1. Water from the discharge line is sampled before reaching the overboard discharge valve.
2. The sample is directed to the PPM monitor, which measures the oil content in parts per million (PPM).
3. The oil content value from the PPM monitor is sent to a comparator, which compares it to a preset allowable limit.
4. If the oil content is within the allowable limit, the overboard valve opens automatically to discharge the water. If the oil content exceeds the set limit, the overboard valve is shut, and the water is redirected to the slop tank.

The PPM monitor works on the principle of scattered light. Light reflected or scattered by oil particles is measured using a photocell. The intensity of scattered light decreases with increasing oil content. This signal is then analysed and sent to the comparator.

(b) The system records the following data:

• Oil content reading (in ppm)
• Ship's speed
• Oily water discharge rate
• Date and time
• Ship's position

1. Response Delay in Sampling Pipe: The delay in transporting water samples from the discharge line to the PPM monitor can result in inaccurate or untimely readings.
2. Clogged Sampling Pipe: Accumulation of debris or oil residues can obstruct the sampling pipe, leading to erratic or incorrect readings.
3. Sealing and Cleaning of Optical Windows: The optical components of the PPM monitor, such as the scattered light window, require regular cleaning and maintenance. Dirty or poorly sealed optical windows can cause inaccurate measurements or system malfunction.