Granular Activated Carbon System

Transcription

1 Granular Activated Carbon System Eliminating Use of Chloramines March 22, worldwide

2 The Jacobs Team Mike McCarty, PE Project Manager Tobin Lichti, PE Water Treatment Engineer Russ Dahmer, PE Water Treatment Engineer Chandra Mysore, PhD, PE Subject Matter Expert 2

3 Objective To evaluate water treatment technologies required to facilitate the return to chlorine disinfection (cease use of chloramines) and to more fully understand the costs of that change. 3

4 Basics of Water Treatment at Hannibal DISINFECTANT CHEMICALS UV RIVER SETTLING FILTRATION DISINFECTION USERS 4

5 Disinfection Regulations Disinfection Rule o Requires potable water to contain a residual concentration of a disinfectant chemical a chemical that will kill pathogenic (disease causing) organisms Disinfection Byproduct Rule o Regulates the amount of disinfection byproducts present in potable water 5

6 What Are Disinfection Byproducts? Disinfection byproducts (DBPs) are chemicals formed when chlorine reacts with total organic carbon (TOC) The two DBP chemical groups are o Total Trihalomethanes (TTHMs) o Haloaceticacids (HAAs) They are regulated contaminants in drinking water 6

7 What Are Chloramines and Why Would We Use Them? Chloramine is an alternative disinfectant in water distribution systems Chlorine + Ammonia = Chloramine Chloramines last longer than chlorine in water distribution systems Chloramines are much less reactive with TOC and thus do not form as high a level of DBPs 7

8 Disinfection Byproducts Levels Why Recent Changes in Disinfection Were Made and the Result 300 Quarterly Measurements 250 Locational Running Annual Average TTHM Concentration at HRH ( ) Chlorine Chloramine Running Average (The Regulated Limit) Nov-13 Jan-14 Mar-14 May-14 Jul-14 Sep-14 Nov-14 Jan-15 Mar-15 May-15 Jul-15 Sep-15 Nov-15 Jan-16 Mar-16 May-16 Jul-16 Sep-16 Nov-16 In Compliance TTHM Limit (Recommended) TTHM Limit (Standards) Quarterly Value LRAA 8

9 Where We Are Today Chloramines (chlorine + ammonia) are used as residual disinfectant DBPs are within regulatory limits 9

10 What To Do If We Eliminate Chloramines Cease ammonia feed Use chlorine as residual disinfectant Modify treatment processes to control DBP formation Cannot be in compliance without this 10

11 Total Organic Carbon The Critical Component DBPs form when chlorine contacts with TOC Improved TOC reduction will be required for compliance Source Water TOC Treated Water TOC TOC (mg/l) Raw Water Average 5.1 mg/l Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13 Jan-14 Jan-15 Jan-16 Treated Water Average 2.7 mg/l 11

12 Control Options for DBPs Use low DBP forming disinfectant (e.g. chloramines) Where we are today Control DBPs in the distribution system Control DBP formation at the water treatment plant (WTP) Solution may be combination of improvements to WTP and distribution system 12

13 Controlling DBPs in the Distribution System Reduce water age (time the water spends in the distribution system) o Water main flushing program o Add mixing to storage tanks Treat DBPs that have formed o Air stripping of DBPs Typically at storage tanks May be necessary if WTP improvements changes do not result in sufficient DBP reduction Pilot testing required 13

14 Controlling DBPs in the WTP Optimize WTP operations Can improve TOC reduction, but not to levels required for DBP compliance Install additional treatment technologies Will be required to return to chlorine disinfection 14

15 Optimizing WTP Operations Enhanced Coagulation o Modify chemical additions at the settling beds to remove more TOC o Small capital costs o Adds operating costs and complicates operations Optimize Chlorine Addition Control o Excessive chlorine leads to higher DBPs o Small capital costs o Adds operating complexity 15

16 Options For New Treatment Technologies Granular activated carbon (GAC) The focus of this discussion Magnetic Ion Exchange (MIEX) Potential alternative to GAC Membrane filtration Tend to be very expensive in both capital and operating cost 16

17 Treatment Technology - GAC GAC reduces the amount of TOC in the water Provides additional water quality advantages o Eliminates tastes and odors o Reduces pesticides and herbicides o Reduces algal toxins o Reduces industrial chemicals such as Volatile organic chemicals (VOCs) Personal care and pharmaceutical products 17

18 Treatment Technology - GAC Requires adequate contact time o USEPA best available control technology calls for 20 minutes empty bed contact time (EBCT) GAC eventually saturates with TOC and must be replaced GAC life depends on many variables o TOC concentration o Optimized coagulation efficiency o Flow rate o Carbon type o Pilot testing needed 18

19 GAC Options at Hannibal Retrofit GAC into the existing filters Add second stage GAC filters 19

20 Retrofit Existing Filters GAC replaces existing anthracite 20 Remove existing gravel and underdrain and replace with low profile underdrain to maximize EBCT

21 Retrofit Discussion With a filter rebuild, the EBCT achievable is approximately 15 minutes at 3.5 MGD (WTP average flow) does not meet USEPA EBCT recommendation Single GAC bed requires close monitoring to avoid breakthrough of TOC inefficient GAC usage The particulate loading on the GAC would be high. This results in a risk of fouling of the GAC, diminishing its capacity Filters are backwashed frequently. Backwash physically abrades the GAC, reducing the volume of GAC, further reducing GAC capacity This configuration is discouraged by Missouri regulators Due to these limitations, retrofit of existing filters is not recommended 21

22 Second Stage GAC Filters Units are manufactured off site and come complete with pipes, valves, and carbon 22

23 Second Stage GAC Filters Configuration Second Stage GAC Filters After sand filters Before UV 23

24 Second Stage GAC Filters Configuration Filters are arranged in parallel / series configuration Several parallel trains provide for flow capacity Two units in series in each train provide for 20 minute EBCT 24

25 Second Stage GAC Filters Layout 25

26 Second Stage GAC Contactors Discussion Second stage GAC filters are designed to provide 20 minutes EBCT at the design flow Series configuration minimizes risk of TOC breakthrough, maximizes GAC utilization GAC following filters see very little solids load, fouling is minimized Minimal backwashing required, protects carbon from abrasion, extends carbon life 26

27 Capital Cost Summary Alternative Total Project Cost GAC Filters as Second Stage Filters (2.7 MGD) $9,367,000 GAC Filters as Second Stage Filters (3.5 MGD) $10,578,000 Total Project Costs Include: Equipment Installation General Conditions Overhead/Profit Engineering Costs Contingency 25% 27

28 Operating Cost Summary Second Stage GAC Filters Carbon Life (Months) Annual Carbon Weight (Lbs.) Carbon Cost ($/Lb.) Annual Carbon Cost ($) Actual carbon life must be determined by pilot testing Carbon Cost Per 1,000 Gallon ($) 3 640, ,024, , , , , , , , , , , Carbon Life (Months) Annual Carbon Weight (Lbs.) 2.7 MGD Design 3.5 MGD Design Carbon Cost ($/Lb.) Annual Carbon Cost ($) Carbon Cost Per 1,000 Gallon ($) 3 800, ,280, , , , , , , , , , ,

29 Possible Impact On Customer Rates Alternative Debt Service per 1000 gallons Operating Cost per 1000 gallons Total cost per 1000 gallons Monthly Cost Increase for 5,000 gallon per month customer GAC Filters as Second Stage Filters (2.7 MGD) GAC Filters as Second Stage Filters (3.5 MGD) $0.84 $0.48 $1.32 $6.58 $0.95 $0.60 $1.54 $7.72 BASIS 4% interest rate on capital 25 year loan on capital outlay 9 month GAC life Costs spread evenly over all water users Water use estimate includes loss of Ralls County as a customer 29

30 Issues That Could Affect Costs Actual carbon life Need for treatment of DBPs in the distribution system Interest rates and available loan term 30

31 Issues That Could Effect User Rates Impact to user rates assumes a per gallon cost for all water sold, including residential and industrial o Hannibal currently changes both a flat meter fee and a per gallon use rate. Costs might be spread between those two o It is uncertain how the rate increase might be spread between residential and industrial customers Rising water costs may make water main replacement a higher priority, increasing system capital outlays 31

32 Necessary Tasks for Eliminating Chloramines Treatability Studies DBP Formation Potential Evaluation 32

33 Treatability Studies Optimized coagulation o Potential for increased TOC removal o Determine best chemicals and doses o Determine optimal ph GAC pilot testing o Determine proper carbon to use o Establish appropriate EBCT o Determine carbon life 33

34 DBP Formation Potential Evaluation Distribution system hydraulic modelling to guide improvements to reduce water age Based on the GAC pilot testing, determine whether treatment for DBPs will be required in the distribution system 34

35 Potential Schedule For Making The Change Back To Chlorine Task Start Date End Date 1. Laboratory testing of selected alternative and initial planning coordination with MDNR April 2017 January Pilot testing January 2018 August Preliminary Engineering Report for SRF application and MDNR plan approval September 2018 November Final Design, MDNR review and permit approval December 2018 September Bid Phase October 2019 December Construction January 2020 January

36 Questions? Thank you Copyright Jacobs March 23, worldwide