Conference Agenda

Increased dewatered cake solids will save approximately $1 million per year in biosolids hauling costs at the Columbia Boulevard Wastewater Treatment Plant (CBWTP). By 2045, CBWTP will thicken up to 724,000 pounds and dewater 260,000 pounds every day. The existing solids handling facility was built in 1970 on a foundation of wood piles, and the aging equipment was in need of replacement. The project presented an opportunity to upgrade primary sludge thickening in addition to WAS thickening to improve digestion performance.

Alternatives to rehabilitate the existing solids processing building were evaluated and due to desire for increased seismic resiliency and operation during construction, the decision was made to build a new solids treatment facility. There are site constraints at the CBWTP, ideally the new solids facility would be located near the existing facility, which is boxed in on multiple sides with existing infrastructure. This led to design of a unique multi-story triangular shaped solids handling facility, with a bridge across an existing channel and additional supports on the other side to allow trucks to pass underneath.

The co-thickening system design includes eight 3-meter-wide gravity belt thickeners, blend tanks, feed pumps, thickened sludge storage tanks and pumps, polymer facilities, and cameras for monitoring. The dewatering system design includes five 29-inch-diameter dewatering centrifuges, feed pumps, polymer facilities and conveyors to hoppers and the loadout facility. Operations and maintenance (O&M) staff were engaged at all stages of design to provide input on access and O&M needs. This led to multiple monorails, bridge cranes, and an elevator to allow for access to all of the equipment that is located on various floors of the new facility. The new biosolids storage and loadout facility provides redundancy and allows automated biosolids hauling 24-hours per day through monitoring/instruments including hoppers equipped with ultrasonic level sensors and weigh cells as well as full-length truck scales in each of the two loadout bays.

The presentation will walk through the decision process for this new state of the art solids handling facility, operations and maintenance considerations, and a live model fly-through of the unique multi-story solids facility.

Located between the cliff and a river, the City of Lewiston’s wastewater treatment plant had little room for expansion. The City’s dewatering system was undersized and required frequent maintenance. The City had a contract with a composting company to provide biosolids within an acceptable solids range. To compound the problems, the belt filter press was located on the second floor of a very small room in the center of the plant. The City was looking for an ideal solution that could fit into the existing space, reduce maintenance for the plant operators, and meet both the capacity and performance requirements.

As part of a performance-based evaluation process, the City selected HUBER Technologies, Inc.’s Q-PRESS 800.2 units. The new screw presses were among the first to include the high-capacity auger system, which consists of two design advances from previous models. The first design advancement being an elongated filtration zone in the inlet area which allows for a relative improvement in free water drainage. The second advancement is a more aggressive auger flight pitch which provides the unit with a higher solid conveyance capacity. These advances allowed the screw presses to dewater sludge 20% faster, reducing the required footprint and time of operation. This presentation will highlight the plant constraints, selection process, and also demonstrate the enhanced performance provided by the new screw presses.