Recent developments in disinfection of water and wastewater. · Disinfection of water and...

transcript

Disinfection of water and wastewater: recent developments

in legislation and technology.

Ronald GehrDepartment of Civil Engineering

III Simposio Internacional en Ingeniería y Ciencias para laSustentabilidad Ambiental y Semana del Ambiente 2006

UAM-Azcapotzalco, Mexico DF, Taller, 7 de Junio

Outline of presentation -Legislation

• Drinking water – WHO framework– The US EPA’s

• Water reuse– The Stockholm Framework– WHO guidelines for water reuse– Water reuse guidelines in the Mediterranean– Italy– Mexico

Outline of presentation -technology

• Electrochemical disinfection• UV and gamma radiation• E-beam• Mixed oxidants (MIOX)• Ferrate• Ozone generation• New UV lamps

Legislation:Drinking water

From the WHO Guidelines for Drinking Water Quality, 3rd edition (2004)

Summary of Drinking Water Legislative Framework in the USA (1)

• The USEPA Surface Water Treatment Rule (SWTR) was finalized in 1989

• Applies to systems using surface waters or groundwater under the direct influence of surface water (GWUDI)

• It focuses on the inactivation of Giardia and viruses• The Interim Enhanced Surface Water Treatment

Rule (IESWTR) and the Long Term 1 ESWTR(LT1ESWTR) include Cryptosporidium, and coincide with Stage 1 of the Disinfectants andDisinfection Byproduct Rule (D/DBPR).

Source: Cotton and Passantino, 2005

Acronyms......

Summary of Drinking Water Legislative Framework in the USA (2)

• The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) will include additional treatment requirements for Cryptosporidium.

• Will be implemented simultaneously with Stage 2 of D/DBPR.

• They introduce the idea of “bins” and toolboxes: Based on a utility’s raw water quality, it will be placed in a bin which then determines the level ofCryptosporidium treatment required, as well as the technology.

• Concept of log removals, rather than final concentrations.

• Should be finalized in 2005.

Source: Cotton and Passantino, 2005

The Disinfection By Product Rule (Stage 1 DBPR)

• Stage 1 EPA Disinfection By Product Rule– Implemented in January 2002 for large surface

water systems (> 10,000 people)– Implemented in January 2004 for ground water

and small systems (< 10,000 people) • This will affect:

– 61% larger systems– 70% smaller systems– 12 – 15% ground water systems– Total of 4,665 systems; 20 m households

Source: Bolek, 2005

DBPR limits

After: Bolek, 2005

Process Residual or by-product Limit (mg/L)

Chlorine 4.0

TTHM 0.08

HAA5 0.06

Chloramination Chloramine 4.0

Chlorine dioxide 0.8

Chlorite 1.0

Ozonation Bromate 0.01

Chlorine dioxide

Chlorination

The USEPA’s second Contaminant Candidate List (CCL2) - 1

• The CCL2 was finalized in February, 2005• It is a list of unregulated contaminants that is being

considered for regulation• CCL (1) of 1998 listed 60 contaminants; CCL2

dropped 9, including:– 1,1,2,2-tetrachloroethane– 1,1-dichloropropene– 1,3-dichloropropane– 1,3-dichloropropene– 2,2-dichloropropane

• Also did not include:– N-nitrosodimethylamine (NDMA)– Enterotoxigenic E.coli

Source: Scharfenaker, 2005

• The third CCL, CCL3, is due in 2008• USEPA plans to propose preliminary

regulations (i.e. values for limits) for at least 5 of the contaminants on CCL2 by summer 2005, and finalize them by August, 2006

• USEPA is authorized to regulate ANY contaminant at ANY time if deemed a public health risk

• They have deferred registered pesticides and endocrine disruptors to CCL3

• Reasons for not including a contaminant on the list:– Lack of information on extent of occurrence for

NDMA– Enterotoxigenic E. coli not included yet, because

they want to reevaluate it in comparison with a wide range of other microbes

Legislation:Water reuse

Simplified framework for developing guidelines for water-related

microbiological hazards

Source: Bartram et al, 2001)

The expanded “Stockholm”framework

Source: Bartram et al, 2001)

Current (1989) WHO guidelines for water reuse

Source: Havelaar et al, 2001

Recommended revised microbiological guidelines for treated wastewater use in

agriculture (Carr et al, 2004)

Category Nematodes (eggs/L)

Fecal coliforms(CFU/100 mL)

A: Unrestricted irrigation

< 0.1 < 103

B: Restricted irrigation

< 1 or < 0.1, depending on who exposed

< 105 or < 103, depending on irrigation technique

C: Localized irrigation; no exposure by workers or public

Water reuse guidelines for the Mediterranean (Bahri and Brissaud, 2004)

• Based on new epidemiological investigations and quantitative microbiological risk assessment (QMRA)

• Aim is to standardize guidelines for the region to facilitate trade, tourism, etc.

• Recognise that for bathing water, an acceptable risk for seasonal gastro-intestinal illness rate is 1 – 2%.

• Guidelines should take local conditions into account, but should not require uselessly expensive treatments.

• Bathing risk for FC of < 200 CFU/100mL is still accepted.

Source: Bahri and Brissaud (2004)

FC SS(CFU/100 mL (mg/L)

Source: Bahri and Brissaud (2004)

FC SS(CFU/100 mL (mg/L)

Italian studies: Wastewater disinfected for agricultural reuse

• Old legislation (1977):– Total coliforms: 2 CFU/100 mL,

unrestricted, 20 CFU/100 mL restricted.• New legislation (2003):

– E. coli: 10 CFU/100 mL for 80% samples; none to exceed 100 CFU/100 mL.

– This new standard is easier to meet and less costly

Caretti and Lubello, 2005

Italian studies, contd.• Assessed:

– PAA 0.5 – 5 mg/L – H2O2 5 – 30 mg/L– UV 50 – 540 mJ/cm2

– O3 4 – 40 mg/L• At these doses, PAA and H2O2 not effective• Combined H2O2/UV and H2O2/O3 also not

effective• PAA/UV and PAA/O3 successful because of

production of •OH, but doses not established

Caretti and Lubello, 2005

Mexico

• Secretariat responsible used to be called SEMARNAP, now called SEMARNAT (since 2003)

• Names of official standards changed from NOM-001/2/3-ECOL-1996/7 to

• NOM-001/2/3/4-SEMARNAT-1996/7/2002• http://portal.semarnat.gob.mx/semarnat/portal

SEMARNAT Standards

• NOM-001 (1996): Allowable levels of pollutants in wastewaters discharged into water bodies

• NOM-002 (1996): …..discharged into municipal sewers

• NOM-003 (1997):…..for water reuse• NOM-004 (2002): Allowable limits of

contaminants in biosolids

Water reuse

NOM-003-SEMARNAT-1997 website

Biosolids

NOM-004-SEMARNAT-2002 website

Technology

Electrochemical disinfection

• Many mechanisms have been proposed:– Destruction caused by the electric field– Inactivation by short-lived radicals such as O2

-•, •OH-, HClO-•, ClO2

-•, etc.– Chlorine may act as a catalyst to generate and

extend the life of •OH-

– Generation of other oxidants, such as persulfate• Li et al (2002, 2004): experiments with

stainless steel cathode, titanium anode coated with RuO2 and TiO2; current = 0 –2.5 A; voltage = 0 – 30 V.

Li et al, 2002

Li et al, 2004

Electrochemical disinfection - conclusions

• For low voltage, continuous DC:– Chloride ions (salinity) are necessary– Kill rate greater than with equivalent

chlorine alone– Disinfection due to combination of action

of chlorine and radicals– Sulfates and other ions have no impact– Chloride ions probably act as catalyst for

the generation of hydroxyl radicals

Li et al, 2002, 2004

UV or gamma radiation for inactivation of Bacillus spores in water or on surfaces

• Bacillus spores can be dispersed asbioterrorism agents in air or water

• Spores are 10 – 75 X more resistant than vegetative cells

• UV or ionizing radiation (from 60Co, 137Cs, or electron beams) can inactivate these spores

• Ionizing radiation more effective than UV for surfaces

Blatchley et al, 2005

UV inactivation of spores in solution

UV inactivation of spores on surfaces

γ inactivation of spores in solution

γ inactivation of spores on surfaces

Accelerated electron injection• Also called “E-beam”• Ionizing radiation which creates both

reducing and oxidizing chemistries• Actually similar to a TV set:

– heated tungsten filament (electron gun) generates thermal electrons

– voltage gradient applied across accelerator tube draws electrons away from the gun and accelerates them through a vacuum tube

– high voltage electron beam passes through oscillating magnetic field, sweeping back and forth across a scan window

Source: Nickelsen et al, 2005

TV vs Electron beam

TV E-beam

Voltage (kV)

Current

25 300 – 10,000

µA 10 – 100 mA

Radioactive isotopes• Most common are 137Cs and 60Co• 60Co is more efficient because it emits two γ

rays with energies of 1.17 and 1.33 MeV.• Quantity of radiation from natural sources is

limited, hence can’t apply to high mass flows• Cannot be inactivated, hence can be used

as weapons themselves!• However advantage is that they can

penetrate ~ 100 cm in aqueous media, compared with ~ 5 cm for E-beams

Disinfection with mixed oxidants (MIOX)• MIOX first demonstrated to the US Navy in

1985• Over 1,200 mixed-oxidant installations

worldwide by 2004• Unit generates a liquid oxidant which is

injected directly into the water supply (or swimming pool)

• Measure by DPD, which quantifies only chlorine, but other oxidants add to itsdisinfection power

Source: Bolek, 2005

Advantages of mixed oxidants (MIOX)• Reduces TTHMs and HAA5s• Uses lower chlorine dose• Can inactivate Cryptosporidium• Eliminates biofilms• Produces more durable chlorine dose• Assists coagulation, and can be used

upstream of settling/filtration, since formation of DBPs is much lower than for chlorine

Source: Bolek, 2005

Iron(VI) - ferrate• Iron(VI) – used as Fe6+O4

• Generated by:– dry-heating potassium- and iron-

containing minerals– electrolyzing an alkaline solution with an

iron anode– wet method, oxidizing a basic solution of

Fe(III) salt by hypochlorite (preferred)

Source: Sharma, 2005

Iron(VI) – ferrate (contd.)• Wet method reactions (the “Thompson”

method):

Source: Sharma, 2005; Kim et al, 2005

• Kim et al (2005) have developed a pilot-scaleunit to produce ferrate on site (“FerratorTM”)using Equation 1. Yield is 60%; must be used in 1 hour.

Source: Sharma, 2005

New developments in ozone generation (1)

• Dielectric barrier discharges (DBDs) • Ozone yields are slowly increasing; can

achieve up to 300 g/kWh in pulsed experiments… but the theoretical limit is 1,220 g/kWh.

• Ozone concentrations as high as 300 g/m3 now possible

Kogelschatz, 2005

New developments in ozone generation (2)

• New power supplies use insulated gate bipolar transistors (IGBTs) or integrated gate-commutated thyristors (IGCTs) which can handle currents of a few kA, and voltages of 5 – 10 kV.

• The largest plant so far is a pulp-and-paper plant in Brasil, producing 12,000 kg/d, but if the City of Montreal or Mexico City would use ozone for disinfection, the plant would have to be as large as 23,000 kg/d!

Kogelschatz, 2005

Park et al, 2006

Conventional

Meshed plate Dielectric barrier discharge

Berlin study to assess O3 for removing pharmaceuticals and pathogens

• Tested secondary effluent• No effect on DOC at O3 doses less than 14 mg/L• Reported doses as

specific ozone consumption zspec= mg/L O3/mg DOC• All acidic drugs removed at zspec = 1.2 mg/mg• Neutral pharmaceuticals removed at zspec > 0.4

mg/mg• Iodinated X-ray contrast media (ICM) hardly removed

at highest O3 dose• 12 – 14 mg/L O3 required to reduce enterococci to <

200 CFU/100 mL

Bahr et al, 2005

New pulsed UV lamp

• Developed by Phoenix Science and Technology inc. (Rschaefer@PhoenixSandT.com)

• Surface Discharge (SD) UV lamp:– High power electrical pulse discharged along the

surface of a dielectric tube within a larger diameter tube

– Discharge occurs in xenon or krypton– Discharge generates a uniform plasma sheet

along the tube which produces an intense UV light pulse

Source: Schaefer et al, 2005

Advantages of the new UV lamp

• Instantaneous on• No mercury in the lamp• Energy efficiency 17%, vs 12% for medium

pressure UV lamps• Light emission over range of wavelengths

may improve inactivation efficiency and reduce photoreactivation

Source: Schaefer et al, 2005

Other new types of UV lamps

• Electrodeless lamps are driven by dielectric barrier discharge (DBD) or capacitive discharge (CD)

• They use rare gases (Rg2), halogen excimers(X2) or a combination (RgX)

• Advantages are absence of mercury, long life (1,000s of hours) and freedom of geometrical design

• Xe2 lamps @ 172 nm produce O3 in air or OH•in water

Oppenlander and Sosnin, 2005

New UV excimer lamps

Oppenlander and Sosnin, 2005

Recent developments in disinfection of water and wastewater. · Disinfection of water and...

Documents