Investigating the effect of magnetisable glass foam particles (MGFP) in an UASB reactor treating synthetic winery wastewater by monitoring biofilm development and activity of colonised MGFP

Dzviti, Rudo Wendy (2017-03)

Thesis

ENGLISH ABSTRACT: The growing of grapes for wine production is a generational, agricultural practice that has been associated with generating large revenue in South Africa. However, due to one of the outcomes of wine production, i.e. the generation of heavily contaminated wastewater, wine industries often face the obligation to treat wastewater prior to discharge to the municipality or irrigation. In addition, with the pressing matter of water scarcity at hand in South Africa, stricter regulations have been imposed on the treatment of winery wastewater (WWW), considering that wine production generates bulk volumes of wastewater. Since this winery wastewater is partially acidic and is characterised by high amounts of organic matter, inorganic ions, total suspended solids and polyphenols, these substances contribute to the pollution of water. Therefore, it is crucial for WWW to be depolluted to the standard specifications lest it negatively disrupts the ecosystem upon its discharge. Among the winery wastewater treatment methods developed and used in the wine industries, biological treatment methods (e.g. anaerobic digestion) are regarded as the most effective in treating winery wastewater (80 - 98% efficiency). The Upflow Anaerobic Sludge Blanket (UASB) bioreactor, which was used in this study, is one of the successful biological methods widely used at a lab-scale and commercial scale. The UASB reactor is primarily centred on the breakdown of organic matter to produce methane, a source of energy. However, the operation of UASB reactors often has the problem of sludge washout, which, consequently, results in reactor performance deterioration. Hence, in an attempt to prevent this problem, biofilm carrier particles known as magnetisable glass foam particles (MGFP) were used in this research. The study was focused on comprehensively investigating the effects of MGFP in an UASB reactor treating synthetic winery wastewater (SWWW) and monitoring biofilm development and activity of the colonised MGFP. The SWWW, which mimics the industrial winery wastewater, was used to make the substrate. The study was divided into two phases, whereby the first phase was aimed at treating SWWW at a gradually increasing organic loading rate (OLR) ranging from 0.5 to 5.0 kgCOD.m-3.d-1. Phase 2 was also focused on treating SWWW at a constant OLR (5.0 kgCOD.m-3.d-1), which resembles the common industrial OLR used in wine industries. Phase 1 was characterised by a high treatment efficiency with an increase in OLR. During Phase 1, from day 0 – 107, the COD reduction ranged from 71.4 to 97.7% in both Rcontrol and Rmgfp. The alkalinity, which indicates the strength of the buffer system, ranged from 450 to 3 075 mgCaCO3.L-1 in both Rcontrol and Rmgfp. The pH and concentration of volatile fatty acids (VFA), which also determine reactor stability and performance, were also within the standard specifications. The average VFA concentration in Rmgfp and Rcontrol ranged from 25 – 425 mg.L-1, which was within the optimal standard of < 500 mg.L-1 in both reactors, while the average pH ranged from 7.48 – 8.40 in Rcontrol and Rmgfp. There was a stable production of a high methane biogas by both reactors (> 55% methane), which ranged from 63 – 74% in Rcontrol and Rmgfp. The concentration of total suspended solids (TSS) measured in the effluent gradually increased with increase in OLR. The TSS increased from 100 - 380 mgTSS.L-1 in Rcontrol and from 80 – 400 mgTSS.L-1 in Rmgfp. Nevertheless, towards the end of the Phase 1, there was a reactor performance disturbance due to sludge washout caused by a high biogas production and this reduced the treatment efficiency of the reactors. Optimal reactor performance was restored in Phase 2 (day 108 - 180) due to improved settling of the sludge bed, moreover, due to stable operation of the reactors. During Phase 2, the water quality parameters were within the optimal standards for operating the UASB. The average COD reduction, alkalinity and pH ranged from 71.4 - 97.7%, 1 500 – 2 750 mgCaCO3.L-1 and 7.53 - 8.25 in Rcontrol and Rmgfp. The average TSS concentration in both reactors reduced from 380 to 360 mgTSS.L-1 in Rcontrol and 720 to 160 mgTSS.L-1 in Rmgfp. When Rmgfp, Rcontrol, control granules and colonised MGFP were analysed with a scanning electron microscope (SEM), a dense biofilm coverage was observed from the second month until the sixth month of the UASB operation. Both cocci and rod-shaped bacteria were observed in all of these samples, except for the control MGFP. In addition, the presence of bacteria and methanogens was corroborated under the fluorescence microscope where normal bacteria were distinguished from methanogens. The normal bacteria illuminated green while methanogens were blue as they auto-fluoresce. After performing granule activity tests, the results noted indicated that, overall, the colonised MGFP had the highest biological activity and acidogenic activity. This was presumably as a result of the presence of iron in the particles that aid in biogas production. However, Rcontrol granules had the highest biological activity when an acetic acid media was used, thus presumably suggesting that the sample had the highest population of active acetoclastic methanogens. Although, the magnetisable particles had negligible effects on the treatment efficiencies of the reactors, overall, the incorporation of the MGFP in an Rmgfp reactor had a positive impact, as an active anaerobic biofilm attached to the particles and produced a higher methane biogas. More so, due to the magnetic properties of the MGFP it was also feasible to extract them with a magnetic rod so that they could potentially be used as a source of multiplying active biomass to either seed another treatment process or be stored for cases of emergency (i.e. reactor failure or loss of biomass).

AFRIKAANSE OPSOMMING: Die verbouing van druiwe vir wynproduksie is ‘n landboupraktyk wat oor generasies verband hou met die generering van groot inkomste in Suid-Afrika. Nietemin, as gevolg van die generering van swaar gekontamineerde afvalwater tydens wynproduksie, is die wynbedryf dikwels genoodsaak om die afvalwater te behandel voor dit aan die munisipaliteit vrygestel of vir besproeiing gebruik word. Met die drukkende kwessie van waterskaarsheid op hande in Suid-Afrika, is strenger regulasies op die behandeling van wynkelderafvalwater (WWW) opgelê, aangesien wynproduksie groot volumes afvalwater genereer. Aangesien hierdie wynkelderafvalwater gedeeltelik suur is en gekenmerk word deur hoë hoeveelhede organiese stowwe, anorganiese ione, totale gesuspendeerde vastestowwe en polifenole, dra hierdie stowwe by tot die besoedeling van die water. Daarom is dit van kardinale belang vir WWW om gereinig te word tot die standaard spesifikasies sodat dit nie die ekosisteem negatief ontwrig tydens afvoer nie. Tussen die kelderafvalwater-behandelingsmetodes wat ontwikkel is en gebruik word in die wynbedryf, word biologiese behandelingsmetodes (bv anaërobiese vertering) beskou as die mees doeltreffende metode in reiniging van kelderafvalwater (80 - 98% doeltreffendheid). Die Upflow Anaerobic Sludge Blanket (UASB) bioreaktor, wat tydens hierdie studie gebruik is, is een van die suksesvolle biologiese metodes wat grootliks op laboratorium en kommersiële skaal gebruik word. Die UASB reaktor is hoofsaaklik gesentreer om die afbreek van organiese materiaal om metaan, 'n bron van energie, te produseer. Die werking van UASB reaktors het egter 'n groot en algemene probleem van slykuitspoeling, wat gevolglik lei tot die agteruitgang van reaktor prestasie. Dus, in 'n poging om hierdie probleem te voorkom, is biofilm draerpartikels, bekend as magnetiseerbare glas skuimpartikels (MGFP) in hierdie navorsing gebruik. Hierdie studie het gefokus op die omvattende ondersoek van die uitwerking van MGFP binne 'n UASB reaktor wat sintetiese kelderafvalwater (SWWW) behandel en die monitering van biofilmontwikkeling en aktiwiteit van die gekoloniseerde MGFP. SWWW, wat die industriële wynkelder afloopwater naboots, is gebruik om die substraat te maak. Die studie is hoofsaaklik verdeel in twee fases, waar die eerste fase gefokus het op die behandeling van SWWW teen 'n geleidelik-toenemende organiese laaikoers (OLR) wat gewissel het tussen 0.5 en 5.0 kgCOD.m-3.d-1. Die tweede fase het ook gefokus op die behandeling van WWW teen 'n konstante OLR (5.0 kgCOD.m-3.d-1), wat soortgelyk is aan die algemene industriële OLR in die wynbedryf gebruik word. Fase een is gekenmerk deur 'n hoë behandelingsdoeltreffendheid met 'n toename in OLR. Tydens fase 1, van dag 0 - 107, het die COD afname gewissel van 77.1% tot 97.7% en 71.4 tot 97.7% in Rcontrol en Rmgfp, onderskeidelik. Die alkaliniteit, wat die sterkte van die buffersisteem aandui, het gewissel van 450 tot 3 075 mgCaCO3.L-1 in beide Rcontrol en Rmgfp. Die pH en konsentrasie van vlugtige vetsure (VFA), wat ook reaktorstabiliteit en werkverrigting bepaal, was ook binne die standaard spesifikasies. Die gemiddelde VFA konsentrasie in Rmgfp en Rcontrol het gewissel van 25 - 425 mg.L-1, wat binne die optimale standaard van <500 mg.L-1 in beide reaktors was, terwyl die gemiddelde pH gewissel het van 7.48 – 8.40 in Rcontrol en Rmgfp. Goeie reaktor werking is ook bewys deur die stabiele produksie van hoë metaan biogas deur beide reaktors (> 55% metaan). Die gemiddelde metaan persentasie het gewissel van 66 - 74% in Rcontrol en 63 - 73% in Rmgfp. Die konsentrasie van die totale gesuspendeerde vastestowwe (TSS) gemeet in die uitvloeisel, het geleidelik toegeneem met toename in organiese laaikoers. Die TSS het toegeneem van 100 – 380 mgTSS.L-1 in Rcontrol en van 80 – 400 mgTSS.L-1 in Rmgfp. Nietemin, aan die einde van die eerste fase was daar 'n reaktor werkingsversteuring weens slykuitspoeling wat veroorsaak is deur 'n hoë produksie van biogas en dit het die behandelingsdoeltreffendheid van die UASB reaktore verminder. Optimale reaktor werking is herstel in die tweede fase (dag 108-180) as gevolg van die verbeterde vestiging van die slykbodem, en ook as gevolg van die stabiele werking van die reaktors. Tydens die tweede fase was die kwaliteit van die water parameters binne die optimale standaarde vir die gebruik van die UASB. Die gemiddelde COD afname, alkaliniteit en pH het gewissel van 71.9 – 97.7%,1 500 – 2 750 mgCaCO3.L-1 en 7.53 - 8.25 in Rcontrol en Rmgfp. Die gemiddelde TSS konsentrasie in beide reaktors het verminder van 380 tot 360 mgTSS.L-1 in Rcontrol en 720 tot 160 mgTSS.L-1 in Rmgfp. Toe die Rmgfp , Rcontrol, kontrole korrels en gekoloniseerde MGFP met 'n skandeerelektronmikroskoop (SEM) ontleed is, is 'n digte biofilmbedekking waargeneem vanaf die tweede maand tot en met die sesde maand van UASB werking. Beide kokki en staaf-vormige bakterieë is in al hierdie monsters waargeneem, behalwe in die kontrole MGFP. Die teenwoordigheid van bakterieë en metanogene was ook gestaaf onder die fluoressensiemikroskoop waar daar tussen normale bakterieë en metanogene onderskei is. Die normale bakterieë het groen verlig terwyl metanogene blou was omdat dit auto-fluoresseer. Na granule aktiwiteitstoetse, het die resultate getoon dat gekoloniseerde MGFP oor die algemeen die hoogste biologiese aktiwiteit en asidogeniese aktiwiteit gehad het. Dit was waarskynlik as gevolg van die teenwoordigheid van yster in die partikels wat help met die produksie van biogas. Nietemin, Rcontrol granules het die hoogste biologiese aktiwiteit getoon wanneer ‘n asynsuur medium gebruik is, wat waarskynlik voorstel dat die monster die hoogste populasie van aktiewe asetoklastiese metanogene besit het. Nietemin die magnetiseerbare partikels het weglaatbare effekte op die behandelingsdoeltreffendheid van die reaktors gehad. Oor die algemeen het die inkorporasie van die MGFP in ‘n Rmgfp reactor ‘n positiewe impak gehad, omdat ‘n aktiewe anaerobiese biofilm vasgeheg het aan die partikels en ‘n hoër metaan biogas geproduseer het. Meer so as gevolg van die magnetise eienskappe van die MGFP was dit ook haalbaar om dit uit te trek met ‘n magnetise staaf sodat hulle moontlik gebruik kan word as ‘n bron vir die vermeenigvuldiging van aktiewe biomassa om òf ander behandelingsprosesse te saai òf gestoor te word vir noodgevalle (m.a.w reaktor mislukking of verlies van biomassa).

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