Ispitivanje biološke stabilnosti vode za piće primenom rotirajućih prstenastih reaktora

Abstract

U radu su predstavljeni rezultati ispitivanja biološke stabilnosti vode za piće primenom rotirajućih prstenastih reaktora (eng. rotating annular reactor, RAR). Pomoću RAR praćen je uticaj odabranih faktora na suspendovani i pričvršćeni mikrobni rast pri kontrolisanim laboratorijskim uslovima koji su simulirali distributivne sisteme. Pored toga, u cilju potpunog razumevanja biološke stabilnosti vode za piće izvršeno je ispitivanje metoda za određivanje biodegradabilne frakcije organske materije, BDOC i AOC test. Poređenjem BDOC testova sa nativnom populacijom bakterija pričvršćenom za pesak iantracit utvrđena je efikasnija primena biološkog aktivnog peska. Primenom peska za inokulaciju uzorka, vrednost BDOC u podzemnoj vodi sa teritorije srednjeg Banata iznosila je 1,27 mgC/l. U ispitivanju AOC testa sa suspendovanim standardnim kulturama Pseudomonas fluorescens P17 (ATCC 49642) i Spirillum sp. NOX (ATCC 49643), AOC iskorišćen od strane NOX je imao veću vrednost u odnosu na P17, što pokazuje da su karboksilne kiseline dominantan supstrat za rast. Vrednost AOC u tretiranoj podzemnoj vodi iznosila 32 μg acetat-C/l. Veće vrednosti BDOC ukazuju na prisustvo jedinjenja veće molekulske mase u ovoj frakciji u odnosu na AOC frakciju biodegradabilne organske materije. U ispitivanju biostabilnosti podzemne vode sa teritorije srednjeg Banatatokom tretmana, najveća količina biofilma je razvijena u RAR sa ozoniranom vodom (13,30 CFU/cm2), što potvrđuje efekte ozonizacije na biodegradabilnost organske materije i ponovni rast mikroorganizama. Tokom tretmana zabeleženo je variranje razvoja biofilma, pri čemu je najmanji stepen rasta biofilma uočen u RAR sa vodom nakon GAC filtracije (1,10 CFU/cm2). Tokom mikrobne kolonizacije test-pločica RAR pri laminarnom i turbulentnom protoku uočen je sličan trend rasta bakterija u biofilmu u sintetičkoj smeši organskih i neorganskih nutrijenata. Međutim, tokom dominacije suspendovanog rasta u sistemu voda-biofilm pri neprotocnim uslovima, ponašanje biofilmova razvijenih pri protočnim (laminarnim i turbulentnim) uslovima je bilo različto. Uočen je manji udeo bakterija prisutnih u vodenoj fazi kod biofilma nastalim pri turbulentnom protoku u odnosu na veće oslobađanje ćelija iz biofilma nastalim pri laminarnim uslovima, nakon 48h 78% i 89% suspendovanih bakterija, redom. Ovi rezultati pokazuju da su biofilmovi razvijeni pri turbulentnom protoku snažniji, stabilniji i jače pričvršćeni nego pri laminarnom protoku. Tokom praćenja sekundarne kolonizacije odvojenih ćelija biofilma uočeno je da se primarni biofilm ponaša kao stalni rezervoar ćelija koje su sposobne da zauzmu nove površine vrlo brzo pri različitim hidrodinamičkim uslovima. Brojnost bakterija u biofilmu razvijenom na sekundarnim test-pločicama nakon 24 h iznosila je 32000±1200 CFU/cm2 u odnosu na 16±1 CFU/cm2 primarne test-pločice. Ustanovljen je izraženiji potencijal kolonizacije novih površina odvojenim želijama iz primarnog biofilma koji je formiran pri turbulentnim uslovima u odnosu na laminarne uslove. Proces stvaranja biofilma na test-pločicama od nerđajućeg čelika (SS), polivinilhlorida(PVC) i polietilena(PE) je bio vrlo sličan. Samo debljina biofilma je bila veća na PE (4,0-5,5 kg/m3) nego na SS i PVC test-pločicama (2,7-3,6 kg/m3 i 2,8-3,9 kg/m3, redom). Ustanovljen je uticaj materijala cevi na rast biofilma u RAR snabdevanim vodom iz distributivnog sistema grada Novog Sada, naročito za vreme početne faze procesa. Biofilmovi formirani na različitim materijalima u RAR su uticali na mikrobiološki kvalitet vode, zavisno od njihove bakterijske gustine. SEM analiza potvrdila je prisustvo biofilma na test-pločicama u eksperimentima, ukazujući na uspe!nu primenu RAR u ispitivanju biofilma i biostabilnosti vode za piće. Rezultati dobijeni tokom ispitivanja ukazuju da se primenom odabranih i optimizovanih, zavisno od cilja ispitivanja i vrste uzorka, BDOC i AOC testova može efikasno definisati biolo!ka stabilnost vode za piće. Pored toga, sistematski pristup odabiru odgovarajućih materijala cevi, koji je zasnovan na pouzdanim testovima i definisanim kriterijumima, može se primeniti u cilju osiguravanja kvaliteta vode sa mikrobiološkog aspekta. Ispitivanja su pokazala uspešnu primenuRAR u simulaciji mikrobnog rasta u cevima pri kontrolisanim laboratorijskim uslovima i značaj istovremenog ispitivanja imobilisanog i suspendovanog rasta u definisanom hidrodinamičkom sistemu. Primena RAR kao model biofilma je ukazala na njegov značaj u ispitivanju potencijala ponovnog naseljavanja površina otkinutih delova i/ili pojedinačnih ćelija biofilma za uspostavljanje efikasne kontrole mikrobnih problema u distributivnim sitemima vode za piće.

This thesis presents theresults of investigation of drinking water biostability using the rotating annular reactor (RAR). The effects of selected factors on the suspended and attached microbial growth under controlled laboratory conditions that simulated the distribution systems were monitored using RAR. In addition, in order to completeunderstanding of the drinking water biological stability, methods for determining biodegradable organic matter fractions, BDOC and AOC methods were tested. Comparing the BDOC tests with the native population of bacteria attached to sand and anthracite, a better application of biologically active sand was established. Using BDOC test with sand, the BDOC value in groundwater from the territory of the Central Banat (Republic of Serbia) was 1.27 mgC/L. In the investigation of AOC tests with standard suspended culture of Pseudomonas fluorescens P17(ATCC 49642) and Sprillumsp. NOX (ATCC 49643), AOC utilized by NOX had a higher value compared to the P17, which shows that the carboxylic acid are dominant substrate for growth. The AOC value in the treated ground water was 32 μg acetate-C/L. The higher BDOC values indicate the presence of higher molecular weight compounds in this fraction compared to the AOC biodegradable fraction of organic matter. In the investigation of biostability during treatment of groundwater from the territory of the Central Banat (Republic of Serbia), the largest amount of biofilm was developed in the RAR with ozonated water (13.30 CFU/cm2), confirming the effects of ozonation on organic matter biodegradability and microbial regrowth. During treatment the variation of biofilm development was detected and in the RAR with water after GAC filtration the lowest level of biofilm growth (1.10 CFU/cm2) was observed. During the microbial colonization of the RAR test-coupons under laminar and turbulent flow, the similar trend of growth of bacteria in the biofilm in synthetic mixture of organic and inorganic nutrients was observed. However, the higher numbers of immobilized bacteria under the turbulent conditions in the same growth period (16 days) were recorded. During the domination of suspended growth in water-biofilm system under non-flow conditions, the behavior of biofilms developed under flow (laminar and turbulent) conditions were different. There was a smaller proportion of bacteria present inthe aqueous phase of the biofilm formed under the turbulent flow over a larger release of cells from biofilms formed under laminar conditions, after 48h 78% and 89% of the suspended bacteria, respectively. These results indicate that biofilms developed under turbulent flow were stronger, more stable and more strongly attached than the ones under laminar flow. During monitoring of the secondary colonization of the dettached biofilm cells, it was noted that the primary biofilm was a constant reservoir of cells that are able to occupy the new areas very quickly under different hydrodynamic conditions. The abundance of bacteria in the biofilm developed on the secondary test-coupons after 24 h was 32 000±1200 CFU/cm2 compared to 16±1 CFU/cm2 on the primary test-coupons. A stronger potential for colonization of new areas by dettached cells from the primary biofilm formed under the turbulent conditions in comparison to laminar conditions was found. The biofilm formation processes on SS, PVC and PE test-coupons werevery similar. Only biofilm thickness was greater on the PE (4.0 to 5.5 kg/m3) than the SS and PVC test-coupons (2.7 to 3.6 kg/m3 and 2.8 to 3.9 kg/m3, respectively). There was a slight influence of pipe material on the biofilm growth, especially during the initial stages of the process. Biofilms formed on different materials in the RAR with water from the distribution system of the city of Novi Sad (Vojvodina, Republic of Serbia) have showed the influence on the microbiological quality of water, depending on their bacterial density. SEM analysis confirmed the biofilm presence on test-coupons in the experiments, indicating the successful implementation of RAR in the examination of biofilm and drinking water biostability. The results obtained during the investigations indicate that the application of selected and optimized, depending on the test objective and sample types, BDOC and AOC tests can effectively define the biological stability. In addition, a systematic approach for electing appropriate pipe materials, which is based on reliable tests and defined criteria, specific for the investigated drinking water distribution system can be applied to ensure he water quality from a microbiological point of view. The investigations have shown the successful application of RAR in the simulation of microbial growth in the pipes under controlled laboratory conditions as well as the importance of simultaneous examination of immobilized and suspended growth under defined hydrodynamic system. Implementation of RAR as amodel biofilm indicated its importance in examining the potential resettlement area by dettached parts and/or individual biofilm cells to establish effective control of microbial problems in the drinking water distribution system.