Environmental Sciences and Pollution

Sludge digestion process can be optimized applying the methods of sludge disintegration. This article analyses the efficiency of the digestion process of disintegrated sludge by methods of ultrasound or high voltage in comparison to the digestion process of non-disintegrated sludge. The sewage sludge from two Lithuanian wastewater treatment plants as used for the research. Both wastewater treatment plants use analogous sludge treatment technology, in both of them the municipal wastewater is treated and the influence of industry on the quality of sewage is analogous. Due to this it has been assumed that the quality of excess sludge is also analogous. The results showed that both analysed methods of disintegration had the same effect on the increase of specific destruction of volatile solids (VSS) and increase of specific biogas production with the maximum values of 22 % and 12–13 % respectively. In case of digestion of disintegrated excess activated sludge applying both methods, the maximum methane content in biogas was 71.9%, whereas in case of digestion of non-disintegrated sludge it was 58.3 % only. The total operation expenses and capital expenditures of ultrasonic disintegration method are more than 8 times higher comparing to the total expenses and expenditures of high voltage disintegration method.

The structure of the study soil was seriously damaged by aggregate carriers. After three drives, soil density in tracks approached the limit value suitable for plant cultivation (1.6 g/cm3). The compaction level in the 16-cm surface soil layer increased 1.10–1.65 times. In deeper layers, its value quickly approached 1. As a result, the physical degradation and cultivation resistance of soil as well as energy input for soil cultivation increased. The environment was increasingly polluted with exhaust gases. Therefore, the ecological experimental technology of potato growing requires reducing the number of drives between the rows. Applying the common technology, the soil crumbling index reached 78.5% using the tractor T-25, and 82.9% using the tractor MTZ-82. Applying the experimental technology, these indices were 73.0% and 78.7% respectively. The potato plant mass grown applying the traditional technology and using the T-25 tractor (with narrower tyres) was by 30.2% larger than the plant mass grown using the MTZ-82 tractor (wider tyres). In the mulched soil with a lower compaction value, the potato plant mass was even by 46.1% larger.