Hi David,
The Lectra/San (now called Electro-Scan and the Purasan are both Type I treatment systems, legal on boats up to 65 feet LOA in areas that are not Federally-designated as No discharge Zones.
Lectra/San (discontinued in 2005 and resurrected as Electro-Scan) was the very first treatment system to gain Coast Guard certification. It's now in its 4th generation, having first been certified in 1975; and the certification has continued, uninterrupted, ever since. It's been on the market for over 30 years, although probably 75% of the boating public isn't even aware of it's existence. It uses proprietary electrodes inside it, that pass low voltage DC current through salt water, which breaks down the salt molecules and generates a chlorine solution that is the actual disinfectant. At the same time, a high speed cutter blade is running, reducing the solids down to a very fine slurry mixture (Coast Guard sez "no VISIBLE FLOATING SOLIDS" in the discharge into the water). The concept was taken from chlorine generators for swimming pools that use salt in them. It was designed strictly for salt water use and heads that flush with raw (salt) water. In areas where the water is fresh or brackish, the unit won't work unless salt is added to the flush water via some external means. You can add dry granular salt to the toilet bowl or we have several optional automatic salt feed systems that can be used. The following information also applies to the Purasan, so I won't have to type it in twice:
A typical flush of a marine toilet ranges anywhere from a pint to a gallon of water. The treatment box of both units holds 3 gallons. Neither system has a pump to empty it. So the effluent is pumped into it from the toilet. There, it is ground up and treated continually for a two minute period. Then the system shuts off. Everything stays inside it; it doesn't empty itself. Successive flushes of the toilet repeat the process (grinding, treating and holding) until the box eventually becomes full. From then on, it stays full - of treated and partially-treated effluent. After having become filled, it works by displacement - what the toilet is pumping into the system to be treated, forces the same amount out the other end of it, which has already been treated, and this goes overboard - strictly by the pumping action of the toilet. Repeat - neither system has a pump inside it, to pump it out. The only way anything gets out of it is by pumping more into it. The original flush of the toilet can go through as many as 6 or 8 complete two minute treatment cycles before it finally winds up in the water. That's how we get the high degree of treatment, through redundancy. It's treated over and over again before it ends up in the outside water.
The Purasan was developed by the request of the large numbers of houseboat rental fleets on the recreational lakes in Kentucky and Tennessee where treatment systems are permitted (although Kentucky is trying to get Lake Cumberland designated as a No Discharge Zone by the EPA - dammit!). They wanted something that didn't require salt, and they didn't want to have the relatively high power requirement of the Lectra/San. So the Purasan was developed to meet that demand. Instead of using salt, it has an additional component - a halogen tablet dispenser. This dispenser has special replaceable cartridges that contain very potent chlorine tablets that resemble swimming pool chlorine tablets, but they're much stronger, and ARE NOT compatible with swimming pool chlorine. In fact, mixing the two can have catastrophic results. Anyway, a portion of the toilet's rinse/flush water is fed to the halogen dispenser where it dissolves a tiny amount of the resident chlorine tablets, which then drains by gravity into the actual treatment box, which is identical in size and appearance to the Lectra/San (Electro-Scan) system. Essentially the same thing goes on inside the treatment box - the halogen solution is mixed with the effluent inside the box and the contents are shredded and broken down, again for a two minute period, then it shuts off. The Purasan uses a lot less battery power to operate, and can be used in fresh water, brackish water or salt water. The effluent flows through the Purasan and out, into the water in the same fashion as with the Lectra/San (Electro-Scan) system. The Purasan was first offered on the marine market in 1995 (I think) and the original series was only certified for use with a Raritan Crown Head, Crown Head II, or Atlantes marine toilet. Nine years later it was re-worked and in 2004 it was re-issued, and it is now certified for use with nearly all marine toilets, not just Raritan models.
