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In tannery waste water, there is a huge concentration of TDS which cannot be reduced by transitional process even by adopting “advanced” Biological treatment like MBR process. TDS are almost deriving from salt used for conservation of raw leather, from salt used in pickle and from salts inside all chemicals used in tanning process. Therefore, the main problem in closing completely the water cycle is the wastewater which compromises the quality of the final concentration of TDS in the wastewater which compromises the quality of the final leather if re-used in some specific tanning process (ex. Post tanning and finishing).


Membrane systems like Reverse Osmosis (RO) provide the possibility of reusing treated effluents provided that most of the residual organic matter is removed and treatment of the reject is economically feasible. Unfortunately, the only way to treat the RO reject is by Multiple Stage Evaporation. Which requires a massive energy consumption which makes ZLD hardly sustainable. Therefore, in zero Liquid Discharge (ZLD) projects, wastewater re-use and recycle policies are strongly recommended to reduce drastically the quantity of wastewater to be treated; evaporation costs, which represent more than 60% of the total cost of the treatment, are in fact proportional to the volume of water to be treated;