Use of Sewage Sludge in Cement Industry

The MENA region produces huge quantity of municipal wastewater which represents a serious problem due to its high treatment costs and risk to environment, human health and marine life. The per capita wastewater generation rate in the region is estimated at 80-200 litres per day. Sewage generation across the region is rising by an astonishing rate of 25 percent every year.

Municipal wastewater treatment plants in MENA produce large amounts of sludge whose disposal is a cause of major concern. For example, Kuwait has 6 wastewater treatment plants, with combined capacity of treating 12,000m³ of municipal wastewater per day, which produce around 250 tons of sludge daily. Similarly Tunisia has approximately 125 wastewater treatment plants which generate around 1 million tons of sewage sludge every year. Currently most of the sewage is sent to landfills. Sewage sludge generation is bound to increase at rapid rates in MENA due to increase in number and size of urban habitats and growing industrialization.

Use of Sewage Sludge in Cement Industry

An attractive disposal method for sewage sludge is to use it as alternative fuel source in a cement kiln. The resultant ash is incorporated in the cement matrix. Infact, several European countries, like Germany and Switzerland, have already started adopting this practice for sewage sludge management. Sewage sludge has relatively high net calorific value of 10-20 MJ/kg as well as lower carbon dioxide emissions factor compared to coal when treated in a cement kiln. Use of sludge in cement kilns can also tackle the problem of safe and eco-friendly disposal of sewage sludge. The cement industry accounts for almost 5 percent of anthropogenic CO2 emissions worldwide. Treating municipal wastes in cement kilns can reduce industry’s reliance on fossil fuels and decrease greenhouse gas emissions.

The use of sewage sludge as alternative fuel in clinker production is one of the most sustainable option for sludge waste management. Due to the high temperature in the kiln the organic content of the sewage sludge will be completely destroyed. The sludge minerals will be bound in the clinker after the burning process. The calorific value of sewage sludge depends on the organic content and on the moisture content of the sludge. Dried sewage sludge with high organic content possesses a high calorific value.  Waste coming out of sewage sludge treatment processes has a minor role as raw material substitute, due to their chemical composition.

The dried municipal sewage sludge has organic material content (ca. 40 – 45 wt %), therefore the use of this alternative fuel in clinker production will save fossil CO2 emissions. According to IPCC default of solid biomass fuel, the dried sewage sludge CO2 emission factor is 110 kg CO2/GJ without consideration of biogenic content. The usage of municipal sewage sludge as fuel supports the saving of fossil fuel emission.

Sludge is usually treated before disposal to reduce water content, fermentation propensity and pathogens by making use of treatment processes like thickening, dewatering, stabilisation, disinfection and thermal drying. The sludge may undergo one or several treatments resulting in a dry solid alternative fuel of a low to medium energy content that can be used in cement industry.


The use of sewage sludge as alternative fuel is a common practice in cement plants around the world, Europe in particular. It could be an attractive business proposition for wastewater treatment plant operators and cement industry in the Middle East to work together to tackle the problem of sewage sludge disposal, and high energy requirements and GHGs emissions from the cement industry.

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About Dirk Lechtenberg

Dirk Lechtenberg is a pioneer in the production and use of alternative fuels. He is the founder and Managing Director of the consulting company MVW Lechtenberg & Partner (Germany). He is the recipient of the Global Fuel award 2012 by the Cement & Lime Magazine.
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10 Responses to Use of Sewage Sludge in Cement Industry

  1. Md.Mohiuddin says:

    Thanks for the nice write up. additionally, the sewage sludge can also be fed as alternative raw material (ARM) in cement kiln.

  2. Redouane says:

    Thanks Dirk for this interesting article. Do you know companies in the MENA region or elswhere able to design and build facilities for transforming the sewage sludge into an alternative fuel?

    • Dear Redoane, unfortunately I dont know any MENA based company- but if you need contact details for suppliers please contact me. We have developed a few sewage sludge to alternative Fuel projects- as consultants.

      • Nasser Alnahhas says:

        Mr. Lechtenberg,
        I found your articles very interesting.
        I am curious as to the use of dried sewage sludge in cement industry kilns in Saudi Arabia. If the kilns are electric or gas fired, how do you convert them to take the dried sludge?

        • Usuammy cement plants are fired with fosssil fuels such as natural gas, fuel oil, coal or petcoke; in the mena region most of the Plants are gas / oilfired. So introducing solid fuels ( such as dried sludge) will need a differnt burner, storage , dosing and feeding system. This is standard in most countries in the world and only a minor technical issue which can be solved with small investments and short time.

    • Nasser Alnahhas says:

      We do this service in Saudi Arabia. If you wish more details, please contact me by email address

  3. Thomas Holliber says:

    Interesting article, in Austria we have some experience in co-grinding sewage sludge with coal or petcoke in the coal mill, up to 30 M% of sludge with up to 30% of moisture.
    A rather easy way to dose the alternative fuel to the burner.

  4. Salman Zafar says:

    Many thanks for sharing Austrian experience. Sewage sludge is a big nuisance and its use as alternative fuel in industries is surely a welcome development.

  5. Dave Stanley says:

    Clearly using sludge as a fossil fuel substitute in cement manufacturing is smarter than dumping to landfill. The bottom line is though it remains an extract use dump process – but with the dump largely to atmosphere. It disrupts the carbon cycle. The high organic content (+ trace elements) but less the pollutants/contaminants discharged ought to be returned whence it came – agricultural soils. Or in the middle east – combatting desertification. Failure to do so means the soils are being mined and degraded, with the consequential loss of fertility which in turn negatively impacts as biodiversity loss, degraded food, and then human health. Sustainability is about thinking whole life cycle!

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