How to prevent the circulation of COVID-19 in urban water system

How to prevent the circulation of COVID-19 in urban water system

      Recently, with the deregulation of the control of the COVID-19 in China, many cities have achieved or will achieve epidemic peak. With the substantial increase of the number of people infected with the virus, news about COVID-19 entering the urban sewage system through human excreta has become a hot topic. Many urban sewage treatment plants have also increased their efforts to prevent COVID-19 in operation: first, they have strengthened the safety protection of operators, and second, they have increased the disinfection dose of the effluent of the sewage plant to reduce the risk of COVID-19 entering the natural water body through the tail water of the sewage plant.

      In foreign countries, recently, 288 (95.7%) of the 301 sewage treatment plants in Malaysia representing the states have detected COVID-19. A large number of studies in Europe and the United States have also found that COVID-19 exists in more samples taken from sewage treatment plants and sewage outlets. Scientists warn that sewage containing COVID-19 may be a serious threat!

      We will analyze the footprint of COVID-19 from the perspective of urban water cycle. The feces of COVID-19 infected people enter the urban sewage pipe network through the toilet drainage pipe, and then enter the sewage treatment plant. Most sewage plants use the traditional biological treatment process, and the removal effect of COVID-19 is very limited. The tail water treated by the sewage plant uses ultraviolet disinfection or sodium hypochlorite and other dosing disinfection processes before discharge, but it is also difficult to completely kill COVID-19. Often, "fish in the net" enter the natural water body.

      The potential risk of COVID-19 in natural water bodies is relatively high. It is possible to have direct contact with humans through swimming, boating, irrigation, etc., and it may also enter the food chain through crop, fruit and vegetable irrigation, and even into water sources. Most existing water treatment plants also adopt traditional treatment processes, and it is crucial to do a good job in the final disinfection of the water treatment plant.

How to stop the circulation of COVID-19 in the urban water system? This involves two key nodes in the recycling process, sewage treatment plants (including recycled water plants) and water treatment plants.

      The sewage treatment plant with traditional process is transformed into MBR ultrafiltration membrane process by membrane method, or the ultrafiltration process section is added behind the original process. High performance ultrafiltration with membrane aperture less than or equal to 30nm (0.03um) is selected, which can completely intercept COVID-19 (including norovirus and various harmful bacteria that often cause extensive health damage to people), and greatly improve the biological safety of the effluent of the sewage treatment plant. The COVID-19 entering the sewage treatment plant will eventually enter the sludge treatment and disposal system through the surplus sludge. The drying incineration sludge disposal process can completely kill COVID-19, and other sludge safety disposal processes can also achieve the killing or safe isolation of COVID-19.

      For recycled water plants that use traditional secondary treatment processes and conventional deep treatment, the risk is greater due to the need for recycled water use, and biosafety needs to be considered more. Regenerated water is currently commonly used for greening irrigation, river water supply, and wetland park water supply. Greening irrigation may lead to infection through air spraying, while river water supply, wetland park water supply, or fruit and vegetable irrigation are prone to contact with people and cause infection.

      For waterworks, membrane transformation can also be carried out, and ultrafiltration process can be added after the original treatment process to provide a "safety barrier" to completely block COVID-19, provide safe and reliable drinking water for urban residents, and ensure the safety of urban water supply. The use of bio safe ultrafiltration membranes in the preparation of tap water is gradually becoming a trend in the industry for high-quality water supply.

      With the rapid development of the international membrane industry in recent years, membrane performance and economy have been continuously improved. Currently, high-performance ultrafiltration MBR membrane processes can achieve lower construction costs than traditional sewage treatment processes, while operating costs can be basically maintained. Combined with the growing concerns of the public regarding biosafety and the control of new pollutant risks, membrane technology will increasingly become the preferred option for upgrading and constructing wastewater treatment plants (recycled water plants).

      Different from the MBR microfiltration membrane with a pore size of 100-200 nm commonly seen in the domestic market, the H-series high-performance ultrafiltration membrane with a pore size of 30 nm, which is standard for drinking water, is selected for the sewage MBR or ultrafiltration system, which can deeply intercept various bacteria, including COVID-19 and norovirus, to ensure the water safety, ecological safety and environmental safety in the tail water discharge and reclaimed water utilization areas of the sewage plant.