Sacyr is working on the implementation of an organic waste treatment plant in Melbourne (Australia). Due to be commissioned in 2019, it will enable organic waste to be transformed into compost or quality organic soil conditioner.
The plant will meet the needs of the 1.2 million inhabitants of eight municipalities of Melbourne's metropolitan area. The future facilities are expected to reduce CO2 emissions by more than 65,000 tonnes and the annual organic waste from this south-eastern area of the Australian city is expected to be transformed into 50,000 tonnes of high-quality compost.
To do this, Sacyr will use technology which is common in Europe but not so in Australia. The air treatment system which will be installed at the plant is among the most advanced waste recovery systems. Its design envisages many different items of equipment which work together to form a highly effective air treatment and odour reduction system.
“First of all, the air is captured from the inside of the warehouse at the treatment plant through suction fans. The warehouse, which will remain at negative pressure, is zoned so that the air inside is renewed in accordance with operation”, explained Carlos Gros, director of Sacyr Environment Australia.
The air then passes through a cooler which will ensure it is at the right temperature so that the following elements of the air treatment work within their optimal range. “The next step consists of passing the air through an acid scrubber, which neutralises the basic chemical elements present in the air which are a source of odour. The air is also moisture-saturated, to favour and optimise biofilter functioning”, highlighted Gros.
The air is next passed through a biological filter (or biofilter) made up of layers of tree bark and wood chips in order, ultimately, to collect the condensates and leachates produced throughout the treatment process and move them to a storage tank. “The equipment dedicated to treating the air is duplicated, in two identical lines, to favour its operability and maintenance”, explained the director.
The composting process imitates the transformation undergone by organic waste in nature under aerobic conditions.
“This is basically a biological oxidation or aerobic fermentation process, but which at facilities such as ours is taken to industrial scale. Here it is done in a more accelerated manner through controlling parameters such as humidity, temperature and oxygen”, he added.
The explanation as to why these types of processes, common in Europe, have not yet been exploited in Australia is due to the fact that the country has no problems with regard to space and has never skimped on transport costs.
Composting has taken place at open-air facilities, far from urban areas, where the problem of the smells affecting or inconveniencing the population does not arise. However, this type of facility does have drawbacks, which has led Sacyr to utilise its twenty years of experience in the European market.
“Although these facilities are sometimes closer to the major consumers of compost, they are further away from the places where most organic waste is generated, which are urban areas, and transportation increases the final cost of the process from generation of the waste until it is applied to the soil”, indicated Gros.
Additionally, at open-air facilities the process is far less controlled than at totally covered facilities, as the former are highly dependent on the weather and it is impossible to influence the conditions in order to optimise the process.
It is not common to find composting facilities in Australia where all the phases of the process are carried out inside a unit and odour emissions to the outside air are controlled at all times through treating the air inside the facilities.
These facilities involve greater investment, somewhat more complex operations and higher operating costs. Due to all this, concluded the director of Sacyr Environment Australia, “our company has found how to get it right through proposing something different to the norm in the Australian market when they were ready to bear a greater cost in order to have facilities that produce a product with a more consistent quality at a location closer to the places where the waste is collected”.