Conference Agenda

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Session Overview
Session 13B: Wastewater Process: Solids Treatment
Tuesday, 10/Sep/2019:
10:30am - 12:00pm

Session Chair: Mark Cullington, Kennedy/Jenks Consultants;
Location: E143-144

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10:30am - 11:15am

Presentation is Canceled

Glenn Thesing, Hong Zhao

Veolia Water Technologies/Kruger, United States of America;

A full-scale sludge liquor treatment using MBBR technology has proven to be an efficient way to treat nitrogen in existing volumes. In 2011, the former sludge liquor treatment (SBR) was retrofitted to an ANITA Mox process, using autotrophic N-removal through anaerobic ammonium oxidation (anammox). In Nov. 2014, a thermal hydrolysis process (THP) upstream of the existing digesters was installed, creating a higher strength sludge liquor. Warm dilution water was added prior to sludge liquor treatment to minimize inhibitory effects of COD compounds generated in the thermal hydrolysis process.

In order to improve the stability of the system, an Integrated Fixed-Film Activated Sludge (IFAS) ANITA Mox configuration, requiring recycling of settled activated sludge, was implemented in May 2018. Prior to installation of the THP system, the ANITA Mox system at Sundets WWTP was receiving an average ammonia nitrogen load of 142 kg/d. After the installation of the THP process, the average ammonia nitrogen load increased to 156 kg/d, and after implementing the IFAS the average load has been 195 kg/d. Average ammonia concentration in the digesters has doubled - from about 800 mg/l prior to THP to about 1600 mg/l after four years of operation and an increased degree of digestion (from 45 to 58%). Energy consumption has decreased from 2 to <1 kWh/kg N-removed and early measurement indicate low emissions of N2O (0,75% of N-removed).

This paper will present data from each of the three stages that the ANITA Mox system at Sundets WWTP has operated under and provide lessons learned from operation of an IFAS ANITA Mox following a high strength THP sludge liquor. Results indicate that the IFAS configuration will be a more stable treatment option and the plant is able to treat all the current sludge liquor water with less dilution water and retained efficiency.

11:15am - 12:00pm

Heating Primary Sludge for Increased Volatile Fatty Acid Production at Short SRT

Adrienne Menniti1, Rachel Golda1, Jana Otero2, Peter Schauer1

1Clean Water Services; 2Kennedy/Jenks Consultants;

The Durham Treatment Facility has been practicing biological phosphorus removal (BPR) for over two decades. The facility relies on primary sludge fermentation to augment influent Volatile Fatty Acids (VFA) and support BPR. The fermentation system currently needs expansion because the solid residence time (SRT) available is too low to provide adequate VFA production when wastewater temperatures are low. A capital project addressing this issue is scheduled for completion in 2022. As an interim solution, primary sludge heating to increase cold weather VFA production will come online in March 2019.

The heat exchanger is designed to increase the temperature of sludge feeding the fermentation process by 5°C. Full-scale data show VFA production approximately doubles as the influent temperature increases from 15 to 20°C. Bench-scale testing shows that the degree of fermentation that has already occurred in the collection system strongly influences the increase in VFA production with a 5°C temperature change. Pre-fermentation appears to decrease the additional VFA production achieved with sludge heating. Efforts to validate the bench-scale observations with activated sludge models have highlighted limitations in the models’ ability to predict the additional VFA production expected with sludge heating. Therefore, efforts to understand model limitations are ongoing.

This presentation will review the 2019 full-scale operational data demonstrating the benefit of primary sludge heating. Bench-scale testing results from 2019 and modelling efforts will also be summarized, providing a comparison of laboratory, full scale, and modeling data. The results have a significant impact on the upcoming fermentation expansion design because the design SRT is a strong function of the fermentation temperature. Full-scale observations coupled with bench scale testing results and modelling efforts will provide a more robust determination of what SRT should be used for design, which ultimately determines the extent of infrastructure investment needed for fermentation.

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