Poop. Generally something non boating 'muggles' don't have to think about that much but if you live on a steel tub, you do. I won't say it dominates your every waking minute, but ask any live aboard boater where the nearest public convenience is and he will be able to give you a run down of locations, types, cleanliness and opening hours. Freezing weather, low on water, black tank is full, all of these can lead to onboard toilets being out of bounds. Overflowing black tanks are not something anyone should want to deal with...

So what are the options? Well, if you really don't care you can just tip it over the side. You run the risk of serious penalties from the Environment Agency should they find out you are doing it and personally I would never consider this as a viable option.

A cassette toilet is an option and a fairly popular one. Low maintenance, easy and low cost but they still need emptying into a suitable sewage point and it is a pretty unpleasant job, especially if the cassette is a bit leaky... (I am dry heaving whilst writing this)

The next option is a black tank. This is a more popular option for those with larger vessels. A 1000 litre tank can last for a couple of months before it needs emptying, but again you are restricted to finding marinas or pump out facilities. It's not so much of a problem given the volume available but there is still a limit.

The last option is some form of sewage treatment system. There are many around and they fall into different categories which are most often referred to as Marine Sanitation Devices (MSD's). The US seems to have taken the lead on these and most information is regularly linked to US Coastguard Standard or EPA standards (see below).

The list of regs governing sewage discharge are long and varied, from the Environment Agency to Harbourmaster, IMO to USCG depending on where you are. Surprisingly there is no Environment Agency policy regarding this and seemed to vary depending on whom you asked and which water course you were asking about. On a personal note I would want to be able to treat sewage to the best standard possible given the factors which were under our control (space, cost, power draw etc).

I started looking at 3 systems, the Marine Fast, Raritan Managerm and Skimoil systems from the US.

The Marine Fast was one of the most capable and able to handle grey water as well (sinks, washing, galleys, showers etc) but the power draw was well above what we could supply from a battery bank. From memory it was a good 500-600W continuously. I didn't get as far as cost as this ruled it out early. Sorry, it's not an embedded video for those clicking frantically on the image, it's merely a screen grab from their website.

The next on the hit list were the Skimoil and Managerm Type II MSD's and although the power load was cut considerably down to a couple of hundred watts or so, they still weighed in at over the $5000 mark.

The Managerm and Skimoil do need desludging at regular intervals (6-12 months) which is guaranteed to be an unpleasant job. They were both running at about 120W load which, although not huge, was still a fair load on the battery bank which would need to be installed in order to cope with this and other loads overnight (pellet boiler for central heating, CH pump, fridge, freezer, lighting etc). It was this which initially prompted me to look at installing one or 2 1kW wind turbines on the mast tips for overnight power generation (although the power system is a whole several blog posts on their own).

In the end I decided on the Headflusher AT 6T unit.

This system (as far as the marketing blurb says) is that it does not need desludging as it has a return system for any solids in the 2nd chamber and it has a power demand of 60W for the aerator pump. This means a lower maintenance, lower power draw system than the others and equally it is lower cost, coming in at about $3800.

With a small import duty and zero rated for VAT under the Qualifying Ships system it should be a cost effective unit to have on board. It also means autonomy from marinas and being able to treat and release sewage back into the environment with minimal effects. It may be an expensive option in some respects, but having spoken at length to the Environment Agency they consider these systems to be 'best practice'. Whether such systems become mandatory in the future is hard to say. I would say it's unlikely for canal barges, primarily due to the space required, but whether it would be mandated for new build barges, that is another question.

Addendum

I have been liaising with the Headflusher people in the states about the Calcium Hypochlorite tablets used for the disinfection, but it turns out that the swimming pool versions of this are unsuitable for sewage treatment (too slow to dissolve and often made from unsuitable chemicals). From this it looks like we will have to opt for the drip chlorinator add on which adds about another $900 to the cost of the system.
They raised concerns about the regulations in the UK about sewage discharge but it seems from the material that this only applies to 400gt ships or those licensed to carry 15 persons or more (which we are neither). I suspect this leaves us in a no man's land but if necessary and there is still doubt I will talk to the MCA direct for clarification as to whether IMO/MEPC regs are relevant or rather as I suspect, as a domestic/leisure vessel' we are going above and beyond.

Link to the MCA sewage guidelines:

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/440749/MGN_385.pdf