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
Source: Cotton and Passantino, 2005
Source: Cotton and Passantino, 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 USEPA’s second Contaminant Candidate List (CCL2) - 2
• 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
Source: Scharfenaker, 2005
The USEPA’s second Contaminant Candidate List (CCL2) - 3
• 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
Source: Scharfenaker, 2005
Source: Scharfenaker, 2005
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
N/A
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)
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
Blatchley et al, 2005
UV inactivation of spores on surfaces
Blatchley et al, 2005
γ inactivation of spores in solution
Blatchley et al, 2005
γ inactivation of spores on surfaces
Blatchley et al, 2005
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
Source: Nickelsen et al, 2005
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
Source: Nickelsen et al, 2005
Source: Nickelsen et al, 2005
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
Source: Bolek, 2005
Source: Bolek, 2005
Source: Bolek, 2005
Iron(VI) - ferrate• Iron(VI) – used as Fe6+O4
2-
• 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
Source: Sharma, 2005
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
Park et al, 2006
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
Bahr et al, 2005
Bahr et al, 2005
Bahr et al, 2005
New pulsed UV lamp
• Developed by Phoenix Science and Technology inc. ([email protected])
• 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
Source: Schaefer et al, 2005
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
Oppenlander and Sosnin, 2005