Conference Agenda

The toxicity of copper depends on complex water chemistry interactions. Water bodies with low ionic strength, organic carbon, and pH can have relatively low copper water quality criteria, resulting in associated low effluent limits for water resource recovery facilities (WRRFs) discharging to them. The Forest Grove WRRF faces low effluent copper targets owing to the water quality characteristics of its receiving stream. Clean Water Services (CWS), which operates the WRRF, conducted a study examining opportunities through source control, design, and operations to ensure that discharges have no reasonable potential to contribute to a water quality standards exceedance.

Further reducing WRRF effluent copper at low levels is challenging and some mechanisms are not well understood. Approaches explored at various facilities have included decreasing loadings from the collection system, solids retention time adjustment, chemically enhanced primary treatment, pH control, and use of targeted chemical precipitants in secondary clarification.

In this study, researchers analyzed historic operational data and conducted full-scale sampling, bench testing, and pilot testing to develop a multi-pronged copper strategy incorporating source control, enhanced treatment, and adjustment to effluent quality. Copper loading data was evaluated to determine the potential impact of enhanced source control on influent and effluent copper. A ten-year dataset was reviewed to analyze and compare removal efficiencies in different treatment processes at the four WRRFs operated by CWS. Additional sampling was carried out to study primary and secondary treatment copper removal during high flow events and to characterize concentrations in mixed liquor suspended solids. A full-scale pilot test of effluent pH control was conducted to determine the impact on copper toxicity thresholds calculated via the Biotic Ligand Model. In addition to full-scale monitoring, jar tests were conducted to evaluate the potential for chemical addition to enhance removal of dissolved and particulate copper in primary and secondary clarification. Trials were also run using settling columns to compare copper removal between bench and full scale and to estimate the copper removal performance of future clarifiers at a range of surface overflow rates.

This presentation will discuss full-scale and bench-scale findings and the resulting approach being pursued for effluent copper management.

Trickling filters have been used in wastewater treatment for more than 120 years and has evolved into a modern solution to meet today’s wastewater treatment needs. Major changes including introduction of lightweight, high-surface-area plastic media and speed control distribution have significantly improved the treatment efficiency of trickling filters. Yet with all these changes, there has been little increased understanding of the added capability provided by TFs. Information from design engineers and end users on trickling filter improvements has been largely unrecognized or poorly reported. Myths of trickling filters may have influence design engineers. This presentation provides an comprehensive overview of the major changes of trickling filter design and clarifies the common misconceptions and myths about trickling filter technology.

This presentation also discusses energy efficiency and carbon footprint based on an extensive literature review. Energy consumptions data from several wastewater treatment plants in the states of Hawaii, Washington, Virginia and Georgia with different biological treatment technologies will also be summarized and analyzed.

An innovative trickling filter system will also be introduced in the presentation. Bethel Park wastewater treatment plant in Pittsburg area, Pennsylvania has two trickling filters in series, which were retrofitted from the original rock filters. Significantly improvement of nitrification has been observed since the retrofit in 2010. Annual average ammonia-N concentration in the effluent has been consistently less than 1 mg/L. A high level of nitrification can be achieved at an ambient temperature of 0 ◦F. The improved nitrification performance can be attributed to the improved oxygen transfer and heat retention features of the system. Dissolved oxygen (DO) in the trickling filter system effluent has consistently been close to saturation or oversaturation. The DO-rich environment promotes nitrifier growth and results in a higher level of nitrification.

Modern trickling filters are environmentally friendly and reliable biological treatment systems that should be given full consideration in 21^st century wastewater treatment plant design. With proper engineering, operation, and maintenance, trickling filters can provide many years of simple, effective, and low-cost treatment.

This presentation will examine the use of disc filters, continuous backwash granular media filters, and compressible media filters at three different facilities. Each case study will provide an overview of the technology and discuss why the technology was selected, project objectives, how the system was designed, how the system is/will be operated, measured/expected performance, and unique challenges for the application. The first case study is addition of cloth disc filters at the 5.6 MGD Redondo WWTP owned and operated by Lakehaven Water and Sewer District, which completed construction in 2022. The Redondo WWTP utilizes primary clarifiers, trickling filters, and secondary clarifiers followed by UV disinfection for treatment. The second case study is improvements to enhance performance of existing continuous backwash granular media filters at the 12.7 MGD City of Marysville WWTP, which is currently in construction. The Marysville WWTP utilizes lagoons for biological treatment and UV light for disinfection. The final case study will be replacement of existing continuous backwash granular media filters with compressible media filters at the 2.8 MGD City of Snohomish WWTP, which is currently in design. The Snohomish WWTP utilizes lagoons with submerged fixed-film media for biological treatment and peracetic acid for disinfection.