Powerboating - Part Eleven

Of all the problems facing the boatowner, none is more contentious than the management and disposal of waste generated while onboard. It is a difficult subject to discuss in print without offending the sensibilities of some people. All I can say is that human biological waste is a fact of life, and if we want to maintain the marine environment in a condition that is enjoyable to all, then we had better learn to apply systems to our pollutants to render them harmless.

Human waste, sewage, threatens public safety if not handled properly. A lot of the devastating plagues that blighted cities in times past were largely attributable to poor hygiene. These plagues are now largely things of the past because we dispose of our effluent safely. The trouble is that what is safe for humans may not necessarily be safe for the environment. Large-scale dumping of sewage into rivers or enclosed waterways degrades the ecosystem until the body of water is literally dead.

Happily, we do have the capacity to learn. Things are a lot better than they used to be, although we still have a way to go. The methods used for waste disposal on boats have changed little over the time I have been messing around in them - basically the deed is done and the results are launched over the side. I suspect that this has been the system since man first took to the water.

First, let's look a little closer at the problem. As I see it, marine sewage has the capacity to affect us in three ways, namely through affecting our health, affecting the environment and lastly by visual impact. Of the above, human health is the most important, so we will examine that first.

HUMAN HEALTH
Human waste contains bacteria, viruses and parasites, all of which can cause us harm if we are exposed to it directly. This normally unlikely event is quite common if people swim in water polluted with human waste.

The level of pollution is important, as is the length of time it has been in the water. The marine ecosystem has a huge capacity to cleanse waste naturally, and most pathogens are rendered harmless after about four hours exposure to sunlight and clean, turbulent seawater.

However, if too much is dumped in the ocean at one time, the system can become overloaded and the dangers of exposure rise. Most times this exposure is through our intestines by way of eating contaminated seafood such as an oyster. An oyster is an extremely efficient filter and gets its food by straining it out of the seawater. Unfortunately, it will also strain out harmful bugs if they are present and retain them in its body. For people who have never experienced it, there is nothing like a night after a bad oyster!

Because polluted and unpolluted water can look exactly the same, we need a method of determining water quality. For this we use a useful little fella called E-coli. This microbe is present in the gut of all warm-blooded creatures and is quite harmless even though it is present in the waste of those creatures.

If we take 100ml of water and count the E-coli, (called 'Colony Forming Units') we can get an indication of sewage pollution. This also allows us to establish standards of what is, and is not, an acceptable level of contamination.

Raw sewage can contain around 10 million CFU per 100ml. For safe swimming the count should be under 150CFU/ml, and no more than 13CFU/ml is permitted in water used for oyster growing.

Recreational boating is considered safe in water with a figure of less than 1000 CFU/ml.

THE ENVIRONMENT
The first stage in solving any problem is to quantify it. We've now done this in relation to human health. The next question is, what impact does sewage have on the environment as a whole?

Here the subject tends to become emotive, to say the least. It is difficult to lay anything down in black and white, but it depends on the type of waterway being discussed. A river is an entirely different system to the ocean. What would almost kill an inland waterway would be harmless to the mid ocean. Likewise, a landlocked bay with little tidal flushing would be more affected than one exposed to the full motion of the sea.

One of the main reasons for this is that biological waste has, besides the micro-organisms already discussed, nutrients. These nutrients can support large colonies of algae, which throws the existing ecosystem completely out of whack. In other words, the balance has been upset and a new set of conditions now apply.

Thus, where in the previous system a certain amount of sunlight filtered through the water and supported plant life growing on the bottom, the vast bloom of algae in the new system now blots that out, with obvious consequences.

As the algae die and decay, they use up a lot of the oxygen in the water. This, in turn, drives out the species that require high oxygen levels and leaves behind life forms that can subsist on lower amounts. The carp, a fish that loves turgid, almost stagnant water, thrives under these conditions, which is why they are almost always found in sick river systems.

The term used to identify this state is Biological Oxygen Demand, or the BOD. The BOD really is only going to apply to enclosed waterways, not the marine system as a whole, and that is why I think it is necessary to describe any water system as enclosed or free.

My definition of enclosed water would be any river system, any lake, whether fresh or salt, or any body of water that did not experience strong tidal flushing on a regular basis. All other waterways would be called free water.

VISUAL IMPACT
The last impact that marine sewage makes is visual, and this is the one that generally upsets us the most. To sit in a calm anchorage surrounded by effluent is to completely destroy the ambience of the occasion, to say the least. To be swimming and make the same discovery is even worse.

Now it just could be that the effluent is completely harmless. By that I mean an efficient treatment plant could have rendered it sterile before release. It wouldn't make one bit of difference. If it quacks like a duck, it probably is a duck - and the same applies to sewage. This is the biggest thing working against onboard treatment systems.

DUMP IT OR HOLD IT?
Basically, there are two methods of dealing with waste: dump it or hold it onboard for disposal at a later time. If we are serious about doing something about marine waste, then direct discharge from a toilet to the ocean, without an intervening holding tank, has to be prohibited. The reason for this is simple: when you have to go, you have to go, and if the 'launch and look to the far horizon' will take place. All the fines and penalties in the world will not stop it. If a holding tank is installed, then at least the contents can be disposed of at a later date.

The holding tank debate has been raging for years, and I have to confess that I have not met too many people who are fans of the things. Basically they stink, and I'm not talking about some minor waft of something unpleasant. Holding tanks can produce smells of nuclear proportions: the gagging, nauseating, gut-wrenching pong that can ruin not only the entire day, but the entire month!

The reason, of course, is that mother nature is going about her business of biological reduction, which unfortunately produces some evil-smelling gases such as methane and hydrogen sulphide. These gases have to be vented from the tank to the outside of the boat through a breather. If you are in a marina berth alongside a boat that has a half-full holding tank and the contents have been there for a few days or so, the stench can be awesome.

Treatment with chemicals helps - formaldehyde and chlorine are the most common - but for holding tanks to operate successfully, they really must be emptied as often as possible, receive a good flushing out, and receive a fair amount of attention and chemical monitoring.

Another alternative is the electric holding tank. I made one for my boat and the results were surprisingly good, as far as both smell and sterilisation were concerned. The system was quite easy to make. I used a tank made of polyethylene that was originally intended for the storage of a fairly high-powered insecticide.

Before I outline how I built the holding tank, I must stress that the plastic used in the entire toilet system, hoses included, must not permit the seepage of gas. If the plastic used is the wrong type, then the methane will diffuse through the pipe, etc, and no amount of venting will remove the smell.

A test for any system is to take a handful of tissues, rub them along the pipe or tank and then smell them. If they smell of sewage, then gaseous diffusion is the problem.

BUILDING AN ELECTIC HOLDING TANK
I placed in the tank two titanium electrodes similar to the type used in saltwater swimming pools. These electrodes are connected to a timer relay, and in this case the time was set for approximately five minutes.

The sequence of operation is simple, but it requires an electric toilet. The toilet is operated by a rubber timer switch that operates it for 30 seconds and at the same time triggers the electrode timer relay. During this period the waste is mixed with the incoming saltwater and macerated with the macerator knives before being pumped to the holding tank.

This tank should be as close to the toilet as possible, to make sure all the waste reaches the tank and is not backed up in the pipe. Longer flush times will otherwise have to be used.

Inside the holding tank, an electric current is passed through the effluent for the period determined by the electric timer - in this case, five minutes. This electric action causes the formation of hypochlorous acid, a powerful disinfectant that reduces the E-coli count of 100ml of the liquid to below 1000.

Remember that water of this quality is considered safe for recreational boating, but not swimming. However, there may still be a high level of viruses present, depending on the health of the person using the toilet.

The electric holding tank controls odours well, because each time the toilet is used the tank's contents get another five-minute sterilisation period. The level of maceration achieved by the toilet is marginal, and if the contents of the tank were discharged overboard, the visual impact would be apparent.

To overcome this I have developed a method that works well on my boat, and will possibly work on yours, too. The outlet from the holding tank is taken to a gulper pump. I have mentioned these pumps before: they are made by Whale and operate on the diaphragm principle, similar to a hand-operated bilge pump.

USING A GULPER PUMP
The advantage of this design is its ability to pass solids through the pump without blocking. Pumps that have rotational parts are a complete waste of time because the shredded toilet paper soon clogs around the impeller of the pump.

The outlet of this pump is taken to a tee-fitting with one branch going overboard where the toilet would normally discharge. This outlet is controlled through Valve A. The other branch of the tee is taken through Valve B to the point where the salt cooling water is injected into the exhaust.

Note that there is also a non-return valve in this branch. Its purpose is to prevent any back circulation from the engine cooling water.

To operate the system is simplicity itself. If I'm motoring offshore and the tank requires emptying, then valve A is opened and the contents discharged through the hull as in a normal installation.

However, if I'm in a situation where the dumping of 20lt of waste would cause a problem, even though it is sterilised, then I close Valve A and open Valve B and start the engine. The gulper pumps the contents into the exhaust at the same point as the cooling water enters, thus there is a turbulent mixing of the waste and saltwater before they are injected into the hot exhaust gases and from there to the ocean.

From my observations of the exhaust, it is impossible to ascertain if anything other than water is being ejected. I have not been able to observe any visible staining or clouding of the surrounding water. Although I have not done any water quality testing on the output, one would imagine that the temperature of the exhaust gases would just about have rendered the mix inert.

When the tank indicator says empty, I flush the loo two or three times to clean out the tank, and the system is ready to go again.

Will it cause a build up in the exhaust pipes? I honestly don't know, ask me in 10 years' time.

My own position on marine sewage pollution is ambivalent. I seriously doubt that there is a problem in most areas, either to the environment or to human health. I have been involved in this subject for a number of years. While I have heard a lot of emotive screeching, there has been very little solid scientific evidence offered.

In my opinion, pump-out facilities are a complete waste of time. The only system that time and technology will enhance is the holding and treatment of waste onboard before it is discharged into the environment. It works for people living on the land, so I don't see why it can't be made to work for people on boats.

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