Incineration of sewage sludge and recovery of residue ash as building material: A valuable option as a consequence of the COVID-19 pandemic

https://doi.org/10.1016/j.jenvman.2021.111966Get rights and content

Highlights

  • Sewage sludge incineration is the safest choice for sewage sludge disposal during Covid-19 pandemic.

  • Sewage sludge ash (SSA) can be reused as adsorbent material and in the manufacture of building materials.

  • ESCAPE methods can be useful to evaluate the sustainability of SSA.

  • ESCAPE methods provide a fast analysis during the design phase of the product (preliminary to LCA).

Abstract

Circular economy principles were adopted by European Commission, to support a sustainable growth. They contain general rules that should be considered in all situations. At present, during pandemic, some waste disposal practices are under evaluation to guarantee safety conditions.

For example, in view of the recent results reporting the presence of SARS-CoV-2 virus in sewage sludge, the possibility that it diffuses in the environment is alarming. The situation may result critical in densely populated cities, which are the largest sources of sewage sludge. In this frame the diffused practice of reuse of this waste in agriculture is under revision.

In this context, incineration may represent a valuable alternative strategy to manage

sewage sludge during pandemic. Indeed, due to thermal treatment, the destruction of organic micropollutants and pathogens, eventually present in the waste, is guarantee.

Moreover, it is fundamental to highlight that also if the management of sewage sludge changes, the ash resulting from its combustion may have suitable reuse opportunities, and their landfilling should be avoided.

This work presents the available possibilities of sewage sludge ash recovery in building applications and shows the results obtained by the analysis of their sustainability. The approach is based on the use of embodied energy and carbon footprint values, to make a simple and fast new method able to be a suitable tool to support and promote sustainability also in critical situations (such as pandemic) and when all the information about a technology are not available, making not possible to perform a full-LCA approach.

This work aims to be not only a reference paper for promotion of strategies able to increase waste management safety, but also an example showing that circular economy principles should be pursued also if boundary conditions can change.

Introduction

With the expected future global population growth of about 500–750 million per decade, the UNEP's International Resource Panel predicts that between 2015 and 2050 material resource use may double (UNEP and IRP, 2017). Considering its high dependence on import of natural materials, EU needs to move toward circular economy (CE), to promote the circular flow and efficient resources manage, to minimize wastage, and decouple economic growth from materials extraction and consumption. Due to its expected economic, environmental, and social benefits, the CE goes beyond efficient resource use and recycling, supporting the development of a suitable framework able to promote new business models. These new models will increase value, use, and life of materials, products and assets by designing out waste from production and consumption (European Inverstment Bank, 2019). However, these models are not conceived to be effective in critical situations, such as the pandemic, the global crisis that invested all the world in 2020.

The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) was discovered in China at the end of 2019 and declared to be a pandemic by World Health Organization (WHO) in March 2020. This disease is mainly transmitted by human-to-human direct interactions (Bontempi, 2020a) (Bontempi et al., 2020). However, both asymptomatic and symptomatic people can spread the infection also through their urine and excreta (Núñez-Delgado, 2020) and for some of them, viral RNA can be found in the feces even if it was not still found in the respiratory tract (Xiao et al., 2020).

Despite that the SARS-CoV-2 viral RNA does not demonstrate that the viral particles are still infectious, its presence in the treated wastewater (Wurtzer et al., 2020) strongly suggests that suitable procedures to manage wastewater and related products must be defined. Indeed, the most diffused wastewater treatments allow the removal of suspended solids and organic matter (Droste and Gehr, 2018). Also some pathogens are generally removed, but with higher efficiency for bacteria than viruses (Dias et al., 2018). Then, through human excreta, the virus is transferred to wastewater and it may also spread in the environment. A recent work has proposed that urban flooding events caused by heavy rainfalls, with the consequence of sewage overflows, may be also related to virus transmission (Han and He, 2021).

In this frame the management of sewage sludge (SS), the waste derived from wastewater treatments, that often is used to enrich agricultural soils, may pose some sanitary issues.

Due to the fact that the main transmission route of SARS-CoV-2 infection was attributed to the inhalation of contaminated aerosols or droplets (Morawska and Cao, 2020), potential risks of virus transmission exist mainly for workers in wastewater management plants, that may directly inhale some contaminated particles (Amoah et al., 2020). Moreover, also general population may be exposed to infection risks, by proximity with not properly treated wastewater and/or SS, also considering a possible direct contact (Kampf et al., 2020). This is also due to the fact that, despite that the literature has shown that generally Coronavirus can survive out of living cells for only few days (Kampf et al., 2020), the potential spread of SARS-CoV-2 in the environment has posed some concerns related to its potential transferability in the air (Bontempi, 2020b), in the form of airborne particulate matter (Yang et al., 2020). The virus transmission possibilities are related to its capability to remain infectious in aerosol for several hours (van Doremalen et al., 2020).

This problem is noticeable because in several countries SS is re-used in agriculture, to take advantage of the nutrients it contains, such as organic matter, nitrogen, and phosphorus. In particular, the major risks are associated to some of SS not subjected to any kind of disinfection treatment, before use.

Some authors have supposed that enterovirus in soil can survive also months depending on the specific environmental conditions, and subsequent to be diffused to surface and ground waters, thus also promoting their diffusion by ingestion of contaminated water (Yang et al., 2020).

In the reported frame, it is obvious that a suitable treatment strategy must be identified, mainly in the case of SS management, to reduce the potential risks of virus transmission, that should be applied primarily during periods of sanitary crisis, when there is a high amount of infected people and a high risk of virus spread (Di Maria et al., 2020).

However, as reported for the reduction of CO2 emissions (Le Quéré et al., 2020), the current pandemic may also represent an opportunity to support sustainable strategies, as for example material recovery, in accord with the CE principles. In particular, despite the safety priority, it is fundamental to proceed in accord with all sustainability pillars, to propose reasonable alternative that may be adopted also in the next future. For example, the application of safe procedures to manage waste that may contain active virus is a current and ongoing need. Indeed, The Circular Economy Action Plan (adopted in March 2020) committed to the Commission the revision of the Sewage Sludge Directive.

Among the available strategies for SS management, in the incineration treatments, the combustion temperature is generally maintained higher than 850 °C with a waste residence in the furnace larger than 1 h (Di Maria et al., 2018). This ensures the inactivation of the SARS-CoV-2 (Chin et al., 2020) resulting in a safe waste treatment strategy. Incineration is reported to convert 1 ton of dewatered SS into around 100 kg of sterile SSA (Nakić et al., 2017).

At the present, in some nations, health institutes recommended incineration as the priority option for management of contaminated wastes (Gruppo di Lavoro ISS Ambiente-Rifiuti COVID-19, 2020).

Moreover, it is clear that the need to decrease the environmental impact of the waste management applied strategies is crucial and fundamental also in the pandemic.

Fig. 1 reports the SS production and disposal strategies for several EU countries (data from EUROSTAT, 2016). It results that SS incineration is applied as the main management option only in Austria, Germany, and Netherland.

Thermal treatments (incineration, pyrolysis, gasification) of SS are disposal alternatives that will gain importance in the future due to the important volume (up to 90%) and mass (up to 70%) reduction, and the sterility of the final obtained by-product, that can be often considered as an inert residue (Lynn et al., 2015).

SS incineration is the most used thermal technology, able to recover waste and energy. In some cases, additional fuel (other than SS) is required, mainly when high-water content SS is used. In other cases SS is co-incinerated with municipal solid waste (Assi et al., 2020a).

Moreover, it is also possible to reuse the ash derived from the incineration, i.e. the sewage sludge ash (SSA).

The possibility to recover and reuse SSA is fundamental, because it allows to apply CE concepts also as a consequence of a change of SS management, due to the pandemic.

In particular, the SSA recovery is in accord with European Green Deal and the 2020 Annual Sustainable Growth Strategy, allowing not only to obtain the material and waste recovery, but also to increase the sustainability of the water sector.

Depending on its physic-chemical characteristics, mainly six uses of SSA are proposed in literature:

  • -

    for phosphorus (P) extraction for soils organic amendment;

  • -

    for adsorbents production;

  • -

    as additives in mortars and concrete (as a pozzolanic material);

  • -

    in the manufacture of light aggregates (as for example in substitution of clay);

  • -

    in the manufacture of ceramic materials;

  • -

    in the manufacture of Portland cement clinker (Donatello and Cheeseman, 2013).

With the exception of the first two applications mentioned, almost all the proposed applications concern building sector. At present, some technologies for P extraction from SSA have been already industrially established (Schipper et al., 2001) (Weigand et al., 2013). For example, in Germany SSA is recovered to obtain materials, to be used as fertilizer (Hermann, 2013).

In the countries where the agricultural applications of SSA are still not applied, other reuse strategies have been also proposed, as for example in building sector (Smol et al., 2015).

The aim of this paper is to promote the CE principles also in crisis times and try to couple safety with environmental sustainability. In particular, wastewater disposal is a fundamental issue in the transition to a CE model, being a carrier of energy (it can be used as fuel) and materials (it contains valuable resource).

For this purpose, this work presents the environmental advantages that can take place in the SSA reuse especially addressed to building materials. Indeed, despite that several papers have already presented the possibilities of SSA reuse, at the best of authors knowledge, the evaluation of the sustainability of SSA reuse is still an open issue. This work has the ambition to be not only a reference paper contributing to promote strategies able to increase the safety in the management of some wastes (that may represent a transmission way for the SARS-CoV-2 virus), but also an example that safety and environmental advantages can be coupled in choosing the most suitable actions, with the aim to increase the sustainability.

To support this strategy, it is possible to use a simplified approach, able to evaluate the sustainability of a material, using only two parameters (embodied energy - EE and carbon footprint - CF). This new tool was recently proposed in view of a need of less onerous method (for example in comparison to a full-LCA analysis) able to evaluate the sustainability of new treatments (Bontempi, 2017a). Then, it may be a support for rapid evaluation of new business strategies, accelerating the industries resilience, in critical situations, such as the COVID-19 pandemic, with great attention to sustainability.

The proposed approach may allow to introduce new indicators in the circular economy monitoring framework, that may not be only related to the waste recovery, but also to be extended to evaluate the circularity in the water management strategies. Indeed, the SS use in farming is currently under investigation in EU: a public consultation, that has been opened in November 2020 aims to understand the views of the citizens and stakeholders about sewage sludge land spread.

Section snippets

SSA characteristics and possible applications in building sector

The extraction of natural materials (as for example aggregates) that are used in building applications is coupled with serious negative environmental effects. In particular, cement industry was evaluated as responsible for a significant portion of CO2 emissions, and of a large quantity of energy consumption. With the aim to limit the construction industry environmental impact, also the reduction of natural materials extraction is fundamental (Costa and Ribeiro, 2020). Indeed, CO2 emissions can

Results and discussion

In the case of a lack of a suitable site for land disposal, as in urban areas, SS can be incinerated and the derived SSA can be proposed as raw material in building applications. Indeed, SSA composition generally falls around the latent hydraulic and pozzolanic regions, supporting its use as a supplementary cementitious material (Lynn et al., 2015).

In several cases SSA is added for partial substitution of raw materials, such as for example Portland Cement (the substitution is generally in the

Conclusions

The EU Commission aims to define new directives for water and wastewater management to protect water resources and environment, but this needs new approaches and strategies, able to be applied also when boundary conditions can change (as for example during pandemic).

This paper aims to support the CE strategies also in particular conditions, when safety is the priority.

Although in many EU Countries SS incineration is not yet the primary choice, this is the safest option for the disposal of this

Funding

This research was partially supported by FANGHI project, financed by Regione Lombardia, in the frame of the call HUB Ricerca e Innovazione.

Authors contribution

All the authors contributed to the paper presented methodology and conceptualization. They all contributed to data analysis and paper writing.

Financial disclosure

This research was partially supported by FANGHI project, financed by Regione Lombardia, in the frame of the call HUB Ricerca e Innovazione.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (58)

  • L. Chen et al.

    Stabilization treatment of soft subgrade soil by sewage sludge ash and cement

    J. Hazard Mater.

    (2009)
  • M. Chen et al.

    Environmental and technical assessments of the potential utilization of sewage sludge ashes (SSAs) as secondary raw materials in construction

    Waste Manag.

    (2013)
  • A.W.H. Chin et al.

    Stability of SARS-CoV-2 in different environmental conditions

    The Lancet Microbe

    (2020)
  • X. Cong et al.

    Effects of microwave, thermomechanical and chemical treatments of sewage sludge ash on its early-age behavior as supplementary cementitious material

    J. Clean. Prod.

    (2020)
  • F.N. Costa et al.

    Reduction in CO2 emissions during production of cement, with partial replacement of traditional raw materials by civil construction waste (CCW)

    J. Clean. Prod.

    (2020)
  • M. Cyr et al.

    Technological and environmental behavior of sewage sludge ash (SSA) in cement-based materials

    Cement Concr. Res.

    (2007)
  • F. Di Maria et al.

    Minimization of spreading of SARS-CoV-2 via household waste produced by subjects affected by COVID-19 or in quarantine

    Sci. Total Environ.

    (2020)
  • F. Di Maria et al.

    On time measurement of the efficiency of a waste-to-energy plant and evaluation of the associated uncertainty

    Appl. Therm. Eng.

    (2018)
  • E. Dias et al.

    The application of bacteriophages as novel indicators of viral pathogens in wastewater treatment systems

    Water Res.

    (2018)
  • S. Donatello et al.

    Recycling and recovery routes for incinerated sewage sludge ash (ISSA): a review

    Waste Manag.

    (2013)
  • A. Fahimi et al.

    Evaluation of the sustainability of technologies to recover phosphorous from sewage sludge ash based on embodied energy and CO2 footprint

    J. Clean. Prod. Submitted.

    (2021)
  • J. Han et al.

    Urban flooding events pose risks of virus spread during the novel coronavirus (COVID-19) pandemic

    Sci. Total Environ.

    (2021)
  • G. Kampf et al.

    Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents

    J. Hosp. Infect.

    (2020)
  • K.L. Lin et al.

    Hydration characteristics of waste sludge ash utilized as raw cement material

    Cement Concr. Res.

    (2005)
  • W.Y. Lin et al.

    Evaluation of sewage sludge incineration ash as a potential land reclamation material

    J. Hazard Mater.

    (2018)
  • C.J. Lynn et al.

    Sewage sludge ash characteristics and potential for use in concrete

    Construct. Build. Mater.

    (2015)
  • J. Monzó et al.

    Reuse of sewage sludge ashes (SSA) in cement mixtures: the effect of SSA on the workability of cement mortars

    Waste Manag.

    (2003)
  • L. Morawska et al.

    Airborne transmission of SARS-CoV-2: the world should face the reality

    Environ. Int.

    (2020)
  • D. Nakic

    Environmental evaluation of concrete with sewage sludge ash based on LCA

    Sustain. Prod. Consum.

    (2018)
  • Cited by (48)

    View all citing articles on Scopus
    View full text