sewage treatment (waste water treatment): the process of purifying sewage to meet the water quality requirements for draining a water body or reusing it. Sewage treatment is widely used in construction, agriculture, transportation, energy, petrochemicals, environmental protection, urban landscape, medical care, catering and other fields, and it has also entered the daily life of ordinary people more and more.

The topic of water pollution has been constantly raised, especially the groundwater pollution. In Hangzhou, Wenzhou and other places in Zhejiang, farmers or entrepreneurs invited environmental protection directors to swim in the river, so as to arouse everyone's concern about the severity of water pollution. Although all environmental protection directors chose to be silent or refuse, the people's awareness of environmental protection has awakened and their concern about water pollution has reached an unprecedented level.

surface water pollution is obvious, but groundwater pollution is shocking. Of China's population of 1.3 billion, 71% drink groundwater, and more than 411 cities in more than 661 cities use groundwater as their drinking water source. However, it is reported that 91% of urban groundwater in China has been polluted.

another set of data also shows that groundwater is facing severe challenges. In 2111, nine provinces and cities, including Beijing and Shanghai, evaluated 857 monitoring wells within their jurisdiction, accounting for 2% of the monitoring wells with Class I and Class II water quality, while as many as 76.8% of the monitoring wells with Class IV and V water quality.

among the nine provinces and cities, Hainan province has the best water quality, with Class II as the main one; Shanghai and Beijing are second, mostly Class III; Heilongjiang and Jiangsu have the highest proportion of Class IV water, while Jilin, Liaoning, Guangdong and Ningxia generally only reach the level of Class V..

With the increasing water pollution, the sewage treatment and recycling industry has received unprecedented attention. In the past two years, the gross profit margin of all regions has remained at around 71%, and even exceeded 1,111% in some regions, which has great development potential.