In water evaporation based zero-effluent discharge systems,water is evaporated from the effluent to concentrate it,reduce its volume and convert it into low-volume,high-TDS sludge.The heat required for this water evaporation is equal to the sensible heat required to raise the temperature of the water up to its boiling point,the heat of solution and the latent heat of evaporation of water.Moreover,the heat source should have a temperature higher than the boiling point of water(which ultimately depends upon the pressure within the evaporator and the nature of the effluent)for effective heat transfer.As we add on all these heat requirements,the quantity of heat required may be equal to 540-720 kcal/kg of water.
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