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

KAPOSVÁ^n^^Effec^nh^ntervenm 27 water in the 80's has been reduced below 10 % from the mid of the 90's. The observation of the organic micro contaminants shows a completely different picture. One part of the primary contaminants disappeared from the water, others show spectacular reduction. However, after the application of ozonization, new aldehide and keto derivatives may form, for which the ultimate solution is still not clear (Claze W. H., 1989). (The detailed description and presentation of the micro contaminants is beyond the scope of this paper.) It should be noted however, that earlier (in the '80s) the primary micro contamination content of the Tisza water was steadily high (Makiéit S. - Dinya Z., 1988). Presently the GC-MS tests show only occasional contaminations. The treatment of the organic micro contaminants is apparently played down as compared to the other tasks of the process. The better control of the process requires the monitoring of the raw Tisza water in respect of the micro contaminants. The reduction of the total organic matter (chemical oxygen demand COD, TOC) is 85-90 %, as compared to the previously achieved 60-65%. This result is jointly achieved by the ozonization and the activated carbon filtering, but along different mechanisms. The role of the ozonization is not the direct reduction of the organic content, but the conversion of the same. It helps improving the operating conditions of the activated carbon filtering. During the shutdowns of the ozonization, the residual chemical oxygen demand is between 1,1 - 1,15 mg/L after the activated carbon adsorber, whereas this value falls between 0,7 - 0,9 mg/L during the uptime of the unit. The conditions of the high ammonia content during wintertime have been improved. The concentration in the treated water can be kept below the acceptable limit (0,5 mg/L). A precisely controlled breakpoint chlorination can be carried out in the sand filtered water basin (retention time is ~ 2,5 - 3,0 hours) right upstream the activated carbon adsorption. This has practically no effect on the operation of the activated carbon filter, but at the same time the risk of THM and AOX formation decreases due to the short contacting time. The condition of the treated water is steadily acceptable in respect of the total bacteria and the indicator bacteria. A relatively small amount of Cryptosporidium and Giardia test results are available. However, these show that living bacteria can not pass the purification process. Further examinations are required to evaluate the performance of the system in respect of the Zooplankton removal. The 21/2002. KÖVIM decree allows zero value in the potable water. However, in the treated water 1-10 planktons usually survive from the 10

2— 10

3 which is contained in the raw Tisza water. 5. Discussion The enhanced treatment process is in operation since December 1998. The ozone production and chemical adsorption, the granulated activated carbon adsorption - biological decomposition, the chlorine-oxide production and dissolution are used in a number of water purification plants and they are proven methods. The experiences collected at the Szolnok plant during the 6 years operation support the positive contribution of the operations. The control of the operation now is more demanding as compared to the previously used, simple physical operations. Among other conditions, the prerequisite for the optimal operation is the data transfer to the "hand" of the operator from the sophisticated process control, measurement and laboratory quality control systems. The ozonization —» sand filtering —> granulated active carbon treatment together can deliver the solution of the purification tasks. At certain quality statuses of the raw Tisza water the role of the oxidization or the adsorption comes forward. In the removal of taste and odor the ozone is effective. The circumstances of the operation have to be strictly monitored. The chemical structure of the taste and odor components and the conditions of the ozonization (pH, specific concentration, retention time) strongly influence the efficiency. For example, with the modification of the pH, the system can be shifted towards the direct (0

3) or to the indirect (OH°, 0

2°) side, depending on whether geosmin or phenolic effect is the prevailing. Exact chemical detection of the taste and odor components can not be done every day. In the actual daily practice the human sensation helps in identifying the characteristic cases to which the conditions of the ozonization can be assigned and adjusted (Glaze W. H., 1990, Dugnet J. P., 1985, Claze IV. H„ 1989, Lalezary S„ 1986, Anselme C„ 1988). The H

20

2/0

3 Advanced Oxidation Processes can be implemented without having the risk of bromate formation. The bromate concentration is below 5 |ig/l in the treated water. In the activated carbon filter, the adsorption and biological metabolism processes help in the removal of the organic materials. During the commissioning of the activated carbon filter a captive bacteria flora has been adapted in 25-30 days. The average number of bacteria 2,2 10

5 e/g carbon. During the first 20 days the residual COD

P

S increased to ~ 1

,2 from 0,9-1,0 mg/L after the carbon filters and now it steadily varies between 0,65-1,0 mg/L. The average value is Ccod s 0,85 mg/L. The composition of the residual organic matter after the ozone-active carbon treatment is favorable for the proper operation of the distribution network. The condition of absorbable organic carbon AOC< 50 |igC/L is met (Van der Cooij D., 2000). The biological stability is on the edge of the biofilm forming tendency. The reason for the continuous application of the post-sterilization is primarily the operability and quality of the distribution network. The actual chlorine consumption of the discharged water is c

ci < 0,25 g/m

3. The chlorine consumption in additive and ring rupturing reactions (humic agents, phenol, aromatic amine, etc.), in the oxidative residual organic content is insignificant. The £ THM < 10 Hg/L, and the water absorbed halogenide concentration is AOX < 30 ngd/L. The after generation of THM, AOX in the distributed water is insignificant with the standard retention times. The total THM is below 10 |ig/L in 95 % of the cases. The controllability, the setting of the parameters and their reproducibility, as well as the water quality parameters are steady, the variations remain within a narrow band. The total residual chemical oxygen demand (COD) is permanently below 1,0 mg/L which is clearly shown by the daily data series of 2004 in Fig 2. According to the observations, the variations are related to the operation of the flocculation plant and the ozonization, rather than to the quality of the raw water. The increases in the residual CODps values always coincided with adverse variations in the efficiency of the flocculation.