Novel Electrochemical Treatment of Spent Caustic from the Hydrocarbon Industry Using Ti/BDD

Table 1

Physicochemical analysis of spent caustics.

Parameter	Value		Value reference
	Simple sample	Mixture	Spent caustic	Typical refinery wastewater
Total phenol (mg L^−1)	7,270.89	11,041.74	30,600 [3]	13 [16], 172.50 [18], 3.17 [17], 192.90 [9], 141 [7], 113 [19], 23 [96]
Oil and grease (mg L^−1)	239.70	3,399.70	—	85 [97], 1.96 [17], 12.70 [19], 15 [98]
BOD5 (mg L^−1)	6,930	7,811	—	323 [97], 40.25 [16], 570 [3]
COD (mg O2 L^−1)	72,065	98,750–102,842.50	72,450 [1], 320,100 [3]	3,150 [97], 100 [16], 4,450 [18], 2,323 [13], 257 [17], 590 [9], 602 [7], 935 [19], 2,746 [98], 1,220 [96]
BOD5/COD	0.09	0.07	—	0.60 [19]
Sulfides (mg L^−1)	<37.29	<37.29	34,517 [1], 48,500 [3]	19 [19]
Ammonia (mg L^−1)	—	—	—	13.10 [19]
Cyanides (mg L^−1)	<0.25	<0.25	—	—
pH	13.02	13.50	12.97 [1], 13 [3]	8 [16], 8.60 [18], 8.05 [13], 7.60 [17], 9.20 [7], 8.10 [19], 7.59 [98], 10 [96]
TOC (mg L^−1)	—	20,137.50	53,900 [3]	370 [19], 1,500 [96]
Hydrocarbons (mg L^−1)	—	—	—	11.72 [17], 0.02 [19]
Conductivity (mS cm^−1)	129.20	208.44	126.70 [1]	6 [18], 13.06 [13], 15.63 [7], 1.73 [7], 0.06 [98]
Alkalinity, CaCO3 (mg L^−1)	52,266.35	—	15,500 [3]	3,990 [96]
Total dissolved solid (mg L^−1)	—	169,680	—	5,000 [18], 7,990 [13], 1,333 [7], 4,380 [98]
Settleable solids; (mg L^−1)	—	40	—	—
Total suspended solids; (mg L^−1)	—	3,940	—	22.80 [16], 35 [18], 100 [13], 1,000 [96]
Toxicity (%)	100	100	—	—
F^− (mg L^−1)	50	135	—	—
Cl^− (mg L^−1)	86	54,900	37,900 [3]	63 [97], 112 [7], 200,000 [96]
Br^− (mg L^−1)	12	<0.30	—	—
(mg L^−1)	11	<0.25	—	—
(mg L^−1)	381	<0.30	4,600 [3]	—
(mg L^−1)	608	1,882	20,300 [3]	1,054.50 [13], 212 [7], 1,650 [96]
ORP (mV)	−334.20	—	—	—
Turbidity (NTU)	—	—	—	6.10 [16], 37 [17], 37 [19]