Lactic Acid Fermentation (LAF) is a biological treatment option using lactic acid bacteria (LAB) with the ability to form significant quantities of lactic acid and thereby aid in inactivating pathogens in faecal sludge. LAB are easily obtainable and can be made from molasses, milk and probiotic drinks.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. Simple, single cell organisms that are found everywhere on earth. They are essential for maintaining life and performing essential “services”, such as composting, aerobic degradation
of waste, and digesting food in our intestines. Some types, however, can be pathogenic and cause mild to severe illnesses. Bacteria obtain nutrients from their environment by excreting enzymes that dissolve complex molecules into more simple ones which can then pass through the cell membrane.

The process by which biodegradable components are biologically decomposed by microorganisms (mainly bacteria and fungi) under controlled aerobic conditions.
The utilisation of products derived from a sanitation system.
Any cellular or non-cellular microbiological entity capable of replication or of transferring genetic material (e.g. bacteria, viruses, protozoa, algae or fungi).
Any substance that is used for growth. Nitrogen (N), phosphorus (P) and potassium (K) are the main nutrients contained in agricultural fertilisers. N and P are also primarily responsible for the eutrophication of water bodies.
A sanitation system in which excreta and wastewater are collected and stored or treated on the plot where they are generated.
An organism or other agent that causes disease.A diverse group of unicellular eukaryotic organisms, including amoeba, ciliates, and flagellates. Some can be pathogenic and cause mild to severe illnesses.
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
An infectious agent consisting of a nucleic acid (DNA or RNA) and a protein coat. Viruses can only replicate in the cells of a living host. Some pathogenic viruses are known to be waterborne (e.g., the rotavirus that can cause diarrheal disease).
Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

Lactic acid, in its dissociated form can penetrate cell membranes and inactivate and destroy pathogens. The inactivation of pathogens is triggered when the concentration reaches approximately 20–30 g of lactic acid per litre of faecal sludge. This corresponds to a lowering of pH; pH conditions of less than pH 4 induce pathogen inactivation.

Design Considerations

It is recommended that the LAF process is carried out under batch conditions in sealed vessels (container or bladder). The vessel size may vary depending on the amount and frequency of sludge generated. LAB is cultured in an inoculum before being added to the fresh sludge. The inoculum for the first batch is a mixture of milk (99.8 %) and LAB from, for example, Yakult (0.02 %) that has been mixed and stored at room temperature for 48 hours. For subsequent batches the treated sludge can be used as an inoculum. For the biological process, the inoculum is initially added to the tank in the ratio of 10 % of the overall sludge wet weight. The fresh faecal sludge is pumped into the vessel and recirculated to get a homogenous mix of fresh sludge and the inoculum. The sludge is then stored over a period of 2 weeks monitoring the pH daily to ensure a sanitised sludge is produced.

Materials

LAF Treatment needs a vessel, preferably sealable as LAB are most efficient under anaerobic conditions. However, LAB are aero-tolerant and therefore open tanks can be used if no sealed vessel is available. To achieve a homogeneous mix within the vessel a recirculation pump is required. The type of pump depends on the thickness of the sludge. For liquid sludge, a diaphragm pump may be used, whereas thicker sludge may need a screw pump or a vacuum pump. In addition, an initial supply of milk and a probiotic drink is needed to prepare the LAB molasses. To monitor the pH level and pathogens in the vessel a water testing kit is needed.

Applicability

LAF Treatment is considered an emerging technology that has not yet been widely used in emergency settings. However, first pilot projects and studies are promising and growing evidence suggests that LAF Treatment may be a suitable treatment option particularly for the acute response phase due to its short treatment time (around 2 weeks), a relatively simple process and use of readily available materials. It can be applied as an on-site treatment option for pit and trench latrines S.1 S.3 S.4 .

Operation and Maintenance

Regular maintenance of pumps is required, especially due to the corrosive nature of the treated sludge. For each new batch of faecal sludge an initial amount of sludge from the previous batch should remain in the reactor vessel as an inoculant for LAB production in the sludge.

Health and Safety

Molasses, milk or the LAB do not pose any significant health risk. However, proper personal protective equipment (PPE) should still be considered when handling the treated sludge as the final product may not be sufficiently treated and may still contain pathogens.

Costs

LAF Treatment can be considered a relatively cheap treatment option. Costs may vary depending on the availability and costs of local materials. To treat 1 m3 of faecal sludge an initial amount of 100 L of milk and 200ml of a probiotic drink is needed. For subsequent batches the treated sludge can be used as the inoculum.

Social Considerations

PPE should be worn and training for involved staff is needed to ensure the proper functioning of the technology.