Pre-Treatment is the preliminary removal of wastewater or sludge components, such as oil, grease, and solid material. Sequenced before a conveyance or (semi-) centralized treatment technology or pump, Pre-Treatment units can prevent the accumulation of solids and minimise subsequent blockages, help reduce abrasion of mechanical parts and extend the life of sanitation infrastructure.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.Describes the transport of products from one functional group to another. Although products may need to be transferred in various ways between functional groups, the longest, and most important gap is usually between the user interface or collection and storage/treatment and (semi-) centralised treatment. Therefore, for simplicity, conveyance only describes the technologies used to transport products between these two functional groups. In the technology overview graphic, the conveyance functional group is subdivided into the two subgroups: “Emptying and Transport” and “Intermediate Storage”. This allows for a more detailed classification of each of the listed conveyance technologies.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.

Oil, grease, sand and suspended solids can impair transport and/or treatment efficiency through clogging and wear. It is therefore crucial to prevent these from entering the system and early removal of this material that does enter the system is essential for its durability. Preventive measures at individual level (source control) and along conveyance systems are important. For example, sewer inspection chambers should always be closed with manhole covers to prevent extraneous material from entering the sewer. Pre-Treatment Technologies are generally installed at the point where wastewater enters a treatment plant or leaves larger institutions. These technologies use physical removal mechanisms, such as screening, flotation, settling and filtration.

Design Considerations

Screen Screening aims to prevent coarse solid waste, such as plastics and other trash, from entering a sewer or treatment plant. Solids are usually trapped by inclined screens or bar racks. Spacing between the bars is usually 1.5 to 4 cm, depending on cleaning patterns. Screens can be cleaned by hand or mechanically raked. The latter allows for a more frequent solids removal and, correspondingly, a smaller design. Grease Trap These trap oil and grease for easy collection and removal. Grease traps are chambers made of either brickwork, concrete or plastic, with an odour-tight cover. Baffles or tees at the inlet and outlet prevent turbulence at the water surface and separate floating components from effluent. A grease trap can either be located directly under the household sinks, or, for larger amounts of oil and grease, a grease interceptor can be installed outdoors. If designed large enough, grease traps can also remove grit and other settleable solids through sedimentation, similar to Septic Tanks S.13 . Grit Chamber Where subsequent treatment steps could be hindered or damaged by sand in the wastewater, grit chambers or sand traps allow for the removal of such heavy inorganic materials by settling them out. There are three general types of grit chambers: horizontal-flow, aerated, and vortex chambers. All of these designs allow heavy grit particles to settle out, while lighter, principally organic particles remain in suspension.

Materials

Screens, grease traps and grit chambers can all be built with locally available materials, such as concrete and metal bars. The last two are also available as prefabricated units, or can be made out of prefabricated containers. For automatic screens electricity is required. Tools to de-scum, desludge and to remove solid waste are needed, including personal protective equipment for the workers performing these tasks.

Applicability

Grease traps should be applied where considerable amounts of oil and grease are discharged (e.g. restaurants, cantines). Grease removal is especially important where there is an immediate risk of clogging, e.g. greywater treatment in Constructed Wetlands T.6 . Screening is essential to prevent solid wastes from entering sewer systems and treatment plants. Trash traps, e.g., mesh boxes, can be applied at strategic locations such as market drains. A grit chamber is especially recommended where roads are not paved and/or stormwater may enter the sewer system, and in sandy environments.

Operation and Maintenance

Pre-Treatment products separated from wastewater or sludge should be removed regularly, with a frequency depending on the accumulation rate. For screens, removal should be done at least every day. An under-the-sink grease trap must be cleaned often (once a week to once a month), whereas a larger grease interceptor is designed to be pumped out every 6–12 months. As for grit chambers, special care should be taken after rainfall. If maintenance is too infrequent, strong odours can result from the degradation of accumulated material. Insufficiently maintained pre-treatment units can eventually lead to the failure of downstream elements of a sanitation system (especially through clogging). The Pre-Treatment products should be disposed of as solid waste in an environmentally sound way. If no solid waste management infrastructure X.8 exists, the solid wastes should be buried.

Health and Safety

People involved in Pre-Treatment may come into contact with pathogens or toxic substances; therefore, adequate protection with proper personal equipment, i.e. boots and gloves, is essential, as is safe disposal to prevent the local population from coming into contact with the solid wastes.

Costs

The capital and operating costs of Pre-Treatment Technologies are relatively low. The costs of a constant electrical supply have to be considered for automated types of screens. All technologies require regular descumming and desludging and therefore require trained workers.

Social Considerations

Removal of solids and grease from Pre-Treatment Technologies is not pleasant and, if households or community members are responsible for doing this, it may not be done regularly. Hiring professionals for this may be the most efficient option but can be costly. Behavioural and technical source control measures at the household or building level can reduce pollution loads and keep Pre-Treatment requirements low. For example, solid waste and cooking oil should be collected separately and not disposed of in sanitation systems. Equipping sinks and showers with appropriate screens, filters and water seals can prevent solids from entering the system.