Alternatives for Stormwater Treatment and Reuse for the Nevada Department of Transportation
Loading...
Authors
Martin, Austin James
Issue Date
2024
Type
Thesis
Language
Keywords
Aluminum Sulfate , Coagulation , Stormwater , Transportation
Alternative Title
Abstract
The Nevada Department of Transportation (NDOT) sponsored research at the University of Nevada, Reno (UNR) to evaluate the treatment and reuse of vacuum truck wastewater (VTWW) to reduce overall water consumption, decrease maintenance costs, and improve the productivity of work crews. NDOT vacuum truck operators are required to travel long distances to maintain stormwater infrastructure, such as drains and culverts in rural areas of the state. In addition, the locations where VTWW can be discharged may be limited. The three primary objectives of the research included: 1. Improve stormwater management and infrastructure maintenance practices 2. Reduce overall maintenance costs by reusing treated VTWW and improve productivity of work crews. 3. Address impacts of water scarcity in the southwestern U.S. The most effective way to address the objective of reducing overall maintenance costs is to reduce labor costs and fuel costs. This prompted the testing of a pilot-scale water treatment system that could be relocated to different regions of the state when crews are performing maintenance activities in remote locations. Samples of VTWW were collected from multiple locations within District 2 of NDOT and concentrations of various constituents including total suspended solids (TSS), total petroleum hydrocarbons (TPHs), heavy metals, and dissolved organic carbon (DOC) were monitored. Previous research by O'Hair (2021) focused heavily on the characterization of solids in samples of VTWW. A literature review was then performed to identify current practices in stormwater management by different municipalities and departments of transportation (DOTs) in various states to evaluate the most applicable treatment processes based on the quality of the VTWW. A pilot-scale water treatment system that incorporated the conventional treatment processes of coagulation, flocculation, and sedimentation was constructed and tested in the Water Resources Engineering Laboratory at UNR. During the most recent phase of the research, five trials were performed using the pilot-scale treatment system to treat different samples of VTWW. Trial 5 performed the best, maintaining the effluent turbidity of the settled water below the target goal of 20 nephelometric turbidity units (NTU) throughout the entire time of the trial. Settled effluent collected from the Lamella plate clarifier consistently showed that the removal of TSS ranged from 94 to 99 percent during each of the trials. The removal of DOC ranged from 36 to 67 percent while the removal of TPHs ranged from 46 to 83 percent. Finally, the removal of copper and zinc ranged from 78 to 90 percent and 92 to 94 percent, respectively. The use of a granular activated carbon (GAC) filter maximized the removal of DOC at 95 percent and increased the removal of TPHs to 87 percent. The estimated cost of a similar trailer-mounted mobile water treatment system from WesTech, Inc., is approximately $228,000. Field testing using either the pilot-scale treatment system developed at UNR or an engineered package water treatment system such as the WaterBoy-14 available from WesTech, Inc., is recommended to validate the performance of a mobile treatment system during maintenance operations in remote locations. Although the pilot-scale water treatment system proved effective at treating VTWW sufficiently to allow treated VTWW to be reused in vacuum jet trucks (VJTs) for additional cleaning cycles, it may not reduce overall maintenance costs due to the increased costs associated with the additional equipment as well as the need for an additional vehicle to transport a mobile treatment system and the increased costs for labor, materials, and supplies needed to operate the mobile treatment system. Because of these critical factors, the use of recycling vacuum trucks (i.e., recyclers), that incorporate both physical separation and filtration systems to remove suspended solids was also assessed. An economic analysis was performed to demonstrate that although a recycler truck resulted in increased capital costs compared to a traditional vacuum truck, an estimated savings ranging from approximately $114,000 to $220,000 over the 10-year lifespan of a vacuum truck was predicted if the productivity of work crews increased by 46 percent as a result of reduced labor costs and fuel costs. Field testing and sampling during the operation of recycler trucks by NDOT maintenance crews is recommended to validate the performance of the systems related to treatment and reuse of treated VTWW for additional cleaning cycles. Demonstrations and training offered by recycler truck manufacturers should be used to assess the performance and operator satisfaction before considering their purchase.