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Resource recovery of sludge as a micro-media in an activated sludge process
Advances in Environmental Research 7 (2003) 629–633
Resource recovery of sludge as a micro-media in an activated sludge process Chang Gyun Kima,1,*, Hyung Sool Leea,2, Tai Il Yoonb,3 a
Regional Research Center for Coastal Environments of Yellow Sea, Inha University, 253 Yong Hyun Dong, Nam Gu, Inchon, 402-751, South Korea b Division of Environmental and Geosystem Engineering, Inha University, Inchon, South Korea
Abstract An experiment was conducted to evaluate the feasibility of sludge reuse as a micro-medium in an activated sludge (AS) process. Two experimental protocols were employed. A conventional activated sludge was tested as a control, while the other involved addition of clinoptilolite (ZR) of which 4000 mgyl was unvaryingly sustained in an aeration basin. Two experiments were performed for ZR. In one, clinoptilolite was used as micro-media for 60 days (Model 1). The other used dried excess sludge for 55 days (Model 2). For sludge being recovered as micro-media, organic matter in the sludge was eliminated by 86% at 300 8C. It was completely removed at 500 8C within 30 min, which was regarded as the optimal drying condition. For Model 1, the concentration of biomass was increased by 4720 mg MLVSSyl. It was greater by a factor of two than that of the control. Moreover, it is shown that organic matter could be removed up to 95%. In addition, the sludge settling properties were greatly enhanced by clinoptilolite being implemented as floc seeds. Nitrification was considerably improved by more than 90%, due to the high concentration of nitrifiers attached to micro media. For Model 2, the improved performance was sustained on applying burned sludge into the AS. It was concluded that dried sludge could be reused as micro-media in an activated sludge process. 䊚 2002 Elsevier Science Ltd. All rights reserved. Keywords: Micro-media; Sludge reuse; Nitrification; Activated sludge; Sludge settling
1. Introduction Sludge disposal by landfilling may no longer be appropriate owing to land scarcity and increasingly stringent environmental control regulations (Vesilind, 1979). Therefore, future sludge management will be moving towards minimization and reutilization of sludge as useful resources (Mossakowska et al., 1998). Meanwhile, many efforts have been made to upgrade the AS process by application of powdered minerals, e.g. talc, clay and zeolite. It has been reported that enhanced nutrient treatment was attained by addition of powdered *Corresponding author. Tel.: q82-32-860-7715; fax: q8232-872-7734. E-mail address: [email protected] (C.G. Kim). 1 Research Professor. 2 Research Associate. 3 Professor.
minerals into AS, including improved sludge settleability (Chudoba and Pannier, 1994; Cantet et al., 1996; Christopher and Peter, 1999). These materials commonly have rough surfaces, and sizes ranging from dozens to hundreds of micrometers, and are mainly composed of SiO2, CaO, MgO, Al2O3 and Fe2O3 (Olah et al., 1989). Besides, burned sludge originating from an incinerator primarily consists of SiO2 , CaO and MgO, which have the same physical properties as powdered minerals (Belevi and Langmeier, 2000). A feasibility test was thus conducted to address suitable reuse of sludge as contacting media in an AS process. In addition, potential reduction of sludge and nitrification performance was also investigated. 2. Materials and methods Two different types of experimental protocols were employed. One was to add clinoptilolite into AS and
1093-0191/03/$ - see front matter 䊚 2002 Elsevier Science Ltd. All rights reserved. PII: S 1 0 9 3 - 0 1 9 1 Ž 0 2 . 0 0 0 4 6 - 1
630
C.G. Kim et al. / Advances in Environmental Research 7 (2003) 629–633
X’pert MPD) and inductively coupled plasma (ICP) mass spectroscopy (SPQ 9000). Nitrate formation rate (NFR) was observed to verify nitrifiers activity. It was determined using 300 ml of mixed liquor suspended solid (MLSS) taken from the aeration basin and placed into a 1-l beaker where 10000 mgyl of NH4Cl solution was diluted to 50 mgyl of NHq 4 –N. Diffused air was supplied into the beaker so that DO was maintained at 3–4 mgyl. At the same time, temperature, MLVSS, DO and pH were coincidentally monitored. The sample was then taken every 30 min, thereby the nitrate concentration was then observed. 3. Results and discussion 3.1. The determination of optimal condition for sludge reuse Fig. 1. Schematic diagram of AS reactors.
the other was a conventional AS which was tested as a control. The apparatus consisted of an aeration tank (5 l) and a clarifier (3.3 l) as shown in Fig. 1. AS reactors were seeded with sludge taken from a municipal wastewater treatment plant. The reactors were operated at pH 7.0–7.5 and 20 8C ("2 8C). Dissolved oxygen (DO) was maintained ranging from 3 to 5 mgy l. Synthetic wastewater was used for influent as illustrated in Table 1. Influent chemical oxygen demand (COD), N and P were unvaryingly sustained at 250, 70 and 3 mgyl, respectively. Hydraulic retention time (HRT) and solid retention time (SRT) were fixed at 6 h and 20 days, respectively. For ZR, 4000 mgyl of media concentration was kept up in the aeration basin, which was determined by mixed liquor suspended solids (MLFSS) concentration. Two experiments were conducted for ZR. In one, clinoptilolite was used as micromedia for 60 days (Model 1) and the other used dried sludge as micro-media for 55 days (Model 2). A constant MLFSS concentration was accurately maintained in the reactor by adding a nominal amount of micro-media. The withdrawn sludge was dried in a furnace after the optimal drying temperature was obtained for the range of 100, 300, 500 and 800 8C. Subsequently, a residual level of organic content was determined at 10, 30, 60 and 180 min at a given drying temperature. y Influent and effluent COD, NHq 4 –N, NO3 –N and SS were determined by standard methods (APHA, 1998). Organic contents in incinerated sludge were determined by total organic carbon (TOC) using a combustion infrared method (APHA, 1998). Physico-chemical characteristics of clinoptilolite and residuals from dried sludge were obtained by X-ray diffraction (Philips
TOC was obtained on dried sludge treated at different temperatures and durations. As shown in Fig. 2, TOC of sludge incinerated at 100 8C was marginally eliminated at 8% and 370 mgyl of TOC still remained. However, increasing the temperature to 300 8C for 180 min led to TOC removal of 86%. Furthermore, it was shortened by 30 min at 500 8C, and inorganic particulates were formed. At a given specific drying period, there was no significant difference in the degree of removal of residual organic compounds between 500 and 800 8C. XRD was used to characterize the original clinoptilolite and dried excess sludge at different temperatures ranging from 100 to 800 8C. As shown in Fig. 3, the structure of original clinoptilolite remained unvaried at incineration below 500 8C. However, the structure was partially deteriorated at 800 8C. The XRD pattern of dried excess sludge at 500 8C corresponded closely to infant clinoptilolite as illustrated in Fig. 3. Moreover, SiO2, Al2O3 and Fe2O3 were abundant constituents of the residual materials of the sludge, which completely coincided with the composition of clinoptilolite as illusTable 1 Composition of lab prepared wastewater Constituents
Concentration (mgyl)
Glucose NH4Cl KH2PO4 K2HPO4 MgSO4Ø7H2O FeCl3 NaHCO3 CaCl2
180 120 15 10 30 5 600 15
C.G. Kim et al. / Advances in Environmental Research 7 (2003) 629–633
631
Fig. 2. TOC removal of excess sludge at different drying conditions.
trated in Table 2. This is consistent with the findings of Klieve and Semmons (1980). They found that pretreatment of clinoptilolite with NaOH, HNO3 and steam could not improve the zeolite’s performance. However, heat pretreatment at 600 8C for 1 h significantly improved the zeolite’s selectivity for ammonium exchange. Ammonium removal capacity was increased by approximately 17% for heat-treated clinoptilolite. In this study, drying of the original mineral had little influence on the ammonium exchange property showing 5 mg NHq 4 –Nyg.
3.2. The enhancement of wastewater treatment by clinoptilolite For Model 1, ZR commonly removed as much as 90% of the soluble organic matter, which was similar to that of the control. On the other hand, up to 95% of the total organic compounds were removed by the ZR, which was 32% greater than observed in the control. This indicates that the particles contribute to seeding resulting in dense and agglomerated floc, which in turn is better able to separate organic matter from the liquid
Fig. 3. XRD of origin and excess sludge dried at different temperatures.
C.G. Kim et al. / Advances in Environmental Research 7 (2003) 629–633
632
Table 2 The comparison of physico-chemical properties between infant clinoptilolite and residual materials obtained from excess sludge incinerated Parameters
C.E.C (mg NHq 4 –Nyg) Components (wt.%) SiO2 Al2O3 Fe2O3 PbO MoO3 MnO MgO CaO Ig-lossa a
Infant clinoptilolite
Residues dried from sludge
5.12
5.00
61.26 12.40 1.54 0.02 0.053 0.058 0.84 1.30 14.02
64.63 13.27 1.61 0.019 0.053 0.056 0.87 1.51 4.65
Ignition loss.
phase being discharged to an effluent. Fig. 4 shows improved SS removal for ZR compared to the control. Effluent SS from the ZR were lower (3–12 mgyl) as compared to 8–34 mgyl for the control. The preferable sludge separation using powdered clinoptilolite has been reported by previous investigators (Olah et al., 1989; Son et al., 2000). They reported that the turbidity and SS of effluent were gradually decreased due to the formation of a biofilm on the surface of the zeolite in comparison to the control. The enhancement of sludge separation was also unvaryingly sustained for Model 2. It was deduced that seeding of dense floc or biofilm formation were significantly dependent on the surface
Fig. 5. NFRs of both reactors at different conditions.
characteristics e.g. roughness as noted by Liu (1997). In regard to the effect of clinoptilolite on biomass, MLSS and MLVSS in ZR were progressively augmented up to 9580 and 4760 mgyl, respectively, in Model 1. However, the microbial concentration of the control was 2850 and 2030 mgyl, respectively. For Model 2, high biomass was sustained to the same degree as in Model 1. The high concentration of microbes associated with use of powdered mineral, e.g. clay, clinoptilolite, talc, etc., has been reported by many investigators (Olah et al., 1989; Son et al., 2000; Chudoba, and Pannier, 1994). They commonly reported that biofilm was formed on the surface of powdered materials or microbial concentration was considerably increased compared to the conventional AS. For Model 1, enhanced nitrification using ZR was also observed to be as high as 38% compared to the
Fig. 4. TCOD elimination according to effluent SS at both reactors.
C.G. Kim et al. / Advances in Environmental Research 7 (2003) 629–633
control. Even though 120 mg NHq 4 –Nyl of peak load was given, the same extent of improvement was constantly maintained, while it deteriorated remarkably in the control. This effect was attributed to a high concentration of nitrifying microorganisms present in ZR. As shown in Fig. 5, the NFR of ZR was 8.39 mg NOy 3 – NylØh, which was greater by a factor of two than that of the control. However, the NFR per microbe was similar in both cases (1.82 for the control and 1.97 mg NOy 3 –NygØMLVSSØh for ZR). For Model 2, improvement of nitrification for ZR was unvaryingly observed, revealing 8.24 mg NOy 3 –NylØh of NFR compared to 4.23 mg NOy 3 –NylØh for the control. 4. Conclusions The feasibility of sludge reuse as micro-media was evaluated in an AS process with addition of clinoptilolite. The optimal condition for drying sludge was concluded to be 500 8C for 30 min. At the given condition, residues from sludge almost physically corresponded to the composition of infant clinoptilolite, which showed a similar XRD pattern. In addition, the ammonium exchange property of the residual material was absolutely recovered at the level of 5 mg NHq 4 – Nyg, which was consistent with the level of original clinoptilolite. For Model 1, biomass was increased to 4720 mg MLVSSyl with ZR addition, which was higher by a factor of two compared to the control. In addition, ZR presented high removal of total organic compounds, due to improvement of sludge settling by clinoptilolite, as well as SS elimination. Nitrification was improved up to 38% higher than the control at the normal condition. At 120 mg NHq 4 –Nyl of peak load being given, advanced nitrification for ZR of 56% was obtained, whereas merely 31% was observed at the control. Moreover, for Model 2, enhanced performance in terms of SS removal and nitrification was obtained, to the same extent as for Model 1. Consequently, it was concluded that reuse of excess sludge containing clinoptilolite would efficiently improve wastewater treatment economically and help to solve the sludge disposal problem.
633
Acknowledgments This work was partly supported by the Regional Research Center (RRC) program, the Ministry of Science and Technology (MOST) and the Korea Science and Engineering Foundation (KOSEF). References American Public Health Association (APHA), American Water Works Association (AWWA), Water Environment Federation (WEF), 2000. Standard Methods for the Examination of Water and Wastewater, 20th ed., Washington DC. Belevi, H., Langmeier, M., 2000. Factors determining the element behavior in municipal solid waste incinerators. 2. Laboratory experiments. Environ. Sci. Technol. 34, 2507–2512. Cantet, J., Paul, E., Clauss, F., 1996. Upgrading performance of an activated sludge process through addition of talqueous powder. Water Sci. Technol. 34, 75–83. Christopher, M.B., Peter, L.D., 1999. Evaluation of correlations for zone settling velocity parameters based on sludge volume index-type measures and consequences in settling tank design. Water Environ. Res. 71, 1333–1344. Chudoba, P., Pannier, M., 1994. Use of powdered clay to upgrade activated sludge process. Environ. Technol. 15, 863–870. Klieve, J.R., Semmons, M.J., 1980. An evaluation of pretreated natural zeolites for ammonium removal. Water Res. 14, 161–168. Liu, Y., 1997. Estimating minimum fixed biomass concentration and active thickness of nitrifying biofilm. J. Environ. Eng. 123, 197–205. ¨ Mossakowska, A., Hellstrom, B.G., Hultman, B., 1998. Strategies for sludge handling in the Stockholm region. Water Sci. Technol. 38, 111–118. Olah, J., Meszaros-kis, A., Mucsi, G.Y., Kallo, D., 1989. Simultaneous separation of suspended solids, ammonium and phosphate ions from wastewater by modified clinoptilolite. In: Karge, H.G., Weitkamp, J. (Eds.), Zeolites as Catalysts, Sorbents and Detergent Builders. Elsevier Science, Amsterdam, The Netherlands. Son, D.H., Kim, D.W., Chung, Y.C., 2000. Biological nitrogen removal using a modified oxicyanoxic reactor with zeolite circulation. Biotechnol. Lett. 22, 35–38. Vesilind, P.A., 1979. Treatment and Disposal of Wastewater Sludges. Ann Arbor Science, Michigan.
Resource recovery of sludge as a micro-media in an activated sludge process Chang Gyun Kima,1,*, Hyung Sool Leea,2, Tai Il Yoonb,3 a
Regional Research Center for Coastal Environments of Yellow Sea, Inha University, 253 Yong Hyun Dong, Nam Gu, Inchon, 402-751, South Korea b Division of Environmental and Geosystem Engineering, Inha University, Inchon, South Korea
Abstract An experiment was conducted to evaluate the feasibility of sludge reuse as a micro-medium in an activated sludge (AS) process. Two experimental protocols were employed. A conventional activated sludge was tested as a control, while the other involved addition of clinoptilolite (ZR) of which 4000 mgyl was unvaryingly sustained in an aeration basin. Two experiments were performed for ZR. In one, clinoptilolite was used as micro-media for 60 days (Model 1). The other used dried excess sludge for 55 days (Model 2). For sludge being recovered as micro-media, organic matter in the sludge was eliminated by 86% at 300 8C. It was completely removed at 500 8C within 30 min, which was regarded as the optimal drying condition. For Model 1, the concentration of biomass was increased by 4720 mg MLVSSyl. It was greater by a factor of two than that of the control. Moreover, it is shown that organic matter could be removed up to 95%. In addition, the sludge settling properties were greatly enhanced by clinoptilolite being implemented as floc seeds. Nitrification was considerably improved by more than 90%, due to the high concentration of nitrifiers attached to micro media. For Model 2, the improved performance was sustained on applying burned sludge into the AS. It was concluded that dried sludge could be reused as micro-media in an activated sludge process. 䊚 2002 Elsevier Science Ltd. All rights reserved. Keywords: Micro-media; Sludge reuse; Nitrification; Activated sludge; Sludge settling
1. Introduction Sludge disposal by landfilling may no longer be appropriate owing to land scarcity and increasingly stringent environmental control regulations (Vesilind, 1979). Therefore, future sludge management will be moving towards minimization and reutilization of sludge as useful resources (Mossakowska et al., 1998). Meanwhile, many efforts have been made to upgrade the AS process by application of powdered minerals, e.g. talc, clay and zeolite. It has been reported that enhanced nutrient treatment was attained by addition of powdered *Corresponding author. Tel.: q82-32-860-7715; fax: q8232-872-7734. E-mail address: [email protected] (C.G. Kim). 1 Research Professor. 2 Research Associate. 3 Professor.
minerals into AS, including improved sludge settleability (Chudoba and Pannier, 1994; Cantet et al., 1996; Christopher and Peter, 1999). These materials commonly have rough surfaces, and sizes ranging from dozens to hundreds of micrometers, and are mainly composed of SiO2, CaO, MgO, Al2O3 and Fe2O3 (Olah et al., 1989). Besides, burned sludge originating from an incinerator primarily consists of SiO2 , CaO and MgO, which have the same physical properties as powdered minerals (Belevi and Langmeier, 2000). A feasibility test was thus conducted to address suitable reuse of sludge as contacting media in an AS process. In addition, potential reduction of sludge and nitrification performance was also investigated. 2. Materials and methods Two different types of experimental protocols were employed. One was to add clinoptilolite into AS and
1093-0191/03/$ - see front matter 䊚 2002 Elsevier Science Ltd. All rights reserved. PII: S 1 0 9 3 - 0 1 9 1 Ž 0 2 . 0 0 0 4 6 - 1
630
C.G. Kim et al. / Advances in Environmental Research 7 (2003) 629–633
X’pert MPD) and inductively coupled plasma (ICP) mass spectroscopy (SPQ 9000). Nitrate formation rate (NFR) was observed to verify nitrifiers activity. It was determined using 300 ml of mixed liquor suspended solid (MLSS) taken from the aeration basin and placed into a 1-l beaker where 10000 mgyl of NH4Cl solution was diluted to 50 mgyl of NHq 4 –N. Diffused air was supplied into the beaker so that DO was maintained at 3–4 mgyl. At the same time, temperature, MLVSS, DO and pH were coincidentally monitored. The sample was then taken every 30 min, thereby the nitrate concentration was then observed. 3. Results and discussion 3.1. The determination of optimal condition for sludge reuse Fig. 1. Schematic diagram of AS reactors.
the other was a conventional AS which was tested as a control. The apparatus consisted of an aeration tank (5 l) and a clarifier (3.3 l) as shown in Fig. 1. AS reactors were seeded with sludge taken from a municipal wastewater treatment plant. The reactors were operated at pH 7.0–7.5 and 20 8C ("2 8C). Dissolved oxygen (DO) was maintained ranging from 3 to 5 mgy l. Synthetic wastewater was used for influent as illustrated in Table 1. Influent chemical oxygen demand (COD), N and P were unvaryingly sustained at 250, 70 and 3 mgyl, respectively. Hydraulic retention time (HRT) and solid retention time (SRT) were fixed at 6 h and 20 days, respectively. For ZR, 4000 mgyl of media concentration was kept up in the aeration basin, which was determined by mixed liquor suspended solids (MLFSS) concentration. Two experiments were conducted for ZR. In one, clinoptilolite was used as micromedia for 60 days (Model 1) and the other used dried sludge as micro-media for 55 days (Model 2). A constant MLFSS concentration was accurately maintained in the reactor by adding a nominal amount of micro-media. The withdrawn sludge was dried in a furnace after the optimal drying temperature was obtained for the range of 100, 300, 500 and 800 8C. Subsequently, a residual level of organic content was determined at 10, 30, 60 and 180 min at a given drying temperature. y Influent and effluent COD, NHq 4 –N, NO3 –N and SS were determined by standard methods (APHA, 1998). Organic contents in incinerated sludge were determined by total organic carbon (TOC) using a combustion infrared method (APHA, 1998). Physico-chemical characteristics of clinoptilolite and residuals from dried sludge were obtained by X-ray diffraction (Philips
TOC was obtained on dried sludge treated at different temperatures and durations. As shown in Fig. 2, TOC of sludge incinerated at 100 8C was marginally eliminated at 8% and 370 mgyl of TOC still remained. However, increasing the temperature to 300 8C for 180 min led to TOC removal of 86%. Furthermore, it was shortened by 30 min at 500 8C, and inorganic particulates were formed. At a given specific drying period, there was no significant difference in the degree of removal of residual organic compounds between 500 and 800 8C. XRD was used to characterize the original clinoptilolite and dried excess sludge at different temperatures ranging from 100 to 800 8C. As shown in Fig. 3, the structure of original clinoptilolite remained unvaried at incineration below 500 8C. However, the structure was partially deteriorated at 800 8C. The XRD pattern of dried excess sludge at 500 8C corresponded closely to infant clinoptilolite as illustrated in Fig. 3. Moreover, SiO2, Al2O3 and Fe2O3 were abundant constituents of the residual materials of the sludge, which completely coincided with the composition of clinoptilolite as illusTable 1 Composition of lab prepared wastewater Constituents
Concentration (mgyl)
Glucose NH4Cl KH2PO4 K2HPO4 MgSO4Ø7H2O FeCl3 NaHCO3 CaCl2
180 120 15 10 30 5 600 15
C.G. Kim et al. / Advances in Environmental Research 7 (2003) 629–633
631
Fig. 2. TOC removal of excess sludge at different drying conditions.
trated in Table 2. This is consistent with the findings of Klieve and Semmons (1980). They found that pretreatment of clinoptilolite with NaOH, HNO3 and steam could not improve the zeolite’s performance. However, heat pretreatment at 600 8C for 1 h significantly improved the zeolite’s selectivity for ammonium exchange. Ammonium removal capacity was increased by approximately 17% for heat-treated clinoptilolite. In this study, drying of the original mineral had little influence on the ammonium exchange property showing 5 mg NHq 4 –Nyg.
3.2. The enhancement of wastewater treatment by clinoptilolite For Model 1, ZR commonly removed as much as 90% of the soluble organic matter, which was similar to that of the control. On the other hand, up to 95% of the total organic compounds were removed by the ZR, which was 32% greater than observed in the control. This indicates that the particles contribute to seeding resulting in dense and agglomerated floc, which in turn is better able to separate organic matter from the liquid
Fig. 3. XRD of origin and excess sludge dried at different temperatures.
C.G. Kim et al. / Advances in Environmental Research 7 (2003) 629–633
632
Table 2 The comparison of physico-chemical properties between infant clinoptilolite and residual materials obtained from excess sludge incinerated Parameters
C.E.C (mg NHq 4 –Nyg) Components (wt.%) SiO2 Al2O3 Fe2O3 PbO MoO3 MnO MgO CaO Ig-lossa a
Infant clinoptilolite
Residues dried from sludge
5.12
5.00
61.26 12.40 1.54 0.02 0.053 0.058 0.84 1.30 14.02
64.63 13.27 1.61 0.019 0.053 0.056 0.87 1.51 4.65
Ignition loss.
phase being discharged to an effluent. Fig. 4 shows improved SS removal for ZR compared to the control. Effluent SS from the ZR were lower (3–12 mgyl) as compared to 8–34 mgyl for the control. The preferable sludge separation using powdered clinoptilolite has been reported by previous investigators (Olah et al., 1989; Son et al., 2000). They reported that the turbidity and SS of effluent were gradually decreased due to the formation of a biofilm on the surface of the zeolite in comparison to the control. The enhancement of sludge separation was also unvaryingly sustained for Model 2. It was deduced that seeding of dense floc or biofilm formation were significantly dependent on the surface
Fig. 5. NFRs of both reactors at different conditions.
characteristics e.g. roughness as noted by Liu (1997). In regard to the effect of clinoptilolite on biomass, MLSS and MLVSS in ZR were progressively augmented up to 9580 and 4760 mgyl, respectively, in Model 1. However, the microbial concentration of the control was 2850 and 2030 mgyl, respectively. For Model 2, high biomass was sustained to the same degree as in Model 1. The high concentration of microbes associated with use of powdered mineral, e.g. clay, clinoptilolite, talc, etc., has been reported by many investigators (Olah et al., 1989; Son et al., 2000; Chudoba, and Pannier, 1994). They commonly reported that biofilm was formed on the surface of powdered materials or microbial concentration was considerably increased compared to the conventional AS. For Model 1, enhanced nitrification using ZR was also observed to be as high as 38% compared to the
Fig. 4. TCOD elimination according to effluent SS at both reactors.
C.G. Kim et al. / Advances in Environmental Research 7 (2003) 629–633
control. Even though 120 mg NHq 4 –Nyl of peak load was given, the same extent of improvement was constantly maintained, while it deteriorated remarkably in the control. This effect was attributed to a high concentration of nitrifying microorganisms present in ZR. As shown in Fig. 5, the NFR of ZR was 8.39 mg NOy 3 – NylØh, which was greater by a factor of two than that of the control. However, the NFR per microbe was similar in both cases (1.82 for the control and 1.97 mg NOy 3 –NygØMLVSSØh for ZR). For Model 2, improvement of nitrification for ZR was unvaryingly observed, revealing 8.24 mg NOy 3 –NylØh of NFR compared to 4.23 mg NOy 3 –NylØh for the control. 4. Conclusions The feasibility of sludge reuse as micro-media was evaluated in an AS process with addition of clinoptilolite. The optimal condition for drying sludge was concluded to be 500 8C for 30 min. At the given condition, residues from sludge almost physically corresponded to the composition of infant clinoptilolite, which showed a similar XRD pattern. In addition, the ammonium exchange property of the residual material was absolutely recovered at the level of 5 mg NHq 4 – Nyg, which was consistent with the level of original clinoptilolite. For Model 1, biomass was increased to 4720 mg MLVSSyl with ZR addition, which was higher by a factor of two compared to the control. In addition, ZR presented high removal of total organic compounds, due to improvement of sludge settling by clinoptilolite, as well as SS elimination. Nitrification was improved up to 38% higher than the control at the normal condition. At 120 mg NHq 4 –Nyl of peak load being given, advanced nitrification for ZR of 56% was obtained, whereas merely 31% was observed at the control. Moreover, for Model 2, enhanced performance in terms of SS removal and nitrification was obtained, to the same extent as for Model 1. Consequently, it was concluded that reuse of excess sludge containing clinoptilolite would efficiently improve wastewater treatment economically and help to solve the sludge disposal problem.
633
Acknowledgments This work was partly supported by the Regional Research Center (RRC) program, the Ministry of Science and Technology (MOST) and the Korea Science and Engineering Foundation (KOSEF). References American Public Health Association (APHA), American Water Works Association (AWWA), Water Environment Federation (WEF), 2000. Standard Methods for the Examination of Water and Wastewater, 20th ed., Washington DC. Belevi, H., Langmeier, M., 2000. Factors determining the element behavior in municipal solid waste incinerators. 2. Laboratory experiments. Environ. Sci. Technol. 34, 2507–2512. Cantet, J., Paul, E., Clauss, F., 1996. Upgrading performance of an activated sludge process through addition of talqueous powder. Water Sci. Technol. 34, 75–83. Christopher, M.B., Peter, L.D., 1999. Evaluation of correlations for zone settling velocity parameters based on sludge volume index-type measures and consequences in settling tank design. Water Environ. Res. 71, 1333–1344. Chudoba, P., Pannier, M., 1994. Use of powdered clay to upgrade activated sludge process. Environ. Technol. 15, 863–870. Klieve, J.R., Semmons, M.J., 1980. An evaluation of pretreated natural zeolites for ammonium removal. Water Res. 14, 161–168. Liu, Y., 1997. Estimating minimum fixed biomass concentration and active thickness of nitrifying biofilm. J. Environ. Eng. 123, 197–205. ¨ Mossakowska, A., Hellstrom, B.G., Hultman, B., 1998. Strategies for sludge handling in the Stockholm region. Water Sci. Technol. 38, 111–118. Olah, J., Meszaros-kis, A., Mucsi, G.Y., Kallo, D., 1989. Simultaneous separation of suspended solids, ammonium and phosphate ions from wastewater by modified clinoptilolite. In: Karge, H.G., Weitkamp, J. (Eds.), Zeolites as Catalysts, Sorbents and Detergent Builders. Elsevier Science, Amsterdam, The Netherlands. Son, D.H., Kim, D.W., Chung, Y.C., 2000. Biological nitrogen removal using a modified oxicyanoxic reactor with zeolite circulation. Biotechnol. Lett. 22, 35–38. Vesilind, P.A., 1979. Treatment and Disposal of Wastewater Sludges. Ann Arbor Science, Michigan.