# A Low-Temperature and Low-Pressure Distillation Plant for Dairy Wastewater
## 4 Conclusions  
The experimental results of the trials carried out bring some observations regarding the two main investigated parameters: the treatment temperature and the solid content SC in the final product. (1) With regard to the effect of the treatment temperature, a high operating capacity of the plant was observed at high temperature (60 \({}^{\circ}\)C), at which up to 6 L/h of raw whey can be processed with a relatively low energy cost, due to the reduced treatment time. Unfortunately, this economical advantage results in a worse quality of the concentrated product, resulting in a significant loss due to a higher amount of denatured whey protein, as a result of their poor tolerance to high temperature. On the other hand, at a low operating temperature, the treatment time is longer and the energy consumption is higher. (2) With regard to the obtainable solid content SC, it seems evident that the objective to achieve high SC causes a worse operational capacity of the plant. This is due to the increase in treatment time, which is a consequence of the global heat transfer coefficient decrease caused by the higher viscosity of the concentrated product, which is from raising the ebullioscopic temperature of the solution and from the blanketing phenomenon. On the other hand, prolonging the treatment time in order to achieve high SC has been revealed to be inefficient in the pollutant-content removal by the distillate (the removal efficiency being greater at the beginning of the treatment and decreasing as time elapses). However, this helps to retain the greatest amount of pollutant into the concentrated fraction. (3) The best operative conditions of the plant are dependent on the two different objectives that can be achieved:  
* When the plant is required to reduce the polluting load in the distillate, while the concentrate quality is neglected, a quick solution might be operating at a high treatment temperature with high operating capability, low energy costs, and large amounts of processed whey;* Alternatively, when a high quality of the recovered product is required, then a low treatment temperature must be adopted, however, consequences will be a worse processing rate and a decreased cost saving. (4) In any case, it is not convenient to push the evaporation up to the achievement of a high value of SC in the concentrate, as the overall heat exchange coefficient tends to decrease. As a significant conclusion, the interpretation of the experimental results suggests that the driving parameter governing and limiting the evolution of the evaporative phenomenon is the overall heat transfer coefficient. Since this coefficient depends on the Reynolds number, the system could be supplied with a device simply moving the liquid concentrated phase in contact with the exchanger hot side in order to improve the overall heat exchange. In addition, the productivity of the plant can be improved by increasing the transfer rate of the mass of the evaporated water from the boiling chamber to the condensation chamber by means of a mechanical system, however, this feature may not be as useful because it has been experimentally found that the pressure in the chamber decreases slightly according to the decrease of the boiling temperature. Thus, the limiting factor in this process is the global heat transfer coefficient, which decreases when the whey concentration increases. Finally, the above considerations suggest that an optimal system solution can be reached through the adoption of two concentration treatments in parallel. Since the concentration at low pressure is discontinuous, this could optimize the loading and discharge phase and the reaching of the low pressure in the ebullition chamber. On the whole, the results obtained in the present work have demonstrated that the proposed treatment technology can be suitable both to departee-making industry wastewater and to recover whey products.