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Abstrak :
During the last decade, water scarcity in terms of quantity and quality degradation has become a major issue in Indonesia. In 2006, Universitas Indonesia (UI) supported by the Ministry of Public Works built a recharge pond as a field model to overcome flood and drought in Jakarta and its surroundings. However, since then, a lack of research has been conducted to monitor and analyze the rate of change in water quality in the UI recharge pond. The purposes of this study are to identify the characteristics of UI recharge pond and evaluate the surface water quality changes. Water samples were taken from the pond and analyzed in the laboratory for water quality tests. The evaluation method used for simulation of water quality was a numerical model using Runge-Katta Order 4. Laboratory analysis results show concentrations of Mn, Fe, BOD and COD are exceeding the water quality standards (GR No.82/2001). The water purification process in the pond was found to be faster in response to BOD (?= 0.5 d-1) and for Mn, Fe, and COD are found to have similar results at ?= 0.4 d-1. The 95% response time of the pond was found to be longer for Mn, Fe, and COD (t95 = 7.5 d) and the faster rate is BOD (t95 = 6.0 d). The result of numerical modeling demonstrates Mn concentration in the pond will be doubled (0.45 mg/L) on the day-15th and asymptotically converges on a steady state. The Fe, BOD, and COD reaches the steady state concentration around on the day-11th (0.95 mg/L), on the day-13th (56.6 mg/L), and on the day-17th (224 mg/L), respectively.

Abstrak :
Air merupakan sumber daya alam yang sangat penting bagi kehidupan makhluk hidup dan harus selalu terjaga kualitasnya. Pengujian kualitas air perlu dilakukan segera setelah pengumpulan sampel, namun seringkali laboratorium tidak dapat menganalisis sampel air secara langsung dan memungkinkan penyimpanan sampel memerlukan waktu tunggu (holding time). Penelitian ini bertujuan untuk menganalisis dinamika perubahan konsentrasi terhadap waktu tunggu, menganalisis laju reaksi penguraian, serta menyimulasikan perubahan konsentrasi BOD dan COD untuk mengetahui konsentrasi awal. Perubahan konsentrasi terhadap waktu tunggu diketahui melalui metode pengujian parameter BOD dan COD yang diambil dari sampel air Danau Mahoni dan diuji di laboratorium pada t(0), t(0,25), t(2), t(5), t(7), dan t(14) dalam satuan hari. Adapun analisis laju reaksi dilakukan perhitungan kesetimbangan massa dan disempurnakan menggunakan ‘Solver’ pada Microsoft Excel. Sedangkan simulasi perubahan konsentrasi BOD dan COD untuk mengetahui konsentrasi awal dilakukan dengan perhitungan solusi persamaan diferensial dari model yang telah dibuat. Berdasarkan analisis, diperoleh bahwa perubahan konsentrasi parameter BOD dan COD terhadap holding time cenderung menurun pada semua sampel. Konsentrasi BOD secara keseluruhan mengalami penurunan signifikan konsentrasi BOD yang terjadi setelah pengukuran t(2). Konsentrasi COD sampel dengan pengawetan mengalami penurunan signifikan pada pengukuran t(2). Sedangkan konsentrasi COD sampel tanpa pengawetan menurun signifikan setelah waktu pengukuran t(2) dan t(7). Nilai KD BOD dengan pengawetan 1 dan 2 berturut-turut adalah 0,064/hari dan 0,059/hari. Sementara itu, KD BOD pada sampel tanpa pengawetan 1 dan 2 berturut-turut adalah 0,124/hari dan 0,0827. Nilai KD COD dengan pengawetan 1 dan 2 berturut-turut yaitu 0,004/hari dan 0,0169/hari. Sementara itu, pada sampel tanpa pengawetan 1 dan 2, diperoleh nilai KD COD berturut-turut yaitu 0,039/hari dan 0,047/hari. Nilai KD BOD dan COD pada sampel dengan pengawetan cenderung lebih rendah dibandingkan dengan sampel tanpa pengawetan. Hal ini menunjukkan bahwa pengawetan mampu memperlambat laju penguraian BOD dan COD dalam sampel air. Pemodelan parameter BOD dan COD sampel dengan pengawetan maupun tanpa pengawetan untuk memperkirakan nilai konsentrasi awal secara efektif dapat digunakan hingga t(2). ......Water is a natural resource that is very important for the life of living things and its quality must always be maintained. Water quality testing needs to be done immediately after sampling, but laboratories often cannot analyze water samples directly and allow sample storage to require holding time. This study aims to analyze the dynamics of changes in concentration during holding time, analyze the rate of decomposition reactions, and simulate changes in concentrations of BOD and COD to determine initial concentrations. The change in concentration during holding time is known through the BOD and COD parameter testing methods taken from Lake Mahoni water samples and tested in the laboratory at t(0), t(0.25), t(2), t(5), t(7) ), and t(14) in days. The reaction rate was carried out by calculating the mass balance and using 'Solver' in Microsoft Excel. Meanwhile, the simulation of changing the concentration of BOD and COD to determine the initial concentration was carried out with differential solutions from the model that had been made. The analysis found that changes in the concentration of BOD and COD during holding time tended to decrease in all samples. BOD concentration as a whole experienced a significant decrease in BOD concentration that occurred after t(2) measurement. The COD concentration of the samples with preservation decreased significantly in the t(2) measurement. In contrast, the COD concentration of samples without preservation was significantly reduced after the measurement time t(2) and t(7). KD BOD values with preservation 1 and 2 were 0.064/day and 0.059/day, respectively. Meanwhile, the samples without preservation 1 and 2 were 0.124/day and 0.0827 respectively. The KD COD values with preservation 1 and 2 were 0.004/day and 0.0169/day, respectively. Meanwhile, the KD COD values were obtained for samples without preservation 1 and 2, respectively, 0.039/day and 0.047/day. KD BOD and COD values in samples with preservation tended to be lower than those without preservation. This condition shows that pickling can slow down the rate of decomposition of BOD and COD in water samples. BOD and COD modeling with or without preservation to determining initial concentration values can be used up to t(2).

Abstrak :
Pengisian air melalui waduk resapan di Universitas Indonesia, Depok telah menimbulkan pencemaran. Dari hasil pengujian melalui laboratorium, parameter DO, COD, Nitrogen dan Phosfat melebihi nilai yang disyaratkan menurut Peraturan Pemerintah No.82 Tahun 2001 (Kelas I) Tentang Pengelolaan Kualitas Air dan Pengendalian Pencemaran Air. Untuk mengetahui sebaran pencemaran maka diperlukan pemodelan. Pemodelan didasarkan pada hukum kekekalan massa dengan mempertimbangkan proses adveksi dan dispersi. Pemodelan komputer dalam Visual Basic Application for Excel dibuat dengan pendekatan metode beda hingga dan menghasilkan visualisasi berupa grafik konsentrasi dan jarak. Dari berbagai variasi didapat jarak pencemaran terjauh 3500 m dengan konsentrasi tertinggi 370,30 mg/l. ......Water recharge through artificial pond at university of indonesia, Depok caused water pollution. From the laboratory test, DO, COD, Nitrogen and phosphat parameter exceed the value that admitted by Goverment Regulation No. 82 year 2001 (class I) about Water quality management and water pollution control. For that, to understand the pollution distribution, it is necessary a numerical simulation. Numerical simulation based on the conservation of mass law by considering the advection and dispersion process. Numerical simulation by computer in visual basic application for excel made with finite-difference method approach and produce concentration and distance graphic visualitation. from many variation result that the longest pollution distance 3500 m with the highest concentration 370,30 mg/l.