Integrated Infrastructure Systems for Fast-Growing Cities

  • 2017/10/31     Dresden, Germany

    Image: iStock/PeopleImages

    Reporting by Jiwon Park, Intern, Communications & Advocacy Unit

    Cities offer great possibilities not only for people to live together by enabling interaction, but also facilitating sustainable use of shared resources. On World Cities Day, we look at how integrated and sustainable water use and waste management make cities safer and more resilient.

    The global population living in urban areas will reach 6.5 billion by 2050. This makes up two-thirds of all humankind. Rapid urbanisation frequently comes with the challenges of inadequate maintenance of water and wastewater infrastructure and poor solid waste management. Poor water quality and insufficient water availability, waste-disposal problems, and high energy consumption make cities especially vulnerable to global changes.

    SEMIZENTRAL Approach as an Integrated Infrastructure System

    The UNU-FLORES publication “Implementation of SEMIZENTRAL: An Integrated Infrastructure Approach for Fast-Growing Cities” (2016) introduces an alternative integrated infrastructure approach called SEMIZENTRAL and describes its inaugural implementation in China. Dealing particularly with challenges of fast-growing urban areas, SEMIZENTRAL increases energy efficiency by reusing urban water and treating food waste and sewage sludge.

    SEMIZENTRAL addresses challenges of urbanisation with regard to the supply of water and the treatment of biowaste and wastewater by integrating the infrastructure of the three elements into one system. At the SEMIZENTRAL Resource Recovery Centre (RRC), wastewater is treated and reused as service water for toilet flushing and irrigation. Biogas generated from co-digestion of sewage sludge and biowaste is used to produce electricity and heat for the operation of the RRC. Residual biosolids can be used for landscaping or soil improvement.

    A key element of SEMIZENTRAL is its application on the systems scale; it lies between an entirely centralised and decentralised concept. Operating somewhere in between allows it to work district-wise, this helps reduce planning and investment risks. SEMIZENTRAL is thus advantageous for the long-term development of fast-growing urban areas. It allows infrastructure to grow at the same rate as a city’s population.

    First Full-Scale Implementation of SEMIZENTRAL in Qingdao, China

    Johanna Tolksdorf, Susanne Bieker and Peter Cornel. 2016. “Implementation of SEMIZENTRAL: An Integrated Infrastructure Approach for Fast-Growing Cities”, Dresden Nexus Conference Working Paper Series DNC2015/2. Dresden, Germany: UNU-FLORES.

    The SEMIZENTRAL concept was implemented for the first time in full-scale in Qingdao, China. In Qingdao, wastewater is collected in two separate sewer systems. Treated greywater is used as service water for toilet flushing, and treated blackwater for irrigation. Wastewater separation can help considerably to improve water quality and energy savings. For example, using service water for toilet flushing saves 10% of the energy required for tap water production.

    World Cities Day for Better Cities, Better Life

    A more efficient reuse of urban water and solid waste management is required to maximise the capacity of cities for the future. Making urban environments sustainable is closely linked to achieving Goal 11 of the UN Sustainable Development Goals (SDGs). As outlined by SDG 11, the safe removal and management of solid waste represents one of the most vital urban environmental services.

    “By 2030, reduce the adverse per capita environmental impact of cities, including by paying special attention to air quality and municipal and other waste management.”

    – SDG 11, Target 11.6

    Since 2013, the United Nations has designated 31 October as World Cities Day to promote successes of urbanisation, address challenges resulting from urbanisation, and contribute to sustainable urban development around the world. This year, the UN has selected the theme Innovative Governance, Open Cities.

    The publication is an outcome of the Dresden Nexus Conference 2015 jointly organised by UNU-FLORES, TU Dresden, and IOER. Get your free digital copy here.


    Tolksdorf, JohannaBieker, Susanne and Cornel, Peter. 2016. “Implementation of SEMIZENTRAL: An Integrated Infrastructure Approach for Fast-Growing Cities.” DNC Working Paper Series. Dresden: United Nations University Institute for Integrated Management of Material Fluxes and of Resources (UNU-FLORES).