MARSHALLTOWN: A BODY OF WORK

For 36 years, FOX Engineering has provided planning, design, and construction administration services for the wastewater treatment facilities in Marshalltown. FOX is grateful to the city for the confidence they have placed in us over the years.

When you enter the WPC grounds, it is immediately apparent that City staff takes great pride in their plant and its surroundings. That is seen in the special architectural elements preserved over the years, well-manicured lawns, and the pristine condition of equipment and processes. If you were wearing a blindfold and told you were at a wastewater plant, you wouldn’t believe it. Attention to maintenance and design are critical to achievable aesthetics and odor control. Marshalltown staff and the engineers at FOX take this seriously and it shows!

Air lines for aeration basins

Air lines for aeration basins

The first FOX project with Marshalltown was designed in 1980 by Dave Fox, one of our founding partners. The work focused on dissolved air flotation improvements and new buildings for vehicle storage. In 1982 and 1983, improvements included a new primary clarifier (#5), new headworks screening, flow measurement, pumping, and grit removal to replace the original 1940 treatment units, complete replacement of the aeration systems (jet), the addition of three final clarifiers, two raw waste pumps, and a belt filter press with associated polymer feed system and pump.

SBR Lime Silo, aeration in foreground

Lime Silo, aeration in foreground

Since that time, the bulk of the work to upgrade the plant has taken place in three phases.

Phase I (1986) included a preliminary treatment building, a 2 million gallon (MG) sludge lagoon, a 14 MG flow equalization basin, a second DAF thickener, and various electrical upgrades.

Phases II and III included significant improvements. Two sequencing batch reactor (SBR) tanks for treating high strength industrial waste from a local food processing plant to then new stringent ammonia standards were designed and constructed; the project included an SBR pump and blower building. Phase III included a 2 MG sludge storage tank, aluminum dome covers for the final clarifiers, ultraviolet disinfection, a new plant-compressed-air system and upgraded electrical generators to produce up to 1000 KW of power from the methane gas generated from anaerobic digestion.

Phase IV (1996) saw a new lime silo and feed system for the SBRs, SBR sampling and transfer pumping, and the installation of the Iowa River effluent diffuser pipe.

In 2002, the city took on ambitious biosolids improvements which included three new digester lids and conversion of Digester #1 to a Thermophilic/Mesophilic digestion system. Improvements to the remaining digesters included new tank mixers, heat exchangers, and sludge system piping. Four of six raw wastewater pumps were upgraded in the preliminary treatment building. Also significant for their impact on cost-saving were the new high efficiency natural gas boilers and a multi-fuel boiler and piping.

Mechanical screens

Mechanical screens

Teacup grit removal

Teacup grit removal

2010 saw major peak holding and pumping improvements: a new 2.7 MG sludge storage tank (#6) with three floating mixers and associated pumping and piping. A new 30 MGD pump station using Archimedes Screw Pumps was constructed along with piping, electrical systems, and flow meters. A dike was removed between the EQ basin and previous sludge storage basin to create a larger basin, and a new 18.75 MG EQ basin was constructed. The flow EQ project included an 800 KW diesel generator.

Gas bubble on right, aeration tanks in foreground

Gas bubble on right, aeration tanks in foreground

Performance Edge, a project developed in cooperation with Alliant Energy, began in 2011. The mission was to identify improvements that could be made to the facility that would reduce the plant’s energy consumption with a payback of five to seven years. The project, completed in 2014, included replacing the jet aeration system with a more efficient fine bubble aeration system and a new high efficiency turbo blower. Interior lights were replaced with multi-lamp T8 fluorescent fixtures, and occupancy sensors were installed in most spaces to control the lighting. Based on data compiled since the system was put into service, it appears that the plant has reduced its electrical power requirements by approximately 25 to 30 percent.

Installation of a new ultra violet disinfection system and reconstruction of the UV channels took place in 2013.

Sludge Storage

Sludge Storage

Replacing digester cover

Replacing digester cover

Currently, in addition to significant infrastructure collection system work, FOX is assisting the city with replacement of a biogas generator; preliminary design and procurement are complete. Design of installation is proceeding, and completion is scheduled for winter 2017.

Marshalltown WPCP continues to use FOX Engineering because of our commitment to working with staff to provide innovative, cost-effective, operator-friendly solutions.

Archimedes Screw Pump Station - during construction

Archimedes Screw Pump Station – during construction

SBR lower left Flow EQ and lagoon upper right

SBR lower left Flow EQ and lagoon upper right

FOX Engineering is an environmental engineering firm based in Ames, Iowa. We specialize in water and wastewater solutions for our diverse municipal and industrial clients. Our work varies in size and scope and can be found throughout the Midwest and beyond.