Ordering Information:
ORDER NUMBER:  91215
DATE AVAILABLE: Fall 2008

PRINCIPAL INVESTIGATORS:
John E. Tobiason, William R. Knocke, Joseph Goodwill, Anjuman A. Islam, Paul Hargette, Ryan Bouchard, and Lauren Zuravnsky

OBJECTIVES:
The overall goal of this project was to increase knowledge of the control of manganese (Mn) by adsorption to oxide surfaces. Project objectives included (1) characterizing the nature and Mn uptake capacity of various types of granular media from full-scale plants, (2) evaluating media regeneration requirements, (3) studying impacts of operational variables on Mn removal, (4) conducting case studies of Mn control, and (5) providing guidance to utilities regarding use of oxide-coated media for Mn control.

BACKGROUND:
Removal of elevated levels of Mn in drinking water supplies to address aesthetic concerns (staining of laundry and fixtures, discoloration of water) is an ongoing challenge for water suppliers. Earlier AwwaRF studies documented several aspects of the process of removing Mn via sorption to Mn-oxide surfaces on standard granular filter media and subsequent oxidation. This project expanded knowledge of factors affecting this process and examined alternate operation strategies via laboratory and full-scale experiments.

HIGHLIGHTS:
Results further demonstrated the effectiveness and use of pre-filter chlorination and oxide-coated media for Mn control while providing important documentation and guidance on alternate strategies involving seasonal chlorination and intermittent regeneration. Utilities must be diligent in monitoring the possibility of Mn release from Mn coated media if continuous chlorination is not practiced. Results demonstrated that pre-filter chlorination increased DBP production so utilities may have reasons to investigate alternate approaches. Finally, this project provided proof-of-concept for the use of post-filter contactors for the control of low levels of Mn, which should be considered by utilities that use some degree of free chlorination in the treatment process.

APPROACH:
The research approach consisted of seven tasks: (1) laboratory characterization of media samples from full-scale plants for levels of metal oxide coating, Mn uptake capacity, size, and surface area and microscopic analysis for some samples; (2) laboratory assessment of intermittent and continuous media regeneration; (3) laboratory scale column investigation of operational and water quality variable impacts on Mn uptake; (4) full-scale case studies involving collection of the media samples for Tasks 1 to 3 and documentation of full-scale practice and the results of certain field-scale trials of changed treatment practice; (5) field and laboratory investigation of the impact of pre-filter chlorination on subsequent disinfection by-product (DBP) formation; (6) laboratory and pilot-scale investigation of post-filter contactors; and (7) preparation of guidance for engineers and utilities.

RESULTS/FINDINGS:

Utility Case Studies
The effectiveness of previously established operating practices using continuous pre-filter chlorination was confirmed. Use of only seasonal pre-filter chlorination was generally successful but attentiveness to the potential for Mn release from coated media is needed. Mn coatings remained intact for periods of 6 to 12 months with no chlorine and resumed Mn uptake upon regeneration with free chlorine.

Media Characterization
Mn levels ranged from <0.01 to >100 mg Mn/g media on anthracite, sand, or GAC media, depending on which media was first exposed to dissolved Mn(II) and free chlorine. Mn uptake capacity of media as assessed by a developed laboratory procedure was useful for understanding, comparing, and predicting media performance. Media surface coatings contained aluminum and iron along with Mn at consistent ratios.

Media Regeneration
Continuous regeneration with pre-filter chlorination was the most effective and robust method of operation. Intermittent regeneration by backwashing had limited effectiveness but may be very useful.

Impact on DBPs
Pre-filter chlorination can cause a 10–50 percent increase in simulated distribution system trihalomethane and haloacetic acid levels as compared to post-filter chlorination.

Post-Filter Contactors
An important component of this project was the proof-of-concept assessment of the use of post-filter contactors for robust control of low levels of reduced Mn prior to finished water distribution. Laboratory and pilot experiments were conducted using 3 inch diameter columns with 20 inch depths of three different coarse media: 3–6 mm gravel with Mn oxide coating, 2–2.5 mm torpedo sand with Mn oxide-coating, and 2–2.4 mm proprietary pyrolucite. Results for the sand and pyrolucite were better than for the gravel media and demonstrated the feasibility of using this approach at full-scale.

IMPACT:
The results of this project may impact the approach taken by utilities to control Mn in surface water supplies, particularly those utilities that currently use, or plan to use, oxide-coated media and chlorine for Mn uptake and removal. The results provide guidance on alternate strategies and the need for careful monitoring of process performance. Finally, the results demonstrate a potentially new approach for use of oxide-coated media via post-filter contactors designed for Mn uptake only.

MULTIMEDIA:
This report includes a CD-ROM with Appendix C Microscopy Results, containing many electronmicrograph images of filter media.

RESEARCH PARTNER:
USEPA

PARTICIPANTS:
Eight utilities participated in this project, seven from North America and one from the United Kingdom.

ISBN 978-1-60573-014-1