Full-scale biofilter reduction efficiencies assessed using portable 24-hour sampling units

Figures & data

Table 1. Biofilter characteristics

Site	BiofilterNo.	BiofilterType	Media	MediaDepth(m)	Biofilter LengthandWidth(m)	Media Age	WaterManagement	Design AirflowRate (m^3/s)	DesignEBCT(sec)
1	1	Deep-bed	SW ^a	2.0	15×6	Several months	None	2.8	64
	2	Deep-bed	SW	2.0	6.7 × 2.4	Several months	None	0.5	64
2	1	A-frame	WC ^a	0.3–0.6	18 × 5.8	1.5 yr	Soaker hoses	11	4
	2	Flat-bed	WC ^b	0.4	18 × 8	3.5 yr	Garden sprinkler	11	5
3 ^c	1	Flat-bed	WC	0.4	13.4 × 5.5	3 yr	None	5.5	5
	2	Flat-bed	WC	0.4	8.5 × 5.5	3 yr	None	3.7	5
4 ^c	1	Flat-bed	WC	0.4	13.4 × 5.5	2 yr	None	4	7
	2	Flat-bed	WC	0.4	7 × 4	2 yr	None	2	6
Notes: ^aSW = shredded wood; WC = wood chips. ^bWood chips with fine particles. ^cDesign information for the biofilters at sites 3 and 4 was provided by Ken Folie, retired Dodge County Feedlot Officer, through personal communications.

Figure 1. Schematic of the A-frame biofilter at site 2 with a pit fan (cross-sectional view).

Figure 2. Top view of the 24-hr air sampling at the swine nursery farm (air sampling units were enlarged).

Table 2. Biofilter media characteristics (n = 3)

Site	Biofilter No.	Porosity (%) ^a	Density (kg/m^3) ^a	Water Absorption Capacity (%) ^a
1	1	74.9 ± 0.7^A	203 ± 61.8^C	32.6 ± 2.0^C
	2	76.3 ± 2.5^A	160.0 ± 4.6^D	54.3 ± 7.0^B
2	1	58.7 ± 2.2^C	210.7 ± 7.6 ^C	71.9 ± 15.1^A
	2	53.5 ± 3.8^D	408 ± 4.6^A	44.9 ± 8.3^B
3 ^b	1	56.7 ± 0.5^CD	435 ± 15^A	47.1 ± 2.0^B
	2
4 ^b	1	65.3 ± 0.8^B	248.7 ± 7.6^B	26.3 ± 1.9^D
	2
Notes: ^aThe capital letters show results used to compare means. Within each column, means that are connected with the same letter are not significantly different (P < 0.05). ^bSince same media was used for biofilters 1 and 2, media collected from two biofilters were combined and analyzed together.

Figure 3. Biofilter media unit pressure drop versus unit airflow rates for biofilters at four sites: (a) site 1, (b) site 2, (c) site 3, (d) site 4.

Figure 4. Particle size distribution by weight of the biofilter media at four sites: (a) site 1, (b) site 2, (c) site 3, (d) site 4.

Table 3. Comparison of inlet and outlet air CO₂ concentrations of biofilters

	CO2 Concentration (ppm)
	Biofilter 1			Biofilter 2
Sampling Date (Month/Day)	Inlet ^a	Outlet ^a	% Difference ^b	Inlet	Outlet	% Difference
Site 1
6/10–6/11	618	624	−0.97	3085	3065	0.65
7/15–7/16	897	891	0.67	2823	2825	−0.07
8/11–8/12	716	713	0.42	2950	2970	−0.68
9/21–9/22	1120	1123	−0.27	2980	2980	0.00
Site 2
6/16–6/17	1023	1025	−0.20	1251	1253	−0.16
7/20–7/21	854	858	−0.47	1185	1183	0.17
9/1–9/2	803	801	0.25	1180	1172	0.68
9/30–10/1	810	811	−0.12	1267	1263	0.32
Site 3
6/29–6/30	1040	1045	−0.48	1585	1575	0.63
7/28–7/29	763	766	−0.39	662	668	−0.91
9/16–9/17	1845	1835	0.54	1825	1830	−0.27
10/5–10/6	1865	1890	0.27	1815	1820	−0.28
Site 4
7/8–7/9	940	943	−0.32	951	954	−0.32
8/3–8/4	1095	1080	1.37	1004	1005	−0.10
8/26–8/27	1380	1385	−0.36	1145	1148	−0.26
10/14–10/15	1430	1440	−0.70	1145	1145	0.00
Notes: ^aAverages of two measurements were shown for each sampling day. ^bPercent difference is the difference between inlet and outlet CO2 concentrations.

Table 4. Comparison of H₂S and NH₃ reduction efficiencies measured by semicontinuous sampling and 24-hr sampling systems

	Percent reduction efficiencies
	Biofilter 1			Biofilter 2
Sampling Date(Month/Day)	24-HrSampling	Semicont.Sampling	% Difference ^a	24-HrSampling	Semicont.Sampling	% Difference
H2S
6/16−6/17	46.63	43.33	7.07	81.51	78.87	3.23
7/20–7/21	41.05	38.36	6.55	82.39	80.47	2.33
9/1–9/2	53.61	59.50	−10.98	82.07	79.11	3.61
9/30–10/1	54.02	68.32	−26.48	93.18	94.20	−1.09
NH3
6/16–6/17	45.28	46.88	−3.52	86.49	87.13	−0.73
7/20–7/21	45.62	44.44	2.59	88.28	91.98	−4.19
9/1–9/2	82.17	85.53	−4.09	84.15	85.33	−1.40
9/30–10/1	72.51	72.62	−0.15	86.06	89.71	−4.24
Note: ^aPercent difference is the difference between reduction efficiencies of semicontinuous sampling and 24-hr sampling.

Table 5. Inlet gas concentrations

Site	Biofilter No.	NH3(ppm)	H2S(ppb)	SO2(ppb)	CH4(ppm)	N2O(ppb)	CO2(ppm)
1	1	4.7 ± (1.7) ^a	656 ± (107)	34.7 ± (6.9)	139 ± (10.3)	392 ± (27.7)	838 ± (205)
		2.31–6.44 ^b	473–785	25.5–45.3	124–152	352–422	613–1140
	2	37.6 ± (2.6)	17,537 ± (2577)	410 ± (46.4)	898 ± (68.8)	355 ± (10.3)	2959 ± (130)
		34.4–42.1	14,013–20,800	360–456	810–970	338–369	2800–3125
2	1	3.8 ± (0.79)	327 ± (156)	6.5 ± (0.9)	7.9 ± (1.7)	390 ± (18.0)	872 ± (95.1)
		2.6–4.6	144–484	5.1–7.4	5.2–10.1	358–406	795–1025
	2	14.3 ± (4.2)	833 ± (886)	7.8 ± (0.8)	126 ± (39.3)	480 ± (115)	1221 ± (41.6)
		9.5–20.1	189–2280	6.2–8.5	68.9 ± (172)	403–666	1179–1269
3	1	15.0 ± (3.8)	316 ± (108)	19.5 ± (4.0)	231 ± (124)	405 ± (10.3)	1378 ± (521)
		10.4–18.9	202–425	13–24	105–376	389–415	737–1890
	2	15.5 ± (2.6)	322 ± (119)	21.4 ± (4.1)	237 ± (120)	410 ± (16.3)	1472 ± (511)
		11.4–18.1	201–439	15–26	110–377	381–423	624–1830
4	1	8.7 ± (1.0)	256 ± (31)	9.4 ± (2.3)	146 ± (36)	430 ± (51)	1211 ± (222)
		7.4–10.1	202–292	5.5–12	109–189	352–475	925–1450
	2	9.7 ± (1.1)	218 ± (47)	10 ± (1.4)	148 ± (50)	460 ± (15)	1061 ± (95)
		7.8–11.2	147–269	8–12	90–204	436–480	950–1150
Notes: ^aAverages of eight measurements (2 measurements per visit × 4 visits = 8 measurements) were shown in the first row. Standard deviations were given in parentheses. ^bMinimum and maximum values were shown in the second lines of the rows.

Figure 5. Overall percent gas reduction efficiencies of the sites (averages of eight measurements were reported for each gas): (a) site 1, (b) site 2, (c) site 3, (d) site 4.

Figure 6. Percent gas reduction efficiencies of the biofilters (averages of two measurements were reported for each sampling date): (a) site 1, biofilter 1, (b) site 1, biofilter 2, (c) site 2, biofilter 1, (d) site 2, biofilter 2, (e) site 3, biofilter 1, (f) site 3, biofilter 2, (g) site 4, biofilter 1, (h) site 4, biofilter 2.

Table 6. Average temperature, dew point, relative humidity, and total precipitation of the sites

Site 1
Sampling date (month/day)	6/10–6/11	7/15–7/16	8/11–8/12	9/21–9/22
T (°C)	17.68	23.05	24.48	9.57
DP (°C)	16.28	16.71	21.01	5.43
RH (%)	91	67	82	77
Precipitation (cm)	3.12 (0.13)	None (none)	None (none)	None (none)
Site 2
Sampling date (month/day)	6/16–6/17	7/20–7/21	9/1–9/2	9/30–10/1
T (°C)	22.58	21.57	17.73	12.56
DP (°C)	16.73	16.63	11.78	4.46
RH (%)	72	76	71	61
Precipitation (cm)	None (none)	None (none)	None (none)	None (none)
Site 3
Sampling date (month/day)	6/29–6/30	7/28–7/29	9/16–9/17	10/5–10/6
T (°C)	16.19	20.46	12.53	15.51
DP (°C)	8.53	15.91	10.85	7.22
RH (%)	61	76	90	59
Precipitation (cm)	None (none)	None (3.25)	None (5.71)	None (none)
Site 4
Sampling date (month/day)	7/8–7/9	8/3–8/4	8/26–8/27	10/14–10/15
T (°C)	21.63	25.39	21.04	11.14
DP (°C)	15.13	21.73	15.90	2.12
RH (%)	69	80	74	58
Precipitation (cm)	None (0.05)	None (none)	None (none)	None (none)
Notes: Temperature, dew point, relative humidity, and precipitation data were measured every 20 min. Averages for each sampling period (from the time 24-hr sampling started to the time sampling finished) were calculated. Precipitation data were summed to find total precipitation during the sampling period. Precipitation 24 hr prior to sampling is given in parentheses.