Community-level analysis of the microbiology in constructed wetlands treating distillery effluent

Du Plessis, Keith R. (Keith Roland) (2006-04)

Dissertation (PhD)--University of Stellenbosch, 2006.

Thesis

ENGLISH ABSTRACT: Constructed wetlands have been widely used in the treatment of industrial and domestic wastewater to reduce biological and chemical oxygen demand (BOD and COD), to remove nitrate and enteric viruses as well as to generally improve water quality. Distillery wastewater has a complex character due to high concentrations of sugars, lignins, hemicellulose, dextrins, resins, polyphenols and organic acids, leading to a high COD that may exceed 100 000 mg/L. The potential application for the treatment of distillery wastewater by means of constructed wetlands is relatively unexplored. In 1999 a study was initiated at Distell Goudini distillery, Western Cape, South Africa, to explore the possibility of using constructed wetlands to treat distillery wastewater. It was found that constructed wetlands do have the ability to treat distillery wastewater providing that the influent COD does not exceed 15 000 mg/L for extended periods and the correct substrate material is used. The present study expanded on the above-mentioned study and specifically aimed to provide information on the microbiological controls in wetland systems in an applied sense that may contribute to improved treatment efficiency. Furthermore, this project aimed to contribute to our fundamental understanding of the microbial ecology of constructed wetlands used for the treatment of distillery wastewater. This study revealed that a highly dynamic microbial composition exists within wetlands. Furthermore it was found that wetlands can efficiently remove COD even though a low degree of similarity exists between microbial communities in various zones of the same wetland and those between different wetlands, as well as low similarity between communities sampled from the same zone over time. This demonstrates that it will be difficult to define the ‘ideal’ degradative community in terms of microbiological criteria and serves as a reminder that various indicators should be considered for monitoring system health. Furthermore the shifts in microbial community composition illustrate the ability of microbial communities to adapt to changes in the environment without compromising their functional efficacy. When studying the attached microbial communities within wetland systems it was found that different morphotypes are detected at certain stages of biofilm development while some organisms are present at most phases of biofilm formation. Measurement of CO2 production and dissolved organic carbon (DOC) removal in laboratory scale columns showed that grazing protists had a notable effect on overall microbial activity and that organic loading influenced these predator-prey interactions. Interestingly, increased clogging of pores occurred in the presence of protists, resulting in reduced flow through the porous matrix. Terminalrestriction fragment length polymorphism (T-RFLP) analysis of biofilms on gravel in experimental wetlands indicated that the presence of protists and algae had an effect on the microbial community composition. Scanning electron microscopy (SEM) showed that the presence of algae also had an influence on biofilm structure suggesting that the algae provided labile nutrients that were utilized by the bacterial and yeast members of the community. Finally, augmentation with a commercial mixture or microbial populations isolated from distillery effluent demonstrated that the concentration at which supplements are applied influence degradative efficiency.

AFRIKAANSE OPSOMMING: Kunsmatige vleilande word wêreldwyd gebruik in die behandeling van indusriële en huishoudelike afvalwater om biologiese en chemiese suurstof aanvraag (BSA en CSA) te verminder, om nitrate en ingewandsvirusse te verwyder asook om waterkwaliteit in die algemeen te verbeter. Distilleerafvalwater het komplekse eienskappe as gevolg van hoë konsentrasies suiker, lignien, hemisellulose, dekstrien, harpuis, polifenole en organiese sure, wat lei tot ‘n hoë CSA wat 100 000 mg/L kan oorskry. Daar is tot op hede relatief min studies gedoen oor die potensiële gebruik van kunsmatige vleilande vir die behandeling van distilleerafvalwater. In 1999 is ‘n studie by Distell Goudini distilleeraanleg in die Wes Kaap van Suid Afrika onderneem om die moontlikheid van kunsmatige vleilande vir die behandeling van distilleerafvalwater te bestudeer. Daar was bevind dat kunsmatige vleilande die vermoë het om distilleerafvalwater te behandel gegewe dat die invloeiende CSA nie 15 000 mg/L oorskry nie en dat die regte substraat materiaal gebruik word. Die huidige studie het by die bogenoemde studie aangesluit met die doel om informasie oor die mikrobiologiese kontroles in vleilandsisteme op ‘n toegepaste wyse te voorsien, wat tot verbeterde behandeling doeltreffendheid kan lei. Hierdie studie het verder beoog om by te dra tot ons fundementele kennis van die mikrobiese ekologie van kunsmatige vleilande wat gebruik word vir die behandeling van distilleerafvalwater. Dié studie het bevind dat daar ‘n hoogs dinamiese mikrobiese samestelling binne vleilande bestaan. Daar was verder bevind dat CSA steeds effektief deur vleilande verwyder kan word alhoewel daar ‘n lae graad van ooreenstemming is tussen mikrobiese gemeenskappe in verskeie sones van dieselfde vleiland en verskillende vleilande, asook ‘n lae graad van ooreenstemming tussen gemeenskappe wat in dieselfde sone oor tyd gemonster is. Dit demonstreer dat dit moeilik sal wees om die ‘ideale’ degraderende gemeenskap te vind in terme van mikrobiologiese kriteria en dien as ‘n herinnering dat verkeie indikatore in ag geneem moet word om die welstand van ‘n ekologiese sisteem te monitor. Die verskuiwings in mikrobiese gemeenskapsamestelling illustreer verder die vermoë van natuurlike sisteme om aan te pas by veranderinge in die omgewing sonder om funksionele doeltreffendheid te verminder. Die studie van aangehegte mikobiese gemeenskappe het aangedui dat veskillende morfotipes bespeur kan word tydens sekere fases van biofilm formasie terwyl sekere organismes tydens meeste van die fases teenwoordig is. Die bepaling van CO2 produksie en die verwydering van opgeloste organiese koolstof in laboratoriumskaal kolomme het geïlustreer dat voedende protiste ‘n waarneembare effek gehad op die algehele mikrobiese aktiwiteit en dat die organiese lading hierdie predator-prooi interaksie beïnvloed het. Dit was interessant om te vind dat die teenwoordigheid van protiste die verstopping van porieë aangehelp het en dus tot verlaagde vloei deur die poreuse matriks gelei het. Terminale-restriksie fragment lengte polimorfisme (T-RFLP) analiese van biolfilm op klipgruis in eksperimentele vleilande het aangedui dat die teenwoordigheid van protiste en alge ‘n effek gehad het op die mikrobiese gemeenskapsamestelling. Skandeerelektronmikroskopie (SEM) het bewys dat die teenwoordigheid van alge ook ‘n invloed op biofilm struktuur gehad het wat daarop dui dat alge maklik afbreekbare voedingstowwe aan die bakterieë en giste van die mikrobiese gemeenskap beskikbaar gestel het. Laastens was bewys dat die konsentrasie van toevoeging van ‘n kommersiële mikrobiese mengsel of mikrobiese populasies wat uit afvoer geïsoleer was, die effektiwiteit van degradering kan beïnvloed.

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