Disinfection of water and wastewater: recent developments in legislation and technology. Ronald Gehr Department of Civil Engineering III Simposio Internacional en Ingeniería y Ciencias para la Sustentabilidad Ambiental y Semana del Ambiente 2006 UAM-Azcapotzalco, Mexico DF, Taller, 7 de Junio
71
Embed
Recent developments in disinfection of water and wastewater. · Disinfection of water and wastewater: recent developments in legislation and technology. Ronald Gehr Department of
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
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
– 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