Thermal utilization of municipal sewage sludge – example of waste water treatment plant in sitkowka nowiny

In Poland there are about 4500 waste water treatment plants, which have equipment for treatment of sewage sludge. The volume of resulting sewage sludge is estimated at about 1-2 % of volume of flowing waste water in the waste water treatment plants [1].
In 2011, Poland generated 519,2 thousand tons of sewage sludge dry matter [3]. The amount of sewage sludge demanding disposal reaches an amount of 212,4 thousand more tons, which are accumulated on the areas of waste water treatment plant from the past years [3]. The realization of Council Directive [4] requirements contributes to the growth of produced sewage sludge. According to predictions, in the year 2014, the amount of municipal sewage sludge is to reach 651 thousand tons of dry matter, and in the year 2018 – 726 thousand tons [5].

The prevailing EU regulations limit the deposit of municipal sewage sludge on landfills. The processing of municipal sewage sludge should be performed in accordance with regulations defining the waste disposal principles

[6-8]. From 1 January 2016, the disposal of sludge which has not been processed properly is forbidden [7,9]. Under the regulations [9], landfilling of municipal sewage sludge is allowed only for sewage sludge which has the calorific value lower than 6,0 MJ/kg d.m., contains less than 5 % of total organic carbon, and its loss on ignition is not higher than 8 % d.m. Municipal sewage sludge includes total organic carbon in the amount of more than 5 % [2,10].
In Poland main methods of municipal sewage sludge utilization are: applied in agriculture (22,4 % of dry mass of sewage sludge generated in the year 2011), applied in land reclamation including reclamation of land for agricultural purposes (10 %) and landfilled (10,4 %) [3]. 
The environmental use of sewage sludge allows us to benefit from its fertilizer qualities. However, the reuse of sewage sludge on the agricultural lands is limited by the high levels of the heavy metals, polycyclic aromatic hydrocarbons, tetrachlorodibenzodioxin, polychlorinated biphenyl and pathogenic organisms contamination [11]. 
The environmental use of sewage sludge gains no social acceptance, and in addition, it is seasonal and is regulated by waste act [6], regulations [12,13], and the directive [14]. Furthermore, there are no suitable areas for this purpose. According to the National Waste Management Plan, only 7,5 % of total number of sewage treatment plants provide sludge which can be used in agriculture [15].
The solution of this situations is an increase of the amount of incinerated sewage sludge. The thermal methods of sludge utilization have a range of advantages: reducing the mass and volume of the waste before it is further processed; a sludge volume of 1 m3 and of hydration in the amount of 65 % is reduced to ca. 0,1 m3 of ash, ability to reuse the energy contained sewage sludge, ability of monitoring the deleterious substances emissions, the solid products and post-process remains which are sanitary safe; post-process waste requires further utilization by reason of the potentially negative effect on the environment [16].
According to Best Available Techniques Reference Document of August 2006 for specifying Best Available Techniques (BAT) for waste combustion, “In installations working mainly for purpose of sewage sludge combustion, BAT is regarded to be the technology based on the fluid bed, because of the fact that it performs a high combustion efficiency and a low volume of exhausts generated” [17].
The aim of this research was an evaluation of utilization of sewage sludge in the law aspects and mobility of heavy metals in sewage sludge ash in waste water treatment plant in Sitkówka – Nowiny.
Materials and methods
This waste water treatment plant is located in Świętokrzyskie Region. This plant receives waste water from separating the sewer system Kielce - capital of this region, municipalities Sitkowka Nowiny and western part of the municipality Masłow. The nominal flow capacity of this sewage treatment plant equals 270 000 PE. The total amount of waste water influent are municipal  waste water 85 % and 15 % of industrial waste - mainly from the food and metal industries. This waste water treatment plant releases around 12 thousand tons of activated sludge per year. Thermal sludge utilization station in this waste water treatment plant operates from November 2011.The maximum daily amount of incinerated sludge equals 88.8 Mg/d. The working hours of this thermal sludge utilization station is 7500 hrs./year. This sludge thermal utilization installation is composed of such main elements as:
– receipt and storage of sewage sludge,
– sludge drying in discs dryer - drying in 215 oC, after drying sewage sludge has 36% of dry mass. The heat for the drying is obtained from the thermal treatment of sludge and received from the flue gas in a heat exchanger. Dried sludge after leaving the dryer are directed to the mixing tank. In this tank dried sludge is mixed with screenings, sand and fat.
– combustion in fluid bed – combustion at 850 oC. Dried sludge is delivered to the sand zone of fluid bed. The combustion of sewage sludge is in the upper part of the chamber of fluid bed, where the gases are removed to heat exchanger and cleaning equipment.
This sewage sludge ash was taken from storage container. Grain size distribution of sewage sludge ash was made by laser diffractometr, Helos Partical Size Analysis.
The BCR test was applied to determine the heavy metal fraction in sewage sludge ashes. The sequential extraction method used allows one to determine the mobility degree of metals which are present in the matrix. The analytics suggested by European Community Bureau of Reference was used. The tests were conducted in accordance with the four-step BCR sequential extraction procedure [18], introducing a change in the method of residual fraction mineralisation, i.e. aqua regia was used in the process of mineralization [19]. The heavy metals in the obtained extracts were determined using a optical spectrometer with inductively coupled plasma ICP Perkin-Elmer Optima 8000.
In the sewage sludge ash, the smallest concentration of the tested heavy metals was found for Cd. The highest concentrations in ash were found for Zn and Pb (tab.1.) The contribution per cent of mobile fractions (fractions I and II) of ash equalled less than 20 %, except Cd (more than 30 %). The dominant fraction of heavy metals were immobile fractions (fractions III and IV) and theirs contribution equaled more than 80 %, except Cd.

Figure1. Cumulative distribution and density distribution of sewage sludge ash from waste water treatment plant in Sitkówka-Nowiny

Table 1 – Speciation of heavy metals in sewage sludge ash from waste water treatment plant in



Heavy metals [mg/kg d.m.]










































Disposal of sewage sludge on waste water treatment plant Sitkówka Nowiny meets the requirements of Polish and EU regulations. Thermal treatment station of sewage sludge in this sewage treatment plant allowed the inclusion of agglomeration Kielce among European agglomerations that lead a modern and green management of the disposal of sewage sludge using the best available technique. The researched sewage sludge ash is not potentially danger to the environment in this aspect.  The project was funded by the National Science Centre allocated on the basis of the decision DEC-2011/03/D/ST8/04984.

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  3. Environment, Statistical Information and Elaborations, Central Statistical Office, Warsaw, 2012.
  4. Commission of European Communities, Council Directive 91/271/EEC of 21 March 1991 concerning urban wastewater treatment (amended by the 98/15/EC of 27 February 1998.
  5. The National Urban Wastewater Treatment Program 2014, Journal of Laws, No. 101, point 1183, 2010 (in Polish).
  6. The Law on Waste, Journal of Laws, No. 0, point 21, 2013 (in Polish).
  7. Commission of European Communities, Council Directive 99/31/EC of 26 April 1999 on the landfill of waste
  8. Environmental Law,  Journal of Laws, No. 62, point 627, 2001 (in Polish).
  9. The Ordinance of Minister of Environment of 8.01.2013 on criteria and procedure for the permission of waste to disposal into the type of landfill, Journal of Laws, No. 0, point 38, 2013 (in Polish).
  10. Gawdzik J., Latosińska J., Speciation of heavy metals in municipal sewage sludge from the three sewage treatment plants, Structure and Environment, 2, 2010, P. 39-44.
  11. Bezak-Mazur E., Dańczuk M., Sorption capacity of conditioned sewage sludge in environmental conditions, Archives of Waste Management and Environmental Protection, 15, 2013, 1, Р. 87-92
  12.  The Ordinance of the Minister of Environment of 13.07.2010 on the sewage sludge, Journal of Laws No. 137, point 924, 2010 (in Polish).
  13. The Ordinance of the Minister of Agriculture and Rural Development of 18.06.2008, on the implementation of certain provisions of the act on fertilizers and fertilization, Journal of Laws No 119, point 765, 2008 ((in Polish).
  14. Commission of European Communities, Council Directive 86/278/EEC of 4 July 1986 on the protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture.
  15. The National Urban Wastewater Treatment Program, Regulation of the Ministry of Environment, Republic of Poland, M.P.03.11.159 Warsaw, 2003 (in Polish).
  16. Rećko K.: Wykorzystanie osadów ściekowych do termicznej utylizacji, pod red. Wandrasza J.W., Pikonia K.: Paliwa z odpadów, t. IV, Gliwice, 2003, s. 419–422.
  17. Integrated Pollution Prevention and Control, Reference Document on Best Available Techniques in Common Waste Water and Waste Gas Treatment, Management Systems in the Chemical Sector, European Commission, 2003.
  18. Ming C., Xiao-Ming L., QI Y., Guang-Ming Z., Ying Z., De-Xiang L., Jing-Jin L., Jing-Mei H., Liang G.,

    J. Hazard. Mater., 2008, 160, 324.
  19. Latosińska J., Gawdzik J., The effect of incineration temperatures on mobility of heavy metals in sewage sludge ash, EPE Journal, 2012, 3, vol. 38, 31-44.

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