A novel biosensing system for rapid and sensitive detection of heavy metal toxicity in water.

Toxicity biosensors have recently gained significant attention due to their potential use in online monitoring. However, the effects of toxicants and the influence of dose, exposure time, and type and concentration of respiration substrate (RS) on the performance of a bioreactor are species-specific. Although these factors need to be investigated case-by-case as they can lead either to damage or self-repair of the affected microorganisms, they have seldom been considered in previous studies. Therefore, this work examined, for the first time, the effects of resting time and RS concentration on the performance of the biosensing system for toxicity of Cr6+ in water. In addition, it is also the first time that a novel non-contact fluid delivery system was applied to a toxicity biosensing system to prevent unstable responses. By choosing the best RS concentration and balancing the resting and exposure times, the proposed procedure exhibits promising results in terms of minimum detectable concentration (MDC), limit of detection (LOD), detection range, linearity, sensitivity, reproducibility and accuracy. The recovery time was only a few hours and the coefficients of variation of inhibition and recovery were only 12% and 9.6%, respectively, during six times reuse over one month of storage.

Simple approach for the rapid estimation of BOD5 in food processing wastewater.

A simple approach was developed for the rapid and accurate estimation of 5-day biochemical oxygen demand (BOD5) in food processing wastewater. Immobilization of the natural microbial consortium that was collected from an aerobic compartment of a food processing wastewater treatment plant was simply performed by adhesion using a low-cost porous carrier. Pseudomonas aeruginosa, Bacillus cereus, and Streptomyces, whose salt-tolerance and ability to break down organic compounds have been widely reported, were found to be predominant. These microorganisms may cause an enhancement of the bioreactor response in the presence of sodium chloride. Consequently, a modified glucose-glutamic acid (GGA) calibration standard was proposed in which an appropriate amount of NaCl was added; this solution was found to be more effective in terms of accuracy and practicality than both conventional GGA and the synthetic wastewater recipe from the Organisation for Economic Cooperation and Development (OECD). The calibrated self-built packed-bed bioreactor exhibited good precision of 3% or less in predicting BOD5 in influent, which is similar to the performance of the most common commercial biochemical oxygen demand (BOD) bioreactors. There was a statistical agreement between the results obtained from this rapid BOD biosensor and the conventional methods, even when testing treated wastewater samples.