Urban waste for biomethane grid injection and transport in urban areas

City of Zagreb

The City of Zagreb is producing around 250,000 tonnes of municipal solid waste (MSW) per year which is mostly being landfilled (92.6% in 2011) at the landfill site Jakuševec – Prudinec. Recently the life span of this landfill site has been extended even though most of the landfilled waste is biodegradable (paper, cardboard, kitchen and green waste - approx. 62%).
The Republic of Croatia has to divert 65% of biodegradable municipal waste of the total amount (by weight) of biodegradable municipal waste produced in 1997 from landfills by the end of 2020 according to EU legislation. Furthermore, the City of Zagreb must meet the goals of the Landfill Directive and has the obligation to placing biofuels on the national market. Implementation of the waste-to-biomethane (WtB) concept in the City of Zagreb would meet these requirements, increase biofuel consumption, reduce GHG emissions, and contribute to the development of sustainable urban transport.
A pre-requisite for introducing a source separated bio-waste system, constructing a biogas plant and to establish mid to long term contracts for bio-waste delivery, is the adoption of the Waste Management Plan that is still pending. In that sense, the City of Zagreb and its Office for Energy, Environmental Protection and Sustainable Development are the main stakeholders in deciding in overall WtB framework in organisational, ownership, financing and operational aspects.
Developing a separate waste collection system along with the increased number of recycling yards will significantly increase the quantity of separately collected bio-waste suitable for biogas production. The part of the currently collected bio-waste (e.g. from gardening) is used in a composting plant. Compared to composting, the emissions to the air are significantly lower and easier to control in anaerobic digestion (AD) process than in a composting facility, as AD is conducted in closed reactors.
Bio-waste is separately collected from restaurants, schools and kindergarten canteens, market places, shopping centres and green waste from households. Even though it is questionable if the total potential amount of the bio-waste that could be collected is sufficient for the AD, the WtB concept can be closed regardless on the waste management concept implemented for the City of Zagreb as biogas can be produced from both, source separated bio-waste and bio-waste collected as mixed bulk in the remaining MSW. From the point of energy sustainability, less energy is needed if bio-waste is collected separately.
Also, the lack of education and awareness among citizens and inadequate penalties for polluters, could contribute to the unsatisfactory results in waste separation. However, the survey implemented in the UrbanBiogas project showed that citizens support the WtB concept. Therefore, constant communication with the public seems to be the most important non-technical assignment. Namely, if source separated collection is chosen as waste management concept, its collection rate and quality of the bio-waste will depend on the willingness of the citizens to contribute.
One of the advantages of the overall implementation of the UrbanBiogas project in Zagreb has been the support of all important stakeholders. An additional advantage is that the beginning as well as the end of the WtB value chain could be implemented by different branches of Zagreb City Holding, a company in 100% ownership of the City. The waste management could be operated by the Čistoća branch, the biomethane use in transport could be implemented by the ZET branch, the urban public transport company that currently has 60 public transport busses powered by CNG, or the biogas injection in the natural gas grid could be implemented by the GPZ branch, the city gasworks company.
Criteria for choosing the location for biogas plant construction should be: road access, neighbourhood acceptance, access to sufficient electrical power capacity, access to low or medium pressure natural gas grid, economic feasibility of the investment via maximisation of biogas production, availability of (additional) substrate, maximisation of useful energy obtained from biogas, sufficient space for the plant, the distance of waste water treatment facility, and minimal spatial alterations. The Spatial Plan of the City of Zagreb defines locations for overall waste management systems in the City of Zagreb:

  • Location 1: Prudinec - area of existing land-filling site - overall plausible location
  • Location 2: Resnik - joint areas of existing waste water management site and considered thermal waste processing plant - overall plausible location
  • Location 3: Markuševac - area of existing composting plant
  • Location 4: Dumovečki Lug

From technical, energy and economic point of view, it seems that organizing thermal (solid) and anaerobic (wet) waste treatment adjacent to the waste water treatment facility would create so called "industrial symbiosis" where the sum of performance of this symbiosis would be higher than adding each of the individual performances to the other. Industrial symbiosis is a subset of industrial ecology, with a particular focus on material and energy exchange. Given the efforts of the City of Zagreb on its green and sustainable profile already made, forming an industrial symbiosis while implementing WtB concept would be added value not only to the waste management, but to the overall life standard of the citizens.
A biogas upgrading plant will depend on the hourly production of biogas and the desired quality of biomethane. The produced biomethane should be injected in the natural gas grid or used in transport. Expected biomethane productions for all concerned scenarios are too little for capacities of planned filling stations of ZET. Consequently, the optimal solution could be to inject biomethane into the high pressure distribution grid. Due to the consumption patterns and gas grid features, pressurised water scrubbing or pressure swing adsorption (PSA) is proposed as upgrading technologies, suitable for high pressure distribution grid injection.
The sales concept for biomethane could include an agreement between the biomethane production company and the waste management company (Čistoća), but also with GPZ (City Gasworks Company) and ZET (Urban Public Transport Company for the City of Zagreb).
The actual time frame for the biogas plant construction, however, is difficult to predict. ZCH Čistoća and EIHP have made a lot of efforts in finding truly interested investors and some of them negotiated with the ZCH and city officials (Vienna Holding). As a result of EIHP’s and ZCH’s efforts, other potential investor Austep SPA (Milano) has also expressed interest by signed Letter of interest.

Reports about Zagreb

  • Municipal waste management in the City of Zagreb/Croatia EN
  • Results of the survey on waste management in Zagreb EN
  • Report on the Public Consultation in Zagreb - Croatia (including the results of the Survey) EN
  • Biogas & Biomethane Production in the City of Zagreb EN
  • Biomethane use for cities: grid injection & transport in City of Zagreb/Croatia EN
  • Report on the competition event for biogas plant companies in Zagreb - Croatia EN
  • Report on the National expert consultation meeting about biomethane use in Croatia EN
  • Summary report on promotion of sustainable waste management in City of Zagreb city EN
  • Biogas Production from Organic Part of Municipal Solid Waste. The UrbanBiogas Project EN
  • Economic Feasibility of WtB Concepts for Valmiera, Zagreb and Graz EN


  • Upotreba biometana u gradovima: utiskivanje u plinsku mrežu i promet u Zagrebu/Hrvatskoj HR
  • Proizvodnja bioplina i biometana u Zagrebu/Hrvatskoj HR
  • Doprinos Primjene Koncepta "Iz Otpada do Biometana" Ostvarivanju eu Ciljeva HR


City of Zagreb (Zagrebacki Holding)

Contact: Monika Kruhek
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Phone: +38 5998022342
Website: www.zgh.hr

Energy Institute Hrvoje Požar

Contact: Robert Bošnjak
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Phone: +385 1 6326 105
Website: www.eihp.hr/english/

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