KWS Manufacturing

City of Austin, Texas Truck Load-Out System for Lime Sludge

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City of Austin, Texas Truck Load-Out System for Lime SludgeEnd User or Owner

Austin Water Utility
Austin, TX

Consulting Engineer

Carollo Engineering
Austin, TX


Laughlin-Thyssen, Inc.
Houston, TX 77043

Plant Name and Location

Austin #4 WTP
Austin, TX 78732

General Description

WTP4 is the newest water treatment plant in Austin, Texas. The plant is located on Lake Travis and capable of treating 50 million gallons a day (MGD) with room to expand to 300 MGD. This investment adds reliability by giving utility customers an additional plant that draws from Lake Travis instead of Lake Austin. In addition, the new plant saves energy by serving the north and northwest Desired Development Zone and provides for continuous service during shutdowns and repairs of Austin’s two other treatment plants and aging pump stations which are critical to getting water to customers. WTP4 featured an unprecedented environmental commissioning process that worked to protect the environment at every step of construction and into the future.

As part of WTP4, the City of Austin needed an integrated storage and truck loading system to handle water residuals that can no longer be returned to the lake untreated.

Centrifuges are used to dewater lake sludge and the residuals are gravity fed to a four (4) chamber storage hopper. Each chamber is equipped with a pneumatically actuated knife gate through which residuals are loaded to trucks. Hopper vibrators are used to fluidize the sludge and allow it to flow more easily. The hoppers are mounted on weigh cells which allow trucks to be loaded accurately and completely.

Design Parameters

  1. Type of Sludge: Dewatered Lime Sludge from Water Treatment
  2. Material Density: 120 lbs. per Cubic Foot
  3. Solids, Percent by Weight: 50 to 68% Total Solids
  4. Hopper Capacity: 1,080 Cubic Feet

The storage hopper continuously receives dewatered lime sludge from multiple centrifuges. The storage capacity is a minimum of 40 cubic yards.

KWS Advantages

KWS designed, manufactured, supplied and commissioned an integrated system which required expertise with; process conditions, design and fabrication of hoppers, structural support steel, slide gates, chutes, application engineering of instrumentation, weigh system, vibrating discharge system and participated with the design of PLC based controls with touch screen OITs.

Special Features

It was important to the City of Austin that the Truck Load-Out System did not include any maintainable components inside the hoppers. With a complete understanding of the characteristics of the lime sludge, KWS designed the hoppers with a geometry that limited bridging. A vibrating, hopper agitation system was included to fluidize the sludge when the dry solids content was at the high end of the range.

The system required water tight knife gates as the dry solids can be very low and egress from the hoppers into the truck bay is not acceptable. The hoppers were supported on weigh cells to provide real time weight in the hoppers. Feedback from the weigh cells was used to accurately load trucks to maximize each truck load and reduce hauling costs.

KWS is unique in the industry because our engineering and manufacturing capabilities allow us to provide a complete engineered solution to address Customer needs.


"The system does exactly what is needed. We are planning to use this system on future projects that require residuals handling."

Mike Borrero, P.E., Project Manager – Carollo Engineers

Biosolids / Sludge

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