Full Scale Evaluation Of On-Line Ultraviolet Nitrate And Nitrite Monitoring Systems

Results are provided from an evaluation of on-line nitrate and nitrite monitoring systems, utilizing quantification of ultraviolet absorption, tested directly in mixed liquor at the Budd Inlet Wastewater Treatment Plant (BITP) in Olympia, Washington. Included are a discussion of alternatives for on-line measurement, technical background regarding nitrate/nitrite monitoring systems, descriptions of several nitrate/nitrite monitoring systems tested, results from the in-plant testing, and evaluation of results. Additionally, the rationale and role for the on-line monitoring system in the BITP process control scheme is discussed. Recommendation for system modifications to implement automation of methanol feed are provided to optimize denitrification, based on the results of a process evaluation.For this study, three systems that use ultraviolet spectrophotometry for nitrate/nitrite quantification were evaluated at the BITP. These systems each use a different approach to quantify nitrate/nitrite, as well as to compensate for interference from other nitrogen species, organics, and suspended pArticles. Results from the on-line nitrate/nitrite testing were compared against laboratory analysis conducted with methods from Standard Methods (APHA, WEF, AWWA). The analytical precision and bias of the three on-line systems were quantified relative to the laboratory methods. Also, results from recent operation of the selected system are provided. The results and accompanying discussion illustrate the potential for, and challenges of, on-line nitrate/nitrite analysis in high solids streams such as mixed liquor.