Valorisation of residues from municipal wastewater sieving through anaerobic (co-)digestion with biological sludge

Abstract

The Circular and Green Economy principles is inspiring new approaches to municipal wastewater treatment plants (MWWTPs) design and operation. Recently, an ever-growing interest is devoted to exploring the alternatives for switching the WWTPs from being able to ‘simply’ removing contaminants from water to biorefinery-like plants where energy and material can be recovered. In this perspective, both wastewater and residues from process can be valorised for recovering nutrients (N and P), producing value added products (i.e. biopolymers), energy vectors and biofuels (i.e. bio-H2, bio-CH4 and bioethanol). As an additional benefit, changing the approach for WWTPs design and operation will decrease the overall amount of landfilled residues. In this context, the present research is aimed at evaluating the CH4 production potential of MWW screening units’ residues. While such a stream is typically landfilled, the expected progressive increase of biodegradable matter content due to the ban on single-use plastic along with the boost of bioplastics makes the investigation of different biochemical valorisation routes more and more interesting from an environmental and economical perspective. Thus, a full-scale data collection campaign was performed to gain information on screening residues amount and properties and to analyse the relationship with influent flowrate. The most relevant residue properties were measured, and lab-scale tests were carried out to evaluate the bio-CH4 potential.

Waste to Energy from Municipal Wastewater Treatment Plants: A Science Mapping

“…These terms continue to evolve to be applied for wastewater treatment plants as a solution to generate the highest benefit from these facilities and represent a step forward to pave the way for a bio-based circular economy and the obtaining of bio-based chemicals, biofuels, bioenergy, and food [31]. Thus, moving towards a circular economy, WWTPs are now conceived as biorefineries because both wastewater and residues from them can be valorised for recovering nutrients, and producing value-added products, energy vectors, and biofuels [15]. Although the sizes of the circles of keywords in cluster 4 are similar, they are slightly larger in the case of microalga, in reference to a bio-treatment that is particularly attractive because of their photosynthetic capabilities, converting solar energy into useful biomasses and incorporating nutrients such as nitrogen and phosphorus, causing eutrophication [32].…”

“…The absence of keywords that address the treatment of screening waste, from the point of view of obtaining energy, as a viable alternative to its current landfill disposal [15,18,35] shows the low interest in this type of waste because it has historically been an unrepresented part of the waste generated compared to sludge [46]. In fact, only some works have dealt with the possible application of anaerobic digestion [15][16][17][18], and they have reported difficulties in the process because of the presence of plastics and textiles [31] and a low methane production yield because it requires higher biomass concentrations [15].…”

“…The absence of keywords that address the treatment of screening waste, from the point of view of obtaining energy, as a viable alternative to its current landfill disposal [15,18,35] shows the low interest in this type of waste because it has historically been an unrepresented part of the waste generated compared to sludge [46]. In fact, only some works have dealt with the possible application of anaerobic digestion [15][16][17][18], and they have reported difficulties in the process because of the presence of plastics and textiles [31] and a low methane production yield because it requires higher biomass concentrations [15]. However, the higher fraction of sanitary textiles and other fractions, such as paper and cardboard, vegetables, and plastics, translate into a lower calorific value and low values on the chlorine and mercury contents; therefore, it could be considered suitable to produce solid fuel recovered for energy recovery in thermochemical processes [46].…”

“…Waste to Energy (WtE) technologies have been extensively applied to produce energy from sludge produced from municipal WWTPs, including the production of biogas from the digestion [9] and co-digestion [7] of the sludge, which is converted in a combined heat and power system into electricity and heat; biodiesel production [10]; combustion [11] and co-combustion [12]; gasification [13] and pyrolysis [14]. In relation to waste from the pretreatment process, only some studies have analyzed the application of anaerobic digestion [15][16][17][18].…”

Analysing the Sustainability of the Production of Solid Recovered Fuel from Screening Waste

“…Screening is a waste with a high moisture content and is described as a solid mixture of organic matter, sanitary textiles, paper and plastics [3]. It generally has no energy recovery within the circular economy guidelines [4] and is mainly disposed of in landfills, generating economic and environmental problems [5]. In Europe, landfill is bound to disappear since, with the new restrictions raised in Directive 850/2018 in 2035, the amount by weight of municipal waste deposited in landfill will have to be reduced to a maximum of 10% of the total [6].…”