# Water Consumption, Quantity and Quality of Wastewater and Sewage Sludge from Polish Dairies
## 4 Conclusions  
Surveys were conducted in 18 dairies with different water, wastewater and sewage sludge management models. Only two plants used closed water circuits. This shows that it will be possible to reduce water consumption in most plants in the future by implementing this type of solution. The water consumption per unit ranged from 1.5 L of water per litre of milk processed to 3.71 L per L. In most cases, the values for water consumption per unit were within the recommended values and fulfilled the BAT criteria. In three of the four dairies where the water consumption per unit was above 3.0 L/L, the product range was very diversified. Such fragmentation of production is associated with the operation of many smaller, specialized production lines and consequently higher water consumption per unit. When analysing the data, no explicit effect of whey processing on the increase in the volume of water per unit was found compared to dairies where such processing did not take place. This confirms that water consumption is mainly determined by the unitary solutions of water and wastewater management in a given plant. The dairies differed in the unit volume of wastewater produced during the processing of 1 L of milk. The lowest value of this indicator was 1.18 L per L of milk, while the highest value was 5.78 L per L. In some plants, especially those that process whey, a higher amount of wastewater may result from the discharge of permeate from membrane whey thickening into the sewage system and from milk and whey losses during production processes. The parameter that illustrates the state of water and wastewater management on the dairies is the unit volume of wastewater per 1 litre of water consumed (L/L). In two dairies,  
Figure 7: The amount of sludge produced per pollutant load removed depending on wastewater flow. the volume of wastewater discharged was less than the volume of water consumed, which could be due to very economical water management. In one dairy, wastewater accounted for 234% of the water consumed, which could indicate significant milk losses during production as this dairy plant does not process whey. The concentrations of dairy fed into WWTPs were comparable to the concentrations of dairy wastewater in other European countries. Depending on the size of the plant, technologies based on simple solutions, such as activated sludge chambers aerated with Kessen brushes, up to UASB- and MMBR-type reactors, MBR and oxygen aeration, are used for its treatment. In turn, degreasing plants or flotation plants (DAF) are used to remove fats. In most WWTPs, excess activated sludge was stabilized aerobically, directly in the activated sludge chambers or in separate stabilization chambers, followed by a solution combining aerobic and anaerobic sludge stabilization (aerobic in activated sludge chambers, anaerobic in separate digestion chambers). Despite the disposal of domestic wastewater in WWTPs, the results of the sanitary examinations of the sludge show that none of the samples contained dangerous pathogenic organisms that would prevent their agricultural application. The analyses of the content of heavy metals showed that the concentrations found were well below the values specified for application on agricultural land. The data on the volume of sludge show that the ratio of sludge to raw milk processing was between 0.137 and 7.927 kg of sludge per 100 L of milk processed. The volume of sludge produced per pollutant (BOD) load removed (Y) ranged from 0.404 to 18.895 kg/kg BOD\({}_{\text{rem}}\). The high values of water consumption per litre of milk processed, the volume of wastewater per litre of water and per litre of milk processed, the ratio between sludge and raw milk processing and sludge production in some dairies show that it is necessary to analyse both water and wastewater management and sludge management in order to rationalize water consumption and reduce the amount of sludge and wastewater produced. The current management of dairy wastewater involves significant costs.