# A Low-Temperature and Low-Pressure Distillation Plant for Dairy Wastewater
## 1 Introduction  
Cheese-making industries, during their process, generally discharge wastewater effluents. Such effluents are mainly made of acid or sweet whey mixed with washing-water [1]. Within the current management of wastewater effluent, the main task is to adopt an appropriate wastewater treatment plant [2]. In order to appropriately fit environmental restrictions and economical needs, the treatment technology should combine both the depurration of wastewater [3] and the recovery of whey products [4, 5]. Some specific purification plants can be used for this kind of wastewater; the most common plants are: trickling filters; aerobic-activated sludge and anaerobic digesters [3, 6]. However, these plants are inadequate to reduce very high BOD5 and COD loads of a typical cheese-making industry wastewater, and they are also unable to recover whey products. Purification techniques generally need to be combined with recovery technologies for whey components in the treatment process. For this reason, other alternative or integrative plants are needed. Among these, some recovery technologies that can be adopted are reverse-osmosis [7], spray evaporation, membrane ultra-filtration and ion exchange, in sequence or in parallel [4, 8]. These technical systems, although able to recover whey products while also preserving their high quality (e.g., whey protein concentrate; lactose), are much more expensive [9, 10]. This high financial cost consistently decreases the interestin adopting these recovery technologies [11], especially in small cheese-making factories. These factors suggest the need to study an alternative treatment strategy to purify wastewater and to recover whey products, which can be competitive in comparison with other available systems. Distillation at low-pressure, also known as vacuum distillation, is a process commonly employed in industry processes to extract or purify essential oils, to deodorize vegetable oils and to purify and dry some chemicals. However, the early scientific papers or patents on vacuum distillation technology have been focused on seawater desalinization [12; 13]. The field of utilization of the vacuum distillation technique is wider, comprising biodiesel refining, organic synthesis and wastewater treatment [14; 15]. Particularly, on the subject of wastewater treatment, scientific studies have demonstrated that the vacuum distillation technique performs remarkably in removing different pollutants such as: total suspended solids (TSS), total dissolved solids (TDS), biochemical oxygen demand (BOD), chemical oxygen demand (COD). It is also effective at removing and recovering heavy metals and various mineral compounds dispersed in an aqueous solution [16; 17]. Vacuum distillation, often combined with membrane technology, is commonly employed to treat industrial olive oil wastewater and food process wastewater. More specifically, in olive oil wastewater treatment, the potentialities of vacuum distillation have been studied in combination with membrane process [18; 19]. Furthermore, vacuum distillation has been used as a subsequent stage to the extraction process of Phenol, in the treatment of olive mill wastewater [20; 21]. Depending on the type of dairy production, the curdling process produces a quantity of whey equal to approximately 85-90% of the volume of processed milk [22]. The organoleptic characteristics of the whey, which also determine its economic value, are strictly connected to the specific chemical composition. Dairy wastewater, being characterized by a high polluting load, does not allow its direct discharge, but requires a purification treatment [23]. Furthermore, whey is an unstable product due to the fermentation process produced by the bacteria present in the milk; this makes its management difficult and causes environmental problems for the dairy industry [5]. Nevertheless, whey is a potentially important resource to be economically utilized [4; 24].