Resource recovery and waste-to-energy from wastewater sludge via thermochemical conversion technologies in support of circular economy: a comprehensive review

Abstract

With the rapid rise in global population over the past decades, there has been a corresponding surge in demand for resources such as food and energy. As a consequence, the rate of waste generation and resultant pollution levels have risen drastically. Currently, most organic solid wastes are either land applied or sent to landfills, with the remaining fraction incinerated or anaerobically digested. However, with the current emphasis on the reduction of emissions, nutrient recovery, clean energy production and circular economy, it is important to revisit some of the conventional methods of treating these wastes and tap into their largely unrealized potential in terms of environmental and economic benefits. Wastewater sludge, with its high organic content and fairly constant supply, provides a great opportunity to implement some of these strategies using thermochemical conversion technologies, which are considered as one of the alternatives for upcycling such waste streams. This paper summarizes the results of prominent studies for valorizing wastewater sludge through thermochemical conversion technologies while drawing inferences and identifying relationships between different technical and operating parameters involved. This is followed by sections emphasizing the environmental and economic implications of these technologies, and their corresponding products in context of the broader fields of waste-to-energy, nutrient recycling and the progress towards a circular economy.

Review of Thermochemical Technologies for Water and Energy Integration Systems: Energy Storage and Recovery

“…This type of technologies may also be referred as Wastewater-to-energy (WWtE) technologies and subsists not in the direct use of discharge water and waste heat streams as valorized water and energy inputs, respectively. Rather, these subsist on the use of the liquid water streams or the sludge streams which result as by-products in WWT units for the production of additional quantities of fuels [51]. The selected energy recovery technologies have been chosen based on its adequacy in terms of the produced fuels bearing considering the end-users, namely, combustion-based thermal processes.…”

“…Hydrogen production based on the use of fossil fuels (such as natural gas and coal) represents 95% of the total produced hydrogen, while the remaining 5% correspond to water electrolysis [51,[55][56][57]. Presently, electrolysis is the most mature green hydrogen technology, and the one with highest technology readiness level (TRL).…”

Alternativas para la estabilización de lodos generados en estaciones depuradoras de aguas residuales desde un enfoque sistémico: una revisión

“…A nivel mundial, el crecimiento demográfico y la demanda del agua hacen que los volúmenes de aguas residuales se eleven cada día más (Bora et al, 2020;Patel et al, 2019;Potisek-Talavera et al, 2010). Las diferentes actividades productivas y domésticas producen grandes cantidades de aguas residuales y por ende de lodos.…”

“…Esto causa que sea de gran preocupación la gestión que se les da a dichos residuos, ya que ponen en riesgo la salud y el medio ambiente (Castillo et al, 2020;Magee et al, 2018;Meng et al, 2016). No obstante, estos tienen un gran contenido de materia orgánica que generan frecuentemente, brindando así múltiples oportunidades de implementar modelos o estrategias de reutilización (Bora et al, 2020).…”

Retrofitting Municipal Wastewater Treatment Facilities toward a Greener and Circular Economy by Virtue of Resource Recovery: Techno-Economic Analysis and Life Cycle Assessment

“…These resources, if properly recovered, would offset energy use and significantly reduce the environmental impacts induced by WW treatment. By 2050, approximately 66% of the world population is expected to concentrate in the urban area, exerting critical pressure on the urban WW infrastructure. , The conventional practice of WW treatment, however, is typically energy-intensive and wasteful of nutrients, , which further intensifies the need for upgrading the existing WW infrastructure . Simply expanding the WW service system is an ill-considered option due to the competition of land use with the city development, and new facilities are capital cost-prohibitive for many municipalities running local WWTFs.…”