Examples for more low-tech, often less expensive sewage treatment systems are shown below. They often use little or no energy. Some of these systems do not provide a high level of treatment, or only treat part of the sewage (for example only the toilet wastewater), or they only provide pre-treatment, like septic tanks. On the other hand, some systems are capable of providing a good performance, satisfactory for several applications. Many of these systems are based on natural treatment processes, requiring large areas, while others are more compact. In most cases, they are used in rural areas or in small to medium-sized communities. 
For example, waste stabilization ponds are a low cost treatment option with practically no energy requirements but they require a lot of land. Due to their technical simplicity, most of the savings (compared with high tech systems) are in terms of operation and maintenance costs. 
* Anaerobic digester types and anaerobic digestion, for example:
** Upflow anaerobic sludge blanket reactor
** Septic tank
** Imhoff tank
* Constructed wetland (see also biofilters)
* Decentralized wastewater system
* Nature-based solutions
* On-site sewage facility
* Sand filter
* Vermifilter
* Waste stabilization pond with sub-types: 
** e.g. Facultative ponds, high rate ponds, maturation ponds
Examples for systems that can provide full or partial treatment for toilet wastewater only:
* Composting toilet (see also dry toilets in general)
* Urine-diverting dry toilet 
* Vermifilter toilet