An online respirometer based on ammonia oxidizing biofilm for prompt toxicity analysis

Abstract

Wastewater toxicity may significantly disturb the performance of activated sludge processes, the core unit of most wastewater treatment plants, and thus needs to be monitored. The frequently used respirometer with suspended microorganisms is faced with problems of microbial stability and sensitivity. In this study, we designed an online respirometer with ammonia oxidizing biofilm growing in a fixed bed reactor. The toxicity of typical substances (thiourea, 2,4-dichlorophenol, pyridine, Zn²⁺, Co²⁺, Cr⁶⁺) was measured with the reduction and the reducing trend of their oxygen uptake rates as a key indicator. The detection limits can be down to 1.25 mg/L for thiourea and 25 mg/L for Zn²⁺ with measuring time down to 10 min. The IC₅₀ of thiourea, 2,4-dichlorophenol, pyridine, Zn²⁺, Co²⁺, Cr⁶⁺observed at 0.37 mg/L, 7.42 mg/L, 378 mg/L, 168 mg/L, 191 mg/L 733 mg/L, respectively. The toxicity values were in a good linear correlation with the traditional raspatory. Moreover, the regeneration time of biofilm after toxicity measure of 5 mg/L 2,4-dichlorophenol and 100 mg/L Zn²⁺ was also evaluated in range of 6–24 h.