N. Sapari*, A. F. Ismail*, S. S. M. Idris*, M. Hastuti*and M. N. Adlan**

Transcription

1 The Treatment of Oily Wastewater and Septic Tank Effluent by Biofiltration System N. Sapari*, A. F. Ismail*, S. S. M. Idris*, M. Hastuti*and M. N. Adlan** * Department of Civil Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Tronoh, Perak, Malaysia. Tel: Fax: ( nasiman@petronas.com.my, asmafarah@gmail.com) ** School of Civil Engineering, Universiti Sains Malaysia, Engineering Campus, Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia. Tel: Fax: ( cenordin@eng.usm.my) Abstract Many petrol stations discharge the effluent from their septic tanks and oil traps into storm drains. The treatment system at the station provides only partial treatment of the wastewater, thus additional treatment is required. This study examines the potential of biofiltration system as a further treatment of the effluent for the removal of organic pollutants and nutrients. Four laboratory scale biofiltration columns of 50 cm in length and 12 cm in diameter consisting of sand layer, activated carbon layer and potting mixed soil layer were used in this study. The columns were used for the treatment of combined oily wastewater with treated sewage effluent under unsaturated and saturated conditions. The influent and effluent samples were collected and analyzed for total oil and grease (TOG), chemical oxygen demand (COD), total suspended solids (TSS), turbidity, ammonia, nitrate and total phosphorus. Results from the unsaturated condition indicated COD breakthrough at about 10 pore volumes while oil and grease at about 12 pore volumes. Nitrate reached its breakthrough after 2 pore volumes where ammonia did not show any breakthrough throughout the experiment. The saturated biofiltration removed oil and grease, COD, TSS, turbidity, ammonia, nitrate and phosphorus by 97%, 90%, 70%, 77%, 86% and 85%, respectively. Biofiltration treatment for combined wastewater from petrol stations under saturated condition has better performance than the treatment by unsaturated flow. Keywords: Biofiltration system; oily wastewater; organic pollutants; petrol stations INTRODUCTION Many urban rivers, lakes and ponds are rendered unfit for use as drinking water sources due to being flooded and overloaded with pollutants. The pollutants include degradable organics, heavy metals, nutrients and petroleum hydrocarbon. Evaluation of the river water quality revealed that more than 60% of Malaysian inland water is polluted by point and non-point source pollutants particularly in urban areas (MASMA, 2000). MASMA (Manual Saliran Mesra Alam Malaysia) is a manual that provides proposed strategies for stormwater management in Malaysia. The strategies incorporated several options for the management of flood, water quality improvement and ecological enhancement in the downstream areas. In Malaysia, most of the stormwater flows directly to streams and rivers without any treatment. Among the urban stormwater runoff, some are stormwater contaminated with oily wastewater from petrol stations. This may have long term health effects on people particularly in areas where water from the river is being used as drinking water source. Such pollution of water bodies was described by Taylor et al. (2005) and Yang et al. (2000).

2 Oily wastewater from petrol station is generally treated by primary treatment using oil trap. This trap is acceptable in areas where effluent regulations permit direct discharge to the environment. According to the law in Malaysia, the areas for direct discharge must not be part of the drinking water catchment (Environmental Quality Act, Sewage and Industrial Effluent Regulations, 1979). However in practice, many petrol stations are located in drinking water catchments. As the development of the country progresses, this problem becomes serious due to more and more point and non-point sources discharging the wastewater into the river and one of the sources is petrol station. Oily wastewater generated by various industries, frequently occurring in the form of oil in water emulsion, creates a major problem around the world (Benito et al., 2002; Gryta et al., 2001; and Scholz and Fuchs, 2000). The emulsion with surfactants has very high stability due to the small oil droplets and if present in wastewater, it gives problems in the treatment process (Lee, 1984). Oily wastewater is generated by different activities such as refinery, petrochemical and lubricant productions, metal finishing, metal works, textile industry and paper mills (Poulopoulos et al., 2005; and Ullmann, 1987). The oily wastewater is considered as hazardous industrial wastewater because it contains toxic substances such as phenols, petroleum hydrocarbons and polyaromatic hydrocarbons which are inhibitory to plant and animal growth and also mutagenic and carcinogenic to human being (Phan Thanh Tri, 2002). Physical treatment of oily wastewater such as API gravity separator, dissolved air floatation (DAF) and ultra filtration does not remove the pollutants completely but just transfer them to a more concentrated waste (Scholz and Fuchs, 2000). Therefore, there is a need to develop a more efficient treatment technique for oily wastewater to protect the environment from the pollution. The application of biofiltration for the treatment of stormwater was found to be an appropriate technology for most developing nations, where climate favors natural degradation of organic matter. The treatment was found to be effective for the removal of nitrogenous compounds, heavy metals, BOD and COD (Metcalf and Eddy, 2004; Viessman and Hammer, 1993; and Tebbutt, 1991). Biofiltration systems (also referred to as bioretention systems or biofilters) are increasingly being used to improve the quality of stormwater runoff in order to reduce pollution of urban waterways (Henderson et al., 2007; Kim et al., 2003; and Davis et al., 2001). Filtration and sorption of pollutants in runoff through a specially constructed biofiltration system was found to be a cost effective treatment method for stormwater where it could remove suspended solids (98%), nitrogen (50%), phosphorus (85%) and heavy metals (90%) in the stormwater (FAWB, 2007). Fecal coliform can also be removed by biofiltration system up to 87.8% (Rusciano and Obropta, 2007). This study was conducted to examine the use of biofiltration system for further treatment of wastewater from petrol stations. METHODOLOGY Effluent sampling from petrol stations Effluent samples from six petrol stations located within 10 km radius from Universiti Teknologi PETRONAS (UTP) were collected and analysed for total oil and grease. The stations were identified as PS1, PS2, PS3, PS4, PS5 and PS6. The stations were provided with oil traps for oily

3 wastewater treatment and septic tanks for toilets wastewater treatment. Effluent from the treatment facilities are discharged into the nearby stom drain. Biofiltration columns setup Laboratory scale biofiltration systems were used in this study. Four biofiltration columns were constructed using PVC pipes of 50 cm in length and 12 cm in diameter. The pipes were first washed to remove dirt and contaminants. The bottom part was closed with a PVC cap and glued all along the connection to ensure no leakage. A hole was drilled through the PVC cap and connected to a flexible tubing for the bottom drainage of the column. The tube was used for the collection of effluent samples from the column and also for the determination of the hydraulic conductivity of the media. The media used in the system include sand for the bottom layer, activated carbon and potting mixed soil for the top layer. The packing arrangement of the column is shown in Fig. 1 and the setup of the biofiltration system is shown in Fig. 2. [pic] Fig. 1. Packing arrangement of the column Fig. 2 Experimental setup of biofiltration columns The biofiltration system was operated under unsaturated and saturated conditions with controlled flow. The columns were fed with a combined wastewater (oily wastewater and septic tank effluent were combined with a ratio of 1:1). The oily wastewater was taken from the oil trap effluent of one of the petrol stations (PS6) and the septic tank effluent was also collected from the same petrol station. The combined wastewater was analyzed to determine their characteristics in terms of total oil and grease (TOG), chemical oxygen demand (COD), total suspended solids (TSS), turbidity and nutrients (ammonia-nitrogen, nitrate-nitrogen, and total phosphorus). Soil analysis ph. Prior to the column operation, ph was determined to ensure the condition within the soil was suitable for bacteriological processes to occur. The ph of the soil was determined according to Hersyey (1992) where the soil was mixed with distilled water with proportion of one volume of

4 soil to two volumes of distilled water (ratio 1:2). Hydraulic conductivity. The hydraulic conductivity of the filter media in the biofiltration column was determined using the constant-head method. Initially, the columns were filled with water from the bottom until the media was saturated. The level of water was maintained throughout the process to ensure that the head was constant. Thereafter, water was allowed to flow through the soil under a steady state and the volume of water flowing through the soil was measured. The flow rate was measured by collecting water to a certain volume in a fixed time interval. Operation of biofiltration columns Unsaturated flow. The column experiment was conducted batch wise. Feeding of the column with septic tank effluent was conducted from the top of the column at the beginning of the experiment and 3 liters (equal to 2 pore volume) of the wastewater was allowed to infiltrate through the column. This initial feeding was aimed to introduce a biological population into the column. One week after the initial feeding, the combined wastewater was introduced as the feed water to the biofiltration column until a breakthrough was reached. Effluent samples were collected from the bottom of the column and analyzed in terms of TOG, COD, ammonia and nitrate levels. Saturated flow. Before the saturated flow experiment, the columns were allowed to dry for a period of two weeks. After two weeks, the columns were fed with the combined wastewater until they became fully saturated with the wastewater. The wastewater was drained from the columns at different periods. The summary of sample collection day is shown in Table 1. Column number Retention time 1 0 (immediate drainage) 1 2 days 2 4 days 3 7 days 4 10 days Table 1: Summary of samples collection day The influent and effluent samples were collected and analyzed for TOG, COD, TSS, turbidity, ammonia, nitrate and total phosphorus. RESULTS AND DISCUSSION Effluent sampling from petrol station Table 2 shows the total oil and grease (TOG) concentrations in the samples collected before and after the oil traps from six petrol stations. Table 2: Oil and grease concentrations from six petrol stations Petrol TOG (mg/l) Remarks Station Influent Effluent PS Small station in rural area with convenient store but not providing garage. PS New petrol stations operating less than 5 PS years complete with convenient store and PS garage. PS

5 PS Old station operating more than 15 years with convenient store and garage. The results of the analysis indicate that the level of TOG in the effluent varies considerably from station to station. The level of oil and grease in the effluent from oil traps ranges from 3 mg/l to 425 mg/ L. Two of the stations i.e., PS5 and PS6 exceeded the discharge limit of the national regulation of 10 mg/l. This violation was found in petrol stations that are operating with convenient store and garage facilities. Influent analysis The quality of combined wastewater is shown in Table 3. Table 3: Combined wastewater quality Parameter Units Value Oil and grease mg/l 135 COD mg/l 356 TSS mg/l 73.2 Turbidity NTU 29.2 Ammonia NH3-N mg/l 8.1 Nitrate NO3-N mg/l 17.7 Total phosphorus PO43- mg/l 31.2 The table showed that the levels of oil and grease and COD exceeded the minimum limit for discharge of 10 mg/l and 100 mg/l, respectively. The high levels indicated that the effluent wastewater was potentially polluting the nearby surface water with organic pollutants. According to the law in Malaysia, (Sewage and Industrial Effluent Regulations, 1979), the effluent quality in terms of oil and grease of any discharge into inland water shall meet the minimum requirements of 10 mg/l for areas located outside the catchments for drinking water supply. Soil analysis ph. Results from the ph measurement of the soil showed that the average ph of the soil was 7.6. Studies indicate that the suitable ph range for the existence of most biological life is ph 6-9 (Metcalf and Eddy, 2004). If the ph is too acidic, it will harm the bacteria in the biofiltration system which plays important roles in degrading pollutants in the wastewater. Since the soil is in the range of ph 6-9, it was considered to be appropriate as the media for the biofiltration system. Hydraulic conductivity. The average hydraulic conductivity for the filter media was mm/sec (63.72 mm/hr). This value fulfills the minimum requirement of the hydraulic conductivity for biofiltration system which is mm/sec (Hunt, 2003). Operation of bio-filtration columns

6 Unsaturated flow. Results of water analysis of the effluent samples from the columns in terms of nitrate and ammonia are shown in Fig. 3. Fig. 3 Nitrate and ammonia concentration in the effluent of the biofiltration column The results showed that the nitrate in the effluent from the column reached a maximum of 20 mg/l at two pore volumes (PV), whereas the nitrate level in the combined wastewater influent was only 17.7 mg/l. Therefore the higher nitrate level of 20 mg/l in the effluent was obviously coming from the existing nitrate in the soil. After 2 PV, nitrate concentration decreased gradually to a level lower than the influent concentration. On the other hand, ammonia concentration in the effluent samples were always lower than the influent concentration of 8.1 mg/l. these results showed that the ammonia was adsorbed by the media. Nitrification was not likely to take place in the column due to the rapid infiltration of the wastewater through the media and short detention time. The organic pollutants attenuation through the soil in biofiltration system was determined from oil and grease and COD analysis as shown in Fig. 4. Fig. 4 Breakthrough pattern of organic pollutants as measured in COD. Fig. 4 shows that the organic pollutants were adsorbed by the media in the biofiltration system. It was also observed that the COD concentration gradually increased from almost 0 mg/l to a level

7 almost similar to the initial concentration of 356 mg/l over 11 pore volumes. Similar trend was observed for oil and grease concentration. Unsaturated biofiltration resulted in breakthrough of oil and grease at about 12 pore volumes. Pollutants which include oil and grease, COD and nitrate; penetrated the biofiltration columns after 2 to 12 pore volumes. Saturated flow. The results of TOG in the influent and effluent of the biofiltration system are shown in Fig. 5. Fig. 5 Results of TOG Fig. 5 shows that the effluent oil and grease was always lower than the influent. The concentrations were below 10 mg/l at all sampling days. After 10 days, the oil and grease was reduced by 97.04%. Fig. 6 shows the results of COD in the influent and effluent of the biofiltration system. Fig. 6 Results of COD The result showed that the effluent COD was lower than the influent and the reduction of COD varied according to the sampling days. After 4 days, the COD decreased from 356 mg/l to 52 mg/l. The COD reduced further to 22 mg/l after 7 days and after 10 days the COD reduction was found to be 90.45%. Detail results of TSS for the influent and effluent of wastewater are shown in Fig. 7.

8 Fig. 7 Results of TSS Fig. 7 shows that the TSS of effluent was much higher than the influent when the effluents were collected immediately after feeding and after 2 days of detention. This was because some of the particles from the soil in the biofiltration system were washed out together with the effluent. After 2 days, the TSS value started to decreased and after 10 days it reduced to 9 mg/l from the initial concentration of 81 mg/l. The reduction of TSS after 10 days was 87.69%. The turbidity of influent and effluent wastewater was determined and the results are as in Fig. 8. Fig. 8 Results of turbidity Fig. 8 shows that the turbidity of effluent collected after 2 days and after 4 days was higher than the influent. This was because some of the particles from the filter media such as clay and silt were washed out with the wastewater during the initial stages. Turbidity showed a similar trend as TSS where the biofiltration system increased the turbidity of the effluent in the initial stages of the operation and required a longer detention time for turbidity reduction. However after 10 days, the turbidity was reduced by 70.3%. This indicated that the biofiltration system was ineffective in removing turbidity in a short period of time. Results of analysis on ammonia-nitrogen in the influent and effluent wastewater are shown in Fig. 9.

9 Fig. 9 Results of ammonia-nitrogen The results showed that there was reduction of ammonia-nitrogen after the wastewater passed through the biofiltration system. It was probably due to nitrogen conversion during the treatment. Ammonia-nitrogen was converted to nitrate-nitrogen by nitrification process as indicated by the increase in nitrate in effluent of subsequent result of experiment as shown in Fig. 10. The removal of ammonia-nitrogen after 10 days was 70.39%. [pic] Fig. 10 Results of nitrate-nitrogen The nitrate-nitrogen of influent and effluent wastewater was determined and the results are shown in Fig. 10. The removal of nitrate-nitrogen by biofiltration system was not very effective particularly at two-day detention time. Leaching of nitrate from nitrified ammonia during drying period was likely the reason for the high nitrate in the effluent collected after 2 days of detention time. At longer detention times, some nitrate was denitrified in the biofiltration system. This was indicated by the nitrate removal up to 85.92% after 10 days detention time. The phosphorus of influent and effluent wastewater was analysed and the results are shown in Fig. 11. Fig. 11 Results of phosphorus

10 The result indicated that there were reductions of total phosphorus in the effluent collected from the biofiltration treatment system. The percentage removal was 86.4% after 10 days. Phosphorus was removed probably by adsorption onto soil particles and assimilation with microorganisms in the biofiltration system. CONCLUSIONS Unsaturated biofiltration will result in breakthrough of COD about 10 pore volumes while oil and grease at about 12 pore volumes. Nitrate reached its breakthrough after 2 pore volumes. However, ammonia was adsorbed by the column and did not show any breakthrough throughout the experiment. Results from the saturated biofiltration using combined wastewater indicate reduction in most of the pollutants where oil and grease, COD, TSS, turbidity, ammonia, nitrate and phosphorus were removed by 97%, 90%, 70%, 77%, 86% and 85%, respectively after 10 days of detention time. Biofiltration treatment for combined wastewater from petrol stations under saturated condition has better performance than the treatment by unsaturated flow. REFERENCES Benito J.M., Rios G., Ortea E., Fernandez F., Cambiella A., Pazos C. and Coca J., ( 2002). Design and construction of a modular pilot plant for the treatment of oil-containing wastewaters. Journal of Desalination, 147(2): Davis A., Shokouhian M., Shaarma H., and Minarmi C., (2001). Laboratory study of biological retention for urban stormwater management. Journal of Water Environment Research, 73: Environmental Quality Act, (1974). Parameter limits of effluents of standards A and B. Environmental Quality (Sewage and Industrial Effluents) Regulations Facility for Advancing Water Biofiltration (FAWB), (2007). Retrieved in the website on November Gryta M., Karakulski K., and Morawski A.W., (2001). Purification of oily wastewater by hybrid UF/MD. Journal of Water Research, 35(15): Henderson C., Greenway M. and Phillips I., (2007). Removal of dissolved nitrogen, phosphorus and carbon from stormwater by biofiltration mesocosms. Journal of Water Science and Technology, 55(4): Hersyey D.R., (1992). Evaluating metal probe meters for soil testing. Journal of American Biology Teacher, 54: Hunt, W.F., (2003). Pollutant Removal Evaluation and Hydraulic Characterization for

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