Merchant-Wells, Nicholas

Nick Merchant-Wells works as Project Engineer at the Northeast Ohio Regional Sewer District where he provides technical support to Operations and Maintenance personnel. For the last two years, his work has been focused on optimization efforts at the Districts centralized biosolids handling facility. Nick is a proud graduate of the Civil and Environmental Engineering Department at Case Western Reserve University.

Titles from this speaker

Optimizing Fluid Bed Combustion

Abstract

The Northeast Ohio Regional Sewer District operates the Renewable Energy Facility (REF) at the Southerly Wastewater Treatment Center. Commissioned in 2014, the REF includes sludge dewatering, incineration, and energy recovery processes. The facility receives an average of 120 dry tons per day of biosolids from two of the District's three treatment plants. Combustion in a fluidized bed incinerator is a complex process with many factors that affect operation. The incineration process at REF faces two primary challenges to realizing efficient process operation: first, the biosolids loading is approximately 20% lower than the projections used for design conditions and second, the volatile solids proportion is relatively low as a result of the District's majority combined sewer collection system. In order to overcome these challenges and maximize autogenous operation, the following three strategies are in various stages of deployment: 1.Implementation of informational tools to fully optimize combustion process 2. Full use of a Grease Merchant Facility 3. Exploration of an Intermittent Operating Strategy In 2021, operations and engineering staff began an FBI optimization effort. As part of this work, a mass and energy balance was developed to represent operating conditions in the process. This tool is able to be implemented in real time by integrating with the Plant's process management software to quickly pull in new data as it becomes available. By using this tool, operations staff is able to build a more robust understanding of the process and predict the effect of various operational changes when deciding on a course of action to take. In 2016, the Grease Unloading Station (GUS) was completed. This is a merchant facility that allows the grease processing system to receive a higher volume of loads from grease trap haulers. This is a significant benefit to the incineration process which allows grease addition to the cake feed system. Despite representing about 5% of the biosolids feed by weight, the grease can account for 20-30% of the chemical energy in the feed. Currently District operations staff are planning a full pilot of an intermittent operating strategy for the three incinerator trains at the REF. Each train is rated to process 100 dry tons of biosolids per day and the average daily loading to the facility is 120 dtpd. This means that, when running at a steady state, our units are loaded at approximately 60% of capacity. In order to maintain a higher uptime of operation without supplemental fuel addition, intermittently operating one and two units at a time would fully load each incinerator that is operating. Past attempts at this strategy have not fully utilized the capacity of the incinerators and it's expected that an updated implementation of this operating strategy would yield much improved results from past attempts. Note to reviewers: There are two main components to this prospective presentation: (A) an introduction/overview of the mass and energy inputs/outputs to the fluid bed combustion process and (B) a demonstration of how we use this understanding to optimize operation at our facility with the three parts I discuss above. Part A is more a presentation on the fundamentals of the process and Part B is geared towards presenting data and a unique challenge at our facility. If selected, I can tailor the presentation towards one end or the other depending on feedback from the conference program committee and how it is intended to fit with other sessions.

This paper was presented at the WEF Residuals and Biosolids Conference in Columbus, Ohio, May 24-27, 2022.

SpeakerMerchant-Wells, Nicholas

Presentation time

9:00:00

9:30:00

Session time

8:30:00

10:00:00

Session number09

Session locationGreater Columbus Convention Center, Columbus, Ohio

TopicFluidized Bed Incinerator, incineration, Thermal Oxidation

Author(s)

N. Merchant-Wells

Author(s)N. Merchant-Wells1

Author affiliation(s)Northeast Ohio Regional Sewer District; 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May, 2022

DOI10.2175/193864718825158393

Volume / Issue

Content sourceResiduals and Biosolids

Word count5

PFAS Data Guidelines and Implications to Fate through Thermal Processes

Abstract

Introduction Per- and polyfluoroalkyl substances (PFAS) have dominated public attention recently given their environmental contamination. PFAS resist environmental degradation and can accumulate in the urban water cycle, including wastewater systems (Winchell et al., 2021). Furthermore, various PFAS will migrate to wastewater solids (termed biosolids when stabilized) where conventional treatment technologies have little to no effect on the PFAS content of the solids (Loos et al., 2018, Gallen et al., 2018, Kim Lazcano et al., 2019). PFAS in biosolids have the potential to derail beneficial reuse via land application due to the potential impacts to groundwater, and transfer into agricultural crops (Navarro et al., 2017, Ghisi et al., 2019). Thermal treatment is the only process currently identified to reliably destroy PFAS (USEPA, 2020), but destruction efficiency must be confirmed to avoid worsening atmospheric pollution and deposition (Shafer et al., 2020). Several research initiatives have commenced to document the fate of PFAS through thermal processes, including the Water Research Foundation (WRF) Project 5111 focused on sewage sludge incinerators (SSIs). The treatment of the data when reviewing these fate studies has profound impacts on the defensible conclusions offered by researchers. This paper will present the procedures implemented for the quantifiable data from the WRF project soon to be published (Winchell et al., in review). Data Usage Guidelines Data collected as part of any research project must undergo a strict quality assurance and control program to support defensible conclusions. Data from the WRF study was subjected to a four-step assessment process (Table 1). Data were verified, validated, and qualified prior to the final assessment on usability. The research team then reviewed the quality control information and deemed reported values usable or not. This final step is critical in advancing scientific knowledge on sound information. Molar Basis Moles matter. Too often researchers sum multiple PFAS compounds on a mass basis. While convenient this can lead inappropriate assessments of process performance. For example, consider a scenario where a mixture of PFBA (MW = 214.04 g/mol) and PFHxDA (MW = 814.13 g/mol), two analytes found in the WRF study, are reported. Let's assume 100 grams of each compound entered a process, while 1 and 90 grams exit, irrespective of compound, the summed mass removal would be 55%. On a molar basis, if PFBA were the 1 gram emission the summed removal increases to 80%. Or, if PFBA were the 90 gram emission the summed removal molar removal decreases to 29%. Each researcher must consider whether the arbitrary combined mass of PFAS is critical compared to the number of molecules present. Destruction and Removal Efficiency (DRE) Researchers and regulators often characterize process pollution control in terms of DRE. Summed DRE characterizations suffer from several complications in addition to the molar discussion previously. First, current analytical capabilities can only quantify roughly 0.62% of suspected PFAS compounds (Eurofins, 2022; USEPA, 2021). Second, confident DRE assessments require reportable values of the targeted pollutant in each input and output stream. Samples absent reportable values, possible values ranging from zero to the limit of quantification, can significantly impact the significant figures in the DRE calculation. A difference between 99% and 99.9% DRE can determine regulatory compliance. Last, some input or output streams can misleadingly impact a DRE assessment as discussed in the following section. Given these complications the WRF study did not attempt to report a DRE. Instead, the average molar load of targeted PFAS were compared in the dewatered sewage sludge and stack (air emissions). From the multiple hearth furnace (MHF), only 12 µmols escape the stack while none left fluidized bed furnace (FBF), resulting in over 95% removal of PFAS, see Figure 1. Consequential Impacts of Inconsequential Streams Some input and output streams in an SSI can have impractical impacts on DRE assessments if not evaluated with scrutiny. In the WRF study, the reportable levels of PFAS in the wet scrubber supply water and drain influence DRE estimates and bias the environmental relevance of the SSI performance. Perhaps the best illustration of this paradox comes from the observation of PFHxS in the wet scrubber supply and drain, but in no other samples. The calculated DREs for each run range from 4—25%. Because the values in the wet scrubber supply slightly exceed that measured in the drain, though not statistically significant (2-tailed, α = 0.05, paired), one might attribute the entire SSI with a low DRE for this compound if applying a narrow interpretation. However, given a wet scrubber is not intended to treat PFAS contained in the supply water, the resulting DREs for PFHxS mischaracterize the performance of the thermal process. Conclusions PFAS and the data collected thereon is complicated and misuse can lead to misleading interpretations. Establishing the data base upon which confident conclusions can be supported requires application of the discussed usage guidelines. Even with a defensible dataset researchers must be wary of misleading interpretations. If properly applied, the approach discussed herein will lead to sound scientific advancement to support industry initiatives.

This paper documents the data usage approach used for the Water Research Foundation Project 5111 studying the fate of PFAS through sewage sludge incinerators. Examples are presented on the complexity and potentially misleading representations of data collected. Vastly different conclusions can be arrived at but proper treatment and interpretation of the data lead to defensible findings that advance the science of support decisions made to address the PFAS challenge.

SpeakerWinchell, Lloyd

Presentation time

15:30:00

16:00:00

Session time

15:30:00

17:00:00

SessionPFAS in Biosolids: Remove and Track it

Session number417

Session locationRoom 238

TopicBiosolids and Residuals, Intermediate Level, PFAS

Author(s)