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Environmental Business Specialists, LLC * 1930 Surgi Dr., Mandeville, LA 70448 *www.ebsbiowizard.com * 985-674-0660

System Evaluation: Depth Survey, Performance Profile, and

Tracer Study Project Synopsis

Environmental Business Specialists (EBS) was requested to conduct a comprehensive evaluation of the Aerated Stabilization Basin (ASB). The purpose of this study was to determine the retention time of the basin and to identify performance and/or loading trends that signal system deterioration and increased potential for wastewater compliance issues. The main components of the evaluation included a depth survey to determine the current depth and volume, a tracer study for retention time and flow pattern determination, and a performance profile to provide a snapshot of the basin during the sampling period.

The wastewater treatment system consists of a primary clarifier followed by a 39 acre ASB (Figure 1). Influent to the ASB is introduced via three pipes (west, central, and east) at the north end of the basin. Currently, the eastern influent is closed. The ASB is divided into 5 Zones separated by baffles and contains a total of 29 - 75 hp aerators. Effluent from the ASB flows into a 560-acre holding pond before being discharged.

Project Outline The depth survey portion of the project was completed using an electronic sonar and GPS device. 6,402

depth measurements were taken throughout the ASB, from the sludge layer to the water's surface.

The tracer study was initiated with the introduction of two - 55 gallon drums of 40% Lithium Chloride Brine (approximately 80 lbs. of lithium) to the outer ring of the primary clarifier. Automated samplers were set up at the ASB effluent and samples were collected for three times the theoretical retention time. In addition to the samples collected at the ASB effluent, lithium profile samples were collected throughout the basin at five and twenty-four hours after the tracer study was initiated. The data collected from the lithium profile sampling is used to determine flow patterns throughout the basin. All lithium samples were analyzed by A&E Testing in Baton Rouge, LA using atomic emission spectroscopy. The resulting data were analyzed per the NCASI Bulletin 408.

During the lithium profile sampling, a performance profile was conducted. Eighteen samples were collected at various locations throughout the ASB in addition to an influent and effluent sample. These samples were analyzed for soluble and total biochemical oxygen demand (BOD5), soluble and total chemical oxygen demand (COD), total suspended solids (TSS), volatile suspended solids (VSS), nutrient residuals (nitrogen and phosphorus), dissolved oxygen uptake rate (DOUR), and sulfides. Direct readings were taken at each sampling location for temperature, pH, dissolved oxygen (DO), and oxidation-reduction potential (ORP).

System Evaluation: Depth Study, Performance Profile, and Tracer Study 2

Environmental Business Specialists, LLC • 1930 Surgi Dr., Mandeville, LA 70448 • www.ebsbiowizard.com • 985-674-0660

Figure 1: Aerial view of the Aerated Stabilization Basin



Contents I. Depth Survey ....................................................... 4

II. Performance Profile ............................................ 7 III. Tracer Study ........................................................ 24 IV. Appendix A: Analytical Methods ........................ 29

Key Findings

• Current volume of the ASB is 39.7 MG o 2015 ASB volume: 41.6 MG

• Theoretical retention time of the ASB based on the depth survey and average flow rate of 13.4

MGD is 3.0 days

• Calculated retention time of the ASB based on the tracer study is 2.9 days. o Lithium was initially detected at the ASB effluent in 8 hours, with a peak concentration

detected at 1.6 days. In the event of an upset, the higher loading is expected to follow this same pattern

• Based on the performance profile, the ASB removed 88.6% total BOD5 and 95.7% of the soluble

BOD5 entering the system o This equates to 53,084 lbs/day of total and 39,338 lbs/day of soluble BOD5 removed at a

flow rate of 13.4 MGD o Based on the available aeration, the system should theoretically remove 65,250 lbs/day of BOD5

as long as all other growth pressures are met

• Aerator placement throughout the basin is not ideal. This limits the utilization of available aeration and allows solids to build up in areas where sufficient mixing is not present

o Mathematically there is enough mixing energy to keep solids suspended but the zones of aeration overlap thus reducing the effectiveness of the available aeration

o Aerator configuration is of additional importance after dredging. In areas with insufficient mixing, solids will continue to settle out and accumulate in the basin, reducing the amount of volume available for treatment

• Oxygen deficiency in the basin is limiting treatment o Dissolved oxygen concentrations were less than 1 mg/L in Zones 1-3 and Zone 5 o Dissolved oxygen uptake rates indicate complete treatment does not occur



Depth Survey During the survey, the ASB pond level was 2" above the surface of the catwalk grating located at the ASB

effluent. A total of 6,028 readings were used to calculate the volumes and average depths shown below in Table 1. Also, shown in Table 1 are the results from the 2015 depth survey normalized to the 2016 pond level for comparison purposes. During the 2015 study the pond level was 0” above the surface of the catwalk grating located at the ASB effluent.

Figure 2 is a contour map depicting the ASB's current bathymetry. Figure 3 shows the same contour map next to a map created from the normalized 2015 data for comparison.

Table 1: Depth survey results

Area (Acres)

Average Depth (ft.)

Volume (MG) Change in

Volume (MG) 2015 Normalized 2016 2015

Normalized 2016

Zone 1 3.6 6.1 5.7 7.1 6.7 -0.40

Zone 2 4.1 5.7 6.2 7.6 8.3 +0.70

Zone 3 6.7 5.3 5.3 11.7 11.6 -0.10

Zone 4 6.0 3.1 3.2 6.0 6.2 +0.20

Zone 5 18.3 1.5 1.2 9.2 6.9 -2.30

Total ASB 38.7 3.3 3.1 41.6 39.7 -1.90



Figure 2: 2016 ASB bathymetry



Figure 3: 2015 (normalized) and 2016 ASB bathymetry

System Evaluation: Depth Survey, Performance Profile, and Tracer Study 7


Performance Profile The performance profile sampling included eighteen samples within the basin, along with an ASB influent

and the ASB effluent; Figure 4. Direct field readings were collected using an In-Situ SmarTroll at each site; parameters measured were pH, temperature, dissolved oxygen concentration, and oxidation-reduction potential; Table 2. Water samples were tested for dissolved oxygen uptake rate (DOUR) and sulfides the day of sampling, and were then shipped to the EBS lab to be analyzed for soluble and total BOD5, soluble and total COD, total suspended solids, volatile suspended solids, and nutrient residuals; Table 3. Each parameter measured during the profile study would be plotted on a graph of the ASB similar to Figure 4.

Temperatures in the ASB ranged from 30.5-38.4 °C. The data collected from the Troll is shown at the appropriate sample location. For a typical ASB, optimal bacterial growth occurs within a temperature range of 20-35 °C. Different types of bacteria can acclimate and still thrive at temperatures slightly warmer than this range, but even high temperature bacteria cannot survive in temperatures above 45 °C.

Areas of high bacterial activity are characterized by high dissolved oxygen uptake rates (DOURs) and low dissolved oxygen (DO) levels. As activity slows and the oxygen demand in the basin decreases, DO residuals tend to increase and DOUR values decrease. The DO data collected shows the system generally follows the increasing pattern from Zone 1 to Zone 4 with concentrations above 2 mg/L starting in Zone 4. DO concentrations experienced a sharp decrease in the settling zone of Zone 5 due to the lack of aeration.

The DOUR values (Figure 5) remained elevated throughout the majority of the basin. Based on the DOUR values, complete treatment did not occur in the basin as some soluble BOD5 is going through the system untreated. A DOUR of 3 mg/L/hr typically indicates complete treatment. Sufficient treatment doesn’t take place in the system due to growth pressure limitations such as retention time and available oxygen.

Another variable to consider when looking at DO and DOUR data is the presence of sulfides. The sulfide data indicates that the highest concentrations are seen in Zone 2. Sulfide concentrations become negligible after the first baffle. Sulfides act as oxygen scavengers which drive down DO and increase DOURs. This combined with biological activity resulted in very low DO concentrations and elevated DOURs.

When DO concentrations fall below 0.5 mg/L, the oxidation-reduction potential (ORP) becomes a more reliable parameter to measure and determine metabolic conditions within a system. The ORP values found in Zones 1 - 3, and the unaerated portion of Zone 5 indicate anaerobic conditions, while Zone 4 through the first half of Zone 5 indicate anoxic conditions.

The optimal pH range for an ASB is 6.5-8.5. The pH within the basin averaged 7.87, with a minimum of 7.21 and a maximum of 8.18.

Nutrient concentrations, primarily nitrogen in the form of ammonia and phosphorus in the form of orthophosphate, are vital to overall bacterial health, their ability to reproduce, and their ability to treat BOD5. The typical ASB target range for these nutrients is 0.1-0.3 mg/L. Figure 6 includes the ammonia and orthophosphate data. The ammonia concentrations were high throughout the basin; with a minimum of 1.34 mg/L and a maximum of 4.64 mg/L. Orthophosphate concentrations were within the target range with the exception of Sample #7.

System Evaluation: Depth survey, Performance Profile, and Tracer Study 8


Percent volatile suspended solids (VSS) in ASB’s are typically 70-90% organic. Any non-biodegradable particulate matter that enters the ASB will settle out and reduce system capacity. 86% of the solids in the basin are organic and degradable.

Biochemical oxygen demand (BOD5) represents the amount of organic material present that can be degraded and converted to biomass by the bacteria in the system. The standard BOD5 test measures the amount of dissolved oxygen required by the bacteria to break down the organic material over a five-day period. Soluble BOD5 concentrations (Figure 7) were greater than 20 mg/L until the end of Zone 4. Taking into account the performance profile is a snapshot of the ASB’s biological activity, the data indicated 88.6% of the total BOD5 was being removed by the effluent. Of that percentage removed, 95.7% was soluble BOD5. In terms of a removal rate in pounds of BOD5 per day, the basin removed 53,084 lbs of total BOD5 and 39,338 lbs of soluble BOD5. At the effluent, total BOD5 was composed of 26.2% soluble BOD5. Historical total BOD5 concentrations (01/01/16-07/22/16) averaged 37,511 lbs/day at the lift station and 8,329 lbs/day at the ASB outlet. The average removal during that time period was 29,182 lbs/day or 77.8%. Based on an average of 30 lbs. of BOD5 removed per horsepower of aeration, the current system set up should be able to remove 65,250 lbs/day of BOD5. The difference between the theoretical and historical BOD5 removal rate is due to growth pressure limitations – primarily dissolved oxygen deficiency and short retention time.

The system includes twenty-nine 75-hp aerators or 2,175 total hp of aeration currently in operation. There is enough mixing energy to keep solids in suspension (minimum of 14 hp of aeration/MG of volume), but the aerator placement is limiting the benefits this level of aeration could provide. Less than optimal aerator placement can limit treatment and allow solids to build up in areas where sufficient mixing is not present. This becomes particularly important after dredging, as those areas will continue to accumulate solids if sufficient mixing is not met.



Figure 4: Profile study sample locations



Table 2: Field Readings

Sample

ID Temperature

(°C) pH

(SU) D.O.

(mg/L) ORP (mV)

Influent

1 35.6 7.85 0.06 -286.0

2 36.5 7.93 0.03 -308.3

3 36.8 7.88 0.03 -281.8

4 37.5 7.92 0.03 -293.5

5 38.4 7.85 0.03 -288.7

6 37.5 7.76 0.02 -281.7

7 35.6 7.96 0.01 -302.2

8 35.1 7.95 0.01 -268.3

9 34.6 7.35 0.05 -385.0

10 34.7 7.21 0.08 -335.5

11 34.3 7.69 0.02 -296.0

12 33.3 8.00 3.81 -32.4

13 32.7 8.03 3.17 2.9

14 32.5 8.01 2.16 14.2

15 32.3 8.03 2.92 -24.6

16 31.6 8.18 4.82 14.7

17 31.2 8.09 3.83 -113.4

18 31.7 8.05 0.09 -141.6

Effluent



Table 3: Profile study data

Sample ID

NH3 as N (mg/L)

oPO4 as P (mg/L)

TSS (mg/L)

VSS (mg/L) %VSS

Soluble COD

(mg/L)

Total COD

(mg/L)

Soluble BOD

(mg/L)

Total BOD

(mg/L)

DOUR (mg/L/hr.)

Sulfides (mg/L)

Influent 6.42 0.50 330 275 83 1108 1582 368 536 25.0

1 4.52 0.18 490 410 84 562 114 4.6 0.1

2 4.64 0.24 650 570 88 621 119 8.5 2.2

3 4.44 0.26 1960 1580 81 597 131 7.8 3.6

4 4.56 0.24 3780 2860 76 632 133 8.1 11.2

5 4.27 0.20 2840 2220 78 775 188 7.3 19.2

6 3.37 0.40 500 400 80 586 147 5.6 6.0

7 2.55 0.04 450 390 87 486 87 5.7 0.1

8 1.82 0.10 520 440 85 507 . 68 8.6 1.1

9 1.49 0.18 410 370 90 451 68 9.1 0.2

10 2.10 0.14 480 440 92 495 74 6.3 0.2

11 1.34 0.10 490 440 90 423 42 5.2 0.1

12 1.92 0.18 380 340 89 544 27 5.4 0.0

13 2.27 0.12 340 320 94 405 21 6.3 0.0

14 2.21 0.14 453 393 87 419 19 5.1 0.0

15 2.78 0.10 427 360 84 394 19 5.5 0.0

16 3.31 0.16 467 393 84 389 19 2.4 0.0

17 3.26 0.18 420 347 83 388 19 4.0 0.0

18 4.05 0.26 260 245 94 389 18 4.1 0.0

Effluent 3.29 0.14 267 227 85 375 841 16 61 3.4 0.0



Figure 5 - Dissolved Oxygen Uptake Rate (mg/L/hr)



Figure 6 - Nutrients (mg/L) Ammonia in blue, Orthophosphate in green



Figure 7 - Soluble BOD5 (mg/L)



Tracer Study

The results from the tracer study (Table 4) provide a calculated retention time of 2.9 days. Lithium initially appeared at the ASB effluent in 8 hours and the highest concentration reached the effluent in 1.6 days. In the event of an upset, the higher loading is expected to follow this same pattern. Figure 8 shows the lithium concentrations collected at the ASB effluent throughout the study.

Table 4: Lithium tracer study results

Parameter or Value 2015 2016

Average flow during study (MGD) 15.2 13.4[1]

Basin volume (MG) 41.6 39.7

Theoretical retention time (Days) 2.7 3.0

Initial lithium appearance in sample (Hours) 4 8

10% Recovery of tracer (Days), t10 1.2 1.1



Peak concentration (Days) 2.0 1.6

Morrill index, t90/t10 4.7 5.1

Total tracer recovery 100% 83.3%

Calculated retention time (Days) 3.0 2.9

Basin utilization 110% 97.4%

Calculated retention time (Days) at 13.4 MGD 3.3 --

[1] Average flow during the study was calculated using the mill’s flow data.



Morrill index is a ratio of the 90% tracer recovery time to the 10% tracer recovery time, representing the deviation from pure plug flow characteristics. A Morrill index of 1 indicates pure plug flow and an index of 21.5 indicates complete mix. The Morrill index of 5.1 indicates that the system exhibits plug flow characteristics in the basin. Compared to the Morrill index of 4.7 in 2015, the flow patterns in the ASB have not changed significantly.

Basin utilization estimates how much of the basin's volume is being utilized for treatment; it's the calculated retention time divided by the theoretical retention time. A basin utilization value of 97.4% indicates that the system is utilizing the majority of the currently available volume. Dredging would be required in order to increase the retention time considering the current available volume is being utilized.

The five-hour lithium profile (Figure 9) shows the lithium is concentrated in Zone 1 and Zone 2. The highest concentrations were centered around the aerators between the western influent and central influent of Zone 2 and moving into Zone 3. The increased concentrations in those areas are due to flow being localized through the western and central influent and no flow entering the basin through the eastern influent. Concentrations decreased in Zone 3 with the higher concentrations in the zone being found along the southern zone baffle. Starting in Zone 4, all concentrations were below 0.026 mg/L throughout the remainder of the basin.

The twenty-four-hour lithium profile (Figure 10) shows lithium concentrations are well mixed and more evenly dispersed throughout the ASB. The highest concentrations were detected in Zones 3 and 4. Two data points in Zone 5 were less 0.075 mg/L indicating very little flow is reaching these two areas. As flow enters the settling zone in Zone 5 it is highly channelized due to solids accumulation, leaving a bulk of the zone under-utilized. The higher concentration located closer to the effluent, 0.136 mg/L to the west, is an area where an aerator was previously located and therefore has some available volume for flow to enter.



Figure 8 - Lithium concentrations at the ASB effluent over time (mg/L)

System Evaluation: Depth Survey, Performance Profile and Tracer Study 18


Figure 9 - Lithium concentrations (mg/L) 5 hours after introduction



Figure 10 - Lithium concentrations (mg/L) 24 hours after introduction

System Evaluation: Depth Survey, Performance Profile and Tracer Study 20


Appendix A: Analytical Methods

Type of Analysis Procedure Dissolved Oxygen Uptake Rate (DOUR)

Standard Methods 22nd edition, 2012, Method 2710 B (Revised)

Ammonia as Nitrogen Standard Methods 22nd edition, 2012, Method 4500 NH3-D

Orthophosphate as Phosphorus Hach DR 4000 procedure #8048, PhosVer 3 (ascorbic acid) method for reactive phosphorus (orthophosphate)

Total Suspended Solids (TSS)

Standard Methods 22nd edition, 2012, Method 2540 D

Volatile Suspended Solids (VSS)

Standard Methods 22nd edition, 2012, Method 2540 D and 2540 E

Chemical Oxygen Demand (COD)

Hach DR 2010 procedure #8000, Reactor digestion method for Chemical Oxygen Demand

Biochemical Oxygen Demand (BOD)

Standard Methods 22nd edition, 2012, Method 5210 B

Sulfide Hach Method #8131, Methylene Blue Method

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