Hydrated Lime Treatment is a cost-effective chemical treatment for faecal sludge from pits and trenches. It uses hydrated or slaked lime (calcium hydroxide: Ca(OH)2) as an additive to create a highly alkaline environment. It significantly reduces the public and environmental health risks of latrine 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.
The common name for calcium oxide (quicklime, CaO) or calcium hydroxide (slaked or hydrated lime, Ca(OH)2). It is a white, caustic and alkaline powder produced by heating limestone. Slaked lime is less caustic than quicklime and is widely used in water/wastewater treatment and construction (for mortars and plasters). It can also be used for on-site treatment of faecal sludge. See S.17A 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.

Hydrated lime is used to increase pH and create an alkaline environment in blackwater or sludge, making it no longer a viable habitat for pathogens. The optimum dosage to reach a recommended pH of above 12 should be between 10–17 g lime/kg of faecal sludge with a contact time of a at least 2 hours. The exact amount of time required depends on the quality of the lime and the characteristics of the blackwater or sludge. Its effect can be enhanced by increasing the contact time or dosage. The treatment should be undertaken as a batch process. It is a robust technology that can be used to treat both solid and liquid sludge. Above pH 10.4 hydrated lime also acts as a coagulant with precipitation of Mg(OH)2 and allows for separation of sludge and effluent for liquid sludge with < 3 % dry solids. To increase the precipitation of solid particles, and depending on the presence of an excess of magnesium cations in blackwater or sludge, magnesium sulphate can be added. After treatment, the pH falls towards neutral usually within 24 hours and the treated sludge decants. After pH neutralisation, the supernatant can be pumped off and safely infiltrated into the soil (e.g. D.10 ) or used for irrigation or landscaping purposes. However, groundwater pollution may be an issue due to the high nutrient load. The treated solids can be used as a soil amendment or dried and used as cover for landfills.

Design Considerations

Hydrated Lime Treatment should be carried out in a leak-proof cistern or tank, If the tank is located below ground, care should be taken to ensure it is absolutely water tight to avoid the leakage of highly alkaline effluent into the soil. In areas with high groundwater level or in flood prone areas it is recommended to use above ground tanks. Separate tanks may be needed for preparation of the lime slurry and for post-neutralisation of the treated effluent respectively.

Materials

Hydrated Lime Treatment needs a reactor vessel. A smaller additional container is needed to prepare the lime slurry (e.g. a 200 L plastic drum). For an even distribution of hydrated lime throughout the sludge, constant mixing is required (either manually or with a mixing pump). The type of pump required depends on the consistency of the sludge. A separate pump is needed to remove the treated effluent from the tank and a shovel or vacuum pump to remove the solid material. In addition a water testing kit (particularly for pH, E.coli, total suspended solids and turbidity) is needed as well as personal protective equipment (PPE) including masks, gloves, boots, apron or suit and respective chemicals (hydrated lime, magnesium sulphate if needed).

Applicability

Hydrated Lime Treatment is particularly suitable for the rapid response phase due to its short treatment time, simple process and use of readily available materials. With trained and skilled staff, it allows for safe, cost-effective and rapid treatment of faecal sludge with outputs that can be safely used for irrigation or soil amendment or can be safely infiltrated or disposed of, if the environmental conditions permit.

Operation and Maintenance

Lime is corrosive in nature due to its alkalinity and regular maintenance of the pumps used for mixing will be required. Due to the potential health risks when handling hydrated lime, skilled staff are required who follow appropriate health and safety protocols.

Health and Safety

Hydrated lime is a powder and corrosive to skin, eyes and lungs. Therefore, adequate PPE must be worn when handling hydrated lime to prevent irritation to eyes, skin, respiratory system, and gastrointestinal tract. Protection from fire and moisture must also be ensured. Lime is an alkaline material that reacts strongly with moisture. Staff must be carefully trained to follow health and safety protocols.

Costs

Hydrated Lime Treatment is a relatively cheap treatment option. Costs may vary depending on the availability and costs of local materials and chemicals/lime. As part of an appropriate health risk management, costs for personal protective equipment and staff trainings need to be considered.

Social Considerations

Proper health and safety protocols should be in place and include the provision of PPE and respective trainings for involved staff.