The first biological treatment was established around 1887 and it was an intermittent sand filter in the state of Massachusetts. In 1899 the Refuse Act was the first federal regulation of sewage, which prohibited discharge of solids into navigational waters without permits from the US Army Corps of Engineers. The sewered population kept increasing from late 1800s to 1940s, and there was a development of secondary treatment. Around 1944 the secondary treatment to remove biological oxygen demand (BOD) was developed. By 1948 the government enacted the Federal Water Pollution Control Act (FWPCA), which was based on provision of federal funds for water quality surveys. By 1960s about 50% of US population had access to some sort of wastewater treatment.
