Guidance Document for Integrating UV-based Advanced Oxidation Processes

29 Pages·2015·0.54 MB·English

Guidance Document for Integrating UV‐based
Advanced Oxidation Processes (AOPs) Into Municipal
Wastewater Treatment Plants

Ministry of the Environment and Climate Change
Showcasing Water Innovation Program (SWI)

January 2015
Table of Contents

Table of Contents ....................................................................................................................... 1 
1.0   Introduction ..................................................................................................................... 2 
2.0   Objectives/Scope of Document ....................................................................................... 2 
3.0   Background ..................................................................................................................... 2 
3.1   Lake Simcoe Region ................................................................................................... 2 
3.2   Regulatory Outlook ..................................................................................................... 3 
3.3   Advanced Oxidation Processes (AOPs) ...................................................................... 3 
3.4   Pre-treatment Options for Organic Matter Removal ................................................... 4 
4.0   Description of Study ....................................................................................................... 5 
4.1   Purpose of the study .................................................................................................... 5 
4.2   Description of Plant Process ....................................................................................... 5 
4.3   Overview of Study ...................................................................................................... 5 
4.4  Findings ....................................................................................................................... 9 
4.5  Energy & Cost Analysis ............................................................................................ 13 
4.5.1  Energy Requirements ......................................................................................... 13 
4.5.2  Cost Analysis ..................................................................................................... 15 
4.6  Final Conclusions & Lessons Learned ...................................................................... 21 
5.0  Full-Scale Facilities - Integrating AOPs ....................................................................... 22 
5.1  Reducing Effluent Organic Matter Concentration .................................................... 22 
5.2  Other Considerations ................................................................................................. 23 
5.3  Approach for Assessing Energy Requirements ......................................................... 23 
5.4  Approach for Assessing Cost Implications ............................................................... 24 
References ................................................................................................................................ 25 
APPENDIX A .......................................................................................................................... 27 
APPENDIX B .......................................................................................................................... 28 

1
1.0 Introduction

This document summarizes results from a project called “The Removal of Micropollutants
from Municipal Wastewater”, which was sponsored by the Ontario Ministry of the
Environment and Climate Change, as part of their Showcasing Water Innovation Program for
Ontario municipalities. The overall goal of the project was to demonstrate the ability of
ultraviolet (UV)-based advanced oxidation technologies to destroy micropollutants during
wastewater treatment, and to identify simple methods to reduce these treatment costs. In
addressing the treatment of micropollutants, this document is intended to provide
municipalities with information to assist in understanding the factors and limitations that
should be taken into consideration from an operational and economic perspective when
integrating UV-based advanced oxidation into a wastewater treatment plant.

2.0 Objectives/Scope of Document

The information provided in this guidance document is generally applicable to municipal
wastewater treatment facilities where the influent is comprised primarily of sewage from
residential areas. The objectives of the work were as follows:
1. Outline an approach that can be used to improve the economic and practical feasibility of
using UV-based advanced oxidation processes (AOPs) for treating micropollutants in
municipal wastewater.
2. Identify operational and design criteria that should be considered in a full-scale facility
when implementing this technology.
3. Outline an approach that can be used to assess the cost and energy requirements for
implementing advanced oxidation technology in a full-scale facility.
Evaluating the application of the approaches outlined in this study to any specific treatment
facility must involve detailed consideration of plant-specific factors prior to implementing
technologies. Some considerations for integrating advanced oxidation technologies are
discussed further in section 5.
3.0 Background

3.1 Lake Simcoe Region

Emerging contaminants or micropollutants refer to trace organic compounds that are present
in the environment in µg/L (microgram per litre) and ng/L (nanogram per litre)
concentrations such as pharmaceuticals, endocrine disruptors, personal care products and
household cleaners. Detecting these compounds is possible because of improvements in
analytical capabilities at very low concentrations, and the presence of these contaminants in
the environment is a growing concern worldwide as the potential effects of these compounds
are not well understood. Through human consumption and use these compounds become part
of the influent to wastewater treatment plants. Current wastewater technologies are not
2
designed to remove these compounds and so the compounds are found in the environment
due to the discharge from wastewater treatment plants, septics and farm runoff to surface
water bodies. These water bodies are the final receiving points for the effluent, and also
function as the source for water intakes to drinking water treatment facilities.
Whole lake studies conducted at the Experimental Lakes area in northwestern Ontario
demonstrated that some micropollutants can potentially eliminate entire fish species by
disrupting spawning patterns and reproductive activities and functions.1-4 Hence, preventing
the release of these compounds to the environment should help to improve the water quality
of lakes and ensure the sustainability of our aquatic ecosystems.
Lake Simcoe was selected as the site for the project since it is the largest and one of the most
intensively fished inland lakes in Ontario. At Lake Simcoe, fishing, particularly ice-fishing, is
a primary industry3 such that recreational activities contribute $200 million annually to the
local economy.2 The lake supports a population of approximately 350,000 persons and serves
as the intake source for 7 water treatment facilities serving 6 municipalities, and the final
discharge point for 14 water pollution control plants (WPCP).5, 6
3.2 Regulatory Outlook

It is anticipated that the presence of micropollutants in the environment may increase over
time because of the higher human use of prescription and over-the-counter drugs, personal
care products, as well as agricultural and veterinary medications. At present, the removal of
these compounds during wastewater treatment is not regulated. However, organizations such
as Environment Canada, the U.S. Environmental Protection Agency, and the World Health
Organization (WHO) have focused their efforts in collecting comprehensive information on
analytical methodologies, occurrence and environmental fate, and the response of these
compounds to different treatment strategies.15,16 The U.S. EPA has established a strategy
which aims to improve the scientific and public understanding of these micropollutants, and
create partnerships with research groups and organisations through federal collaborations and
working groups.16 In Canada, the Wastewater Systems Effluent Regulations, S.O.R./2012-
139 made under the Fisheries Act, R.S.C., 1985, c.F-14 establishes federal effluent quality
standards as well as requirements for monitoring water quality and environmental effects.
Ongoing initiatives in Canada, the United States, and elsewhere aim to improve our
understanding of the potential effects of these compounds in the environment and on human
health.
3.3 Advanced Oxidation Processes (AOPs)

Studies have shown that activated carbon, membranes, and advanced oxidation are options
that can be considered for treating micropollutants. Of these, numerous research studies have
shown that advanced oxidation processes are very effective for the degradation of these
compounds in waters of varying quality.7-10 Typical AOPs include ultraviolet light (UV)-
based or ozone (O )-based AOPs such as using hydrogen peroxide with ultraviolet light
3
3
(UV/H O ) or ozone (O /H O ), ozone and UV(O /UV), chlorine and UV(HOCl/UV), as well
2 2 3 2 2 3
as the Fenton’s reagent (Fe2+/H O ) and photocatalysis using titanium dioxide and UV
2 2
(TiO /UV). AOPs are effective for the degradation of these target pollutants due to the
2
generation of the highly reactive hydroxyl radical (•OH). The radical is non-selective in its
reactions with other compounds so it can oxidise a wide range of compounds, thereby making
it suitable for complex wastewater matrices.
In Ontario, UV is typically the preferred alternative for wastewater disinfection. This is due
to strict regulations for residual chlorine in the treated effluent of less than or equal to 0.02
mg/L.17 Hence, UV-based AOPs would be a practical choice for integrating AOPs into
wastewater treatment facilities. The purpose of disinfecting the final effluent in wastewater
plants is to reduce the microbial content of the effluent before it is released to the
environment, so using AOPs as the final step can achieve a dual purpose of disinfection of
the final effluent and removal of trace organic contaminants which were not removed during
upstream treatment. Therefore, with an UV-AOP system, a separate disinfection system
would not be required. Using UV in an AOP mode (UV photolysis) would require
substantially more power than UV solely for disinfection purposes, which would increase
plant energy costs.
3.4 Pre‐treatment Options for Organic Matter Removal

Elevated concentrations of dissolved organic matter in wastewater effluents exert an oxidant
demand. In an AOP process, the dissolved organic matter reacts with the hydroxyl radicals,
reducing the concentration of the radicals available for reacting with and destroying the target
micropollutant compounds. Hence, larger AOP doses are required to account for the demand
exerted by the dissolved organic matter and to ensure the desired level of removal of the
micropollutants in the effluent. A consequence of these higher doses is an increase in energy
and operating costs. Therefore, measures to reduce the concentration of dissolved organic
matter in the water prior to applying AOP treatment can improve the effectiveness of the
AOP process, and reduce associated cost and energy requirements. Coagulation and activated
carbon adsorption are two proven and standard technologies typically used for removing
organic matter during drinking water treatment, but are not widely used in the wastewater
treatment industry for removing dissolved organic matter.

Traditionally, secondary clarifiers are used to separate solid particles from the secondary
effluent prior to disinfection and subsequent release to the environment. This is the only point
after secondary treatment and prior to discharge for which there is an opportunity for organic
matter to be removed from the secondary effluent. However, a significant portion of organic
matter remains dissolved and will not settle using this traditional approach. Enhanced
coagulation focuses on removing dissolved organic matter instead of only particles during the
clarification process. Therefore, using enhanced coagulation or activated carbon adsorption
will improve the removal of dissolved organic matter in the effluent.

4
4.0 Description of Study

4.1 Purpose of the study
The purpose of the study was to demonstrate an innovative and feasible approach that can be
used to integrate advanced oxidation processes into wastewater treatment plants to reduce the
concentration of micropollutants released to the environment. In this approach, enhanced
coagulation/activated carbon adsorption was combined with advanced oxidation to treat
micropollutants in secondary municipal wastewater effluent. Two advanced oxidation
processes were evaluated in the study: UV/hydrogen peroxide (UV/H O and UV/titanium
2 2)
dioxide (UV/TiO ). In comparison to UV/H O treatment, UV/TiO is a relatively new or
2 2 2 2
emerging technology. It was included in the case study as a demonstration of its potential
capabilities for micropollutant removal.

4.2 Description of Plant Process
The project was undertaken at the Keswick Water Pollution Control Plant which is owned
and operated by the Regional Municipality of York. The Keswick plant uses an extended
aeration treatment process, and has a peak capacity of 64,500 m3/day. Figure 1 shows a
schematic of the plant.

4.3 Overview of Study
A grab sample of secondary effluent was collected after the secondary clarifier, but prior to
any tertiary treatment or disinfection (Figure 1). This sampling point was selected to account
for wastewater treatment plants that do not apply tertiary treatment to the secondary effluent,
although AOP treatment would typically occur after tertiary treatment in order to maximize
organic matter removal prior to the AOP. The effluent sample was characterized (Table 1)
and initial bench-scale tests were performed to identify the optimum coagulant and powdered
activated carbon dose for reducing the concentration of dissolved organic matter (DOM) in
the effluent. These doses were determined using the Point-of-Diminishing-Returns analysis
where the PODR is the dose for which a 10 mg/L incremental increase in the applied
coagulant or activated carbon dose results in a change in DOM removal of less than 0.3
mg/L.11 The optimum doses and percentage reductions in DOM concentration are shown in
Table 2. The coagulants used included aluminium sulphate (alum), polyaluminum chloride
(PACl), and ferric chloride. The powdered activated carbons included WPH-1000 and WPC
products from Calgon Carbon Corporation. Details of the bench-scale tests are in Appendix
A.

5
Table 1: Water quality characteristics of the secondary wastewater effluent
Parameter Secondary Effluent
pH 7.1
Temperature (oC) 20
UVA (cm-1) 0.13
254
UVT (%/cm) 64
Conductivity (µS/cm) 1086
SUVA (L/mg-cm) 2.2
254
TOC (mg/L-C) 9.7
DOC (mg/L-C) 8.4
TIC (mg/L-C) 37.7
Carbonate (mg CO 2-/L) 0.02
3
Bicarbonate (mg HCO -/L) 32.4
3
Total Alkalinity (mg CaCO -/L) 185
3
Nitrite (mg/L-N) < 0.08*
Nitrate (mg/L-N) 25.1
*Method detection limit

Definition of Acronyms:

UVA – UV absorbance at 254 nm
254
SUVA – specific UV absorbance at 254 nm
254
TOC – total organic carbon
DOC – dissolved organic carbon
TIC – total inorganic carbon

6
Sampling Point
Figure 1 – Schematic of the Keswick Water Pollution Control Plant
7
Table 2: Optimum doses and percentage removals for the pretreatment options
% Removal of Dissolved
Treatment Optimum Dose
Organic Carbon (DOC)
Ferric chloride 60 mg/L as FeCl 39
3
Aluminium sulphate 12 mg Al/L 41
Polyaluminium chloride 16 mg Al/L 34
WPH-1000 activated carbon 80 mg/L 61
WPC activated carbon 80 mg/L 31

The identified pretreatment optimum doses were used in the pilot study. The objective was to
evaluate the influence of the combined treatment approach on the cost and energy
requirements of treating micropollutants in the secondary effluent. The approach uses
enhanced coagulation or activated carbon adsorption followed by AOP treatment using
UV/H O or UV/TiO . Enhanced coagulation and activated carbon adsorption were
2 2 2
conducted in a 100L stainless steel tank. AOP treatment was performed using either a Calgon
Carbon Rayox Advanced Oxidation Batch Pilot Reactor for UV/H O treatment (Figure 2),
2 2
or a pilot-scale Purifics UV/TiO reactor (Figure 3). Additional details of the pilot study are
2
outlined in Appendix B.

Figure 2: Calgon Carbon Advanced Oxidation Batch Reactor
8
Figure 33: Pilot-scaale Purifics UV/TiO Reactor
2
4.4 Findings
For UVV/H O testing, the secondaryy effluent was spikeed with 500 µg/L off seven
2 2
micropoollutants (caffeine, carbamazeepine (CBBZ), naprroxen, 177β-estradioll (E2),
sulphammethoxazolee (SMZ), diiclofenac, cllofibric acidd) and treated at 0, 10 and 20 mg//L H O .
2 2
For treatment with UV/TiO using 1 gg/L TiO , tthe secondaary effluennt was spikked with
22 2
caffeinee and carbammazepine oonly as thesee were founnd to be thee most recallcitrant commpounds.
The 1 gg/L TiO dose was usedd based on tthe recommmendation off the manuffacturer of thhe pilot-
2
unit. Thhe micropoollutant commpounds inn the studyy were seleected to bee representative of
differennt classes oof micropoollutants, annd on the basis of ttheir commmon occurrrence in
wastewwater effluennts as reported in thhe literaturre.12,13 The spike conncentration for the
micropoollutants exxceeds the typical vaalues foundd in wastewwater efflueents, but thhis high
concenttration was necessary tto monitor the degradaation of thee compoundds during treeatment.
Powderred activateed carbon uused as a ppretreatmennt agent in this study is also cappable of
removinng micropoollutant commpounds19. HHowever, rremoval of the compouunds by addsorption
was noot within thhe scope off this case study, theerefore for waters preetreated witth PAC,
micropoollutants weere spiked into the effffluent after the activatted carbon was removved. The
UV trannsmittance (UVT) of tthe effluentt for these eexperimentss was in thee order of 774% per
cm afteer pretreatmment (UVT wwas 64% peer cm prior to pretreatmment). This is a compaaratively
low UVVT since a 774% per cmm UVT is a relatively ttypical averrage for seccondary wastewater
effluentts from acttivated sluddge treatmeent processees with no pretreatmeent of the eeffluent.
Higher UVT valuees in the ordder of 85% per cm or mmore may bbe expectedd in some effluents.
The UVV dose requuirements, annd thereforee costs, are dependent on UVT vaalues. Highher UVT
will ressult in lowwer costs aand vice veersa. The eeffluent useed in the ccase study can be
characteerised as ““challengingg” (and theerefore exppensive) to treat whenn using UVV-based
disinfecction or advvanced oxiidation proccesses, commpared to mmany other wastewateers. This
informaation shouldd be kept in mind whenn interpretinng the subseequent resultts.
9