Second generation biofuels - Fuels that use special-energy non-food crops, that have the effect of not diverting food supplies away from the food chain, and waste biomass containing lignin and cellulose.

Secondary treatment solutions - Solutions that substantially remove the biological content of sewage (including derivates of human waste, food waste, soaps and detergent).

Sedimentation - Traditional water treatment method that is based on the settling of particulates at the bottom of a body of water.

Sludge - Semi-solid material left from industrial, water treatment or wastewater treatment processes.

Sludge treatment and disposal - Solutions (including dewatering, landfill storage and fertilizer conversion) that treat sludge generated from wastewater treatment in order to remove usable substances and properly dispose of residual wastes.

Smart buildings - Buildings that rely on integrated IT-based resource use measurement and monitoring, intelligent analysis of the internal environmental and performance data, and automation of connected building systems.

Smart grid networks - Networks supported by digital technology capable of exerting “smart control” over all aspects of the electric power sector (including generation, transmission, distribution, customer service and power dispatch at all voltage levels). They deliver power in an efficient manner and can better integrate power from renewable sources.

Sodium-sulfur (NaS) batteries - Batteries with high energy density and high efficiency of charge/discharge that require high operating temperatures.

Solar photovoltaics (PV) - Photovoltaics (solar cells) are devices that convert light into direct current using the photoelectric effect. Solar PVs are the main technology used in China for the generation of electric solar power.

Solar water heaters (SWH) - Systems that heat water by absorbing the energy from the sun, normally consisting of solar thermal collectors, fluid systems to transport the heat and a water tank where water is heated and stored.

Solidification/stabilization (S/S) - Common method used for treatment, management and the reuse of contaminated waste (especially treated industrial hazardous waste and contaminated material). This process involves mixing Portland cement with the contaminants which results in a brick which can be reused on-site.

Standard operating procedures (SOPs) - Set of prescriptions for employees, often mandated, on how to execute specific tasks or to react to circumstances in the most efficient and effective ways.

Standard operating procedures (SOPs), training, feedback - Collection of management tools designed to improve the efficiency of employees as well as the effectiveness of the management at an industrial site.

Stop-start systems - Systems that safely stop and restart a locomotive’s engine during idling operation to conserve fuel and reduce air and noise pollutions.

Subcritical power generation - Coal-fired subcritical power plants that operate at very high temperatures, resulting in much higher heat efficiencies.

Sulfur dioxide (SO₂) - By product resulting from the combustion of coal and oil containing sulfur. When combined with nitrogen dioxide, sulfur dioxide forms acid rain.

Supercapacitors - Electrochemical capacitors (tasked with storing electrical charge) that have an unusually high energy density when compared to com- mon capacitors, typically on the order of thousands of times greater than a high capacity electrolytic capacitor.

Sustainable materials - Materials gathered in environmentally responsible ways (including recycled materials, certified wood and biodegradable plastics).

Sustainable urban planning - Urban planning that optimizes the use of the built environment, transportation system, energy, water and land, while aiming to mini- mize the negative impact of the community on the natural environ- ment.

Sweet sorghum bioethanol - Bioethanol produced from sweet sorgum crop.