An increasingly effective systemLess sludge and a new rainwater collection tank

Feb 07, 2019
Posted in: , Focus on Depuration

The chemical engineer Nicola Andreanini, director of Depuratore Aquarno, illustrates the most recent progress of the Santa Croce consortium water treatment system and the progress of the “Tubone” project which aims to integrate the civil and industrial purification of 42 Tuscan Municipalities and which will be fully operational in 2022.

 The Tuscan tanning district water treatment system is considered an efficiency model. What are its main strengths?

“One of the distinctive elements of a purifier’s features is certainly the one linked to the destruction of the pollutants to be removed. I would therefore say that it is exactly  amplitudes and the constancy of the purifying yields that best describe the complexity and effectiveness of the purification processes we use. Consider that, for the majority of the parametres, we are able to obtain removals greater than 98.5% of the concentrations of incoming pollutants. However, I must add that, in this particular period, another element distinguishes us and makes the most of all the efforts and the energies involved in minimising environmental impacts. I am referring to the substantial elimination of landfill disposal as a destination for the sludge flow produced by the purifier. For many years now we have been dealing with the entire sludge flow produced by the purifier at the sludge treatment plant in via S. Andrea where the outgoing inert, which after the various treatments to which it is subjected, represents a tenth of the incoming mass flow, is anyway going to be recycled in the construction industry. In this particular historical phase where it is extremely difficult to find destinations for sludge flows of civil purifiers, we are in the presence of an industrial sector that has solved, on its own account and without significant impacts, the issue of reducing landfill”.

What recent progress are you most proud of?

“Among the many interventions carried out in the Depuratore Aquarno, I am particularly pleased to underline two initiatives, one in the purifier and one in the sludge treatment plant, which characterised the current year. As for the purifier, the new tank specifically dedicated to the temporary storage of rainwater will soon be operational. In this tank the incoming water will be collected during periods of heavy rainfall so that it can be stored temporarily, without weighing down with an excessive hydraulic load on the functionality of the plant, in order to be subsequently treated downstream after the most intense precipitation period. As for the site of via S. Andrea, in August we completed the whole replacement of the air filtration section which, together with some recent interventions on the recovery boiler, allowed us to earn, for a strong simplification of maintenance operations, potential spaces that can be used to further reduce the outgoing sludge flow during scheduled maintenance operations. As I mentioned earlier, landfill flow has been reduced in such important terms that, at present, it can be estimated at about 3.5% of the sludge flow that was sent to landfill before the entry into operation of the sludge treatment but, despite this flattering result, it is right to continue to look for solutions that will allow us to achieve even more important reductions. It is too early to tell, but it is likely that, within the current year, we will also be able to halve even this residual outgoing flow”.

Could you explain the salient points of the new purification system known as “Tubone”? What stage has been reached in the work and when will the plant function at full capacity?

“What is now summarised as “tubone” is in reality a very broad and ambitious project that provides, through the collection of new flows of domestic waste to the Leather District, the achievement of multiple objectives. In the first instance we want to ensure the purification of domestic waste of large areas of the regional territory where the purification is currently too fragmented and does not allow to obtain satisfactory results. Secondly we intend to exploit this new arrival in order to have a water flow that can be appropriately refined and then be returned into the production sites in place of the waters emitted from the subsoil. The works that come within our competence have been going on since the end of 2012 – the first intervention is the one which has allowed us to centralise on the Santa Croce plant the purification of industrial and domestic wastewater previously treated at the Ponte a Cappiano plant – and so far they mainly concerned the industrial line. We are, however, close to starting the preliminary authorisation procedures for the construction of the works that will allow the collection of domestic wastewaters from the next collection. The arrival of domestic wastewaters is scheduled for 2021 and it is therefore likely that the system will be fully operational in the following year”.

How does the Acqua 360 project fit in this context? How are experiments at the specially constructed pilot plant progressing?

“The Acqua 360 project aims to test technologies that will be used for refining domestic wastewaters. It is a good-sized pilot plant – it is able to produce about 100 cubic metres/day of refined water – which has allowed us to test, together with the three partner tanneries of the initiative, the characteristics of the water refined in the production processes. The results were encouraging as there were no indications against the use of this recovery water instead of the well water commonly used by the partners. It is however interesting to underline how, once that experiments with the tanneries involved in the project have been completed, the pilot plant will be available to anyone who wants to test the recovery water to develop own checks and provide any indications: anyone interested in conducting this kind of test is therefore invited to get in touch with the purification plant to define modalities and details of any tests”.

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