17-Regional Biosolids Solids Solution Conceptual Study - Phase 2 (Brown and Caldwell, April 2025).pdf

February 12, 2025

Regional Biosolids Solution Conceptual Study Phase 2

TECHNICAL MEMORANDUM prepared for Regional Biosolids Solution Working Group

April 16, 2025

FINAL - Technical Memorandum

Limitations:

This document was prepared solely for Regional Biosolids Solution Workgroup in accordance with professional standards at the time the services were performed and in accordance with the contract between Broward County and Brown and Caldwell dated November 5, 2024. This document is governed by the specific scope of work authorized by Broward County; it is not intended to be relied upon by any other party except for regulatory authorities contemplated by the scope of work. We have relied on information or instructions provided by Regional Biosolids Solution Workgroup and other parties and, unless otherwise expressly indicated, have made no independent investigation as to the validity, completeness, or accuracy of such information.

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Prepared for: Broward County

Technical Memorandum

Subject: Regional Biosolids Solution Conceptual Study Phase 2 - FINAL

Date: April 16, 2025

To: Regional Biosolids Solution Workgroup

From: Brown and Caldwell

Prepared by:

DJ Wacker, PE

Matt Mastin, PE (NC)

Reviewed by:

Marie Burbano, PhD, PE

Natalie Sierra, PE (MA)

Tracy Chouinard, PhD, PE (NH)

Celia Earle, PhD, BCEEM

Tracy Chouinard, PhD, PE (NH)

Natalie Sierra, PE (MA)

Natalie Sierra, PE (MA)

Celia Earle, PhD, BCEEM

Marie Burbano, PhD, PE

Matt Mastin, PE (NC)

DJ Wacker, PE

Regional Biosolids Solution Conceptual Study Phase 2 Technical Memorandum ii

Table of Contents List of Figures ............................................................................................................................................................iv

List of Tables...............................................................................................................................................................v

List of Abbreviations..................................................................................................................................................vi

Executive Summary

Section 1: Introduction

Section 2: Site Selection

2.1 Site Criteria and Initial Scoring

2.2 Narrowed Site Breakdown

2.3 Final Ranking and Recommended Site

Section 3: Solids Production

3.1 Current / Future Solids Production

3.2 Design Solids Loading

Section 4: Dryer Technologies

4.1 General Overview

4.2 Drum Dryers

4.3 Belt Dryer

4.4 Paddle Dryer (Indirect Dryer)

4.5 Thin Film (Indirect Dryer)

4.6 Thin Film (Mechanical Vapor Recompression, MVR)

4.7 Rotary Kiln Dryer (Stircor)

4.8 Dryer Facility Components

4.8.1 Cake Receiving and Storage

4.8.2 Backmixing

4.8.3 Pelletizer

4.8.4 Dried Product Storage Silos

4.9 Dryer Product Market

4.10 Preliminary Technology Screening

Section 5: Technology Selection Design Parameters

5.1 Detailed Analysis

5.2 Number of Units per Technology

Section 6: Technology Layouts on Selected Site

6.1 Drum Dryer Layout

6.2 Belt Dryer with Pelletizer Layout

6.3 Thin Film – MVR Dryer Layout

6.4 Estimated Equipment Layout Summary

Section 7: Cost Evaluation iii

7.1 Construction Costs

7.2 Operational Costs

Section 8: Technology Evaluation and Final Selection

8.1 Technology Evaluation Overview

8.2 Technology Evaluation Criteria and Scoring

8.3 Final Technology Selection

Section 9: Conceptual Design Criteria for Belt Drying Facility and Conclusions

9.1 Variable Dewatered Cake Solids Content

9.2 Revised Design Parameters

9.3 Regional Drying System Conceptual Design

9.4 Auxiliary Systems Conceptual Design Criteria

9.5 Proposed Regional Drying Facility Scope

9.6 Proposed Regional Drying Facility Utility Requirements

9.7 Estimated Construction Cost of Proposed Biosolids Drying Facility

9.8 Conclusions

Attachment A: Workshop Presentations ...............................................................................................................A-1 iv

List of Figures Figure 2-1. Overview of Seven Shortlisted Sites from Phase 1 Study

Figure 2-2. Overview of Five Refined Sites from Phase 2 Workshop 1

Figure 2-3. Site 1 Example Thermal Dryer Layout

Figure 2-4. Site 7 Preferred Thermal Dryer Layout

Figure 2-5. Site 7 Layout Thermal Dryer Alternative

Figure 4-1. Drum Dryer Schematic

Figure 4-2. Representative Drum Dryer Operation Schematic

Figure 4-3. Representative Drum Dryer Model

Figure 4-4. Belt Dryer Schematic

Figure 4-5. Representative Indirect-Fired Belt Dryer Operation Schematic

Figure 4-6. Sludge Extruder Head (left) and Sludge Extrusion Output Being Spread onto Belt Dryer (right)

Figure 4-7. Representative paddle dryer photograph

Figure 4-8. Representative indirect, paddle dryer operation schematic

Figure 4-9. LCI Thin Film Model(left), Installation (middle), and Cross-Sectional View (right)

Figure 4-10. LCI Thin Film System Diagram

Figure 4-11. Process Flow Diagram of the Varcor Process

Figure 4-12. Labelled diagram of the drying process via ‘Spindle’ apparatus

Figure 4-13. Stircor Dryer (left), Hopper Loading (center), and Product (right)

Figure 4-14. Cake Receiving Station and Storage Examples

Figure 4-15. Sludge Backmixing Example with 16% TS Feedstock

Figure 4-16. Pelletizer Feed (left) and End Product (right)

Figure 4-17. Dried Product Storage Silos (left) and Truck Scale (right)

Figure 4-18. Commercial Outlets by County

Figure 4-19. Dryer Product from Drum Dryers (left), Belt Dryers (center), and Thin Film Dryers (right)

Figure 6-1. Site 1 Layout – Drum Dryer System

Figure 6-2. Drum Dryers Layout with Dryer Facility Components

Figure 6-3. Site 1 Layout – Belt Dryers

Figure 6-4. Belt Dryers Layout with Pelletizer and Facility Components

Figure 6-5. Site 1 Layout – Thin Film – MVR Dryers

Figure 6-6. Layout with Pelletizer and Facility Components

Figure 7-1. Construction Costs (ROM)

Figure 9-1. Site Layout of 6-Belt Dryer System with Future PFAS Treatment v

List of Tables Table 2-1. Summary of Seven Shortlisted Sites from Phase 1 Study

Table 2-2. Criteria for Ranking Seven Shortlisted Sites

Table 2-3. Ranking for Seven Shortlisted Sites

Table 2-4. Ranking for Two Final Sites

Table 3-1. Current Regional Biosolids Solution Workgroup Facilities

Table 3-2. Minimum Design Solids Loading

Table 4-1. Acres of Farmland in Nearby Counties

Table 5-1. Conceptual Design Criteria Parameters

Table 5-2. Dryer Quantities - Full Solids Production

Table 5-3. Select Conceptual Design Criteria Scenarios Versus Evaporative Capacity

Table 5-4. Number of Units per Technology for Each Focused Conceptual Design Criteria Scenario

Table 6-1. Estimated Equipment Layout Summary

Table 7-1. Estimated Construction Costs Versus Number of Installed Dryer Trains

Table 7-2. Annual Operational and Maintenance (O&M) Cost

Table 8-1. Dryer Advantages and Disadvantages

Table 8-2. Operations and Maintenance Simplicity

Table 8-3. Number of Installations per Technology

Table 8-4. Technology Comprehensive Scoring

Table 9-1 Dry Wet Cake Product Versus Varying Dewatered Cake Solids

Table 9-2 Expected Operating Conditions at Current Annual Average Solids Loadings Versus Viable Cake Solids Content

Table 9-3 Expected Operating Conditions at Design Maximum Month (2043) Solids Loadings Versus Variable Cake Solids Content

Table 9-4 Recommended Conceptual Design Criteria for Regional Drying System

Table 9-5 Recommended Dewatered Cake Storage Conceptual Design Criteria

Table 9-6 Recommended Dried Product Storage Conceptual Design Criteria

Table 9-7. Utility Requirements Estimates

Table 9-8. Estimated Construction Cost of Regional Biosolids Drying Facility

Regional Biosolids Solution Conceptual Study Phase 2 vi

List of Abbreviations $/wt cost per wet ton %APR annual percentage rate AACEI Association for the Advancement of

Cost Engineering International BEBR Broward County and Municipal

Population Forecast and Allocation Model

BMSC Broward Municipal Services District CFR Code of Federal Regulations CWSRF Clean Water State Revolving Funds DDS Drum Dryer System dtpy dry tons per year EPA Environmental Protection Agency FAC Florida Administrative Code FDEP Florida Department of

Environmental Protection ILA Interlocal Agreement kWh kilowatt-hour MVR mechanical vapor recompression M million MMBtu million British thermal units NMP Nutrient Management Plan NPC net present cost NRWWTP North Regional Wastewater

Treatment Plant O&M operation and maintenance

PAN plant available nitrogen PFAM Broward County and Municipal

Population Forecast and Allocation Model

PFAS Per- and polyfluoroalkyl substances PFOA perfluorooctanoic acid PFOS perfluorooctane sulfonate PPP Public/Private Partnership RBS Regional Biosolids Solutions RECs renewable energy credits RINs renewable identification numbers RNG renewable natural gas RTO regenerative thermal oxidization SDR secondary dryer SWEET Solids Water Energy Evaluation Tool THP thermal hydrolysis TM technical memorandum TS total solids VS volatile solids wt wet tons wtpy wet tons per year WWS Broward County Water and

Wastewater Services WWTP Wastewater Treatment Plant

Phase 2 Regional Biosolids Solution Conceptual Study Executive Summary

Executive Summary

BACKGROUND

The "Regional Biosolids Solution Conceptual Study Phase 2" report, prepared by Brown and Caldwell for the Regional Biosolids Solution Workgroup (RBS Workgroup), was an effort to continue to narrow the information provided in Phase 1 of the Regional Biosolids Solution Conceptual Study. Phase 1 aimed to address the challenges and uncertainties surrounding biosolids management in Broward County, Florida, while Phase 2 focused on narrowing the location and technology.

Phase 1 was initiated due to decreasing landfill space, fewer potential land application sites, community opposition, increased costs, new regulations, and long-term regulatory uncertainty regarding biosolids disposal. These trends are continuing. The land application sites in Florida have been steadily decreasing over the past few years. In 2021, there were 130 sites, and by the end of Phase 1 in May 2024 there were around 58 and, in March 2025, there were 45 sites left, which may be seen in Figure ES-1 below. With these diminishing land application sites, alternative options for biosolids disposal must be addressed.

Figure ES-1. Active Permitted Class B Disposal Sites in the State of Florida

The Phase 1 Study, finalized in May 2024, started with a Universe of Options consisting of over 50 possible biosolids stabilization technologies. The group, through seven workshops, evaluated 19 technologies for biosolids stabilization, narrowing them down to two viable options: thermal hydrolysis and thermal drying, with thermal drying being the recommended technology. Each technology had multiple alternatives. The Phase 2 Study further refined the alternatives in the thermal drying technology sector.

The Phase 1 Study focused on selecting the top future facility sites from an initial 794 sites, for final consideration throughout Broward County, favoring government or municipal entities and excluding parks, recreational areas, colleges, and hospitals. The site selection process for the biosolids drying facility involved a structured and detailed evaluation to identify the most suitable location. Initially, a matrix of core requirements was presented, including criteria such as proximity to wastewater treatment plants, site size, availability of reclaimed water, natural gas, and power, as well as environmental concerns and public

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Pe rm its acceptance. Seven potential sites were shortlisted based on these criteria. The Phase 2 Study further evaluated the seven remaining sites to ultimately select the preferred site.

PHASE 2

Thermal Drying Technology Discussion

The study provided an overview of various dryer technologies used for biosolids drying. These technologies included drum dryers, belt dryers, paddle dryers, thin film dryers (indirect), thin film mechanical vapor recompression (MVR) dryers and rotary kiln dryers.

Each dryer technology discussed above was presented to the RBS Workgroup members. After discussing the reliability, cost range, and operational and maintenance requirements of each technology, it was decided to move forward with three dryer technologies for a detailed evaluation. The three technologies included:

• Drum Dryer

• Belt Dryer

• Thin Film - MVR Both drum dryer and belt dryer technologies are well-established conventional drying technologies for biosolids with hundreds of installations worldwide. Although the thin film – MVR dryer is an emerging technology with minimal experience with biosolids compared to conventional drying technologies, it was included as an alternative due to potential cost savings.

The technology selection process considered various design conditions to evaluate the three technologies.

Design conditions included peaking factors, operational schedule, redundancy, total solids (TS) content of feed cake and other factors. Numerous scenarios were developed for varying design conditions to estimate the number of drying units required for the drum, belt, and thin film – MVR dryers. Each scenario had varying degrees of risk and capital cost, with risk and capital cost being inversely proportional to one another.

Those three drying technologies were used to create five alternatives. The belt dryer and thin film – MVR dryer each had two alternatives, with and without a pelletizer, to create a higher quality product, if required.

The alternatives were scored based on weighted evaluation criteria the RBS Workgroup developed in Phase 1.

The table with comprehensive scoring is provided in Section 8.2 of the technical memorandum. The belt dryer with accompanying pelletizer emerged as the highest ranked technology. Belt dryers were the recommended technology due to operational simplicity and reliability, lower overall cost of ownership, flexible product quality (with the pelletizer), lower temperatures and safer operations.

Site Selection

In the Phase 2 Study, new criteria were developed to further refine the site selection. The seven shortlisted sites from the Phase 1 Study were eventually reduced to five, as sites 3, 4, and 6 were combined into one option. These sites were reviewed to assess their ability to meet the criteria, with input from all municipalities involved in the RBS Workgroup. Figure ES-2 presents these sites.

Figure ES-2. Overview of Refined Sites from Phase 2 Workshop 1

The refined site analysis ranked the top sites based on factors such as availability, ingress, egress, reclaimed water availability, power availability, natural gas availability, environmental concerns, and public acceptance. Sites 1 and 7 were the highest ranked due to their alignment with the core criteria and likelihood of minimizing potential roadblocks or delays to implementation.

The final evaluation required further refined criteria to distinguish between Sites 1 and 7 due to their close scores in the initial evaluation. Site 1 was ultimately selected due to its superior overall score in the evaluation process, achieving higher marks in key criteria such as flexibility, ingress, egress, constructability, ease of layout, functionality, and expandability.

Preliminary layout drawings for three different dryer technologies were developed to better visualize the space required for each option. The space allocation for each technology was considered, including necessary ancillary equipment, building, and site needs, with an emphasis on accommodating stormwater management and truck traffic patterns. Each site layout included a viable location for future PFAS treatment.

Both the drum dryer and belt dryer layouts were able to fit within the proposed site, but the thin film – MVR dryer would likely require alternative stormwater management methods and relocation of the septage receiving facility.

The proposed 6-train belt dryer facility occupies approximately 5.3 acres. A conceptual site layout is provided in the figure below.

Figure ES-3. Site 1 Layout – Belt Dryers Sizing the Regional Facility

The study evaluated existing and future conditions and practices of biosolids management in Broward County and its neighboring communities. The total current solids production rate was 34,635 dry tons per year (dtpy) with an average cake solids content of 16.19 percent total solids (TS). By 2043, the solids production rate is expected to increase to approximately 38,980 dtpy.

Table ES-1. Minimum Design Solids Loading

Units Quantity

Annual Total Solids Production (2043) dtpy 38,980

Average Dewatered Cake Solids Content %TS 16.19%

Average Daily Dewatered Cake Production wtpd 659

Minimum Dried Product Solids Content %TS 92%

While the estimated 2043 total solids production rate varied from Phase 1 to Phase 2, the differences were relatively small. The solids production rates were calculated each time using the best available data provided by the utilities. These revisions are documented and discussed in detail in Sections 3 and 9 of the technical memoranda. The total solids production rate in Table ES-1 is the most current projection for 2043.

Conceptual Design Criteria for Belt Drying Facility

A conceptual basis of design was provided based on all 11 members of the RBS Workgroup participating in the regional drying facility. It emphasized the importance of designing the dryer system to handle a range of dewatered cake solids content to ensure flexibility and reliability. This meant that the system should be capable of processing biosolids with varying moisture levels, which could fluctuate depending on the source and the dewatering performance of each utility involved.

Broward County would need to optimize its dewatering performance and negotiate minimum cake solids content with partnering utilities. This is crucial because the efficiency of the drying process is directly related to the solids content of the dewatered cake. Higher solids content means less water needs to be evaporated, leading to cost savings and improved system performance.

It was recommended that the dryer system be designed to handle a minimum of 38,980 dry tons per year (dtpy) at an average solids content of 15.58 percent total solids (TS). This equated to an average wet cake production rate of 788 wet tons per day (wtpd). The recommended conceptual design criteria also included considerations for redundancy, operating schedule, peaking factors, and other parameters to ensure the system's reliability and efficiency. Based on the design conditions in Table ES-2, the proposed dryer facility has an annual capacity of approximately 287,000 wet tons per year.

Table ES-2 Recommended Conceptual Design Criteria for Regional Drying System

Design Parameters Units Current Design

Annual Solids Production dry tons/yr 34,635 38,980

Average Cake Solids %TS 15.58% 15.58%

Daily Wet Cake Production wtpd 609 788

Operating Schedule hrs x d/wk 24x5 24x6

Peaking Factor % 0% 15%

Loading Condition AA/ MM Annual Average Max Month

Dryer Loading Rate Wet lbs/hr 71,056 76,638

Dried Product TS % 92% 92%

Evaporative Rate Required lbs H2O/hr 59,023 63,660

Evaporative Capacity Per Dryer lbs H2O/hr 12,738 12,738

Number of Duty Dryers No. 4.6 5.0

Number of Dryers in Standby No. 1.4 1.0

Total Number of Installed Dryer Trains No. 6.0 6.0

Redundancy Factor N+1 N+1

Total System Evaporative Capacity lbs H2O/hr 76,428 76,428

Capacity Required 77% 83%

Dryer Type Belt Dryer

Cost Evaluation

Capital and operational costs were developed for the three shortlisted technologies. The estimated construction cost for each technology varied greatly depending on the number of dryer trains, with drum dryers ranging from $360M to $580M, belt dryers from $390M to $500M, and thin film - MVR dryers from $415M to $670M. It should be noted that the cost for a pelletizer was included in both the belt dryer and thin film options. Annual operating and maintenance costs were estimated based on assumptions such as final product hauling/disposal costs, natural gas prices, electricity costs, labor costs, and rehabilitation and replacement costs.

The estimated construction cost of the proposed facility is $500 million. This includes all equipment, installation, building, site work, utilities, auxiliary systems, and 50% contingency.

Phase 2 Conclusions It is the consensus of the RBS Workgroup that they should proceed with designing and ultimately constructing a regional drying facility. The components and location recommendations are as follows:

• Belt dryers were the recommended technology due to operational simplicity and reliability, lower overall cost of ownership, flexible product quality (with the pelletizer), lower temperatures and safer operations.

• Site 1 was ultimately selected due to its superior overall score in the evaluation process, achieving higher marks in key criteria such as flexibility, ingress, egress, constructability, ease of layout, functionality, and expandability.

• The dryer system should be designed to handle a minimum of 38,980 dry tons per year (dtpy) at an average solids content of 15.58 percent total solids. The proposed dryer facility should have an annual capacity of approximately 287,000 wet tons per year

• The estimated construction cost of the proposed facility is $500 million, which includes all equipment, installation, building, site work, utilities, auxiliary systems, and 50% contingency.

Phase 2 Regional Biosolids Solution Conceptual Study Final Technical Memorandum

Section 1: Introduction The Regional Biosolids Solution Conceptual Study conducted by Brown and Caldwell for the Regional Biosolids Solutions (RBS) Workgroup in Broward County, Florida, aimed to explore potential regional solutions for biosolids management as the future is uncertain due to:

• Decreasing landfill space for biosolids;

• A decreasing number of potential land application sites for biosolids;

• Locality-specific community opposition to land application of biosolids;

• Increased costs of utilizing land application of biosolids as a disposal strategy;

• New Florida regulations making Class-B land application more difficult; and,

• Regulatory uncertainty concerning biosolids disposal over the long term.

The RBS Workgroup consisted of Broward County Water and Wastewater Services, the City of Cooper City, the Coral Springs Improvement District, the Town of Davie, the City of Fort Lauderdale, the City of Hollywood, the City of Margate, the City of Miramar, the City of Pembroke Pines, the City of Plantation, and the City of Sunrise.

The land application sites in Florida have been steadily decreasing over the past few years. In 2021, there were 130 sites, and by the end of Phase 1 in May 2024 there were around 58 and, in March 2025, there were 45 sites left, which may be seen in Figure 1-1 below. With these diminishing land application sites, alternative options for biosolids disposal must be addressed.

Figure 1-1. Active Permitted Class B Disposal Sites in the State of Florida

The Phase 1 Study that was finalized in May 2024, evaluated a comprehensive list of available technologies for biosolids stabilization, referred to as the "universe of options" consisting of over 50 possible biosolids stabilization technologies. These were reduced to 19 technologies for biosolids stabilization and then further reduced to seven representative technologies after applying a pass/fail assessment. The remaining technologies were scored based on their ability to meet non-cost goals and objectives, such as producing Class AA biosolids, reducing biosolids volume, and minimizing environmental impacts. The assessment, in conjunction with the Solids Water Energy Evaluation Tool (SWEET), narrowed the viable technologies to two technology alternatives for further analysis: thermal hydrolysis and thermal drying, with additional evaluation

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Pe rm its of hybrid options. The RBS Workgroup selected thermal drying as the recommended technology due to its proven success, significant volume reduction, and production of a sellable product.

The Phase 1 Study focused on selecting the top future biosolids facility sites from an initial 794 sites, for final consideration throughout Broward County, favoring government or municipal entities and excluding parks, recreational areas, colleges, and hospitals. Based on criteria developed, such as land area, proximity to utilities, access, and environmental impacts, the number was reduced to seven potential sites, and these were all County-owned. The study also evaluated different governance and delivery models. The findings of the Phase 1 Study led to the Phase 2 Study as further refinement was required.

This technical memorandum (TM) presents the Phase 2 Study, which involved two main tasks: Refined Technology Evaluation and Refined Site Selection. The first task focused on refining the evaluation of drying technologies to a single dryer technology, considering factors such as sizing, reliability, staffing constraints, and final product quality. The second task involved reviewing the seven existing sites, assessing their capacity to meet core requirements, and selecting up to three sites for further development based on new criteria, with the final selection of a single site. This structured approach ensured that the project would result in transparent and defendable decisions with consensus from all participating utilities. It should be noted that the RBS Workgroup for the Phase 1 Study remained the same for the Phase 2 Study.

Section 2: Site Selection The process for site selection involved a structured and detailed evaluation to provide the most suitable location for the biosolids drying facility. Initially, a matrix of core requirements for siting a biosolids dryer facility was presented, which included criteria such as proximity to wastewater treatment plants (WWTP), site size (greater than 5 vacant acres), availability of reclaimed water, natural gas, and power, as well as environmental concerns, and public acceptance. In the Phase 1 Study, the site criteria focused on several key factors to select the top sites for final consideration throughout Broward County for biosolids drying facilities. These included ownership preferences favoring government or municipal entities excluding parks, recreational areas, colleges, and hospitals. The top seven ranked sites from Phase 1 Study are depicted in the Figure 2-1 and the area of each site along with their distances to the Broward County North Regional Wastewater Treatment Plant (NRWWTP) and landfill summarized in Table 2-1.

Figure 2-1. Overview of Seven Shortlisted Sites from Phase 1 Study

Table 2-1. Summary of Seven Shortlisted Sites from Phase 1 Study

Area Distance (miles) to:

Site

(Acres) WWTP Landfill

1 11.39 0.15 0.55

2 36.58 0.03 0.69

3 3.21 0 0.57

4 25.39 0 0.65

5 22.06 0.13 0.57

6 30.99 0 0.71

7 Broward WWTP 0.72

In an effort to further refine the site selection, for this Phase 2 Study, new criteria were developed, and these seven sites were reviewed to assess their capacity to meet these criteria requirements, and the findings presented for discussions with the municipalities. This process allowed for input from all the municipalities and gave credence to both scorable criteria, as well as certain intangibles, so that an optimal site could be selected for the project's needs.

From these sites, five alternatives were selected for final consideration with sites 3, 4, and 6 being combined for consideration as a single site entitled 3/4/6. Figure 2-2 depicts the sites selected for final evaluation from the Phase 1 Study.

Figure 2-2. Overview of Five Refined Sites from Phase 2 Workshop 1

2.1 Site Criteria and Initial Scoring

The site criteria for Phase 2 were developed to refine the remaining sites, to select the most desirable site for the biosolids drying facility as listed below. These were:

• Availability

• Ingress & Egress

• Reclaimed Water Availability

• Power Availability

• Natural Gas Availability

• Environmental Concerns

• Public Acceptance

These criteria included the availability of critical resources, as well as the site’s ability to accommodate ingress and egress. Additionally, environmental concerns and public acceptance were considered as indicators of potential delays and efficacious implementation.

The refined site analysis ranked the top- sites for biosolids drying facilities based on the refined criteria.

Each site was scored on these factors, and the total scores were used to rank the sites. Table 2-2 summarizes the site ranking with the refined criteria.

Table 2-2. Criteria for Ranking Seven Shortlisted Sites

Site 1 2 3/4/6 5 7

Availability 3 2 2 1 3

Ingress & Egress 3 3 3 2 2

Reclaimed Water Availability 3 3 3 2 3

Power Availability 3 3 3 2 3

Natural Gas Availability 2 2 2 2 2

Environmental Concerns 3 2 1 1 3

Public Acceptance 3 1 2 1 3

TOTAL 20 16 16 11 19

Sites 1 and 7 were the highest ranked sites due to their alignment with the core criteria for siting a biosolids dryer facility and likelihood to minimize potential roadblocks or delays to implementation. Site 1 and Site 7 outranked other sites evaluated primarily due to their excellent access to required resources along with their ability to eliminate concerns for potential delays or issues arising from environmental concerns or public acceptance. The final site ranking is summarized in Table 2-3 below.

Table 2-3. Ranking for Seven Shortlisted Sites

Site Ranking

1 1

7 2

2 3 (tied with Site 3/4/6)

3/4/6 3 (tied with Site 2)

5 5

Given that Sites 2 and 3/4/6 tied for third and their gap to the top two sites, it was decided that only Sites 1 and 7 would be evaluated for further consideration.

2.2 Narrowed Site Breakdown

The next step in the site evaluation required refined criteria to distinguish between Sites 1 and 7 due to their close scores in the initial evaluation. Both sites were evaluated based on several factors such as flexibility to accommodate multiple configurations, ease of ingress and egress, constructability, ease of layout, functionality, ability to allow for future process expansions, and relative ease of permitting (Permittability).

The cost of the property would also be a critical factor in the evaluation of sites if both sites being evaluated were not owned by Broward County and instead owned by a private entity. Given that both sites are currently owned by Broward County, the cost of the land did not play a role in selecting the final recommended site location. Broward County could lease the land back to the Regional Facility in the future.

As part of the evaluation, the sites were assessed for their feasibility and efficiency to manage traffic. Traffic entering the facility will primarily consist of trucks delivering wet cake and chemicals, as well as empty trucks arriving to pick up Class AA product. Traffic exiting the facility will include empty trucks that delivered wet cake and chemicals, and trucks receiving the Class AA product. Potential traffic routing patterns for each site were evaluated and discussed with the RBS Workgroup to help determine acceptable preliminary layouts of the facilities on each site.

Preliminary facility layouts were created as part of the Refined Technology Evaluation for the various technologies and utilized in this section to analyze potential site layout alternatives. The facility layouts provided conservative clearances between various equipment for this purpose and allowed for future refinement of the layouts for the provision of smaller footprints. The layouts represent sufficient units to provide for N+1 redundancy at future maximum month conditions and include designated areas for key utilities, required process equipment, and receiving and dispensing facilities. If PFAS treatment is required in the future, the potential location for advanced thermal process equipment (i.e., pyrolysis, gasification, thermal oxidizer, etc.) should also be identified and included in the evaluation.

The preliminary site layouts at each site are shown on the following pages and utilize preliminary facility layouts for drum dryers for comparative purposes. Anticipated traffic patterns are indicated with colored arrows with dark blue arrows symbolizing traffic entering the site, light blue arrows symbolizing traffic exiting the site, and orange arrows representing traffic patterns to pick up Class AA biosolids.

Site 1 provides an efficient layout of the facilities, as well as multiple options for future expansion, especially noting that the 36 acres of Site 2 (owned by Broward County Solid Waste Department) is located directly adjacent and south of Site 1. This led to the recommendation of relocating the existing Septage Receiving Facility to the Northern portion of Site 1 where traffic entry access could be separately provided and facilitate more cost-effective future biosolids or PFAS treatment facility expansion options, as well as accommodating more suitable process and operational flexibility. Additionally, the New Septage Receiving Facility would only require a portion of the New Septage Receiving Facility Area depicted in the figure and, as such, some of this area would also be available for potential future process expansion.

Figure 2-3. Site 1 Example Thermal Dryer Layout

Site 7 was far more restrictive in comparison to Site 1. The space at the County’s NRWWTP is very limited, making it challenging to accommodate the biosolids facilities in a singular building. As a result, the biosolids facilities are divided into two buildings since a single building could not fit. Additionally, truck traffic through an operational wastewater treatment plant site was a major concern with minimal traffic paths for ingress and egress routing prioritized. As such, the following site layout for Site 7 was preferred. However, this location severely limited future expansion options, ease of layout, and operational flexibility. Therefore, an alternative site layout was developed utilizing Site 3/4/6 with access through the NRWWTP. Although Site 3/4/6 provides for preferable flexibility, ease of layout, and future expandability in relation to the Preferred Site 7 Layout, its ingress and egress is very limited. Ingress and egress to Site 3/4/6 require access either through Site 7 or through a portion of Site 4, which has considerable environmental and public acceptability concerns that essentially eliminated it from final consideration in the previous site evaluations. Thus, the alternative Site 7 layout essentially provides alternative access to this site through the wastewater treatment plant. As can be observed, this access requires significantly lengthy traffic paths through the treatment plant that would prove to be problematic. Figures 2-4 and 2-5 illustrate the alternative layouts for Site 7.

Figure 2-4. Site 7 Preferred Thermal Dryer Layout

Figure 2-5. Site 7 Layout Thermal Dryer Alternative

2.3 Final Ranking and Recommended Site

After review of site conceptual sketches, utility connections, truck travel paths, and clearance, the sites were ranked with revised criteria. The following table describes the refined criteria and ranking. (Score rating: 3 = highest ranking and 1 = lowest ranking)

Table 2-4. Ranking for Two Final Sites

Site 1 7

Flexibility 3 2

Ingress & Egress 3 2

Constructability 3 3

Ease of Layout 3 2

Functionality 3 3

Expandability 3 2

Permittability 3 3

TOTAL 21 17

In the final evaluation, Site 1 was selected due to its superior overall score in the evaluation process. It scored higher in key criteria such as flexibility, ingress and egress, constructability, ease of layout, functionality, and expandability, achieving a total of 21 points compared to Site 7's 17 points. Therefore, these factors collectively led to Site 1 being the choice for the biosolids facility.

Section 3: Solids Production

3.1 Current / Future Solids Production

As part of Phase 1, the Regional Biosolids Solution Conceptual Study Technical Memorandum dated May 1, 2024 (Phase 1 TM), existing and future conditions and practices of biosolids management in Broward County and its neighboring communities were evaluated. All utilities within the RBS Workgroup contributed their existing solids data and a combination of 2020 US Census data and the Broward County and Municipal Population Forecast and Allocation Model were used to estimate future population growth for each utility.

The population growth data was used to estimate solids production rate out to the design year 2043 (20 years into the future). The current total solids (TS) production rate is 33,606 dry tons per year (dtpy) at an average cake solids content of 14.29 percent TS and 2043 projection of 37,780 dtpy.

During the technology evaluation portion of Phase 2, there was one notable revision to the current and future solids production data for the RBS Workgroup. The City of Hollywood currently adds lime to its dewatered cake to produce Class AA biosolids. During development of the Phase 1 TM, it was estimated that without lime addition, Hollywood’s dewatered cake solids would decrease to 10.6 percent TS. However, this was adjusted at the start of Phase 2 and, without lime addition, it was estimated that Hollywood’s dewatered cake solids would be 16 percent TS. Hollywood provided several data points from the end of 2024 and early 2025 that showed the average cake solids pre-lime was around 18 percent TS, however the sample size was limited to four days. As a result, 16 percent TS was used for the technology evaluation in Phase 2. The current and future solids projection data for all RBS Workgroup utilities used during the Phase 2 technology evaluation is provided below in Table 3-1.

Please note, following the technology evaluation and selection of the belt drying technology, several conceptual design criteria parameters were revised based on RBS Workgroup preferences, belt dryer manufacturer clarifications, and updated data received from RBS Workgroup members. The design loading rates used throughout the evaluation process were calculated using the best available data provided by the utilities. All revisions are documented and discussed in detail in Section 9. It is noted that the aggregate cake solids content could be further refined in the future after review and analysis of larger data sets.

Table 3-1. Current Regional Biosolids Solution Workgroup Facilities

Current Data Summary (average 2020-2022) Projected Data (2043)

Region Wet Solids

(wtpy) Dry Solids

(dtpy) Percent Total Solids (%TS)

Wet Solids (wtpy)

Dry Solids (dtpy) % Growth

Current Stabilization

Process

Broward County 87,252 14,833 17.00% 95,294 16,200 9.2% Anaerobic Digestion

Cooper City 3,668 491 13.40% 3,731 500 1.7% Aerobic digestion

Coral Springs Improvement District 2,546 308 12.10% 2,810 340 10.4% Aerobic digestion

Town of Davie - System ll 2,697 337 12.48% 3,040 380 12.9% Aerobic digestion

Town of Davie - System IV 992 110 11.05% 1,086 120 9.4% Aerobic digestion

Fort Lauderdale 29,457 5,150 17.48% 36,550 6,390 24.1% Aerobic digestion

Hollywood 43.181 6,909 16.00% 49,438 7,910 14.5% Lime stabilization

City of Margate 4.016 657 16.37% 4,644 760 15.6% Rotating Biological Contactors

City of Miramar 14,130 1,707 12.08% 15,484 1,870 9.6% Anaerobic Digestion

Pembroke Pines 3,028 485 16.00% 3,188 510 5.3% Aerobic digestion

Plantation 1,051 129 12.24% 1,226 150 16.6% Anaerobic Digestion

City of Sunrise – Sawgrass 10,050 1,811 18.02% 10,709 1,930 6.6% Aerated sludge holding tanks

City of Sunrise – Springtree 3,470 680 19.59% 3,675 720 5.9% Aerated sludge holding tanks

Total 205,539 33,606 16.35% 230,878 37,780 12.49% Annual Average, tpd 563 92 633 104

Note 1: wtpy = Wet Tons per Year, dtpy = Dry Tons per Year, %TS = Percent Total Solids Note 2: The current and projected solids production data in Table 3-1 were used for the technology evaluation. Refer to Section 9 for solids loading data refined after the evaluation was completed as well as proposed design criteria.

3.2 Design Solids Loading

To evaluate and select the appropriate dryer for a given application, it is essential to consider the various dryer technologies available along with their corresponding models and evaporative capacities. Not only do different types of dryers have different evaporative capacities, but each manufacturer has standard models with variable evaporative capacities. The evaporative capacity is defined as the pounds of water evaporated per hour (lbs H2O/hr), which must be determined for this analysis. Since the dryer solids loading is constrained by the rate of water evaporation per hour, a higher solids percentage (percent TS) in the dewatered cake will necessitate less drying. Consequently, a higher solids percentage will also result in the need for smaller or fewer thermal drying units. Therefore, an efficient dewatering process can lead to efficient cost savings in the drying phase.

Based on the biosolids data summarized in Table 3-1, the thermal dryer system should be sized for a minimum of 37,780 dtpy at an average solids content of 16.35 percent TS. This equatess to an average wet cake production rate of 633 wet tons per day (wtpd), as shown in Table 3-2.

Table 3-2. Minimum Design Solids Loading

Units Quantity Annual Total Solids Production (2043) dtpy 37,780

Average Dewatered Cake Solids Content %TS 16.35%

Average Daily Dewatered Cake Production wtpd 633

Minimum Dried Product Solids Content %TS 92%

Minimum Evaporative Capacity lbs H2O/hr 43,380

At an average dewatered cake production of 633 wtpd at 16.35 percent TS and drying to 92 percent TS, the minimum required evaporative capacity for the system is 43,380 lbs H2O/hr. This evaporative capacity assumes an operation schedule of 24/7/365. Additional design parameters must be considered before determining the final design criteria for the thermal dryer system. Such parameters include redundancy, operating schedule, peaking factors (i.e., maximum month or peak week conditions), and other factors.

These parameters are discussed in Section 5 as part of the dryer technology evaluation and selection.

Minimum dewatered cake solids content must also be considered. Refer to Section 9 of this TM for the recommended conceptual design criteria for the regional drying system. As mentioned previously, Section 9 also documents revised solids production rates based on best available data at the time of the conceptual design.

Section 4: Dryer Technologies

4.1 General Overview

Conventional thermal drying technologies utilized for biosolids drying in the US include drum dryers, belt dryers and indirect dryers. Other technologies include fluidized bed, tray dryers and emerging technologies that are start-up companies, new to processing biosolids or new to the US market. Conventional technologies and a few emerging technologies are discussed in the following sections.

One key difference between dryer technologies is the product throughput or solids loading capacity. Rotary drum dryers typically have a substantially higher throughput allowance than the other technologies, making them the most efficient at large size facilities while also limiting their applications in smaller and medium sized facilities. They also come with a drawback of having substantially more ancillary components which increase operational complexity.

While belt and indirect dryers are more common for smaller to medium sized applications, they often require a larger footprint to meet the same throughput of a drum dryer. Belt dryers typically have a lower capital cost and provide the most flexibility in temperatures and methodologies, which allows for low-temperature waste heat sources like hot water from a cogeneration system or other heating source.

Sludge quality is directly connected to dryer performance and each dryer technology manages sludge quality differently. Sludge quality includes moisture content, stabilized or unstabilized solids, primary sludge, and waste activated sludge, as well as odors, inert material and viscosity. Some dryers will do better than others with more challenging feedstock. All dryers will have challenges processing undigested or unstabilized solids.

In the initial workshop for this study, six thermal drying technologies were discussed. The technical details of these dryers are listed in this section for the following dryer technologies:

• Drum Dryer

• Belt Dryer

• Paddle Dryer (Indirect Dryer)

• Thin Film (Indirect Dryer)

• Thin Film (Mechanical Vapor Recompression, MVR)

• Rotary Kiln Dryer

4.2 Drum Dryers

Drum dryers have been used to treat wastewater solids since the 1920s. Drum dryers are heated via a fuel-burning furnace that exhausts directly into a long, cylindrical steel drum that rotates on roller bearings. Some drums move the solids through in a single pass, while others use interlocked concentric drums to make multiple passes through the drum. Material is propelled through the drum by the hot gas air stream (750 – 1,200°F) and is continuously lifted by the cylinder flights and cascaded through the hot gas. The dryer exhaust and dried product are passed through an air/solids separator, and the dried product is screened and processed for recycling back to the feed solids or routed to storage silos. Figure 4-1 depicts a typical drum dryer schematic.

Figure 4-1. Drum Dryer Schematic

Drum dryers feed a mixture of dewatered sludge and back mixed dry product into a drum in which material is propelled through the drum via the hot gas air stream. Having a steady moisture content with dewatered cake lower in moisture is key in steady operation of the drum dryer. A relatively large volume of dried recycle product is mixed with the dewatered feed solids to increase the average percent TS in the blended feed (60 percent - 80 percent TS) to the dryer. Drum dryers are accompanied by a back mixing system to achieve this.

The back mixing system allows drum dryers to produce a high-quality end product with uniform granules without need for further downstream pellet processing.

Typically, a majority of the air/gas stream (70 percent - 90 percent) is recycled back to the dryer furnace to increase the overall thermal efficiencies and help maintain an inert atmosphere, which reduces the risk for thermal events. Recycling the air also minimizes the volume of exhaust air treated in air pollution and odor control equipment. Typically, additional particulate removal via tray condenser and venturi scrubber is conduced followed by regenerative thermal oxidation (RTO) to destroy odors and volatile organic compounds (VOCs).

Given their higher operating temperatures, drum dryers have a higher throughput compared to other drying technologies and typically can achieve a thermal efficiency better than 1,500 Btu/lb of water evaporated.

The maintenance required for the drum drying system can be high given the quantity of ancillary equipment and the system is the most operationally complex of all dryers.

A process schematic and model of a typical rotary drum dryer are shown in Figures 4-2 and 4-3.

Figure 4-2. Representative Drum Dryer Operation Schematic

Figure 4-3. Representative Drum Dryer Model Courtesy of Andritz

Rotary drum dryer operation requires monitoring and adjustment of several primary variables and ancillary systems. Dryer inlet and outlet temperatures, typically set at 850°F and 200°F, respectively, provide a key indication of dryer performance, but operators must also monitor the dryer wet feed ratio, based on dewatering performance and dried product recycle rate, every 30 minutes to ensure it also stays within target range. The furnace inlet pressure also provides a key indication of system performance as it is a function of several key ancillary systems such as induction and exhaust fan load and flow rate, air/solids system separation performance, and debris collection within the product screening and processing steps.

If high temperature is detected within the recycle or product bins, the system is made inert with a nitrogen purge system. Temperature excursions within the drum vessel are controlled via water deluge water sprays and explosion panels and vents are located at various locations throughout the system. In addition to temperature, carbon monoxide and oxygen instruments are located throughout the system to detect unsafe conditions.

Preventative maintenance, as well as system rehabilitation and repair costs, are considerably more complex and costly than belt or paddle dryers. Component wear is more widespread and extensive as the product is in constant contact with the rotary drum dryer internal vessels and mixing and conveyance equipment. Wet feed and recycle product mixing can be an especially abrasive process and require frequent screw replacement. Drum dryer systems typically have a useful life of 15-20 years and require a major overhaul at that point, typically requiring significant capital improvements to replace larger components such as the rotary drum vessel.

4.3 Belt Dryer

Belt dryers can be configured to run at low temperatures with hot water (194°F) or medium temperatures with steam or thermal oil (284°F). Belt dryers use a series of fans to circulate air within the dryer across and through the sludge layer, exhausting through the downstream condenser and/or odor control system. The sludge is conveyed via a slow-moving belt which may make multiple passes within the dryer. The thermal efficiency of this dryer system is very similar to drum dryers, typically in the 1,300 – 1,500 Btu/lbs H2O evaporated.

Belt dryers have a larger footprint to meet an identical throughput when compared to drum dryers and are known for their low to moderate operational and maintenance complexity. Their end product is less uniform ranging from 1 - 8mm with a lower bulk density compared to a drum dryer, requiring further downstream pelletizing processes to meet a higher quality uniform pellet. A belt dryer process schematic can be seen in Figure 4-4.

Figure 4-4. Belt Dryer Schematic

Belt dryers shape and distribute dewatered solids into noodle or granule shaped particles onto a slow-moving porous belt. Warm process gasses are circulated through the belt chamber to evaporate the water content in the feed solids.