四、請將下列專業英文翻譯成中文：（20 分） Water, oil, and other substances collect at the bottom of the ship in what is known as the bilge. Bilge water is pumped overboard, but must pass a pollution threshold test of 15 ppm（parts per million）of oil to be discharged. Water is tested and either discharged if clean or recirculated to a holding tank to be separated before being tested again. The tank it is sent back to, the oily water separator, utilizes gravity to separate the fluids due to their viscosity.