Emerging Management Solutions
The development of innovative technologies and improvements to conventional systems offer enhanced methods for treating wastewater. Some of these new management strategies are aimed at increasing treatment efficiency, improving the quality of discharge water, or generating profit from a valuable resource recovered from wastewater.
Improving Septic Systems
Widespread usage of septic systems has resulted in the development of a variety of modifications which address unique treatment needs. These additional treatment steps ensure that the wastewater that enters the environment is cleaner. Since these systems are usually paired with wells as a source of drinking water, this improves the quality of drinking water as well.
Chamber Septic Systems
A chamber system is an alternative to the traditional gravel/stone septic design, which is easier to construct. The drainfield is made up of a series of closed chambers surrounded by soil. Wastewater moves through the septic tank and then into the chambers, where microbes in the soil help to remove pathogens.
Chamber septic system. Source: US EPA
Cluster Septic Systems
A cluster or community septic system increases the efficiency of wastewater treatment by combining the wastewater from a group of houses. Each house has its own septic tank providing initial treatment. The effluent comes together and flows through a shared drainfield. These systems work best in rural, growing communities with houses near each other.
Cluster septic system. Source: US EPA
Nutrient Reducing Septic Systems
Reducing nutrient loads in local water bodies is a high priority when developing improved wastewater treatment systems. New septic system technologies are increasing the capacity for nutrient removal from effluent prior to discharge. These system improvements are more and more common, and even required in some places that are especially vulnerable to eutrophication. Sand filters, as shown in the diagram below, provide a high level of nutrient removal. They are more expensive than conventional systems but can help mitigate nutrient levels in nearby water bodies.
Sand filter septic system. Source: US EPA
Aerobic Treatment Units
Aerobic treatment unit. Source: US EPA
In places with aquatic ecosystems that are particularly sensitive to nutrient pollution, aerobic treatment units offer a small-scale version of the treatments used at centralized treatment plants. Adding oxygen increases bacterial activity to reduce nutrient levels. Some systems have additional treatment tanks with a disinfection step to remove pathogens.
See the case study from Long Island, New York describing efforts to replace old septic systems with nitrogen reducing systems with shallow leach fields that can prevent approximately 95% of nitrogen from wastewater effluent from entering the watershed and allow groundwater aquifers to recharge.
Resource Recovery
Resource recovery refers to the capture and reuse of water and solids from human waste. Some strategies for resource recovery include:
- Freshwater reclamation for irrigation and other non-potable uses, which can also reduce water needed for future sanitation and treatment
- Biosolids used to add to soil as fertilizer when treated to appropriate standards (for example, Loop Biosolids Seattle, USA which uses microbes and heat for digestion to create a product to use in gardens and forests)
- Microfiltration, reverse osmosis, and UV (used by Orange County Water District’s groundwater replenishment system, for drinking water in Los Angeles, USA)
- Biogas generation through anaerobic digestion and methane capture – often employed by large scale wastewater treatment plants (WWTPs) to recover resources, treat biosolids, and mitigate greenhouse gas emissions
Resource recovery is gaining traction as a solution for both small, decentralized systems and large, centralized treatment plants. Benefits of resource recovery strategies include:
- Removing nutrients and contaminants that are hazardous to human and ocean health.
- Recovering valuable resources from waste.
- Can be implemented as a sanitation system where one didn’t exist or improve/replace an outdated treatment system.
Two operations are presented in more detail below, offering examples of container-based and municipal-scale innovations.
SOIL
In Haiti, the non-governmental organization SOIL (Sustainable Organic Integrated Livelihoods) is applying resource recovery technology to provide container-based sanitation. This system safely provides toilets to those without access and offers a solution to pollution and erosion. Toilets divert urine and isolate solid waste for weekly collection.
Illustration of the SOIL container-based sanitation and resource recovery process. Source: SOIL
SOIL collects and transports waste to a composting facility where it is treated to standards defined by the World Health Organization. The finished fertilizer is sold to farmers to increase their crop yields and reduce erosion.
Janicki Bioenergy
Ideally, resource recovery creates value from waste through an entirely closed loop system, as exemplified by the Janicki Omni Processor. The Omni Processor takes in human waste and garbage and turns it into electric power and clean drinking water. It works like a steam power plant, an incinerator, and a water filtration system combined into one. Though still a prototype in Dakar, Senegal, the system demonstrates the potential to offset costs associated with operations (since it produces its own energy to run) and natural resource inputs (since sewage and trash are free). Recognizing the high initial costs to build this system, the Omni Processor is a prospective replacement for large scale wastewater treatment plants serving cities around the world.
Janicki Omni Processor. Source: Janicki Bioenergy
Nature-based Solutions
Natural treatment processes use plants and microbes to break down, absorb, trap, and/or oxygenate pollutants in contaminated water as it moves through the environment. These natural processes effectively capture and filter contaminated surface and groundwater, including polluted runoff from rainfall, before it is discharged into the ocean.
Opportunities for and benefits from nature-based solutions. Source: IUCN Water
Nature-based solutions include constructed wetlands, bioswales, activated charcoal deposits, settlement ponds, riparian buffer zones, and more. Critics of nature-based solutions claim they may not provide adequate treatment and removal of pathogens. However, an effective strategy to enhance pathogen removal is to ensure that the system provides extended interaction with oxygen and microbes by slowing down flow rates and coupling the nature-based solutions with additional treatment steps from a centralized or decentralized system. These strategies have the added benefit of providing habitat to support biodiversity, supporting recreation (including fishing and tourism), and aesthetic benefits over other treatment technologies.
Explore these two examples for a closer look at natural treatment processes:
- Green infrastructure was used to provide additional treatment to septic tank discharge, enhancing contaminant removal and significantly reducing the volume of wastewater entering Guánica Bay, Puerto Rico.
- Biochar (charcoal produced from organic matter) and vetiver grass were used for erosion control and to remove nutrients in American Samoa.
Setting Regulations
Regulatory inconsistencies, within and between communities, cities, states, and nations, present a complex challenge for wastewater management. Regular monitoring and the establishment of local thresholds for wastewater-borne contaminants should be implemented to identify when pollution events occur. With defined thresholds, communities can better determine when specific responses should be taken, like shutting down beaches for recreation or issuing a boil water advisory. Most existing treatment standards and/or effluent regulations are from temperate regions, but these standards can be used as a model to establish standards for monitoring and interventions to be taken in tropical zones. While regulations may be outside the scope of marine managers’ work, the tools developed as part of the regulations in other countries may help guide the monitoring plans and thresholds to address wastewater pollution. Explore pages 22-28 of A Practitioner's Guide to Ocean Wastewater Pollution to learn more about existing frameworks at the regional and country-level, as well as different categories to consider for relevant regulations and codes.
Several tools have been implemented by the US Environmental Protection Agency (EPA) to establish contaminant thresholds for water bodies and aquatic life. A commonly used threshold tool is a total maximum daily load, or TMDL, which limits the amount of a specific contaminant permitted to enter a water body. This is especially effective for wastewater contaminants that are derived from nonpoint sources. TMDLs are concerned with the amount of contaminants entering a water body rather than their source(s). A few of the additional EPA tools include nutrient data layers (NPDAT), a water quality modeling program (WASP), and a diagnostic tool for biological impairment (CADDIS).
Biological Condition Gradient
Biological Condition Gradient
An emerging regulatory tool from the US Coral Reef Task Force is the Biological Condition Gradient (BCG), which is based on water quality criteria specific to reef environments. The BCG was originally developed as a framework to be used to interpret the effects of different stressors on freshwater environments. With new guidance specific to coral reef ecosystems, the BCG can help managers establish a stress gradient using species relevant to their area: corals, sponges, fish, algae, or plants. This gradient should describe the biological response as stressors increase from minimal to severe. Level one represents the native condition, and should describe the population under normal circumstances. For corals, this may include the ratio of species known to be sensitive to stress compared to those that are more tolerant. As the stress gradient increases, this balance may change. The tool, coupled with examples from research projects, can help managers define a baseline and compile pollution and ecosystem data over time. This information can be used to understand the impact of pollution on ecosystems and predict the impacts of future contamination or long-term exposure on reef systems.
Australia's National Water Quality Management Strategy
Gold Coast, Australia. Photo © Marian Frew/TNC Photo Contest 2019
Another set of guidelines which can be used as a reference when developing regulations or thresholds is Australia’s National Water Quality Management Strategy. This strategy was developed to avoid contamination of water bodies when treatment plants discharge water. While treatment standards for wastewater effluent discharged to coastal waters are set locally, these national guidelines encourage monitoring water quality at several steps during the treatment process to verify that they are removing the contaminants. The document identifies water bodies which are particularly sensitive to contamination due to slower dilution rates, like bays and estuaries, where secondary treatment (at a minimum) and often additional nutrient removal are required to protect ecosystems.
Australia's National Outfall Database
Australia's National Outfall Database map
To aid monitoring and management, the National Outfall Database maps the volume of discharge to outfalls across Australia and reports on the populations served, types of treatments, and various pollutant levels. Wastewater management strategies in Australia are increasingly aligned with marine conservation, exemplified by the Cleaner Seas Alliance wastewater treatment plant upgrade in Cairns.
This database reports monthly average levels of different pollutants including pH, total dissolved solids, nitrogen, phosphorus, and E. coli. Managers can see what locations across Australia are measuring and what value range is normal in each location.
Wastewater Associations
Regional associations are key partners to connect managers with regulators and utilities. Organizations such as the Caribbean Water and Wastewater Association, the Pacific Water and Wastewater Association, and the Pacific Water & Wastes Association are valuable resources for managers looking to navigate the regulatory requirements applicable to them and access data, tools, and other resources.
System Suitability
The chart below presents some considerations to guide system decision-making based on effluent, regulations, and the receiving environment. Tools that account for social, health, and environmental criteria in determining the most appropriate sanitation intervention are currently lacking. As future tools are developed, it is important to include marine practitioner insight into the degree of treatment and the most effective technologies for protecting the ocean.
The schematic above details considerations that integrated system suitability decision support tools may include to consider health, ecosystems, resources, efficacy, acceptability, and sustainability. Source: Adapted from US EPA
Coastal Massachusetts has been facing nutrient loading challenges associated with wastewater pollution for decades. In response, the Cape Cod Commission has put together an interactive website of sanitation technologies, Technologies Matrix. This tool details the attributes and shortcomings of various technologies that make them appropriate in different contexts. Particular emphasis on nutrient removal, coastal remediation, and restoration demonstrate the relevance of this site for marine practitioners. Clicking through these technologies provides more information about available solutions and which may be most compatible for a given circumstance.