All About the Marine Sanitation DeviceABOUT THE MARINE SANITATION DEVICE (MSD) Many sewage systems are being altered from hand pump toilets to electrics, and the stringent requirements for holding tanks and pump out systems has required careful considerations in systems planning. In the USA the Clean Vessel Act of 1992 is the primary legislation. In many countries, similar legislation is being introduced. It is important to comply with laws pertaining to illegal discharges. An MSD is any equipment for installation on board the vessel that is designed to receive, retain, treat or discharge sewage, and any process to treat the sewage. In many locations, there is considerable politics, and confusion relating to the use of devices, and boaters should make sure they understand the requirements. The USCG certifies Marine Sanitation Device (MSD's) which fall into 3 categories: Type I MSD This device treats sewage using chemicals to disinfect it. The discharge must be free of visible solids and meet standards for bacterial content. To do this the sewage must be macerated to break up solids. The fecal coliform bacteria output must be at least 1000 colonies per 100 milliliters or less. Systems that meet this standard are the Raritan Lectra/San. It operates using both salinity and electric current that consists of electrodes to break down the seawater to form chlorine (hypochlorous acid), a chlorinating agent that kills bacteria and disinfect the sewage. After treatment, the acid recombines to reform as salt water. The Raritan PuraSan MSD uses a solid tablet made of chlorine that produces a halogen solution to treat waste. Both systems draw around 45 amps for 3 minutes on each flush, which has considerable impact on the electrical system power requirements. These units cannot discharge into No-Discharge zones. The SeaLand SanX can be used in all waters but installation requirements are considerably more than the others and may suit larger vessels. The SanX injects a chemical disinfectant agent into the treatment tank to mix with the macerated waste. Type II MSD This is a device similar to Type I devices with a higher level of treatment and higher quality discharge. The fecal coliform bacteria output must be at least 200 colonies per 100 milliliters, with suspended solids of less than 1000 parts per 100 milliliters. The best-known devices are those from Microfors and Galleymaid, however cost and installation is considerably greater than Type I devices. Type III MSD This is a holding tank. This means no discharges within nominal limits. Emptying is usually via a deck fitting and tanks have a vent line overboard. ABOUT THE MARINE SANITATION DEVICE (MSD) MSD systems have several process components, and along with various sensors and electrical elements. Some MSD units are PLC controlled, so correct operation of all input sensors and output devices is critical for proper operation. The first stage treatment tanks contain level sensors. The second stage sedimentation tanks do not have ant components. The macerator pump, sludge pump and discharge pump all require routine maintenance. Backwash systems have both a water pump and solenoid valves. The disinfection system has both a flow control system with chemical feed pump, and Chlorination units have a power supply. Ensure that no toilet chemicals incompatible with sodium hypochlorite are being used on the boat. Normal Troubleshooting principles apply, check power supply, auto and manual selection wrong, PLC may require reset, and then check inputs and outputs to level switches or solenoids.
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