Biodegradability of phenolic compounds as single and mixed substrates by ctivated ludge

Abstract

Fenoolsed ühendid on kantud veekeskkonnale ohtlike ainete nimistusse kui ühendid, mille veeheidet või sattumist vette muul viisil peab piirama, sest need võivad põhjustada ohtu inimese tervisele ning kahjustada teisi elusorganisme või ökosüsteeme, mistõttu on fenooliheite piiramiseks ja kontrolliks kohustus seirata heitvee fenoolsete ühendite sisaldust. Käesolevas töös uuriti põlevkivitööstuse reoveele iseloomulike fenoolsete ühendite – fenooli, hüdroksü-, metüül- ja dimetüülfenoolide – aeroobset biolagundatavust nii üksik- kui segasubstraatidena Kohtla-Järve biopuhastusseadme aktiivmuda toimel. Respiromeetrilise mõõtmised võimaldavad hapniku tarbimise kaudu määrata nii substraadi lagunemist ja ärastamisefektiivsust biopuhastis kui ka substraatide mõju mikroobikooslusele. Saadud andmete alusel hinnati erinevate kineetika mudelite sobivust biodegradatsiooniprotsessi kirjeldamiseks. Fenoolsete ühendite biodegradeeritavuse hindamiseks uuriti nii lühiajalist (BODst) kui ka biokeemilist hapnikutarvet (BOD5, BOD7) ning biodegradatsiooni protsessi iseloomustavate kineetiliste parameetrite väärtusi ja substraatide vahelisi vastastikmõjusid. Biodegradatsiooni iseloomustavate parameetrite väärtused varieerusid erinevate aktiivmuda proovide korral ning fenoolide biolagundatavus sõltus ühendi struktuurist: aromaatse tuuma asendajate arvust, nende asendist ja omadustest. Aktiivmuda lagundas fenooli, resortsinoole ja kresoole kergemini kui dimetüülfenoole. Substraatide vahelised vastastikmõjud sõltusid nii mõlema substraadi kontsentratsioonist segus kui ka kumbagi komponendi potentsiaalsest toksilisusest aktiivmuda mikroobikooslusele. Lühiajalise BODst määramise eeliseks biokeemilise hapnikutarbe ees on kiiresti (ca 30 minutiga) saadavad tulemused, mida saab rakendada reoveepuhasti töö optimeerimiseks, pideval monitoorimisel ka puhastusprotsessi toimimise hindamiseks ja vajadusel avariiolukordades kiirete meetmete rakendamiseks.

The designation of phenolic compounds with specific effluent limits has created many challenges in modelling and operating of biotreatment processes. The aerobic biodegradability of different hydroxyl-, methyl- and dimethylsubstituted phenolic compounds characteristic to the wastewater of the oil-shale industry was studied both as single substrates and bi-substrate mixtures at different concentrations in current thesis. As oxygen uptake profiles yield the same information as substrate removal profiles, respirometry makes possible to assess the ability of microbial community to remove substances from the wastewater treatment plant, to determine the effect of the substances on the microbial community and also to quantify substrate degradation. Various kinetic models were applied to describe the biodegradation process. Knowing the rate and extent of degradation, the kinetic and interaction parameters is essential for an understanding of the behaviour of compounds, their persistence and how these compounds may influence each other’s biodegradation. Among all the parameters the biochemical oxygen demand over a period of 5 to 7 days (BOD5, BOD7) and the short-term oxygen demand (BODst) are the most important and widely used parameters in the measurement of organic pollution. The measurement of BODst has some advantages over the conventional BOD method due to the simplicity of procedure and the relative quickness with which the results are obtained (ca 30 min), and it was determined under conditions imitating the processes in the aeration tank from which the activated sludge obtained. The results showed that the biodegradability of phenolic compounds is related to their structures depending on the nature, the number and the position of substituents of the aromatic nucleus. Phenol, resorcinols and cresols were shown to be easily biodegradable compared to dimethylphenols. The interaction parameters indicated that the interaction between substrates in the mixture varied with various activated sludge samples and depended on the concentrations and the nature of substrates. The obtained data could be used for controlling and optimization of the operation of wastewater treatment plant to ensure stable treatment process even under shock loading.