**2.2. Tests with real effluent using oily water from the oil industry**

Through laboratory tests we noted that the real effluent yielded obtained from an oil company did not have high salinity and had high oil and grease content (60 g / L), so it was not characterized as produced water but rather as oily effluent.

We conducted there tests:

16 New Technologies in the Oil and Gas Industry

(a), to guide the operator.

(Tecnopeltron PLTN model 100/15). In this setup, the input power at 60 Hz from the grid is converted to variable frequency output of 1 to120 Hz in order to obtain AC power at the desired level. As with the DC setup, there is a meter to indicate the voltage (V) and current

Figure 5 shows a block diagram where the 60 Hz current from the grid feeds a frequency converter with variable output from 1 Hz to 120 Hz, connected to a variable voltage stepdown transformer, thereby providing appropriate frequency and voltage to the electrode. In the rectification step that occurs in the variable frequency converter, the power is transformed into DC. Then the new direct current is treated in the oscillator module which converts it into pulses with controlled width, forming a new AC waveform, with a frequency that can vary between 1 Hz and 120 Hz depending on the level of feedback (reference) from the load controller. Thus, it has a sinusoidal waveform where the period

> Step-down transformer

> > Voltmeter

Ammeter

Electrode

The electrode is the central element for treatment. Thus, the proper selection of its materials is very important. The most common electrode materials for electroflocculation are aluminum and iron, since they are inexpensive, readily available and highly effective. In this experiment we used a hive array of seven interspersed aluminum plates measuring 10 cm long, 5 cm wide and 3 mm thick. The plates were separated by spacers (1 cm thick each),

The electrodes were connected to specific instruments to control and monitor the current and voltage applied to the system, namely a frequency converter/regulator, potentiometer, step-down transformer, voltmeter, ammeter, bridge rectifier and polarity

varies with the load, to obtain the best performance at active power levels.

inverter

**Figure 5.** Schematic diagram of the experimental AC unit

Frequency Converter

inverter Voltage

allowing varying the distance between the electrodes.

Figure 6 shows an example of hive aluminum electrodes.

reversing switch.

Power 127 V


Table 1 shows the values obtained with the AC and DC electroflocculation processes with the original effluent as received. The results of the AC setup were obtained with the maximum current of the unit (i = 2.5 A), due to the low salinity. The voltage was 11 V. In the case of direct current, the unit only reached a maximum of 1.6 A, so we added 1 g of salt to obtain the same current intensity as the AC unit. By adding salt to the effluent in the DC system, there is an improvement in removal efficiency.

The analysis of the oil and grease parameter (supernatant) was carried out separately, while the remaining parameters were analyzed with the subnatant phase of the effluent. The AC and DC electroflocculation tests were performed with the effluent containing an oil and grease content of 60g/L.

There was an increase in pH during the final AC and DC tests, attributed to the generation of OH-ions during the water reduction step.

$$2\text{H:}\text{O}\_{(l)} + 2\text{e}^{\cdot} \rightarrow \text{H:}\_{(l)} + 2\text{OH}^{\cdot}\_{(l\text{aq})}\tag{5}$$

Although these ions are also used to form the coagulating agent, the remaining quantity results in an increase of the pH value. This was also observed by [43, 67, 68].


Legend: Data: time = 15 min., Delectrode. = 1 cm, vol. = 3L, i = 3 A, f = 60 Hz AC. Note: In the DC setup, 1 g of salt was added to increase the conductivity and the current intensity of the equipment, because it was unable to reach the same as with the AC setup.

**Table 1.** Data from the EF treatment process.

Despite the low conductivity of the effluent, there was high removal of pollutants and complete clarification after treatment for 15 minutes. The removal of ammonia, phenols and sulfides may have been obtained by drag of the gas phase (electroflotation).

Figure 7 shows the evolution of the tests of the raw effluent and after treatment with AC and DC.

**Figure 7.** EF tests with real effluent with low salinity. Legend: a) raw effluent; b) effluent treated with AC electroflocculation; c) effluent treated with DC electroflocculation; and d) comparison of raw effluent with samples treated with AC and DC electroflocculation. Note: The tests performed with t = 15 min.


The test results using the effluent plus NaCl to bring the salinity to 60 g / L, to simulate produced water, are shown in Table 2.

Data: vol. = 3 L, t = 6 min., Delectrode. = 1 cm, vol. = 3 L, i = 3 A, f = 60 Hz AC.

18 New Technologies in the Oil and Gas Industry

as with the AC setup.

and DC.

**Table 1.** Data from the EF treatment process.

**c** 

**a**

Although these ions are also used to form the coagulating agent, the remaining quantity

Despite the low conductivity of the effluent, there was high removal of pollutants and complete clarification after treatment for 15 minutes. The removal of ammonia, phenols and

Figure 7 shows the evolution of the tests of the raw effluent and after treatment with AC

**b** 

**Figure 7.** EF tests with real effluent with low salinity. Legend: a) raw effluent; b) effluent treated with AC electroflocculation; c) effluent treated with DC electroflocculation; and d) comparison of raw effluent with samples treated with AC and DC electroflocculation. Note: The tests performed with t = 15 min.

**d** 

sulfides may have been obtained by drag of the gas phase (electroflotation).

**Parameters Oily wastewater AC DC**  pH 6.7 8.3 8.2 Turbidity (NTU) 840 2 2 Color (Abs. 400 nm) 0.46 0.02 0.01 Salinity (mg/L) 279 340 1210 Conductivity (µS/cm) 580 702 2238 TDS (mg/L) 408 498 1680 Phenols (mg/L) 0.5 < 0.1 < 0.1 Sulfides (mg/L) 2.8 < 0.5 < 0.5 Ammonia nitrogen (mg/L) 36.0 3.7 1.5 O&G (mg/L) 60000 18 22 Current (A) 0 2.5 2.5 Tension (V) 0 11.0 8.5 Legend: Data: time = 15 min., Delectrode. = 1 cm, vol. = 3L, i = 3 A, f = 60 Hz AC. Note: In the DC setup, 1 g of salt was added to increase the conductivity and the current intensity of the equipment, because it was unable to reach the same

results in an increase of the pH value. This was also observed by [43, 67, 68].

**Table 2.** Results obtained during tests of AC and DC electroflocculation using effluent with high salinity.

Since the electrolytic process involves corrosion of the electrode, according to Faraday's laws, there is mass loss of the electrodes. We measured this electrode mass loss by the weight difference before and after each test. High removal efficiencies were observed in tests with the high-salinity effluent. Electrode mass consumption with alternating current was 33% lower than with direct current, with all other conditions the same. Low voltage was applied during electrolysis in the tests to achieve high pollutant removal efficiency. In previous tests, the low conductivity greatly increased the voltage required by the system, leading to high energy consumption. This indicates that high conductivity greatly favors the electrolytic process.

Figure 8 shows the evolution of the tests with high-salinity effluent using the EF technology with alternating current and direct current. Note the total clarification after the tests without filtration.

Table 3 shows the results of the high-salinity effluent treated with the AC and DC processes.

As can be seen from the above table, the high turbidity, color and O&G were almost completely removed (above 99%). The voltage applied to the electrodes was very low, resulting in high efficiency of the technique. The electrode mass consumed with DC was 31% higher than with AC.

A hypothesis for the lower electrode consumption with alternating current is that since DC only flows in one direction, there may be irregular wear on the plates due to the onslaught of the current and subsequent oxidation occurring in the same preferential points of the

electrode. In the case of AC, the cyclical energization retards the normal mechanisms of attack on an electrode and makes this attack more uniform, thus ensures longer electrode life.

**Figure 8.** EF tests with high-salinity effluent. Legend: 60g / L NaCl: a) raw wastewater containing 60g / L of O&G; b) raw wastewater being mixed salt, for EF testing; c) effluent treated with AC (left) and DC (right) electroflocculation.


Note: Data: vol. = 3 L, t = 6 min.

**Table 3.** Results of treating high-salinity effluent with AC and DC electrolysis.

Figure 9 shows the evolution of EF treatment of high salinity effluent during the stages of development using AC and DC.

**Figure 9.** Tests of EF with high-salinity effluent. Legend: (60g/L) of salt. Processing steps: a) emulsified effluent, b) effluent undergoing electroflocculation with formation of supernatant sludge, c) treated effluent, with sludge formation; d) original effluent and after treatment with AC (left) and DC (right) electroflocculation.
