The effect of dissolved oxygen on the development of manganese oxidizing - and reducing biofilms in the lower blyde irrigation system

Carstens, Alno (2018-12-11)

Thesis (MSc)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: The Blyderiver dam in Mpumalanga is an important source of water for the irrigation of a variety of produce on farms in Limpopo and Mpumalanga. Water from this dam is used for gravity fed irrigation to farms via the Lower Blyde Irrigation System (LBIS), a network of pipelines of approximately 150 km. Biofilm development in the system causes a reduction in hydraulic capacity, leading to a reduction in water delivery for irrigation. It was hypothesized that high concentrations of manganese (Mn) in the water of the Blyderiver dam could potentially contribute to the development of these biofilms. Dissolved oxygen (DO) and Mn measurements taken during four sampling events from 2015 to 2017 indicated that the water of the Blyderiver dam has a distinct profile, with DO and Mn concentrations showing a strong inverse correlation. DO concentration typically remained constant between 8 and 9 mg l-1 in the upper 30 + meters of the water column, where after it decreased rapidly to below 2 mg l-1 at deeper depths. In contrast, total Mn concentration remained constant between 10 and 100 μg l-1 in the upper regions of the water column, followed by a rapid increase to higher than 8000 μg l-1 near the bottom. The current point of extraction for the LBIS is located near the bottom of the dam in this water with high Mn content. Mn concentration decreased with distance along the LBIS pipeline. For instance, results of the May 2016 sampling showed a decrease in the bulk aqueous phase Mn concentration from 8631 μg l-1 at the extraction point to 134 μg l-1 at 23 km downstream, while a decrease in Mn concentration could also be seen from 30105.4 mg kg-1 biofilm biomass at 4.5 km downstream to 13727.7 mg kg-1 at 28.4 km downstream. This decrease suggests ongoing incorporation of Mn into the biofilm, and thus potentially further loss in hydraulic capacity. Laboratory simulation experiments of the LBIS pipeline were conducted in which biofilms supplied with growth medium with different DO and Mn concentrations were cultivated. These biofilms were analysed by determining cell release into the effluent, Mn measurements, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), automated ribosomal intergenic spacer analysis (ARISA) as well as confocal laser scanning microscopy (CLSM). Results obtained from colony counts and ARISA indicated that statistically significant differences did exist between biofilms cultivated under different growth conditions in some cases, but that these differences could not be attributed to the effects of different DO and Mn concentrations and were instead due to physical conditions such as shear and flux. These findings were confirmed by CLSM analysis. No statistically significant decrease in Mn concentration could be observed throughout the flow system, indicating that very little to no Mn was incorporated into the biofilm structure under any of the growth conditions tested in the laboratory simulations. SEM/EDS analysis of these biofilms further confirmed that the decreases in Mn concentration observed in both the bulk aqueous phase and biofilms with distance in the LBIS pipeline could not be replicated in these laboratory simulated flow systems. A number of factors were considered to explain this conclusion, including the time period of the experiment, nutrients used in the growth medium and biofilm sorption capacity. Future experimentation should include flow systems in which biofilms will be cultivated for longer time periods, and the use of microfluidic flow channels to provide shear values closer to that in the LBIS.

AFRIKAANSE OPSOMMING: Die Blyderivierspoort dam in Mpumalanga is ‘n belangrike bron van water vir die besproeiing van ‘n verskeidenheid vrugte produkte op plase in Limpopo en Mpumalanga. Water van hierdie dam word gebruik vir gravitasie aangedrewe besproeiing op plase en word voorsien deur middel van die Laer Blyde Besproeiing Sisteem (LBBS), ‘n pyplyn netwerk van ongeveer 150 km. Die ontwikkeling van biofilms in hierdie pyplyn is egter verantwoordelik vir ‘n verlaging in hidroliese kapasiteit, wat verder lei tot verlaagde water voorsiening vir besproeiing. Die hipotese was dat hoë konsentrasies van mangaan (Mn) in die water van die Blyderivierspoort dam moontlik kan bydra tot die ontwikkeling van hierdie biofilms. Opgeloste suurstof (OS) en Mn metings wat geneem is tydens vier monsternemings periodes tussen 2015 en 2017 het aangedui dat die water van die Blyderivierspoort dam ‘n baie spesifieke profiel het, waar OS en Mn konsentrasies ‘n sterk inverse korrelasie toon. OS konsentrasies het tipies konstant gebly tussen 8 en 9 mg l-1 in die boonste 30 + meter van die water kolom, gevolg deur ‘n skerp daling na minder as 2 mg l-1 by dieper dieptes. In teenstelling hiermee het totale Mn konsentrasies konstant gebly tussen 10 en 100 μg l-1 in die boonste dele van die water kolom, waarna dit skielik gestyg het na hoër as 8000 μg l-1 naby aan die bodem van die dam. Die ekstraksiepunt van die LBBS pyplyn is huidiglik naby aan die bodem van die dam in hierdie water met hoë Mn konsentrasie. Mn het afgeneem in konsentrasie met die lengte van die LBBS af. Die resultate van die Mei 2016 monsterneming het byvoorbeeld ‘n afname getoon in die Mn konsentrasie van die vloeistoffase vanaf 8631 μg l-1 by die ekstraksie punt tot 134 μg l-1 teen 23 km verder stroomaf. Biofilms het ook ‘n afname getoon in Mn konsentrasie vanaf 30105.4 mg kg-1 biofilm biomassa by 4.5 km stroomaf tot 13727.7 mg kg-1 by 28.4 km stroomaf. Hierdie afname dui moontlik op die aanhoudende inkorporering van Mn in die biofilm struktuur en dus verdere verlies in hidroliese kapasiteit. Laboratorium simulerings eksperimente van die LBBS pyplyn is opgestel waarin biofilms voorsien van groeimedium met verskillende OS en Mn konsentrasies opgegroei kon word. Hierdie biofilms is geanaliseer deur die sel vrystelling in die uitvloeisel te bepaal, Mn metings, skanderings elektronmikroskopie met energie verspreidende X-straal spektroskopie (SEM/EVS), ge-outomatiseerde ribosomale intergeniese spasie analise (GRISA), sowel as konfokale laser skanderings mikroskopie (KLSM). Die resultate verkry vanaf die tel van kolonies en GRISA het wel aangedui dat statisties relevante verskille in sommige gevalle bestaan het tussen biofilms wat onder verskillende groeitoestande opgegroei is, maar dat hierdie verskille nie toegeskryf kon word aan die effek van verskillende OS en Mn konsentrasies nie, maar eerder ‘n gevolg is van fisiese oorsake soos skeuringskragte en vloeistoestande. Hierdie bevindings is bevestig deur KLSM analise. Mn metings het aangedui dat geen statisties relevante afname in Mn konsentrasie waargeneem kon word regdeur die sisteem nie, wat aandui dat baie min of geen Mn in die struktuur van die biofilm geïnkorporeer is onder enige van die groeitoestande nie. SEM/EVS analise op die biofilms het verder bevestig dat die afname in Mn konsentrasie wat waargeneem is in beide die vloeistoffase en die biofilms met afstand in die LBBS pyplyn nie gerepliseer kon word in hierdie laboratorium simulerings eksperimente nie. ’n Verskeidenheid faktore is in ag geneem om hierdie gevolgtrekking te verduidelik, insluitend die tydsduur van die eksperiment, die voedingstowwe gebruik in die groeimedium en die biofilm se kapasiteit vir opname. Toekomstige eksperimente behoort onder andere te kyk na vloeisisteme waarin biofilms vir ‘n langer tydsduur opgegegroei kan word en die gebruik van mikrovloeikanaal sisteme met skeuringskragte nader aan dit wat in die LBBS waargeneem word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105036
This item appears in the following collections: