Pit Technology
Pits have been used to solve human sanitation needs since early times. In modern times, the use of pits of various designs are often the only viable option for regions that are rural, or resource constrained. The most primitive type of pit is the cesspool (essentially a reinforced pit that leaches wastewater into the surrounding soil) and while banned in many countries, is still commonly used. Cesspools do offer a safer immediate user experience than an open latrine, but depending upon construction methods and soil characteristics, may also pose a hazard to the environment from liquid waste that leaks into the surrounding soil. Rainstorms can cause a cesspool to flood and overflow. Cesspools built near low-lying coastal areas are at risk of being submerged and breached by rising sea levels. In areas where with porous soils, wastewater can seep directly into the groundwater. Some of these risks also exist for more modern implementations; consequently, the technology must meet the criteria highlighted in this section.
All contemporary designs leverage the basic concept of a pit and from there, innovate to create healthier, more human friendly and more environmentally sound implementation. Variations include the use of such things as multiple pits, facilitating ventilation, optimizing safe biodegradation of waste, alternating waterless pits, harvesting both waste for agricultural use or as fuel and/or managing the use of water.
Septic Tanks
Septic tanks are a primary treatment collection system for greywater and blackwater that are commonly used for a single property or a small group of properties in rural areas or where city wastewater utilities are unavailable. It is a watertight chamber of concrete, fiberglass, or plastic that relies on the settling and anaerobic processes to reduce solids and organics and the disbursement of fluids into leach fields (or similar technologies) in which the effluent can be absorbed into the soils. The sludge and scum accumulate in the tank and need to be periodically removed. Septic tanks may be implemented in various configurations (see Types of Septic Systems) and advanced options (e.g., Aerobic Treatment Units (ATUs)).
Filtering Technology
Filter technology comprises a broad category of various types of filters ranging from rudimentary filters that screen out debris (from stormwater) prior to treatment to membranes for nutrient removal and production of potable and non-potable water reuse. Filters are commonly used for solid separation, allowing removal of effluent for further treatment or disposal using drip irrigation/systems or leach fields into the surrounding soils. Treatment plants may include a series of baffles in which the wastewater passes from one treatment area to another, progressively becoming cleaner and cleaner. Systems may incorporate anaerobic filters and trickling filters as part of sophisticated nutrient removal mechanisms. Nutrient removal filters may be constructed of cloth, engineered materials, or even sand as a final polishing medium. Effluent Reverse Osmosis, a membrane filtering technology, frequently found in homes to ensure healthy drinking water, is also used on a larger scale in the wastewater process to produce potable water. Two-stage passive biofilters are used in the denitrification/nitrification multi-chamber nutrient removal process. Filters are a fundamental part of blackwater and greywater treatment incorporating passive, mechanical and/or active filtering involving pressure, chemicals, and electrolysis as part of the process. The waste treatment industry has dozens of companies focused on engineering better processing and treatment systems, with filtering devices and mechanisms found in all phases of treatment. The technology is extensive.
Biogas Reactor
A biogas reactor uses a three-step process in which sludge is pretreated prior to putting it into an airtight reactor chamber. The chamber serves as an anaerobic digester that converts blackwater, sludge and/or biodegradable waste to digested sludge and biogas. It does this by breaking down the organic matter in the sludge and, through the fermentation process, producing a biogas mixture of methane and carbon dioxide. Additionally, in this step the digested sludge is stabilized, and its dry matter content is reduced. The final step in the process is post treatment of the reactor products for resource recovery and disposal. The biogas can be used as fuel for electricity, heat and biofuel production and the stabilized sludge can be safely disposed of into the environment.
Container-based sanitation systems have evolved over the last decade into a viable low-cost sanitation option, and “are particularly well-suited to low-income urban settlements where demand for sanitation is high and on-site sanitation and sewerage are not feasible or cost-effective” (Russel et al., 2019). These systems address the entire sanitation service chain (including emptying, collection, transport, treatment and reuse), offer a variety of service-based models and are affordable to people living in marginalized and informal urban settlements. These systems capture wastes in sealable containers that are then transported to treatment facilities. Container-based sanitation solutions are affordable, cost-effective, flexible, adaptable, and modular. They reduce water usage and have low greenhouse gas emissions. They are hygienic and provide protection for women and girls.
Conveyance
Conveyance technologies are simply the way in which waste moves from one location to another as it passes from one functional element of the sanitation system process to another. Other than manual transport that may occur in some developing regions, conveyance, appropriate for systems that do not include on-site treatment and disposal/reuse, is typically accomplished either by a network of municipal sewer lines that convey wastewater from a property to a centralized treatment plant or by transport by truck to centralized locations for further treatment or disposal. Specialized septic trucks transport sludge or, in situations where on-site systems support urine collection, urine storage tanks or jerrycans may be transported by trucks directly to agricultural locations or to storage locations for later distribution. Urine is safe to store and valuable for reuse in agriculture. Sludge requires further treatment.
Disposal and Reuse
Apart from untreated human waste, all sanitation system outputs are eventually returned to the environment, either as useful resources or reduced-risk materials. The challenge is to ensure safe and sustainable disposal and, where possible, recover and reuse valuable resources. The nutrients that pollute our waterways can be harvested. Water can be recycled into potable and non-potable supplies. Outputs from different types of treatments vary with the treatment. Overall, these outputs include effluent, sludge, desiccated feces, urine, pit humus, compost, nutrients (phosphorus and nitrogen), and water, both potable and non-potable. Of these, urine, compost, recovered nutrients, and desiccated feces can be reused as fertilizer for agriculture. This is common practice in some places and treated with greater caution in others depending on cultural context and experience. Non potable water can be reused for irrigation for agriculture and public/private lands, used as flush water, recycled back into the treatment process, used as process water for industry (e.g., power plants, refineries, mills, and factories, concrete mixing and construction), and environmental restoration, as well as supply artificial ponds/lakes and inland or coastal aquifers. Wastewater can be recycled for municipal water supplies to be used for drinking water. Water reuse is becoming more common, and examples are available at WateReuse’s Water360, an interactive map to learn about specific projects around the world. Reframing wastewater as a valuable resource has a huge socioeconomic and environmental upside.