Assessment of Excess Sludge Ultrasonic, Mechanical and Hybrid Pretreatment in Relation to the Energy Parameters

Anaerobic digestion is the most common stabilization process at large sewage treatment plants. To improve its effects, a sludge pre-conditioning process called disintegration is recommended. The aim of the presented study was to compare the direct effects of various types of mechanical disintegration, performed for the same excess sludge, in relation to the energy parameters and effectiveness of the process. Four different disintegration methods were used: mechanical disintegration in semi-technical and laboratory scale homogenizing mixers, ultrasonic disintegration (US) and combined (hybrid) process. The disintegration was performed for volumetric energy EV = 4.67–100 kWh m−3, the results were evaluated based on dispersion (kdCOD, kdCST), lysis (kdSCOD), acidification (kdVFA) and nutrient release (kdTN, kdTP) disintegration indicators. The statistical analysis of the results indicates the influence of disintegrator type (mixer/US/hybrid), scale (laboratory/semi-technical) and energy input on the direct results of disintegration. Hybrid disintegration delivered better direct results than two pre-treatment processes used separately. The efficiency of the hybrid process defined as the increase of the indicator (disintegration products—∆FCOD, ∆SCOD) per unit of energy was considerably higher than for a single stage disintegration process