Razvoj sistema za čiščenje odpadnih voda, ki vsebujejo antibiotične učinkovine

Boševski, Igor (avtor), Žgajnar Gotvajn, Andreja (mentor)

Zaradi široke uporabe antibiotikov v moderni družbi so te snovi v majhnih koncentracijah prisotne tudi v okolju. To sicer ne povzroča neposrednih negativnih učinkov na organizme, prispeva pa k razširjanju odpornosti bakterij na antibiotike, kar postaja vedno bolj izrazit zdravstveni problem. Namen doktorske disertacije je bil ugotoviti, s katerim naprednim oksidacijskim postopkom in s kolikšnimi dozami oksidantov dosežemo, da antibiotiki postanejo primerni za konvencionalno biološko čiščenje. Za to je treba zmanjšati strupenost in povečati biorazgradljivost. Z uporabo oksidacije kot postopkom obdelave pred konvencionalnim biološkim čiščenjem, bi namreč lahko učinkovito omejili širjenje biološko nerazgradljivih antibiotikov v okolje. V doktorski disertaciji smo kot modelni antibiotik uporabili veterinarski slabo biorazgradljivi in okoljsko obstojni tiamulin. Za primerjavo in potrditev učinkov oksidacijskih procesov smo uporabili dva antibiotka s skrajnimi lastnostmi - biološko nerazgradljivi fluorokinolon levofloksacin ter biorazgradljivi betalaktam amoksicilin. Preizkusili smo tri napredne tehnike oksidacije, in sicer ozon, ozon v kombinaciji z vodikovim peroksidom in Fentonov reagent. Cilj je bil doseči delno mineralizacijo, predvsem pa povečati biorazgradljivost antibiotikov oziroma zmanjšati strupenost tako v vodi kot v matriksu biološkega blata. Doze ozona, potrebne za pomembno izboljšanje biorazgradljivosti, so za tiamulin 660 mg O3 g-1 (biorazgradljivost s 17 na 60 %) in za levofloksacin 534 mg O3 g-1 (biorazgradljivost z 0 na 100 %). Ozoniranje amoksicilina z 267 mg O3 g-1 pa deluje nasprotno, saj biorazgradljivost poslabša (s 100 na 80 %). Stopnje mineralizacije ob tem so bile od 13 % za tiamulin, 39 % za levofloksacin in 49 % za amoksicilin. Strupenosti za Vibrio fischeri z ozoniranjem nismo odpravili niti pri tiamulinu niti pri levofloksacinu. Strukturne spremembe, ki jih ozoniranje povzroči v tiamulinu, se začnejo z napadom ozona na vinilno dvojno vez in tvorbo karboksilne skupine, nato sledi oksidacija žvepla in dušika, ter zatem postopna razgradnja molekule. Razpad vinilne dvojne vezi in tvorba karboksilne skupine pomeni tudi izgubo antibiotične aktivnosti molekule. Pri tiamulinu in levofloksacinu sledi časovni potek zmanjševanja TOC in KPK kinetiki ničelnega reda, a v dveh stopnjah, kjer je hitrost reakcije v prvi večja kot v drugi. Stopenjsko naravo reakcije je mogoče utemeljiti z analizo strukturnih sprememb molekule med ozoniranjem, ker se v procesu pojavljajo vmesni produkti, ki z nadaljevanjem ozoniranja reagirajo dalje in izginejo, pojavijo pa se končni produkti, ki z ozonom ne reagirajo več. Pri amoksicilinu pa izmerjeni podatki kažejo, da zmanjševanje TOC in KPK s časom sledi kinetiki spremenljivega reda (od ničelnega k prvemu). Fentonova oksidacija daje primerljive učinke kot ozoniranje, vendar ob zelo velikih dozah oksidanta. Za doseganje 80 % biorazgradljivosti pri levofloksacinu namreč potrebujemo 1.955 mg H2O2 g-1, kar je glede na oksidant enakovredno 2.760 mg O3 g-1. Analogno kot ozoniranje, strupenosti s Fentonovim reagentom ne moremo odpraviti. Ozonirali smo tudi z antibiotiki kontaminirano (400 mg L-1) biološko blato, pri tem smo pokazali na sinergijo učinka utekočinjenja blata in deaktivacije antibiotikov. Inhibicijo produkcije bioplina smo z ozoniranjem blata v dozah med 36 in 70 mg O3 gvss-1 povsem odpravili in obenem povečali količino metana v bioplinu. Rezultati študije kažejo, da pri uporabi naprednih oksidacijskih tehnik ni enotnega merila, kateri postopek je bolje uporabiti za določeno vrsto antibiotika, ker so rezultati slabo predvidljivi, predvsem z vidika produktov oksidacije, ki imajo lahko povsem drugačne lastnosti kot izhodiščna molekula. Kljub temu ima ozoniranje brez dvoma velik potencial za uporabo v realnih sistemih biološkega čiščenja, še posebej kot tehnika obdelave z antibiotiki kontaminiranega blata pred anaerobno stabilizacijo.

• Jezik: Slovenski jezik
• Ključne besede: antibiotiki, biološko čiščenje, biorazgradljivost, napredni oksidacijski procesi, odpadno blato, oksidacija, ozon, strupenost
• Vrsta gradiva: Doktorsko delo/naloga
• Tipologija: 2.08 - Doktorska disertacija
• Organizacija: FKKT - Fakulteta za kemijo in kemijsko tehnologijo
• Leto izida: 2021
• PID: 20.500.12556/RUL-131883
• COBISS.SI-ID: 85212163
• Datum objave v RUL: 05.10.2021

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Development of a system for treatment of wastewaters, containing antibiotic substances

Izvleček

Due to the widespread use of antibiotics in modern society, these substances are also present in low concentrations in the environment. While this does not cause direct negative effects on organisms, it contributes to the spread of bacterial resistance to antibiotics, which is becoming an increasingly pronounced health problem. The purpose of this doctoral dissertation was to determine which advanced oxidation process and what doses of oxidants shoudl be used in order that antibiotics become suitable for conventional biological treatment. To achieve that it is necessary to reduce toxicity and increase biodegradability of the antibiotics. The use of oxidation as a pretreatment before conventional biological treatment could effectively limit the spread of non-biodegradable antibiotics into the environment. Veterinary, poorly biodegradable and environmentally sustainable Tiamulin was used as the model antibiotic. Two antibiotics were used to compare and confirm the effects of oxidation techiques; biodegradable betalactam Amoxicillin and non biodegradable fluoroquinolone Levofloxacin. We tested three advanced oxidation techniques; ozone, ozone in combination with hydrogen peroxide, and Fenton reagent. The aim was to achieve partial mineralization and, above all, to increase the biodegradability of antibiotics both in water and in the biological sludge matrix. The doses of ozone required to significantly improve biodegradability are for Tiamulin 660 mg O3 g-1 (biodegradability improved from 17 to 60 %) and for Levofloxacin 534 mg O3 g-1 (100 % biodegradability achieved). Ozonation of Amoxicillin with 267 mg of O3 g-1 has the opposite effect, as it reduces biodegradability from 100 to 80 %. Mineralization rates ranged from 13 % for Tiamulin, 39 % for Levofloxacin and 49 % for Amoxicillin. Vibrio fischery toxicity was not eliminated by ozonation neither with Tiamulin nor with Levofloxacin. The structural changes caused by ozonation in Tiamulin begin with the attack of ozone on the vinyl double bond and the formation of a carboxyl group, followed by the oxidation of sulfur and nitrogen atom, and then the gradual decomposition of the molecule. The disintegration of the vinyl double bond and the formation of a carboxyl group also results a loss of antibiotic activity of the molecule. Fenton oxidation gives comparable effects as ozonation, however by application of comparativelly high oxidant doses. To achieve 80 % biodegradability of levofloxacin, 1.955 mg of H2O2 g-1 is needed, which is in terms of oxidant equivalent to 2.760 mg of O3 g-1. Analogous to ozonation, toxicity with Fenton's reagent cannot be eliminated. In the case of tiamulin and levofloxacin, the removal of TOC and COD follows zero-order kinetics, however in two stages, where the reaction rate is higher in the first stage of the reaction. The stepwise nature of the reaction may be justified by the analysis of structural changes of the molecule during ozonation, as intermediates appear in the process, which react further with ozone forming end products, which no longer react with ozone. For amoxicillin, however, measurements indicated that the removal of TOC and COD follows variable-order kinetics (from zero to first). Antibiotic-contaminated (400 mg L-1) biological sludge was also ozonated, showing a synergy between the effect of sludge solubilisation and antibiotic deactivation. Inhibition of biogas production was completely eliminated by ozonation of sludge in doses between 36 and 70 mg of O3 gvss-1 and at the same time the yield of methane in biogas was increased. The results of the study show that when using advanced oxidation techniques there is no single guide on what to use for which antibiotic, because the results are poorly predictable, especially in terms of oxidation products, which may have completely different properties than the parent molecule. Nevertheless, ozonation undoubtedly has great potential for use in industrial scale biological treatment systems, especially as an antibiotic treatment technique for contaminated sludge prior to anaerobic stabilization.

• Ključne besede: antibiotics, biological treatment, biodegradability, advanced oxidation processes, sludge waste, oxidation, ozone, toxicity