BR2
MT Sep c Tank
Mix Fill and React (1 hr)
React Draw (1 hr)
PERMEATE TANK
Average influent concentrations: COD = 270-560 mg/L sCOD = 110-210 mg/L NH4+-N = 24-37 mg/L Ortho-P = 8-16 mg/L BR1 On-demand applications
Figure 1: Mines Park process
flow (below).
Detail of the SBMBR at Mines Park (right).
E1.3 – Landscape irrigation
E1.6 – Food crops irrigation
ON-SITE REUSE AT MINES PARK
SUMMARY
More than half of the world’s human population is urbanized. The increased demand for water within urban centers, combined with the uncertainties of climate change, drought, and decaying water infrastructure, lead to depletion of local water supplies. Looking for new solutions to address the needs of sustainable development, domestic wastewater is now being seen as an untapped resource harboring energy, fertilizers, and a source of freshwater. Integrating decentralized water treatment systems for reclamation and reuse of wastewater into an existing urban infrastructure is one option for managing water resources more sustainably. Investigating energy demand of tailored water treatment and reducing these demands through more efficient upgrades will improve feasibility of wide spread decentralized systems.
Re-Inventing the Nation’s Urban Water Infrastructure (ReNUWIt)
Sara Newell
1, Jason Coontz
2, Ryan Holloway
2, Tzahi Cath
21
Humboldt State University, Arcata, CA ;
2Colorado School of Mines, Golden, CO
D
ECENTRALIZED
W
ASTEWATER
T
REATMENT
Bench-scale Investigation of Oxygen Transfer Rate for System Upgrades
to a Novel Sequencing Batch Membrane Bioreactor
R
ESEARCH
O
BJECTIVES
1. Conduct a bench-scale clean water study of oxygen transfer to prepare for the upgraded full-scale system study.
2. Document problems that arise in conducting the study and using the nonlinear regression model.
3. Assist in preparation of upgrades by drafting design drawings of the system.
A
ERATION
I
MPORTANCE AND
E
NERGY
C
ONSIDERATIONS
R
ELEVANCE AND
I
MPLICATIONS
O
XYGEN
T
RANSFER
T
EST
Oxygen transfer rate: Measurement of the mass of oxygen per unit of time dissolved in a volume of water by an aeration device.
Compare performance and efficiency of oxygenation devices in clean water.
Nonlinear regression model fits mass transfer model (Equation 1) to observed DO concentration values.
F
UTURE
W
ORK
Conduct full-scale, clean and in-process OTR testing on current and upgraded SBMBR system.
Oxygen transfer testing on a bench-scale bioreactor tank was performed in preparation of full-scale tests. A nonlinear regression model was successful in fitting a mass transfer model to observed DO concentration values. Estimation of in-process oxygen transfer rates using the standard oxygen transfer rate from clean water testing resulted in a negative near zero value which may indicate issues with procedure or demonstrate sensitivity in predicting
Procedure Decentralized wastewater treatment is the collection, treatment, and discharge or
reuse of wastewater from a single dwelling or cluster of dwellings nearby the point of generation. Water can be treated, to various nutrient concentrations for localized tailored application (e.g. landscaping, toilet flushing, or groundwater recharge).
Aeration is vital to the biological treatment of wastewater due to the insufficient solubility of oxygen as well as air-water interface at the surface of treatment tanks. The second largest energy use of the SBMBR is in the aeration system therefore reducing these demands will have a significant improvement on system efficiency while maintaining or improving effectiveness.
Upgrade Potential
Coarse-bubble aeration fine-bubble aeration
Results from aeration energy model predict a power reduction from 1.23 kW to 0.55 kW or ~45%.
𝑪 = 𝑪
∞∗− 𝑪
∞∗− 𝑪
𝟎𝒆
−𝑲𝑳𝒂𝒕 Eq. 1Where:
𝐶 = DO concentration, mg/L
𝐶∞∗ = Steady-state DO saturation concentration, mg/L 𝐶0 = Initial DO concentration, mg/L
𝐾𝐿𝑎 = apparent volumetric mass transfer coefficient, 1/hr
Figure 2: Bench-scale SBMBR system OTR test configuration
Figure 3: Clean water OTR test results for three runs.
A
CKNOWLEDGEMENTS
Impeller motor Impeller Fine-bubble aerator Impeller control DO probeAir flow gauge
Air flow valves Aeration pump
Measurement Every test series – beginning
Every test – beginning
Every test – beginning and end
Water volume
Cobalt chloride hydrate mass Sodium sulfite mass
Temperature of water Total dissolved solids (or conductivity)
Airflow
Prop speed Prop direction
Ambient air pressure
The method of conducting an oxygen transfer test involves the addition of chemicals to deoxygenate steady state test waters to near zero DO concentration. Aeration is then reintroduced and the nonlinear absorption of dissolved oxygen in the water is measured until saturation is reached. Methodology based on the ASCE standard for clean water testing, ASCE/EWRI 2-06.
Add dissolved cobalt chloride hydrate to configured OTR test tank to between 0.1 – 0.5 mg/L (~36 mg per test series used).
Run OTR test system with aeration and mixing until DO saturation concentration is reached. Record saturation value.
Add dissolved sodium sulfite solution in excess of the 7.88 mg/L per 1.0 mg/L DO concentration requirement (~3.5 g per test run) to tank and turn off aeration, leave mixing on.
Wait until DO concentration drops to < 0.5 mg/L.
Begin timing test and recording DO concentrations every 15 seconds when aeration is turned back on.
Continue recording until 98% of saturation concentration is reached.
In-process testing is based on the same principles as the clean water test with some exceptions:
Deoxygenation chemicals are not used
Aeration is turned lower instead of off. Measurement starts at low aeration steady state and ends after reaching steady state at higher aeration (change in DO concentration of at least 2 mg/L is required).
Table 1: Frequency of Clean Water OTR Test Measurements.
Standard Conditions C*∞ , mg/L 7.73 KLa (Not TDS corrected), 1/hr 18.32 KLa (TDS corrected), 1/hr 19.62 Test Conditions C*∞ , mg/L 7.42 KLa, 1/hr 19.52 Model Calculations SOTR (g/hr) 30
Ω (pressure correction factors) 1.007
τ (temperature correction
factors) 0.953
Table 2: Average parameter values from
nonlinear regression model
Clean Water OTR Results
This research was supported by the National Science Foundation and Re-inventing the Nation’s Urban Water Infrastructure Research Group. Special thanks also goes out to Dotti Ramey, Dr. Pam McLeod, Dr. Andrea Achilli, and Dr. Margaret Lang.
Three clean water test runs were performed and nonlinear regression was used to fit Equation 1 to the measured values. Good agreement between measured and calculated DO concentrations was observed (Figure 3). SOTR was calculated and found to be 30 g/hr (Table 2).
𝑺𝑶𝑻𝑹 = 𝑽/𝒏
𝒊=𝟏 𝒏
𝑲𝑳𝒂𝟐𝟎𝒊𝑪∞𝟐𝟎𝒊∗ Where:
𝑆𝑂𝑇𝑅 = Standard oxygen transfer rate, kg/hr
𝐶∞20𝑖∗ = Steady-state DO saturation concentration corrected to 20oc and 1.00 atm., mg/L
𝐶0 = Initial DO concentration, mg/L 𝐾𝐿𝑎20 = 𝐾𝐿𝑎 corrected to 20oc, 1/hr
𝑛 = number of DO concentration determination points (probes) Eq. 2 0 2 4 6 8 10 0 5 10 15 20 DO con ce ntration (mg/l ) Time (minutes)
Run 1: Observed concentration Run 2: Observed concentration Run 3: Observed concentration Calculated concentration
U
PGRADES TO
D
ATE
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 20 40 60 80 100 D O co n cen tr ati o n (mg /l ) Time (minutes) Observed concentration Calculated concentrationFigure 4: In-process (batch) OTR test results at a TSS of
2,500 mg/L.
Preliminary In-process OTR Results
𝑶𝑻𝑹𝒇 = 𝟏
𝑪∞𝟐𝟎∗ 𝜶 𝑺𝑶𝑻𝑹 𝜽𝑻−𝟐𝟎 (𝝉𝜷𝛀𝐂∞𝟐𝟎∗ − 𝑪)
Where:
𝑂𝑇𝑅𝑓 =oxygen transfer rate estimate for system under average process conditions at average DO, C, and temperature, T 𝛼 = ratio of 𝐾𝐿𝑎 in process water to 𝐾𝐿𝑎 in clean water
𝜃 = Temperature correction factor Ω = Pressure correction factor
Other variables as previously defined
Eq. 3
Standard Conditions Model Calculations
C* ∞ 4.49 C 6.84 Kla(Not TDS corrected) 1.8 T 24.1 Kla (TDS corrected) 1.9 α 0.098271 Co -0.28 αTDS 0.096856 Test Conditions θ 1.024 C* ∞ 4.17 Ω 1.03 Kla 1.98 τ 0.926 β 0.581 OTRf -0.00119 OTRf.TDS -0.00642
Table 2: Average parameter values from nonlinear
regression model
One run of in-process testing at a TSS of 2,500 mg/L was performed and displayed good agreement between observed and calculated DO concentrations (Figure 4). OTR calculated from equation 3 resulted in near zero values (Table 2).
Figure 5: Design drawing (left, SketchUp), mixer motor support plate(center left, SketchUp), installed mixer motor on
