Solid waste or resource?

This week some of my workmates and I paid a quick visit to Toowoomba in South East Queensland. The primary purpose of our visit had very little to do with recycled water (we do occasionally work on other things, you know!).

We were visiting for a project which involves investigating the fate of contaminants in waste products from beef cattle feedlots. We’re working with the meat and livestock industry to help them better understand how different management practices affect the degradation of chemical contaminants and the inactivation of pathogens.

If you’ve ever visited a large feedlot (something that all carnivores should do at some time), then you may have an idea of the scale of the challenges associated with managing the waste products from 20,000 head of cattle. If not, then maybe the photos below might give some indication..





On Monday we visited three different feedlots and the management practices employed by them were noticeably quite different. However, a common theme was the need to remove manure from the feedlot pens and store it in a way that allowed it to be sufficiently stabilised for it to then be utilised as valuable by-product of the feedlotting process.

One of the three feedlots managed the manure by mounding it within the pens. Another focused on stockpiling it outside the pens for up to 12 months and then sieving it into two grades for various types of land application. The third feedlot went one step further by employing carefully managed composting processes in order to convert what was previously a waste product into a significantly more valuable fertiliser. All three feedlots typically sell their processed manure to local farmers for the production of crops such as sorghum.





Since we were going to be too late to fly back to Sydney on Monday night, we decided to stay over in Toowoomba. This gave us the opportunity to pay a quick visit to the Wetalla Water Reclamation Facility on Tuesday morning. I was particularly interested to visit this plant to find out more about the 43-year contract that had recently been achieved to sell 3000 ML/year recycled water (treated effluent) to New Acland Coal Mine by March 2009. This agreement involves selling the effluent from the plant to the coal mine, which is then responsible for pumping the water about 40 kilometres to wash coal at the mine. The price that the coal mine have agreed to pay is $1.30 per kilolitre, which is roughly equivalent to the average consumer price for drinking water here in Sydney. This gives some indication of the value of water security for a thirsty industry in a dry region.





Of course, not everybody is happy. The effluent from the Wetalla plant is currently discharged to Gowrie Creek and subsequently used by irrigators downstream. The irrigators had previously rejected the opportunity to secure this water for $0.15 per kilolitre in 2000. However, they are now unsurprisingly unhappy about losing this free resource. I think there are lots of interesting (and potentially quite heated) discussions to be had on this topic, -covering such issues as water rights and property, environmental justice, public good, etc. But I’m not going to get into any of them now..

One feature of the Wetalla plant that I was completely unaware of is the new (not quite completed) solar sludge drying facility. Sludge is a byproduct of sewage treatment, which contains a significant amount of solid material, primarily as a result of biological growth during secondary treatment.

Depending on how the sludge is treated and further processed, it can still contain around 90% water. Its composition and sheer volume produced can render sludge disposal one of the major challenges (and costs!) associated with wastewater treatment. Sydney Water, for example, transports most of its sludge on tanker trucks to western NSW towns such as Parkes for land application. The sludge from Wetalla is also trucked to local destinations for disposal and this is a significant cost to the plant (and thus to Toowoomba City Council and the local community).

As a means of reducing the trucking costs, Toowoomba City Council have commissioned the development of an innovative solar-powered sludge drying facility. This is observable as the long rectangular shed in the bottom right-hand corner of the below aerial photograph.



After mechanical dewatering, the sludge is dispersed along the floor of the facility, where it is turned and aerated to facilitate drying. After some period of time (which is variable, depending on the weather), a completely dry hard product is produced with a small fraction of the wet sludge mass. While we learnt about the process from the folks at Wetalla, they seemed quite impressed with the significant reductions in disposal costs which they would achieve; and fair enough -they are significant. However, personally, I couldn’t help thinking about the cattle feedlots that we had visited the previous day and the success that they had had with converting a waste product into a valuable resource. I wanted to bring some of the dried sludge pellets home to try them out as plant fertiliser. If I find some spare time this year (yeah, right!), I’d be interested to do some analyses for contaminants such as pesticides and heavy metals. Something tells me that the City of Toowoomba has a valuable product to sell, which should be making –not just saving- money to dispose of.






Sometimes it can be difficult to distinguish a valuable recourse from a troublesome waste product. Factors such as drought, population growth, climate change, fossil fuel availability and nutrient exhaustion may cause us to seriously reassess our perspective sometime very soon.