Nature-based solutions

Application ID	Croatia
Application Name	Sludge Drying Reed Beds in Kaštelir
Application Location	Country	Croatia	Country 2 (in case of transboundary applications)
	NUTS2 code
	River Basin District Code		Mirna
	WFD Water Body Code
	Description		The WWTP Kaštelir is situated in municipality of Kaštelir-Labinci, which lies in the karst area of the Istrian peninsula in Croatia. Area of 34 km² consists of 15 settlements and has 1483 inhabitants (2011). The village Kaštelir is located at an altitude of 220 m
Application Site Coordinates (in ETRS89 or WGS84 coordinate system)	Latitude: 45.291856		Longitude: 13.673172
Target Sector(s)	Primary:		Urban
	Secondary:		Agriculture
Implemented NWRM(s)	Measure #1:		Sludge drying reed beds
	Measure #2:
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Application short description	Sludge drying reed beds (RBs) enable sewage sludge dewatering, stabilization, mineralization and hygenization. They are an alternative to mechanical treatment (e.g. belt presses, centrifuges) and enable long-term storage. In the process, sludge is spread on a filter media (substrate) of an open bed after which drainage and evaporation takes place. Planted RBs enable effective dewatering of sewage sludge and produce a mineralized product that can be used as a soil amendment in agriculture and other uses

Brief description of the problem to be tackled	With the construction and expansion of municipal infrastructure (sewage and wastewater treatment plants), the amount of sludge produced by the wastewater treatment plants is increasing. Sewage sludge is the main waste by-product of wastewater treatment. The excess sludge presents biomass and microorganisms that contain organic matter, nutrients, and persistent pollutants that originate from wastewater. The project addresses a need to link access to resources from sewage sludge with minimal financial costs and environmental impact. RBs were constructed as a cost-effective solution to solve problems of sludge treatment, storage, and disposal in the Municipality of Kaštelir-Labinci. Constructed wetland (CW) for wastewater treatment with a capacity of 1900 P.E. was completed in 2015. Until the sludge drying reed bed was constructed in 2016, the generated sludge was transported to the central WWTP for further treatment and final disposal. Because this was an only temporary solution, they were looking for the alternative, which could solve the problem locally and for many years. Limited disposal options were the key drivers of change in technology.
What were the primary & secondary targets when designing this application?	Primary target #1:
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	Remarks:		sludge dewatering, stabilization, mineralization and hygenization
Which specific types of pressures did you aim at mitigating?	Pressure #1:	WFD identified pressure	wastewater and sludge
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Which specific types of adverse impacts did you aim at mitigating?	Impact #1:	WFD identified impact	chemical and physico-chemical quality elements
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Which EU requirements and EU Directives were aimed at being addressed?	Requirement #1:	WFD-mitigation of significant pressure	Sludge from WWTP
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	Remarks:
Which national and/or regional policy challenges and/or requirements aimed to be addressed?	Sludge drying reed beds as NBS for cost-efficient sludge treatment; Biosolids use in agriculture and other uses (requires cross-sectoral collaboration on the regional level and environmental and economic assessment of feasible options); Sludge treatment and disposition agenda building with all relevant stakeholders (authorities and engaged sectors).

Dominant Land Use type(s)	Dominant land use	3.1.1
	Secondary land use	2.4.2
	Other important land use	2.4.3, 2.2.1
	Based on data from Corine Land Cover data, 65% of the total area falls under agricultural land. The most intensively cultivated arable land is in the Mirna River valley area. Given that the Municipality is located on fertile land, favorable for the economy, and due to its favorable climate, it boasts numerous olive growers, winemakers, beekeepers, lavender and vegetable producers, fruits and flowers growers.
Climate zone	warm temperate dry
Soil type	The greater part of the Municipality of Kaštelir-Labinci is formed by dolomites and limestones. The most widespread soil in Istria and in the Municipality is terra rossa on a carbonate base.
Average Slope	nearly level (0-1%)
Mean Annual Rainfall	0 - 300 mm
Mean Annual Runoff
Average Runoff coefficient (or % imperviousness on site)
	Remarks: -
Characterization of water quality status (prior to the implementation of the NWRMs)
Comment on any specific site characteristic that influences the effectiveness of the applied NWRM(s) in a positive or negative way	Positive way: The efficiency of the system is influenced by climate, which affects the rate of sludge drying
	Negative way: Dry summers can negatively affect the plant growth

Project scale	Medium (eg. public park, new development district)	WWTP Kaštelir with sludge drying reed beds (1.900 PE)
Time frame	Date of installation/construction (MM.YYYY)	2016
	Expected average lifespan (life expectancy) of the application in years	At least 30 years
Responsible authority and other stakeholders involved	Name of responsible authority/ stakeholder	Role, responsibilities
	Croatian Waters	Project initiator / project implementation
	Global Environment Facility	Provision of funds / donor
	Municipality of Kaštelir-Labinci	WWTP Owner
	Public utility	WWTP Operator
The application was initiated and financed by	Global Environment Facility and Croatian Waters
What were specific principles that were followed in the design of this application?	Treatment efficiency, long-term biosolids accumulation and storage, potential of biosolids reuse, acceptable operational costs, functionality, usability, aesthetic benefit, impact on public perception & acceptability
Area (ha)	Number of hectares treated by the NWRM(s)
	Text to specify
Design capacity	1900 PE
Reference to existing engineering standards, guidelines and manuals that have been used during the design phase	Reference	URL
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Main factors and/or constraints that influenced the selection and design of the NWRM(s) in this application?	The biggest limitation in the application of reed beds technology is space availability; the technology is land-intensive. As there was enough space on the property owned by the Municipality, the technology was applied without additional problems (land acquisition or time-consuming administrative processes)

Impact category	Impact description	Impact quantification
		Parameter value; units and/or	% change in parameter value as compared to the state prior to the implementation of the NWRM(s)
Runoff attenuation / control
Peak flow rate reduction
Impact on groundwater	The system has no direct impact on groundwater, because the bed is sealed with waterproof membrane
Impact on soil moisture and soil storage capacity	The system can generate soil amendment (biosolids). It can improve soil characteristics to which biosolids are applied
Restoring hydraulic connection
Water quality Improvements	In terms of positive affect of WWTP application
WFD Ecological Status and objectives	In terms of positive affect of WWTP application
Reducing flood risks (Floods Directive)
Mitigation of other biophysical impacts in relation to other EU Directives (e.g. Habitats, UWWT, etc.)	Both NBS solutions, constructed wetland for wastewater treatment and reed bed for sludge treatment, are built as green space and support habitat/wildlife and reduce emissions
Soil Quality Improvements	Natural dewatered sludge from RB, can be a source of beneficial nutrients (nitrogen, phosphorous, potassium) and thus used in agriculture in compliance with valid conditions, standards, regulations, and legislation	System produces around 469 tons of biosolids per operating cycle

What are the benefits and co-benefits of NWRMs in this application?	The technology enables long-term and sustainable storage of sludge with low operating and maintenance costs. It can completely replace dehydration which currently represents significant cost on existing wastewater treatment plants or transport of sludge to central WWTP. With this technology different types of sewage sludge can be treated. The sludge is stored in the reed beds normally between 8 to 10 years. Due to parallel operation of physical (drying) and biological processes (mineralization) the treatment results in significant (above 90%) sludge volume reduction. The end result of the process is a compost-like soil that can be reused as fertilizer in agriculture, cover layer for landfills or construction material. It can also be used for revitalization of quarries or other degraded areas, sanitation of erosion, on green areas or parks, etc.
Financial costs Value in € (Total + possible breakdown)	Total	€	Investment
	Capital:	262.626,00 €	Construction
	Land acquisition and value:	0 €	Land owned by the Municipality
	Operational and Maintenance:	3.984,00 €/year	Labor costs Electricity consumption costs Monitoring costs Maintenance costs of mechanical equipment Replacement costs and repairs Sludge disposal – biosolids reuse
	Other:	0 €
Were financial compensations required? What amount?	Was financial compensation required: No, it was 100% grant capital cost.
	Total amount of money paid (in €): -
	Compensation schema: -
	Comments / Remarks: -
Economic costs	Actual income loss: -
	Additional costs: -
	Other opportunity costs: biosolids selling (not yet initiated)
	Comments / Remarks: there is no economic cost
Which link can be made to the ecosystem services approach?	Sludge drying reed beds as NBS for cost-efficient sludge treatment; Protection of water resources Health security (control of waterborne diseases) Biomass production Nutrient circulation Soil formation Erosion control Gases regulation Shelter

What were the main implementation barriers?		RB in Kaštelir is the first-ever constructed RB for the treatment of sludge from the Imhoff tank of the constructed wetland (CW) in the Balkan Mediterranean Region. The engineers faced capacity challenges related to technical specifications. Kaštelir is a tourist village characterized by seasonal load. This required special attention focusing on the effect on the RB operation.
What were the main enabling and success factors?		Kaštelir was one of the areas to be addressed among the priority pollution hotspot sites, as identified by UNEP-MAP in 2003 and then confirmed by the World Bank study in 2011. Project addressed untreated wastewater discharges, which could seriously affect tourism (industry contributes 28% of GDP in the region), the pillar of the local economy. Thus, investing decisions (initial investment) was made top-down with the initiative from the Ministry, which was looking at whole picture. The project was fully funded through grant agreement by the GEF. RB in Kaštelir is the first-ever constructed NBS for sludge treatment in Croatia and was very well accepted among all involved stakeholders. Since then, three more RBs were constructed (Čakovec, Mrkopalj, Ravna Gora) and up to ten are in the plan to be built in the next years. In Croatia, RBs are not anymore perceived as novel technology but as an alternative to mechanical dewatering.
Financing		Global Environment Facility – 100% grant
Flexibility & Adaptability		This solution is adjusted depending on the load and the location of the WWTP and still long-term.
Transferability		Reed beds are land intensive technology. Limiting factors usually are RBs land requirements, spatial planning and its administrative risks, land cost and legislation. Generally, technology is more likely to be adopted and implemented by smaller settlements and cities where the price of land is low or land is already owned by state or municipality. Along the Mediterranean coastline, RBs implementation is limited by the availability and high prices of land. Nevertheless, this case showed that RBs can be implemented in inland regions of coastline where land is cheaper or owned by the Municipality.

Source Type	Project Report
Source Author(s)	Limnos Ltd.: Alenka Mubi Zalaznik Anja Potokar Urša Brodnik Tea Erjavec Gregor Plestenjak Martin Vrhovšek Alenka Fajs Aberon Ltd (Chapter 4): Ivan Kolev Cveta Dimitrova Aarhus University: Carlos A. Arias (Review) Pedro Carvalho (Micropollutants)
Source Title	Treatment of wastewater sludge or manure from livestock (TSM) in a Mediterranean environment
Year of publication	May 2020
Editor/Publisher	The Joint Research Centre
Source Weblink
Key People	Name / affiliation	Contact details
	Alenka Mubi Zalaznik	alenka(at)limnos.si

Source Type	Interview
Source Author(s)	Limnos Ltd.: Anja Potokar Martin Vrhovšek
Source Title	Interviews with public utility MARTINELA d.o.o., Municipality of Kaštelir-Labinci
Year of publication
Editor/Publisher
Source Weblink
Key People	Name / affiliation	Contact details
	Alenka Mubi Zalaznik	alenka(at)limnos.si

Monitoring requirements		Management of sewage sludge in Croatia is defined by a Rulebook on the management of sludge from wastewater treatment plants when sludge is used in agriculture (Official Gazette of Croatia, No. 38/08). It is recommended to analyze sludge once per year. For biosolids reuse sludge must comply with national regulations: Limit values for heavy metal in sludge; Limit values for soil to which sludge is applied; Limit values for organic compounds in sludge; Limit values for pathogens; Maximum annual load of dry matter in agriculture. Sludge analyses include: heavy metals, organic compounds, dry matter, pathogens. Soil analysis include: heavy metals (cadmium, copper, nickel, lead, zinc, mercury and chromium).
Maintenance requirements		Regular maintenance works of RBs consists of: weekly check of plants; weekly check if the sludge is drying out; monthly control of the water level in the filter layer; monthly check of external parts of drainage pipes and manholes; cleaning od pipes and manholes as needed; Service of the pumps as needed.
What are the administrative costs?

Which assessment methods and practices are used for assessing the biophysical impacts?
Which methods are used to assess costs, benefits and cost-effectiveness of measures?		“Unit value transfer method” for assessing direct and indirect benefits of RBs in Kaštelir had been used.
How cost-effective are NWRM's compared to "traditional / structural" measures?		In this case, alternative to reed bed was pumping and transport of sludge to central WWTP, which didn’t want to take sludge from small WWTP Kaštelir. Mechanical dewatering as more traditional measure would still not solve the problem of final sludge disposal. The quest for a sustainable solution was imminent. The analysis showed that sludge pumping and transport to the central WWTP would be a cheaper option compared to investment costs in sludge drying reed bed. However, operational costs of RBs are in the same range as sludge transport to the central WWTP.
How do (if applicable) specific basin characteristics influence the effectiveness of measures?		Basin characteristics does not influence the effectiveness of measures.
What is the standard time delay for measuring the effects of the measures?		Efficiency can begin to be measured after the first growing season of plants.

An example of sludge drying Reed Beds (RBs) implementation: the Kaštelir case

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