What are the Different Sanitation Systems and How to Select the Most Appropriate System for Specific Conditions?

An appropriate sanitation system is a combination of compatible technologies that provide a socially and environmentally acceptable service at an affordable cost. A sanitation system is a set of technologies and services which together manage sanitation products along the five functional groups of the sanitation service chain. A viable sanitation system is composed of compatible technologies that collect or store, transfer, transform, safely reuse or dispose of sanitation products. The selected technologies are then assessed using geophysical, technical, socio-cultural, legal and financial criteria as well as capacity and management considerations. 

Relevance/Importance

Both the technologies and accompanying services selected to deliver safe sanitation dictate the type of system—networked, non-networked or hybrid—and its ongoing operation and maintenance. Therefore, it is important to understand the differences between the most common sanitation systems and how those differences affect future management decisions, especially for different phases of an emergency. The most common systems primarily fall into one of the following four categories:  

• Dry on-site storage and treatment that does not require emptying such as Arborloos 
• Dry on-site storage and treatment without sludge such as Urine Diversion Dry Toilets or Container-Based Toilets that require emptying and safe disposal 
• Water-based systems with sludge or pit humus production, such as Pit Latrines or Septic Tanks and Pour-Flush Toilets, that require emptying and faecal sludge transport, treatment and safe disposal. These systems are sometimes also called Faecal Sludge Management (FSM) 
• Water-based systems that connect to a centralised treatment system 

All of these systems can be upgraded for resource recovery by, for example, introducing safe reuse of dried sludge in agriculture, urine diversion or storage and reuse at the source for gardening. These systems may include urinals, greywater, and stormwater management solutions. 

Overview

Sanitation systems are made up of a mix of sanitation technologies that together manage sanitation products along the sanitation service chain. Each sanitation system can be defined by five functional groups. They are the user interface, on-site collection and/or storage, conveyance, (decentralised or centralised) treatment and reuse or disposal. A viable system is composed of compatible technologies through which the products are collected or contained, transferred, transformed or safely reused or disposed of.  

The main factors that distinguish different sanitation systems are (Spuhler et al. 2022): 

• The type of user interface: this can be either a dry system (no flush but optional anal cleansing water) or a water-based user interface (cistern and pour-flush toilet). The system selected will influence what type of collection and treatment is required downstream 
• The degree of centralisation: some systems treat or dispose of excreta and sludge on-site, while others use transportation or other means to transfer the sanitation products to decentralised or centralised treatment systems or to disposal/reuse technologies. Hybrid systems collect and treat or dispose of excreta and sludge on-site but the effluent is collected in e.g. a Simplified Sewer.  
• The type of transport: if the excreta or sludge is not disposed of on-site, the sanitation products are transported either through a sewer if these are in place and water for flushing is available, or, more commonly, through Manual or Motorised Emptying and Transport in trucks or barrels. 

In the acute response phase, the focus is always on the user interface and safe disposal, while the aim for the stabilisation and recovery phases is to have a full sanitation system in place. Simple on-site systems with trenches (e.g. Shallow Trench Latrines or Deep Trench Latrines) are a common solution in the initial phase. These technologies should be upgraded as soon as possible to an improved user interface (e.g. a latrine) and storage (e.g. single pit or cesspit). Later on, pits must be emptied and the products treated and disposed of either on or off-site. 

The simplest on-site treatment is burying, but this can lead to groundwater pollution. Dry composting or dehydration systems (such as Urine Diversion Dry Toilets) are a viable alternative with fewer flies and reuse options but are more difficult to maintain and may not be socially acceptable. Rapid and simple off-site treatments of sludge from water-based systems focus on pathogen reduction (e.g. Lime Treatment) and burying (e.g. Fill and Cover). These solutions can, over time, be replaced with more advanced treatments (such as Activated Sludge systems) which require high levels of energy and operation and maintenance or with passive systems such as Waste Stabilisation Ponds or Anaerobic Baffled Reactors. 

There is a plethora of possible system configurations but they all fall under one of the following categories (also called system templates, based on Tilley et al. 2014, WHO 2018 and Spuhler et al 2022):

In general, dry on-site systems reduce the risk of greenhouse gas emissions. Wet systems require high-frequency emptying and transportation to avoid uncontrolled anaerobic digestion leading to greenhouse gas emissions. 

Regardless of the type of system used, sustainability criteria are always the same: a sustainable sanitation system is one that protects human health and the environment, is technically appropriate, financially viable, socio-culturally and institutionally acceptable and allows for resource recovery and reuse (SuSanA 2008). 

Note that sanitation systems are not only about the technologies and how they are combined but also about the models of service delivery, logistics, Operation and Maintenance, Software and Financing.

Process & Good Practice

• Start with a rapid assessment to determine the requirements for different system types. The following information is required:  
  • Availability of water for flushing 
  • Cultural aspects such as anal cleansing to decide if dehydration and composting toilets are an option 
  • Space availability on-site (for on-site storage, treatment, and disposal) and off-site (for centralised treatment and disposal) 
  • Soil infiltration capacities, rainfall patterns, risk of flooding 
  • Soil type to determine whether excavation is possible 
  • Slope and vehicular access to assess the feasibility of sewered or motorised collection 
  • Possibilities for reusing biofuel, biomass for soil improvement, effluent water for irrigation or stored urine for gardening 

• Identify two to three feasible system options based on the collected assessment data 
• Identify Appropriate Technologies for each Functional Group for the selected system options again using criteria such as water and energy requirements, space requirements, excavation, vehicular access and synergies with existing infrastructure 
• Select the most appropriate sanitation system solution based on: 
  • Operation and maintenance requirements in terms of capacities and skills 
  • Capital and operational expenditure requirements 
  • Scalability and lifetime 
  • End-product and possibilities for recovery or safe disposal 

• Develop a decision matrix, together with the stakeholders, ranking different systems against these factors leading to a systematic comparison and system selection. Sanichoice provides a dashboard where criteria can be directly compared between different system options 
• Consider that selecting the most appropriate sanitation system configuration is an iterative process  
• Consider the interlinkages with other services such as greywater management, stormwater management and organic Solid Waste Management. Positive interactions could be the synergies between a joint on-site treatment or collection to centralised treatment. Negative interactions would be the overflow of septic tanks due to high greywater inflows or high groundwater tables or the clogging of drainage with organic solid waste