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Zero Discharge 

Zero Discharge is a target on many difficult sites but is rarely achieved.


Zero dicharge is normally achieved by heating the waste water until it is evapourated (usually under vacuum to increase the yield and lower the required temperature). The remaining salt (or more usually slurry) is then disposed of by land fill. Although this process is used in some parts of the world for sewage treatment, it is very rare. The system is very expensive to build and run. The expertise required  is substantial. An alternative is to treat the sewage and then use spray evaporators. This needs large expanses of land and the process is prone to maintenance issues (mostly from salt causing blockages). This article explores an alternate realistic zero dicharge possibility . 

Rhizopod Systems  Sewage treatment systems on small sites such as hotels, houses and caravan parks need to be simple and reliable. The Rhizopod system meets this requirement. It is fundamentally a septic system that feeds an aerated outlet storage. The outlet storage water is then fed though a closed pipe network of rhizopod tanks. These tanks consist of media which support the growth of high water demand plants.  Any excess water is drained back to storage. if the storage becomes too full, the system is alarmed to ensure there is no spill. Treated water can be trucked off site.

Although the system sounds basic, there has been considerable research in the time and duration of feeding water into each tank and the type of Flora in the tank.

How the system works The septic tank at the start of the system is a proven element. It captures solids and foreign object. It allows the sewage to go anaerobic. This allows partial consumption of BOD and some of the nutrients. A good proportion of the urea is converted to ammonium (80% ammonification). The aeration of the post septic storage tank will provide some nitification (conversion of ammonia to nitrate). When the water flows through the rhizopod tanks, the rock whithin the tanks harbours  protozoa. These "bugs" perform multiple tasks including denitrification, biological uptake, and adsorption. They effectively remove over 98% of nitrogen from the septic effluent. The flora within the tanks (usually a high water usage bamboo) uses water though evapotranspiration. 


A Rhizopod system has been validated and approved by the Victorian EPA for use on sites up to 5000L/day. The supplier is Arris.

On sites environmentaly fragile, within water catchments or with vulnerable ground water, the rhizopod system  is an ideal system. It is not the cheapest treatment but it is a simple, reliable treatment where no other systems can be used.