Table 1
Treatment descriptions of seventeen 72-h batch tests with Dissolved Reactive Phosphorus (DRP) concentration reduction and removal per mass dry woodchip
--------------------- Treatment combination ---------------------
|
---- P removal at test end -----
|
Test
|
Wood
|
Size
|
Initial conc. and source
|
Autoclaved?
|
Concentration reduction
|
mg DRP removed /kg woodchip
|
#
|
Common name
|
mm
|
mg P/L
|
Y/N
|
%
|
|
1
|
Poplar a
|
6.3–13
|
1.0 DI
|
N
|
11 ± 3.2% *
|
2.0 ± 0.6
|
2
|
White oak a
|
6.3–13
|
1.0 DI
|
N
|
-7.2 ± 3.2% *
|
-1.2 ± 0.5
|
3
|
Hickory
|
6.3–13
|
1.0 DI
|
N
|
2.8 ± 1.2% *
|
0.4 ± 0.2
|
4
|
Cypress
|
6.3–13
|
1.0 DI
|
N
|
-6.1 ± 5.0% *
|
-1.0 ± 0.8
|
5
|
Field bioreactor a
|
6.3–13
|
1.0 DI
|
N
|
84 ± 16% *
|
13 ± 2.5
|
6
|
Cedar a
|
6.3–13
|
1.0 DI
|
N
|
3.5 ± 11%
|
0.6 ± 1.7
|
7
|
Maple
|
6.3–13
|
1.0 DI
|
N
|
7.3 ± 5.0% *
|
1.1 ± 0.8
|
8
|
Poplar a
|
6.3–13
|
1.0 DI
|
Y
|
-3.3 ± 0.8% *
|
-0.6 ± 0.1
|
9
|
Hickory
|
6.3–13
|
1.0 DI
|
Y
|
4.7 ± 1.6% *
|
0.8 ± 0.3
|
10
|
Cypress
|
6.3–13
|
1.0 DI
|
Y
|
-99 ± 12% *
|
-16 ± 1.9
|
11
|
Field bioreactor
|
6.3–13
|
1.0 DI
|
Y
|
-0.3 ± 1.2%
|
0.0 ± 0.2
|
12
|
Poplar a
|
6.3–13
|
0.78 River
|
N
|
87 ± 3.2% *
|
12 ± 0.4
|
13
|
White oak
|
6.3–13
|
0.68 River
|
N
|
-36 ± 17% *
|
-4.1 ± 1.9
|
14
|
Hickory
|
6.3–13
|
0.61 River
|
N
|
-3.6 ± 7.9%
|
-0.3 ± 0.8
|
15
|
Poplar
|
3.2–6.3
|
1.0 DI
|
N
|
24 ± 2.2% *
|
3.8 ± 0.4
|
16
|
White oak
|
3.2–6.3
|
1.0 DI
|
N
|
4.3 ± 6.1%
|
0.8 ± 1.1
|
17
|
Poplar
|
6.3–13
|
0.10 DI
|
N
|
67 ± 4.8% *
|
1.2 ± 0.1
|
a A subset of batch solutions from one replicate of these tests were analyzed for metals and trace elements by Inductively Coupled Plasma-atomic Emission Spectrometry |
* indicated the final test concentration mean at t = 72 h was significantly different (either lower or higher) from the initial test concentration (ɑ = 0.05). |
For each test, 3 g of air-dried woodchips (n = 4) was added to 45 mL of either P-dosed (potassium phosphate monobasic, KH2PO4) DI water or river water in a polypropylene conical tube. Once corrected for moisture content, this resulted in a 16:1–18:1 liquid to solid ratio, loosely following Svensson et al. (2014) who used a ratio of 20:1 in sawdust batch leaching tests. The tubes were secured to a shaker table set at 200 rpm and eleven sample events spanned the 72 hours (2 min, 10 min, 30 min, 1 h, 3 h, 6 h, 9 h, 24 h, 33 h, 48 h, and 72 h). Each tube was destructively harvested; that is, samples were not collected repeatedly over time from the same tube. The tests were performed at 21°C except for the river water treatment (see below). All water samples were filtered within 15 min of sample collection (0.45 µm membrane), frozen, and analyzed for DRP (Lachat Quickchem, method 10-115-01-1-A instruments, Loveland, CO, USA). Sample pH was measured within 24 h of collection (pH meter Fisher Scientific AE150, Waltham, MA, USA).
Four wood types (Table 1: poplar, hickory, cypress, and field bioreactor woodchips) were autoclaved at high temperature (120°C) and high pressure (150 psi) for the autoclaving treatments. For the three river water treatments (Table 1: poplar, white oak, and hickory), water was sourced from the upper Embarras River near Urbana, Illinois, in winter (January 2020) and stored at 4°C to minimize room temperature-associated changes in the water chemistry. The river water had an initial DRP concentration of 0.05 ± 0.01 mg DRP/L and was dosed to 1.0 mg DRP/L using KH2PO4. However, the dosed river water was mistakenly not shaken before the batch test which resulted in the initial dosed river water samples having concentrations ranging from 0.61 to 0.78 mg DRP/L. For the particle size testing, two size ranges (3.2–6.3 vs. 6.3–13 mm for poplar and white oak; Table 1) were selected based on availability once the woods were chipped. The 3 g of woodchips used in both sets of tests entailed approximately 35 and 20 woodchips in the small (3.2–6.3 mm) and large (6.3–13 mm) particle size ranges, respectively. Finally, one test was performed with a low initial concentration of 0.10 mg DRP/L compared to the other tests’ initial concentration of 1.0 mg DRP/L (Table 1: poplar).
A subset of batch solutions was selected for additional post-hoc trace elements analysis by Inductively Coupled Plasma-atomic Emission Spectrometry (ICP; Illinois Water Survey, Champaign, IL, USA; US EPA Method 200.7). Due to analytical cost, samples from only six of the seventeen tests were analyzed (Table 1: tests #1, 2, 5, 6, 8, and 12). These six were selected to give a range across wood types (tests #1, 2, 5, 6: poplar, white oak, field bioreactor, and cypress chips) and across the several of the controlled independent factors (e.g., poplar tests #1, 8, and 12 including river water and autoclaving). Only one replicate for the selected treatments and only the sample events at t = 0, 2 min, 10 min, 1 h, 24 h, and 72 h were analyzed. The water samples were stored frozen for approximately 9–12 months prior to this supplemental analysis.