Characteristics of wastewater treatment using a multi-soil-layering system in relation to wastewater contamination levels and hydraulic loading rates

Figures & data

Figure 1  Structure of the multi-soil-layering system.

Figure 2  Changes in (a) biological oxygen demand (BOD), (b) total phosphorus (T-P) and (c) total nitrogen (T-N) concentrations in wastewater and treated L-500, L-2000, H-500 and H-2000 waters, and (d) the air and water temperatures. HWW, high level of wastewater; LWW, low level of wastewater; 500 and 2,000, hydraulic loading rates of 500 and 2,000 L m−2 day−1, respectively.

Table 1 Mean level of contamination (mean ±standard deviation) and mean removal percentage† of selected parameters in wastewater and treated water during the experiment

Treatment	pH	ORP (mV)	SS (mg L^−1)		BOD (mg L^−1)		CODcr (mg L^−1)		NH4–N (mg L^−1)
LWW	7.41 ± 0.25	232 ± 78	27.8 ± 21.9		32.1 ± 20.9		43.9 ± 21.5		3.34 ± 1.08
L-500	7.49 ± 0.24a	335 ± 51a	1.8 ± 2.8a	(93)	1.2 ± 1.1b	(94)	3.7 ± 3.7b	(89)	0.05 ± 0.08b	(98)
L-1000	7.51 ± 0.33a	327 ± 60a	1.9 ± 2.4a	(90)	1.3 ± 1.1b	(94)	5.5 ± 4.7b	(84)	0.05 ± 0.06b	(98)
L-1250	7.48 ± 0.24a	326 ± 60a	1.3 ± 1.8a	(91)	1.3 ± 0.8b	(94)	5.7 ± 4.4b	(83)	0.05 ± 0.07b	(98)
L-1500	7.40 ± 0.30a	321 ± 68ab	1.0 ± 1.2a	(92)	1.1 ± 0.5b	(95)	4.8 ± 4.5b	(86)	0.05 ± 0.04b	(98)
L-2000	7.37 ± 0.24a	324 ± 67ab	0.7 ± 0.8a	(94)	1.5 ± 1.3b	(91)	5.6 ± 5.2b	(85)	0.06 ± 0.05b	(98)
HWW	7.40 ± 0.18	177 ± 126	78.3 ± 75.3		69.5 ± 52.7		121.6 ± 96.7		6.61 ± 2.13
H-500	7.47 ± 0.27a	333 ± 55a	1.7 ± 3.3a	(95)	1.1 ± 1.0b	(98)	5.0 ± 4.5b	(94)	0.05 ± 0.06b	(98)
H-1000	7.41 ± 0.21a	330 ± 61a	1.2 ± 1.9a	(96)	2.1 ± 2.9b	(94)	6.7 ± 6.3b	(92)	0.06 ± 0.06b	(98)
H-1250	7.41 ± 0.25a	302 ± 65ab	1.8 ± 2.4a	(93)	2.1 ± 2.5b	(95)	7.8 ± 6.9ab	(91)	0.08 ± 0.07b	(98)
H-1500	7.36 ± 0.26a	301 ± 86ab	2.1 ± 3.8a	(92)	2.7 ± 4.2b	(94)	9.7 ± 7.7ab	(90)	0.19 ± 0.22b	(96)
H-2000	7.33 ± 0.22a	264 ± 93b	3.3 ± 4.9a	(91)	6.2 ± 8.1a	(88)	12.1 ± 7.6a	(87)	0.41 ± 0.54a	(93)
Treatment	NO3–N (mg L^−1)	NO2–N (mg L^−1)	T-N (mg L^−1)		PO4–P (mg L^−1)		T-P (mg L^−1)
LWW	0.9 ± 0.5	0.07 ± 0.08	6.3 ± 1.7		0.49 ± 0.12		0.76 ± 0.30
L-500	2.1 ± 1.1b	0.01 ± 0.01b	4.0 ± 2.1abc	(44)	0.11 ± 0.05de	(74)	0.15 ± 0.11cd	(73)
L-1000	2.0 ± 1.1b	0.01 ± 0.01b	3.1 ± 1.4bc	(48)	0.13 ± 0.04cd	(72)	0.21 ± 0.19bcd	(69)
L-1250	2.0 ± 1.2b	0.01 ± 0.01b	2.9 ± 1.5bc	(51)	0.16 ± 0.06cd	(65)	0.20 ± 0.14bcd	(69)
L-1500	2.1 ± 1.0b	0.01 ± 0.01b	3.3 ± 1.8bc	(47)	0.18 ± 0.08abc	(60)	0.23 ± 0.12abc	(66)
L-2000	1.7 ± 1.1b	0.01 ± 0.01b	2.5 ± 1.4c	(56)	0.21 ± 0.09abc	(56)	0.24 ± 0.11abc	(63)
HWW	0.9 ± 0.7	0.01 ± 0.01	9.6 ± 2.7		0.73 ± 0.27		1.47 ± 1.16
H-500	4.0 ± 2.0a	0.01 ± 0.01b	5.3 ± 3.3a	(45)	0.09 ± 0.04e	(86)	0.10 ± 0.04d	(89)
H-1000	3.2 ± 2.5ab	0.01 ± 0.01b	4.2 ± 2.6abc	(54)	0.12 ± 0.04cde	(82)	0.14 ± 0.06cd	(85)
H-1250	3.0 ± 3.1ab	0.03 ± 0.05ab	4.0 ± 2.9abc	(56)	0.17 ± 0.07bcd	(72)	0.22 ± 0.13abcd	(74
H-1500	3.5 ± 3.3ab	0.06 ± 0.20ab	4.8 ± 2.6ab	(48)	0.24 ± 0.13ab	(64)	0.31 ± 0.21ab	(71)
H-2000	2.4 ± 2.7ab	0.16 ± 0.45a	3.9 ± 2.4abc	(57)	0.25 ± 0.11a	(62)	0.34 ± 0.20a	(65)
^†Mean removal percentage represents the average of the values at respective sampling times. Means within a column followed by the same letter are not significantly different according to a Tukey's test (P > 0.05). HWW, high level of wastewater; LWW, low level of wastewater; L(H)−500(−2,000), treatment with LWW (HWW) at a hydraulic loading rate of 500 (−2000) L m^−2 day^−1. BOD, biological oxygen demand; chemical oxygen demand using the potassium dichromate method (CODcr); ORP, oxidation–reduction potential; SS, suspended solids; T-N, total nitrogen; T-P, total phosphorus.

Table 2 Mean removal rate (g m−2 day−1) of selected contaminants†

	SS	BOD	CODcr	T-N	T-P
L-500	13	15	20	1.2	0.31
L-1000	26	31	38	3.2	0.56
L-1250	33	39	48	4.3	0.71
L-1500	40	47	59	4.6	0.81
L-2000	54	61	77	7.6	1.05
H-500	38	34	58	2.2	0.68
H-1000	77	67	115	5.5	1.32
H-1250	96	84	142	7.1	1.56
H-1500	114	100	168	7.3	1.73
H-2000	150	127	219	11.5	2.26
^†The clogging period was omitted from the calculation. BOD, biological oxygen demand; chemical oxygen demand using the potassium dichromate method (CODcr); SS, suspended solids; T-N, total nitrogen; T-P, total phosphorus.

Figure 3  Relationship between the oxidation–reduction potential (ORP) and the removal percentage of total nitrogen (T-N). **P < 0.01.