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Construction and demolition (C&D) waste recycling constitutes an indispensable component in the overall waste management strategy. Unlike the traditional recycling approaches whereby C&D waste is transported to off-site facilities for treatment, construction managers are actively exploring the possibility of on-site recycling where C&D waste is treated directly at source. This study reports the barriers and facilitators of implementing on-site C&D waste recycling by contextualizing it in Hong Kong. It does so by adopting a mixed-method approach combining case study, site visits, and interviews. It is discovered that the barriers include (1) site space constraints, (2) narrow window of opportunity to trade recycled products, (3) vulnerable business case, (4) lack of support from off-site recycling, and (5) lack of government policy support. A series of facilitating measures are also proposed, including (1) developing customized on-site recycling equipment, (2) establishing a demand-supply information-sharing platform, (3) developing more thriving off-site recycling, and (4) providing more government support. This study probes into the real-life on- and off-site waste recycling practices in Hong Kong's prominent C&D management system. It can also provide useful references for others in developing their own C&D waste recycling strategies by rationally deploying on- and off-site recycling., Graphical abstract Unlabelled Image, Highlights • Identified five major barriers to on-site C&D waste recycling in Hong Kong; • Developed four facilitators to promote on-site C&D waste recycling in Hong Kong; • The facilitators discussed may serve as useful reference for other economies.

Worldwide, natural disasters and conflicts result in damaged or collapsed buildings requesting clearing of debris and reconstruction. The on‐site recycling of concrete waste into new structural concrete reduces the utilization of raw materials, decreases transport and production energy cost, and saves the use of limited landfill space. Currently, recycling involves the use of recycled concrete aggregates (RCA) as road base material or in non‐structural concrete with low strength requirements. Hence, the application in structural concrete is limited. In order to improve the applicability of RCA in structural concrete, an optimised crushing and sieving method is advised. To this aim, a modular rapid deployable clearing kit has been designed, clearing (concrete) debris, and processing this into quality aggregates for new concrete to be used in local reconstruction. Since the quality of the initial concrete is unknown, errors can be made when it was produced (e.g. not enough cement, too much water, etc.). These defects are not detectable by the naked eye; however, they cause a weakening of the structure. In term, clearing the hardened cement paste from the aggregates via optimised crushing minimises the influence of the initial concrete quality on the quality of the recycled concrete aggregates. Together with the fact that cement paste absorbs a significant volume of water, optimised crushing makes application of recycled concrete into new concrete far less troublesome.

Worldwide, natural disasters and conflicts result in damaged or collapsed buildings requesting clearing of debris and reconstruction. The on‐site recycling of concrete waste into new structural concrete reduces the utilization of raw materials, decreases transport and production energy cost, and saves the use of limited landfill space. Currently, recycling involves the use of recycled concrete aggregates (RCA) as road base material or in non‐structural concrete with low strength requirements. Hence, the application in structural concrete is limited. In order to improve the applicability of RCA in structural concrete, an optimised crushing and sieving method is advised. To this aim, a modular rapid deployable clearing kit has been designed, clearing (concrete) debris, and processing this into quality aggregates for new concrete to be used in local reconstruction. Since the quality of the initial concrete is unknown, errors can be made when it was produced(e.g. not enough cement, too much water, etc.). These defects are not detectable by the naked eye; however, they cause a weakening of the structure. In term, clearing the hardened cement paste from the aggregates via optimised crushing minimises the influence of the initial concrete quality on the quality of the recycled concrete aggregates. Together with the fact that cement paste absorbs a significant volume of water, optimised crushing makes application of recycled concrete into new concrete far less troublesome.

REFERAT Övergödning är ett högst reellt hot mot många av Sveriges sjöar och vattendrag och inte minst mot Östersjön. Utsläpp av ej tillräckligt renat avloppsvatten och läckage av näringsämnen från jordbruksmarker är problem som länderna kring Östersjön måste lösa. Sverige arbetar både nationellt och internationellt med att förbättra Östersjöns ekologiska status. Riksdagen har satt upp flera miljökvalitetsmål som bland annat tydliggör att Sverige måste minska tillförseln av näringsämnen till sjöar och vattendrag. Orsaken är att dessa föroreningar är en bidragande orsak till övergödning. Det här har resulterat i en ökad ansträngning från kommunerna att åtgärda diffusa utsläpp som enskilda avlopp. Ett enskilt avlopp antas vara en avloppsanläggning med en lokal hantering av hushållsavloppsvatten och är inte kopplat till ett regionalt ledningsnät och reningsverk. Avloppsvatten från hushåll består av BDT-vatten, vatten från bad, disk och tvätt, samt vatten från toalett. Avloppsvatten innehåller näringsämnen såsom fosfor och kväve samt organiskt material och bakterier. Om utloppsvattnet når recipienter utan att tillräcklig rening finns risk för övergödning och smittspridning. För att skydda grund- och ytvatten föreslår Naturvårdsverket att krav ställs på reduktion av näringsämnen och organiskt material för att det enskilda avloppet ska bli godkänt av kommunen. Sverige har uppskattningsvis en miljon enskilda avlopp varav nästan hälften bedöms vara undermåliga och i behov av att göras om. Det kan vara svårt för fastighetsägare att överblicka de krav som ställs och de många olika alternativ som finns för att anlägga eller göra om en avloppsanläggning. Ett verktyg som hanterar produkter och typlösningar för enskilda avlopp har tagits fram. Verktyget benämns LEA vilket står för Lösningar för Enskilda Avlopp och har utvecklats i Microsoft Excel®. LEA genererar och presenterar lösningsförslag utifrån plats- och kundspecifika parametrar vilka matas in i verktyget. Jämförelse kan göras mellan de föreslagna lösningsalternativen med avseende på olika parametrar, som exempelvis reduktionsgrad, utsläpp av näringsämnen och organiskt material, möjlighet till lokalt kretslopp och kostnad. LEA förväntas användas av sakkunnig och syftar till att effektivisera utredningar av enskilda avloppsanläggningar. Att användaren kontinuerligt uppdaterar och kompletterar databasen är centralt för verktygets fortsatta funktion och tillförlitlighet. ABSTRACT Eutrophication is a serious threat to many of Sweden's lakes and streams, and in particular to the Baltic Sea. Discharge of inadequately treated waste water and leaching of nutrients from agricultural lands are problems that the countries surrounding the Baltic Sea have to find a solution to. Sweden strives both nationally and internationally towards improving the ecological status of the Baltic Sea. The government has decided upon several Environmental Quality Objectives that sets out that Sweden must reduce the emissions of nutrients to the sea, lakes and streams. This is of great importance as these are contributing factors to eutrophication. This has initiated the Swedish municipalities to investigate diffuse discharges such as small scale on-site sewage systems. An on-site sewage system is assumed to locally treat domestic waste water and is not connected to a waste water treatment plant. Domestic waste water includes greywater, which is the effluent from kitchen and bathroom, and most often also water from toilet use. The waste water contains nutrients such as phosphorus and nitrogen as well as organic matter and bacteria. If the waste water reaches the receiving waters without adequate treatment this is associated with a risk of eutrophication and contamination. The Swedish EPA has recommended reduction levels to be reached for organic matter, nitrogen and phosphorus. The municipalities are recommended to require these levels to be met for the on-site sewage system to be approved. Sweden has approximately one million on-site sewage systems of which nearly 50% is considered substandard and in need of upgrading. It may be difficult for property owners to overview the requirements as well as the large number of products and options available to construct or modify an on-site sewage system. A program, LEA, which handles products for household sewage systems, has been developed in Microsoft Excel®. The tool generates suggestions of different sewage systems depending on customer and site-specific parameters. Comparisons are made between the proposed solutions with respect to various parameters which include reduction efficiency, effluent emissions, on-site recycling and cost. The user of LEA can update and supplement the database, which is central to the tool's continued function and reliability. LEA is expected to be used by experts and aims to enhance investigations in the choice of on-site sewage systems.