Client Name | PROJECT NAME
Little Patuxent Water Reclamation Plant
Howard County, Maryland
Black & Veatch completed two important project assignments for the Howard
County Bureau of Utilities. These assignments include an engineering study to
improve the performance and reliability of the Little Patuxent Water
Reclamation Plant’s existing BNR treatment process and design and
construction management services for a major plant capacity expansion and
treatment process modifications.
Project Elements
 Optimization of biological
nitrogen and phosphorus
removal
 Demonstration testing of
advanced BNR process
technology
 Upgrading solids
processing to Class A
biosolids stabilization
 Overall treatment plant
optimization
 Capacity Expansion
Services
Winter Capacity Restoration
Study
The 18 mgd Little Patuxent Water
Reclamation Plant was designed for
year round nitrification and
biological nutrient removal.
Treatment goals were 8 mg/L total
nitrogen on an annual average basis
and 1 mg/L total phosphorus on a
monthly basis. Because of poor
activated sludge settling
characteristics, the plant could not achieve high enough mixed liquor solids
concentrations or long enough solids retention times to maintain complete
nitrification at rated treatment capacity during cold winter months. In addition,
unexplained effluent phosphorus concentration spikes occurred intermittently
throughout the year.
Engineering Studies, Design
and Construction
Management Services
Key Team Members
Mike Hanna
Bob Rectanus
Period of Service
November 1997 to January
2005
Cost
See end of document
Client Reference
Mr. Don Campbell, P.E.
8900 Greenwood Place
Savage, MD 20763
(410) 313-1438
dfcampbell@howardcounty
md.gov
The objectives of this study were to evaluate process modifications and control
strategies to restore winter treatment capacity and improve the reliability of
biological phosphorus removal. The study was divided into two phases. Phase 1
reviewed existing process performance and process control to identify
performance problems and develop alternative solutions. Phase 2 involved
demonstration scale testing of process modifications and process control
techniques to evaluate effectiveness. Based on the results of the study, an
interim solution involving periodic chlorination of return activated sludge was
initiated to control filamentous organism dominance. Process reactor
configuration changes and flow distribution improvements were recommended
as part of the long term improvements to maximize the capacity and nutrient
removal capabilities of the existing biological reactor basins.
Little Patuxent Water Reclamation Plant Sixth Addition
Black & Veatch designed the Sixth Addition Improvements for the Little
Patuxent Water Reclamation Plant. The project included a comprehensive
evaluation of treatment process alternatives for expanding treatment capacity
from 18 mgd to 25 mgd, improving nitrogen removal performance of existing
biological treatment facilities, and complete renovation of solids processing
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Client Name | PROJECT NAME
facilities. A Project Development Report, prepared as part of the preliminary
facilities design evaluation, included plant scale demonstration testing of
proposed BNR process reactor modifications and primary sludge fermentation.
The fermenters were proposed for supplementing volatile fatty acid production
for improving biological phosphorus removal and providing readily degradable
carbonaceous BOD needed for higher levels of denitrification. The
demonstration testing confirmed the ability of the process modifications to
achieve consistent biological phosphorus removal to less than 0.5 mg/L and
total nitrogen concentrations below 6 mg/L. The project included demolition of
an existing electrical substation, existing sludge drying beds, and part of an
existing aerobic digester basin.
The Project Development Study - Recommended dividing
the Sixth Addition construction work into six separate
construction contracts to minimize the impact of construction
on existing plant operation and treatment performance during
construction. In addition to the preliminary engineering and
project planning services provided for preparation of the
Project Development Report, Black & Veatch provided detailed
design for each of the six construction contracts and overall
construction management services for major equipment
procurement, construction contract administration, submittal
review, construction inspection, and process start-up
assistance. The scope and features of each of the six construction contracts
included:
 Contract 1: BNR Capacity Expansion - Added three new biological treatment
process reactors configured for enhanced biological nitrogen and phosphorus
removal, three new final clarifiers, a new blower building, a new activated
sludge pumping station, two new anaerobic fermenter basins for primary
sludge, and odor control system for the anaerobic fermenters. The new
biological nutrient removal process was designed to utilize readily degradable
soluble BOD and volatile fatty acids produced in the anaerobic fermenters for
optimizing nitrogen and phosphorus removal.
 Contract 2: Solids Processing Facilities - Improvements to the plant solids
processing facilities included renovation of two existing primary sludge
gravity thickeners, renovation of two existing DAF thickeners for waste
activated sludge, addition of a third DAF thickener, replacement of existing
belt filter presses with two new high solids centrifuges for sludge dewatering,
replacement of an existing lime stabilization system with a new lime
pasteurization system to produce Class A stabilized biosolids, new lime feed
and storage facilities, and new polymer feed and storage facilities.
 Contract 3: Preliminary and Primary Treatment Improvements - The
existing plant headworks facilities and raw wastewater pumping station were
renovated to improve raw wastewater screening and pumping efficiency.
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Client Name | PROJECT NAME
Three existing “climber” type bar screens were rebuilt to reduce the clear
opening between bars from ¾-inch to 5/8-inch to capture more of the plastics
and stringy material that were contaminating plant sludge and causing
problems with sludge pump maintenance. The improvements included the
addition of a new Auxiliary Raw Wastewater Pumping Station to increase raw
wastewater pumping capacity, a new scum concentrator for handling primary
clarifier scum, a new primary clarifier for additional primary treatment
capacity, and new primary sludge and scum pumps.
 Contract 4: Existing BNR Treatment Process
Improvements - Eight existing biological process
reactors were reconfigured to improve the performance
of nitrogen and phosphorus removal. The Improvements
included new internal recycle pumps, fermenter VFA
liquor addition, new automatic flow distribution gates and
changes to internal partition walls. Modifications were
also made to four existing final clarifiers and the addition
of new plant effluent flow metering.
 Contract 5: Laboratory Renovations - The existing plant analytical and
process control laboratory was completely redone to support process control
and water quality monitoring requirements for the treatment plant. New
laboratory equipment included nutrient auto-analyzers, new fume hoods and
new solids analysis equipment.
 Contract 6: Plant Control System Upgrades - The existing Foxboro
Distributed Plant Control System was upgraded with new process monitoring
and control stations located throughout the plant and expanded I/O capability
to support the expanded treatment plant capacity. Additional data
management functions were added to the plant control system and a new
Laboratory Information Management System (LIMS) was added.
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Client Name | PROJECT NAME
Services:
Contract Amount:
Final:
Engineering Design
$3,590,813
$3,729,000
Notes:
Preliminary Engineering Study and detailed design for 6
Construction and 2 procurement contracts - Reason for
higher final cost: project broken up into 6 separate
construction bid packages and 2 equipment procurement
packages
Services:
Contract Amount:
Final:
Construction Management
$4,590,760
$5,951,000
Notes:
Construction phase services including 4 full-time field
staff - Reason for higher final cost: Owner initiated major
re-design changes after receipt of bid; Construction
contract time extension
Services:
Contract Amount:
Construction Cost
$48,000,000 (Original Engineering Estimate of
Construction Cost)
$46,351,000 (Final Construction Cost)
Total of 6 construction & two procurement contracts
Bid Award
$43,905,000
Final:
Notes:
Services:
Final
Brief Summary of the Results of the Project:
The 6th Addition included 7 mgd in capacity expansion and modifications to
biological nitrogen and phosphorus removal processes for the entire plant.
Phosphorus removal was improved from unstable performance with effluent
phosphorus varying from 1 - 3 mg/L to stable performance with effluent
phosphorus consistently <0.5 mg/L with no chemical addition. Nitrogen
removal was improved from effluent Total Nitrogen of 8 mg/L to less than 5.5
mg/L.
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