Wastewater is used water. It includes substances such as human waste, food scraps, oils, soaps and chemicals. In homes, this includes water from sinks, showers, bathtubs, toilets, washing machines and dishwashers. Businesses and industries also contribute their share of used water that must be cleaned. 

We consider wastewater treatment as a water use because it is so interconnected with the other uses of water. Much of the water used by homes, industries, and businesses must be treated before it is released back to the environment.

Wastewater treatment plants (WWTPs) produce a variety of odors, including hydrogen sulfide (H2S), mercaptans, ammonia, and amines. These odors can be unpleasant and even harmful to human health. Wastewater odor control is important to protect public health and the environment. 

Small concentrations from these odor has a negative impact on the human body and the environment, and their degree of nuisance is described as high. The values recognized for H2S cause lacrimation, coughing, olfactory impairment, psychomotor agitation, and swelling of the cornea with photophobia.