Evaluation of hydrogen as energy source for biological sulphate removal in industrial wastewaters

Eloff, Estie (2005-03)

Thesis (MSc)--University of Stellenbosch, 2005.

Thesis

ENGLISH ABSTRACT: Biological removal of sulphate from wastewater can be achieved by using a gas mixture consisting of 80% hydrogen and 20% carbon dioxide as energy and carbon sources. A novel reactor, including a venturi device for optimal hydrogen gas-liquid contact, and geotextile for immobilisation of the sulphate reducing bacterial community, was introduced. Efficient, relatively stable sulphate removal was obtained when the reactor was operated in continuous mode. The maximum sulphate removal rate obtained when the reactor was 8% packed with geotextile, was 1 g S04/(L.d) and 4 g S04/(L.d) when the reactor was 80% packed with geotextile. Kinetic batch studies showed that the highest sulphate removal rates were obtained at 29.5 °C; a pH of 7.5; initial sulphate concentration of 4000 mg/L; initial alkalinity of 1600 mg/L; cobalt concentration of 3 mg/L and when excess hydrogen gas was fed compared to what is stoichiometrically required (900 ml/min). Nickel addition showed inhibition at increased concentrations (>3 mg/L). The biofilm structure was observed on the geotextile with electron microscopy, while the viability of the biofilm was indicated with fluorescence microscopy. These observations indicated the suitability of the geotextile as a support material for biofilm formation in the sulphate reducing system. The stability of the sulphate reducing community was analysed, using the T-RFLP protocol. It was shown that the composition of the community changed after a period of 3 months, when the reactor was subjected to environmental changes. The reactor was also observed to be more efficient in terms of sulphate removal after the environmental changes, of which the temperature change from an average of 39 to 29.5 °C was the most prominent. Subsequently, it was speculated that the population shift was in favour of a more efficient system for sulphate removal. A dynamic, viable, mesophilic sulphate reducing community was therefore observed on the geotextile support, responsible for successful sulphate removal in a novel venturi-reactor. Defining optimal operating conditions, and a knowledge of biofilm structure and composition may contribute to the successful implementation of the biological sulphate removal component of the integrated chemical-biological process for the treatment of industrial wastewater, when hydrogen and carbon dioxide are supplied as the energy and carbon sources, respectively.

AFRIKAANSE OPSOMMING: Ongewenste industriële afval-water kan biologies behandel word deur 'n gasmengsel van 80% waterstof en 20% koolstofdioksied te gebruik vir sulfaat verwydering. 'n Reaktor wat 'n venturi apparaat bevat vir optimale waterstofgas-vloeistof kontak, asook geotekstiel vir die immobilisasie van die bakteriële sulfaatverwyderende gemeenskap, is bekend gestel. Effektiewe, relatief stabiele sulfaatverwydering is waargeneem sodra die reaktor op 'n kontinue basis gevoer is. Die optimale sulfaat verwyderingstempo wat bereik is as die reaktor 8% met geotekstiel gevul was, was 1 g S04/(L.d) en 4 g S04/(L.d) wanneer die reaktor 80% met geotekstiel gevul was. Kinetiese groepstudies het getoon dat die beste sulfaatverwydering bereik is by 'n gemiddelde temperatuur van 29.5 °C; pH van 7.5; aanvanklike sulfaatkonsentrasie van 4000 mg/L; aanvanklike sulfied konsentrasie van 268 mg/L; aanvanklike alkaliniteit van 1600 mg/L; kobalt konsentrasie van 3 mg/L, asook wanneer 'n oormaat waterstofgas gevoer is (900 ml/min), in vergelyking met wat stoichiometries benodig word. 'n Verhoogde byvoeging van nikkel by die voerwater (3 mg/L), het tekens van inhibisie getoon. Die biofilm struktuur is waargeneem op die geotekstiel met behulp van 'n elektronrnikroskoop, terwyl die lewensvatbaarheid van die biofilm aangedui is met behulp van fluoressensie mikroskopie. Hiermee is die bruikbaarheid van geotekstiel as 'n ondersteunings-matriks bevestig. Die stabiliteit van die sulfaatverwyderende gemeenskap is ondersoek deur die T-RFLP protokol te gebruik. Hiermee is aangedui dat die samestelling van die gemeenskap verander het na die 3 maande toets periode, toe die reaktor onderhewig was aan omgewings veranderinge. Die reaktor het ook 'n verbetering in sy sulfaatverwyderings vermoë getoon na hierdie tydperk van omgewingsveranderinge, waarvan 'n temperatuur verandering vanaf 'n gemiddeld van 39 na 29.5 °C die prominentste was. Dit is dus gespekuleer dat die populasie verskuiwing ten gunste was van 'n beter sisteem vir sulfaatverwydering. 'n Dinamiese, lewensvatbare, mesofiliese sulfaatreduserende gemeenskap, verantwoordelik vir die sulfaatverwydering in die venturi-reaktor, is dus waargeneem op die geotekstiel as 'n ondersteuningsmatriks. Met hierdie evaluasie kan die insig wat verkry is in die reaktor samestelling en die optimale kondisies vir die reaktor werking, bydra tot die suksesvolle implementasie van die biologiese komponent, in die geïntegreerde chemies-biologiese proses vir die behandeling van industriële afval water, wanneer 80% waterstof en 20% koolstofdioksied gas as energie en koolstofbron respektiewelik, gebruik word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/50344
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