Pelarutan, Pemisahan, dan Recovery Alum dari Lumpur Pengolahan Air Minum

Barakwan, Rizkiy Amaliyah (2021) Pelarutan, Pemisahan, dan Recovery Alum dari Lumpur Pengolahan Air Minum. Doctoral thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Kadar aluminium yang tinggi pada lumpur pengolahan air minum diakibatkan oleh penggunaan aluminium sulfat atau alum sebagai koagulan. Lumpur alum berpotensi menyebabkan pencemaran lingkungan. Konsentrasi aluminium yang tinggi di lumpur alum berpotensi untuk di-recovery sebagai koagulan alum. Pada recovery koagulan, langkah pertama yang harus dilakukan adalah pelarutan aluminium dari lumpur yang dapat dilakukan secara kimia dan biologis. Pengolahan secara kimia termasuk asidifikasi yaitu dengan menambahkan asam sulfat, sedangkan bioleaching menggunakan mikroorganisme untuk melarutkan aluminium dari lumpur. Namun, asidifikasi secara kimia dan bioleaching adalah proses nonselektif karena terlarutnya logam-logam lain dan zat organik. Oleh karena itu, proses lebih lanjut diperlukan untuk memisahkan aluminium terlarut dari kontaminan lain. Proses ini dapat dilanjutkan dengan metode elektrolisis menggunakan membran penukar ion semipermeable untuk meningkatkan kemurnian material hasil recovery. Tujuan dari penelitian ini adalah mengkaji karakteristik fisik dan kimia serta toksisitas lumpur pengolahan air minum sebagai dasar penentuan metode pengolahannya yang tepat, membandingkan efisiensi pelarutan aluminium dari lumpur pengolahan air minum secara kimia dan biologis, mengkaji efektifitas metode elektrokimia untuk pemisahan alum hasil recovery dari pengotor, dan mengkaji efektifitas metode elektrokimia optimum pada skala pilot untuk pemisahan alum hasil recovery dari pengotor. Sampel lumpur alum diambil dari unit clearator di Instalasi Pengolahan Air Minum (IPAM) 1 Jawa Timur, Indonesia. Karakterisasi lumpur meliputi karakteristik fisik dan kimia serta toksisitas terhadap organisme Daphnia magna dan mikroorganisme. Asidifikasi secara kimia dilakukan dengan menambahkan asam sulfat sampai pH 2 dengan pengadukan selama 2 jam menggunakan magnetic stirrer. Selanjutnya, sentrifugasi dilakukan selama 20 menit pada 3.000 rpm untuk memisahkan fase cairan dari padatan lumpur. Bioleaching tahap 1 dilakukan dalam reaktor batch dengan pengadukan 150 rpm selama 15 hari. Jenis mikroorganisme yang digunakan adalah fungi (Aspergillus niger, Penicillium simplicissimum) dan bakteri (Pseudomonasfluorescens, dan Acidithiobacillus ferrooxidans). Komposisi media (M) dan lumpur alum (L) adalah 50/50, 25/75, 12,5/87,5, dan 0/100 (v/v). Bioleaching tahap 1 dilakukan menggunakan lumpur alum steril. Hasil optimumnya diikuti dengan penentuan adanya pengaruh mikroorganisme indigenous lumpur alum pada bioleaching aluminium. Parameter yang diukur adalah konsentrasi aluminium dan pH setiap 3 hari sekali. Konsentrasi logam lain (besi, mangan, zink, timbal, kromium, dan tembaga), COD, N-total, dan P-total diukur pada awal dan akhir percobaan. Recovery alum dilakukan dengan metode elektrolisis pada skala laboratorium. Volume sel elektrolisis dan luas permukaan elektroda masing-masing adalah 200 mL dan 24 cm2 . Uji voltametri siklik dilakukan untuk mendapatkan jenis material anoda dan katoda yang optimum untuk elektrolisis dengan elektrolit dari hasil asidifikasi lumpur alum. Jenis anoda dan katoda adalah karbon (C)/ perak (Ag), platina (Pt)/ platina (Pt), dan platina (Pt)/ stainless steel A304 (SS A304). Kuat arus listrik diperoleh dari hasil uji polarisasi pada masing-masing jenis elektroda. Larutan elektrolit yang digunakan adalah supernatan hasil asidifikasi pada pH 3. Konfigurasi reaktor elektrolisis yang digunakan adalah elektrolisis tanpa membran dan elektrolisis dengan membran. Membran penukar ion semipermeable yang digunakan adalah cation exchange membrane (CEM) dan anion exchange membrane (AEM). Elektrolisis skala pilot dirancang dengan menyamakan nilai rasio luas penampang elektroda dan sel elektrolisis (Ae/Ac) serta perbandingan luas penampang elektroda dan volume reaktor (Ae/V) berdasarkan kondisi optimum elektrolisis skala laboratorium. Volume sel elektrolisis dan luas permukaan elektroda masing-masing diperbesar menjadi 400 mL dan 48 cm2 . Volume feedtank diperbesar dari 1 L (skala laboratorium) menjadi 5 L pada skala pilot dengan waktu elektrolisis diperpanjang menjadi 10 jam. Elektrolisis dilakukan pada kuat arus 400 mA, 600 mA, dan 800 mA untuk mendapatkan densitas arus seperti pada skala laboratorium. Total dissolved solids dan nilai pH pada elektrolisis skala laboratorium dan pilot diukur setiap jam. Konsentrasi aluminium, mangan, besi, zink, timbal, kromium, dan tembaga diukur menggunakan ICP Agilent Technologies 700 Series ICP-OES pada awal dan akhir elektrolisis. Endapan-endapan yang terbentuk ditimbang dan diukur pada akhir proses. Hasil penelitian menunjukkan bahwa lumpur alum mengandung konsentrasi aluminium (1.194-6.736,3 mg/L), besi (1.077,09-3.800 mg/L), mangan (1.041 mg/L), dan COD (2.166,67-4.914 mg/L) yang tinggi. Konsentrasi polutan lebih tinggi pada musim hujan dibandingkan kemarau. Toksisitas lumpur alum pada D. magna terjadi pada konsentrasi 10,12%. Metode pelarutan aluminium dari lumpur alum yang paling sesuai adalah metode kimia dengan asidifikasi menggunakan asam sulfat. Hal ini karena asidifikasi membutuhkan waktu yang lebih cepat dibandingkan bioleaching. Jenis elektroda yang sesuai untuk elektrooksidasi pada proses recovery alum berdasarkan hasil uji voltametri siklik adalah platina sebagai anoda dan SS A304 sebagai katoda. Proses elektrolisis yang optimum pada recovery alum adalah 67,56% dengan komposisi kandungan aluminium (90,94%), mangan (5,78%), besi (3,10%), zink (0,17%), dan tembaga (0,0087%). Alum hasil recovery bebas dari kontaminan organik karena penggunaan CEM pada elektrolisis. Densitas arus optimum pada elektrolisis skala pilot adalah 12,5 mA/cm2 dengan efisiensi recovery alum sebesar 68,06% dan nilai SEC 53,47 kWh/kg. Komposisi kandungan aluminium pada alum hasil recovery dibandingkan dengan logam lainnya adalah 91,23% dengan peningkatan konsentrasi aluminium dalam kompartemen katoda mencapai 61,77%. Elektrolisis skala laboratorium dan pilot memiliki efektifitas yang tidak jauh berbeda pada densitas arus yang sama. Aplikasi teknologi ini sangat bermanfaat bagi lingkungan, namun teknologi ini juga dinilai tidak layak secara ekonomi dengan nilai NPV negatif dan BCR<1. ================================================================================================= The high level of aluminum in drinking water treatment sludge (DWTS) or alum sludge is due to the use of aluminum sulfate or alum, as a coagulant. The alum sludge is potential to cause environmental pollution. The high aluminum concentration in the alum sludge is potential to be recovered as alum coagulant. First step in coagulant recovery is the dissolution of aluminum from the sludge which can be carried out by chemical or biological methods. The chemical process includes acidification using sulfuric acid, while bioleaching uses microorganisms for separating aluminum from the sludge. However, chemical acidification and bioleaching are non-selective processes due to the dissolution of other metals and organic matter. Therefore, further process isrequired to separate the dissolved aluminum from contaminants. These processes can be followed by electrolysis using a semipermeable ion exchange membrane to increase the purity of the recovered material. Aims of this study are to examine the physical and chemical characteristics and toxicity of the DWTS as a basis for determining the appropriate treatment method, to compare the efficiency of aluminum dissolution from DWTS using chemical and biological methods, to examine the effectiveness of electrochemical methods for separating the recovered alum from impurities, and to examine the effectiveness of optimum electrochemical method in the pilot scale for separating the recovered alum from impurities. Alum sludge samples were collected from clearator unit in drinking water treatment plant (DWTP) 1 East Java, Indonesia. Alum sludge characterization included physical and chemical characteristics and toxicity to Daphnia magna and microorganisms. Chemical acidification was carried out by adding sulfuric acid to pH 2 and stirring for 2 hours using magnetic stirrer. Then, centrifugation was carried out for 20 minutes at 3,000 rpm to separate the liquid phase from the sludge solid. Bioleaching in first stage was carried out in a batch reactor and stirred at 150 rpm for 15 days. The types of microorganisms used were fungi (Aspergillus. niger, Penicillium simplicissimum) and bacteria (Pseudomonas fluorescens, and Acidithiobacillus ferrooxidans). The composition of the medium (M) and alum sludge (L) were 50/50, 25/75, 12.5/87.5, and 0/100 (v/v). First stage of the bioleaching was carried out using sterile alum sludge. The optimum results was followed by determination of the effect of indigenous microorganisms to the sludge. Parameters measured were aluminum concentrations and pH every 3 days. Other metal concentrations (iron, manganese, zinc, lead, chromium, and copper), COD, N-total, and P-total were measured at the initial and end of the experiment. Alum recovery was carried out using electrolysis methods in a laboratory scale. The electrolysis cell volume and the electrodes cross-sectional area were 200 mL and 24 cm2 , respectively. Cyclic voltammetry test was carried out to obtain the optimum type of anode and cathode materials for electrolysis with electrolyte from acidified alum sludge solution. Types of anode and cathode were carbon (C)/silver (Ag), platinum (Pt)/platinum (Pt), and platinum (Pt)/stainless steel A304 (SS A304). Electrical current was obtained from polarization test results on each type of electrode. The electrolyte solution was the supernatant from the acidification at pH 3. Configuration of the electrolysis reactors were electrolysis without membrane and electrolysis with membranes. The membranes were semipermeable ion exchange membrane, namely cation exchange membrane (CEM) and anion exchange membrane (AEM). The pilot-scale electrolysis cell was designed by using similar ratio of the electrodes and cell cross-sectional areas (Ae/Ac) and the ratio of electrodes cross�sectional area and reactor volume (Ae/V) of earlier the optimum condition of laboratory�scale experiment. The electrolysis cell volume and the electrodes cross-sectional area were enlarged to 400 mL and 48 cm2 , respectively. The feedtank volume was enlarged from 1 L (in laboratory-scale) to 5 L in pilot-scale with the electrolysis time extended to 10 h. The electrolysis was performed at electrical currents of 400, 600, and 800 mA to get similar current density variation as those in the laboratory-scale. Total dissolved solids and pH in laboratory and pilot scale reactors were measured every hour. The concentrations of aluminum, manganese, iron, zinc, lead, chromium, and copper were measured using ICP Agilent Technologies 700 Series ICP-OES at the initial and end electrolysis. Those of the deposits were measured at the end of experiment. The results showed that the alum sludge had high concentrations of aluminum (1,194 to 6,736.3 mg/L), iron (1,077.09 to 3,800 mg/L), manganese (1,041 mg L), and COD (2,166.67 to 4,914 mg/L). Pollutant concentrations in the alum sludge was higher in the rainy season than in the dry season. The toxicity of alum sludge to D. magna occurred at a concentration of 10.12%. The most suitable method of aluminum separation from alum sludge was chemical method with acidification using sulfuric acid. It was caused the acidification required a shortertime than the bioleaching process. The suitable electrodes types for electrooxidation according to the cyclic voltammetry test were platinum as anode and SS A304 as cathode. Optimum electrolysis efficiency in alum recovery was 67.56% with composition of aluminum (90,94%), manganese (5,78%), iron (3,10%), zinc (0,17%), and copper (0,0087%). The recovered alum was free from organic impurities due to the used of CEM during electrolysis. The optimum current density in the pilot-scale electrolysis was 12.5 mA/cm2 with alum recovery of 68.06% and SEC value of 53.47 kWh/kg. The aluminum content in the recovered alum compared to other metals was 91.23% with an increase of the aluminum concentration in the cathode compartment reaching 61.77%. Laboratory and pilot-scales electrolysis had the similar effectiveness at the same current density. Application of this technology is very beneficial for the environment, howeverthis technology was also considered economically inadequate with a negative NPV and BCR<1.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Asidifikasi, bioleaching, elektrolisis, lumpur alum, recovery alum. ================================================================================== Acidification, alum recovery, alum sludge, bioleaching, electrolysis.
Subjects: T Technology > TD Environmental technology. Sanitary engineering > TD420 Water pollution
T Technology > TD Environmental technology. Sanitary engineering > TD433 Water treatment plants
T Technology > TD Environmental technology. Sanitary engineering > TD455 Chemical precipitation. Coagulation. Flocculation. Water--Purification--Flocculation.
T Technology > TD Environmental technology. Sanitary engineering > TD480.5 Electrodialysis
T Technology > TP Chemical technology > TP159.M4 Membranes (Technology)
T Technology > TP Chemical technology > TP248.25.M45 Membrane reactors
T Technology > TP Chemical technology > TP255 Electrochemistry, Industrial.
Divisions: Faculty of Civil Engineering and Planning > Environment Engineering > 25001-(S3) PhD Thesis
Depositing User: Rizkiy Amaliyah Barakwan
Date Deposited: 22 Aug 2021 12:45
Last Modified: 22 Aug 2021 12:45
URI: https://repository.its.ac.id/id/eprint/88447

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