PHOTO 1
The Carson Filter Plant is slated as the first plant to incorporate GAC filter design criteria into rehabilitation efforts.

PHOTO 2
Filter gallery at the BWWSB Putnam Station Treatment Plant.

PHOTO 3
Photo shows technician visually inspecting filter media condition during the pilot-scale studies. After a year long evaluation, results indicated that an innovative hybrid technology - GAC biofilters without ozone - was a viable approach under typical conventional filter operational conditions.

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Project Description Project Description
Introduction

With limited funds available for capital improvements and system growth, the Birmingham Water Works & Sewer Board (BWWSB) needed an affordable approach for complying with the upcoming federal Stage 2 Rule mandating removal of disinfection byproducts (DBP) in drinking water. Tasked with developing a new, least-cost strategy for compliance, Malcolm Pirnie provided planning level analysis of granular activated carbon (GAC) treatment options.

The precedent-setting GAC Master Planning project involved conducting simultaneous bench- and pilot-scale testing, capital and operational cost evaluations, and facility specific recommendations for incorporating GAC into the BWWSB's existing treatment processes.

As part of the effort, the Malcolm Pirnie team identified an innovative, cost-effective approach to DBP precursor removal -- modifying the utility's existing conventional GAC filters to create GAC biofilters, taking advantage of both adsorption and biological modes of operation without ozone as a cost effective approach to DBP precursor removal and compliance with Stage 2 regulations.

Integrated Approach

Water quality goals are achieved within the framework of the utility's overall priorities. The innovative GAC biofilter approach will comply with DBP precursor removal standards, producing high-quality, good-tasting drinking water at an affordable cost while protecting the public health and enabling the facility to proceed with other infrastructure needs.

Targeted GAC treatment approach minimizes carbon waste and air emissions. Traditional GAC treatment facilities require frequent replacement of GAC, resulting in exhausted carbon waste and high operational costs for either virgin replacement carbon or carbon reactivation, which also requires a large amount of energy and creates air emissions. Malcolm Pirnie's GAC biofilter approach extends media life three to five times, significantly reducing carbon handling, and waste generated.

Lower cost solution avoids water rate increases. The relatively low capital and operational costs for GAC biofilters will help the BWWSB avoid sharp water rate increases necessary to fund new plant construction and operation.

Quality

The project met the BWWSB's significant compliance challenges with respect to complexity, constructability, schedule, and cost by investigating an innovative alternative to conventional GAC treatment approaches – modifying existing GAC filters to create GAC biofilters.

Study identifies lower cost solution that will achieve multi-million-dollar savings. Before this project, the BWWSB had decided to construct expensive post-filter GAC contactors to achieve Stage 2 compliance. Instead, the study identified a much lower capital and operational cost solution that will dovetail easily with previously planned filtration upgrades. This approach will save approximately $35 million at just one of BWWSB's four treatment facilities. Relatively minor changes to planned filter upgrades can be incorporated easily into the five-year capital plan, meeting the Stage 2 compliance deadline.

BWWSB stakeholders were involved in developing the solution and gaining GAC knowledge. BWWSB staff and leadership learned along with the Malcolm Pirnie team and were engaged throughout development of the study approach, performance testing, and final recommendations. At workshops and meetings, BWWSB operations staff provided valuable insight regarding current plant operations and limitations to system modification. They accompanied Malcolm Pirnie staff on site visits to other utilities using GAC for roundtable discussions regarding performance and maintenance of GAC facilities. Through the project, BWWSB staff developed a solid understanding of GAC use and limitations.

Complexity

Solution met complex criteria. The BWWSB needed a Stage 2 compliance strategy that could be incorporated into its four existing water treatment facilities within the next five years and meet several key criteria. Ideally it would minimize changes to treatment/distribution operations, minimize operational complexity, avoid plant shutdowns and derating during summer months, and avoid significant capital and operational cost.

Limited space for new facilities created constraints. Most of the BWWSB's plants have very limited space for new treatment facilities. This study proved that through relatively minor modifications to existing plant infrastructure, GAC biofilters can be used to meet all the construction, treatment performance, operational, and cost challenges of the BWWSB.

Originality and Innovation

Malcolm Pirnie's year-long evaluation of an innovative approach -- GAC biofilters without ozone -- proved the viability of this hybrid technology under typical conventional filter operational conditions. GAC is widely used in water treatment, either as an adsorbent in a filter cap or post-filter contactor, or as a medium in a post-ozone biofilter. With filter caps -- shallow layers of GAC added to conventional filters to address short term taste and odor events -- adsorptive capacity is quickly exhausted, requiring frequent carbon replacement. Deep bed post-filter GAC contactors, providing long-term contaminant removal, still require annual replacement with virgin or reactivated carbon and are costly to construct, resulting in significant operational costs.

Biofilters, provide long-term organic contaminant removal, taking advantage of GAC's ability to support the growth of microbes in the absence of chlorine, consuming organic compounds in the water as it passes through the filter media.

New approach eliminates need for costly ozone pretreatment. Malcolm Pirnie's survey of water utilities found that the facilities currently using GAC biofilters generally had to pre-treat water with ozone ahead of the biofilters to make organic contaminants more biodegradable – involving major costs to retrofit existing
facilities with ozone.

Social and Economic Advancement.

This innovation opens the door for low-cost plant upgrades for regulatory compliance. Both capital and operating cost savings can be achieved with this new approach to GAC treatment. While traditional options require large capital and operational funds for plant upgrades or significant changes to system operation and chemistry, the hybrid GAC biofilter approach leverages existing treatment infrastructure -- filter modifications for GAC biofilters can cost less than 20 percent of post-filter contactors and approaches using ozone, providing a lower cost option for Stage 2 compliance.

Approach avoids violating other regulations or increasing public health risk. Existing low-cost compliance strategies rely on changes to water chemistry that can unintentionally lead to violations of other water quality regulations, often increasing the risk to public health. The use of GAC biofilters minimizes changes to current operating conditions without jeopardizing simultaneous compliance with other regulations, and also results in less risk of system upset or adverse effects on public health.


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