A novel FIA configuration for the simultaneous determination of nitrate and nitrite and its use for monitoring an urban waste water treatment plant based on N/D criteria

Visual determination of nitrite and nitrate in waters by color band formation method

A spot test for aqueous nitrate and nitrite for controlling nitrogen removal performance in small-scale wastewater treatment facilities is proposed. In this method, NO(2)(-) ion in water samples was allowed to react with sulfanilic acid and 1-naphthol to form an anionic azo dye. The resulting colored solution was introduced onto a mini column (similar to a gas detecting tube) packed with PVC particles coated with benzyl cetyl dimethyl ammonium chloride (BCDMA) and biphenyl. The NO(2)(-)-N concentration was determined visually by measuring the color band length (CBL) in the column. The CBL correlates linearly with nitrite concentration in the 4-20 mg-N l(-1) range. The concentration of nitrite+nitrate was determined after reduction to nitrite with zinc. The concentration of NO(3)(-)-N species was calculated by difference. This method was used to visually determine the concentrations of NO(2)(-)-N and (NO(2)(-)+NO(3)(-))-N in domestic wastewater samples with maximum suspended solid (SS) and chemical oxygen demand (COD) concentrations of 114 mg l(-1) and 73.9 mg l(-1), respectively.

Determination of nitrite by flow injection spectrophotometry using a home-made flow cell detector

A simple, rapid, low cost and accurate determination using flow injection spectrophotometry with a home made flow cell detector, in combination with green LED and photodiode, had been developed for nitrite based on the Griess-Saltzman reaction, measuring the absorbance at 525 nm. The proposed system is able to monitor nitrite in freshwater samples at a throughput of 60 samples per hour with a relative standard deviation (%RSD) of less than 2.4% and a detection limit of <7 microg dm(-3). The calibration graph was linear between 0.010 - 1.0 mg dm(-3).

Improving the nitrogen removal efficiency of an A2/O based WWTP by using an on-line knowledge based expert system

The results obtained using an expert system to control an activated sludge process involving nutrient removal are reported. The study was conducted at a pilot plant using an Anaerobic/Anoxic/Oxic (A2/O) scheme for which a distributed control system was specially developed. The system allows various expert operational approaches to be developed with a view to minimize nitrogen levels in the outlet while using the minimum amount of energy. The proposed distributed control system is supervised by a Knowledge Based Expert System (KBES) constructed with G2 (a tool for expert system development) and permits the on-line implementation of every operating strategy of the experimental system. A set of experiments involving variable loads and flow-rates was carried out. It revealed that the amount of removed nitrogen could be increased by 11% compared to the usual operating conditions. This increase resulted in a decrease in the amount of total nitrogen and ammonium nitrogen in the outlet by 49% and 64%, respectively. These improvements were achieved with little energy cost because the performance of the treatment plant was optimised using operating rules implemented in real time.