Transparent, odourless, colourless: is this really the case?Wastewater, its management and impact: Venetian chemists discussed the technologies to protect water for a cleaner discharge
Venetian chemists gathered in Chiampo for the 9th Technical Congress to discuss the very delicate theme of “Economy, technologies and water protection in the tanning sector”. The event was hosted and moderated by Renato Bertoli, National Executive Director of AICC, who, at the beginning of the work sessions, thanked the Municipality of Chiampo (“Which has been hosting us for some years”) represented by the Mayor and Provincial Councillor for the Environment, Matteo Macilotti. In turn, the Mayor reiterated how the AICC can call Chiampo “its home” and stressed the importance of the topic of the works “for encouraging good practices of those who really invest in research and development, so that this valley can be a valley that knows how to produce excellent leather, while focusing on an eco-friendly production.”
Analysis of the area
The valley was presented by the geologist, Doctor Giuseppe Franco Darteni, who drew a picture of the water resources of the valleys of Agno and Chiampo. The report presented the geological formation of the area and the dynamics of the underground water outflow, together with the relevant genesis of the water reserves and their collection, which is very high in this area. A consumption of almost 135 million cubic meters per year is estimated. A huge quantity that over the last sixty years has led to an average lowering of the aquifer by about 5 meters. Great attention was also paid to the “vulnerability” of the stratum, directly connected to the permeability of the soil, which allows the infiltration of contaminants that the rain finds on the surface. After the polluting peak of the 1980s, the environmental regulations in the agricultural, industrial and civil sectors have gradually improved.
The advantages of enzymes
This was followed by a presentation prepared by Biodermol Ambiente – a company based in Lavis (TN) engaged in the development, production and use of enzymes and auxiliaries for the tanning industry – which analysed the advantages of the use of enzymes in the soaking and liming phases. Due to their characteristics, enzymes have become more and more popular in many manufacturing industries, including the tanning industry, as explained by Doctor Elisa Sartori, head of Biodermal Ambiente’s Research and Development Laboratory. One of the advantages they offer, especially from an ecological perspective, is the fact that their high specificity allows reactions that do not lead to the generation of by-products (often polluting or however undesirable). In addition, they are totally biodegradable. Translated, for example, into the soaking phase, they act on certain molecular targets in the leather, degrading them, removing them and allowing more effective penetration of water and chemical products inside the fibres. This results in less need for water and chemical agents. This, in turn, has an impact on the processing of wastewater, where the levels of COD, TKN and sulphides and solphydrates are much lower. There are also advantages on the product, where the enzymes emphasise the physical properties: cleaner grain, supported belly and clear and clean pelt. From theory to practice: Doctor Mattia Lusente, Tanning Technician at Biodermol Ambiente, brought these studies to the Conference, for the protection of water. The average percentages of abatement obtained from Italian and foreign industrial experiences in a 24-month period, by applying an enzymatic technology in the stages of soaking and liming, recording about half of COD, more than 60% less TKN and 65% less sulphides.
Let’s shed some light on catalysts
Some very interesting ideas also came from a study being carried out by the Experimental Station for the Industry of Leather and Tanning Materials on purification by photocatalysts. The engineer, Daniela Caracciolo, Advisor for Safety and the Environment, head of SSIP Waste Management talked about the use of zinc oxide based catalysts, prepared in the laboratory, which exploit light energy at a precise wavelength, modifying the speed of a chemical reaction, triggering the oxidation of contaminants that are difficult to degrade. The process is not selective and therefore allows the removal of more pollutants, even of different nature and difficult to remove, without generating sludge and in economy, since it takes place at room temperature and at an atmospheric pressure. After the first tests on dyeing water from the textile industry, the system was transferred to tanning wastewater. The levels of TOC and some metals were analysed in order to get a more complete picture of the concentration of pollutants present in the effluent. A 30% reduction of TOC in dyeing wastewater was achieved; while in finishing wastewater, which has a much higher concentration, there was a reduction of almost 50%.
A new treatment: ozonisation
Going back to the concrete reality of the valley, the engineer Daniele Refosco, Technical Manager of the Water purification Plant of Chiampo Spa (which treats – in the industrial line – 30 thousand m3 of wastewater a day), explained how in recent years the changes in the tanning processes have led to an increase in the outflow of wastewater, of non-biodegradable COD concentrations and the quantity of soluble chrome. An increase in the content of fatty substances was also recorded (which is reflected in the purification phases); the foam in the biological oxidation vats have become very significant; and there is an increase in colloidal substances that are difficult to flocculate. Against this background, it was necessary to develop a new purification treatment, with a plant – at the end of the biological treatment – for the ozonisation of purified wastewater. When fully operational, residual CODs, chromium concentration and suspended solids, and wastewater discolouration are expected to decrease, while disinfection is expected to increase as ozone is a powerful disinfectant. These results are certainly positive, but they lead to a significant increase in costs. Furthermore, for a synergic action with tanneries, which seek to optimise their own tanning processes, the engineer Mirco Zerlottin, head of the Water Research and Development Division of Chiampo Spa, explained how he implemented the biodegradability tests with a standardised method, in order to be able to evaluate the variations adopted in terms of purification results.
Who pollutes, pays
In conclusion, the experience of the Tuscan colleges was also shared with the study of the engineer Andrea Ricotti, Research and Development Manager of the Consorzio Cuoio Depur Spa, who summarised the Lightan process which the Consortium is currently involved in, and which should lead to new criteria in discharge prices. The current system involving the sum of fixed operating costs (depending on the number of user actions) and variable costs (proportional to the quantity and quality of the water to be purified) is considered to be outdated and the Lightan project, which aims at lowering environmental impacts through an integrated approach among all the actors that manage the individual processing phases, introduces the principle that whoever pollutes less is rewarded with lower rates.
Appointment on the website
All the presentations of the Conference are also published on the Association’s website to allow colleagues from other districts to read and to keep up with what is happening in the sector.