Hidrológiai Közlöny 2006 (86. évfolyam)

3. szám - Kaposvári Kázmér: Effect of the intervening ozonizing and Biologie Activated Carbon treatmant to drinking water produced by water supply intake at the River Tisza Szolnok

KAPOSVÁRI K : Efleet of the intervening ozonizing and BAG treatment

. 25 2.3. The deficiencies of the earlier water treatment technology The water plant was renewed and recommissioned in 1979. However, from technological point of view it carried certain compromises. With a deviation from the plans, the ozonization, the GAC adsorption and the chlorine-oxide post-sterilization was not implemented. However, the installed Graever type cleaners, quick sand filters better served the satisfaction of the increasing volume demands as compared to the earlier used facilities. It is the consequence of the process used in the water plant that it was basically suitable only for mechanical cleaning, for pre- and post-sterilization as well as for partial chemical purification. The water quality of the Tisza river at average and seasonal conditions, as well as during emergency situations created so strict requirements against the process, what the 0,5-0,8 g/m

3 KMn0

4, 10-15 g/m

3 activated carbon powder dosing and the pretty low mixing efficiency aluminium sulphate settling/flocculation (labyrinth type mixer, G<40s ) was not able to satisfy. The applied 3,0-3,5 g/m

3 concentration, oxidative pre-chlorination led to THM, AOX problems, which were unanimously justified by the official examinations. The insufficient design of the water treatment plant provided a major contribution to the development of the complained water quality. According to the opinion of the operators the technological problems of the potable water production were the following: - Low efficiency, which was inheritedly accompanied by the selective cleaning ability. Entrance or bypass of numerous raw-water related organic micro contaminants and directly sensible materials in almost full or reduced, but still problematic concentration into the treated water. - The inflexible and low variability system was unable to follow the changes in the quality of the raw Tisza water. - The equipment installed during the construction phase were not easily operable, their control was difficult and the settling of their parameters was inadequate. (

Kaposvári K., 2000) Table 3: Besides the direct water quality complaints the behavior of the treated water in the distribution network created daily problems as well, which were related to the biological instability of the system. In this respect a number of strongly interrelated parameters were subject to revision - total residual organic matter, biologically decomposable solved organic matter, biofilm creating tendency, chlorine demand, mutation tendency. The results of the high specific concentration chlorine post-sterilization are the secondary toxicity, the chlorination byproducts which are subject to strict sanitary inspections and control. 3. Targets of the water quality enhancement program, the technical content of the technological developments The development of the water purification plant was the execution of a series of tasks interrelating in detail with each other. The major elements were the following: - consumer complaints caused by sense perceptions, - medical risks related to the presence of the toxic organic micro contaminants, - biological (alga and Zooplankton) complaints. Considering the requirements of the potable water production the following elements should not be ignored either: - achievement of the biological stability which are responsible for creating water quality variations in the distribution network, - limitation on the chlorinc demand used for post-sterilization purposes and on the formation of the consequential chlorine byproducts. These byproducts - residual organic matter; considering chemical oxygen demand concentration < 1,0 mg/L, AOC < 50 |ig/L and AOX < 20 pg/L indicator values - posed big challenges against the process design. The water quality enhancement program established for the solution of the problems defined a number of process and technology related tasks - Table 3. Process operation Technical solution Expected results Chemical cleaning Ozone oxidization (interfacial) 0,8-3,5 g/m

3, T

1

0ui = 16 min Two stage counterflow absorption Control from the residual ozone GAC adsorption CHEMVIRON F300 9 adsorber units (open) A = 9 x 54 m

2 Surface load, nominal 3,85 m

3/m

2/h T„

0„, = 21,8 min Elimination of taste and odor problems Decomposition of toxic organic micro contaminants and heavy molecule organic matters, Oxidization of iron vas, manganese C-source for the BAC reactor Adsorption bonding of special organic matters Reduction of the BAC metabolism and the residual COD Reduction of AOC, BDOC Eliminating the pre-chlorine oxidization On demand / intermittent injection D = 0,5 - 2,5 g/m

3 Reduction in the THM, AOX, MX and mutation Chemical injection, intensification FLASH injection in to the discharge piping G>200 sec"

1 Removal of the labyrinth mixing Optimization of the coagulation Alternative post-sterilization Chlorine oxide 0,05 - 0,4 mg/L Chlorine gas 0,1 - 0,6 g/L Prevention of the recontamination in the distribution network Network THM controlling Balanced hydraulic load Expansion of the clear water storage space: V=5000 m

3 new storage Elimination of the surges in the system Steady state conditions Alternative flow paths within the plant Establishment of bypasses Elimination of total breakdowns due to failures Process control Installation of a central control and monitoring system Efficiency optimization To achieve these targets the installation of different technical solutions was required in the water purification plant, ultimately resulting in a high performance system (see Fig I). These solutions also included those operational and control elements which resulted in the enhancement of the efficiency, variability and controllability of the system. The application of further efficiency enhancement solutions (Advanced Oxidation processes) is a potential way forward.