Application of Hydrodynamic Cavitation in the Disintegration of Aerobic Granular Sludge—Evaluation of Pretreatment Time on Biomass Properties, Anaerobic Digestion Efficiency and Energy Balance

Abstract

The use of aerobic granular sludge is a promising and future-proof solution for wastewater treatment. The implementation of this technology requires the development of efficient and cost-effective methods for the management of excess sludge. The aim of the research was to evaluate the effects of hydrodynamic cavitation on the efficiency of aerobic granular sludge digestion. Respirometric measurements were performed at a temperature of 38 °C and an initial organic load of 5.0 gVS/L. The changes in the properties of the pretreated biomass, the kinetics of methane fermentation, the amount and composition of the biogas produced, and an energetic evaluation of the process were carried out. A significant influence of hydrodynamic cavitation on the transfer of organic compounds into the dissolved phase was demonstrated. The degree of solubilisation was 37% for COD and 42% and for TOC. The efficiency of CH4 production from the pretreated sludge reached a value of 496 ± 12 mL/gVS, which corresponds to an increase of 19.6% compared to the raw biomass. The influence of cavitation on the CH4 content of the biogas was not observed. Strong correlations were found between the efficiency of anaerobic digestion and the concentration of dissolved organic compounds and the hydrodynamic cavitation time used. The gross energy yield was closely correlated with the amount of CH4. The highest comparable values of 3.12 Wh/gTS to 3.18 Wh/gTS were found in the variants in which the hydrodynamic cavitation (HC) time was between 15 min and 50 min. The highest net energy production of 2890 kWh/MgTS was achieved after 15 min of pretreatment.

Optimisation of Biogas Production in the Co-Digestion of Pre-Hydrodynamically Cavitated Aerobic Granular Sludge with Waste Fats

“…Prior to the AD process, the AGS separated in the secondary settling tank and concentrated to 4.9 ± 0.2% TS was subjected to hydrodynamic cavitation (HC) for 15 min. Detailed information on the origin of the AGS and the design data of the HC used were presented in a previous research paper by the authors [25]. In these experiments, optimisation work was carried out to determine the most effective pre-treatment time in terms of methane production and energy balance.…”

“…In these experiments, optimisation work was carried out to determine the most effective pre-treatment time in terms of methane production and energy balance. The highest technological and economic effects were achieved in the variant in which the HC time was 15 min [25]. Therefore, such a disintegrated AGS was used in the AD with WF.…”

“…In variant 1 (V1), which served as a reference for the subsequent research phases, AD was exposed to the AGS monosubstrate, which was pretreated with HC for 15 min [25]. The basis for the selection of the pretreatment time was a multivariate investigation aimed at obtaining the highest technological effect in terms of CH 4 production, as well as the operational and economic effect resulting from the energy balance performed [25]. The hydration of the AGS used was 4.91 ± 0.18% with a VS content of 72.9 ± 1.1%TS.…”

“…The experiments presented are directly in line with current trends in the development of biorefinery systems and make a significant new contribution to the current state of knowledge on AGS fermentation processes. The work describes the next step in multi-stage AD optimisation research, following the previous selection of the hydrodynamic cavitation process parameters [25]. This is the first report in which the performance of AC-D subjected to AGS pretreatment was analysed with a high lipid concentration of waste fats (WF) from the poultry sector.…”

The Use of Hydrodynamic Cavitation to Improve the Anaerobic Digestion of Waste from Dairy Cattle Farming—From Laboratory Tests to Large-Scale Agricultural Biogas Plants

“…Recently, attention has been paid to the possibility of building and using HC generators to intensify biological processes, including the treatment of toxic [41] and biodegradable [42] wastewater, the stabilisation of sewage sludge [43], including granulated sludge [44], or to increase the efficiency of bioenergy technologies, including methane [45] or hydrogen fermentation [46] as well as the production of bioethanol [47] and biodiesel [48]. The results of the experimental work carried out so far indicate efficient destruction of complex organic structures present in the pretreated medium, which increases the efficiency of their further conversion, transformation and biodegradation by specialised groups of microorganisms [49].…”