Adams Field Parallel Treatment & Nutrient Removal

Project Description

The Little Rock Water Reclamation Authority (LRWRA) is the first utility in EPA Region 6 to leverage a landmark Eighth Circuit Court Ruling to the benefit of their rate payers. In 2012, the United States Eighth Circuit Court of Appeals ruled against the Environmental Protection Agency on a suit brought by the Iowa League of Cities that contended that the regulatory agency had overstepped its authority through its dictation of allowable treatment methods. In short, the Ruling overturned a long-held EPA policy against blending as a viable treatment method for mitigating peak wet weather flows at municipal wastewater treatment plants. At the same time that this Ruling was being handed down in St Louis, Hawkins-Weir was working on the design of a new 51-million gallon wet weather equalization storage facility for LRWRA. HW recognized the potential value that this Ruling held for LRWRA and spearheaded a permit modification effort for the Utility. Following a pilot study, LRWRA was successful in negotiating the first permit in Arkansas and in the Sixth District of the EPA that recognized blending as an acceptable treatment method. This permit modification allowed an increase in the peak discharge of the Adams Field WWTP from 72 MGD to 94 MGD. It also reduced the required equalization storage volume by 34 million gallons. These changes resulted in a savings of over $10 million for LRWRA. After securing the necessary permit, HW teamed with Black & Veatch, Inc. for the design phase of LRWRA’s Parallel Treatment and Nutrient Removal Project. The parallel treatment portion of the project included a dual use cloth disc filter to provide primary screening during wet weather peak flow events and tertiary filtration during average flow. The project also expanded the UV disinfection capability at the plant from 72 to 94 MGD. This project was one of the first installations of the Aqua Aerobics’ AquaStorm filtration process worldwide. The project also included a 94 MGD effluent pump station and a new non-potable plant water system. The nutrient removal portion of the project converted the facility into a step-feed biological nutrient removal (BNR) process designed to comply with ammonia limits while conserving limited influent alkalinity and minimizing oxygen demand. The improvements included aeration basin modifications with large bubble mixing systems to create anoxic zones and new fine bubble aeration for the aerobic zones, new multi-stage blowers, secondary clarifier rehabilitation that included weir covers and the revolutionary McKinney Floor Baffle system, and a new return activated sludge pump station. This project also included a new dual primary electrical feed with an automatic transfer switch to provide emergency backup for all of the treatment plant’s systems at a fraction of the cost of stand-by generators.