• What is meant by co-processing? 

Co-processing means the substitution of fossil fuel and primary raw material by waste derived materials in industrial processes. 

  • What are the benefits of using waste derived fuels and raw materials in cement production?

Through co-processing, cement plant creates positive impact on the environment and local communities:

  • Reducing CO2 emissions, replacing fossil fuels by alternative fuels 
  • Contributing to a Zero Waste Future by reducing quantities of waste going to landfills or illegal dumps, where they can contaminate land and water, and generate the greenhouse gas methane 
  • Offering a local waste management solution
  • Preserving natural resources as primary raw materials are replaced by alternative raw materials
  • Re-purposing residues from other local industries

  • Why is co-processing also a recycling operation?

The mineral portion of waste often consists of chemical elements needed in the cement manufacturing process. For example the metallic structure of tires is made of iron which melts at the temperature in the kiln. Iron is one of the constituent of clinker/cement, this iron is replacing natural iron oxide, it is a recycling operation. The same principle applies to the inorganic fraction of all alternative fuels and raw material co-processed in a cement plant (e.g. glass). 

  • Which countries allow co-processing in cement plants? 

The United Nations’ Basel Convention recognizes co-processing as a suitable and recommended technology for waste management.  Today there are more than 50 countries worldwide, including France, Switzerland, Germany, Japan, having co-processing in cement plants.  

  • Are all cement plants capable of co-processing?

Not all cement plants are capable of co-processing.  There are differences in what type of waste can each cement plant co-process, depending on facility, availability of feed point, operator skill and process control. Generally there are more than 180 cement plants in the world doing co-processing

  • What is the difference between co-processing and waste incineration?

Co-processing and incineration are two different approaches and technology. Incineration is primarily a disposal technology to reduce waste volumes, to reduce the potential negative impact of the waste material and to a certain extent recover energy. Co-processing leaves no residue where incineration leaves ash that need to be landfilled.  In addition, there is no secondary waste generation in co-processing while incineration will generate secondary waste as the process requires input of chemicals.

  • Can co-processing replace landfilling as waste management alternative?

Co-processing is only one element in a country’s integrated waste management scheme. In the general waste management hierarchy, co-processing is preferred option compared to landfilling. However, not all waste material is suitable for co-processing. For those types of waste (for example wastes not meeting Waste Acceptance Criteria) conventional waste management options such as landfilling may be an alternative. 

  • Why co-processing?  Why not recycle?

Not all wastes can be recycled, either due to its condition (for example food packaging) or due to economic reasons.  In such instance, co-processing is a preferred waste management solution over landfilling. 


  1. What is the technical capability of a cement kiln to co-process waste?

A cement kiln is by its nature an efficient tool for final management of waste:

  • Complete burn-out of waste.  2000°C burner flame heats materials to 1450°C. 
  • Long residence time 
  • High level of oxygen and high temperature enable complete destruction of organic components.
  • Sorption of gaseous components such as HF, HCl, and SO2 on lime rich raw materials.
  • Zero residue; no residue to be landfilled.  No risk to be managed by future generations.
  1. Which types of waste are the most suitable for co-processing?

    There is a wide range of waste material suitable for co-processing, ranging from agricultural wastes to industrial wastes such as water treatment plant sludge and non-recyclable packaging material, and sorted municipal solid waste. 

While the cement kiln can treat a wide range of wastes, Waste Acceptance Criteria is strict in order to ensure no negative impact on health, safety and environment, and the quality of cement produced. 

  1. Which types of waste are not accepted for co-processing?

    Electronic fraction of electrical and electronic waste (e-waste), whole batteries, waste of unknown or unpredictable composition including unsorted municipal waste, radioactive waste, asbestos-containing waste, explosives, weapons and ammunition, self-reactive / thermally unstable compounds / organic peroxides exhibiting explosive properties, and anatomical and infectious health care waste are not suitable for co-processing.  Reasons for excluding them are the risk of excessive emissions, health and safety provisions, negative impact on kiln operation, or the observation of the general waste hierarchy principles.
  1. Can sorted municipal solid waste be co-processed?

Unsorted municipal waste should not be used for co-processing as it is too heterogeneous. However, sorted municipal solid waste is suitable for co-processing. The combustible part of municipal solid waste – after a pre-treatment process – can be used as alternative fuel in cement kilns.

  1. Is recyclable waste used in co-processing?

The objective is to always follow the waste management hierarchy. If there is a feasible solution available higher up in the hierarchy, that solution should be pursued. However, if recycling is not meaningful from an environmental and economic point of view, co-processing offers an environmentally better solution compared to incineration or landfilling.

  1. Why is pre-processing required for certain waste materials?

Waste generally cannot be used directly as ARM and AF, but must undergo a preparation process. This step delivers a stable product that complies with the technical specifications of cement production and guarantees that environmental standards are met. Pre-processing could include shredding, homogenization, drying or sorting.


  1. Can heavy metals, which are contained in waste, be found in cement? And can it have a negative health impact on final users? 

The presence of heavy metals in cement, whatever their source, are limited to concentrations which do not in any way modify the quality of construction products, and have no particular impact on the environment or on health.

Heavy metals are omnipresent in nature in small quantities and a variety of everyday products contain them. Trace quantities of heavy metals have always been present in the natural raw materials and fossil fuels used in the making of cement. Chemical analyses of cement mortar and concrete demonstrate heavy metal concentration either below threshold levels (cannot be detected) or similar to the levels found in many natural rocks. Leachate testing, done to simulate the harshest environmental exposure, also demonstrates that heavy metals do not dissolve back. That is why cement and related products can be used in water storage and transportation applications without any risk to human health. 

During co-processing, the organic portion of the waste is destroyed in the kiln.  The inorganic residues which may contain heavy metals and other elements are fully integrated in stable clinker structure.

A high number of studies (35) completed from 1990 to 2003 and referenced by Cembureau in a document dated February 2005 confirm: 

  • There are generally no significant differences between cement produced with or without alternative fuels and raw materials
  • The amount of trace elements that leach out of monolithic concrete are well below EU limits for drinking water
  • The mere presence of trace elements is not a useful indicator of cement’s environmental acceptability, since there is no consistent relationship between trace element content and tendency to be released or leach.
  1. Would clinker produced with ARM and AF contain heavy metals from the waste?

Extensive investigations have shown that the effect of ARM and AF on the heavy metal content of clinker is marginal on a statistical basis. Heavy metals are permanently bonded into the clinker matrix. These become fixed into the impermeable structure of the finished product of concrete. The one exception is the widespread use of tires which will raise zinc levels. With careful input control and limitation of heavy metal content, an accumulation of these pollutants in clinker is prevented.

It should be noted that the principal source of heavy metals is natural rock and not the use of industrial wastes.


  1. What health impacts does co-processing have on populations close to the cement plant?

Several scientific studies have been carried out on the potential health effects of co-processing waste in cement kilns. Available toxicological and public health studies have concluded that co-processing, when performed in compliance with the best available techniques and best environmental practices, does not create additional risk when compared to the baseline situation without co-processing. 

  • Does co-processing adversely affect a cement plant’s atmospheric emissions?

The use of ARM and AF doesn’t negatively affect the emissions of a cement kiln stack. When basic rules are followed regarding selection of correct feed points as well as having the right facility, co-processing does not increase overall emissions from a cement plant. 

  • How does the government protect local residents and public from potential risks associated with co-processing?

  1. Quality control of scheduled waste received by cement plant using Waste Acceptance Criteria
  2. Permit : Qualification, facility, technology, handling process, ERP
  3. Emission monitoring : compulsory to cement plant to use Continues Emission Monitoring System (CEMS) and comply to the standard limit.
  4. Audit : frequency of inspection on the cement plant by DOE