Single-/triple-stage biotrickling filter treating a H₂S-rich biogas stream: Statistical analysis of the effect of empty bed retention time and liquid recirculation velocity

Figures & data

Table 1. 3² FFD matrix containing tested levels of the independent variables along with the values of responses used in this study (adapted from Chaiprapat et al. 2015).

	Independent variable		Response
Experimental run	X1	X2	Y1 (%)	Y2 (%)
1	180 (+1)	7.10 (+1)	93.0	96.7
2	180 (+1)	4.75 (0)	96.0	94.3
3	140 (0)	7.10 (+1)	86.6	92.2
4	100 (−1)	4.75 (0)	76.5	82.0
5	180 (+1)	2.40 (−1)	89.1	87.9
6	140 (0)	2.40 (−1)	79.1	83.3
7	100 (−1)	2.40 (−1)	62.0	69.0
8	100 (−1)	7.10 (+1)	70.0	84.5
9	140 (0)	4.75 (0)	88.8	91.9

Note. X₁: EBRT (sec); X₂: LRV (m³ m⁻² h⁻¹); Y₁: H₂S removal efficiency (%) in SBTF; Y₂: H₂S removal efficiency (%) in TBTF; Parenthesis in data indicates coded values of independent variables; 4.7 was taken as 4.75 (the centre point for LRV of 2.40 and 7.10 m³ m⁻² h⁻¹).

Table 2. Sequential model sum of squares for H₂S removal efficiency in SBTF and TBTF.

Bio-trickling filter	Model	SS	df	MS	F-value	p-value	Remarks
SBTF	Linear	870	2	435	17.8	0.003	significant
	2FI	4.2	1	4.2	0.15	0.716
	Quadratic	130	2	64	15.6	0.026	significant
TBTF	Linear	498	2	249	21.2	0.002	significant
	2FI	11.2	1	11.2	0.95	0.375
	Quadratic	52	2	26	10.9	0.042	significant

Note. SS: sum of squares; df: degree of freedom; MS: mean square; F-value: Fisher’s function value; p-value: probability value (level of significance); 2FI: two-factor interaction; Significant at the 0.05 probability level.

Table 3. Model summary statistics for H₂S removal efficiency in SBTF and TBTF.

Bio-trickling filter	Model	R^2	R^2adj.	R^2pred.	PRESS	Remarks
SBTF	Linear	0.856	0.808	0.664	341
	2FI	0.860	0.776	0.222	790.9
	Quadratic	0.988	0.967	0.857	145.4	Selected
TBTF	Linear	0.876	0.835	0.709	165.4
	2FI	0.896	0.833	0.454	310.4
	Quadratic	0.987	0.966	0.847	86.8	Selected

Note. R²: coefficient of determination; Subscripts “adj.” and “pred.” stand for “adjusted” and “predicted”, respectively; PRESS: predicted residual error sum of squares; 2FI: two-factor interaction.

Table 4. ANOVA analysis for the quadratic model of H₂S removal efficiency in SBTF and TBTF.

Response	Term	Effect	Coeff.	St. Error	t-value	p-value
Y1	Intercept		89.6	1.52	59.0	.000
	X1	23.2	11.6	0.83	13.9	.001
	X2	6.47	3.23	0.83	3.88	.030
	X1^2	−7.47	−3.73	1.44	−2.59	.081
	X2^2	−14.27	−7.13	1.44	−4.95	.016
	X1X2	−2.05	−1.03	1.02	−1.01	.389
Y2	Intercept		91.7	1.152	79.6	.000
	X1	14.47	7.23	0.631	11.47	.001
	X2	11.07	5.53	0.631	8.77	.003
	X1^2	−6.80	−3.40	1.093	−3.11	.053
	X2^2	−7.60	−3.80	1.093	−3.48	.040
	X1X2	−3.35	−1.68	0.773	−2.17	.119

Note. Y₁ and Y₂ represent H₂S removal efficiency (%) in SBTF and TBTF, respectively; X₁ and X₂ represent independent variables EBRT and LRV in coded values, respectively.

Figure 1. Comparison between predicted and experimental (actual) values for the responses (a) H₂S removal efficiency in SBTF (Y₁) and (b) H₂S removal efficiency in TBTF (Y₂).

Figure 2. Normal probability plot of residuals for the responses (a) H₂S removal efficiency in SBTF (Y₁) and (b) H₂S removal efficiency in TBTF (Y₂).

Figure 3. Internally studentized residuals versus predicted values of responses (Y₁: H₂S removal efficiency in SBTF; Y₂: H₂S removal efficiency in TBTF).

Figure 4. (a) 3D response surface and (b) 2D contour plots illustrating the effect of EBRT and LRV on H₂S removal efficiency in SBTF (Y₁).

Figure 5. (a) 3D response surface and (b) 2D contour plots illustrating the effect of EBRT and LRV on H₂S removal efficiency in TBTF (Y₂).

Table 5. Effect of EBRT and LRV on H₂S removal efficiency in SBTF and TBTF (data from Figures 4 and 5).

	LRV (m^3 m^−2 h^−1)
	LRVL		LRVC		LRVH
EBRT (sec)	Y1 (%)	Y2 (%)	Y1 (%)	Y2 (%)	Y1 (%)	Y2 (%)
100	62.86	70.02	74.89 (5.5)	84.45 (7.0)	71.38	84.44
140	79.22	82.33	89.96 (5.3)	93.68 (6.5)	85.69	93.40
180	88.11	87.84	97.63 (5.1)	96.48 (5.9)	92.53	95.56

Note. LRV_L and LRV_H represent the lowest and highest LRV tested in this study, 2.4 and 7.1 m³ m⁻² h⁻¹, respectively; LRV_C is the critical LRV at which the H₂S removal efficiency reached an optimum value; Y₁ and Y₂ are H₂S removal efficiency in SBTF and TBTF, respectively; Parenthesis in data indicates the LRV_C; EBRTs of 100, 140 and 180 sec correspond to H₂S-S loading rates of 304, 218 and 165 g-S m⁻³ h⁻¹, respectively.