# Water Consumption, Quantity and Quality of Wastewater and Sewage Sludge from Polish Dairies
## 3 Results and Discussion
In three plants, the volume of wastewater was practically equal to the volume of water consumed (97, 100 and 104%). In one dairy, wastewater accounted for 234% of the water consumed, which could indicate considerable milk losses during production, as this dairy plant did not process whey. In four dairies processing whey as well as milk, the volume of generated wastewater was over 130% (134, 143, 137 and 147%) of the water consumed, which can be explained by the discharge of permeate into the sewerage system and the losses of whey and/or milk in the production process (Figure 3). In both cases, we are dealing with a loss of valuable raw materials [41]. The main difference between the surveyed treatment plants of the dairies was their capacity. The smallest plant treated 78 m\({}^{3}\)/d, while the largest treated 8710 m\({}^{3}\)/d. In 10 plants, the average daily flow was over 1000 m\({}^{3}\)/d. Four treatment plants had a capacity of over 3000 m\({}^{3}\)/d and one had a capacity of over 8700 m\({}^{3}\)/d. In 8 of the 13 WWTPs, the wastewater treatment technology was based on aerobic processes, whereas 5 were operated based on aerobic and anaerobic processes. The mechanical section of the WWTP is dominated by screen traps, screens, grit chambers and sieves. Many plants use equalization tanks, flotation tanks (dissolved air flotation (DAF)) or degreasing plants. DAF is used in many plants around the world [2]. Multiphase aeration chambers in combination with secondary clarifiers are mainly used in the biological section, but also UASB and MBBR bioreactors. These modern systems are increasingly being used worldwide [42; 43]. In some plants, older technological solutions are still used (BIOBLOK, BIOKON and other activated sludge chambers, e.g., with Kessen brushes). These solutions are among the technologies used for the treatment of dairy wastewater [44]. Figure 2: The volume of wastewater per litre of processed milk depending on the production volume. “\(\ast\)” the volume of processed whey. The concentration of organic compounds in the wastewater flowing into the treatment plant, expressed by the BOD\({}_{5}\), was in the range of 465-3275 mg O\({}_{2}\)/L; in nine plants, it was above 1000 mg O\({}_{2}\)/L, whereas in the others it was below this value. For COD, the concentration range was 850-5032 mg O\({}_{2}\)/L. In nine plants, the COD value was above 2000 mg O\({}_{2}\)/L, and in the others it was below this value. The concentration of total suspended solids ranged from 75 to 1109 mg/L, nitrogen 16.2 to 168.4 mg/L and phosphorus 9.0 to 52.5 mg/L. The concentration of fats ranged from 22.0 to 400.0 mg/L. The pH of the wastewater was in the range of 6.5-9.5. In seven facilities, the pH value was below 8.0. The highest concentrations of BOD\({}_{5}\), COD, total suspended solids, nitrogen and phosphorus were found in the largest facility, which processes 2.8 million litres of milk and 2.0 million litres of whey per day. With such a high production, all these plants could struggle with milk and whey losses (discharge of permeate into the sewerage system); they could also encounter problems related to the quality of some of the raw materials fed to the system that are unsuitable for processing. Despite the highest values of the indicators among the diaries examined, the wastewater concentrations are within the ranges specified in the literature. The BOD\({}_{5}\) and COD values do not differ from the data obtained in Ireland [2; 6; 45; 46]. At the same time, the BOD and COD concentrations were si2 gnificantly lower than the values measured in Brazil [47]. These are higher values than those found in previous studies by [PERSON] et al. [48], which could be due to the fact that water consumption in dairies in Poland has decreased over the last decade or so due to the increased cost of water purchase, environmental taxes and, most importantly, the introduction of water-saving solutions using \"cow water\" as a water source in some processes.