Characterisation and perspectives of energetic use of dissolved gas recovered from anaerobic effluent with membrane contactor

Co-digestion and co-treatment of sewage and organic waste in mainstream anaerobic reactors: operational insights and future perspectives

The global shift towards sustainable waste management has led to an intensified exploration of co-digestion and co-treatment of sewage and organic waste using anaerobic reactors. This review advocates for an integrated approach where organic waste is treated along with the sewage stream, as a promising solution to collect, treat, and dispose of organic waste, thereby reducing the environmental and economic burden on municipalities. Various efforts, ranging from laboratory to full-scale studies, have been undertaken to assess the feasibility and impacts of co-digestion or co-management of sewage and organic waste, using technologies such as up-flow anaerobic sludge blankets or anaerobic membrane bioreactors. However, there has been no consensus on a standardized definition of co-digestion, nor a comprehensive understanding of its impacts. In this paper, we present a comprehensive review of the state-of-the-art in liquid anaerobic co-digestion systems, which typically operate at 1.1% total solids. The research aims to investigate how the integration of organic waste into mainstream anaerobic-based sewage treatment plants has the potential to enhance the sustainability of both sewage and organic waste management. In addition, utilizing the surplus capacity of existing anaerobic reactors leads to significant increases in methane production ranging from 190 to 388% (v/v). However, it should be noted that certain challenges may arise, such as the necessity for the development of tailored strategies and regulatory frameworks to enhance co-digestion practices and address the inherent challenges.

The dissolved methane recovery from treated sewage in upflow anaerobic sludge blanket (UASB) reactors: The energy demand, carbon footprint and financial cost

The goal of this research was to quantify the energy demand and carbon footprint over the life cycle, along with the financial cost, of sewage treatment with the recovery of dissolved methane (d-CH₄). The sewage treatment is composed of pre-treatment, followed by treatment in upflow anaerobic sludge blanket (UASB) reactors, trickling filter and secondary decanter, post-treatment with disinfection, and biogas recovery in the three-phase separator of the UASB reactor. The methods used in this study were attributional life cycle assessment and techno-economic analysis - LCA and TEA, respectively. The energy demand, carbon footprint and financial cost for 1 m³ sewage treatment in the evaluated scenario without d-CH₄ recovery (S1) were 3.4 MJ, 1.7 kg CO₂eq and 0.17 USD respectively, while those with d-CH₄ recovery (S2) varied by 12%, -16% and 2.3% compared to S1. The produced biogas for lower heating value in S2 (2.6 MJ) was 27% higher than that in S1 (2.0 MJ) and this varied from 1.3 MJ to 4.6 MJ in the scenarios for different influent chemical oxygen demand (COD) in the sewage treatment plant (STP) and COD removal efficiency in the UASB reactor. The highest eco-efficiency for 1 MJ heat production from the STP biogas was achieved in the scenario with d-CH₄ recovery, higher influent COD, higher COD removal efficiency in the UASB reactor, d-CH₄ saturation, photovoltaic electricity supply, and a higher energy efficiency in d-CH₄ recovery combined (S2,COD+,R+,S,PV,EE+), which reduced the energy demand by 55%, carbon footprint by 66% and financial cost by 63% compared to S1. Furthermore, the STP functionality change from a single-product (biogas) to a multi-product (biogas, water for reuse and biosolid fertilizer) approach (S1,WR, BF and S2,WR,BF) made the biogas a competitive product compared to those from fossil sources. Therefore, resource recovery from the sewage treatment in higher influent COD, higher COD removal efficiency, the use of a more efficient, clean and economical electricity source and higher energy efficiency in d-CH₄ recovery in a multi-product STP contribute to achieving the energy self-sufficiency over the life cycle while reducing the carbon footprint and financial cost of its products.