The lacto-fermentation process (also lactic acid fermentation) is a biological anaerobic degradation process (similar to silage production process in agriculture), but without gas formation. During this process, sugars such as glucose, fructose, and sucrose, are converted into cellular energy and the metabolic by-product lactic acid. Lacto-fermentation is used throughout the world to preserve foods. When the acidity rises due to lactic acid fermenting organisms, many other pathogenic microorganisms are killed. Yogurt and sauerkraut are some of the most famous products produced by lacto-fermentation. Most lactic acid bacteria obtain energy only from the metabolism of sugars and hence are usually restricted to habitats in which sugars are present. The two most important subgroups of the lactic acid bacteria depend on the nature of the products formed from the fermentation of sugars: one group, called homofermentative, produces a single fermentation product, lactic acid, whereas the other group, called heterofermentative, produces other products, mainly ethanol and CO2 as well as lactate. Even though anaerobe, most lactic acid bacteria have the advantage not to be sensitive to O2, allowing them to grow in its presence as well as in its absence (they are aerotolerant anaerobes). Synonyms: Lactic Acid Fermentation, Lactofermentation
Lakes are discrete, largely isolated ecosystems in which the interplay between physical, biogeochemical and organismal processes can be studied, understood, and put to use in effective management.
Lake Ecosystems
A landfill is a land disposal site for waste, which is designed to protect from environmental pollution and health risks. It is not the same as an open dump. Landfills are built to concentrate the waste in compacted layers to reduce the volume and monitored for the control of liquid and gaseous effluent in order to protect the environment and the human health. In reality, the term is often also used for unprotected waste dumping sites. Synonyms: Engineered Landfill, Landfilling, Sanitary Landfill

Large-scale Hydro Power
Hydropower uses the power of moving water (kinetic energy) to generate electricity, usually requiring the construction of dams to store large quantities of water. Generally, large-scale hydropower produces over 100 MW. Synonyms: Large Hydroelectric Power
Abbreviation: LHP

Leach Field
A leach field, or drainage field, is a network of perforated pipes that are laid in underground gravel-filled trenches to dissipate the effluent from a water-based collection and storage/treatment or (semi-)centralized treatment technology. They allow for a further treatment of the effluent and to recharge groundwater bodies.
The liquid fraction that is separated from the solid component by gravity filtration through media (e.g., liquid that drains from drying beds).
Lead, a heavy, bluish-gray, soft, ductile metal, the chemical element of atomic number 82. (Symbol: Pb)
Abbreviation: Pb

Learning Needs Analyses
Learning needs analyses are undertaken to determine the gap between the existing skills, knowledge and abilities and those desired. Once this gap is determined, decisions can be taken as to the type of training required. The procedure for conducting such an analysis can be quite simple but usually requires quite a bit of time before a training.

Life-Cycle Cost Approach
The life-cycle cost approach is a methodology for monitoring and costing sustainable water, sanitation and hygiene (WASH) services by assessing costs and comparing them against levels of service provided.
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).
Linear alkylbenzenesulfonate
Linear alkylbenzenesulfonate (LAS) is the most widespread anionic surfactant used in domestic and commercial detergent formulations, primarily in laundry detergents and cleaning products. LAS, derived from petroleum bi-products, is quite rapidly degraded aerobically, but only very slowly or not at all under anaerobic conditions. Synonyms: LAS
Abbreviation: LAS

Support of the sides of an excavation made out of concrete, bricks, stone or precast concrete rings. During construction, the lining provides protection against caving and collapse and prevents crumbling ground from filling up the dug hole. After completion of the well it retains the walls.
Linking Relief, Rehabilitation and Development
Linking relief, rehabilitation and development (LRRD) was coined and subsequently validated in the 1990s in a report from the European Commission to the European Parliament. Under that approach, the conceptual groundwork for sustainable development is ideally laid when humanitarian aid starts. Likewise, reconstruction/rehabilitation and long-term development cooperation should help reduce the population’s vulnerability to disaster, mitigate the impact of disasters and enable people to help themselves in disaster situations. Synonyms: LRRD
Liquified Petroleum Gas
A mixture of light gaseous hydrocarbons (ethane, propane, butane, etc.) made liquid by pressurisation and used as fuel. Synonyms: Autogas, GPL, LP Gas, LPG
Abbreviation: LPG

Log Reduction
Organism removal efficiencies. 1 log unit = 90%, 2 log units = 99%, 3 log units = 99.9%, and so on.
Logical Framework Approach
A strategic planning and project management approach.
Abbreviation: LFA

Low-flush Toilet
A low-flush or low flow toilet is a flush toilet that uses significantly less water than a full-flush toilet. That means, they use 4 to 6 litres instead of the 8 to 20 litres. Low-flush toilets use a special design of the cistern and the siphon in order to allow the removal of faeces and excreta with less water. Most often, they also include a-dual flush system, with one flush being designed for urine only using less than half a litre for flushing. Today, there are many suppliers of different models of low-flush toilets all over the world. Low-flush toilets reduce the water consumption, however, low-flush toilet still require large amounts of fresh water and with certain models, users have to flush even twice in order to achieve the complete removal of faeces from the bowl. Synonyms: Low Consumption Toilet, Low-flow Toilet
Low-pressure membranes
Low-pressure membranes are used for microfiltration and ultrafiltration.

Low-rate Digestion
Low-rate anaerobic digestion processes do not retain biomass and the relatively long HRT is equal to the SRT. These processes are adapted for the treatment of homogeneous high-strength wastes, such as agricultural slurries or municipal organic wastes. Synonyms: Low-rate Anaerobic Digestion
Low-solids Digestion
Low-rate anaerobic digestion systems are classified according to the percentage of total solids (TS) in the waste stream. Wet digestion means that the TS content is lower than 20 %. Synonyms: Wet Digestion