# A Low-Temperature and Low-Pressure Distillation Plant for Dairy Wastewater
## 2 Materials and Methods  
A low-temperature and low-pressure distillation (LTPD) laboratory plant, able to process the cheese effluent in batch mode, was used in this work. We carried out a series of experiments to study its performance. A photograph of the LTPD laboratory plant is shown in Figure 1a, and its corresponding layout is shown in Figure 1b; the main components of the plant are shown and numbered: a heat pump, a low-pressure chamber equipped with two heat exchangers (hot side and cold side), and a circulation pump and a Venturi ejector to create the low pressure into the evaporation chamber. The plant worked in batch mode: it was fed by whey wastewater through an opening into the vacuum chamber when the plant was turned off. The operative capacity of the plant consists of a volume of 60 L regarding the ebullition chamber and a volume of 24 L with regard to the distillate tank. The distillation rate of the process was about 5 L/h (influent). The plant required an overall electric power of about 2 kW. This plant was able to treat the wastewater through an evaporation process at a low temperature of about 35 to 65 \({}^{\circ}\)C thanks to the low-pressure conditions in the evaporation chamber, where the absolute pressure reached about 6.0-6.5 kPa. The first preliminary operation to carry out is to completely fill the distillate tank with demineralized water (100 uS/cm). The treatment process starts by feeding the ebullition chamber with the wastewater, then the centrifugal pump is activated until the absolute pressure decreases and the low-pressure condition is reached. Subsequently, the compressor is started and contemporarily, the treatment temperature (35 to 65 \({}^{\circ}\)C) of the ebullition chamber can be regulated, according to the manometer of the refrigerant gas high pressure side (hot side), operating the fan of the heat exchanger of the refrigerant under-cooling (hot side), and, at the same time, by allowing the cooling of the condensation chamber and of the distillate tank (cold side). These operations cause the product temperature to rise to its boiling temperature, depending on the chamber pressure, and the contents begin to evaporate. The vapor moves up towards the condenser (cold side), where the temperature is lower with respect to that in the condensation chamber, so the condensed vapor is discharged through the pipe connected to the Venturi ejector and accumulated  
Figure 1: Image (**a**) and simplified layout (**b**) of the low-temperature low-pressure vapor distillation laboratory plant: (1) compressor; (2) heating envelope (hot side); (3) ebullition chamber; (4) refrigerant under-cooling heat exchanger (hot side); (5) thermostatic valves of expansion; (6) condensation chamber (cold side); (7) Venturi ejector creating the low-pressure (with sampling open); (8) distillate tank; (9) distillate cooling (cold side); (10) centrifugal pump; (11) inflow electro-valve from whey tank (not shown) and (12) outflow discharge hand-valve to collecting concentrate tank (not shown). into the distillate tank. From here, it can continuously exit by overflow at environmental pressure. At the end of the process, the plant is turned off, and the concentrated fraction can be extracted by opening the ebullition chamber. In order to monitor the overall LTPD process, the plant is equipped with several measurement devices: a PT100 sensor to measure the temperature in the ebullition chamber; a vacuum-meter (Bennert's U-type) for pressure measurement into the ebullition chamber; a flow-meter to measure the distillate effluent; a temperature sensor and a manometer sensor for refrigerant (for both the high- and low-pressure circuits) and a bulb thermometer to measure the environmental temperature. In addition, an electrical energy/power recording unit was used to monitor both the electrical power requirement and the overall electrical energy consumption of the plant. Both the concentrate and the distillate fraction of the wastewater were analyzed.