Accuracy of Rapid Tests Used for Analysis of Advanced Onsite Wastewater Treatment System Effluent.

Rapid tests provide an inexpensive, desirable alternative to standard laboratory analyses for testing advanced onsite wastewater treatment system (OWTS) effluent in the field. Despite their potential utility, their accuracy for analysis of effluent from advanced OWTS has not been assessed. We evaluated the accuracy of an initial suite of rapid tests commonly used to analyze wastewater (test strips for ammonium, pH, nitrate and alkalinity; pH pocket meter; titration kit for dissolved oxygen (DO)) by comparing values obtained in the field to values obtained using standard laboratory methods. We tested final effluent from three different advanced nitrogen removal OWTS technologies sampled monthly for seven months at 42 different sites within the greater Narragansett Bay watershed in Rhode Island, USA. Significant differences between values obtained using field and standard methods were found only for nitrate and pH test strips when the data were analyzed using ANOVA on ranks. However, regression analysis indicated that all test strip-based rapid methods and the DO titration kit produced values that deviated significantly from correspondence with standard analyses. When effluent samples were analyzed in the laboratory (to minimize sources of variability) using the same rapid tests, significant differences between rapid tests and standard analysis disappeared for all tests. Evaluation of a suite of alternative rapid tests for ammonium, nitrate, pH and alkalinity indicated that tests kits for NH₄⁺, multi-analysis test strips for pH, and a photometer for NH₄⁺ and NO₃^- provided accurate results in the field. Our results indicate that the accuracy of rapid tests needs to be evaluated under field conditions before they are used to assess effluent from advanced N-removing OWTS.