Evaluation of conventional and alternative anaerobic digestion technologies for applications to small and rural communities

From Circular Economy to Circular Ecology: A Review on the Solution of Environmental Problems through Circular Waste Management Approaches

“…The publications summarized in Tables 1-4 present different methods to solve environmental problems through circular approaches and combining heterogeneous processes, i.e., by applying CE L principles. Among the papers proposing new circular approaches for WM, the majority of them propose solutions to generate valuable products (e.g., adsorption materials, cellulose, chemicals, biofuels, fertilizers and soil improvers from agro-forestry, and zootechnical and food waste) [97,99,[102][103][104][105][106]110,111,113,[117][118][119][120][121]124,131,133,135,141], recover precious nutrients [128,134,136,137], exploiting sustainable sources of energy [45,100,101,109,110,114,115,123,125], and eliminate residual waste [112,126,129,132,[138][139][140].…”

“…The authors applied the index to municipal solid waste, considering recycling and reuse as positive contributors to CE, and incineration and landfilling as negative contributors. However, waste-to-energy processes (including incineration) still play a fundamental role in an integrated WM vision aimed at minimizing the impacts on the environment [45]. The concept of Life Cycle Thinking (LCT) was introduced to assess the impacts of WM by considering the whole supply chain, from raw material extraction and conversion, manufacture and distribution, use and/or consumption, to treatment and disposal [46].…”

“…The wet process allows for higher biogas production but implies higher soil occupation. [45] WM-Agroforestry waste…”

Circular Economy Concepts Applied to Waste Anaerobic Digestion Plants

“…The anaerobic co-digestion (AcoD) is a solution proposed in real scale in order to manage the problems indicated above and to be in concordance with the CE concepts and can be used for small and large communities [63]- [65]. AcoD consists of a mixture of two or more biodegradable substrates as raw and conventional biomasses, wastewater sludge, manure, agricultural waste, etc.…”

“…AcoD consists of a mixture of two or more biodegradable substrates as raw and conventional biomasses, wastewater sludge, manure, agricultural waste, etc. The advantages of the AcoD are recognized at national and international level: nutrients balance, degradation rates and buffer capacity and digestate stability improvements, dilution of toxics and/or inhibitory compounds [65]- [69]. Moreover, when applied to an existing plant of mono-digestion (specifically of wet digestion), the advantage is an increased exploitation of the volume already available; however, verifications must be made to the compatibility (or upgradability) of each step of the plant; receiving, pre-treatment and feeding stages, maximum viable load, bulky agent availability for the increased post-treatment stream, final refining efficiency with the new stream; additionally, the increased biogas production must be analysed in terms of compatibility with the existing treatments and exploitation devices (e.g.…”