Sustainable Sewage Design

Sewage, also called blackwater, is a complex mixture of contaminants containing pathogens, toxic chemicals, heavy metals, debris, nutrients, nitrates and phosphates. It is wastewater from both domestic and industrial sources, from faeces and urine, to bleach and cleaning products, paint, solvent and oils - everything that is flushed down a toilet or poured down a drain.
Most homes in the UK are connected to the mains sewers, whereby sewage travels through a system of pipes to be collected by an industrial treatment plant. It is then treated with chemical and mechanical processes to remove contaminants and separate sludge from liquid. The liquid is discharged into the nearest large body of water or reused, and the sludge is incinerated or partially used in agriculture as a controlled fertiliser.
In the UK there are strict government regulations and standards related to sewage collection and treatment, but still 300 million gallons of raw or partially treated sewage is discharged directly into the sea, destroying aquatic life and posing significant risks to human health. Worldwide sewage dumping is an even bigger problem. This environmental threat, combined with the energy intensive processes of conventional sewage plants, has facilitated the development of sustainable sewage systems.
Ecological Sewage Systems
Ecological or biological sewage systems are based on natural ecosystems that use ecological processes for water purification and nutrient recycling. Their exact design is dependent on location, climate and population, but all involve wastewater being passed through a managed or constructed environment where a diversity of plant and animal organisms transform the waste in the water.Aquatic plants such as water hyacinths, reeds, rushes, lilies, and duckweeds, break down toxic chemicals, nitrates and phosphates through their root microbes, and bioaccumulate heavy metals in their stems and leaves. These plants are an integral part of an ecologically-engineered whole system that provides an oxygenated environment in which bacteria, fungi, snails, fish and aquatic invertebrates can thrive and also play their part in the water purification process. There are two main types of ecological sewage systems: constructed reed beds, and solar aquatic systems.
Constructed Reed Bed Systems
Also known as artificial wetland systems, Constructed reed bed systems are the reconstruction of freshwater wetland ecosystems to treat wastewater. They are often used in combination with other conventional treatment facilities, including septic tanks. There are three basic types of wetland construction:
- Horizontal Flow - wastewater is continually fed through an inlet / outlet gradient system
- Vertical Flow - wastewater is applied in batch and allowed to drain each time
- Pond Systems - a series of shallow ponds linked by a constructed wetland container
Solar aquatic systems model the processes of wetland ecosystems in a controlled and intensified environment. Anaerobically treated wastewater is passed through a series of tanks in a greenhouse, using sequenced ecologies of specified aquatic plants and animals to break down sewage. The resulting water is pure enough to be used for non-drinking purposes and can be safely discharged into the environment. Dr. John Todd of Ocean Arks International pioneered this technology in a patented design called 'Living Machines'. He has now developed this into the design of restorers, assemblies of engineered ecologies that can be floated as a raft to treat sewage in constructed canals or lagoons.
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