The effects of digestate pyrolysis liquid on the thermophilic anaerobic digestion of sewage sludge - Perspective for a centralized biogas plant using thermal hydrolysis pretreatment

Towards the implementation of hydrothermal carbonization for nutrients, carbon, and energy recovery in centralized biogas plant treating sewage sludge

In recent years, extensive experimental research on hydrothermal carbonization (HTC) of sewage sludge has been performed, to study the effects of process conditions on hydrochar characteristics and nutrient, carbon, and energy recovery from sewage sludge. To promote the implementation of HTC, this study assessed HTC (230 °C, 30 min) integration into an advanced centralized biogas plant by analyzing its theoretical effects on the fates of sewage sludge solids, nitrogen, phosphorus, and carbon. The study used the mass and nutrient flows and concentrations obtained from laboratory studies, and the studied biogas plant had an original layout that employed hygienization. HTC integration decreased the solid product volume by up to 56 % and, increased the recovery of ammonium in ammonia water by 33 % and methane by 1.4 %, while increasing the biogas plant energy demand by 4 %. The changes in the nutrient and solids flows and their recovery potentials show the need to consider the rearrangements of the liquid and gas flows in the biogas plant and the re-dimensioning of stripping process.

Evolution and Prospects in Managing Sewage Sludge Resulting from Municipal Wastewater Purification

Municipal sewage sludge is the residual material produced as a waste of municipal wastewater purification. It is a sophisticated multi-component material, hard to handle. For many years, it has been landfilled, incinerated, and widely used in agriculture practice. When unproperly discharged, it is very polluting and unhealthy. The rapidly increasing global amount of municipal sewage sludge produced annually depends on urbanization, degree of development, and lifestyle. Some diffused traditional practices were banned or became economically unfeasible or unacceptable by the communities. In contrast, it has been established that MSS contains valuable resources, which can be utilized as energy and fertilizer. The objective of the review was to prove that resource recovery is beneficially affordable using modern approaches and proper technologies and to estimate the required resources and time. The open sources of information were deeply mined, critically examined, and selected to derive the necessary information regarding each network segment, from the source to the final point, where the municipal sewage sludge is produced and disposed of. We found that developed and some developing countries are involved with ambitious and costly plans for remediation, the modernization of regulations, collecting and purification systems, and beneficial waste management using a modern approach. We also found that the activated sludge process is the leading technology for wastewater purification, and anaerobic digestion is the leading technology for downstream waste. However, biological technologies appear inadequate and hydrothermal carbonization, already applicable at full scale, is the best candidate for playing a significant role in managing municipal sewage sludge produced by big towns and small villages.