# A Low-Temperature and Low-Pressure Distillation Plant for Dairy Wastewater
## 3 Results and Discussion
### Evaporation Capacity and Energy Costs  
By grouping the tests for the selected different treatment temperatures of the heat exchanger (hot side), considering the data of the product treatment capacity and of the electrical energy consumption, the measured data were expressed considering the average measured electrical energy consumption per unit volume of treated whey (kWh/L) and the average operational capacity of the system (L/h), corresponding to each operating condition of treatment temperature (Table 9). In addition, Table 9 evaluated the coefficient of performance (COP) of the plant as the ratio between the evaporation energy absorbed by the distilled vapor, considering the enthalpy of the water vapor at the pressure of the ebullition chamber and the treatment temperature, and the measured electrical energy consumption also taking into account the electrical consumption of the ancillary equipment. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Min** & **Max** & **Median** & **Mean** & **Standard Deviation** \\ \hline Conductivity & 94.6\% & 97.7\% & 95.9\% & 96.1\% & 1.0\% \\ BOD5 & 98.3\% & 99.5\% & 98.9\% & 98.9\% & 0.4\% \\ COD & 98.7\% & 99.6\% & 99.4\% & 99.3\% & 0.3\% \\ TN & 98.2\% & 99.3\% & 98.9\% & 98.9\% & 0.3\% \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Removal efficiency of the specific pollutant: 100 minus the ratio between volumetric pollutant amount into distillate and into raw whey expressed as percentage. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Coding**} & **Treatment** & **Processed Whey** & **Measured Electrical Energy** & **Coefficient of Performance** \\  & **Temperature** (\({}^{\circ}\)C) & **Measured Flow Rate (L/h)** & **Volume of Processed Whey** & **of the Plant (COP)** \\  & & & **(kWh/L)** & \\ \hline P1-P2-P3 & 60 & 5.79 \(\pm\) 1.43 & 0.35 \(\pm\) 0.02 & 1.48 \(\pm\) 0.15 \\ P4-P5-P6 & 53 & 3.65 \(\pm\) 0.49 & 0.38 \(\pm\) 0.03 & 1.47 \(\pm\) 0.19 \\ P7-P8-P9 & 46 & 2.61 \(\pm\) 0.34 & 0.76 \(\pm\) 0.08 & 0.75 \(\pm\) 0.11 \\ P10-P11-P12 & 39 & 2.03 \(\pm\) 0.26 & 0.99 \(\pm\) 0.04 & 0.55 \(\pm\) 0.06 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Relationship between the treatment temperature and the energy cost (measured electrical energy consumption during the trial) per unit volume of processed product; the average volumetric processing rate per unit volume of processed product and the coefficient of performance (COP) as ratio between the absorbed thermodynamic energy of evaporation and the measured electrical energy consumption. The standard deviation of the mean is reported after the \(\pm\) character. The average rate of evaporation approximately decreases when the temperature of the heat exchanger decreases; furthermore, with regard to the temperature of the hot side exchanger, a marked decrease can be observed in the slope of the data describing the evolution of the SC of the concentrate by increasing the process time. It is evident that when increasing the operating temperature from 39 \({}^{\circ}\)C to 60 \({}^{\circ}\)C, the operating capacity increases from about 2 L/h (at 39 \({}^{\circ}\)C) to 6 L/h (at 60 \({}^{\circ}\)C) of processed raw whey. This result is a direct consequence of the greater amount of heat transfer, with a correspondent increase of evaporated water. The measured electrical energy consumption shows that by increasing the treatment temperature, a reduction in energy costs for each unit volume of processed whey can be obtained: a better operating capacity for the plant has been obtained by reducing the operating time, due to a more rapid water evaporation and a more rapid reaching of the prefixed concentration. However, the results obtained have highlighted that it is significantly less expensive to operate at a certain temperature (in this case, 53 \({}^{\circ}\)C), above which the specific energy consumption is minimized towards about a constant level (COP of approximately 1.5).