Small measures ensure that both rainwater and wastewater are discharged up to standard
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The lids of the underground sewage tank wells on the facility are often at the same level as the floor surface, as shown in the design drawings. In heavy rain, water flows along the terrain into sewage tanks, resulting in an increase in the volume of industrial wastewater discharged. In addition to the increase in the total amount of wastewater discharged (for which limits are specified in the environmental impact assessment approval), the cost of wastewater treatment also rises, and those who exceed these limits face environmental fines.
A simple measure to achieve the separation of rainwater and sewage is to raise the embankment at the inlet of the sewage tank to prevent rainwater from flowing in. Ultimately, rainwater and wastewater are collected and treated separately, ensuring that both are discharged up to the required standards.
The design of the facility takes into account the separation of rainwater and sewage. We previously designed two separate networks for rainwater and sewage, but their performance was not satisfactory. Sewage trenches are underground, and it is truly difficult to meet quality standards whether it comes to installation and construction, corrosion prevention, or subsequent maintenance. So generally, after two or three years, many problems arise, and it gradually can no longer be used properly. The current practice is to install sewage collection tanks on-site at the production facility as needed; they do not have to be very large, and a lift pump is used along with open-pipe transportation. The sewage collection tanks on site are equipped with rainwater and sewage separation valves, which ensure proper collection of sewage without any leaks and prevent clean rainwater from entering the sewage system.
Separation of rainwater and sewage is a principle that is well established in the design of water supply and drainage systems; however, there are often shortcomings at the detailed level, with heavy rainfall causing rainwater to back up into sewage tanks or sewage to overflow into rainwater drainage systems, thereby leading to mutual contamination. Therefore, it is still necessary to consider the design details in order to prevent the mixing of rainwater and sewage.
During design, careful handling of a single detail can greatly affect the proper operation of the system; therefore, designers must take into account the actual conditions of the project and conduct thorough on-site investigations!
The key to separating rainwater and sewage lies in its performance during the rainy season
Wastewater from non-rainy seasons must also not be discharged into the rainwater drainage system, such as wastewater discharge in case of accidents.