Photo-fermentative treatment of wastewaters: surveying local sources and examining their treatment by Rhodopseudomonas palustris

Uys, Phillippus Rudolph Spies (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Owing to rapid industrialization, environmental pollution in the form of industrial wastewater is a growing concern. Additionally, global energy requirements are mostly dependent on fossil fuels and at current fossil fuel consumption rates, these limited resources will inevitably be depleted. In order to counteract the exhaustion of fossil fuels as well as to compensate for their negative impact on the environment, hydrogen has been proposed as a future energy provider. The experimental work completed throughout this research arose due to the need for high organic content industrial wastewater treatment. South African industries are both major users and polluters of water, and produce wastewater streams which are often rich in recalcitrant organic compounds. This project aims to develop a biotechnology process which is able to both reduce the organic loading in these wastewaters and produce a valuable commodity product, in the form of hydrogen gas. This is achieved through an anaerobic photo-fermentation process whereby the bacterium Rhodopseudomonas palustris is able to consume the organic portion of the wastewater. The main aims of this research are firstly to conduct a survey of local literature and industries to determine which organic containing waste streams have the potential to be treated through photo-fermentation, secondly to evaluate the ability of R. palustris to metabolize a variety of waste organic components by generating growth curves when various wastewaters are used as substrates and lastly, to evaluate the wastewater treatment potential and hydrogen production potential of R. palustris. Wastewater from several South African industries was obtained. These include winery, anaerobic digester (AD) effluent, brewery, vinasse waste, olive processing, tannery, fish processing, paper and pulp and textile dye wastewater. For each effluent, a batch photo-fermentative growth and wastewater treatment experiment was conducted with free cells at various dilution rates with carbon and nitrogen free media. Significant growth of Rhodopseudomonas palustris was observed on these wastewaters accompanied by a reduction in chemical oxygen demand (COD). Undiluted winery wastewater proved to be most suitable for photo-fermentative growth and wastewater treatment, exhibiting a 74 % increase in biomass and a 72 % reduction in COD over a 21 day period. Wastewater treatment experiments were then conducted on the undiluted winery wastewater with cells immobilized in polyvinyl alcohol (PVA) cryogels and under continuous operation so as to simulate industrial treatment processes. A consistent COD reduction of approximately 5 % was achieved over a 28 day period when the bioreactor was operated continuously. It was concluded that the overall COD reduction was lengthy (21 days) and commonly longer than current alternative wastewater treatment technologies. However, this was a scoping study which focussed on the photo-fermentative treatment of organic containing industrial wastewaters without any pre-treatment steps. With adequate pre-treatment steps this bio process can be modified to produce hydrogen gas. Therefore, in spite of the lengthy COD reduction, R. palustris remains a candidate organism for wastewater treatment owing to the possible production of valuable commodity products.

AFRIKAANSE OPSOMMING: Weens spoedige industrialisasie is omgewingsbesoedeling in die vorm van industriële afvalwater ʼn groeiende kommer. Boonop is globale energie vereistes meestal afhanklik van fossielbrandstowwe en teen huidige tempo’s van fossielbrandstofgebruik, sal hierdie beperkte hulpbronne onvermydelik uitgeput word. Om die uitputting van fossielbrandstowwe teen te werk, sowel as om te kompenseer vir hul negatiewe impak op die omgewing, is waterstof voorgestel as ʼn toekomstige energie verskaffer. Die eksperimentele werk voltooi deur hierdie navorsing het ontstaan as gevolg van die behoefte vir hoë organiese inhoud industriële afvalwaterbehandeling. Suid-Afrikaanse industrieë is beide groot gebruikers en besoedelaars van water en vervaardig waterafvalstrome wat gereeld ryk is aan weerspannige organiese samestellings. Hierdie projek beoog om ʼn biotegnologie te ontwikkel wat beide die organiese lading in hierdie afvalwater kan verminder en ʼn waardevolle kommoditeitsproduk kan vervaardig, in die vorm van waterstofgas, deur ʼn anaerobierse fotoferementasieproses waar die bakterie Rhodopseudomonas palustris die organiese deel van die afvalwater kan verteer. Die hoofdoelstellings van hierdie navorsing is om i) ʼn opname te maak van plaaslike literatuur en industrieë om te bepaal watter organies-houdende afvalstrome die potensiaal het om behandel te word deur fotofermentasie, ii) om die vermoë van R. palustris om ʼn verskeidenheid afval organiese komponente te metaboliseer, te evalueer deur groeikurwes te genereer as verskeie afvalwaters as substrate gebruik word, en laastens iii) om die afvalwaterbehandeling potensiaal en waterstofproduksie potensiaal van R. palustris te evalueer. Afvalwater van verskeie Suid-Afrikaanse industrieë is verkry. Hierdie sluit in wynmakery, AD rioolwater, brouery, vinasse afval, olyfprosessering, leerlooiery, visprosessering, papier-en-pulp- en kleurstofafvalwater. Vir elke afloopwater is ʼn lot fotofermentasie groei en afvalwaterbehandelingseksperiment uitgevoer met vrye selle en teen verskeie verdunningstempo’s met koolstofvrye- en stikstofvrye-media. Beduidende groei is waargeneem op hierdie afvalwater wat gepaard gegaan het met chemiese suurstofvraag (COD) verwydering. Onverdunde wynmakery-afvalwater is bewys as die mees gepaste afvalwater vir fotofermentasie groei en afvalwaterbehandeling, met ʼn 74% verhoging in biomassa en ʼn 72% afname in COD oor ’n 21 dae periode. Afvalwaterbehandelingeksperimente is toe uitgevoer op die onverdunde wynmakery-afvalwater met selle geïmmobiliseer in poliviniel alkohol (PVA) kriojel en kontinue bedryf sodat industriële behandelingsprosesse gesimuleer word. ʼn Konsekwente COD-reduksie van ongeveer 5% is bereik oor ʼn 28 dae periode toe die bioreaktor kontinu bedryf is. Dis bepaal dat die algehele COD-reduksie langdurig en oor die algemeen langer as huidige alternatiewe afvalwaterbehandelingtegnologieë is. Hierdie was egter ʼn bestekstudie wat gefokus het op die fotofermentasiebehandeling van organies-houdende industriële afvalwater sonder enige voorbehandelingstappe. Met voldoende voorbehandelingstappe kan hierdie bioproses gewysig word om waterstofgas te vervaardig. Daarom, ten spyte van die langdurige COD-reduksie, bly R. palustris ʼn kandidaat organisme vir afvalwaterbehandeling vanweë die moontlike vervaardiging van waardevolle kommoditeitsprodukte.

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