|
Environmental & sustainable water treatment to save the planet |
| Contact us | About us | Search | Shop || |
|
||
Ecosystem Approach
For the Treatment of Landfill Leachate
By.Howard T Dryden
The Ecosystem approach employing stabilized extended diffused aeration is a new approach, developed by Dryden Aqua for the treatment of leachate water from landfill sites.
Ecological diversity among the bacteria, algae, protozoans and other organism is the key to the performance of the effluent treatment process. A suspended culture of aerobic bacteria or activated sludge, is the standard approach in sewerage works and most landfill sites. While there is a considerable species diversity in the sludge, it could still be considered as a wheat field in comparison to a tropical rain forest. The process is simply not conducive to the development of high species diversity, and hence the process tends to be unstable and delicate to maintain. Dryden Aqua, have taken conventional processes several stages further by the development of additional ecological niches in treatment process in order to generate a high species diversity. The net result is a system which is largely self sustaining, while producing an effluent of an extremely high quality suitable for direct discharge to surface waters or reuse for other duties, such as irrigation.
Nature has the ability to treat most effluent as long as the natural ecosystem is not stressed, it would obviously be impractical to allow nature without any assistance to treat the effluent from a landfill site, this is called pollution. However by control over the conditions in a contained environment a very high species diversity of organism can be maintained. This means that organisms will be allowed to developed, mutate and acclimatise to the conditions in the effluent, and after a sufficient period of time most of the pollutants from the site will be bio-metabolised.
In order for us to achieve the above task, a fundamental understanding of the organisms involved is required. Key points include basic concepts such as time and space, for example, some bacteria such as many of the autotrophic species have very long doubling times, sometimes as long as 20 or more days. It is essential therefore that sufficient time is given to allow these organisms to develop in the system. Activated sludge plants operate with very high mixed liquor suspended solids concentrations, the extended diffused aeration systems may have up to 1/10 of the concentration. More space is therefore required for extended ecosystems, but with the extra space, there is much more scope for a higher diversity of bacteria.
In addition to time, and space, maintaining high dissolved oxygen concentration also increases species diversity of organisms, the levels should not be allowed to drop below 5 mg/l in the water column. However the aeration arrangement also permits for solids settlement and the development of an anaerobic zone on the base of the aeration basin. Apart from heavy metals, mineralisation of all the settled solids will occur, with the release of nutrients back into the water column. Effectively therefore, the system will never require de-sludging. There are four or more aeration basins connected in series, and as the effluent passes from one basin to the next, the quality of the leachate changes and hence the diversity of organism will change to follow the quality of the leachate.
 |
Aerobic and anaerobic bacteria are the primary means of effluent treatment in most biological systems. However, algae are as an important group as bacteria, and as a means of effluent treatment they have been almost completely ignored. In the Dryden Aqua ecosystem approach, algae are induced to grow in the third and forth aeration tanks. Algae are able to fix many heavy metals and assimilate nitrate nitrogen much more efficiently than bacteria. Algae also have the added advantage in that they pump oxygen directly into the water, and thereby support the heterotrophic bacteria. However it can be difficult to keep algae in a system, since algae will general float to the surface whereas bacteria sink. This problem was resolved by development of our AFM (Advanced Filtration System). The AFM system incorporates a stainless steel pressure filter using the AFM media to trap particles from the water down to 5 microns in size. Once the particles, including bacterial floc and algae have been captured by the filter, they are returned back into the treatment system. |
| The algae in turn support higher organisms such as crustacean including Daphnia and even frogs and newts. The key now is to keep the system in balance. Nature has many self control processes, and the higher the species diversity the more stable the ecosystem. However in terms of natural processes our condensed ecosystem requires additional nutrient inputs as well as monitoring and control. It is however a much more relaxed process than intensive activated sludge treatment systems, but it still requires attention to insure that the system stays in balance. To achieve this tasked we have developed a dedicated PLC based AquaTraul system, designed specifically for the monitoring and control of leachate systems. We are now in the process of developing intelligent systems that can more intuitively make decisions to maintain the balance. The ecosystem approach to effluent treatment does require a considerable land area, however on landfill sites, space is not usually a limiting factor. The lagoons can be constructed from polyethylene lined lagoons, which is again standard, and relatively low cost for landfill site operators. The benefits of the process are that the system is low cost, it looks after itself, and it produces an effluent water quality of a very high standard. Our web site at http://www.DrydenAqua.com provides additional information and cases studies. |
