In the Caribbean, a large percentage of sewage enters ocean untreated
Coral reefs contain among the most diverse ecosystems on Earth, serving as habitat and shelter for marine life and as the source of nitrogen and other essential nutrients for marine food chains. They help with carbon fixing, nitrogen fixing, and nutrient recycling, while they preserve coastlines from constant battering from waves and storms. The fishing industry relies heavily on reefs because many fish spawn and grow there before braving deep water. The tourism and recreational industries also rely on them as areas for sport fishing and scuba diving.
Climate change and wastewater pollution now pose an existential threat to reef systems worldwide. The discharge of untreated sewage introduces high concentrations of nutrients, chemicals, bacteria, and pathogens into ocean ecosystems. Sediments, fertilizers, and pesticides from other land-based industries — including agriculture, timber, road construction, stock farming, and mining — find their way to the ocean in runoff.
While nutrients such as nitrogen and phosphorous generally are understood to be beneficial for marine ecosystems, coral reefs are adapted to a low-nutrient environment. Too many nutrients in the water, a condition called eutrophication, can devastate corals. Water oversaturated with nutrients upsets reef ecosystems, fostering algae overgrowth that in turn blocks vital sunlight and oxygen. High sediment levels can produce the same threats, but eutrophication additionally promotes the growth of harmful bacteria and fungi.
A Worldwide Threat to Reefs
The situation is grave in the Caribbean. A World Resources Institute (WRI) publication stated that,
[S]ediment and pollution from inland sources threaten about one-third of Caribbean coral reefs. Analysis of more than 3,000 watersheds across the region identified 20 percent of coral reefs at high threat and about 15 percent at medium threat from damage caused by increased sediment and pollution from agricultural lands and other land modification.
Recent research by Dr. Stephanie Wear found that sewage generally enters the sea as inadequately treated or simply untreated discharge or rainwater runoff. In the developing world, with its dearth of infrastructure, most wastewater remains completely untreated. Wear noted, “Some of the greatest sewage pollution in the world occurs in developing countries, where you also have the most coral reefs.”
Approximately half of the homes in the Caribbean are not connected to a sewer grid, and only 17% of houses connect to adequate treatment systems. In the Caribbean, 85% of wastewater that is discharged into the sea remains virtually untreated, and wastewater has been identified as one of the main culprits in heavy coral loss in the region.
On the other side of the globe, a recent United States Geological Survey (USGS) study determined that a wastewater treatment facility in West Maui, Hawaii, is eroding and inhibiting new coral growth on the coral reefs near Kahekili Beach Park. Results of the USGS study:
[…] confirm how valuable nearshore coral reef ecosystems — the cornerstone of Hawaiian tourism, shoreline protection, and local fisheries — are affected by land-based sources of pollution [.]
Similarly, in Thailand, Professor Vipawee Dummee warned of a catastrophic situation in Patong Bay in Phuket, where “not only the existing coral is being damaged and may die, the sediment also prevents the spawning of new coral.” The reef in Patong Bay had just been restored when new discharges were observed too late.
Advances in Wastewater Treatment
In an effort to preserve reefs, the lack of adequate wastewater treatment must be addressed. In addition to widespread poverty, island terrain may make conventional treatment modes impractical. In particular, lack of money and challenging terrain can hinder the installation of widespread piping networks that form the backbone of conventional centralized wastewater treatment.
Decentralized treatment may hold the key to overcoming these obstacles. Instead of a large, central plant, decentralization brings small treatment units to exactly where they’re needed. Technological advances have made this model more and more practical.
For example, Smart Packaged ASPIRAL™ wastewater treatment plants use the membrane aerated biofilm reactor (MABR), which slashes energy use for some aspects of treatment by as much as 90%. This allows the use of alternative energy sources, bringing treatment even to remote, off-the-grid regions and taking advantage of assets the developing world often has in abundance: Sun, waves, and wind.