/H2O2 process requires intensive UV irradiation and energy, which is not practical in many cases. Thus, breakdown products will be formed and of ultimate concern, the toxicological testing of byproducts is mandatory . Take the case of fluorine (FLU), dibenzofuran (DBF) and dibenzothiophene (DBT) as an example , it was stated that at the very beginning the toxicity went up after exposure to UV/H2O2 process in which UV dose was 50mJ/cm2, however later a linear decrease was observed for all three compounds since both the oxidation products and parent compounds were successfully degraded. It was also suggested that in the experiment of DBT, the observed toxicity was likely due to the oxidation products rather than the parent compound.

Table 6 Some byproducts of antibiotics in UV/H2O2 process identified by GC-MS analysis

Modified from


Name and retention time (min)

Molecular structure


4-Oxo-pentanoic acid and 8.89

Butanedioic acid and 26.32


Propanedioic acid and 14.74

1,4-Benzenedicarboxylic acid and 45.68


N,N'-Bis (trimethylsily) and 19.21

gave a more detailed analysis on the change of toxicity of parent compounds (OTC, DTC, and CIP) during UV/H2O2 process. The oxidation happened in two stages: in the first stage, the increase of the byproducts toxicity at respectively certain amount of UV doses originated from partial degradation of the parent compounds (the character structures remained undestroyed); the second stage characterized the conversion of toxic byproducts into non-toxic products under consistent increasing of UV fluence (Table 6). Another discovery was that even though all three antibiotics were degraded and the further toxicity of reaction solution was unable to be measured, TOC removal was considerably slight, revealing that detoxification was easier than mineralization via UV/H2O2 process.

UV oxidation of NOM is reported to result in the formation of genotoxic compounds . A study was conducted on the potential of NOM to form THMs after chlorination process . Because the dissolved organic compounds were released from one test raw water, which was contaminated by domestic wastewater and was in highly eutrophication status, this process increased the THM precursors at the initial of UV/H2O2 treatment. Hydrophobic acids portion was investigated to be the main contributor to THMs formation after chlorination process by using THMFP tests (trihalomethanes formation potential). Additionally, byproducts formation in a phenol-contaminated wastewater revealed that total halophenols formed at 0.03% yield, with bromophenols constituting 60-100% of the total formation, although the concentration of chloride was much higher than that of bromide .

Recently, a model has been developed to computerize the minor pathway and therefore predict the fate of byproducts generated by the hydroxyl radical-initiated chain reactions in aqueous phase AOPs . This model may be greatly helpful to predict whether or not toxic byproducts are to be expected during treatment processes.

2.5. Coupling H2O2/UV process with other treatments

Regarding UV/H2O2 treatment efficiency, the majority of published work have reported the removal of trace quantities of specific compounds and pathogens from many water matrices and the treatment performance is able to be improved to some extent; nonetheless, this treatment is not necessarily accompanied by complete mineralization, particularly, the waters from industrial effluents, pharmaceuticals manufacturing or hospital operation are highly polluted (in the order of g/L COD) . Another point is it is demanding for a full evaluation of an effectively destructive treatment, not only by following the degradation of the target compounds or intermediates, but also by measuring the toxicity of the treated water. In light of this, process integration, for instance, a biological post-treatment may be feasible to maximize the overall treatment performance.

studied the biological treatability of a pretreated synthetic textile wastewater by different AOPs. After the pretreatment of the wastewater by AOPs, an absence of a lag phase from the microbial growth curve was noticed. This can be explained by the molecular modification of contaminants and the susceptibility of contaminants to the existing enzymes in the activated sludge, which was similar to the conclusion drawn by , in which chemical oxidation could convert large molecules in the wastewater into small ones as well as easily biodegradable fragments. Meanwhile, the comparison of relative COD removal efficiency by various applied AOPs together with biological degradation of the wastewater is presented in Figure 3, which demonstrated that the stronger the oxidant, the lower the initial COD value for the following biological step and the higher the overall pollutants elimination level in the wastewater. Although H2O2/UV pretreatment and biodegradation demonstrated a 65% reduction of COD, the stronger the oxidant, the most powerful oxidation agents-three oxidants in combination O3/H2O2/UV was evidenced to reduce 80% of COD.

Figure 3 Comparison of COD removal efficiency of different AOPs along with biological treatment of the textile wastewater: 1-biodegradation alone; 2-O3; 3-UV; 4-H2O2; 5-UV/H2O2; 6-O3/H2O2; 7-O3/H2O2/UV

Taken from

A feasibility study of different AOP combinations (O3 at elevated pH, H2O2/UV, Fenton and photo-Fenton processes) for the degradation and biodegradability improvement of a penicillin formulation wastewater was conducted . UV alone (direct UV-C photolysis) and H2O2/UV experiments (with different H2O2 doses: 30 and 40 mM at pH=7) were firstly surveyed. It was evident that the effluent was not degraded at all via direct UV photolysis; moreover, the addition of H2O2 barely improved the overall COD removal rates, only 22% for 30 mM and 11% for 40 mM. As can been summarized (Table 7), for final TOC, COD and BOD5/COD values and TOC as well as COD removal efficiencies from the oxidative pretreatment processes, photo-Fenton, dark Fenton/Fenton-like reactions and the O3/pH 11.5 process were the most promising methods for penicillin formulation effluent pretreatment. As a result, H2O2/UV treatment was determined to be a relatively less efficient process for the advanced oxidation of penicillin formulation effluent, partially due to the severe inhibition from other strong UV absorbers present in the effluent.

Table 7 Results obtained from various AOPs of penicillin formulation effluent

Adapted from

Oxidation process


Final COD (mg/L)

COD removal (%)

Final TOC (mg/L)

TOC removal (%)

Raw wastewater






O3/pH 3






O3/pH 7






O3/pH 11






UV/pH 7






H2O2 (40mM)/UV/pH 7






H2O2 (30mM)/UV/pH 7






Photo-Fenton/pH 3






Photo-Fenton-like/pH 3






Dark Fenton/pH3






Dark Fenton-like/pH 3






One pilot-scale study was conducted by using the combination of UV/H2O2 and BAC treatment in order to evaluate the effect of the UV/H2O2 treatment on the DBP formation potential and on the structure and biodegradability of NOM in surface water . Table 8 is a brief description of the pilot-scale system, related parameters and results. Further the efficacy of BAC at removing biodegradable products and residual H2O2 was assessed.

Table 8 brief description of the pilot-scale system, parameters and results

Source Sarathya et al. (2011)

Source water

H2O2/UV electrical energy doses (EED)

Biological activated carbon treatment (BAC)

Flow rate of BAC


Diluted surface water (DSW) [TOC] 2.24 mg/L

10 mg/L; 0.18, 0.36 and 0.54 kWh/m3 UVSwift reactor while 0.09, 0.13 and 0.18 kWh/m3 UVPhox reactor

A coconut shell based granular activated carbon (GAC); total empty bed contact time (EBCT) 20 min

150 mL/min; 14-day pass through while first seven days for biomass acclimation

THM formation potential for NOM did not reduce significantly.

BDOC increased by more than threefold.

By monitoring, it was found that significant reductions occurred in chromophoric NOM and in the degree of substitution of aromatic rings. Fragmentation of NOM aromatic rings only partially underwent oxidation rather than complete mineralization, in agreement with the result from bench-scale H2O2/LP UV study which offered the evidence that major changes occurred in molecular weight distribution, polarity, and structure of NOM although little TOC reduction was observed . As for biodegradable dissolved organic carbon (BDOC), with an increasing EED, BDOC went up along with the formation of aldehydes (formaldehyde, FA and acetaldehyde, AA), both of which were readily biodegradable compounds. For instance, aldehydes may contain 25-30% of BDOC . Data associated with the BAC filtration of the water from UV/H2O2 treatment depicted that effective removal of NOM (up to 58% of TOC reduction) could be reached, while haloace