The efficacy of two biochar variants as filtration material for the improvement of river water quality

Febbraio, Tanino (2020-04)

Thesis (MScFoodSc)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: The safety of irrigation water from rivers is continuously diminishing and has a direct effect on the safety of fresh produce. Not only can irrigation water be the source of pathogenic contamination, but it can also be a source of other physical and chemical contamination into the food system. The reduction or removal of these contaminants from river water for irrigational use may be achieved using a combination of water treatments. One such treatment includes the alternative use of biochar as a filtration media to improve the river water quality. Little is known about biochar as a possible adsorbent of contaminants from water mediums in filtration systems. The aim of the study was thus to determine the efficacy of biochar filtration to improve the river water quality. Open-ended filtration columns were constructed with two variants of biochar and compared to granular activated carbon (GAC). Untreated river water was exposed to these columns and analysed to determine the quality of the treated water both microbiologically and physicochemical. The pine and black wattle biochar, as well as the GAC, did not improve the microbiological quality of the untreated river water. In certain runs the heterotrophic plate count (HPC), faecal coliforms and Enterobacteriaceae were increased by the treatments, possibly due to the formation of biofilms in the columns. The pine biochar did, however, have the least negative effect on the microbial status of the untreated river water. Furthermore, the pine biochar was also more effective than the black wattle biochar and GAC at improving the COD, TSS, VSS, turbidity and UVT% of the untreated river water. The pine biochar filtration showed the most promising results and showed the most effective improvement on the UVT% of the untreated river water (from 33.9% to 97.7%). As a result of this improvement it was decided to expose the untreated river water to filtration and UV irradiation. The combined treatment with the biochar filtration and UV treatment lead to more effective and efficient reduction of microorganisms and the removal of STEC. Closed filtration columns were then constructed to enable complete saturation of the pine biochar filtration media. Untreated river water was filtered using these columns and the microbiological and physicochemical characteristics of the filtrates were analysed. The pine biochar filtrates only reduced the faecal coliforms from the untreated river water and more so when the filtrate was resting in the column for three days. The GAC filtrates did not indicate reduction of faecal coliforms. The physico-chemical properties of the untreated river water were best improved by the pine biochar filtration media. The UVT% and turbidity were improved as effectively as with the with open-ended columns. Both these properties of the untreated river water were further improved when the river water sample remained exposed to the columns for three days. Furthermore, improvement of the untreated river water using biochar filtration systems is dependent on the type of biochar as well as the design of the filtration columns. The filtration with biochar alone could not improve the untreated river water to conform to standards for irrigational use. This may be achieved when using it in combination with other treatments such as UV irradiation.

AFRIKAANSE OPSOMMING: Die veiligheid van besproeiingswater vanaf riviere word gedurig verminder en het 'n direkte invloed op die veiligheid van varsprodukte. Nie net kan besproeiingswater die bron van patogeniese kontaminasie wees nie, maar dit kan ook 'n bron van ander fisiese en chemiese besmetting in die voedselstelsel wees. Die vermindering of verwydering van hierdie kontaminante van rivierwater vir besproeiings gebruik kan bereik word met behulp van 'n kombinasie van waterbehandelings. Een so 'n behandeling sluit in die alternatiewe gebruik van biochar as 'n filtrasie media om die rivierwatergehalte te verbeter. Daar is min studies bekend oor die gebruik van biochar in filtrasie stelsels as 'n moontlike alternatief vir die absorpsie van kontaminante vanaf watermediums. Die doel van die studie was dus om die doeltreffendheid van biochar-filtrasie te bepaal om die rivierwatergehalte te verbeter. Oop geëindig filtrasie kolomme is gebou met twee variante van biochar en met korrel geaktiveerde koolstof (GAC) vergelyk. Onbehandelde rivierwater is aan hierdie kolomme blootgestel en ontleed om die gehalte van die behandelde water, beide microbiologies en fisiochemies, te bepaal. Die denne-en swart wattel-biochar, asook die GAC, het nie die mikrobiologiese gehalte van die onbehandelde rivierwater verbeter nie. In sekere gevalle is die heterotrofiese plaattelling (HPC), fekale kolivorme en Enterobacteriaceae verhoog deur die behandelings, moontlik as gevolg van die vorming van biofilms. Die denne-biochar het egter die minste negatiewe uitwerking op die mikrobiese status van die onbehandelde rivierwater gehad. Verder was die denne-biochar ook meer effektief as die swart wattel biochar en GAC met die verbetering in COD, TSS, VSS, turbiditeit en UVT% van die onbehandelde rivierwater. Die denne-biochar filtrasie het die mees belowende resultate getoon en het die mees effektiewe verbetering op die UVT% (97,7%) van die onbehandelde rivierwater (33,9%) gehad. As gevolg van hierdie verbetering was daar besluit om die onbehandelde rivierwater aan biochar filtrasie en UV-bestraling bloot te stel. Die gekombineerde behandeling van die biochar filtrasie en UV behandeling lei tot meer effektiewe en doeltreffende vermindering van mikro-organismes en die verwydering van STEC. Geslote filtrasie kolomme was daarna gebou om volledige versadiging van die denne biochar filtrasie media te verseker. Onbehandelde rivierwater was met behulp van hierdie kolomme gefiltreer en die mikrobiologiese en fisikochemiese eienskappe van die filtrate was geanaliseer. Die denne biochar filtraat het slegs die fekale kolivorme van die onbehandelde rivierwater verminder en meer nog toe die filtraat vir drie dae in die kolom rus. Die GAC filtrate het nie die vermindering van fekale kolivorme aangedui nie. Die fisicochemiese eienskappe van die onbehandelde rivierwater was die beste verbeter deur die denne- biochar filtrasie media. Die verbetering van UVT% en turbiditeit was net so effektief soos met die oop geëindig kolomme. Beide hierdie eienskappe van die onbehandelde rivierwater was verder verbeter toe die rivierwatermonster vir drie dae lank aan die kolomme blootgestel was. Verder is die verbetering van die onbehandelde rivierwater met behulp van biochar-filtrasie stelsels afhanklik op die tipe biochar, asook die ontwerp van die filtrasie kolomme. Die filtrasie met biochar alleen kon nie die onbehandelde rivierwater verbeter om te voldoen aan standaarde vir die gebruik as besproeiingwater nie. Dit kan egter bereik word deur die gebruik van die biochar filtrasie kolomme in kombinasie met ander behandelings, soos UV bestraling.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108048
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