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"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."

"Nitrifikasi adalah proses alami di badan air di mana terjadi pemecahan nitrogen tereduksi, umumnya dalam bentuk amonia (NH4+) menjadi Nitrit (NO2-) dan kemudian menjadi Nitrat (NO3-) oleh bantuan bakteri. Laju nitrifikasi dipengaruhi oleh beberapa faktor. Tujuan dari penelitian ini adalah untuk menganalisis laju nitrifikasi pada Sungai Kali Baru dengan metode batch, menganalisis pengaruh konsentrasi TSS terhadap laju nitrifikasi, dan menganalisis pengaruh nilai laju reaksi hasil percobaan terhadap akurasi model QUAL2Kw. Evaluasi laju nitrifikasi dilakukan dengan mengamati fluktuasi konsentrasi parameter nitrifikasi dari sampel air selama rentang waktu hingga 12 hari, kemudian dilakukan perhitungan menggunakan persamaan kinetika reaksi untuk mendapatkan tetapan laju oksidasi amonia (kai) dan tetapan laju oksidasi nitrit (kin). Nilai kai yang diperoleh merupakan nilai tetapan laju nitrifikasi yang dapat dimodelkan dalam QUAL2Kw untuk kemudian dibandingkan hasil simulasi amonia dan nitratnya dengan laju default (0,1858 /hari). Penelitian ini menguji sampel air Sungai Kali Baru, dan sampel air kondisi artificial. Parameter yang diuji dalam penelitian ini adalah konsentrasi Amonia, Nitrit, Nitrat, dan TSS. Sampel air Sungai Kali Baru memiliki konsentrasi TSS sebesar 113 mg/L, kai sebesar 0,30587 /hari serta kin sebesar 0,14088 /hari. Sampel artificial tidak mengandung TSS sehingga diperoleh kai sebesar 0,00355 /hari, dan kin sebesar 0,04944 /hari. Laju nitrifikasi yang diperoleh dalam penelitian ini 64,6% lebih tinggi dibandingkan dengan laju nitrifikasi default permodelan. Namun, perbedaan laju nitrifikasi ini hanya menurunkan konsentrasi amonia hasil permodelan sebesar 0,17% dan meningkatkan konsentrasi nitrat hasil permodelan sebesar 0,39%.

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Nitrification is a natural process in a water body breaking down reduced nitrogen in the form of ammonia (NH4+) to Nitrite (NO2+) which further oxidises into Nitrate (NO3-) by the help of bacteria. The rate of nitrification is affected by several factors. This study aims to analyze the nitrification rate of Kali Baru River using a batch method, analyzing the effect of TSS concentration in water to the nitrification rate, and analyzing how nitrification rate achieved from this study affected the accuracy of a previous QUAL2Kw model. The evaluation of nitrification rate is done by observing the fluctuation of nitrification parameter concentration in a water sample ranging to 12 days, then a kinetical rate analysis is done to gather the ammonia oxidation rate (kai) and the nitrite oxidation rate (kin). The kai value is determined to be the nitrification rate that can be modelled in QUAL2Kw. The ammonia and nitrate concentration modelled by using the kai from this study will be compared to the default value of nitrification rate from the previous modelling (0,1858 /day). This study tested the water quality of Kali Baru River water sample and an artificial condition water sample. The parameters tested in this study are ammonia, nitrite, nitrate, and TSS concentration. Samples from Kali Baru River resulted a 113 mg/L TSS concentration and a kai, and kin value of 0,30587 /day and 0,14088 /day respectively. Artificial condition water sample did not result in any TSS concentration and resulted a kai, and kin value of 0,00355 /day and 0,04944 /day respectively. The nitrification rate acquired from this study is 64,6% higher than the default nitrification rate but only decreased the modelled ammonia concentration by 0,17% and increased the modelled nitrate concentration by 0,39%."

"Contains recent ideas and results in three areas of growing importance in curve and surface design: algebraic methods, variational surface design, and some special applications. Leading researchers from throughout the world have contributed their latest work and provided several promising solutions to open issues in surface modeling."

"A methodology for characterizing ground water quality of watersheds using hydrochemical data that mingle multiple linear regression and structural equation modeling is presented...."

"Danau Mahoni adalah salah satu danau yang berada di kawasan Universitas Indonesia dengan fungsinya sebagai daerah resapan air dan sebagai penampung limbah-limbah yang berasal dari fakultas yang berada disekitarnya. Pencemar yang masuk ke badan air ini dapat menurunkan kualitas air danau dan membahayakan ekosistemnya. Salah satu proses pengelolaan air yang dapat meningkatkan kualitas air adalah proses aerasi. Tipe aerator yang umum digunakan adalah aerator berjenis kincir air (paddle wheel). Penelitian ini bertujuan untuk menganalisis perubahan parameter DO, amonia, dan nitrat pada lingkup area yang ditinjau dengan variasi jarak horizontal, menganalisis jarak optimum dari pengaruh pengoperasian aerator kincir air pada saat aerasi selama 4 jam, Menganalisis pengaruh durasi pengoperasian aerator yang lebih lama terhadap perubahan parameter air danau yang ditinjau, dan menganalisis pengaruh pengoperasian aerator terhadap perubahan parameter pada air di belakang aerator. Data yang diperoleh nantinya akan dianalisis menggunakan metode uji T, uji korelasi, dan presentase perubahan nilai. Berdasarkan analisis hasil penelitian, diperoleh bahwa aerator tipe kincir air dapat meningkatkan DO dari 3,58 mg/L menjadi 7,86 mg/L atau sebesar 54,44% pada waktu pengoperasian selama 5 jam. Pengoperasian aerator ini juga dapat menurunkan konsentrasi amonia dari 2,3 mg/L menjadi 0,82 mg/L atau sebesar 179,64% pada pengoperasian selama 5 jam. Pada parameter lainnya yaitu nitrat, terjadi peningkatan dari 1,7 mg/L menjadi 2,1 mg/L pada pengoperasian selama 5 jam. Pengoperasian aerator kincir air juga memberikan pengaruh yang signifikan ke arah belakang dari peletakan aerator kincir air. Secara keseluruhan waktu optimum aerator kincir air yang diperoleh dari penelitian ini adalah 5 jam dengan jangkauan maksimal hingga 5,5 meter, pengoperasian pada waktu optimum tersebut dapat meningkatkan konsentrasi parameter DO dan nitrat hingga memenuhi baku mutu kelas I dan untuk parameter amonia memenuhi baku mutu kelas III.

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Lake Mahoni is one of the lakes located in the University of Indonesia area with its function as a water catchment area and as a reservoir for waste originating from the faculties around it. Pollutants that enter these water bodies can reduce the quality of lake water and endanger the ecosystem. Substances that have the potential to pollute Mahogany Lake are organic pollutants such as ammonia, nitrate, nitrite, phosphorus, and other elements. One of the water management processes that can improve water quality is the aeration process. This process will add oxygen to the water and then reduce the pollutant content in the water. One type of aerator commonly used is the paddle wheel type aerator. This study aims to analyze changes in DO, ammonia, and nitrate parameters in the scope of the area reviewed by varying horizontal distances, analyzing the optimum distance from the effect of operating a waterwheel type aerator when aeration is carried out for 4 hours, analyzing the effect of operating duration of a waterwheel type aerator that is longer time on changes in lake water parameters under review, and analyze the effect of operating a waterwheel type aerator on changes in parameters in the water behind the aerator. The data obtained will later be analyzed using the T test method, correlation test, and the percentage change in value. Based on the analysis of the research results, it was found that the waterwheel type aerator could increase DO from 3.58 mg/L to 7.86 mg/L or by 54.44% during 5 hours of operation. Operation of this aerator can also reduce the concentration of ammonia from 2.3 mg/L to 0.82 mg/L or 179.64% in operation for 5 hours. In other parameters, namely nitrate, there was an increase from 1.7 mg/L to 2.1 mg/L in operation for 5 hours. The operation of the waterwheel aerator also has a significant influence towards the rear of the placement of the waterwheel aerator. Overall, the optimum time for the waterwheel aerator obtained from this study is 5 hours with a maximum range of up to 5.5 meters, operation at this optimum time can increase the concentration of DO and nitrate parameters to meet class I quality standards and for ammonia parameters to meet class I quality standards. III."

"Solar panel terapung merupakan sumber energi terbarukan yang dapat memenuhi kebutuhan energi bersih dengan keunggulan yang tidak memakan lahan. Menutup permukaan air dengan solar panel membatasi masuknya sinar matahari ke perairan yang dibutuhkan organisme autotrof untuk berfotosintesis sehingga mempengaruhi kualitas air permukaan. Penelitian ini bertujuan untuk mengetahui pengaruh variasi luas tutupan permukaan terhadap perubahan kualitas air danau. Pengujian dilakukan dengan meletakkan 4 buah mesocosm di Danau Mahoni dan memvariasikan persentase tutupan sebesar 0%, 30%, 50%, dan 100%. Selama 5 minggu pengukuran dilakukan pengukuran klorofil-a, DO, nitrat, dan fosfat. Pengolahan data menggunakan statistik deskriptif dan statistik inferensial. Melalui uji ANOVA satu arah didapatkan variasi tutupan permukaan berpengaruh signifikan terhadap perubahan klorofil-a dan tidak berkolerasi signifikan terhadap parameter DO, nitrat, dan fosfat. Sedangkan uji korelasi dengan regresi menunjukkan trendline negatif pada seluruh parameter seiring penambahan persentase tutupan mesocosm. Kemudian dilakukan uji korelasi menggunakan Pearson untuk mengetahui hubungan konsentrasi klorofil-a dengan DO akibat variasi tutupan permukaan mesocosm. Hasilnya menunjukkan korelasi bervariasi pada masing-masing mesocosm.

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Floating solar panels is a renewable energy source for clean energy demands that do not require much space. Covering the water's surface with solar panels affects water quality since it can restrain the access of sunlight into the waters, which autotrophs organism need to do photosynthesis. This research aims to determine the effect of surface cover variations on lake water quality. The study was carried out on a small scale by setting four mesocosms in Mahoni Lake, Universitas Indonesia and altering the cover percentage from 0%, 30%, 50%, to 100%. During five weeks of the experiment, the chlorophyll-a, DO, nitrate, and phosphate parameters were processed using descriptive and inferential statistics. The one-way ANOVA test revealed that the variations of surface cover percentage significantly affected changes in chlorophyll-a and did not correlate significantly with DO, nitrate, and phosphate. The correlation test with regression showed a negative trendline for all parameters along with the increasing percentage of mesocosm cover. The correlation test was conducted using pearson to specify the relationship between chlorophyll-a and DO due to variations in mesocosm surface cover. The results show that the correlation value varies in each mesocosm."