STUDIES ON THE PURIFICATION OF WASTEWATER FROM COKE-CHEMICAL PLANTS FROM PHENOLS AND OILS USING LIGNIN-BASED SORBENTS

S. A. BABENKO, L. F. PROSEKOVA, V. P. ZHUCHKOV, L. A. PERSHINA

(Presented by the scientific seminar of the departments of OChT and PMAChP)

The data available in the literature [1—5] indicate that sorption methods for the purification of wastewater from coke-chemical plants are used mainly for the removal of phenols.

As sorbents, brown coal, brown-coal ash pretreated with hydrochloric acid, and synthetic ion exchangers are used: the anionites AV—17, AN—2F, EDE—10p, sulfonated carbon of grade SK-2, and others. It is noted [2] that, in order to avoid fouling of the ionites, the water was filtered free of oils before purification from phenols. Thus, at present there is no inexpensive sorbent that would simultaneously absorb from wastewater all organic substances dissolved in it over a broad pH range.

The absorption of dissolved substances by the surface of solids opens up broad possibilities also for removing undesirable impurities of an organic character from water. The rate of adsorption from solutions is determined by a number of factors: the structure of the adsorbent, the degree of its subdivision, temperature, the pH value, mixing conditions, and, finally, the nature and size of the adsorbed substance.

For the purification of wastewater from phenols and oils we used a sorbent prepared on the basis of lignin.

To determine the optimum operating conditions of the sorbent under static conditions, we studied different ratios of sorbent to water, different temperatures and contact times, and the influence of the medium on the degree of purification. The sorbent-to-water ratios used were 1 : 20, 1 : 40, 1 : 80. The contact time of the sorbent with the water was varied from 5 to 15 min. Water was purified from phenols and oils by bringing the water into contact with the sorbent in a flask, after which the sorbent was rapidly filtered off on a Büchner funnel. The phenol content in the wastewater was determined photocolorimetrically, and the oil content by the gravimetric method. The present study was carried out on a wastewater sample delivered from the Kemerovo Coke-Chemical Plant. The phenol content in the water was 600 mg/l; oils, 1220 mg/l; water pH, 9. To clarify the chemical composition of the oil present in the wastewater, an attempt was made to separate it into its constituent fractions. To determine the saturation time of the sorbent, weighed portions of sorbent of 10, 5, and 2.5 g were mixed in a flask with 200 ml of wastewater at a temperature of 20°C and left in contact for 5, 10, and 15 min.

The results obtained indicate that the principal absorption of phenol and oil occurs within 10 min, and a further increase in the contact time of the water and sorbent has practically no effect on the degree of

Table 1

Composition of the oil contained in wastewater

Extraction of phenol and oil from water at any ratio of sorbent to water.

Experiments on water purification with the sorbent at different water:sorbent ratios and the same contact time showed that the degree of purification decreases correspondingly when the amount of sorbent per given volume of treated wastewater is reduced. With an initial phenol content in water of 600 mg/l and oil content of 1220 mg/l, at a sorbent:water ratio of 1:20 the degree of purification from phenol was 64.4%, and from oil, 66.7%; correspondingly, at a ratio of 1:40 the percentage purification from phenol was 24.6%, and from oil, 40%; and at dilution of 1:80 the wastewater was purified from phenol by only 14%, and from oil by 33.9%.

Determination of the sorbent capacity for phenol and oil was carried out at temperatures of 20, 40, and 60°C. The sorptive capacity of the sorbent increases with increasing temperature. In order to determine the optimum temperature for the sorption process of oils and phenols under static conditions, a series of experiments was conducted to study the effect of temperature on the degree of wastewater purification. An analysis of the results obtained shows a quite definite regularity—the degree of wastewater purification increases with increasing temperature.

Table 2

Sorption capacity of the sorbent at various temperatures

Table 3

Effect of temperature on the degree of wastewater purification at a water:sorbent ratio of 1:20

Experiments on wastewater purification with the sorbent at different pH values of the medium—alkaline pH = 9, neutral pH = 7, and acidic pH = 4—indicate that the pH of the medium does not affect the degree of extraction of phenol from water. At any of the selected pH values it remained constant. Oil, however, is extracted much better in an acidic medium.

A study of the possibility of using a sorbent prepared on the basis of lignin for wastewater purification raised the question of the need for its regeneration. The simplest method of regenerating the sorbent, in our opinion, consists in calcining the saturated sorbent at a temperature of 300°C. At this temperature the phenols and oils absorbed by the sorbent should burn out, and the calcined sorbent was then reused as an absorbent. According to experimental data, during regeneration not only did the absorbed components burn out, but the sorbent itself also partially burned out, amounting to about 20% of its weight. The sorptive capacity of the sorbent after regeneration decreased by a factor of 2 compared with the initial value.

Conclusions

1. The experiments carried out showed that a sorbent obtained on the basis of lignin possesses sufficient sorption capacity and can be used for treating wastewater from coke-chemical plants to remove oils and phenols.

2. With a single treatment of wastewater with the sorbent, at a ratio of 1:20 and a temperature of 60°C, it was possible to reduce the phenol content in the water to 140 mg/l, and the oil content to 170 mg/l.

3. Threefold contacting of the wastewater with a fresh portion of sorbent made it possible to purify the wastewater of the Kemerovo Coke-Chemical Plant to a residual phenol content of 65 mg/l and oil content of 100 mg/l. With such an oil content, the wastewater may be sent for biological treatment.

Literature

1. I. I. Rashkevich, V. I. Dal’. Ukrainian Chemical Journal, vol. 33, no. 2, Kiev, 1967.

2. B. P. Krasnov, I. V. Ovchinnikov. Treatment of wastewater to remove phenol and pyridine with ionites. Coke and Chemistry, No. 8, Moscow, 1966.

3. O. R. Skorokhod, I. B. Stankevich. On the influence of cations on the sorption of phenols by sulfocationite. In: Ionites and Ion Exchange, Nauka, Moscow, 1966.

4. V. G. Sinyavskii. Selective Ionites, “Tekhnika,” Kiev, 1967.

5. Yu. Yu. Lur’e, B. P. Krasnov. On the sorption of phenol by ion-exchange resins. In: Treatment of Industrial Wastewater. Proceedings. State Publishing House for Construction, Architecture, and Building Materials, Moscow, 1962.