THE EFFECT OF IRON IN WASTEWATER ON UV LAMP SLEEVE FOULING

The effect on UV lamp sleeve scale formation of ferrous iron addition to the activated sludge process was investigated. High concentrations of ferrous iron (> 70 mg/L) were added to samples of anaerobic digester sludge and allowed to react. The total iron in the sludge supernatant, that had formed during a seven day period, was found to be in the neighborhood of 0.5 mg/L. This reduction was primarily due to the precipitation of iron as sulfide salts in the anaerobic sludge. Mixtures of this supernatant and either return activated sludge or activated sludge mixed liquor were then aerated over a six-hour period. The concentration of iron was further diminished by oxidation to concentrations comparable to those currently experienced at the wastewater treatment plant from which samples were obtained.UV lamp fouling test results indicate that the composition of the scale forming deposits is extremely heterogeneous. The predominant metals in the scale, by weight, were found to be calcium, sodium, iron and aluminum. The amounts of metals deposited per unit area were found to be similar in the control and spiked samples. Specifically, the amount of iron in the deposits was virtually the same in the experimental and control samples. The transmittance of light at 254 nm was also found to be virtually the same through samples of UV lamp sleeve that had been subjected to experimental conditions as that through glass samples used in the control experiments.