# A Low-Temperature and Low-Pressure Distillation Plant for Dairy Wastewater
## 2 Materials and Methods
The capability of the LTPD process to recover high-quality products was evaluated considering the concentrate fraction, while the ability of the LTPD process to departate the effluent was evaluated by considering the distillate fraction. Additionally, thermal and energetic conditions were considered to identify optimal processing conditions. The samples were taken:  
* At the tank of influent flow, where the raw whey resided;
* At the outlet of the distillate tank, where the effluent distillate resided;
* At the vacuum chamber, where the concentrate resided (at the end of the run). The measurements were carried out on each stage of the wastewater: raw whey, distillate and concentrate. The measured characteristics of the samples were as follows: pH, conductivity, chemical oxygen demand (COD), biochemical oxygen demand after 5 days (BOD5), total nitrogen (TN), total phosphorus (TP) and solid content (SC). Specifically, the measurements were executed according to the following methods: COD by the dichromate reflux method; BOD5 by the respirometric method; TN and TP by the [PERSON]'s alkaline persulfate digestion method [25; 26] and SC by the desiccation method, at 105 \({}^{\circ}\)C. Additionally, the following characteristics of the products were measured in an external laboratory: proteins, fats and lactose. No specific conditions of samples storage were adopted because the analysis was performed within about one hour of the sampling phase. Density of the samples was measured by a Quevenne lacto-dense-meter; viscosity was measured by a viscous-meter (Brookfield HBD VII+, Brookfield Engineering Laboratories Inc., Stoughton, MA, USA); conductivity was measured by a conductivity-meter (HD 8706-R1, Delta Ohm, Padova, Italy) and pH was measured by a pH-meter (Hanna Instruments, pH 301, Padova, Italy). In order to obtain measures at different operating conditions, we operated it on two parameters: one related to the plant and one related to the concentrated product. Since the heat necessary to the evaporation is supplied by the hot side of a refrigeration cycle, the first parameter considered was the refrigerant temperature on the hot side, that the plant allowed us to set. Accordingly, four different test values: 39 \({}^{\circ}\)C, 46 \({}^{\circ}\)C, 53 \({}^{\circ}\)C and 60 \({}^{\circ}\)C were selected. However, these values fluctuated around their set-point average value, with an inevitable oscillation during the plant functioning. The parameter we considered was the final concentration of the concentrated product. Considering an initial average solid content of whey of 6.5%, as indicated in the literature, the goal was to achieve three different values of SC%: 30%, 50% and 70%. This was performed by monitoring the volume of water evaporated in each test and by stopping the operation of the plant once the calculated water volume to be removed was reached. However, due to the variability of the initial characteristics of the whey, the values of the final SC we actually obtained were slightly different from those intended. The combinations of the two variable parameters required 12 tests, and since each one was repeated 3 times, in total, 36 tests were performed as reported in Table 1.  
In the first phase of the work, the performance of the LTPD plant was separately studied with two different fluids: the first one was distillate water and the second consisted of saline water (NaCl). Then, several trials were carried out at different operating conditions in order to identify the best operational conditions. In the second phase of the work, a set of \"optimal\" operating parameters was selected to ensure the process's effectiveness when treating the whey wastewater. All experiments were carried out employing raw whey wastewater (20 L each run), coming from a cheese-making industry, located at nearby Potenza (Southern Italy), derived from the manufacturing of cheese from cow milk. The main characteristics of the whey wastewater are listed in Tables 2 and 3.