Studi Adsorpsi dan Desorpsi Fosfat oleh Sedimen Permukaan di Litoral Teluk Kendari, Sulawesi Tenggara

Abstract

Teluk Kendari merupakan salah satu wilayah pesisir yang penting bagi kehidupan masyarakat sekitarnya. Sedimentasi dan pencemaran antropogenik berpotensi meningkatkan laju pertumbuhan alga (blooming algae) yang dikenal dengan istilah eutrofikasi. Salah satu zat antropogenik penyebab pertumbuhan alga adalah fosforus (P) dalam bentuk ortofosfat atau fosforus reaktif terlarut, disingkat SRP (soluble reactive phosphorus). Dinamika kimiawi P dalam sedimen sangat penting untuk memprediksi terjadinya eutrofikasi. Penelitian ini bertujuan menyelidiki karakteristik adsorpsi-desorpsi fosfat pada sedimen Teluk Kendari, mempelajari hubungan kapasitas adsorpsi dengan karakteristik sedimen dan fraksi fosforusnya, dan mengevaluasi potensi kontribusinya terhadap kolom air di atasnya. Penelitian dilaksanakan sejak bulan Mei hingga Oktober 2022 di perairan Teluk Kendari, Provinsi Sulawesi Tenggara. Penelitian dilakukan dengan metode survey dan eksperimen di laboratorium terhadap kualitas air (pH, oksigen terlarut, salinitas, kekeruhan, dan ortofosfat) dan karakteristik sedimen (gugus fungsi, ukuran partikel, bahan organik, logam makro, dan fraksi fosforus). Eksperimen yang dilakukan yaitu kinetika adsorpsi-desorpsi fosfat dan eksperimen adsorpsi isotermal. Hasil pengamatan dianalisis secara statistik menggunakan korelasi pearson dan analisis gerombol. Dari pengukuran kualitas air menunjukkan nilai pH di lokasi studi cenderung basa dengan kisaran nilai 8,8 hingga 9,9. Konsentrasi oksigen terlarut berkisar 2,6–4,0 mg/l, salinitas 16,5‰–17,7‰, kekeruhan 52–171 NTU, dan SRP 0–0,004 mg/l. Analisis gugus fungsi terhadap sedimen menunjukkan keberadaan karbonat, besi hidroksida, dan bahan organik. Partikel sedimen didominasi fraksi lumpur berkisar antara 74,8%–9,25%, bahan organik 25,2%–68,4%, logam makro didominasi oleh logam besi (Fe) berkisar 4,520–9,077 mg/g. Nilai rata-rata fraksinasi fosforus diperoleh konsentrasi total fosforus (TP) sebesar 0,360 mg/g, fosforus organik (OP) sebesar 0,069 mg/g, P yang mudah lepas disingkat Ex-P (Exchangeable Phosphorus,) 0,007 mg/g, P terikat aluminium (Al-P) 0,014 mg/g, P terikat Fe (Fe-P) 0,043 mg/g, dan P terikat Ca (Ca-P) 0,227 mg/g. Eksperimen kinetika adsorpsi dan kinetika desorpsi menghasilkan persamaan model kinetika orde kedua semu (pseudo-second order) dengan koefisien regresi (R2) masing-masing 0,865–0,936 dan 0,886–0,947. Konsentrasi fosfat pada kesetimbangan (Qe) adsorpsi dan desorpsi masing-masing berkisar 17,4–25,4 mg/kg dan 13,1–15,9 mg/kg. Eksperimen adsorpsi isotermal mengikuti model persamaan Langmuir dengan R2 = 0,964. Dari model Langmuir didapatkan nilai kapasitas adsorpsi maksimum (Qmax) sebesar 156,3–227,3 mg/kg dan nilai konsentrasi fosfat pada kesetimbangan nol (EPC0) sebesar sebesar 0,0026–0,0047 mgP/l. Nilai EPC0 lebih tinggi dari konsentrasi SRP menunjukkan potensi resuspensi ion fosfat ke kolom air. Terdapat korelasi nilai Qmax dengan OP, Al-P, Fe-P, partikel lempung, dan bahan organik.

Kendari Bay is a coastal area that is important for the lives of the surrounding community. Sedimentation and anthropogenic pollution can potentially increase the algae growth rate, known as eutrophication. One of the anthropogenic substances that causes algae growth is phosphorus (P) in the form of orthophosphate or soluble reactive phosphorus (SRO). The chemical dynamics of P in sediment is very important to predict the occurrence of eutrophication. This research aims to investigate the characteristics of phosphate adsorption and desorption in Kendari Bay sediments, study the relationship between adsorption capacity and sediment characteristics and its phosphorus fraction, and evaluate its potential contribution to the overlying water column. The research was carried out from May to October 2022 in the waters of Kendari Bay, Southeast Sulawesi Province. The research was carried out using survey methods and laboratory experiments on water quality (pH, dissolved oxygen, salinity, turbidity, and orthophosphate) and sediment characteristics (functional groups, particle size, organic matter, macro elements, and phosphorus fractions). The experiments carried out were kinetic phosphate adsorption-desorption and isothermal adsorption experiments. The observation results were analyzed statistically using Pearson correlation and cluster analysis. Water quality measurements show that the pH value tends to be alkaline, with a value range of 8.8 to 9.9. Dissolved oxygen concentrations ranged from 2.6–4.0 mg/l, salinity 16.5–17.7‰, turbidity 52–171 NTU, and SRP 0–0.004 mg/l. Functional group analysis of the sediment showed the presence of carbonates, iron hydroxide, and organic materials. Sediment particles are dominated by silt fractions ranged from 74.8%–9.25%, organic matter 25.2%–68.4%, and macro elements dominated by iron (Fe) ranged from 4,520–9,077 mg/g. The average value of phosphorus fractionation obtained was a total phosphorus (TP) concentration of 0.360 mg/g, organic phosphorus (OP) of 0.069 mg/g, Exchangeable Phosphorus (Ex-P) 0.007 mg/g, P bound to aluminum 0.014 mg/g, P bound to Fe 0.043 mg/g, and P bound to Ca (Ca-P) 0.227 mg/g. Adsorption kinetics and desorption kinetics experiments produced pseudo-second-order kinetic model equations with regression coefficients (R2) of 0.865–0.936 and 0.886–0.947, respectively. The phosphate concentration at equilibrium (Qe) for adsorption and desorption ranges from 17.4–25.4 mg/kg and 13.1–15.9 mg/kg, respectively. The isothermal adsorption experiment follows the Langmuir equation model with R2 = 0.964. From the Langmuir model, the maximum adsorption capacity (Qmax) value was 156.3–227.3 mg/kg and the phosphate concentration value at zero equilibrium (EPC0) was 0.0026–0.0047 mgP/l. The EPC0 value is higher than the SRP concentration, indicating the potential for resuspension of phosphate ions into the water column. There is a correlation between Qmax values with OP, Al-P, Fe-P, clay particles, and organic materials.