Effectiveness Of Treatment Of Domestic Sewages Using Vetiveria Zizaniodes In Constructed Wetlands J. Sohaili*, A. Noraziah** and Z.N. Syamimi

Department of Environmental Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Malaysia *(E-mail: johansohaili@utm.my) **(E-mail: pu3_safi@yahoo.com)   Abstract Sewage is one of the major problems in the domestic sewage management. Treatment that low cost, need less maintenance and environmental friendly are among target on how to treat the domestic sewage. This research was focused on the capability of the Vetiveria Zizaniodes plant to remove pollutant through the constructed wetland. The study carried out through two type different flow systems, which were 5-days retention time and zero retention time. The constructed wetlands were planted with Vetiveria Zizanoides in different population for each cell. The efficiency of the systems to reduce the concentration of oil and grease, ammonia nitrogen (NH3-N), Biochemical Oxygen Demand (BOD), total suspended solid (TSS), and orthophosphate (PO4

3) were determined. The performance of dissolved oxygen (DO) and pH are also considered. From the study it was found that the constructed wetlands using higher populated Vetiveria Zizaniodes is significantly contributed in removal efficiency of BOD, orthophosphate and nitrate ammonia on 5-days retention time while on zero retention time, it’s contributed in removal efficiency of TSS. The results showed the ability of constructed wetland using the Vetiveria Zizaniodes to reduce up to 55.80% of ammonia nitrogen removal, 79.05 % of phosphate, 53.08% of BOD and 50.75% oil & grease after 60 days of treatment for 5-days retention time. On the other side wetland was able to remove 61.92% of TSS after end of experiment for without any HRT on day 60 of treatment. It can be conclude that Vetiveria Zizaniodes posed a great role in removing orthophosphate, ammonia nitrogen, BOD, TSS and oil and grease under different hydraulic retention time.  Keyword Sewage, Hydraulic retention time, Constructed wetland, Vetiveria Zizaniodes

 INTRODUCTION Wetlands represent the transition zone between terrestrial and aquatic environments. The application of wetlands for industrial wastewater treatment is a promising alternative. Many studies have shown that wetlands provide effective nutrient sinks and organic and inorganic pollutants removals. Even though conventional treatment method that have been used and practiced for long is suitable and efficient but, it still can be improved by focusing to the nutrients, organic and inorganic matters removal, a method to polish the effluent from sewage treatment plant prior to discharge. The construction of artificial wetlands for wastewater treatment is now widely accepted and increasingly demanded as a treatment alternative. Constructed wetlands were initially utilized for nutrient removal in residential and municipal sewage, storm water and agricultural runoff displaying a wide range of removal efficiencies. There are two categories of wetlands, namely natural and constructed wetland. The constructed wetlands have been used at most of the country as secondary treatment after sewage treatment plant. There are two types of constructed wetlands namely surface flow wetland (SFW) and subsurface flow wetland (SSF). Both of these methods are normally used for treating sewage and also identified as Best Management Practice (BMP) for flood management and small urban drainage system. Olson (1992) and Mitsch (1992) stated that constructed wetlands have been used

as an attractive low-cost method for controlling water pollution from both point and non-point sources. Dunbabin and Bowmer (1992) also reported that constructed wetland show good potential for removal metals from industrial effluents. Wetlands were also reported of having a potential to prevent the contamination of groundwater by preventing it from infiltrates into the wetland (Kadlec et al., 2000). As reported by Olson (1992), wetlands can contribute in reducing nutrient significantly in sewage thus improving the water quality. On the other hand, constructed wetlands are also used to improve or restore some water bodies such as rivers and water basins (Nairn and Mitsch, 2000; Mitsch et al., 2005; Mitsch and Day, 2006) especially during draught season. Constructed wetlands possess as the wastewater treatment through various physical, chemical and biological processes, while the conventional system relies on compact energy-intensive operations with short residence times. In contrast, wetlands are large passive systems with long detention times. Among the aquatic treatment systems, constructed wetlands have a greater potential in sewage treatment because they can tolerate with higher organic loading rate (OLR) with shorter hydraulic retention time (HRT). These can then improve the effluent characteristics discharged (Chongrak and Lim, 1998). The study is conducted to demonstrate on the capability of the Vetiveria Zizaniodes plant to remove pollutant through the constructed wetland under different hydraulic retention time. MATERIALS AND METHODS The experiments were conducted separately in three (3) cells filled with different numbers of Vetiveria Zizaniodes where Cell A with 60 plants, Cell B with 30 plants, while Cell C without plant acts as a control unit. Two types of experiment were conducted, i.e. the experiments are conducted without flow rate namely zero retention time and with flow rate of hydraulic retention time 5 days, namely 5-days retention time. The 5-days retention time is carried out with Q of 3.125 x 10-6 m3/s. The 3 cells used for the study shown in Figure 1, were constructed with an impervious concrete, located at the Environmental Engineering Laboratory, Faculty of Civil Engineering, Universiti Teknologi Malaysia. Each cell was constructed with same dimension of 0.5 m x 4.0 m x 0.5 m (width x length x depth), and a bed slope of 1%. The support media of these units consisted of large gravel (2 cm in diameter) on the bottom, followed with medium gravel (1 cm in diameter) and finally sand on the top layer with a total depth of 15 cm. Gravel was selected because of its high hydraulic conductivity, ease of maintenance and consistency of specification, allowing greater predictability of performance than other soil media. While sand is used to filter any settled particle from passing through the gravels. The experiments were carried out under well-ventilated open space with transparent roof. The three constructed wetland cells were set up together with the inlet pipe and valve connected to the sewage storage tank. The sewage depth is maintained at 0.3 m high from top of the media. The outlet pipe is placed at approximately 20 cm below water surface, i.e. at the lowest level of the cell. The Vetiveria Zizaniodes were attached on top of the media in Cell A and B with different population as mentioned earlier. Thus, approximately 10 cm of the roots were submerged in the sewage. The sewage were collected from operating oxidation pond and was fed into each cells continuously for one week, to acclimatize the soil microbes and to support growth of the Vetiveria Zizaniodes plants in Cell A and B. The treatment was start immediately after acclimatization, by continuously fed each cells with fresh sewage for two months. The inlet and outlet of the pond were maintained with a same flow rate. The experiment of 5-days retention time and zero retention time were carried out separately. Analyses of samples were taken on day 15, 33, 39, and 51 of the experiment. The effluents from

each cell were sampled from cell outlet and analyzed for pH, DO, BOD, TSS, O&G, NH3-N and PO4

3- according to standard methods (APHA, 2005). The collected data were statistical analyzed to determine any significant pollutants removals among different cells system and under different hydraulic retention time. The analysis of the parameter analyzed in the study is tabulated in Table 1.     

 

 

 Figure 1. Development of constructed wetlands using Vetiveria Zizaniodes for sewage treatment from day 1 (A), during treatment (B) and after 60 days of treatment (C) Table 1. The parameter observed in sewage analysis Parameter Units Methods pH - APHA 4500-H+ B Dissolved Oxygen (DO) mg/L APHA 4500-O G Biochemical Oxygen Demand (BOD) mg/L APHA 5210 B Total Suspended Solid (TSS) mg/L APHA 2540 D Oil & grease (O&G) mg/L APHA 3114 C Ammonia Nitrogen (NH3-N) mg/L APHA 3120 B Orthophosphate (PO4

3-) mg/L APHA 3120 B  RESULTS AND DISCUSSION The experimental studies were carried out for two months for each batch of experiment i.e. 5-days retention time and zero retention time. Statistical analysis has been used to reveal any significant differences for all type of treatments. The analysis not only considers the percentage of removal but also the time efficiency to remove the pollutant. Table 2 shows the initial pollutants concentrations in raw sewage before treatment. Table 2. Proximate analysis of raw sewage Parameter Concentrations DO, mg/L 4.86 ± 0.45 pH 7.36 ± 0.26 BOD, mg/L 185.22 ± 0.25 TSS, mg/L 54.03 ± 0.15 O&G, mg/L 52.55 ± 0.21 PO4

3-, mg/L 29.37 ± 0.05 NH3-N, mg/L 49.63 ± 0.31  Percentage of removal for Cell A, Cell B and Cell C with 5-days retention time of sewage treatment is summarized in Table 3, while removal under zero retention time was presented in Table 4. The analysis was done to study the efficiency of treatment using Vetiveria Zizaniodes with different number of plants and hydraulic retention time. It shows number of plants had major contribution in

A B C

reducing pollutants in sewage. The removal of pollutants also occurs for zero retention time of treatment for all cells. Comparison of pollutants removal efficiencies were made for each cells under zero retention time and 5-days retention time. Table 3. Percent of removal of selected parameter with 5-days retention time at 60 days of sewage treatment Parameter unit Cell A (%) Cell B (%) Cell C (%) DO mg/L 1.47 ± 0.21 1.73 ± 0.25 1.70 ± 0.04 pH - 7.26 ± 0.12 7.27 ± 0.22 7.29 ± 0.01 BOD mg/L 60.00 ± 0.15 44.86 ± 0.02 21.08 ± 0.25 PO4

3- mg/L 91.83 ± 0.22 66.63 ± 0.14 44.16 ± 0.10 NH3-N mg/L 60.71 ± 0.21 50.13 ± 0.40 45.60 ± 0.15 TSS mg/L 40.74 ± 0.05 40.74 ± 0.17 51.85 ± 0.21 O&G mg/L 55.77 ± 0.29 40.38 ± 0.21 31.70 ± 0.08

 Table 4. Percent of removal of selected parameter with zero retention time at 60 days of sewage treatment Parameter unit Cell A (%) Cell B (%) Cell C (%) DO mg/L 1.25 ± 0.01 1.27 ± 0.11 1.31 ± 0.14 pH - 7.14 ± 0.23 7.28 ± 0.20 7.25 ± 0.22 BOD mg/L 32.00 ± 0.11 28.57 ± 0.22 22.29 ± 0.1 PO4

3- mg/L 85.94 ± 0.25 78.91 ± 0.31 67.97 ± 0.13 NH3-N mg/L 75.00 ± 0.16 72.62 ± 0.21 53.33 ± 0.25 TSS mg/L 79.37 ± 0.10 73.02 ± 0.10 38.10 ± 0.11 O&G mg/L 61.11 ± 0.19 50.00 ± 0.18 38.89 ± 0.28  Total Suspended Solid Total suspended solids (TSS) that include all particles suspended in sewage that not pass through a filter are measured. Mason (1998) and Boulton and Brock (1999) reported that too much particles in the water will decrease light penetration in water thus, reducing photosynthesis of water plants, decreased water depth due to sediment build-up and increased heat absorbed by the water, lowering dissolved oxygen, facilitating parasite and disease growth and increasing the toxicity of ammonia. Figure 2 below shows the percentage of TSS removal for both of HRTs’.

Figure 2. The percentage of TSS removal for system with (A) 5-days retention time, and (B) zero retention time The study shows that the performance of zero retention time in reducing TSS is higher compared to 5-days retention time, where the percentage removal at day 21 for 5-days retention time is 61.92%

A B

compared to 32.28% for 5-days retention time. Day 21 is choose because at this day the percentage of TSS removal (refer graph A) is almost constant. The analysis found that there is a significant difference between zero retention time and 5-days retention time for cell with more plants with value p<0.05. Higher removal of TSS in zero retention time is because the TSS in the sewage is undisturbed and easily settles due to gravity force and leaves the clean water throughout the experiment. They are typically designed to support long retention times in order to allow the suspended solids and other particles to settle out. For disturbed sewage with flow rate in the case of 5-days retention time, some of the particle is settle down, while some of the suspended particle will remain suspended because of the settled particle is disturbed from simply settle cause of flow. Further analyses were conducted to determine the performance of TSS percentage removal in term of HRTs variation. We can conclude that the percentage removal is decrease with the increased of HRT for both cells with Vetiveria Zizaniodes, while increase for control cell. These results reveal that higher flow rate of the sewage flowing through the cell will increase the disturbance to the suspended and settled particles, cause the difficulty for the particle to settle, which result lower TSS percentage of removal. Analysis was also conducted to determine the effect of Vetiveria Zizaniodes population to the percentage TSS removal. Results show that percentage removal is increased with the increased of population. The removal will further increases if more density of plants is used in the experiment. However too much plant used, may cause increased in nutrients as the plant will finally rotten and increase the nutrient contents in the sewage. Biochemical Oxygen Demand BOD is a measurement of the oxygen consumption by microorganisms during the oxidation of organic matter and inorganic materials. The test is usually run for 5 days (BOD5) to indicate the amount of readily degradable organic matter in the sewage. The percentage removals of BOD were given in Figure 4.  

Figure 4. The percentage of BOD removal for system with (A) 5-days retention time, and (B) zero retention time

Based on the analysis, results shows that the highest percentage removal for 5-days retention time was 61.06% compared to the zero retention time which is only 32% at day 17. At day 21, the percentage removal for cell with more plant is 53.08% for 5-days retention time and 16.60% for zero retention time. Generally, BOD could be removed by settling the particulate of BOD and utilization of degradable carbon compound during metabolic process. Higher BOD removal efficiencies were due to the higher organic decomposition rate by the Vetiveria Zizaniodes, hence, resulted in CO2 and acid production, which finally lower the effluent pH (refer Table 1, where initial pH is 7.36). Refer also Table 2 and 3 where the pH value is increased for all cells after treatment. There is a significant difference between zero retention time and 5-days retention time

A B

for more cell with more plant with value of p<0.05. According to Sartaj et al., (1999), wetland systems can significantly reduce BOD content. Oil & Grease The capacity of wetland plants to uptake nutrients varies with the species of plants, sewage quality, the growth and the depth of roots. The wetland plants on the soil of oxygen carrying capacity and root functions of water conduction are related to the development of root system (Liu et al, 2003). The analysis found that, the percentage of O&G removal after 21 days of treatment with 5-days retention time in control cell, cell with less plant and cell with more plant are 15.43%, 40.05% and 50.75% respectively, while for zero retention time system are 6.20%, 11.16%, and 16.60% respectively. Figure 5 illustrated the removal percentage for 5-days retention time and zero retention time. Oil & grease was trap by the Vetiveria Zizaniodes massive roots, especially in flowing system compare to system without flowing sewage.          

Figure 5. The O&G percentage removal for system with (A) 5-days retention time, and (B) zero retention time The analysis found that the ability of 5-days retention time to remove oil & grease in the sewage is higher than using zero retention time with a significant difference for cell with more plant in system 5-days retention time and zero retention time is p<0.05. Most of oil & grease is trap in zero retention time system by roots of the Vetiveria Zizaniodes, but for 5-days retention time, both roots and media trapping oil & grease while sewage is flowing through the cell and media. As oil & grease was suspended on top of the sewage undisturbed, the percentage of removal was higher for cell with more plant compare to cell with less plant, and in control cell. Comparison was then made on the oil & grease removal for both 5-days retention time and zero retention time at day 21. We found that the removal for 5-days retention time was much higher compared to zero retention time for any of the cells. Chantkeo et al, (2002) confirmed that most of the roots in vetivers’ massive root system were very fine, with average diameter of 0.5-1.0mm and readily to remove any pollutants in the wastewater that passing through it. Nutrients Two types of nutrients were studied in these research i.e. Orthophosphate (PO4

3-), and Ammonia nitrogen (NH3-N). Richness in nutrients will results in growth of algae; high levels of organic matter decomposition and exhaustion of dissolved oxygen whereby the O2 is highly consume by organic matter in the sewage, and finally will cause eutrophications. Orthophosphate. The percentage of PO4

3- removal after 21 days of treatment for 5-days retention time in control cell, cell with less plant and cell with more plant are 44.16%, 66.63% and 91.83% respectively. The percentage removals for zero retention time are 67.97%, 78.91%, and 85.94%

A B

respectively. Figure 6 illustrated the removal percentage of 5-days retention time and zero retention time system.       

 

 

 

Figure 6. The PO4

3- percentage removal for system with (A) 5-days retention time, and (B) zero retention time Results show that the PO4

3- removal in 5-days retention time system become uniform after 21 days of treatment for all cells. The 5-days retention time removal for cell with more plant at day 21 was 79.05% higher than zero retention time with a value of 46.59%. There is a significant difference between 5-days retention time and zero retention time for every cells with a value of p<0.05. Results also revealed that the flowing system did obtained higher PO4

3- removal compared to stagnant or non-flowing system. This was also similar for BOD, oil & grease and NH3-N. According to Chongrak and Lim (1998), the higher removal efficiency was due to the reason that the plant uptake and microorganisms biodegradation were the major mechanisms in PO4

3- removal. Instead of that, Kanokporn and Monchai (2008) said that the phosphorus in sewage may also be removed through sedimentation, adsorption and precipitation, and exchange process between soil and overlying water column. Nitrogen Ammonia. Figure 7 shows the percentage of NH3-N removal. The NH3-N is an important index of sewage treatment effect. The NH3-N removal mainly depends on oxygen supply capability of plants (Sun, et.al, 2009). The percentage of NH3-N removal after 21 days of treatment for 5-days retention time in control cell, cell with less plant and cell with more plant were 37.48%, 48.02% and 55.80% respectively, compared to the zero retention time system with the value of 21.32%, 31.20%, and 38.13% respectively. The analysis stated that there is a significant difference between both zero retention time and 5-days retention time. The study also shows that constructed wetland did enhance the performance of NH3-N removal in sewage. The zero retention time systems showed lower percentage of removal at day-21 compared to 5-days retention time system as shown by both cells with plants. However, the study found out that the percentage of removal in zero retention time increasing with days of treatment. It shows that zero retention time had ability to reduce ammonia nitrogen in sewage with requirement of longer treatment time, compared to 5-days retention time. According to the Dunbabin and Bowmer, (1992), the nitrogen removal of constructed wetlands system is relying on nitrification – denitrification reaction, plant absorption and ammonia nitrogen volatilization. Nitrification – denitrification reaction is non-stop process throughout of the system.        

A B

           Figure 7. The NH3-N percentage removal for system with (A) 5-days retention time and (B) zero retention time From this study, we can conclude that Vetiveria Zizaniodes used in constructed wetland to treat sewage is an innovative alternative technology that has tremendous potential. Vetiveria Zizaniodes contributed in the removal of nutrient, TSS, BOD and oil and grease. Comparing with chemical and biological sewage treatment, constructed wetland technology has the characteristics of low construction cost, low operation cost, good treatment effect, ecological restoration function and building ecological landscape as also being mentioned by Sun et al., (2009) and, Boonsong and Chansiri, (2008). Removal efficiency of the constructed wetland in this study show an effective performance as predicted. Presence of Vetiveria Zizaniodes for the selected plant did increase the ability of the constructed wetlands to decrease the level of organic matters and increase removal of nutrients as the analyses were made. The percentage of removal for all parameter except TSS in cell with higher populations is higher in a flowing system. The best treatment day is at day-21. The HRT is also one of the elements to contribute the ability of constructed wetland with Vetiveria Zizaniodes to reduce the contaminant in sewage. From the study, we found that constructed wetland with 5-days retention time is better in pollution reduction rather than zero retention time. The analysis found out that there is a significant difference between zero retention time and 5-days retention time for all cells with a value of p<0.05. The percentage removal for every parameter for 5-days retention time is acclimatized at day-21 compared to the percentage removal for zero retention time which is gradually increased even after 21 days of treatment. For the future research, there should be more extensive studies that need to be carried out include the implementation of other types of plant, HRT and number of plant population used in the experiment. A longer period of the experiment is necessary to determine the fullest capacity of the free water surface flow constructed wetlands in terms of pollutant removal. ACKNOWLEDGEMENT The work was funded by Frangipani Resort, Langkawi. We are grateful to Mr Anthony Wong for the fund and helpful discussion REFERENCES APHA 2002 Standard methods for Examination of Water and Wastewater. 21th edition.

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