Anaerobic digestion and gasification coupling for wastewater sludge treatment and recovery

Abstract

Sewage sludge management is an energy intensive process. Anaerobic digestion contributes to energy efficiency improvement but is limited by the biological process. A review has been conducted prior to experimentation in order to evaluate the mass and energy balances on anaerobic digestion followed by gasification of digested sludge. The purpose was to improve energy recovery and reuse. Calculations were based on design parameters and tests that are conducted with the anaerobic digester of a local wastewater treatment plant and a small commercial gasification system. Results showed a very significant potential of energy recovery. More than 90% of the energy content from sludge was extracted. Also, approximately the same amount of energy would be transferred in both directions between the digester (biogas) and the gasifier (thermal energy). This extraction resulted in the same use of biogas as the reference scenario but final product was a totally dry biochar, which represented a fraction of the initial mass. Phosphorus was concentrated and significantly preserved. This analysis suggests that anaerobic digestion followed by dehydration, drying and gasification could be a promising and viable option for energy and nutrient recovery from municipal sludge in replacement of conventional paths.

New opportunities for agricultural digestate valorization: current situation and perspectives

“…For instance, in a recent study, Zhong et al, (2015) investigated the production of sustainable biodiesel by combining AD and aerobic fungal fermentation of solid digestate for biogas and lipids production 194 . Similarly, few studies focused on solid digestate conversion through other thermo-chemical processes, like gasification, but these mainly concern digestate from wastewater sludge 195,196 . Hoffman et al (2013) modelled an integrative-cascade process by combining AD and hydrothermal liquefaction 105 .…”

Life cycle assessment indicators of urban wastewater and sewage sludge treatment

“…biogas and syngas production) is an important energy source, capable to sensibly reduce plant's dependency on fossil resources, thus mitigating its energy-related environmental burdens. To this end, the combined application of anaerobic digestion, dehydration and gasification has proved to be one of the most promising technologies in terms of both energy recovery and sludge mass reduction (Lacroix et al, 2014;Cao and Pawlowski, 2013). The latter gain is also noteworthy, as the delivery and disposal of sludge have resulted to be among the most important contributions to the environmental profile of WWTPs (Corominas et al, 2013).…”

The nexus of syntrophy‐associated microbiota in anaerobic digestion revealed by long‐term enrichment and community survey

“…Anaerobic digestion (AD) process is an essential technology that effectively decomposes organic compounds in wastewater and produces methane gas (CH 4) as a reusable energy source. Almost all of the municipal sewage treatment plants operated with AD to decompose excess sludge generated from aerobic activated sludge process (Angelidaki et al, 2003;Lacroix et al, 2014). In addition, more than 2200 AD in various configurations, including for example anaerobic fluidized bed, upflow anaerobic sludge blanket and expanded granular sludge blanket, are widely operated worldwide to treat industrial wastewater (Lettinga, 1995;van Lier et al, 2008).…”