Validation of a Modified Procedure for the determination of Chemical Oxygen Demand using standard dichromate method in industrial wastewater samples with high calcium chloride content

Abstract

Background/ Objectives: Chemical Oxygen Demand (COD) is a widely used aggregate organic pollutant index in national discharge standards and is one of the critical parameters for water quality assessment. The conventional COD determination by wet oxidative method encounters the problem of chloride interference in water samples with high chloride content. The dichromate reflux method oxidizes 85-95% of organic matter and also 100% of chloride ions in the samples, without an appropriate chloride masking strategy. The standard method cannot measure COD accurately in samples containing more than 2000 mg L -1 chloride. The present study demonstrates and validates a modified procedure for the determination of COD in industrial sample with high calcium chloride content and low organic load. Method: Petrochemical industries manufacturing Propylene Oxide and Propylene Glycol via chlorohydrin route generate wastewater with high calcium chloride content. Due to high chloride content, the standard analysis method could not produce reliable data for COD values with known precision and accuracy. The standard method based on dichromate was modified, with an additional mixing step for a specified time to enhance the chloride masking by mercuric sulphate. Undiluted sample (20 mL) was mixed with the required amount of mercuric sulpahte to maintain 10:1 ratio to chloride content and 10 mL of sulphuric acid at 150-175 RPM for 20 minutes at room temperature to increase the contact time/ chloride masking. Method validation attributes of the modified procedure were assessed and found to be complying with the acceptance criteria. Findings: We developed a modified procedure for the standard dichromate based chemical oxygen demand (COD) determination in industrial wastewater samples rich in calcium chloride. An additional mixing step is introduced in the standard procedure to enhance the chloride masking with mercuric sulphate in samples containing high chloride. The amended procedure resulted in accurate COD values in samples with low organic load, rich in calcium chloride and the modified

Pengujian Kadar Chemical Oxygen Demand (COD) pada Air Limbah Tinggi Kalsium Klorida Menggunakan Metode Refluks Terbuka

“…Salah satu parameter yang umumnya diuji dalam limbah cair laboratorium adalah kadar COD (Chemical Oxygen Demand). Hal ini dikarenakan, parameter COD dianggap sebagai indikator paling kuat pencemaran limbah organik di dalam air, dibandingkan dengan BOD, TOC, dan TOD (Gnanavelu et al, 2021).…”

“…Metode penentuan analisis COD menggunakan refluks terbuka merupakan metode konvensional yang paling disukai karena aplikasinya yang mudah untuk berbagai air limbah (Gnanavelu et al, 2021). Metode ini didasarkan pada pengukuran zat pengoksidasi berlebih yang tersisa dalam campuran larutan setelah proses refluks.…”

“…Metode ini didasarkan pada pengukuran zat pengoksidasi berlebih yang tersisa dalam campuran larutan setelah proses refluks. Salah satu oksidan yang paling disukai untuk penentuan kadar COD adalah dikromat (Gnanavelu et al, 2021). Adapun diagram alir metode penentuan kadar COD disajikan pada Gambar 1.…”

“…Namun demikian, metode analisis konvensional ini membutuhkan prosedur yang panjang, waktu optimasi yang lama, dan penggunaan banyak reagen beracun (Geerdink et al, 2017). Kelemahan paling penting adalah keberadaan zat pengganggu terutama ion klorida (Gnanavelu et al, 2021). Metode penentuan kadar COD konvensional, interferensi ini diminimalisasi dengan menggunakan kompleks merkuri sulfat dengan perbandingan 10:1.…”

“…Metode konvensional, tidak tidak dapat mengatasi gangguan matriks dari tinngginya kadar kalsium klorida ini. Untuk mengatasi gangguan matriks, metode penentuan COD mengacu pada hasil penelitian (Gnanavelu et al, 2021). Dalam modifikasi yang diusulkan, sampel diambil tanpa pengenceran apapun dan setelah penambahan merkuri sulfat, dilakukan pencampuran.…”