Process Biochemistry 37 (2002) 693– 698 www.elsevier.com/locate/procbio Effect of zeolite media for the treatment of textile wastewater in a biological aerated filter Won-Seok Chang, Seok-Won Hong *, Joonkyu Park Korea Institute of Science and Technology, PO Box 131, Cheongryang, Seoul 130 -650, South Korea Received 7 February 2001; received in revised form 10 June 2001; accepted 7 July 2001 Abstract A biological aerated filter (BAF) was applied to treat textile wastewater. The performance of two lab-scale biofilters was monitored for 7 months to compare the effect of natural zeolite with sand as media. Under organic load varying from 1.2 to 3.3 kg COD/m3 day, the overall chemical oxygen demand (COD) reductions of the biofilter supported by natural zeolite and sand averaged 88 and 75%, respectively. Higher nitrogen removal in the biofilter with natural zeolite was attributable to its ion exchange capacity with NH4 + . The results of cell counting showed that the numbers of nitrifying bacteria within the biofilm were higher on natural zeolite than on sand. Both biofilters were able to remove about 97% of suspended solids (SS) with loading of 1–3 kg SS/m3 day. A pilot-scale BAF supported by natural zeolite with capacity to treat up to 12 m3/day of textile wastewater was also monitored for 5 months. This system was able to remove about 99% biochemical oxygen demand, 92% COD, 74% SS, and 92% T-N with hydraulic load of 1.83 m3/m2 h. Operation with a higher hydraulic load (2.3 m3/m2 h) and at lower temperatures (range of 4–10 °C) resulted in decreasing the T-N removal efficiency while the reduction in terms of organic matter was less affected. Regardless of increasing hydraulic loading rate, colour removal (average of 78%) was effective in the biofilter with natural zeolite due to its adsorption capacity. © 2002 Elsevier Science Ltd. All rights reserved. Keywords: Biological aerated filter; Textile wastewater treatment; Natural zeolite 1. Introduction Biological aerated filters (BAF) represent an attached growth process on media which are stationary during normal operation with aeration. The initial purposes of these processes were to obtain carbon oxidation and solid filtration. In recent years, several technologies using BAF were developed to treat wastewater from slaughterhouses, and from pulp and mill industries [1,2]. The BAF process has a number of primary advantages which confer benefits for the adaptation of this technology in several areas [3 – 6]. The attached growth on an inert granular media in BAF allows for a much higher concentration of active biomass than a suspended growth activated sludge system so that the size of reactor can be reduced. In addition, suspended solids * Corresponding author. Tel.: +82-2-958-5844; fax: + 82-2-9585839. E-mail address: [email protected] (S.-W. Hong). (SS) in the influent can be captured physically by the media and this eliminates the requirement for separate secondary clarification. Overall, these result in a spacesaving layout that uses only one-third the footprint space of an activated sludge process [6]. As BAF technology is applied to industrial wastewater treatment, the selection of granular media plays an important role in maintaining a high amount of active biomass and a variety of microbial populations. Using the media with adsorption capacity, an approach for the integration of biological removal and adsorption can be possible. The beneficial aspects of integrated biodegradation/adsorption were reported in studies using activated carbon as a media in municipal wastewater treatment [7,8]. The effluents from the textile industry are one of those wastewaters that are hard to treat satisfactorily because they are highly variable in composition [9]. The most notorious characteristic of the textile wastewater is strong colour. If not properly dealt with, the colour 0032-9592/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 2 - 9 5 9 2 ( 0 1 ) 0 0 2 5 8 - 8 W.-S. Chang et al. / Process Biochemistry 37 (2002) 693–698 694 would cause a significantly negative impact on the aquatic environment due to the increment of turbidity and high polluting strength. Traditional technologies to treat textile wastewater include various combinations of biological, physical and chemical methods [9,10], but these methods require high capital and operating costs. This paper reports the application of BAF for textile wastewater treatment using natural zeolite as media. Natural zeolite has an adsorption capacity for organic substances and is also capable of cation exchange for example NH4 + [11]. The wastewater from a textile industry was fed to lab- and pilot-scale downflow biofilters and the performance of biofilters with natural zeolite and sand media was observed. In addition, the experimental results obtained from a BAF pilot plant filled with natural zeolite are presented. 2. Materials and methods 2.1. Wastewater characteristics The wastewater used for the laboratory experiment was obtained from J textile factory in Seoul, Korea. The fibres used in the textile industry can be divided into two types: natural and man-made. The two major natural fibres are wool and cotton. The latter includes polyester, nylon, polyacrylic and polyamide. From March to September 1998, raw textile wastewater samples were collected monthly in 20 l plastic containers, which had been already washed and rinsed with distilled water, and kept in a refrigerator (below 5 °C) during the experiment. The characteristics of textile wastewater are summarized in Table 1. Table 2 shows the composition of textile wastewater fed to a pilot plant which was installed at T textile industrial complex in Korea. The textile waste effluents from several dyeing and finishing plants were mixed together in the equalization storage tank. About 70% of total waste effluent were generated from the polyester deweighted process. The mixed wastewater was then primarily treated with ferric chloride and polymer. After chemical coagulation, the treated textile wastewater was stored in a second equalization tank. Table 1 Characteristics of textile wastewater fed to a laboratory-scale BAF system Parameter Range (mg/l) Average (mg/l) COD BOD5 TKN NH4+-N SS Alkalinity 830–1050 320–460 86–145 54–84 540–980 330–390 920 390 115 69 760 360 Table 2 Characteristics of textile wastewater in evaluating pilot-scale BAF system Parameter Range Average COD (mg/l) BOD5 (mg/l) SS (mg/l) T-N (mg/l) Colorimetry (CU) 1860–2490 1350–1910 45–93 62–90 560–928 2150 1630 63 72 740 2.2. Reactor description Laboratory-scale BAF reactors were made of acrylic and are shown in Fig. 1. The reactor height was 33 cm and the rectangular cross-section 18 cm (length) and 12 cm (width) with a working volume of 2.8 l. One was packed with natural zeolite and the other with sand. All packings were sieved through a 5× 8 mesh (2.36–4.0 mm). The hydraulic flow rates were controlled in the range of 0.35–1.56 m3/m2 h. The biofilter was backwashed periodically so that the accumulated SS and the excess biomass produced were removed. The backwash sequence included air scour, followed by combined air scour and water backwash. The backwash air application rate was 4 l/min. An extensive laboratory-scale experimental programme led to the development of a pilot-scale BAF system to treat textile wastewater effectively. A pilot plant with capacity to treat up to 12 m3/day had a cross-section area of 1.05 m2 and height of 3 m (volume of 3.15 m3), and was made of steel. The volume of empty bed was 2.0 m3. The bed was packed with natural zeolite which had a specific gravity of 1.42. A percolated plate was placed in the reactor to support the media and distribute backwash water and air. The backwash sequence was the same as in laboratory-scale experiments, and was controlled automatically using a microprocessor and automated values. The effluent was collected in a storage tank to provide backwash water. A schematic of a pilot plant is shown in Fig. 2. 2.3. Analytical methods Samples were collected weekly from March 1998 to February 1999 for the influent and effluent of lab- and pilot-scale BAF. The chemical oxygen demand (COD), biochemical oxygen demand (BOD), SS, total Kjeldahl nitrogen (TKN), and nitrite nitrogen (NO2-N) plus nitrate nitrogen (NO3-N) were analysed according to standard methods. Additionally, the colour of the influent and effluent was determined using the ADMI tristimulus filter method [12]. The temperature, dissolved oxygen (DO) and pH were routinely monitored during the experimental period. W.-S. Chang et al. / Process Biochemistry 37 (2002) 693–698 695 Fig. 1. Experimental schematic of laboratory-scale BAF system. 2.3.1. Counting of nitrifying bacterial population Samples of media covered with biomass were collected at the top, middle, and bottom sections of the biofilter. A membrane filter method was used to count viable heterotrophic and nitrifying bacteria. To count heterotrophic bacteria, albumin agar medium was used. A medium containing only the ammonium ion as an electron donor was used to detect the presence of ammonia-oxidizing bacteria, Nitrosomonas. For nitriteoxidizing bacteria, Nitrobacter, a medium containing the nitrite ion was used. These media and details of viable cell counting are described elsewhere [13]. adsorption capacity of natural zeolite for organic substances. Linear regression of effluent TKN concentrations against loading rates for the biofilter with natural zeolite and sand had an R 2 of 0.66 and 0.81, respectively (Fig. 5). The average residual TKN concentration in the effluent from the biofilter with natural zeolite was 13.6 mg/l while the residual from the other was 34.8 mg/l. In the biofilter supported by sand, the percentage of TKN removal decreased drastically with the increment of TKN loading rates over the ranges applied in this experiment. On average, less than 62% TKN was removed. 3. Results and discussion 3.1. Comparison between natural zeolite and sand using lab-scale reactors Two lab-scale biofilters media were monitored for 7 months. Throughout the experiment, DO was maintained above 3 mg/l and water temperature was kept between 12 and 15 °C. The effluent pH decreased slightly compared with that of the influent, the average being 7.0 (6.8–7.2). A plot of effluent COD concentrations versus organic loading rates (OLR) for two reactors is shown in Fig. 3. A linear regression of the data is also shown to illustrate the trend. The volumetric OLR varied from 1.2 to 3.3 kg COD/m3 day. The COD removal efficiency of the biofilter with zeolite and sand averaged about 88 and 75%, respectively. A linear regression of the data in Fig. 4 indicated that effluent BOD concentrations from the biofilter with zeolite are lower than those from the other, at all BOD loading rates. This was expected because more reduction should be attributable to the Fig. 2. Schematic of pilot-scale BAF system. 696 W.-S. Chang et al. / Process Biochemistry 37 (2002) 693–698 Fig. 5. Relationship between TKN loading rate and effluent concentrations. Fig. 3. Relationship between COD loading rate and effluent concentrations. In terms of removing TKN, the efficiency of the biofilter with natural zeolite decreased slightly with increased hydraulic loading rates. However, it was capable of removing more TKN at higher loading rates as the regressed lines indicate. More than 80% of fed TKN was removed. As nitrogen load increased with a higher hydraulic loading rate, so did organic load. In general, higher organic loading suppresses nitrification but not in the biofilter with natural zeolite. This can be explained by the effect of natural zeolite that is capable of exchanging ions with NH4 + . First, some portion of NH4 + in the influent is adsorbed onto the surface of natural zeolite. Then, natural zeolite concentrated with NH4 + and an intensely aerated environment provide favourable conditions for autotrophic bacteria attach- Fig. 4. Relationship between BOD loading rate and effluent concentrations. ment. This may lead to the oxidation of nitrogen as well as organics. The SS concentration in the effluent from each biofilter, was also plotted against loading rate of SS (Fig. 6), but showed no significant difference. SS loading rate varied from 1 to 3 kg SS/m3 day. The effluent SS concentrations out of each biofilter supported by natural zeolite and sand averaged 30 and 34 mg/l, respectively. 3.2. Nitrifying bacterial population Samples for viable cell counting of heterotrophic and nitrifying bacteria were taken at ten different locations of the biofilter. The results of cell counting are shown in Fig. 7. The number of heterotrophic bacteria in the biofilm grown on natural zeolite was similar to that on sand. However, the number of heterotrophs in the Fig. 6. Relationship between SS loading rate and effluent concentrations. W.-S. Chang et al. / Process Biochemistry 37 (2002) 693–698 Fig. 7. Numbers of heterotrophic and nitrifying bacteria in biofilm grown on natural zeolite and sand, and activated sludge (AS). biofilm on both the zeolite and sand was greater than that in an activated sludge process. The numbers of heterotrophs were counted at 1.3×109 and 1.2×109 in biofilm grown on natural zeolite and sand, respectively. On the other hand, the numbers of nitrifiers depended on the media on which the biofilm grew. The numbers of nitrifiers were greater on natural zeolite than sand. In the biofilm grown on natural zeolite, Nitrosomonas and Nitrobacter were counted at 3.0× 108 and 2.2 × 109 CFU/ml, respectively, while those on sand were counted at 4.5× 108 and 6.5×108 CFU/ml, respectively. It concludes that a more favourable environment for the growth of Nitrobacter would be provided in the BAF supported by natural zeolite. 3.3. Pilot test of the BAF supported by natural zeolite A pilot-scale BAF supported by natural zeolite was operated at two different hydraulic loads, 1.83 and 2.3 m3/m2 h for 5 months. Thus, this pilot experiment can be divided into two stages in accordance with the influent loading. At each stage, the range of water temperature was 10– 18 and 4– 10 °C, respectively, and the DO concentration was kept above 2.0 mg/l. 697 The average performance of the BAF system is summarized in Table 3. As hydraulic loading rate increased, organic load was also increased from 1.5 to 2.1 kg BOD/m3 day which is higher than that (0.5–1.0 kg BOD/m3 day) in municipal wastewater treatment [14]. Under such a high organic loading condition, overall reductions for BOD and COD were 99 and 86– 92%, respectively. The residual BOD concentration in the effluent was always less than 20 mg/l. However, SS removal was dependent on hydraulic load. When hydraulic loading rate increased from 1.83 to 2.3 m3/m2 h, the residual SS concentration in the effluent was also increased from 16 to 35 mg/l. Some of the SS may be filtered by the media in the BAF, but it is also being utilized by the bacteria attached on the media and converted to microbial biomass. At a lower hydraulic loading rate, the T-N reduction averaged 92%. The loss of nitrogen could be due to either ammonia volatilization or simultaneous nitrification/denitrification in the biofilm. Although neither process was directly measured in this study, the former could be occurred rarely since the environment in the system (e.g. pH, an average of 6.3 in the effluent, and intensity of aeration) limited the possibility of ammonia volatilization. On the other hand, simultaneous nitrification/denitrification might have occurred within the biofilm. It was suggested by Laursen et al. [15] that the removal of nitrate in BAF takes place deeper into the biofilm, as long as organic matter is present to be used as an electron donor. In the case when hydraulic load was increased, however, T-N reduction was decreased to 75%. The increased hydraulic and organic load should lower the activity of autotrophs in the biofilm. However, the main effect of causing lower T-N reduction is considered to be a decrease of temperature rather than an increase of hydraulic load. Since the temperature ranged from 4 to 10 °C, the biological activity of nitrifying bacteria which was more sensitive to temperature [16], should be affected. At different hydraulic loading rates, the colour reduction averaged 77 and 79%, respectively. The results indicate that the primary colour removal mechanism in Table 3 The result of pilot test of BAF with natural zeolite Parameter COD (mg/l) BOD (mg/l) SS (mg/l) T-N (mg/l) Colour (unit) Hydraulic load (1.83 m3/m2 h) Hydraulic load (2.3 m3/m2 h) Influent Effluent Reduction (%) Influent Effluent Reduction (%) 2230 1574 62 79 717 176 17 16 6 165 92.1 98.9 73.8 92.0 76.9 2150 1711 62 67 773 295 20 35 16 156 86.3 98.8 43.7 75.2 78.9 698 W.-S. Chang et al. / Process Biochemistry 37 (2002) 693–698 this system is adsorption. This suggests that, given sufficient time to contact, colour-causing organics are able to penetrate and fully saturate the pores of zeolite. Subsequently, those organics are degraded completely by a number of microorganisms attached to the media. Therefore, it requires no external steps to renew the media in order to maintain such colour removal efficiency for a protracted period. 4. Conclusions (1) BAF technology was employed for the treatment of textile wastewater. An experiment was conducted under laboratory conditions to investigate the effect of media. In terms of removing organic matter and TKN, the performance of the biofilter with natural zeolite was superior to that with sand. Ion exchange capacity of natural zeolite with NH4 + leads to higher nitrogen removal. (2) The results of cell counting indicated that the numbers of Nitrosomonas and Nitrobacter in the biofilm grown on natural zeolite were 3.0× 108 and 2.2× 109 CFU/ml, respectively, while those on sand were 4.5× 108 and 6.5×108 CFU/ml, respectively. A more favourable environment for nitrifying bacteria was, therefore, provided in the biofilter with natural zeolite due to its ion exchange capacity. Subsequently, the adsorption surface was renewed within the process by the biological regeneration which converts ammonia to nitrate nitrogen. (3) The results obtained from the operation of a pilot-scale BAF indicate that natural zeolite is a superior media for textile wastewater treatment. Reductions for COD (86– 92%), BOD (99%) and colour (77–79%) were not significantly dependent of hydraulic load. A temperature range of 4–10 °C could be considered as the main effect causing a lower total nitrogen removal at a higher hydraulic load. References [1] Kantardjieff A, Jones JP. Aerobic biofilter treatment of slaughterhouse effluent. In: Proceedings of 51st Purdue Industrial Waste Conference, Ann Arbor, MI, 1996. p. 595 – 600. [2] Kantardjieff A, Jones JP. 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