Co-Combustion of Sludge through the process of incineration is an effective disposal and resource recovery option for dewatered faecal sludge.Mixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies, i.e. it has not been transported through a sewer. It can be raw or partially digested, a slurry or semisolid, and results from the collection and storage/treatment of excreta or blackwater, with or without greywater. Wastewater sludge (also referred to as sewage sludge) originates from sewer-based wastewater collection and (semi-)centralised treatment processes. The sludge composition will determine the type of treatment that is required and the end-use possibilities.Describes technologies for on-site collection, storage, and sometimes (pre-) treatment of the products generated at the user interface. The treatment provided by these technologies is often a function of storage and is usually passive (i.e. requires no energy input), except a few emerging technologies where additives are needed. Thus, products that are ‘treated’ by these technologies often require subsequent treatment before use and/or disposal. In the technology overview graphic, this functional group is subdivided into the two subgroups: “Collection/Storage” and “(Pre-)Treatment”. This allows a further classification for each of the listed technologies with regard to their function: collection and storage, (pre-) treatment only or both.Refers to the methods through which products are returned to the environment, either as useful resources or reduced-risk materials. Some products can also be cycled back into a system (e.g. by using treated greywater for flushing).A functional group is a grouping of technologies that have similar functions. The compendium proposes five different functional groups from which technologies can be chosen to build a sanitation system:
User interface (U), Collection and Storage/Treatment (S), Conveyance (C), (Semi-) Centralised Treatment (T), Use and/or Disposal (U).
A sanitation system is a multi-step process in which sanitation products such as human excreta and wastewater are managed from the point of generation to the point of use or ultimate disposal. It is a context-specific series of technologies and services for the management of these sanitation products, i.e. for their collection, containment, transport, treatment, transformation, use or disposal. A sanitation system comprises functional groups of technologies that can be selected according to context. By selecting technologies from each applicable functional group, considering the incoming and outgoing products, and the suitability of the technologies in a particular context, a logical, modular sanitation system can be designed. A sanitation system also includes the management and operation and maintenance (O & M) required to ensure that the system functions safely and sustainably. The utilisation of products derived from a sanitation system.
A sanitation system in which excreta and wastewater are collected and stored or treated on the plot where they are generated.
The means of safely collecting and hygienically disposing of excreta and liquid
wastes for the protection of public health and the preservation of the quality of public water bodies and, more generally, of the environment.

Waste matter that is transported through the sewer.
An open channel or closed pipe used to convey sewage. See C.3 and C.4
Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

In Co-Combustion the pathogens are killed and the sludge is sanitised. As part of the process energy is generated, which can be used for heating or the production of electricity.

Design Considerations

In Co-Combustion of Sludge or more general thermo-chemical conversion, some form of heat is applied to sanitation products such as faecal sludge to destroy pathogens and drastically reduce the sludge volume, with energy produced in the form of heat. Before incineration, sludge needs to be dewatered e.g. in Unplanted or Planted Drying Beds T.9 T.10 . Co-Combustion (or incineration) of Sludge together with solid waste happens at temperatures of 850–900 °C. The energy can be used for example, to power cement kilns. The ash produced can be used in construction or can be safely disposed of. The ash may be hazardous as it could have a high heavy metal content, depending on the source of the sludge. Methods for incineration include mass burn incineration, fluidised-bed incineration and co-incineration with municipal solid waste or in cement factories. An emerging technology in heat application treatment is pyrolysis or gasification of faecal sludge. Pyrolysis or gasification happens through heating in an oxygen-depleted environment, thus preventing combustion. Gasification occurs at temperatures above 800 °C, pyrolysis between 350 and 800 °C. In these processes char is produced, which can be used in furnaces and kilns in the same way as coal.

Materials

The main requirement for incineration is an incineration furnace. An incineration furnace requires many different special parts and materials, particularly for the treatment of the exhaust gases, which can be dangerous for public and environmental health. The required special parts are often not locally available. With an existing solid waste incineration plant, Co-Combustion of Sludge can be done immediately. Pyrolysis and gasification reactors can be constructed with locally available materials (e.g. oil drum, locally produced burner) on a small scale.

Applicability

Co-Combustion of Sludge is an option, if a functioning incineration plant is within an acceptable distance to keep transport costs down. With an existing, functional incinerator, this technology can be used straight away in the acute phase of an emergency. As there is only some dewatering needed as a pre-treatment, sludge can be disposed of very quickly. The necessities in terms of skills, institutional set-up and financial resources to implement such a system from scratch are very high and only suitable for the recovery phase.

Operation and Maintenance

Highly skilled workers are needed to operate and maintain an incinerator and a pyrolysis or gasification reactor. Since high temperatures are reached, only trained staff should operate and maintain the reactor and be in the vicinity. Regular monitoring of the plant or reactor is needed.

Health and Safety

Along with heat, by-products of incineration and pyrolysis include several gaseous pollutants, as well as tar, ash and unburned solid residues. These byproducts need further treatment or safe disposal, as they might be hazardous to human and environmental health.

Costs

The costs of installing a new incinerator are very high. Operation and maintenance (O & M) costs are also high, as specialised personnel must operate the plant. Other important costs to consider are the transport of products to the plant, which is often located outside of urban settlements. Capital costs for small-scale pyrolysis or gasification reactors are low to medium while O & M costs are relatively high as specialised personnel is needed.

Social Considerations

Co-Combustion of Sludge may not be appropriate in all cultural contexts. The incineration of sludge coming from human excreta and the use of incinerated sludge products in the cement industry might therefore be disregarded and need to be properly addressed as part of awareness raising measures.