EFFECT OF WATER DEPTH AND AERATION ON A CONTACT MEDIA CHANNEL PURIFICATION PROCESS FOR WASTEWATER RECLAMATION

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1 J. Environ. Eng. Manage., 17(5), (7) EFFECT OF WATER DEPTH AND AERATION ON A CONTACT MEDIA CHANNEL PURIFICATION PROCESS FOR WASTEWATER RECLAMATION Tzu-Yi Pai, 1, * Chwen-Jeng Tzeng, 2 Chen-Lung Hsu, 3 Yao-Sheng Tsai 1 and Wen-Jui Hsu 1 1 Department of Environmental Engineering and Management Chaoyang University of Technology Taichung 413, Taiwan 2 Water and Environmental Engineering Department CECI Engineering Consultants, Inc. Taipei, 16, Taiwan 3 Department of Safety, Health and Environmental Engineering National United University Miaoli, 3, Taiwan Key Words: Natural purification ecological engineering, contact media channel purification process, aeration, water depth, water reclamation ABSTRACT In this study, contact media channel purification process (CMCP) filled with honeycomb media was adopted to implement continuous flow experiments when aeration and water depth varied. The water depth was set at.2,.5 and, respectively. Three aeration values including 3, 5 and 7 m h -1 were operated at each water depth. The results indicated that the removal efficiencies of total chemical oxygen demand (COD), soluble COD, biochemical oxygen demand (BOD), suspended solids (SS), total nitrogen (TN), total Kjeldahl nitrogen (TKN), ammonia were highly correlated with aeration. The removal efficiencies of BOD, SS, TN, TKN and NH 4 were highly correlated with water depth. When water depth increased from.2 to, their removal efficiencies increased remarkably. All effluent quality investigated in this study at the water depth of met the Soil Treatment Standards. Since the groundwater shortage and pollution are severe in Taiwan, the effluent from this CMCP could be used for groundwater recharge. INTRODUCTION Because of the increase of population and industry development in Taiwan, the water demand increases significantly. But it is difficult to seek a new water resource because of the rare new dam sites, serious polluted river water and excess water usage. In this situation, reclaimed water reuse becomes an important issue. In general, approaches of reclaimed water reuse include storage of rain water, recycle and reuse of municipal wastewater, industrial wastewater, agriculture irrigation water and so on. If the wastewater can be reclaimed, reused and recycled appropriately, it will be helpful to overcome the problem of water shortage. In order to meet different types of reclaimed water quality criteria, different treatment processes should be applied [1]. The technologies by which the pollutants were removed or transformed according to natural recycle or purification principles in natural bulk water are called water quality purification ecological engineering [2]. The water quality purification ecological engineering included aeration process, gravel bed contact oxidation process, wetland process, contact media channel purification process (CMCP) and so on. Among these processes, bacteria, virus, parasites, solids, organic carbon, nitrogen and phosphorus were removed via precipitation, filtration, adsorption, sedimentation, absorption by aquatic plants and microbial degradation. There are many irrigating channels and drainage systems receiving different types of effluent in Taiwan. The flow characteristics in these systems are shallow, slow and biofilms are attached to the bottoms of these transportation systems. When the natural selfpurification ability could be enhanced appropriately, the effluent pollutant removal from a wastewater treatment plant for water reclamation could be *Corresponding author bai@ms6.hinet.net

2 3 J. Environ. Eng. Manage., 17(5), (7) achieved. Some experiments related to CMCP were carried out to observe the transportation and transformation of microorganism and pollutants [3-8]. In these studies, gravel was adopted to fill in channels for water purification. Two properties of the media were of major importance. These were (1) the specific surface area of the media (the greater the surface area, the greater the amount of biomass per unit volume), and (2) the percentage of void space. In order to achieve certain removal efficiency in a limited volume, some specific media with high specific surface area and void space, like honeycomb media, should be adopted, although stone-media were costless and convenient. In this study, CMCP filled with honeycomb media was adopted to implement continuous flow experiments. The steady influent, effluent quality and removal efficiency of different pollutants were observed at different type of aeration and water depth. The possibility for water reclamation was also discussed. MATERIALS AND METHODS 1. Description of Artificial Channel The experimental equipment is shown in Fig. 1. The wide channel was compartmented into 6 stages, the length of each stage was 1 m resulting the total length of m. At the channel bottom, there were sludge tank for sediment collection and several aerated pipes installed for air supply. A tail-weir was used to control water depth. The PVC honeycomb media was filled in the channel. The specific surface area and volume of each media were 18 m 2 m -3 and.25 m 3, respectively. The flow velocity was.36 m s - 1. The hydraulic retention time was 4.59 h at depth of. The effluent from a domestic wastewater treatment plant (WWTP) was introduced into the CMCP process to polish. 2. Description of Experiments P tank The channel was seeded with a mixed culture Fig. 1. Diagram of contact media channel purification process. from a domestic WWTP under steady flow. The water depth was set at.2,.5 and respectively. Three aeration values include 3, 5 and 7 m h -1 were operated at each water depth totally resulting 9 test runs (duration for each run was 4.59 h). In each test run, when effluent concentration was constant, the biofilm were considered to be in a stable condition. During the experimental period, the dissolved oxygen (DO) and ph were and , respectively. Temperature was between and 25 C. They were monitored by the DO and ph meters. Then the concentrations of total chemical oxygen demand (TCOD), soluble COD (SCOD), biochemical oxygen demand (BOD), suspended solids (SS), total nitrogen (TN), total Kjeldahl nitrogen (TKN), ammonia and phosphate were measured. All analytical methods were performed according to Standard Methods [9]. RESULTS AND DISCUSSION 1. Concentration According to the experimental data, the average influent and effluent concentrations of TCOD, SCOD, BOD, SS, TN, TKN, NH 4 and PO 4 3- in different test conditions are shown in Table Removal Efficiency Relating to Test Conditions 2.1 TCOD/SCOD The removal efficiencies of TCOD/SCOD in different test conditions are shown in Figs. 2a. and 2b. TCOD/SCOD removal efficiencies decreased as aeration increased, on the other hand, they were not highly correlated with water depth. Based on the calculated linear regression equations, the removal efficiencies were highly correlated with aeration (R 2 >.66 and >.78 for TCOD, SCOD, respectively). The possible reason was that when aeration increased, some organic matters in the sediment would be resuspended into bulk water. So aeration showed a significant effect on COD removal. When water depth increased, settling effect would increase. It eliminated some effect of sediment resuspension, so the tendency was not obvious as water depth varied. 2.2 BOD Figure 2c reveals the removal efficiencies of BOD. They decreased when aeration increased and had highly correlated with water depth too. According to the linear regression, the removal efficiencies were highly correlated with aeration (R 2 >.82). Increased aeration would result in sediment resuspension. Therefore aeration showed a significant effect on BOD removal. Additionally, when water depth increased from.2 to, the removal efficiency increased remarkably from 54 to 87% at the aeration of 3 m 3 hr -1. When water depth increased, settling effect and the

3 Pai et al., CMCP Process for Wastewater Reclamation 341 Table 1. and effluent concentrations in different test conditions Items Aeration m 3 hr -1 TCOD SCOD BOD SS TN TKN NH 4 -N NO - 2 -N NO - 3 -N NO X -N PO 3-4 -P The numbers of samples were 3 for each item. media surface on which the biofilm attached would be increase. Sediment resuspension would be eliminated and biodegradation would be enhanced. Consequently the trend that removal efficiencies increased with the water depth was obvious. 2.3 SS The removal efficiencies of SS are shown in Fig. 2d. They decreased as aeration increased but increased as water depth increased. The removal efficiencies were highly correlated with aeration (R 2 >.79). Increased aeration would result in sediment resuspension. For that reason, aeration showed a significant effect on SS removal. Additionally, when water depth increased from.2 to, the removal efficiency increased from 77 to 89% at the aeration of 3 m 3 h -1. When water depth increased, settling effect would increase. Sediment resuspension would be eliminated; the trend that removal efficiencies increased with the water depth is obvious. According to the behaviours of TCOD, SCOD, BOD and SS, it implied that inert organic matters would release from sediment when aeration increased. 2.4 TKN and NH 4 The removal efficiencies of TKN and NH 4 are shown in Figs. 2f and 2g. They increased when aeration and water depth increased. The removal efficiencies were highly correlated with aeration (R 2 >.57 for TKN, R 2 >.76 for NH 4 ). Increased aeration would result in aerobic and nitrifying condition in which the autotrophic bacteria would grow in quantity. Consequently, the aeration showed a significant effect on TKN and NH 4 removal. Additionally, when water

4 342 J. Environ. Eng. Manage., 17(5), (7) (a) (b) (c) (d) (e) (f) (g) Aeration (m (m 3 min 3 h -1-1 ) Aeration (m (m 3 min 3 h -1-1 ) Fig. 2. Removal efficiencies of different components in different test conditions. (a) TCOD, (b) SCOD, (c) BOD, (d) SS, (e) TN, (f) TKN, (g) NH 4 and (h) PO The dots indicate the experimental values, while the lines indicate the linear regression equations of those experimental values related to different aeration. (h) depth increased from.2 to, the TKN and NH 4 removal efficiencies increased from 34 to 71% and from 32 to 96%, respectively at the aeration of 7 m 3 h -1. When water depth increased, the media surface on which the biofilm are attached would increase. Since biodegradation would be enhanced, the trend that removal efficiencies increased with the water depth was apparent. 2.5 TN, NO X, NO and NO 3 Figure 2e shows the removal efficiencies of TN, while the variations of NO X, NO - 2, NO - 3 are shown in Table 1. TN removal efficiencies increased as aeration and water depth increased. The removal efficiencies were highly correlated with aeration (R 2 >.92). According to Table 1, NO X averagely increased g L -1 at the aeration of 3 m 3 h -1, but it averagely increased to 2.1 at the aeration of 7 m 3 h -1. It suggests that although increased aeration would enhance nitrification, it inhibits denitrification. Additionally, when water depth increased from to, the TN removal efficiency increased from 22 to 46% at the aeration of 7 m 3 h -1. In addition, NO X averagely increased 3.6 at the water depth of.2 m, it averagely decreased.6 at the water depth of. When water depth increased, the me-

5 Pai et al., CMCP Process for Wastewater Reclamation 343 dia surface on which the biofilm attached and the volume of bulk water would increase. An aerobic/anoxic condition was easily created. Since nitrification and denitrification would be enhanced, the trend that removal efficiencies increased with the water depth is obvious PO 4 The removal efficiencies of PO 3-4 are shown in Fig. 2h. The tendency was not highly correlated with aeration and water depth. Since phosphorus cannot be changed into gas phase with any oxidation state, the possible method to remove phosphorus from bulk water is only to withdraw the sediment from CMCP. In this study, the removal efficiencies of TCOD, SCOD, BOD, SS, TN, TKN, NH 3-4 and PO 4 fell within the range of 26-65%, 22-69%, 36-87%, 69-89%, 12-46%, 17-84%, 16-96% and -2-5%, respectively. Compared to other analogous process for river water purification, their purification efficiencies were 75-9% (BOD), 75-9% (SS), 1-% (TN), 1-% (total phosphorus) [7]. 3. Possibility for Reclamation If surveying some water reclamation standards in Taiwan, it was found that the effluent from this CMCP did not meet the Irrigation Water Quality Standard (IWQS). The IWQS strictly prescribes that TN should be lower than 1. for the irrigating water. Once the irrigating water contained TN that was higher than 1., the rice will not grow well. But all effluent quality investigated in this study at the water depth of could met the Soil Treatment Standards. The effluent from this CMCP could be used for groundwater recharge. Some detailed items, such as sodium absorption ratio, sulphur, sulphate should be further investigated. Since the groundwater shortage and pollution are severe in Taiwan, the reclaimed water is also a good resource for groundwater recharge. CONCLUSIONS In this study, CMCP filled with honeycomb media was adopted to implement continuous flow experiments when aeration and water depth varied. The results indicated that the removal efficiencies of TCOD, SCOD, BOD, SS, TN, TKN and NH 4 were highly correlated with aeration. The removal efficiencies of BOD, SS, TN, TKN and NH 4 were highly correlated with water depth. When water depth increased from.2 to, increasing trends of their removal efficiencies at different aeration were described as follows. BOD: increasing from 54 to 87% at the aeration of 3 m 3 h -1. SS: increasing from 77 to 89% at the aeration of 3 m 3 h -1. The TN removal efficiency increased from 23 to 46% at the aeration of 7 m 3 h -1. TKN and NH 4 removal efficiencies increased from 34 to 71% and from 32 to 96%, respectively at the aeration of 7 m 3 h -1. All effluent quality investigated in this study at the water depth of met the Soil Treatment Standard. Since the groundwater shortage and pollution are severe in Taiwan, the effluent from this CMCP could be used for groundwater recharge. REFERENCES 1. Mujeriego, R. and T. Asano, The role of advanced treatment in wastewater reclamation and reuse. Water Sci. Technol., (4-5), 1-9 (1999). 2. Mitsch, W.J. and S.E. Jorgensen, Ecological Engineering: An Introduction to Ecotechnology. John Wiley & Sons, Inc., New York (1989). 3. Gantzer, C.J., B.E. Rittmann and E.E. Herricks, Mass transport to streambed biofilms. Water Res. 22(6), (1988). 4. Gantzer, C.J., B.E. Rittmann and E.E. Herricks, Effect of long-term velocity changes on streambed biofilm activity. Water Res., 25(1), 15- (1991). 5. Nagaoka, H. and S. Ohgaki, Effect of turbulence on biofilm activity. Proce. 2 nd IAWPRC Asian Conference on Water Pollution Control, Bangkok, Thailand, (1988). 6. Leu, H.G., C.F. Ouyang and J.L. Su, Effects of flow velocity changes on nitrogen transport and conversion in an open channel flow. Water Res., 3(9), (1996). 7. Shirasaki, M., H. Tanaka, T. Yokota and Y. Matumiya, evaluation and perspective of river water purification plants for the last years in Japan. Process in water pollution control in Japan, Japan Sewage Works Association, Tokyo, Japan (1999). 8. Hiratsuka, J., J.H. Kim, H. Tanaka, H. Sasaki and R. Sudo, Influence of stream-side surface area on aquatic biota and biofilm activity A case study by test channel experiment. Proc. 1 st IWA Asian- Pacific Regional Conference, Fukuoka, Japan, (). 9. APHA, Standard Methods for the Examination of Water and Wastewater. 19 th Ed. American Public Health Association, Washington, D.C. (1995). Discussions of this paper may appear in the discussion section of a future issue. All discussions should be submitted to the Editor-in-Chief within six months of publication. Manuscript Received: March 9, 7 Revision Received: June 4, 7 and Accepted: June 15, 7