Analisis zona pesisir terdampak berdasarkan model dispersi thermal dari air buangan sistem air pendingin pt. Badak ngl di perairan bontang kalimantan timur

Abstract

Simulation of cooling-water discharges from PT. Badak NGL was conducted to predict the pattern of thermal dispersion by using hydrodynamic model and 3-D thermal transport by applying POM model (Princeton Ocean Model) (Mellor 2003). Driving forces used in this model were tides, flows of cooling water discharge and rivers discharge. Choice of time step (Δt)=0.5 second, with 118 grids (west-east) and 187 grids (north-south), grid size Δx=Δy=30 m. Initial value : u=v=ζ=0, T0=28 oC and S0=32 ‰. Verification of elevation and temperature between results of models and direct measurement showed a good suitability with correlation value was 0.97 for elevation verification, correlation 0.90 and 0.87 for thermal verification during spring and neap tides, respectively. Results of simulation revealed the most extreme difference in pattern of surface thermal dispersion that found during spring tide for sampling condition of maximum tide and ebb. Distinct difference was especially found at station 8 (mixing point) i.e. 41 oC during maximum ebb and 35 oC during maximum high tide. Whereas, significantly high thermal difference between upper layer and bottom layer was found at station C i.e. around 2.54 oC for dry season scenario and 2.32 oC for wet season scenario. Effects of elevated water temperature from a thermal discharge on phytoplankton and coral reef was studied by using simulation results, where field observation for phytoplankton was adjusted with the time of output model.

Peningkatan suhu air laut dapat menyebabkan meningkatnya laju metabolisme organisme dan mengurangi konsentrasi oksigen terlarut (Poornima et al. 2005) sehingga dapat mengakibatkan makhluk hidup dalam air mati karena kebutuhan O2 tinggi sedangkan yang tersedia sedikit (Effendi 2003). Model hidrodinamika dan dispersi thermal 3-dimensi mampu mensimulasi keadaan stratifikasi perairan dan menjelaskan distribusi kenaikan suhu secara temporal dan spasial (Maderich et al. 2008) serta dapat memprediksi dampak kenaikan suhu berdasarkan berbagai skenario hipotetis kondisi alam (Wu et al. 2001, Hamrick dan Mills 2000). PT. Badak NGL membuang air pendingin ke perairan Bontang dengan debit buangan air pendingin cukup besar yakni train A-F sebesar 141 000 m3/jam, train G sekitar 34 359 m3/jam, train H sebesar 36 254 m3/jam (Pertamina 2003). Selain debit yang besar, suhu buangan air pendingin tersebut tercatat juga tinggi yang berdasarkan hasil pengukuran menunjukkan suhu air di muara kanal pendingin train A-F sebesar 43.89 oC saat pasang dan 45.56 oC saat surut sedangkan di lokasi muara pendingin train G terukur 40 oC pada saat pasang dan 40.56 oC pada saat surut (Pertamina 2003). Penelitian ini bertujuan untuk menganalisis pola sebaran suhu dengan menggunakan model hidrodinamika dan dispersi thermal 3-dimensi dan menggunakan hasil model tersebut untuk menganalisis dampak kenaikan suhu perairan terhadap fitoplankton dan terumbu karang yang ada di sekitar buangan air pendingin PT. Badak NGL.