Qatar's largest sewage plant: Doha West Wastewater Treatment Plant
Doha, the capital of Qatar, has a total area of 132 square kilometers. It has the largest sewage treatment plant in Qatar - Doha West Sewage Plant, with a total daily treatment capacity of about 280,000 tons.
Sewage treatment process: grille - sand settling - activated sludge process - secondary settling tank - sand filter - ultrafiltration - ultraviolet disinfection
Today we mainly talk about chlorine disinfection and ultraviolet disinfection.
1. Chlorine disinfection VS ultraviolet disinfection
During the fifth expansion of Doha West Sewage Plant, the original chlorine disinfection was changed to ultraviolet disinfection, the purpose of which was to prevent accidents caused by chlorine gas leakage and eliminate the generation of disinfection by-products.
By comparing ultraviolet disinfection and chlorination disinfection, we can see that,
1) Pertinence: Ultraviolet disinfection is to remove its reproductive ability to inactivate, so it has an inactivation effect on most viruses and bacteria; the biggest problem with chlorination disinfection is that it is ineffective against some viruses and spores.
2) By-products: Since the ultraviolet disinfection technology does not add any chemicals,the ultraviolet rays will not cause secondary pollution to the water body and the surrounding environment,and will not change any components in the water;sodium hypochlorite disinfection will produce more disinfection by-products,such as trichlor Acetic acid,diaminoacetic acid,chloroform, etc.; after the tail water is disinfected by liquid chlorine,the residual poison will produce an odor,which is strongly irritating,and toxic disinfection by-products will be produced during the disinfection process.
3) Operation management: Ultraviolet disinfection is powered by electricity, and it is convenient for daily operation.The ultraviolet lamp and quartz sleeve only need to be replaced and removed regularly;sodium hypochlorite disinfectant should not be stored for a long time,and generally only a few days are reserved to meet the disinfection effect; Chlorine gas risk Higher, more security precautions, relatively complex management.
4) Subsequent disinfection: ultraviolet disinfection cannot provide the remaining disinfection capacity.After the treated water leaves the reactor, some microorganisms killed by ultraviolet rays will repair the damaged DNA molecules under the photoreactivation mechanism to regenerate the bacteria; after liquid chlorine disinfection ,there is still a certain amount of residual chlorine in the tail water,and liquid chlorine disinfection has residual disinfection capacity.
5) Water quality requirements: The ultraviolet disinfection process is not suitable for water quality with low ultraviolet light penetration rate (sewage with SS higher than 30mg/L),which will not only increase energy consumption, but also cause poor disinfection effect.The ultraviolet penetration rate of treated sewage and reclaimed water is generally 40-80%,and it is a good choice to adopt ultraviolet disinfection;chlorination disinfection does not have high requirements on water quality,and generally can meet the water quality requirements of sewage treatment tail water.
6) Treatment contact time: The contact time for liquid chlorine disinfection is generally 10-30 minutes,the time for sodium hypochlorite disinfection is slightly shorter,and the time for ultraviolet disinfection is the shortest.
