Table 1.

Box–Behnken design for the three independent variables on biodegradation of waste engine oil and corresponding E ₂₄ of the culture broth

Runs	X 1 (temperature °C)	X 2 (pH)	X 3 (oil conc. v/v  %)	E 24 value (%)	Percent degradation (%) of WEOa
					Observed	Predicted
1	34	6	5	42.63	26.32	26.68
2	40	6	5	40.2	16.14	15.12
3	34	8	5	52.5	40.36	41.88
4	40	8	5	50.24	32.43	30.32
5	34	7	3	54.75	42.5	43.26
6	40	7	3	50.5	32.67	31.7
7	34	7	7	55	42.43	39.10
8	40	7	7	41	24.31	27.54
9	37	6	3	52.9	34.25	32.30
10	37	8	3	58.63	45.34	47.5
11	37	6	7	50	26.25	28.15
12	37	8	7	60.52	45.7	43.34
13	37	7	5	72.4	56.21	55.08
14	37	7	5	70.67	54.25	55.08
15	37	7	5	71.68	55.43	55.08

^aAll values are represented as (mean ± SD) based on triplicate assays