Land Application

[1]:
import PFAS_SAT as ps
import numpy as np
import matplotlib.pyplot as plt
from IPython.display import Image
import pandas as pd
pd.set_option('display.max_colwidth', 0)
import warnings
warnings.filterwarnings('ignore')

Model document

Finished compost and dewatered, stabilized WWT solids are both suitable for land application. Once these materials are land applied, PFAS may volatize, be released to surface or ground- water, or sorbed to the soil/waste stream mixture. The flow of PFAS from land application is modeled using a liquid-solid partition coefficient normalized to the amount of organic carbon, combined with a water balance to track the flow of PFAS from the soil. Model predictions are based on achievement of equilibrium. By default, it is assumed that no volatilization occurs, but a user can enter a fraction of PFAS that volatilizes. It is further assumed that the land applied material is well mixed with the top layer of soil (thickness is a user input). The partition coefficient is used to estimate the concentration of PFAS in the liquid and solids. The concentration in the liquid changes throughout the year as PFAS runs off or is leached to the groundwater (i.e., it is assumed that annual precipitation is uniform throughout the year and continuously removes PFAS from the mixture). The user enters a run-off coefficient based on the soil type, land use, grade, and vegetation. The run-off is assumed to be released to surface water. Another fraction of the precipitation is removed via evapotranspiration (ET) based on the local climate and vegetation. The remaining precipitation is assumed to leach into groundwater. The PFAS remaining in the soil may be taken up by and bioaccumulate in plants. While PFAS uptake by plants was not modeled in this initial version of the SAT, it may be an important PFAS fate pathway as plants may enter the food chain depending on what is grown.

Assumptions and Limitations:

  1. The organic carbon-normalized partition coefficient assumes that the organic carbon in the soil has the same PFAS sorption capacity as the organic carbon in either the compost or the dewatered, stabilized WWT solids in the land applied material.

  2. The water balance model is averaged over a year and ignores potential effects from intense rains that may lead to substantial additional erosion and loss of solids and associated PFAS.

  3. Apart from precipitation, the water balance does not consider other external water inputs such as irrigation. This could be included by adjusting the precipitation input value.

  4. Volatilization is assumed to be zero by default due to a lack of data. However, the user may assign a fraction of the PFAS to be volatilized.

  5. Future work is also required to implement a dynamic model to account for changes in the organic C content of over time as land-applied materials decompose, and to account for episodic precipitation events.

  6. The loading rate for the land application of dewatered WWT solids will vary based on solids properties among other factors. The loading rate default values given here reflect a typical annual loading rate for application to agricultural land growing corn.

Input Parameters for Land Application model

[2]:
LandApp = ps.LandApp()
LandApp.InputData.Data[['Category','Dictonary_Name','Parameter Name', 'Parameter Description', 'amount', 'unit','minimum','maximum','Reference']]
[2]:
Category Dictonary_Name Parameter Name Parameter Description amount unit minimum maximum Reference
0 Log partition coefficient LogPartCoef PFOA PFOA Log Koc (soils/sediments) 2.190 log L/kg OC 1.300 4.500 [2,3,4,5]
1 Log partition coefficient LogPartCoef PFOS PFOS Log Koc (soils/sediments) 3.040 log L/kg OC 2.400 4.700 [2,3,4,5]
2 Log partition coefficient LogPartCoef PFBA PFBA Log Koc (soils/sediments) 1.880 log L/kg OC 1.300 1.880 [2,3,4,5]
3 Log partition coefficient LogPartCoef PFPeA PFPeA Log Koc (soils/sediments) 1.370 log L/kg OC NaN NaN [2,3,4,5]
4 Log partition coefficient LogPartCoef PFHxA PFHxA Log Koc (soils/sediments) 1.770 log L/kg OC 1.310 2.100 [2,3,4,5]
5 Log partition coefficient LogPartCoef PFHpA PFHpA Log Koc (soils/sediments) 1.970 log L/kg OC NaN 2.190 [2,3,4,5]
6 Log partition coefficient LogPartCoef PFNA PFNA Log Koc (soils/sediments) 2.630 log L/kg OC 2.300 3.180 [2,3,4,5]
7 Log partition coefficient LogPartCoef PFDA PFDA Log Koc (soils/sediments) 3.240 log L/kg OC 2.650 3.780 [2,3,4,5]
8 Log partition coefficient LogPartCoef PFBS PFBS Log Koc (soils/sediments) 1.510 log L/kg OC NaN 1.790 [2,3,4,5]
9 Log partition coefficient LogPartCoef PFHxS PFHxS Log Koc (soils/sediments) 2.790 log L/kg OC 2.050 2.875 [2,3,4,5]
10 Land application LandApp appl_dens kg dry applied per area 2.000 kg TS/m2 0.800 18.000 [7]
11 Land application LandApp depth_mix Depth of soil mixed 0.100 m 0.050 0.200 [8]
12 Soil Properties SoilProp bulk_dens Soil bulk density - wet 1300.000 kg/m3 1100.000 1800.000 [9]
13 Soil Properties SoilProp ts_cont Soil total solids content -wet 0.850 kg TS/kg 0.700 1.000 [10]
14 Soil Properties SoilProp C_cont Soil organic C content -dry 0.015 fraction TS 0.005 0.050 [9]
15 Precipitation Data Precip ann_precip Annual precipitation 1.000 m/yr NaN NaN [11]
16 Precipitation Data Precip frac_runoff Run-off fraction of precipitation 0.050 frac NaN NaN [12]
17 Precipitation Data Precip frac_ET Evapotranspiration fraction of precipitation 0.500 frac 0.033 1.000 [13]
18 Volatilization Volatilization frac_vol_loss Fraction of PFAS lost to volatilization 0.000 fraction NaN NaN NaN

Incoming Compost to land application

[3]:
IncominWaste = ps.IncomFlow()
IncominWaste.set_flow('Compost', 1000)
IncominWaste.calc()
Compost = IncominWaste.Inc_flow
Compost.report()
[3]:
Parameter Unit Amount
0 Mass flow kg 1000
1 Solids flow kg 600
2 Moisture flow kg 400
3 VS flow kg 360
4 Carbon flow kg 168
5 PFOA μg 5240
6 PFOS μg 7375
7 PFBA μg 3267
8 PFPeA μg 3424
9 PFHxA μg 16407
10 PFHpA μg 826
11 PFNA μg 1045
12 PFDA μg 2710
13 PFBS μg 7360
14 PFHxS μg 190

PFAS balance in land application

[4]:
LandApp.calc(Inc_flow=Compost)
LandApp.report(normalized=True)
[4]:
Volatilized Remaining in Soil Leachate Runoff
PFOA 0.0 25.35 67.19 7.47
PFOS 0.0 81.56 16.60 1.84
PFBA 0.0 7.10 83.61 9.29
PFPeA 0.0 0.10 89.91 9.99
PFHxA 0.0 3.68 86.69 9.63
PFHpA 0.0 11.14 79.98 8.89
PFNA 0.0 59.62 36.34 4.04
PFDA 0.0 87.89 10.90 1.21
PFBS 0.0 0.45 89.59 9.95
PFHxS 0.0 69.75 27.22 3.02
[5]:
LandApp.plot_sankey()
../_images/Notebooks_LandApp_9_0.png
[6]:
LandApp.plot_sankey_report(margin=0.5)
../_images/Notebooks_LandApp_10_0.png