Analysis of Water Quality in Tasi-tolu Lake due to domestic wastewater pollution using the Pollutant Index Method: A case study from Dili Municipality, Timor- Leste

Domestic wastewater pollution is a pollutant of community activities that can decrease water quality. Tasi-tolu lake is used by the community for their daily necessities, but there is a lack of public awareness about disposing of wastewater into the lake, causing the death of an ecosystem in the water. Research using the pollutant index method according to Environmental Ministry Decision No. 115 in the year 2003 about the Water Quality Status Determination guideline to determine the class of water to compare quality standards according to PP No.82 of 2001. The result of the study showed the pollutant index value showed the water quality of Tasi-tolu lake for class II in the upstream and middle part was moderately polluted with IP values of 6,065 and 6,112, while class III quality standards were lightly polluted with IP values of 1,88 and 2,12, while class IV in the upstream meets quality standard IP value of 0,76 and in the middle part is lightly polluted with an IP value of 1,41. Keyword: domestic wastewater, Tasi-tolu Lake ,and the IP Method


Introduction
Tasi-tolu lake was used as a biodiversity conservation area, but as the population grew, the lake was used for settlements, plantations, livestock raising, and freshwater fish cultivation. Tasi-tolu lake is a lake used by residents for a variety of household activities, including the discharge of wastewater and the disposal of solid waste that can harm the environment and ecosystems in the water (Putri et al., 2018) Domestic wastewater is generally divided into grey water and black water, with the sources coming from toilets, baths, washing clothes, and kitchen laundry (Shaikha Binte Abedin, 2013) (Petta, 2008) (Corcoran, E., C. Nellemann, E. Baker, R. Bos, D. Osborn, 2010). Pollution of lake water is caused by a lack of public awareness, as well as the lack of a wastewater treatment system, which means that all wastewater from washing, bathing, and toilets is dumped into the lake, as well as the inability of the lake's capacity for wastewater because the water is stagnant and cannot be neutralized, so it is necessary to monitor the status of the water quality to determine the level of pollution that occurs in Tasi-tolu lake. According to the Minister of the Environment's Decree No. 115 of 2003 governing guidelines for evaluating the status of water quality, is the level of polluted or good conditions in water sources when compared to water quality standards that have been established (Peraturan Pemerintah Republik indonesia, 2001) In this study, the pollutant index was used as one of the methods to determine the contamination in a river or lake(Menteri Negara Lingkungan hidup, 2003) Water quality management employs the Pollution Index (IP) method to determine the level of pollution to take action to improve water quality in the event of a decrease in quality caused by organic or inorganic polluting compounds (Muhammad Ali Wafa, Winardi Dwi Nugraha, 2014). The purpose of this study is to use the Pollutant Index method to analyze the amount of water pollution in Tasitolu Lake and to determine the condition of the lake's water quality to the category in class II, III, and IV quality standards.

Methodology
In this study, two sampling points were chosen to represent areas that are considered polluted by domestic wastewater and are near residential areas. 1. Upstream (point close to settlements or community activities) ADRI INTERNATIONAL JOURNAL OF SCIENCES, ENGINEERING AND TECHNOLOGY VOLUME 6 │ NUMBER 1 │ NOVEMBER 2021 Available online at http://adri.journal.or.id/index.php/ijset/index ISSN: 2549-5518 ; 2549-550X ; 11/02/17 Attribution 4.0 International (CC BY 4.0) You are free to: Sharecopy and redistribute the material in any medium or format, Adaptremix, transform, and build upon the material for any purpose, even commercially 131 2. Middle (Point far from settlements or in the middle of the lake). The appearance of Tasi-tolu lake can be seen in Figure 1. Figure 1. The appearance of Tasi-tolu lake Data processing on the level of pollution in domestic wastewater in tasi-tolu using the Pollutant Index (IP) method in accordance with Decree of the Minister of the Environment No. 115/2003 Attachment II regarding the determination of water quality standards, to determine the quality of water, based on its designation and to take corrective actions to improve water quality in the event of a drop in quality.
The following is the formula used to calculate the pollutant index:

Results and Discussion
Pollution in Tasi-tolu lake is only from non-point sources, such as the disposal of domestic wastewater, agricultural livestock, and fisheries around the lake. The high water pollution of Lake Tasi-tolu is caused by the increase in the surrounding population. Based on East Timor's statistical data in 2010, the total population was 65,404 people (Anonim, 2010), while in 2015 it grew to 76,681 people so pollution in lake water also increased according to population growth (Statistic Timor Leste, 2017). The results of the analysis of the water quality of Tasi-tolu lake using the pollutant index method can be seen in Table 2. ADRI INTERNATIONAL JOURNAL OF SCIENCES, ENGINEERING AND TECHNOLOGY VOLUME 6 │ NUMBER 1 │ NOVEMBER 2021 Available online at http://adri.journal.or.id/index.php/ijset/index ISSN: 2549-5518 ; 2549-550X ; 11/02/17 Attribution 4.0 International (CC BY 4.0) You are free to: Sharecopy and redistribute the material in any medium or format, Adaptremix, transform, and build upon the material for any purpose, even commercially 132 You are free to: Sharecopy and redistribute the material in any medium or format, Adaptremix, transform, and build upon the material for any purpose, even commercially Figure 3. IP value of class IV quality standard The water quality of Tasi-tolu lake is carried out at two points, namely upstream and in the middle. The results of the study can be seen in Figures 2, 3, and 4 in Figure 2. Based on the Decree of the Minister of Environment No. 115 of 2003 concerning guidelines for determining the status of water quality, it shows that the lake water has exceeded the quality standard for classes II, III, and IV. Thus, the IP value of lake water for class II quality standards in the upstream is 6.065 and the middle IP value is 6.112, while for quality standard III, the IP value for the upstream part is 1.88 and the middle is 2.12. However, the water of Tasi-tolu lake upstream still meets the class IV quality standard with an IP value of 0.76. But in the middle, it has exceeded the IV quality standard.
Tasi-tolu lake, as seen from the pollutant index value obtained from each point, is not feasible for class II, III, and IV quality standards. This is caused by domestic wastewater from settlements such as washing clothes, bathing, kitchen laundry, toilets, and surrounding land use. In addition, the pollutant index value in Tasi-tolu lake water getting to the middle the higher IP value can be seen in Figures 2, 3, and 4 because Tasi-tolu lake water pollution does not only come from domestic wastewater but also animal waste, garbage, dirt from rainwater runoff, and fishing activities.

Conclusion
Based on the results of data analysis, it can be concluded that the water of Tasi-tolu lake in the upstream and middle parts has exceeded the quality standards for classes II, III, and IV. This is caused by domestic wastewater from settlements and the surrounding land use. However, Tasi-tolu lake water upstream is still designated for class IV quality standards.

Acknowledgments
Gratitude and praise I ask for the presence of God Almighty and His grace so that I can write and finish the journal titled Analysis of Water Quality in Tasi-tolu Lake due to domestic wastewater pollution using the Pollutant Index Method: A case study from Dili Municipality, Timor-Leste. I'd like to take this opportunity to express my deepest thanks to: 1. My parents, my beloved brothers, and sisters have given me a lot of moral and material support, as well as prayers; 2. Mrs. Dr. Ling. Ir. Sri Sumiyati, S.T., M.Si., IPM and Mr.Prof.Dr.Ir. Syafrudin, CES, M.T., IPM. As Advisors, thank you for the guidance, motivation, and support in the completion of this journal; 3. All Lecture staff and employees majoring in Environmental Engineering Masters, and the International Office (IO) Diponegoro University Semarang, who have contributed significantly to the lecture and administrative processes; 4. President and laboratory manager of Bee Timor-Leste, Empresa Pública (BTL, E.P) gave me a place to do research; 5. Fellow all students of Environmental Engineering at Diponegoro University and my best friend Dina Maria Abel thanks for helping and supporting