We are wanting to eliminate the usage of gaseous chlorine and sulfur dioxide at a 2.5 mgd lagoon WWTP. Are you aware of successful installations of UV for this application? What are the concerns? Any feasible alternatives? We will have a TSS limit of 45 mg/L.

There are several lagoons utilizing UV for disinfection. The main concern is the TSS levels (clarity) in the water. The higher the level, the more bulbs needed.

This must be an aerated lagoon to keep the TSS below 45 or you have some sort of filter before discharge.

Because of the higher flows, I would contact my Trojan UV rep and have them perform a transmissivity test. This will help size the UV units necessary.

At these flows you also want to look at automatic wipers due to the higher number of bulbs that will be needed.

Thanks for responding, Semo. We are going to rent the transmissivity unit so we can observe it for several weeks. It is an aerated lagoon.

Lagoons are not as consistent at producing a low TSS effluent as conventional treatment plants. UV units are very sensitive to water clarity. If you experience a plant upset, UV will not properly disinfect. They are also labor intensive to keep properly maintained.

Although Chlorine requires extra caution by the treatment plant operators, it is a far more effective way to ensure the effluent will meet coliform standards even if the plant experiences an upset. With a 1 ppm residual, the chlorine will continue to disinfect after the effluent has left the plant.

If you make the switch, it is probably wise to keep the old chlorine system mothballed - you may need it again in the future.