A circular economy-based model for assessing the sustainability of construction and demolition waste management

Abstract

In an effort to tackle climate change and decrease the consumption of natural resources, more and more industries worldwide are adopting circular economy principles. The construction industry is no exception; however, the implementation of these principles is beyond satisfactory levels. As a consumer of more than half of the extracted materials and a contributor to more than a third of waste, the construction industry hides great circular economy potential. In recent years, the scientific community has devoted a great effort to investigate different aspects of construction and demolition waste (CDW) management. The assessment of key aspects of sustainability, such as the economic, environmental and social aspects, were particularly studied, mainly to find the optimal management alternative that would be the least detrimental to the environment and the society. However, the available studies rarely included all three pillars of sustainability. Moreover, management alternatives that were assessed included only recycling, backfilling and disposal in most cases, leaving the treatment options that support circular economy principles such as reuse and high-quality recycling unexplored. Additionally, most of the studies performed sustainability assessments on statistical data of CDW quantities that are often unreliable and may significantly underestimate the sustainability performance. The main objective of this research was to propose a new model for the sustainability assessment of CDW management and the selection of the optimal CDW management alternative. To achieve this objective, the following specific goals were addressed: 1) setting up a unique material stock database that includes the types and quantities of materials embedded in buildings; 2) proposing possible CDW management alternatives; 3) proposing a model for estimating future quantities and composition of CDW; 4) proposing a model for assessing the sustainability performance of the proposed alternatives; 5) comparing and ranking of CDW management alternatives; 6) analysis of the ranking results and selecting the optimal CDW alternative. The model was tested in a case study for the management of CDW from residential buildings in Serbia. In this case study, three alternatives: the current CDW management (BAU), the alternative that aims to achieve the EU average CDW recovery rates (EU28(2018)) and the alternative that implements circular economy principles in CDW management practices (CE) were evaluated and ranked. Each alternative was ranked against four different decision-makers scenarios: economic, environmental, social and holistic. The model includes the integration of the existing and widely used methods: bottom-up inventory analysis and dynamic stock modelling for the estimation of the material stock and CDW quantities and composition, Cost-Benefit Analysis for sustainability assessment and Multi-Criteria Decision-Making Analysis (Analytical Hierarchy Process - AHP) for ranking of the CDW alternatives and choosing the optimal CDW management alternative. The implementation of the model in the case study for CDW management in Serbia yielded three sets of results. The first set of results was related to the creation of a unique material stock database that included the list of materials embedded in residential buildings built between 1946 and 1990 with detailed specifics (geometry and physical characteristics). Based on this, viii the total weight and the composition of the materials embedded in these buildings were calculated. The total weight of material embedded was estimated to be 714.6 million tonnes, out of which 601.1 million tonnes were embedded in single-family house (SFH) buildings and 113.5 million tonnes of materials were embedded in multi-family house (MFH) buildings. The materials with a share of over 80% belong to the mineral fraction (concrete, bricks, tiles, ceramics). The second set of results included the potential waste quantities and composition when these buildings in Serbia are renovated or demolished. Depending on the renovation alternative, the total amount of waste in the period 2021—2046 ranged between 40.2 and 41.1 million tonnes, with an average annual contribution between 1.5 and 1.6 million tonnes. The sensitivity analysis of the waste quantities showed that these quantities might range between 0.89 and 2.5 million tonnes if the demolition rate changes up to 30%, while the renovation rates do not bring significant changes to the amount of waste. The highest share of the waste stream (67%) is made up of clay and concrete-based materials. Consequently, the waste composition (waste streams) and the possible treatments of these waste streams determine the sustainability performance of three proposed CDW management alternatives for Serbia. The third set of results was related to the sustainability performance and the ranking of CDW management alternatives. The direct outputs of the Cost-Benefit Analysis (financial and economic net present value) identified cash flow balance and potential economic, environmental and social benefits to the waste operators and the society for each alternative for Serbia. The current CDW management alternative in Serbia was the worst option. The financial and the economic net present values were negative in this alternative, which implies that managing waste under this alternative will not benefit the waste operator or society. On the other hand, the CE alternative was identified as the best option, with both of these indicators positive. The ranking of alternatives with the Multi-Criteria Decision-Making Analysis resulted in the optimal CDW management alternative under different decision-making preferences. In the environmental and holistic decision-making scenarios, the CE alternative was ranked as the optimal, while the current waste management alternative was ranked as the optimal solution under the economic and social preferences. In addition, the sensitivity analysis applied to the sustainability performance revealed several critical variables such as the demolition rate, discount rates, capital and operational costs and unit prices of recovered bricks and aggregates. These are the variables that should be carefully considered when waste management strategies are planned. The case study showed that efficient CDW management practice depends on active participation and partnership of all stakeholders, from policymakers to researchers and practitioners. All these stakeholders may find the proposed model useful from different management aspects. The policymakers may use this model to evaluate the effects of the stricter implementation of the existing regulations and the promotion of new regulations such as the carbon and landfill taxes or even landfill bans for recyclable waste fractions. More advanced instruments would include reusing and recycling subsidies and the implementation of green procurement provisions in public contracts. And finally, in lack of financing for better waste management practices, carefully planned and contracted public-private partnerships may be the right answer that will, in the end, benefit all partners, the environment and the society.

Kao odgovor na klimatske promene i smanjenje potrošnje prirodnih resursa sve više industrija širom sveta usvaja principe cirkularne ekonomije. Građevinska industrija nije izuzetak, međutim primena ovih principa je daleko ispod zadovoljavajućeg nivoa. Zahvaljujući činjenici da troši više od polovine iskopanog materijala i da generiše više od trećine otpada, građevinska industrija ima veliki potencijal za primenu principa cirkularne ekonomije. Naučna zajednica je u skorije vreme, posvetila mnogo napora istraživanju različitih aspekata upravljanja otpadom od građenja i rušenja, posebno procenama aspekata održivosti, kao što su ekonomski, ekološki i društveni aspekt, kako bi pronašla optimalnu alternativu za upravljanje ovim otpadom koja bi bila najmanje štetna po životnu sredinu i društvo. Međutim, dostupne studije retko uključuju sva tri stuba održivosti. Štaviše, alternative za upravljanje koje su procenjivane u studijama su u većini slučajeva uključivale samo recikliranje, nasipanje i odlaganje na deponiju, zanemarujući pri tome opcije tretmana otpada koje podržavaju principe cirkularne ekonomije, kao što su ponovna upotreba i recikliranje koje rezultira kvalitetnim recikliranim agregatom. Dodatno, većina studija je analizirala održivost opcija za upravljanje otpadom od građenja i rušenja na osnovu statističkih podataka o količinama koji su često nepouzdani i mogu značajno potceniti rezultate. Glavni cilj ovog istraživanja je predlaganje modela za procenu održivosti alternativa za upravljanje otpadom od građenja i rušenja i izbor optimalne alternative. Kako bi se postigao ovaj cilj, postavljeno je nekoliko pojedinačnih ciljeva: 1) formiranje jedinstvenog fonda građevinskog materijala, baze podataka o tipu i količini materijala ugrađenih u zgrade; 2) predlaganje mogućih alternativa za upravljanje otpadom od građenja i rušenja; 3) predlaganje modela za procenu budućih količina i sastava otpada od građenja i rušenja; 4) predlaganje modela za procenu održivosti alternativa za upravljanje otpadom od građenja i rušenja; 5) poređenje i rangiranje alternativa za upravljanje otpadom od građenja i rušenja; 6) analiza rezultata rangiranja i izbor optimalne alternative za upravljanje otpadom od građenja i rušenja. U tu svrhu, ovaj model je testiran na stambene zgrade u Srbiji. Alternative koje su procenjivane i rangirane su: alternativa sa sadašnjim načinom upravljanja otpadom od građenja i rušenja (BAU), alternativa koji teži da dostigne prosečne evropske procente iskorišćenja ovog otpada (EU28(2018)) i alternativa koji primenjuje principe cirkularne ekonomije u upravljanju otpadom od građenja i rušenja (CE). Svaka od ovih alternativa je rangirana u skladu sa različitim prioritetima donosioca odluka: ekonomskim, ekološkim, društvenim i sveobuhvatnim. Model koje je predložen integriše postojeće metode koje su široko u upotrebi. Za procenu fonda građevinskog materijala i količinu i sastav otpada od građenja i rušenja korišćena je analiza inventara zgrada i dinamičko modeliranje fonda zgrada, dok je za procenu održivosti i rangiranje alternativa korišćena analiza troškova i koristi i višekriterijumska optimizacija. Primena modela na izabranu studiju slučaja je dala tri grupe rezultata. Prva grupa rezultata predstavlja kreiranje jedinstvene baze podataka koja sadrži listu materijala ugrađenih u stambene zgrade u periodu od 1946. do 1990. godine sa detaljnom specifikacijom geometrije i fizičkih karakteristika zgrada. Na osnovu ovoga izračunata je ukupna količina i sastav materijala ugrađenog u stambene zgrade. Ukupna težina materijala koji je ugrađen u stambene zgrade iznosi 714.6 miliona tona, od čega se 601.1 milion tona odnosi na zgrade namenjene xi porodičnom stanovanju, a 113.5 miliona tona na zgrade namenjene višeporodičnom stanovanju. Materijali koji u ovom fondu materijala učestvuju sa preko 80% pripadaju materijalima mineralnog porekla (beton, opeka, keramika). Druga grupa podataka se odnosi na moguće količine otpada kada se ove zgrade renoviraju ili sruše. U zavisnosti od alternative renoviranja, ukupna količina otpada u periodu 2021—2046 varira između 40.2 i 41.1 miliona tona, sa prosečnim godišnjim prinosom od 1.5 do 1.6 miliona tona. Analiza osetljivosti ovih rezultata je pokazala da se ove količine mogu kretati u opsegu od 0.89 do 2.5 miliona tona ukoliko se stopa rušenja promeni za 30%, dok stope renoviranja nemaju značajniji uticaj na količine otpada. Najveći udeo u količini otpada (67%) imaju materijali na bazi opeke i betona. Shodno tome, sastav i mogući tretmani ovog otpada određuju troškove i prihode tri predložene alternative za upravljanje otpadom od građenja i rušenja u Srbiji. Treća grupa rezultata se odnosi na analizu troškova i koristi i rangiranje alternativa za upravljanje otpadom od građenja i rušenja. Rezultati analize troškova i koristi su identifikovali alternativu sa sadašnjim načinom upravljanja kao najlošiju opciju. Negativna vrednost finansijske i ekonomske neto sadašnje vrednosti impliciraju da upravljanje otpadom od građenja i rušenja u ovoj alternativi ne donose korist ni operatoru otpada ni društvu. Sa druge strane, CE alternativa se pokazala kao najbolja opcija u kojoj su obe neto sadašnje vrednosti pozitivne. Rangiranje alternativa pomoću višekriterijumske optimizacije je rezultiralo izborom optimalna alternative u različitim scenarijima odlučivanja. U ekološkom i sveobuhvatnom scenariju odlučivanja CE alternativa je rangirana kao optimalna, dok se u ekonomskom i socijalnom scenariju odlučivanja, sadašnji način upravljanja otpadom od građenja i rušenja pokazao kao optimalna opcija. Dodatno, analiza osetljivosti procene održivosti je otkrila nekoliko kritičnih parametara kao što su stopa rušenja, diskontne stope, kapitalni i operativni troškovi i jedinične cene opeke za ponovnu upotrebu i recikliranog agregata, koji se moraju pažljivo razmotriti kada se planiraju strategije za upravljanje otpadom od građenja i rušenja. Studija slučaja je pokazala da efikasno upravljanje otpadom od građenja i rušenja zavisi od aktivnog učešća i partnerstva svih zainteresovanih strana, od istraživača do političara i praktičara. Model predložen u ovom istraživanju bi mogao da bude koristan svima. Političari bi mogli da ga koriste prilikom razmatranja strožijih kontrole i bolje primene postojeće regulative kao i promovisanja novih zakonskih instrumenata kao što su porez na emisiju ugljen-dioksida i porez na odlaganje na deponiju ili čak zabrana odlaganja na deponiju otpada koji se može reciklirati. Napredniji instrumenti bi mogli da uključe podsticaje za ponovnu upotrebu i recikliranje kao i primenu zelenih nabavki u javnim ugovorima. I konačno, u nedostatku finansiranja boljih opcija za upravljanje otpadom, pažljivo planirana i ugovorena javno-privatna partnerstva bi mogla da budu odgovor koji bi koristio svim partnerima, kao i životnoj sredini i društvu.