Evaluating an anaerobic digestion (AD) feedstock derived from a novel non-source segregated municipal solid waste (MSW) product
Introduction
Although 84% of MSW is collected globally, only 15% is currently recycled (Zaman, 2016) and, regardless of country income, landfilling is the predominant disposal route (Zaman, 2016). Although the European Directive on Landfill of Waste (European Commission, 1999) has reduced the disposal of biodegradable municipal waste to landfill (Bulkeley et al., 2005, Edwards et al., 2015) a wide variation (5–80%) in diversion rates still exists amongst member states (European Commission, 2015). The European Commission is currently developing a long term vision to address this disparity (European Commission, 2015), however, in countries where diversion of biodegradable waste from landfill has increased from a low baseline such gains have more recently reduced or plateaued. For instance, the UK increased diversion from 11% in 2000–2001 to 43.2% in 2011–2012 (DEFRA, 2012), however, the rate of progress has reduced year on year since 2005 and from 2012 to 2013 the diversion rate only increased by 0.3% (DEFRA, 2013). Often source-segregation is advocated as a ‘key to the success’ in non-landfill waste management systems (Yang et al., 2011), but, success is determined by the complex interplay of environmental, economic, and social factors (Di Maria et al., 2016, Tavares et al., 2009, Rispo et al., 2015, Bulkeley and Gregson, 2009) interacting within changing governance and political systems (Bulkeley et al., 2005). Interestingly, Rispo et al. (2015) has suggested that source-segregation may be particularly challenging within hard to reach high density urban communities. We suggest that to realise a ‘resource efficient, circular economy’ where biodegradable waste becomes a valued resource (DEFRA, 2015, European Commission, 2015), novel and diverse approaches to municipal waste management will be essential including where source-separation is not favoured, practicable, or financially viable (DEFRA, 2013).
Biogas production from ‘waste products’ by Anaerobic Digestion (AD) is often described as an environmentally sympathetic, and economic method of fuel and ‘nutrient-rich fertiliser’ generation (Bolzonella et al., 2006, DEFRA, 2010, Tambone et al., 2010, Di Maria et al., 2013, Massaccesi et al., 2013). AD is, therefore, an important means (Fricke et al., 2005) of addressing the interconnected issues of: sustainable waste management (European Commission, 1999, Edwards et al., 2015); renewable energy provision, and; ‘stabilisation of greenhouse gas (GHG) emission rates’ (UNFCCC, 1997, Beurskens et al., 2011). However, slow adoption of AD within non-agricultural settings is often attributed to availability of high quality secure feedstocks, and limited potential to develop economically and environmentally sustainable markets or disposal routes for the resulting digestates (Brooks and Maxwell-Jackson, 2012, WRAP, 2013, Bulkeley et al., 2005) which are governed by regulatory requirements at both broad international and specific national levels (Saveyn and Eder, 2014). Critically, a common feature of compliance for primary waste feedstocks is their segregated at source (WRAP, 2011, Saveyn and Eder, 2014). Feedstocks produced from non-source segregated materials may require extensive pre-treatments, produce lower or variable biogas yields, and also require more intensive post treatments of liquids and solids discharged from the reactors (Di Maria et al., 2012); all of which will require additional investment and have higher operational costs.
Since the 1990s there has been increasing interest in development and introduction of industrial scale MSW processing facilities aimed at enhancing the recovery and reuse of high value materials from non-source segregated MSW (e.g. Mechanical Biological Treatment) (Gioannis et al., 2009, Montejo et al., 2013). A number of these processes include stabilisation of biodegradable materials, through composting or AD, as a stage within a sorting and separation process (Fricke et al., 2005) e.g. SORting- DIgestion- SEPeration (SORDISEP) (Torfs et al., 2005). In parallel, in the last 25 years, autoclaving has gained interest as a mechanism for the treatment of clinical solid waste, household waste, and non-source segregated MSW (e.g. DEFRA, 2013, Garcia et al., 2012), and it is thought that this process may be applied further e.g. to the rejected fractions of mechanical biological treatment (MBT) to maximise recycling rates (Garcia et al., 2012). Autoclaving is a hydrothermal high pressure treatment process (from temperatures of 121 °C to 145 °C and pressures of up to 3 Bar) routinely used in the decontamination of infectious lab waste, clinical and dental tools. Autoclaving is less physically aggressive than steam explosion which is typically carried out at higher temperatures (of 160–260 °C) and pressures (of 6.9–48.3 Bar), and which are accompanied by a rapid pressure release (e.g. 20 s duration) which aids material transformation e.g. in wood products (Teghammar et al., 2010, Vochozka et al., 2016).
With regard to treatment of mixed household and MSW, autoclaving has been shown to have the potential to reduce the initial volume of waste (through maceration and compaction; Garcia et al., 2012), which if combined with post autoclave material segregation can divide recyclable materials into separate fractions (i.e. glass, plastic, ferrous metals, non-ferrous metals, textiles), and result in the production of a single unified organic material product (Garcia et al., 2012). To date studies of this treatment method have often been carried out using synthesised waste materials, at relatively small lab, or pilot, scale (Houltman et al., 2016, Papadimitriou et al., 2008, Papadimitriou, 2010). Within this study we use a full capacity industrial scale rotational autoclave (roto-autoclave) process as a model system for the production of an AD feedstock from non-source segregated MSW. The aim of this study was to assess both the quality and consistency of this fibrous material produced in this process: in terms of physical, chemical and biological attributes (Fig. 1), and to compare these with commonly used anaerobic digestion feedstocks, and with existing regulations.
Section snippets
Processing
The industrial process was run at full capacity utilising local authority derived MSW for 10 consecutive days. Successive non-sorted batches of the MSW (12 × 20 tonne batches in a 24 h period) were treated by roto-autoclaving, at 140 °C for 45 min at a maximum pressure of 3 bar before depressurisation and cooling (20 min). This process was followed by extensive semi-continuous mechanical separation which included an initial finger screen which removed large items (>200 mm), followed by; air separation,
Quality and consistency of fibrous material
The process of roto-autoclaving produced a visually homogeneous material, which was confirmed as free of pathogen indicator organisms typically present in untreated MSW (i.e. Salmonella (<10 C.F.U/25 g material) and E. coli (<10 C.F.U/g material). Subsequent mechanical separation produced segregated waste streams including the fibrous material. This fibrous material, as received, had an approximately neutral pH (average 7.1 (±0.25), an average moisture content of 44.2 (±2.33)%, C:N ratio of
Bulk characteristics
The composition of untreated municipal solid waste is known to be extremely heterogeneous, as such its composition is predominantly ‘deemed’ visually, rather than characterised by physical or chemical analysis (ASTM D5231-92, 2008). In contrast to MSW the visual and physical composition of the novel fibrous material presented in this study was both spatially and temporally homogenous (over the trial period) at the macro and micro-scale (Fig. 2). Similarly, in contrast to unprocessed source
Conclusion
Within the current EU regulatory landscape, tension exists between protecting the environment, and supporting the development of innovative approaches to waste management. We suggest that use of non-source segregated MSW derived products (produced by autoclaving and mechanical separation) could effectively divert large volumes of mixed waste from landfill, while producing secure, high quality feedstocks for biogas production. We have described a novel homogeneous non-source segregated MSW AD
Acknowledgements
(KTP007181), Graphite Resources Ltd and Newcastle University (2009–2012). All samples were provided by Graphite Resources Ltd. The FT-IR and TG-DSC was funded specifically by Technical Strategy Board (SBRI 048) and Newcastle University Institute for Sustainability. The authors gratefully acknowledge Bernard Bowler for his guidance in the TG-DSC analysis, and Jamie Blake in manuscript preparation.
References (84)
- et al.
Ultrasound-assisted extraction of emerging contaminants from environmental samples
Trends Analyt. Chem.
(2015) - et al.
Characteristics of the organic fraction of municipal solid waste and methane production: a review
Waste Manage.
(2016) - et al.
Inhibition of anaerobic digestion process: a review
Bioresour. Technol.
(2008) - et al.
Methane yield in source-sorted organic fraction of municipal soil waste
Waste Manage.
(2007) - et al.
Landfill gas generation after mechanical biological treatment of municipal solid waste. Estimation of gas generation rate constants
Waste Manage.
(2009) - et al.
Energy production from mechanical biological treatment and composting plants exploiting solid anaerobic digestion batch: an Italian case study
Energy Convers. Manage.
(2012) - et al.
Impact of the pre-collection phase at different intensities of source segregation of bio-waste: an Italian case study
Waste Manage.
(2016) - et al.
A review of policy drivers and barriers for the use of anaerobic digestion in Europe, the United States and Australia
Renew. Sustain. Energy Rev.
(2015) - et al.
Use of thermal analysis techniques (TG-DSC) for the characterization of diverse organic municipal waste streams to predict biological stability prior to land application
Waste Manage.
(2012) - et al.
Comparison of selected aerobic and anaerobic procedures for MSW treatment
Waste Manage.
(2005)
Biological treatment of the organic fibre from the autoclaving of municipal solid wastes: preliminary results
Biosyst. Eng.
Composition of source-sorted municipal organic waste collected in Danish cities
Waste Manage.
The steady state anaerobic digestion of Laminaria hyperborean- effect of hydraulic residence on biogas production and bacterial community composition
Bioresour. Technol.
Production of fermentable sugars from enzymatic hydrolysis of pretreated municipal solid waste after autoclave process
Fuel
Coupling of thermal analysis with quadrupole mass spectrometry and isotope ratio mass spectrometry for simultaneous determination of evolved gases and their carbon isotopic composition
J. Anal. Appl. Pyrol.
Anaerobic digestion of municipal solid waste and agricultural waste and the effect of co-digestion with dairy cow manure
Bioresour. Technol.
Anaerobic co-digestion of the organic fraction of municipal solid waste with FOG waste from a sewage treatment plant: recovering a wasted methane potential
Waste Manage.
Chemical characterisation of percolate and digestate during the hybrid solid anaerobic digestion batch process
Process Biochem.
Mechanical-biological treatment: performance and potentials. An LCA of 8 MBT plants including waste characterization
J. Environ. Manage.
The impact of separation on heavy metal contaminants in municipal solid waste composts
Biomass Bioenergy
Source segregation and food waste prevention activities in high-density households in a deprived urban area
Waste Manage.
Processing of urban and agro-industrial residues by aerobic composting
Rev. Energy Convers. Manage.
A critical review of the bioavailability and impacts of heavy metals in the municipal solid waste
Environ. Int.
Characterisation of source-separated household waste intended for composting
Bioresour. Technol.
Assessing amendment and fertilising properties of digestates from anaerobic digestion through a comparative study with digested sludge and compost
Chemosphere
Optimisation of MSW collection routes for minimum fuel consumption with 3D GIS modelling
Waste Manage.
Pretreatment of paper tube residuals for improved biogas production
Bioresour. Technol.
Anaerobic co-digestion of food waste and straw for biogas production
Renew. Energy
A comprehensive study of the environmental and economic benefits of resource recovery from global waste management systems
J. Clean Prod.
Characterisation of food waste as feedstock for anaerobic digestion
Bioresour. Technol.
A Biogas Road Map for Europe, Brussels, Belgium
Composition variability of the organic fraction of municipal solid waste and effects on hydrogen and methane production potentials
Waste Manage.
Standard Test Method for Determination of the Composition of Unprocessed Municipal Solid Waste
Standard Guide for Sampling Strategies for Heterogeneous Wastes (Withdrawn 2015)
Standard Guide for Composite Sampling and Field Subsampling for Environmental Waste Management Activities
Renewable Energy Projections as Published in the National Renewable Energy Action Plans of the European Member States: Covering All 27 EU Member States
Dry anaerobic digestion of differently sorted organic municipal solid waste: a full-scale experience
Water Sci. Technol.
Hit the Gas: How to Get the Anaerobic Digestion Sector Moving. Centre Forum report
Solid Biofuels. Determination of Calorific Value
Solid Biofuels. Determination of Total Content of Carbon, Hydrogen and Nitrogen. Instrumental Methods
Characterisation of Waste. Determination of Selected Polychlorinated Biphenyls m(PCB) by Using Capillary Gas Chromatography With Electron Capture or Mass Spectrometric Detection
Solid Recovered Fuels. Determination of Moisture Content Using the Oven Dry Method. Moisture in General Analysis Sample
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2022, Science of the Total EnvironmentCitation Excerpt :Despite the, albeit small, difference of mesh sizes of the sieves, a relatively low variation in the TS, VS and BMP results existed for the analyzed period. Blake et al. (2017) also observed a temporal and spatial homogeneity in the physical and visual composition of the pretreated residual waste <12 mm. Thus, after mechanical pretreatment processes and the removal of impurities (e.g. glass, metals, plastics, electronics scraps, etc.), the homogeneity of the residual waste increases.
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2021, Journal of Cleaner ProductionCitation Excerpt :Published papers including secondary data were discarded and the source of the primary data was entered in the database (Appendix B, Table B1). The studies where the OFMSW is separated by the use of chemicals, water (Dong et al., 2010) or autoclaving process (Blake et al., 2017) were rejected. The bibliography was further screened for relevant papers using the snowball method.