Overview

General Principles and Design Drivers

During the initial design concept stages, we evaluated as many of the current systems as possible. We looked at not only Australian customs and habits, but many other countries around the globe. The most common system of waste disposal we looked at was the septic tank system.

While not ideal and not very successful in most cases, extremely resource wasteful and a high pollution generator, it is the system most countries of the world are familiar with. Normally, there is to some extent some form of septic tank management infrastructure.

We looked long and hard at composting systems and went part way to designing our own compost system. We found during our research that when we looked at the ongoing personal involvement required by the user, and giving consideration to the cultural taboos surrounding waste contact in other countries as well as Australia, the conclusion we came to was that we could not see them being a long term, viable alternative.

Similar to the standard septic tank, the composting systems we studied were unable to accept any large amounts of shock loading without severe overload occurring.

The end result of our research was a waste treatment system with the following design drivers:

1. The system's method of waste removal had to be able to be easily performed without personal contact by:

a. the user in remote areas.
b. waste removal contractors where available.
2. The frequency of waste removal had to be measured in years.
3. There had to be a simple method of measuring the sludge volume in the unit, which would indicate both the volume required for removal and the date of removal.
4. The unit would require no flushing water.
5. With the septic tank being known technology, along with the potential existing infrastructure, it had to be loosely based around it.
6. The inherent ability to accept infrequent but potentially severe overload situations.
7. The ability to fit into a structured date based controlled waste removal control program which could be overseen by the relevant local authorities and/or operated by the authority.
8. Design a system that was as low profile as possible.
9. The entire treatment process had to be completed within the system and be totally isolated from high water tables and high rainfall. On discharge, also have the absolute minimum impact on the surrounding environment.
10. The system had to be cost-effective, easily transported and assembled and have an exceptionally long product life.

We believe that we have managed to achieve all of the above and far more. We, at Gough Plastics and the other members of the PWT team, treat the Hybrid Toilet System as an ongoing R & D program and are constantly testing and trialling improvements and new ideas.

Development and Testing Program

From the initial design stages through to the current date, the Hybrid Toilet System has and is undergoing exhaustive trials. As discussed previously, we designed a system which has greatly reduced the impact on the surrounding environment.

To do this, we have greatly reduced the volume of effluent generated by the system and worked extensively on the quality of that effluent. To our knowledge, there are no standards governing the quality of effluent going to ground.

Whilst this may be so, our research and some very highly publicised incidents of contamination occurring from the septic tank overflow tells us that a great deal of problems that occur are as a result of this lack of a quality standard. This is not a new problem and it exists around the world. The system began its existence from a request by the government of PNG.

Two members of the PWT team travelled to PNG and experienced first hand the problems that were occurring in that country. Their problem was that the population drift to the main city areas that was occurring was severely overloading the waste facilities and pit toilets. With the continued use of this pit toilet system, some of these areas resemble a lunar landscape.

Very high water tables and adverse weather conditions resulted in serious health problems, with the waste from overflowing pit toilets running through the settlements. Our brief was to design a system that would collect the waste, treat and reduce the volume of the waste and deliver a small volume of high quality effluent to ground.

With this in mind, we began designing a system to achieve all of the above. We produced a prototype unit and began a test program at the Mt. St John treatment plant in Townsville. The prototype unit consisted of a primary tank and a secondary tank designed around a totally enclosed sub-surface flow gravel bed. The results that we achieved from our initial trials justified further development of the system.

At this point the Hybrid Toilet System was created. Tube re-design of the secondary part of the unit delivered the quality standards that we had targeted as being acceptable at that point. Concerns about the availability and control of the quality of the gravel led us to the development of our own purpose built plastic media which overcame any concerns we had regarding clogging occurring in the secondary part of the system.

This also took away any third party influence on the secondary process and had the effect of giving the system an average of approximately 100 days contact treatment time. The added advantage of using the plastic media was the substantial increase in surface area to volume ratio. It also guaranteed that at a set loading, the system could deliver a consistent quality of effluent. The plastic media we use is recycled scrap material from the factory.

As part of the approval process for the Queensland Government, a trial unit was to be installed and tested at the Edmund Kennedy National Park. The unit that we installed was a 10 person unit. The testing requirements referred only to the unit installed at the test site.

The testing must include the following: PH, Biological Oxygen Demand BODS, Non-Filterable Residue (NFR) and E-CoWIOOml. Testing of the effluent must continue on at least a three monthly basis for a twelve month period.

The Ranger in charge at the Edmund Kennedy National Park is Mr Richard Lineman, phone (07) 4066 8601. We are continuing to monitor the test unit at Edmund Kennedy and have an ongoing R & D test facility at the Mt. St. John Treatment Plant. The results obtained from our various test programs will assist in the optimisation of the performance of the Hybrid Toilet System units.

We go beyond our laboratory NATA/ISO/IEC accreditation and ISO9000 compliance. We will co-ordinate responses with you as well as with other specialists and GUARANTEE not to leave you on your own. We are available 7 days.

Summary of The Hybrid Toilet Processes

1. Waste Delivery

Waste is delivered via a NonFlush or MicroFlush toilet pedestal.

2. Preliminary Treatment

The waste enters a water-filled, primary tank. It includes significant amounts of suspended solids. Faecal matter and paper are broken down by a combination of dissolution and metabolic actions of a wide variety of aerobic and anaerobic bacteria, which contain cellulytic enzymes.

Since no mixing takes place, one would expect a steady gradient of a toxic zone (at the surface of the primary tank), which is gradually being depleted into an anoxic zone (at the bottom of the primary tank). A significant stable population of ammonia and nitrite oxidizers (nitrifyers) may develop in the upper layers.

Aeration is provided via standard rotary ventilation. The accumulation of sludge settling to the bottom will foster the growth of anaerobes such as the methanogenic bacteria and denitrifyers in the lower layers.

The anaerobic digestion of wastes can be considered a two-step process. First, the complex organic materials including, paper, faecal matter and microbial biomass are depolymerised and converted to fatty acids, carbon dioxide and hydrogen.

A large variety of non-methanogenic bacteria, obligate or facultative anaerobic bacteria participate in this process. In the next step, methane is generated either by the direct reduction of methyl groups to methane, or by the reduction of carbon dioxide, either by molecular hydrogen or by other reduced fermentation products such as fatty acids, ethanol, carbon monoxide.

Anaerobic processes are generally slow and highly dependent on pH (optimum 6-8) and temperature (optimum 30-37C). However, even under suboptimal conditions, the anaerobic processes generally continue, although much slower. The given retention time of sludge in the Hybrid Toilet System is 4-7 years, allowing for substantial digestion and reduction of sludge volumes.

3. Separation Chamber

Gas production (methane, carbon dioxide and small traces of nitrogen, hydrogen, hydrogen sulphide) will cause some sludge to rise. The suspended solids are separated from the liquid by passing the sewage through a separation chamber.

The separation chamber allows liquid to pass to the secondary treatment tank without transfer of solids. This is eliminated by the slots in the side of the twin separation chamber.

4. Secondary Tank

In a simple sewage treatment process, micro-organisms are encouraged to grow on plastic pipe media through which the overflow from the primary tank is channelled through a series of baffles. The large surface area of the plastic medium provides a suitable substrate for the growth of biofilm, which consists of exo-polymers generated by a wide range of bacteria, including Zooglea species amongst others.

This biofilm forms the main matrix which accommodates a heterogenous community of bacteria, fungi, protozoans, nematodes and rotifers. This community feeds on other bacterial matter (eg. Faecal bacteria) and absorbs and mineralises the dissolved organic nutrients in the sewage, further reducing the biochemical oxygen demand in the sewage.

Aeration is provided passively through tank ventilation and surface-overflow. A retention period of up to 135 days provides ample time for mineralisation (dependent on temperature and pH).

5. Disposal

The treated effluent is discharged from the Secondary treatment tank to ground or to a holding tank (for removal). If discharged to ground, adequate drainage and preparation of the discharge zone should be selected similar to those of septic tanks.

Although substantially reduced in potential pollutants, additional improvement of the effluent quality occurs especially in well drained, sandy soils or polishing (grass/reed) beds through which the sewage is trickled. The micro-organisms, which need oxygen to thrive, feed on the remaining nutrients in the sewage and purify the water in similar fashion to a percolating filter.

Dr. Julian Catmull and Dr. Michael ten Lohuis (Ph.D., BscHons, MASM)
Enviro-Check Enterprises Pty Ltd