The evolution of society and the growth of cities and economies have led to an increase in the pollution of our water environments. Even though most national and international organizations have set legal limits and ordinances to control water quality and the wastewater discharges, water pollution is still a serious problem and potential hazard to both the environment and humans. Although different methods have been reported for analyzing water quality, time consuming and complicated procedures always delay the immediate control of pollution. Owing to the advantageous features such as rapidness, simplicity and accuracy, biosensor technology has been introduced to fulfill the requirements of rapid analysis....[ Read more ]

The evolution of society and the growth of cities and economies have led to an increase in the pollution of our water environments. Even though most national and international organizations have set legal limits and ordinances to control water quality and the wastewater discharges, water pollution is still a serious problem and potential hazard to both the environment and humans. Although different methods have been reported for analyzing water quality, time consuming and complicated procedures always delay the immediate control of pollution. Owing to the advantageous features such as rapidness, simplicity and accuracy, biosensor technology has been introduced to fulfill the requirements of rapid analysis.

This thesis will demonstrate applications of biosensor technology in the field of environmental monitoring. Construction and the applications of biosensors for the rapid monitoring of four environmental parameters: inorganic phosphate PO₄^3-), nitrate (NO₃^-), ammonium (NH₄⁺) and biochemical oxygen demand (BOD) have been successfully achieved.

For the measurement of inorganic phosphate (chapter 2), a monoenzyme biosensor employing pyruvate oxidase (PyOD) as a sensing element has been constructed. The measurement is based on the enzymatic generation of hydrogen peroxide (H₂O₂) in the presence of phosphate. The working range of the biosensor was from 7.5 μM to 625 μM phosphate with a detection limit of 3.6 μM.

For the measurement of nitrate (chapter 3), a bienzyme biosensor employing lactate oxidase (LOD) and lactate dehydrogenase (LDH) as a sensing system for NADH has been constructed. A specific nitrate sensing system has been developed by using NaR, which consumes NADH in correspondence with the concentration of nitrate. The nitrate concentration is inversely proportional to the signal response, which was measured as oxygen consumption at -600 mV vs. Ag/AgCl. For the system using an immobilized LOD electrode coupled with soluble LDH and NaR, the linear range was from 12.5 μM to 600 μM nitrate with a detection limit of 12.4 μM. For the system using immobilized LOD/LDH electrode coupled with soluble NaR, the linear range was from 25 μM to 350 μM nitrate with a detection limit of 13.6 μM.

For the measurement of ammonium (chapter 4), a bienzyme biosensor employing glutamate oxidase (GXD) and glutamate dehydrogenase (GIDH) as sensing elements has been developed. The measurement was based on the enzymatic consumption of dissolved oxygen (DO) in the presence of ammonium. The working range of the biosensor was from 10 μM to 300 μM ammonium with a detection limit of 2.1 μM.

For the measurement of BOD content (chapter 5), a microbial sensor employing the yeast strain Arxula adeninivorans LS3 has been designed for fast BOD estimation. The yeast, a multi-receptor for various biodegradable substances with high salt tolerance, has been immobilized on a miniaturized Clark-type oxygen electrode for the measurement of instant oxygen consumption caused by the microbial respiration and oxidation of biodegradable pollutants. It has shown a linear response ranging from 17.2 mg L ^-1 to 412.5 mg L ^-1 BOD. The detection limit was calculated to be 10.5 mg L ^-1 BOD.

The practical usefulness of these biosensors has been studied by monitoring the nutrient content in samples collected from a sequencing batch reactor (SBR), a wastewater treatment facility, and from an aquarium. They showed good correlations with the commercial testing kits or standard method in their respective sample measurements.

For the first time in literature, this work has shown the great potential of biosensors for measuring the most important water pollution parameters. Multi-biosensors in an integrated system may in future monitor biological nutrients for the benefit of environment and people.