engleski

The interaction of zeolite and bacterial cells for denitrification of the Cetina surface water

Nowadays, nitrate contamination of waters has become a worldwide problem, even in the agricultural areas in northern Croatia, the incremental nitrate concentration values were determined. Therefore, the EU water legislation set the Nitrates directive aimed to protect water quality across Europe by preventing nitrates from agricultural sources polluting ground and surface waters. As a result, the new methods for nitrate removal are studied and among them, the biological methods are often investigated. The use of attached bacterial cells or biofilm was studied in order to establish more stable and effective nitrate removal. Furthermore, for the same purpose, the addition of zeolite in an activated sludge unit was investigated and the improvement of nitrate removal was reported. The low cost and the abundance of natural zeolite in many parts of the world along with their superior characteristics and high exchange capacities amenable the use of clinoptilolite as an inexpensive adsorbent and a carrier of an immobilized biofilm or microorganisms. The use of zeolite was thoroughly investigated for efficient removal of heavy metals, ammonium or other cations ; only few studies were reported for anions removal and a recent one dealt with use of zeolites and phosphate accumulating bacteria. The main objective of the present study was the use of zeolite and bacterial cells for establishing the stability and efficiency of the denitrification process and the optimization of the process parameters such as the influence of initially present nitrate, the initial amount of zeolite with bacterial cells, pH and methanol to nitrate-N mass ratio in order to achieve fast and efficient nitrate removal from the Cetina surface water. The natural powdered clinoptilolite was mixed with bacterial cell suspension and the resulting bio clinoptilolite powder (B-NPC) was filtered and acclimated for nitrate removal from the Cetina surface water (CSW). The influence of B-NPC amount was investigated and results revealed 15 g of B-NPC (9 %, w/w) as optimal. The obtained denitrification rates increased in the range of 25.85-37.157 mg NO3-N/Lh. The denitrification of 100 mg nitrate–N/L from the CSW at pH range of 5.82-8.20 and at methanol to nitrate nitrogen (CH3OH/N) mass ratio of 2.5:1-4.5:1 was achieved during 7 and 4 hours, respectively. The rapid nitrate removal was achieved at pH of 6.85 and 7.22, but a higher pH value was optimal due to lower accumulation of nitrite. The required CH3OH/N mass ratio was 2.5:1 and the analysis of results showed denitrification as the zero order reaction with denitrification rate of 25.85 mg NO3-N/Lh. Complete and efficient removal of 100 mg NO3-N/L from the CSW with B-NPC (9% w/w) was achieved at pH of 7.22, 25 °C and at 300 rpm. Among bacteria present in B-NPC, the dominant species were isolated and determined as Pseudomonas stutzeri and Paracoccus sp. Finally, the use of B-NPC was demonstrated as efficient method for complete nitrate removal from the Cetina surface water.

bacteria; zeolite-clinoptilolite; denitrification; methanol; surface water

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