Emerging Management Solutions
Innovative technologies and new management strategies to improve and develop sewage treatment systems are emerging. Several examples are detailed below.
Nutrient Removal in Advanced Onsite Wastewater Treatment Systems (OWTS)
Septic system improvements to increase the capacity for nutrient removal from effluent prior to discharge are an emerging strategy for onsite wastewater treatment systems (OWTS) in areas vulnerable to eutrophication. To reduce nutrient loading, new technologies such as opens in a new windowrecirculating sand filters are becoming widespread and even required in some places.
Leading institutions engaged in developing nutrient removal strategies for OWTS include:
- University of Rhode Island
- Stonybrook University
- opens in a new windowCenter for Clean Water Technology, which develops solutions for increased nitrogen removal
- opens in a new windowMassachusetts Alternative Septic System Test Center
Resource recovery refers to the capture and reuse of water and solids from sewage waste. Resource recovery is gaining traction as a solution for both small-scale OWTS and large, centralized treatment plants. 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, opens in a new windowLoop 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 opens in a new windowOrange County Water District’s groundwater replenishment system, Los Angeles, USA), read the case study
- 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
Lack of sanitation is not the only reason for implementing resource recovery strategies. Outdated treatment systems and unremoved nutrients and emerging contaminants are also hazardous to human and ocean health. ref In addition, resources recovered from sewage waste can be valuable, ranging from freshwater to scarce metals. If done well, resource recovery can create value from waste and contribute to entirely closed loop systems by generating electricity, water, and heat energy needed for treatment, as exemplified by the Janicki Omniprocessor (see description below). This technology can improve or replace existing inadequate treatment systems.
Two operations are presented in more detail below, offering examples of container-based and municipal-scale innovations.
Ecological Sanitation SOIL Haiti
The concept of using ecological processes to treat sewage waste is not new, but doing it safely while providing toilets to those without access has offered a solution to pollution and erosion in Haiti. opens in a new windowSOIL (Sustainable Organic Integrated Livelihoods) is an NGO providing container-based sanitation. They use urine diversion toilets to isolate solid waste for weekly collection and then transport waste to a composting facility for treatment. Through composting, waste is treated to standards defined by the World Health Organization and a finished fertilizer is sold to farmers to increase their yields.
Supported by the Bill & Melinda Gates Foundation, the omniprocessor is a prospective replacement for large scale WWTPs serving cities around the world. This technology turns sewage into steam and ash, which are used to power the plant’s operation. Freshwater is retrieved and treated for potable reuse. Though still a prototype in Dakar, Senegal, the system considers components of sewage as resources and demonstrates the potential to offset operational costs and natural resource inputs. Watch a video about turning waste to wealth.
Sewage management often brings to mind gray infrastructure: cement pipes and underground storage tanks. Natural (green) infrastructure and nature-based solutions (NBS) offer an additional protection against sewage impacts, effectively capturing contaminated surface and groundwater before it is discharged into the ocean. Natural treatment processes, including prolonging exposure of contaminated water to microbial activity, plant uptake, and oxygenation, promote the removal of nutrients and pathogens, as well as potential absorption of other harmful sewage compounds. ref Click on the image below to see opportunities for and benefits of NBS.
There are many examples of NBS efforts, including Ridge to Reefs’ Pollution Reduction in American Samoa using biochar and vetiver grass for bioretention and erosion control to remove nutrients. Other examples include wetlands, bioswales, activated charcoal deposits, mangroves, and riparian buffer zones. A criticism of nature-based solutions (NBS) is that they may not provide adequate treatment and removal of pathogens on their own. However, coupled with additional treatment and extended interaction with oxygen and microbes, this challenge can be overcome and NBS may offer an effective strategy to enhance other treatment mechanisms. Check out this case study from Guánica Bay, Puerto Rico where green infrastructure was used to provide additional treatment to septic tank discharge, enhancing contaminant removal and significantly reducing the volume of wastewater entering the bay.
Regulatory inconsistencies, within and between communities, cities, states, and nations, present a complex challenge for sewage management. However, regular monitoring and establishment of thresholds for sewage-borne contaminants holds potential for measuring pollution events and motivating response and prevention efforts. Most examples of existing treatment standards or effluent regulations are from temperate regions, but even in areas without sewage-specific policies, strategies can be adapted to enhance measurement of existing contamination, inform interventions, and supplement future monitoring.
Several tools have been implemented by the US EPA to establish contaminant thresholds for water bodies and aquatic life. A commonly used threshold tool is a total maximum daily load (TMDL), which limits the amount of a specific contaminant permitted to enter a water body. This is especially effective for sewage 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 opens in a new windowmany additional EPA tools include nutrient data layers ( opens in a new windowNPDAT), a water quality modeling program ( opens in a new windowWASP), and a diagnostic tool for biological impairment ( opens in a new windowCADDIS).
An emerging regulatory tool from the US Coral Reef Task Force (USCRTF) is the Biological Condition Gradient (BCG), which is based on water quality criteria specific to reef environments. The BCG presents a strategy for understanding the impact of pollution on coral reef ecosystems by establishing a baseline and compiling pollution and ecosystem data over time. This tool can be used to predict impacts of future contamination as well as indicate the influence that long-term exposure can have on reef systems.
The Australian Guidelines for Sewerage Systems, Effluent Management acknowledges the need to consider environmental parameters prior to effluent discharge. While treatment standards for sewage effluent discharged to coastal waters are determined locally, the government encourages monitoring of water quality before and after discharge, secondary treatment to reduce pathogens, and disinfection. Bays and estuaries are acknowledged as particularly sensitive to contamination due to slower dilution and require (at minimum) secondary treatment and often additional nutrient removal. ref Sewage management strategies in Australia are increasingly aligned with marine conservation, exemplified by the opens in a new windowCleaner Seas Alliance wastewater treatment plant upgrade in Cairnsopens PDF file .
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.
Coastal Massachusetts has been facing nutrient loading challenges associated with sewage for decades. In response, the Cape Cod Commission has put together an interactive website of sanitation technologies, opens in a new windowTechnologies 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.
Competitions and Challenges
Sanitation can be achieved in many ways, requiring a wide range of resources and deliver different levels of success. The Bill & Melinda Gates Foundation has prioritized innovation to improve sanitation technologies, and funds an annual opens in a new windowReinvent the Toilet Challenge to solicit ideas and support the development of modular sanitation systems that minimize water, electricity, and monetary inputs. opens in a new windowRARE’s 2020 Solution Search focused on behavior change strategies to address climate needs. Accelerating interest in sanitation as a requirement for health and environmental conservation will continue to stimulate new ideas.
Opportunities like these are indicative of the interdisciplinary nature of sewage pollution. While technology, regulatory, and management strategies are essential, lasting solutions require collaboration across sectors. Engagement of marine managers in this effort is essential for protecting the ocean and its resources.