Electrochemical Technologies for Removing Petroleum Hydrocarbons from Produced Water
Table 1: Percentage of Petroleum Pollutants Removal from Selected Petrochemical Wastewaters Obtained by EO, IEO and EF Processes (plus Energy Consumption)
Anode/electrode used Baseline Wastewater origin
Ti/TiO2RuO2IrO2 Oil refinery
Applied current Electrolysis
measurements density (mA/cm-2) time (h) 602[a] 141[b] 112[c]
54
Ti/Ru0.34Ti0.66O2 anode 315[a] Oil extraction industry 887[c]
Ti/RuO2TiO2
Produced water Ti/RuO2
containing PAHs Industry waste containing PAHs
Amphoteric surfactant
solution containing PAHs Pt/Ir electrodes
3,080[a]
Bilge water (seawater + 23,916[b] petroleum pollutants) BDD anode (EO process)
590[a] 193[c]
Petroleum refinery BDD anode (IEO process)
Petroleum refinery Iron electrode (EF process)
Petroleum refinery Ru-MMO electrode (EO process)
Petroleum refinery
Notes: [a] = initial COD (mg/l); [b] = initial phenolics concentration (mg/l); [c] = chloride dissolved (mg/l); [d] = not determined; [e] = NH4+ concentration; [f] = % of NH4+ removal; [g] = initial TOC; [h] = % of TOC removal; [i] = mg Kg of PAHs; [j] = % of PAHs removal; [k] = % of phenol removal.
Key: BDD = boron doped diamond; COD = chemical oxygen demand; EF = electro-Fenton; EO = electro-oxidation; IEO = indirect electro-oxidation; PAHs = polycyclic aromatic hydrocarbons; Ru-MMO = ruthenium mixed metal oxide; TOC = total organic carbon.
solution pH, retention time (tR), stirring or flow rate and applied current density (or cell voltage).10,12,17
For example, the EC processing of phenol
using Al screen as a scarified anode was studied by Abdelwahab et al.12 Experimental parameters such as pH, time, current density, electrolyte concentration, initial phenol concentration and an array of closely packed Al screen anode were investigated. Under optimal experimental conditions, after two hours of EC, 94.5 % of the initial phenol concentration had been removed from the petroleum refinery wastewater (volume = 3.5 l containing 13 mg l-1 of phenol, 2 g l-1 of NaCl and pH 8). Practically, the effluent met discharge standards after two hours of EC with an energy consumption of 1.8 kWh g-1 phenol and an electrode consumption of 0.091 gAl g-1 phenol.
In the first case, oilfield-produced water was treated by an electrochemical process in a laboratory pilot-scale plant, using double anodes with active metal (M) and graphite (C), iron as cathode and a noble metal content catalyst with big surface. Due to the strong oxidising potential of the chemicals and coagulants produced, when the wastewater passed through the laboratory pilot-scale plant, the organic pollutants, including bacteria, were oxidised and coagulated. Both chemical oxygen demand (COD) and biochemical oxygen demand (BOD) were reduced by over 90 % in six minutes, and suspended solids were reduced by 99 %, Ca2+ content by 22 %, corrosion rate by 98 % and bacteria by 99 % in three minutes under 15 V/120 A.10 In the second case, EC was found to be ineffective for treating
Combined EC and EO processes were studied by Ma and Wang10 and Yavuz et al.17
114
petroleum refinery wastewater, achieving removal efficiencies of 8.23 % and 6.27 % for phenol and COD, respectively.17
Also, an
average energy consumption of 32 kWh g-1 was needed, which is approximately five times higher than the energy consumption values obtained with other methods.
Woytowich et al. investigated the treatment of ship bilge water contaminated with high concentrations of oil, suspended solids and heavy metals by a continuous EC process using iron and aluminium electrodes. This process was found to be effective in destabilising oil emulsions and in removing heavy metals.22
Electro-oxidation (EO) EO (see Figure 2) is the most popular electrochemical technology for removing organic pollutants from wastewaters.19–21
It has been
recently used for decolorising and degrading dyes from aqueous solutions. It consists in the oxidation of pollutants in an electrolytic cell by:
• •
direct anodic oxidation (or direct electron transfer to the anode), which yields very poor decontamination; and
chemical reaction with electrogenerated species from water discharge at the anode, such as physically adsorbed ‘active oxygen’ (physisorbed hydroxyl radical [*OH]) or chemisorbed ‘active oxygen’ (oxygen in the lattice of a metal oxide [MO] anode); the action of these oxidising species leads to total or partial decontamination, respectively.
EXPLORATION & PRODUCTION – VOLUME 9 ISSUE 2 590[a] 12.8 5 3 1 4 1 1,5
>0.25 >0.25
3.5 79 90 100 90 70 85–100 96 99[k] 95
193[b] 198[k] 1,775[c] 590[a] 193[b]
75 98[k]
590[b] 193[c]
20 76 70 94[k] 7 kWh g-1 2 kWh g-1 0.15 kWh g-1 13.9–50.9 kWh kg-1 4 kWh g-1
103[e] 1.8[b]
2102[a] Creosote oil solution 237[g] 18,440–7,709[i] 418[i] 9.23 4–13
1.5 6.5 1.5
67
100 45
100 8.6–17.8 9.23 20 70 2 1.5 Current Removal of COD Energy
efficiency (%) or other (%) 7.5
92 5 65 70 57 99[f] 61 26[h] 65 –95[j] 80–82[j] 1,680–735 kWh t-1 5.11 US$ m-3
consumption 105.8 kWh m-3
[d] [d] 42 kWh m-3 Reference
Rajkumar & Panalivelu, 20047
Santos, et al, 20069
De Lima, et al., 200911 Tran, et al., 200913
Tran, et al., 200914
Tran, et al., 201015
Körbahti
and Artut, 201016
Yavuz, et. al., 201017
Yavuz, et. al., 201017
Yavuz, et. al., 201017
Yavuz, et. al., 201017
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