Renew Magazine

So, what is a composting toilet? How does it work? And how can I get one? This article provides an introduction to composting toilets as well as important information about maintenance.

Sewage treatment today

While the modern sewerage system is an integrated engineered marvel, it is also a marvel of wasteful design. In a standard home in a developed city, all black (toilet) and grey (shower and sink) water is combined, usually in the house slab, before leaving site. From that point it is a long downhill trip to our modern wastewater plants. In Melbourne alone, 330,000 million litres of wastewater are processed each year, including trade waste from industry.

Our centralised sewerage system is a case of out of sight out of mind. Waste is processed at primary level—sieved, screened and mashed up. It passes through a series of ponds where oxygen is circulated to aid microbial digestion of the solids. Water from the system is discharged into oceans or streams after being treated with chlorine. As they say, ‘with pollution dilution is the solution.’ However, releasing this water can cause nutrification, blue-green algae, heavy metal concentration, let alone the negative effect large amounts of chlorine has on ecosystems. Just think how 330,000 million litres of water could be used otherwise.

The other system that operates in ‘off pipe’ conditions is the ubiquitous septic tank (septic being from the Greek ‘septikos’ meaning ‘to make putrid’.) After flushing, all solids settle in the bottom of a large concrete tank and are later pumped out by Mr Wiffy. The excess fluid is disposed of in a sub-surface disposal/leach field. These systems are anaerobic and produce a classic stinky sewage smell. There is no separation of cured waste and fresh waste, allowing direct transfer of any pathogens to the leachate field. While very common in Australia, septic systems are increasingly linked to a number of water pollution issues resulting from a high density of the systems in close proximity to water catchments.

Composting toilets operate on completely different principles from conventional wet systems and offer a proven alternative.

Firstly, we should start by looking at what an electric bike actually is. There are two broad categories of design. The first is of a standard style of bike, such as a mountain bike or similar, which has fitted to it a motor and battery, along with some form of speed controller. These are quite common and come in a range of sizes, with many varied drive systems.

The other type of electric bike is known as a ‘step-through’ bike. These more resemble a moped than a regular bike and are often designed so that the motor does all the work—the pedals are not much more than ornaments. Because of this, many riders of such bikes have run afoul of the law, as while they may have a motor power output within the legal 200 watt limit (more on this later), they are considered to be a motor scooter and as such need to be registered. However, because they generally are not designed to be road registered, they don’t meet Australian Design Rules (ADR) requirements and so cannot be registered.
Whether this style of e-bike is considered illegal in your area seems to depend on the powers that be. Some people ride them without problems, others have been pulled over and been told they can no longer ride their bike. This is a rather expensive problem as you are then left with a bike that is designed purely for on-road use, yet can no longer be used on the road.

This issue seems to come about from the more open definition of what a bike is in the countries these types of bikes are made. Of course, these are also countries where bike use is actually encouraged, rather than in countries like Australia, where bike riders have to deal with roads without bike lanes, motorists with bad attitudes (not to say there aren’t bike riders with the same problem) and poorly thought out and overly draconian regulations.

Like a normal bike, e-bikes are used for commuting, car replacement, mobility for less able and elderly, and even just for fun. For many people, they provide the extra assistance needed to get up that steep hill, or a sense of assurance that should you become too tired (or strain a muscle), the motor can get you home.

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The same applies in summer. A properly insulated home will take longer to heat up and if an air conditioner is used it will use less energy than one cooling an uninsulated house.

How does it work?

There are three ways in which heat transfers to or from a house: conduction, radiation and convection.

Conduction means the transfer of heat through a substance, in this case the walls and ceiling of the house. The type of insulation used to reduce conductive heat transfer is known as ‘bulk fill’ insulation.

This is the most common home insulation and may be in the form of fluffy ‘batts’ made of many materials, including polyester fibre, glass fibre and sheep’s wool. Insulation may also be in the form of loose fill material, such as treated cellulose fibre (usually made from recycled paper), which is simply pumped into the roof or wall cavities and sealed with a spray-on ‘cap’. These materials are poor conductors of heat and so when they are installed properly, they reduce the rate of heat flow.

Radiation is a different form of heat transfer. All warm objects radiate heat in the form of infrared radiation. If this heat can be reflected back from where it has come from using reflective foil insulation, then heat loss or gain through radiation can be greatly reduced. The main thing to remember with foil insulation is that it needs an air gap between the shiny side and the roof or wall cladding (assuming it has a shiny side facing that direction). If it is fixed such that the wall or roof materials are in contact with the shiny surface then it will not be effective unless it is a double-sided material which has a shiny surface facing into the cavity. In this instance it is not reflectance, but the low emissivity of the reflective material that prevents the heat transfer.

The first decision you have to make is where the tank will be located. Where you place the tank will determine its size and shape, and possibly even its colour if it needs to blend into the surrounding vegetation or dwelling walls. A large yard offers a number of options. You could place it next to the house or shed, or even under the house.

Tank materials

The six most common rainwater tank materials are concrete, fibreglass, plastic (usually polyethylene), Aquaplate Colorbond, galvanised iron and stainless steel. Each of these materials has advantages and disadvantages, so let’s look at a few of those.

Durability

A water tank can be a considerable expense, even after a rebate, so you want it to last as long as possible. The expected lifetime of any tank should be at least 20 years, and indeed, many tanks come with a 20 or even 25 year warranty. However, a number of factors will determine just how long the tank actually lasts, and that includes water quality, maintenance, and positioning of the tank.

For example, plastic tanks are relatively immune to damage from salty water, so if your tank is regularly topped up from a bore or dam, then a plastic tank might be the best solution. However, if your tank only needs to hold rainwater, then any tank material should be suitable.

The tank’s location can effect the lifetime of the materials. Ideally, the tank should be located in shade if possible, not just to keep the water temperature low and reduce evaporation, but also because some materials are damaged by direct sunlight.

Most poly tanks will slowly degrade over time with exposure to the sun, despite having UV inhibitors added to the plastic. Because the plastic is being used to hold water, there are limits to how much UV inhibitor and other chemicals can be added to the polyethylene, so eventually the tanks will suffer some degradation.

This is the device that converts the extra-low voltage DC electricity from the battery bank into 240 volt AC mains power to run standard appliances. It is important to have a good inverter—if your home relies solely on 240 volt power from the inverter and the inverter fails, you will have no power, even though it is still being generated and stored.

Inverters are divided into two main types depending on the type of power they provide—modified squarewave and sinewave. Modified squarewave (sometimes referred to as modified sinewave to make them sound better!) are the cheaper of the two, but some appliances (such as VCRs, TVs and computers) may not run as efficiently using this type of power, and some may not run at all.

On the other hand, sinewave inverters provide the same type of power that comes from the mains grid. Indeed, the power from a good quality sinewave inverter will usually exceed the grid in terms of quality and voltage stability. For this guide we will only be looking at sinewave inverters, as modified squarewave inverters are becoming less popular in fixed renewable energy systems as the difference in price between the two types steadily reduces.

Another important benefit of such a system is that of greenhouse gas emission reduction. A solar water heater or heat pump can reduce the greenhouse emissions of an average family by as much as four tonnes of CO2 per year—the equivalent of taking a car off the road!

Most state governments  have recognised the advantages of solar and heat pump water heaters and offer incentives in the form of rebates. These vary from state to state, but can save you a great deal on the cost of a new water heater, making them more economically viable. The initial purchase price will probably still be higher than a similarly sized conventional water heater but the savings made in running costs will pay for this difference in less than 10 years—in as few as four years in some cases.

How does it work?

A solar hot water system usually consists of a hot water storage tank connected via pipework to solar collector panels. These collector panels are placed on a north facing roof and at an angle of no less than 15° to the horizontal. The tank can either be situated immediately above the panels on the roof (called a close coupled system), above and a small distance away from the panels within the roof cavity, or at ground level (a split system), in which case a pump and controller is required to circulate water through the panels.

As the sun shines on the collector panel(s) the water in the pipes inside the collectors becomes hot. This heated water rises through the panel and out through a pipe to the insulated storage tank. Cooler water from the bottom of the storage tank enters the panel at the bottom to replace the warmer water.

This is called the thermosyphon process, requires no pumps or other devices and is very simple and effective. However, it does require that the storage tank be situated above the collector panels. The collector panel is the driving force for the circulation, so due care must be taken with its mounting and orientation to get maximum benefit from it.

If the tank cannot be located above the collectors, a pump and a differential temperature controller must be used to provide water circulation. The controller also turns the pump on when the temperature drops to 5°C as a frost protection function.

Some systems don’t heat the water directly but instead heat a fluid similar to antifreeze used in vehicle cooling systems. This fluid flows through a closed loop system (through thermosyphon or pump action) and transfers the collected heat to the water in the tank via a heat exchanger.

There are pros and cons with each system. Close coupled systems require the roof support the full weight of the tank, but they are much simpler than split systems and little maintenance is required.

Split systems have a much slimmer roof profile and are more convenient should tank maintenance be required, but the added complexity of the pump and controller means that failures tend to be more common.