Page 209 Wastewater System Master Plan (WWSMP) – Hot Sp Table 5.15 – Proposed Davidson Dr. WWTP Biosolids Pro Intended U Biosolids Mass/ Volume Drying Design Annual Flow Rate 16 Design Annual Temperature 20 Biosolids Processing Scenario 1A – Near-Term (i.e., WAS to BFP) Minimum WAS to Dewatering1 25,000 Design WAS to Dewatering 1 26,125 Maximum WAS to Dewatering1 33,000 Dewatering Performance 15.1 to 16. Minimum Dewatered Biosolids 19,875 Design Dewatered Biosolids 21,000 Maximum Dewatered Biosolids 27,875 Dewatering Days Per Week 7.00 Dewatering Weeks per Year 52.00 Wet Sludge Weight (@ 15.6 % TS) 134,615 Wet Sludge Volume2 74.69 Design Annual Wet Sludge Weight (@ 15.6 % TS) 24,500 Design Annual Wet Sludge Volume2 27,188 1 Includes the ~900 lbs./ day of tertiary filter backwash solids. 2 Specific gravity of the
9 of 291 prings, Arkansas | Crist Engineers, Inc. oduction Planning Summary – Near-Term – Scenario 1A Use Intended Disposal Units Composting Land Application Landfill MGD oC - dry lbs./ day - - .7 % TS - - dry lbs./ day - - days - weeks - wet lbs./ dewatering day - cubic yards (CY)/ dewatering day - tons/ year - CY/ year e biosolids = 1.07.
Page 210 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. As shown in Scenario 1A, the total estimated amount of biosolids produced from WAS activities are between 25,000 to 33,000 dry-lbs. per day with the estimated amount of dewatered biosolids being between 19,875 to 27,875 dry-lbs./ day. At an estimated performance of 15.6 % total solids this equates to a total estimated wet sludge of 134,615 lbs./ dewatering day or a volume of approximately 75 CY/ dewatering day. 5.2.3.1.1 DRYING A drying facility was not evaluated in the near-term CIP improvements because of the additional assets and cost required for implementation. If a drying facility were implemented, it would be included in the mid-term CIP improvements, see Scenario 2A1 (Alternative B). 5.2.3.1.2 COMPOSTING Near-term CIP improvements to the composting facility were not evaluated because of the additional assets and cost required for implementation. If additional improvements were to be implemented, it would be included in the mid-term CIP improvements, see Scenario 2A1. However, the existing composting facility can compost approximately 13,262 CY per annual. Table 5.16 - Proposed Davidson Dr. Biosolids – Scenario 1A – Existing Composting Costs Analysis Compost – Existing Windrow Annual Volume to Compost @ 15.6% TS 13,262 wet-CY Annual Weight to Compost @ 15.6% TS 11,951 wet-ton Analysis Duration 20 years Total Capital Cost - Estimated Handling and Use Costs $63 $/ wet-CY Estimated Handling and Use Costs $70 $/ wetton Cost per Dry Ton @ 15.6% TS $446.28 $/ dry-ton Average Annual Cost $832,000 5.2.3.1.3 LAND APPLICATION Near-term CIP improvements necessary to achieve Class B biosolids were not evaluated because of the additional assets and cost required for implementation. If additional improvements were to be implemented to permit land application, it would be included in the mid-term CIP improvements, see Scenario 2A1 (Alternative C).
Page 211 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.3.1.4 LANDFILL Near-term CIP improvements are included for the disposal of unclassified biosolids. Disposal of unclassified biosolids into a Class 1 landfill has the advantages that it is already permitted, requires minimal capital investment, and provides for sequestration of T-P. A cost analysis was performed for Scenario 1A to determine an estimated unit cost for landfill disposal. The following assumptions were included in the analysis: 1. provide two (2) 20 CY covered biosolids trailers, one (1) heavy haul tractor and driver to deliver dewatered biosolids from Davidson Dr. WWTP to the Landfill located in Saline County, approximately 80 miles round trip, at 40 miles per hour, 0.5 hours load time, 0.5 unload time two trailers allow for biosolids to continuously be processed and filled while trip to landfill occurs. Figure 5.5 – 20 CY Trailer and Heavy Haul Tractor Example Image found at https://www.oxbodies.com/ox-end-dump-trailers/full-frame on November 10, 2021
Page 212 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Scenario 1A includes the purchasing of the identified equipment, fuel, labor, maintenance, and replacement of equipment was also included in this analysis. Table 5.17 - Proposed Davidson Dr. Biosolids – Scenario 1A – Landfill Costs Analysis Landfill Annual Volume to Landfill @ 15.6% TS 13,9261 wet-CY Annual Weight to Landfill @ 15.6% TS 12,549 wet-ton Analysis Duration 20 years Total Capital Cost $352,500 Estimated Handling and Disposal Costs $70 $/ wet-CY Estimated Handling and Disposal Costs $78 $/ wet-ton Cost per Dry Ton @ 15.6% TS $498.69 $/ dry-ton Average Annual Cost $976,271 1 13,262 wet-CY/ year will be processed at existing composting facility. The total estimated Scenario 1A annual cost for biosolids handling is presented in Table 5.33.
Page 213 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.3.2 SCENARIO 1A (ALTERNATIVE A) Scenario 1A (Alternative A) improvements at Davidson Dr. WWTP include the following: Scenario 1 improvements at Davidson Dr. WWTP include the following: Scenario 1 (Near-Term Improvements CIP) 1.1 Process elimination of: a. lime feed for supplementary alkalinity b. primary clarification and production of primary sludge c. anaerobic digestion 1.2 Addition of magnesium hydroxide for supplemental alkalinity 1.3 Upgrade/ increase airflow rates to aeration basin 1.4 Additional 100 ft secondary clarifier a. Increase total surface 7,854 ft2 (total = 36,970 ft2) 1.5 New tertiary filtration 1.6 WAS to aerated sludge storage no.1 (Alternative A) a. New WAS Pumping 1.7 Aerated sludge storage no. 1 (Alternative A) a. Conversion of one (1) primary clarifier basin to aerated sludge storage 1.14 Use existing TWAS pumps to convey to existing dewatering (BFP) (Alternative A) It is proposed with Scenario 1A (Alternative A) to convey waste activated sludge (WAS) directly from the secondary clarifiers to the new aerated sludge storage to the existing dewatering unit. Wasting and dewatering are planned to be completed approximately 22 hours per day, 6 days per week under this near-term approach. This is not ideal solution because it requires almost continuous operation of the dewatering equipment and does not allow for downtime of the equipment for maintenance or servicing. However, this approach/ strategy does permit biosolids improvements to be improved in the mid-term rather than the near-term. It will allow for continuously conveyance of WAS to the dewatering unit. This approach should maximize the existing dewatering performance (i.e., continuous and consistent) as well as improve the biological efficiency of the near-term proposed secondary treatment process. This approach also permits for mid-term improvements to be completed with minimal interruption to the near-term biosolids handling process while also allowing for the elimination of the anaerobic digesters. The general influent parameters of Scenario 1A (Alternative A) are AD design flow rate (QAD) = 16 MGD (6.7% excess of the projected 2040 average daily influent flow) with the 2040 AD design influent parameters. Scenario 1A (Alternative A) does modify the total dry-lbs. of biosolids produced from the Davidson Dr. WWTP. The simplified process flow diagram and associated biosolids production values are presented in the following figure and table.
Page 214 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 5.6 - Proposed Davidson Dr. WWTP Simplified Process Flo (Alterna
4 of 291 prings, Arkansas | Crist Engineers, Inc. ow Diagram – Biosolids Treatment (Near-Term CIP) – Scenario 1A ative A)
Page 215 Wastewater System Master Plan (WWSMP) – Hot Sp Table 5.18 – Proposed Davidson Dr. WWTP Biosolids Production Intended Use Biosolids Mass/ Volume Drying Co Design Annual Flow Rate 16 Design Annual Temperature 20 Biosolids Processing Scenario 1A (Alternative A) – Near-Term (i.e., WAS to Minimum WAS to Dewatering1 25,000 Design WAS to Dewatering 1 26,625 Maximum WAS to Dewatering1 33,500 Dewatering Performance 15.1 to 16.7 Minimum Dewatered Biosolids (EST.) 18,875 Design Dewatered Biosolids (EST.) 20,000 Maximum Dewatered Biosolids (EST.) 26,875 Dewatering Days Per Week 6.00 Dewatering Weeks per Year 52.00 Wet Sludge Weight (@ 15.6 % TS) 149,573 Wet Sludge Volume2 82.99 Design Annual Wet Sludge Weight (@ 15.6 % TS) 23,333 Design Annual Wet Sludge Volume2 25,894 1 Includes the ~900 lbs./ day of tertiary filter backwash solids and ~500 lbs./ 1.07.
5 of 291 prings, Arkansas | Crist Engineers, Inc. n Planning Summary – Near-Term – Scenario 1A (Alternative A) Intended Disposal Units omposting Land Application Landfill MGD o C o Aerated Sludge Storage No. 1 to BFP) - dry lbs./ day - - % TS - - dry lbs./ day - - days - weeks - wet lbs./ dewatering day - cubic yards (CY)/ dewatering day - tons/ year - CY/ year / day of SWWWTP hauled biosolids. 2 Specific gravity of the biosolids =
Page 216 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. As shown in Scenario 1A (Alternative A), the total estimated amount of biosolids produced from WAS activities are between 25,000 to 33,500 dry-lbs. per day with the estimated amount of dewatered biosolids being between 18,875 to 26,875 dry-lbs./ day. At an estimated performance of 15.6 % total solids this equates to a total estimated wet sludge of 149,573 lbs./ dewatering day or a volume of approximately 83 CY/ dewatering day. 5.2.3.2.1 DRYING A drying facility was not evaluated in the near-term CIP improvements because of the additional assets and cost required for implementation. If a drying facility were implemented, it would be included in the mid-term CIP improvements, see Scenario 2A1 (Alternative B). 5.2.3.2.2 COMPOSTING Near-term CIP improvements to the composting facility were not evaluated because of the additional assets and cost required for implementation. If additional improvements were to be implemented, it would be included in the mid-term CIP improvements, see Scenario 2A1. However, the existing composting facility can compost approximately 13,262 CY per annual. Table 5.19 - Proposed Davidson Dr. Biosolids – Scenario 1A (Alternative A)– Existing Composting Costs Analysis Compost – Existing Windrow Annual Volume to Compost @ 15.6% TS 13,262 wetCY Annual Weight to Compost @ 15.6% TS 11,951 wetton Analysis Duration - years Total Capital Cost - Estimated Handling and Use Costs $63 $/ wetCY Estimated Handling and Use Costs $70 $/ wetton Cost per Dry Ton @ 15.6% TS $446.28 $/ dryton Average Annual Cost $832,000 5.2.3.2.3 LAND APPLICATION Near-term CIP improvements necessary to achieve Class B biosolids were not evaluated because of the additional assets and cost required for implementation. If additional
Page 217 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. improvements were to be implemented to permit land application, it would be included in the mid-term CIP improvements, see Scenario 2A1 (Alternative C). 5.2.3.2.4 LANDFILL Near-term CIP improvements are included for the disposal of unclassified biosolids. As discussed, disposal of unclassified biosolids into a Class 1 landfill has the advantages that it is already permitted, requires minimal capital investment, and provides for sequestration of T-P. A cost analysis was performed for Scenario 1A (Alternative A) to determine an estimated unit cost for disposal. The following assumptions were included in the analysis: 1. provide two (2) 20 CY covered biosolids trailers, one (1) heavy haul tractor and driver to deliver dewatered biosolids from Davidson Dr. WWTP to the Landfill located in Saline County, approximately 80 miles round trip, at 40 miles per hour, 0.5 hours load time, 0.5 unload time two trailers allow for biosolids to continuously be processed and filled while trip to landfill occurs. Scenario 1A (Alternative A) includes the purchasing of the identified equipment, fuel, labor, maintenance, and replacement of equipment was also included in this analysis. Table 5.20 - Proposed Davidson Dr. Biosolids – Scenario 1A (Alternative A)– Landfill Costs Analysis Landfill Annual Volume to Landfill @ 15.6% TS 12,6321 wet-CY Annual Weight to Landfill @ 15.6% TS 11383 wet-ton Analysis Duration 20 years Total Capital Cost $352,500 Estimated Handling and Disposal Costs $70 $/ wet-CY Estimated Handling and Disposal Costs $78 $/ wet-ton Cost per Dry Ton @ 15.6% TS $498.69 $/ dry-ton Average Annual Cost $885,510 1 13,262 wet-CY/ year will be processed at existing composting facility. The total estimated annual cost for Scenario 1A (Alternative A) biosolids handling is presented in Table 5.20.
Page 218 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.3.3 SCENARIO 2A1 Scenario 1 (Near-Term Improvements CIP) 1.8 Process elimination of: a. lime feed for supplementary alkalinity b. primary clarification and production of primary sludge c. anaerobic digestion 1.9 Addition of magnesium hydroxide for supplemental alkalinity 1.10 Upgrade/ increase airflow rates to aeration basin 1.11 Additional 100 ft secondary clarifier a. Increase total surface 7,854 ft2 (total = 36,970 ft2) 1.12 New tertiary filtration 1.13 WAS directly to existing dewatering (BFP) a. New WAS Pumping The proposed biosolids handling process (identified as Scenario 2) is a mid-term projected project and is represented to include the following proposed structural changes/ modifications to the Davidson Dr. WWTP, including those proposed in Scenario 1, represented in the simulation, as follow: Scenario 2 (Mid-Term CIP) 2.11 Addition of sodium aluminate to sequester of orthophosphate 2.12 Addition of aluminum chlorohydrate (ACH) to aid in coagulant/ sequester orthophosphate 2.13 New RAS Pumps 2.14 Modify piping to WAS directly to continuous thickening (centrifugal) a. Dewatering unit sized for ~250 GPM 2.15 Thickened WAS conveyed to aerated sludge storage no. 1 2.16 Aerated sludge storage no. 1 a. Conversion of one (1) primary clarifier basin to aerated sludge storage 2.17 Convey from aerated sludge storage no. 1 to aerated sludge storage 2 2.18 Aerated sludge storage no. 2 a. Conversion of gravity thickeners (x2) to aerated sludge storage 2.19 Convey from aerated sludge storage no. 2 to new dewatering(centrifugal) a. Dewatering unit sized for ~150 GPM at 2500 dry-lbs./hr. 2.20 New sidestream treatment system (suspended air flotation) a. Addition of sodium aluminate to sequester orthophosphate The proposed Scenario 2 modifications are planned to be completed as a mid-term CIP project.
Page 219 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Scenario 2A1 includes proposed planned dewatering operation for 3 days per week with an operating duration of ~7 hours per day (total of 21 hours per week). The total hours per week is 168, therefore the non-dewatering operation per week is 147 hours. The general influent parameters of Scenario 2A1 are AD design flow rate (QAD) = 16 MGD (6.7% excess of the projected 2040 average daily influent flow) with the 2040 AD design influent parameters. The simplified process flow diagram and associated biosolids production values are presented in the following figure and table.
Page 220 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 5.7 - Proposed Davidson Dr. WWTP Simplifie
0 of 291 prings, Arkansas | Crist Engineers, Inc. d Process Flow Diagram – Mid-Term – Scenario 2A1
Page 22 Wastewater System Master Plan (WWSMP) – Hot Sp Table 5.21 - Proposed Davidson Dr. WWTP Biosolids Pro Intended Use Biosolids Mass/ Volume Drying Compo Design Annual Flow Rate 16 Design Annual Temperature 20 Biosolids Processing Scenario 2A1 - Mid to Long-Term (i.e., WAS to N Dewatering) Minimum WAS to Dewatering1 21,600 Design WAS to Dewatering 1 23,000 Maximum WAS to Dewatering1 29,050 Dewatering Performance 20 to 22.5 Minimum Dewatered Biosolids 16,750 Design Dewatered Biosolids 17,875 Maximum Dewatered Biosolids 24,750 Dewatering Days Per Week 3.00 Dewatering Weeks per Year 52.00 Wet Sludge Weight (@ 21 % TS) 198,611 Wet Sludge Volume2 110.20 Design Annual Wet Sludge Weight (@ 21 % TS) 15,492 Design Annual Wet Sludge Volume2 17,191 1 Includes the ~900 lbs./ day of tertiary filter backwash solids and ~500 biosolids = 1.07.
1 of 291 prings, Arkansas | Crist Engineers, Inc. oduction Planning Summary – Mid-Term – Scenario 2A1 Intended Disposal Units osting Land Application Landfill MGD oC ew Thickening to Aerated Sludge Storage No. 1/ 2 to New - dry lbs./ day - - % TS - - dry lbs./ day - - days - weeks - wet lbs./ dewatering day - cubic yards (CY)/ dewatering day - tons/ year - CY/ year lbs./ day of SWWWTP hauled biosolids. 2 Specific gravity of the
Page 222 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. As shown in Scenario 2A1, the total estimated amount of biosolids produced from WAS activities are between 21,600 to 29,050 dry-lbs. per day with the estimated amount of dewatered biosolids being between 16,750 to 24,750 dry-lbs./ day. At an estimated performance of 21% total solids this equates to a total estimated wet sludge of 198,611 lbs./ dewatering day or a volume of approximately 110 CY/ dewatering day. 5.2.3.4 SCENARIO 2A1 (ALTERNATIVE B) Scenario 1 (Near-Term Improvements CIP) 1.14 Process elimination of: a. lime feed for supplementary alkalinity b. primary clarification and production of primary sludge c. anaerobic digestion 1.15 Addition of magnesium hydroxide for supplemental alkalinity 1.16 Upgrade/ increase airflow rates to aeration basin 1.17 Additional 100 ft secondary clarifier a. Increase total surface 7,854 ft2 (total = 36,970 ft2) 1.18 New tertiary filtration 1.19 WAS directly to existing dewatering (BFP) a. New WAS Pumping The proposed biosolids handling process (identified as Scenario 2) is a mid-term projected project and is represented to include the following proposed structural changes/ modifications to the Davidson Dr. WWTP, including those proposed in Scenario 1, represented in the simulation, as follow: Scenario 2 (Mid-Term CIP) 2.21 Addition of sodium aluminate to sequester of orthophosphate 2.22 Addition of aluminum chlorohydrate (ACH) to aid in coagulant/ sequester orthophosphate 2.23 New RAS Pumps 2.24 Modify piping to WAS directly to continuous thickening (centrifugal) a. Dewatering unit sized for ~250 GPM 2.25 Thickened WAS conveyed to aerated sludge storage no. 1 2.26 Aerated sludge storage no. 1 a. Conversion of one (1) primary clarifier basin to aerated sludge storage 2.27 Convey from aerated sludge storage no. 1 to aerated sludge storage 2 2.28 Aerated sludge storage no. 2 a. Conversion of gravity thickeners (x2) to aerated sludge storage 2.29 Convey from aerated sludge storage no. 2 to new dewatering(centrifugal) a. Dewatering unit sized for ~150 GPM at 2500 dry-lbs./hr. 2.30 Convey from new dewatering to new drying/ storage facility (Alternative B)
Page 223 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 2.31 New sidestream treatment system (suspended air flotation) a. Addition of sodium aluminate to sequester orthophosphate The proposed Scenario 2 modifications are planned to be completed as a mid-term CIP project. Scenario 2A1 includes proposed planned dewatering operation for 3 days per week with an operating duration of ~7 hours per day (total of 21 hours per week). The total hours per week is 168, therefore the non-dewatering operation per week is 147 hours. The primary difference between Scenario 2A1 and Scenario 2A1 (Alternative B) is the additions of a drying facility and a dried storage facility. The implementation these units permits the development of Class A biosolids for intended agricultural use. The general influent parameters of Scenario 2A1 (Alternative B) are AD design flow rate (QAD) = 16 MGD (6.7% excess of the projected 2040 average daily influent flow) with the 2040 AD design influent parameters. Scenario 2A1 (Alternative B) does not modify the total dry-lbs. of biosolids produced from the Davidson Dr. WWTP. The simplified process flow diagram is presented in the following figure.
Page 224 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 5.8 - Proposed Davidson Dr. WWTP Simplified Proces
4 of 291 prings, Arkansas | Crist Engineers, Inc. ss Flow Diagram – Mid-Term – Scenario 2A1 (Alternative B)
Page 225 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.3.4.1 DRYING Drying process occurs through utilizing different technologies (heat, vacuum, rotary kiln, et al.) to create an end product that is 90% TS. When 90% TS is achieved the dried biosolids is classified as Class A. Therefore, once Class A biosolids is achieved it has unrestricted use. However, special care has to be taken as not rewet the dried biosolids before use. It should also be noted that dried biosolids has poorer aesthetics than compost which makes it undesirable for use by the general public. Additionally, extra caution has to be given to its generation, storage, transport and application because it is ignitable. Dried biosolids can pose a fire risk with its storage which requires it to be properly stored. Additionally, equipment and components used to handled/ store dried biosolids in an enclosed environment must be XP (explosion proof). A cost analysis was performed for Scenario 2A1 (Alternative B) to determine an estimated unit cost for drying development of intended use biosolids. The following assumptions were included in the analysis: 1. utilize new dewatered biosolids conveyor to divert/ convey dewatered biosolids from dewatering facility to a new 8,000 square ft dryer facility Figure 5.9 – Municipal Biosolids Dryer Example 1 Image found at https://www.komline.com/products/biosolids-sludge-dryer/ on November 10, 2021
Page 226 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 5.10 – Municipal Biosolids Dryer Example 2 Image found at https://vulcandryingsystems.com/application/municipal-biosolids-processing/ on November 10, 2021 2. dryer uses an estimated 750 kWh per ton of water removed from dewatered biosolids with electrical cost of $0.06/ kWh, 3. utilize new dried biosolids conveyor to convey dried biosolids from dryer facility to 20 CY covered biosolids trailer or to a new XP rated 5,000 square ft dried biosolids storage facility, biosolids to be piled in 6 ft high piles, providing 45 days of storage capacity, 4. utilize a new XP rated front end loader and operator to handle (spread, move, re-load) dried biosolids at the new covered storage facility, 5. utilize a new 20 CY covered biosolids trailer, heavy haul tractor and driver to deliver dewatered solids from Davidson Dr. WWTP to the agriculturally intended use sites located in Hot Springs County, approximately 50 miles round trip, at 35 miles per hour, 0.75 hours load time, 0.5 unload time, 6. and utilize a new loading conveyor, farm tractor, spreader, and operator to incorporate biosolids into intended use site. Scenario 2A1 (Alternative B) includes the purchasing of the identified equipment, electricity, fuel, labor, maintenance, and replacement of equipment was also included in this analysis.
Page 227 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Table 5.22 – Proposed Davidson Dr. Biosolids – Scenario 2A1 (Alternative B)– Drying Costs Analysis Dryer Annual Volume to Dryer @ 21% TS 17,191 wet-CY Annual Weight to Dryer @ 21% TS 15492 wet-ton Annual Volume to Dryer @ 90% TS 4011 wet-CY Annual Weight to Use Site @ 90% TS 3615 wet-ton Analysis Duration 20 years Total Capital Cost $15,159,360 Total Present Worth Cost $31,017,431 Estimated Handling and Use Costs $90 $/ wet-CY Estimated Handling and Use Costs $100 $/ wet-ton Cost per Dry Ton @ 21% TS $476.71 $/ dry-ton 5.2.3.4.2 COMPOSTING Composting process occurs through utilizing of different approaches, for the purposes of this section, the two compared technologies are windrow only (Windrow) and a hybrid approach utilizing rotary drum first then windrow for finishing (Rotary Drum/ Windrow). This approached achieve Class A biosolids to permit unrestricted use. Compost aesthetically also is a desirable product for the general public’s use. A cost analysis was performed for Scenario 2A1 to determine an estimated unit cost for compost development (Windrow) of intended use biosolids. The following assumptions were included in the analysis: 1. utilize a new 20 CY covered biosolids trailer, heavy haul tractor and driver to deliver dewatered biosolids from Davidson Dr. WWTP to the Composting Facility, 2. provide new dewatered covered storage to be provided at the existing Composting Facility that provides ~45 days of storage through two (2) covered, 11,000 square ft x 2.5 ft deep, with a total storage capacity of 55,000 ft3 (~2000 CY < 2,222 CY permitted storage), depending on environmental conditions, dewatered biosolids can be utilize immediately (desirable) to create a windrow, 3. utilize an existing front-end loader and operator to handle (spread, move, make windrows) dewatered biosolids at the new covered storage facility,
Page 228 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 5.11 – Compost Windrow Turner Example Image found at https://www.wateronline.com/doc/evolving-from-controlled-biosolids-distribution-to-revenue-generating-compost-0001 on November 10, 2021 4. utilize existing equipment to generate bulking material (wood chips), same recipe to make windrows and turning of windrow approach, assumes bulking material input is not limiting for the generation of windrows, 5. provide new 3.55-acre windrow impervious area for making of additional windrows,
Page 229 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Table 5.23 - Proposed Davidson Dr. Biosolids – Scenario 2A1 – Compost (Windrow) Impervious Area Calculations Composting Annual Volume to Compost @ 21% TS 17,191 wet-CY Available Storage (at any instant) 2222 wet CY Total Annual Processing Capacity 14,969 wet CY Existing Windrow Average Turn Around Period 35 days Proposed Windrow Average Turn Around Period 45 days Volume of Biosolids Per Windrow 240 wet CY Annual Number of Windrows 8.91 Annual Windrows/ Acre Impervious Total Impervious Area Needed 9.00 Acres 2019 Total Impervious Area 5.16 Acres Additional Impervious Area Needed 3.84 Acres 6. windrow turn around period extended from 35 days to 45 days to account for decrease in VS, 7. separate compost from bulking material, utilize existing covered area for covered compost storage, 8. and continue to provide finished compost to customers for intended use, utilize existing front-end loader to load customer. Scenario 2A1 includes the purchasing of the identified equipment, fuel, labor, maintenance, and replacement of equipment was also included in this analysis.
Page 230 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Table 5.24 - Proposed Davidson Dr. Biosolids – Scenario 2A1 – Composting (Windrow) Costs Analysis Compost (Windrow) Annual Volume to Compost @ 21% TS 17,191 wet-CY Annual Weight to Compost @ 21% TS 15,492 wet-ton Analysis Duration 20 years Total Capital Cost $7,022,160 Total Present Worth Cost $39,885,587 Estimated Handling and Use Costs $116 $/ wet-CY Estimated Handling and Use Costs $129 $/ wet-ton Cost per Dry Ton @ 21% TS $613.01 $/ dry-ton A cost analysis was performed for Scenario 2A1 to determine an estimated unit cost for compost development (Rotary Drum/ Windrow) of intended use biosolids. The following assumptions were included in the analysis: 1. utilize a new 20 CY covered biosolids trailer, heavy haul tractor and driver to deliver dewatered biosolids from Davidson Dr. WWTP to the Composting Facility, 2. provide new dewatered covered storage to be provided at the existing Composting Facility that provides ~30 days of storage through two (2) covered, 7333 square ft x 2.5 ft deep, with a total storage capacity of 36,300 ft3 (~1320 CY < 2,222 CY permitted storage), total facility size to be approximately 20,000 square ft, depending on environmental conditions, dewatered biosolids can be utilize immediately (desirable) to be loaded into rotary drum to be mixed with bulking material, 3. utilize an existing front-end loader and operator to handle (spread, move, load rotary drum, unload, et al.) dewatered biosolids at the new covered storage facility, 4. utilize covered storage area (~ 5000 square ft) for placement of 7 new rotary drum composters, utilize existing equipment to generate bulking material (wood chips), similar recipe to make windrows, assumes bulking material input is not limiting for the use in rotary drum,
Page 231 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 5.12 – Rotary Drum In-Vessel Compost Example Image found at https://xactsystemscomposting.com/ on November 10, 2021 5. utilize similar recipe to make windrows and turning of windrow approach, assumes bulking material input is not limiting for the generation of windrows, for finishing of compost,
Page 232 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Table 5.25 - Proposed Davidson Dr. Biosolids – Scenario 2A1 – Compost (Rotary Drum/ Windrow) Impervious Area Calculations Composting (Rotary Drum/ Windrow) Annual Volume to Compost @ 21% TS 17,191 wet-CY Available Storage (at any instant) 2,222 wet CY Total Annual Processing Capacity 14,969 wet CY Rotary Drum Compost Capacity 35 CY Rotary Drum Compost Average Turn Around Period 6 days Total Annual Rotary Drum Processing Capacity 2,000 CY/ unit Total Number of Rotary Drum Composting Units 7 units Existing Windrow Average Turn Around Period 35 days Proposed Windrow Average Turn Around Period for Finishing 24 days Volume of Biosolids Per Windrow 240 wet CY Annual Number of Windrows 8.91 Annual Windrows/ Acre Impervious Total Impervious Area Needed 4.80 Acres 2019 Total Impervious Area 5.16 Acres Additional Impervious Area Needed 0.00 Acres This approach does not require any additional impervious area. 6. windrow turn around period reduced from 35 days to 24 days to account for use of rotary drum composters, 7. separate compost from bulking material, utilize existing covered area for covered compost storage, 8. and continue to provide finished compost to customers for intended use, utilize existing front-end loader to load customer. Scenario 2A1 includes the purchasing of the identified equipment, fuel, labor, maintenance, and replacement of equipment was also included in this analysis.
Page 233 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Table 5.26 - Proposed Davidson Dr. Biosolids – Scenario 2A1 – Composting (Rotary Drum/ Windrow) Costs Analysis Compost - Rotary Drum/ Windrow Annual Volume to Compost @ 21% TS 17,191 wet-CY Annual Weight to Compost @ 21% TS 15,492 wet-ton Analysis Duration 20 years Total Capital Cost $10,153,200 Total Present Worth Cost $44,897,283 Estimated Handling and Use Costs $131 $/ wet-CY Estimated Handling and Use Costs $145 $/ wet-ton Cost per Dry Ton @ 21% TS $690.04 $/ dry-ton
Page 234 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.3.5 SCENARIO 2A1 (ALTERNATIVE C) Scenario 2A1 (Alternative C) improvements at Davidson Dr. WWTP include the following: Scenario 1 (Near-Term Improvements CIP) 1.20 Process elimination of: a. lime feed for supplementary alkalinity b. primary clarification and production of primary sludge c. anaerobic digestion 1.21 Addition of magnesium hydroxide for supplemental alkalinity 1.22 Upgrade/ increase airflow rates to aeration basin 1.23 Additional 100 ft secondary clarifier a. Increase total surface 7,854 ft2 (total = 36,970 ft2) 1.24 New tertiary filtration 1.25 WAS directly to existing dewatering (BFP) a. New WAS Pumping The proposed biosolids handling process (identified as Scenario 2) is a mid-term projected project and is represented to include the following proposed structural changes/ modifications to the Davidson Dr. WWTP, including those proposed in Scenario 1, represented in the simulation, as follow: Scenario 2 (Mid-Term CIP) 2.32 Addition of sodium aluminate to sequester of orthophosphate 2.33 Addition of aluminum chlorohydrate (ACH) to aid in coagulant/ sequester orthophosphate 2.34 New RAS Pumps 2.35 Modify piping to WAS directly to continuous thickening (centrifugal) a. Dewatering unit sized for ~250 GPM 2.36 Thickened WAS conveyed to aerated sludge storage no. 1 2.37 Aerobic Digester (Alternative C) a. Construct new aerobic digester basin with at least 1.2 MG capacity providing at least HRT = 15 days 2.38 Convey from aerobic digester (Alternative C) to aerated sludge storage 2 2.39 Aerated sludge storage no. 2 a. Conversion of gravity thickeners (x2) to aerated sludge storage 2.40 Convey from aerated sludge storage no. 2 to new dewatering(centrifugal) a. Dewatering unit sized for ~150 GPM at 2500 dry-lbs./hr. 2.41 New sidestream treatment system (suspended air flotation) a. Addition of sodium aluminate to sequester orthophosphate The proposed Scenario 2 modifications are planned to be completed as a mid-term CIP project.
Page 235 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Scenario 2A1 (Alternative C) includes proposed planned dewatering operation for 3 days per week with an operating duration of ~6 hours per day (total of 18 hours per week). The total hours per week is 168, therefore the non-dewatering operation per week is 150 hours. The primary difference between Scenario 2A1 and Scenario 2A1 (Alternative C) is the addition of the aerobic digester. As discussed, the addition of an aerobic digester will impede the anaerobic process necessary for luxury T-P uptake as well as increase the recycled T-P found within sidestreams. However, this process was evaluated and considered because of the necessity to achieve Class B prior to land application. The general influent parameters of Scenario 2A1 (Alternative C) are AD design flow rate (QAD) = 16 MGD (6.7% excess of the projected 2040 average daily influent flow) with the 2040 AD design influent parameters. The simplified process flow diagram and associated biosolids production values are presented in the following figure and table.
Page 236 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 5.13 – Proposed Davidson Dr. WWTP Simplified Process Flo Diges
6 of 291 prings, Arkansas | Crist Engineers, Inc. ow Diagram – Mid-Term – Scenario 2A1 (Alternative C) – Aerobic stion
Page 237 Wastewater System Master Plan (WWSMP) – Hot Sp Table 5.27 – Proposed Davidson Dr. WWTP Biosolids Production Aerobic D Intended Use Biosolids Mass/ Volume Drying Compo Design Annual Flow Rate 16 Design Annual Temperature 20 Biosolids Processing Scenario 2A1 – Alternative B - Mid to Long-Term Minimum WAS to Dewatering1 21,600 Design WAS to Dewatering 1 23,000 Maximum WAS to Dewatering1 29,050 Dewatering Performance 20 to 22.5 Minimum Dewatered Biosolids (EST.) 15,425 Design Dewatered Biosolids (EST.) 16,550 Maximum Dewatered Biosolids (EST.) 23,425 Dewatering Days Per Week 3.00 Dewatering Weeks per Year 52.00 Wet Sludge Weight (@ 21 % TS) 183,889 Wet Sludge Volume2 102.03 Design Annual Wet Sludge Weight (@ 21 % TS) 14,343 Design Annual Wet Sludge Volume2 15,917 Design Annual Total Phosphorus (T-P) Weight (@ 2.68 %) 161,892 1 Includes the ~900 lbs./ day of tertiary filter backwash solids and ~500 biosolids = 1.07.
7 of 291 prings, Arkansas | Crist Engineers, Inc. Planning Summary – Mid-Term – Scenario 2A1 (Alternative C) – Digestion Intended Disposal Units osting Land Application Landfill MGD oC m (i.e., WAS to Thickening to Aerobic Digester to Dewatering) dry lbs./ day % TS dry lbs./ day days weeks wet lbs./ dewatering day cubic yards (CY)/ dewatering day tons/ year CY/ year dry lbs./ year 0 lbs./ day of SWWWTP hauled biosolids. 2 Specific gravity of the
Page 238 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. As shown in Scenario 2A1 (Alternative C), the total estimated amount of biosolids produced from WAS activities are between 21,600 to 29,050 dry-lbs. per day with the estimated amount of dewatered biosolids being between 15,425 to 23,425 dry-lbs./ day. At an estimated performance of 21% total solids this equates to a total estimated wet sludge of 183,889 lbs./ dewatering day or a volume of approximately 102 CY/ dewatering day. 5.2.3.5.1 LAND APPLICATION As discussed, land application of biosolids must meet stabilization requirements (i.e., Class B biosolids), and compliance with EPA 40 CFR Part 503, specific heavy metal requirements. Generally, municipal wastewater with minimal industrial influences does not have challenges with achieving compliance with heavy metals. Also, for facilities of this magnitude, can generally achieve VAR and pathogen requirements after 15 days utilizing SOUR compliance. Generally, the limiting factor for application of biosolids is T-P. Facilities that perform luxury phosphorus uptake or chemical phosphorus removal create a biosolids stream that is relatively high in T-P. Aerobic digestion further exacerbates the issue because of the removal of nitrogen through endogenous nitrification (and/ denitrification, when applicable) by creating soluble nitrate that is recycled back to the wastewater treatment plant through thickening, decanting or dewatering activities. Predominantly, nitrate is removed in an aerobic digester through endogenous denitrification, thus removing nitrogen as nitrogen gas. However, independent of how the endogenous nitrification/ nitrate is handled within the biosolids processing side, it generally does not end up in the dewatered biosolid. Therefore, biosolids generated from nutrient removal facilities that contain aerobic digesters have a relatively low nitrogen content. This ultimately creates a biosolids that does not follow the traditional carbon to nitrogen to phosphorus ratio (i.e., 100 T-C:10 T-N:1 T-P). Agricultural practices typically like to use fertilizers with a high nitrogen to phosphorus level. As an example, see Figure 5.14 for the nitrogen uptake for corn, the most agriculturally produce crop in the US.
Page 239 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Figure 5.14 – Agricultural Corn T-N Uptake Example Image found at https://www.conservfs.com/products-services/resource-center/item/post-applied-nitrogen-timing-should-be-synchronized-with-nuptake-for-corn on November 10, 2021 The purpose of the example is to demonstrate the amount of nitrogen required to grow corn per acre. Traditionally, agricultural managers will utilize the lowest cost form of fertilizer that they can obtain. If municipal biosolids were high in nitrogen, it could easily be disposed of onto agricultural fields because it would be a low-cost form of nitrogen fertilizer, but it is the exact opposite. Because municipal biosolids are relatively low in T-N, specifically ammonia, but high in T-P, agricultural managers are disincentivize to utilize it for fertilizer. When T-P removal is employed as required by discharge permit, it further limits it use on most agricultural crops. However, it could still be used for an application site used for grazing of animals. As discussed, grazing of land owned by the utility is the simplest approach to land application of biosolids. This approach allows for the utility to properly control the land application site to ensure all permit requirements are met. It also ensures that the utility has a disposal location available for a given planning period. It also affords the opportunity of the utility to generate positive public reaction by leasing of grazing rights to various agricultural operations based on public bid or at reduced cost. As discussed, grazing animals are not allowed on the land application site until after 30 days from biosolids incorporation. Additionally, biosolids are not allowed to be applied on wet or frozen ground. Typically, at least 45 days’ worth of biosolids storage is provided or the utility must identify an alternative method for disposal approach.
Page 240 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Under this scenario, it is recommended that 45 days of covered storage be provided at the Davidson Dr. composting facility and maintain the permitting capability to dispose of biosolids into a Class 1 landfill. This approach has predominately three main advantages: 1. provides for covered storage of stabilizes biosolids thus eliminating the need for landfill disposal during normal wet/ cold periods, 2. provides an opportunity for the biosolids to further dewatered (i.e., pan evaporation) to increase the TS from 21% to 28%, thus minimizing the wet-hauled volume/ mass by ~25%, 3. and maintains the ability to divert and dispose of biosolids into a Class 1 landfill during periods of excessive cold or wet (i.e., when longer than 45 days). Grazing of animals also for the use of alfalfa for agronomic application rates. Alfalfa has one of the highest T-P uptakes of any crop, thus maximizing the agronomic application which reduces the necessary required land. The Missouri Phosphorus Biosolids Best Management Practices, a common resource used by most land application sites that have biosolids with high concentrations of T-P, is used to identifies quantity land needed for biosolids application. The amount of land needed for land application is presented in Table 5.28. Table 5.28 – Proposed Davidson Dr. WWTP Biosolids Land Application Area Land Application (T-P Limited) Initial T-P Soil Load 375 dry-lbs. per acre Alfalfa Utilization 75 dry-lbs. TP per Year Missouri BMP Max Load 600 dry-lbs. per acre (every 5 years) Total Turn Around Period 8.00 Years Total Land Needed 2159 Acres Usability Factor 1.15 Total Land Needed 2483 Acres The above table utilizes a maximum load of 600 lbs. T-P/ acre-5 years. Therefore, that same area must be fallowed from biosolids application for 3 years until the T-P is utilized for Alfalfa uptake which equates to a total turn around period of 8 years. A usability factor of 1.15 was identified to account for offsets from adjacent landowners, streams, rivers, wells, land in excess of 6% slope, inaccessible property, roads, et al. This analysis does not include heavy metals analysis because the concentration of metals is highly site specific, however, it does imply that at some point, soil heavy metal concentration will eliminate the permitted land application sites. Essentially, because of heavy metals, a land application site has an expiration date where it can no longer be used for biosolids application.
Page 241 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Traditionally, however, it does not eliminate the property from being sold or permitted for alternative uses. Therefore, the value of the property could be recovered after its use. Additionally, because of recent development with PFAS and PFOA being found within certain municipal wastewaters, it has become even more restrictive to utilize municipal biosolids in land application. Careful considerations to the land application site and biosolids testing should be conducted before selection of the land application biosolids disposal strategy. A cost analysis was performed for Scenario 2A1 (Alternative C) to determine an estimated unit cost for land application disposal. The following assumptions were included in the analysis: 9. provide for a new 1.2 MG aerobic digester with additional 400 HP aeration capacity, 10. utilize a new 20 CY covered biosolids trailer, heavy haul tractor and driver to deliver dewatered biosolids from Davidson Dr. WWTP to the Composting Facility, 11. provide new dewatered covered storage to be provided at the existing Composting Facility that provides ~45 days’ worth of storage through two (2) covered, ~11,000 square ft x 2.5 ft deep, with a total storage capacity of ~55,000 ft3 (~1,800 CY < 2,222 CY permitted storage), 12. utilize a new front-end loader and operator to handle (spread, move, re-load) dewatered biosolids at the new covered storage facility, Figure 5.15 – Front End Loader Example Image found at https://cat-engines.blogspot.com/2020/04/cat-front-end-loader-world-class.html on November 10, 2021
Page 242 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 13. utilize a new 20 CY covered biosolids trailer, heavy haul tractor and driver to deliver dewatered biosolids from the Composting Facility to the land application site located in Hot Springs County, approximately 50 miles round trip, at 35 miles per hour, 0.75 hours load time, 0.5 unload time, 14. and utilize a new loading conveyor, farm tractor, spreader, and operator to incorporate biosolids into land application site. Figure 5.16 – Biosolids Loading Conveyor, Farm Tractor and Spreader Example Image found at http://www.hangingtenranch.com/biosolids-use-in-boulder-county/ on November 10, 2021 Scenario 2A1 (Alternative C) also includes the purchasing of the identified equipment and ~2500 acres of property at $2000/ acre. Fuel, labor, maintenance, and replacement of equipment was also included in this analysis.
Page 243 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Table 5.29 – Proposed Davidson Dr. Biosolids – Scenario 2A1 (Alternative C) – Land Application Costs Analysis Land Application Annual Volume to Sludge Storage @ 21% TS 15,917 wet-CY Annual Weight to Sludge Storage @ 21% TS 14,343 wet-ton Annual Volume to Land Application Site @ 28% TS 11,609 wet-CY Annual Weight to Land Application Site @ 28% TS 10,461 wet-ton Analysis Duration 20 years Total Capital Cost $19,940,400 Total Present Worth Cost $31,559,299 Estimated Handling and Disposal Costs $99 $/ wet-CY Estimated Handling and Disposal Costs $110 $/ wet-ton Cost per Dry Ton @ 21% TS $523.88 $/ dry-ton 5.2.3.5.2 LANDFILL Near-term CIP improvements are included for the disposal of unclassified biosolids. As discussed, disposal of unclassified biosolids into a Class 1 landfill has the advantages that it is already permitted, requires minimal capital investment, and provides for sequestration of T-P. A cost analysis was performed for Scenario 2A1 to determine an estimated unit cost for landfill disposal. The following assumptions were included in the analysis: 1. provide two (2) 20 CY covered biosolids trailers, one (1) heavy haul tractor and driver to deliver dewatered biosolids from Davidson Dr. WWTP to the Landfill located in Saline County, approximately 80 miles round trip, at 40 miles per hour, 0.5 hours load time, 0.5 unload time two trailers allow for biosolids to continuously be processed and filled while trip to landfill occurs. Scenario 2A1 includes the purchasing of the identified equipment, fuel, labor, maintenance, and replacement of equipment was also included in this analysis.
Page 244 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. Table 5.30 – Proposed Davidson Dr. Biosolids – Scenario 2A1 – Landfill Costs Analysis Landfill Annual Volume to Landfill @ 21% TS 17,191 wet-CY Annual Weight to Landfill @ 21% TS 15,492 wet-ton Analysis Duration 20 years Total Capital Cost $352,500 Total Present Worth Cost $24,103,486 Estimated Handling and Disposal Costs $70 $/ wet-CY Estimated Handling and Disposal Costs $78 $/ wetton Cost per Dry Ton @ 21% TS $370.45 $/ dryton Average Annual Cost $1,205,174 As shown in Table 5.31, Landfill is the lowest cost option with an average disposal cost approximately 22% lower than the next lowest cost option. Landfill disposal of unclassified biosolids requires the lowest capital cost investment and is the simplest to operate. Table 5.31 – Proposed Davidson Dr. WWTP Biosolids Estimated Cost Unit Quick Summary Intended Use Intended Disposal Units Drying Composting - Windrow Land Application Landfill Scenario 2 $476.71 $613.01 $523.88 $370.45 $/ dry-ton Cost Ranking 2 4 3 1
Page 245 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. 5.2.3.6 SCENARIO 3A As discussion in other sections, interest was placed on investigation of processes beyond the planning period (i.e., MA Influent Flow Rate - Qi >16 MGD, i.e., 24 MGD). Preliminary modeling investigations were conducted on the use of integrated fixed-film activated sludge (IFAS) within the existing boundary of the wastewater treatment plant (i.e., using the existing aeration basins, with additional clarification). The permit effluent limits are suspected that they would approach similar levels as identified within the current planning period. IFAS uses synthetic media either fluid suspended in the basin or fixed to allow for a place for biological growth to affix to (i.e., biomass) within an aeration basin. IFAS essentially allows for biomass to concentrate to a higher concentration (i.e., more bugs) to facilitate the treatment of additional loading (cBOD, NH3, etc.) within the same volume of aeration basin. The fixed film will sluff off Scenario 3 builds and replaces components from Scenario 1A and 2A through the addition of IFAS, anaerobic selector basins. Presented below is the near-term improvements CIP summary: Scenario 1 (Near-Term Improvements CIP) 1.8 Process elimination of: a. lime feed for supplementary alkalinity b. primary clarification and production of primary sludge c. anaerobic digestion 1.9 Addition of magnesium hydroxide for supplemental alkalinity 1.10 Upgrade/ increase airflow rates to aeration basin 1.11 Additional 100 ft secondary clarifier a. Increase total surface 7,854 ft2 (total = 36,970 ft2) 1.12 New tertiary filtration 1.13 WAS directly to existing dewatering (BFP) (strike through indicates modifications from previous scenarios) a. New WAS Pumping Scenario 2 (Mid-Term CIP) 2.11 Addition of sodium aluminate to sequester of orthophosphate 2.12 Addition of aluminum chlorohydrate (ACH) to aid in coagulant/ sequester orthophosphate 2.13 New RAS Pumps 2.14 Modify piping to WAS directly to continuous thickening (centrifugal) a. Dewatering unit sized for ~250 GPM 2.15 Thickened WAS conveyed to aerated sludge storage no. 1 2.16 Aerated sludge storage no. 1 a. Conversion of one (1) primary clarifier basin to aerated sludge storage 2.17 Convey from aerated sludge storage no. 1 to aerated sludge storage 2 2.18 Aerated sludge storage no. 2
Page 246 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. a. Conversion of gravity thickeners (x2) to aerated sludge storage 2.19 Convey from aerated sludge storage no. 2 to new dewatering(centrifugal) a. Dewatering unit sized for ~150 GPM at 2500 dry-lbs./hr. 2.20 New sidestream treatment system (suspended air flotation) a. Addition of sodium aluminate to sequester orthophosphate Scenario 3 (Beyond Planning Period, Long-Term CIP) 3.15 Add additional headworks processes (physical unit processes) a. Additional screening b. Additional grit removal 3.16 Addition of anaerobic selector basins a. Additional conveyance piping/ splitter/ junction boxes b. Conversion of two (2) primary clarifier basin to anaerobic selectors 3.17 Conversion of existing anoxic basin to aerated/ mixed basin a. To be used as a swing basin b. Add new coarse air diffusers 3.18 Internal recycle pumping and conveyance piping a. ~96 MGD capacity (400%Qi) 3.19 Blower and aeration capacity increase up to 27,000 SCFM a. New blowers to accommodate additional aeration requirements b. New coarse bubble diffusers 3.20 IFAS aeration basin a. Addition of IFAS media b. New aeration laterals from new blowers c. Coarse bubble diffusers d. Modify RAS piping, add additional piping to convey RAS to anaerobic selection basins e. New RAS/ WAS pumping station (expand RAS Pumping) 3.21 WAS directly to continuous thickening (centrifugal), add additional thickening a. Each dewatering unit sized for ~250 GPM (total = 500 GPM) 3.22 Additional 100 ft secondary clarifier (x5) a. Increase total surface 39,270 ft2 (total = 76240 ft2) b. Additional conveyance piping/ splitter/ junction boxes 3.23 Additional tertiary filter (x1) a. Increase total tertiary filtration capacity by 48 MGD (total = 96 MGD) 3.24 Thickened WAS conveyed to aerated sludge storage no. 1 a. Increase aeration/ mixing capacity 3.25 Convey from aerated sludge storage no. 1 to aerated sludge storage 2 a. Increase TWAS pumping capacity 3.26 Aerated sludge storage no. 2 a. Increase aeration/ mixing capacity 3.27 Convey from aerated sludge storage no. 2 to new dewatering(centrifugal), add additional dewatering unit
Page 247 of 291 Wastewater System Master Plan (WWSMP) – Hot Springs, Arkansas | Crist Engineers, Inc. a. Dewatering unit sized for ~150 GPM at 2500 dry-lbs./hr. (total = 300 GPM at 5000 dry-lbs./hr. 3.28 New sidestream treatment system (suspended air flotation), add additional unit The proposed Scenario 3A modifications are planned to be completed as long-term CIP project. Scenario 3A is also represented to include the following operational changes/ modifications to the Davidson Dr. WWTP, represented in the simulation as follows (Influent Flow Rate - Qi = 24 MGD) with the 2040 DA design influent parameters:
Page 24 Wastewater System Master Plan (WWSMP) – Hot Sp Figure 5.17 – Proposed Davidson Dr. WWTP Biosolids Productio Scena
8 of 291 prings, Arkansas | Crist Engineers, Inc. on Planning Summary – Beyond Planning Period – Long-Term – rio 3A
Page 249 Wastewater System Master Plan (WWSMP) – Hot Sp Table 5.32 – Proposed Davidson Dr. WWTP Biosolids Productio Scena Intended Use Biosolids Mass/ Volume Drying Comp Design Annual Flow Rate 16 Design Annual Temperature 20 Biosolids Processing Scenario 3A – Beyond Planning Period – Long-Ter New Dewatering) Minimum WAS to Dewatering1 34,365 Design WAS to Dewatering 1 36,200 Maximum WAS to Dewatering1 39,100 Dewatering Performance 22 to 23 % Minimum Dewatered Biosolids 25,300 Design Dewatered Biosolids 27,050 Maximum Dewatered Biosolids 30,000 Dewatering Days Per Week 3.00 Dewatering Weeks per Year 52.00 Wet Sludge Weight (@ 23 % TS) 274,420 Wet Sludge Volume2 152.27 Design Annual Wet Sludge Weight (@ 23 % TS) 21,405 Design Annual Wet Sludge Volume2 23,753 1Includes the ~1000 lbs./ day of tertiary filter backwash solids and ~500 lbs./ day of SWW