City of Davis Biological Treatment Hex Chromium Pilot Study Results California-Nevada Section AW WA 2013 Annual Fall Conference Presenters: Joe Drago, P.E., Ph.D. Sarah Laybourne, P.E. Kennedy/Jenks Consultants October 2, 2013 Sacramento, CA

Key Contributors •

City of Davis • • • •

•

Jacques DeBra Dianna Jensen Marie Graham Gary Wells

•

Kennedy/Jenks • • • • •

Lynn Takaichi Tim Williams Joe Drago Sean Maguire Sarah Laybourne

Envirogen • Todd Webster • Sam Wong

• UC Davis • Jeannie Darby • Bonnie Robison

Project Funding @ $150k • SWRCB Cleanup and Abatement Program • Water Resources Association of Yolo County • Sacramento Groundwater Authority • City of Davis

Presentation Outline • Background • Biological treatment pilot description • Pilot study results • Footprint and site specific cost estimates

Background

Motivation for Study • Evaluate effectiveness of concurrently removing multiple contaminants: • Evaluate residual management impacts and management options • Evaluate co-removal potential of nitrate, selenium and perchlorate

• Evaluate the potential for disinfection to convert any remaining chromium 3 to chromium 6 • Prove efficacy of an alternative technology to others already studied: • Weak and strong base anion exchange • Reduction, coagulation, and filtration

• Compare results with the WRF Project 4450 – Impact of Water Quality on Cr6 Removal Efficiency & Costs

August 2013 CDPH Cr6 MCL Proposal • MCL range considered: 1-30 µg/L • MCL proposed:

10 μg/L

• Total Chromium MCL remains at 50 μg/L • Chromium speciation studies in distribution system for some public water systems that chlorinate

Best Available Technologies for Cr6 Removal • Reduction coagulation filtration (RCF) • Ion Exchange • Strong base anion exchange (SBA) - regenerated • Weak base anion exchange (WBA) - single use

• Reverse Osmosis • Effect of water quality on cost of RCF, SBA, and WBA technologies evaluated in Water Research Foundation Project #4450

Why Biological Treatment • Promising emerging technology for drinking water • Capable of addressing multiple contaminants • • • •

Chromium 6 Nitrate Selenate Perchlorate (BAT)

Biological Process Electron donor Acetic acid CO2 + H2O O2 NO3ClO4CrO42HSeO4-

Nutrient Phosphoric acid

Bacteria

N2 ClCr3+ HSeO3-

Excess bacteria (cell growth)

Biological Process • Biological process in drinking water in CA requires • • • •

Use of indigenous microbes Post Aeration – if anoxic Filtration Disinfection

• Biological Fluidized Bed Reactor (FBR) is Best Available Technology (BAT) for perchlorate in CA

Biological Treatment Pilot Description

Biological Filtration - Fluidized Bed Reactor • Fluidized Granular Activated Carbon (GAC) bed • Chemical Feed • State NSF 60 Approved Acetic Acid – Electron Donor • Phosphoric Acid – “Nutrient” Mix

• Nitrate is the main electron acceptor • 8-9 mg/L Nitrate as N • 40-45 µg/L chromium as chromium 6

• Anoxic environment to grow denitrifying and chromium reducing bacteria • Co-reduction of nitrate and chromium 6

• Testing at 4 different Hydraulic Residence Times (HRT): 60, 40, 20, & 15 Minutes • Other potentially treated constituents • Selenium • Perchlorate

Pilot Study: Conceptual Design Diagram

City of Davis Well 20 – Pilot water source

Pilot System @ Booster Pump Station

Pilot System

Biological FBR in Action

Well 20 Water Quality • Total Chromium: 44-50 µg/L* • Hexavalent Chromium: 40-50 µg/L* • Nitrate-N: 7.5-10 mg/L* • Selenium: