Abstract
In the present work a brief literature review focusing the analysis of water systems in the pulp and paper industry is presented and the Water Sources Diagram (WSD) method is applied in a case study. This algorithmic procedure emerged as a viable alternative to minimize the water consumption in process plants, including the pulp and paper industry, and its robustness allows dealing with large-scale problems in the presence of multiples contaminants. The procedure also allows to obtain simultaneously the network structure and the minimum fresh water consumption target. WSD rules to achieve minimum consumption are (Gomes et al., 2007): (1) Use external water sources only when internal water sources are not available, (2) Transfer all the possible amount of contaminant inside a concentration interval and (3) For operations those are present in more than one interval, the stream must continue to flow through the same operation until its end. This last heuristic avoids the division of operations. The WSD methodology is here applied in the bleaching section and focuses the minimization of water consumption through maximum reuse. Three washers compose the bleaching section: Chlorine washer, Alkali washer and Hypo washer.
According to original data (Shukla et al., 2012) the bleaching section requires 8,628 m3/d of fresh waterand generates 5,097 m3/d of wastewater without integration. Applying the WSD methodology the total fresh water requirement decreased to 5,085.51 t/d and the total wastewater generation is 1,548.52 t/d;846.21 t/d from the chlorine washer, 642 t/d from the hypo stage washer and 60.31 t/d from the alkali washer. Therefore the WSD indicates a possibility of 41 % reduction in fresh water consumption and 69.61% reduction in wastewater generation. The comparison among the WSD results and the results of Shukla et al. (2012), for the same problem, could not be made because it was identified an violation in COD contaminant concentration in the alkali washer in the results of these authors.
The WSD methodology has shown to be an important tool when it’s desired to set new alternatives for water reuse in a systematic and efficient manner, such as in programs of water resource management in the industry.
