Project Data

This project included the design of all biological and engineering aspects of the wastewater treatment through to construction and commissioning of the designed system. The wastewater treatment plant system is made up of a number of different treatment process including , an  Anaerobic digester, reactor lagoon, facultative lagoon, and evaporation lagoon.

The first covered anaerobic pond is followed by two uncovered anaerobic ponds in series,  These reactors have several process advantages including: organic removal performance and management of the sludge load to the facultative ponds, further breakdown of complex organics.

The facultative pond has been sized such that surface aeration is not required. The reason for adopting this approach is because the available land and ease of civil works makes it more economical (and environmentally friendly) than adopting a small area but requiring additional oxygen transfer through surface aeration.

The effluent from the facultative pond is theoretically sized to achieve a 20:30 effluent.  However, due to a number of process factors, such as, resolubalising of organic load from the sludge, potential for algae growth, wind action, temperature impacts, etc it is more likely that a little higher organic but at times significantly higher solids effluent will result.

A conservative approach to the water balance has been adopted in that the evaporation system has been sized for the final stage of 57,000 SPU and no sludge wasting.

It is estimated that with 57,000 SPU the bore water use per year is 99 Ml. This is the additional water that has to be disposed of, by evaporation. If this evaporation takes place within the treatment units then the TDS will rise significantly. It is therefore intended to bleed off from the recycled flushing water to an evaporation pond, which is designed to totally remove the water, resulting in an accumulation of contaminated salt. Leachate from the salt will be prevented from contaminating the ground water by the liner.

Over the average 4 months when rainfall exceeds evaporation, the excess water can be stored in the facultative pond and/or be taken to the evaporation pond. During the average 8 month period when the evaporation is higher than the rainfall, potentially the water level in the facultative pond will drop. This water balance management tool allows the TDS in the system to be maintained at long-term sustainable levels.

An evaporation pond of 100 x 150 m has been constructed. This is larger than required for the process adopted but has been used as the excavated material is required for fill. The pond is operated using a serpentine flow path with a recycled spray system in the first path. The spray system allows for continuous water loss, which with recycling at about 11 l/s the required water balance is obtained and a zero discharge is achieved for Stage 1 up to 28,000 SPU.

It is considered the above is a conservative design to manage the site’s water balance. Experimental work is currently being undertaken to determine the impact of using black body radiation for enhance evaporation in the first pass. This approach has been tried successfully in Victoria but it is anticipated that there will be significant advantages due to the climatic conditions in Western Australia. In effect, the approach is to spray the liquid such that it forms a thin film on a sloping black liner. Depending on the additional evaporation resulting from this approach, energy savings can be realized in the spray recycles system.

The dried contaminated salt will accumulate in the evaporation pond that has capacity, if required, for several decades’ storage.

The make up of the sludge depends on the waste source and the amount of the biological degradation that has taken place. It is anticipated that the sludge will have a greater nutrient ratio than 100 carbon:5 nitrogen:2 phosphorus plus trace elements. There will be a higher potassium value than normal domestic sludge due to the piggery source and the potash could be 3%. The salt component will depend on the method of water balance discussed above but should not affect its potential as a soil conditioner.

The utilization of the biogas is not required for the wastewater disposal. A preliminary evaluation suggests that it will be economic to use the biogas for co-generation.

The biogas volume generated in the anaerobic pond per day from the 57,000 SPU is subject to a number of variables and it is estimated that there will be about 11,850 m³/d of methane burned (> 98% of that collected). By burning the methane and converting to carbon dioxide this results in an equivalent greenhouse gas emission reduction of about 72.5 million tonnes/year.

The following sizes are generally given as a minimum. Detail design and construction methods which gave an economic approach, but will not affect the process outcomes.

The covered anaerobic lagoon has been constructed at 47.4 x 102.4 x 7.4 m depth. This gives a water volume of about 15,200 m³. It is the heart of the treatment process carrying out the majority of organic waste removal.

The anaerobic lagoon is covered and lined to collect the biogas and prevent seepage into ground water respectively.

The lagoon incorporates a recycle system, capable of drawing from 3 different locations. The purpose is to seed the waste giving additional performance and stability. The recycle system also allows solids to be removed as required.

The biogas generated will be collected and flared reducing the environmental greenhouse gas impact of an uncovered lagoon. In the future the biogas may be used for power generation.

A lagoon 47.4 x 41 x 6.5 m depth divided in two by a floating curtain. These lagoons offer process advantages for organic load removal and sludge management through to the facultative lagoon. The reactor lagoons are also lined to prevent seepage into ground water.

The recycle facility includes a draw off from the bottom of the first of the reactor lagoons to enable continuous sludge management as required.        

The facultative lagoon is 150 x 66 x 4.5 m deep,. The facultative lagoon has been sized to avoid the use of surface aerators. There is no provision for sludge removal. Taking into account the sludge management in the anaerobic lagoons and the depth of the lagoon, it is not anticipated that any desludging will be required for decades. Again the  facultative lagoon is lined to prevent any seepage into ground water.

The design allows for average daily recycle pump flow. The recycle flow will be taken from the end of the facultative lagoon. The method of control (on/off) and flow rate has to be finalised after discussion with the piggery management requirements.

 Summary of Pond sizes