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Project for recovery and reuse of industrial waters and trivalent chromium generated by tannery waste processing (RIWAC)
Start date: Oct 1, 2005, End date: Sep 30, 2008 PROJECT  FINISHED 

Background In Europe, wastewater from tanneries is currently discharged directly to wastewater treatment plants. However, some components in the waste could be recovered for destruction or recycling, in particular ammonia, calcium sulphate and chrome. In Italy, most of the chrome-containing waste is used in agriculture as organic fertiliser, but no chrome recovery is performed. Objectives Process water containing a high ammonia concentration - chromium (III) present in the residual sludge is usually disposed into landfills. The RIWAC project aimed to implement an innovative process that combined two processes. In particular, it aimed to combine the process for ammoniacal water recovery with the production process,for chromium (III) recovery. With the first process the ammonia is removed and is then converted to molecular nitrogen making it reusable, whilst with the second process, chromium (III) is purified to obtain chromium (III) basic sulfate liquour, suitable for utilisation in the tannery industry as a tanning agent. Results The project achieved one of its two main objectives: the recovery of industrial water in a closed loop and the elimination of ammonia related emissions. The implementation of the process allowed the following environmental benefits: Industrial water is recovered in a closed loop (450t/d), according to the proposal. Elimination of fresh water suction from wells and elimination of discharges of WWTP (450t/d). Elimination of related ammonia emissions into the atmosphere. Absorbtion of ammonia with sulphuric acid and entire recovery of the substances as concentrated ammonium sulfate solution. Ammonia absorption is very efficient (>99,9%), with only negligible emissions of ammonia into the atmosphere ( Recovery of ammonium sulphate (30-40%) and elimination of discharges to the WWTP. This corresponds to industrial/commercial specifications and to agricultural requirements (D.Lgs 217/06 - Italian law on Fertilizers). It can be used among others as nutrient for biological WWTP, in metal production processes, as de-liming agent in tannery industry and in the wood industry. The use of thermal processes to convert ammonia is avoided and nitrogen oxides produced/emitted into the atmosphere are eliminated. No fossil fuels are used to heat raw gases, thus contributing to avoid emissions of greenhouse gases. The economic balance is positive compared to other alternatives: investments costs are by far lower than thermal/catalytic technologies, and ammonium sulfate is recovered and sold. In all other cases, including the proposed thermo-catalytic process, no economic return was foreseeable, only operational costs. The relevant equipment is integrated in the current shaving processing and is properly functioning, producing refined sludge with the required protein recovery rate (increased by 6-8%), and an increased dry matter content (55% vs. 30%), achieving a 45% reduction (90t/day – 19 000 ton/year) ) in the amount of sludge to be disposed of.) The second core objective – chrome and calcium sulphate recovery from sludge – was not achieved. Iron-ions (causing black spots on the tanned hides) could not be entirely eliminated, thus preventing the implementation of this process. The aim is to now obtain another liquor equivalent chromium(III) solution free of unwanted iron ions and proteins. Currently, 70% iron/chrome separation efficiency has already been attained, but 99% efficiency remains the goal in order to guarantee the economic viability of the process as the investment costs were very high. Steps are being taken to ensure this goal is reached as the entire new LIFE funded process implemented in the tanning industry has great economic potential and would likely qualify as a BREF. Though at a reduced rate, sludge disposal in landfills is ongoing, while chrome recovered at lab-scale needs further investigation – calcium sulphate cannot be recovered yet, since the relevant process steps are suspended.

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