The effect of winery wastewater irrigation on the properties of selected soils from the South African wine region

Mulidzi, Azwimbavhi Reckson (2016-12)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Due to an increase in wine production as well as an intensification of environmental legislation in South Africa, the need for guidelines for sustainable management of winery wastewater has increased. To address this, the first part of the study focused on the seasonal dynamics of the volumes and quality of undiluted winery wastewater. The soil chemical dynamics were monitored in two different soils that were irrigated with undiluted winery wastewater for three years. Over-irrigation with undiluted winery wastewater in combination with winter rainfall caused large amounts of cations, particularly K+ and Na+, to leach beyond 90 cm soil depth. Consequently, the leached elements are bound to end up in natural water resources over time. Irrigation with undiluted winery wastewater did not have a pronounced effect on soil pH(KCl). This was probably due to the decomposition of organic matter and the fact that the applied salts as well as dissolved organic or mineral acids leached beyond 90 cm depth. The practical application of irrigation with diluted winery wastewater was assessed in a pot experiment. Irrigations were applied under a rain shelter over four simulated irrigation seasons. Four soils varying in texture were irrigated with winery wastewater that was diluted to 3000 mg/L chemical oxygen demand (COD). The four soils were irrigated with municipal water as a control. The rate of K+ increase in the soil containing 20% clay was higher than in soils containing 13% clay, or less. This suggested that heavy soils will aggravate the risk of high K+ levels. The risk of Na+ accumulation increased linearly with the clay content in the soil. Low Ca2+ and Mg2+ concentrations in the diluted wastewater had no effect on the soil, irrespective of clay content. Irrigation with diluted winery wastewater increased soil pH(KCl) substantially in all soils over four simulated seasons. The soil pH increase was attributed to the addition of organic and mineral salts via the diluted winery wastewater to the soil. The effect of simulated rainfall on soils irrigated with winery wastewater was also assessed in a pot experiment. Six soils with different clay content were irrigated with winery wastewater diluted to 3000 mg/L over one simulated irrigation season. Thereafter, good quality river water simulating winter rainfall was added to the pots. The rainfall was simulated according to the long term averages of the regions were the soils originated. Leaching of cations, particularly K+ and Na+ occurred only from four of the six soils when winter rainfall was simulated. In one of the sandy soils, the simulated rainfall was too low to allow leaching. In the case of other soil where there was no leaching, high clay content of 35% in combination with low rainfall prevented leaching. Where three soils received the same amount of rainfall, more cations leached from the sandy soils compared to the two heavier soils. These trends indicated that leaching of cations was a function of soil texture and rainfall.

AFRIKAANS OPSOMMING: As gevolg van die toename in wynproduksie, asook ‘n verskerping in omgewingswetgewing in Suid-Afrika, het die behoefte vir riglyne vir volhoubare bestuur van kelderafvalwater ‘n belangrike aspek van wynproduksie geword. Om dit aan te spreek, het die eerste deel van die studie op die seisoenale dinamika van die volumes en gehalte van onverdunde kelderafvalwater gefokus. Die grondchemiese dinamika in twee verskillende gronde wat met onverdunde kelderwater besproei is,by twee verskillende kommersiële kelders oor drie seisoene gemonitor. Oorbesproeiing met die onverdunde kelderafvalwater, in kombinasie met winterreënval, het veroorsaak dat groot hoeveelhede katione, veral K+ en Na+, dieper as 90 cm gronddiepte geloog het. Die nagevolg hiervan is dat die geloogde elemente oor tyd in natuurlike water hulpbronne sal beland. Besproeiing met onverdunde kelderafvalwater het nie ‘n noemenswaardige effek op grond pH(KCl) gehad nie. Dis was heel waarskynlik te wyte aan die feit dat die organiese materiaal ontbind het, en dat die toegediende katione as opgeloste organiese of mineraal soute verby 90 cm diepte geloog het. Die praktiese toepasbaarheid van besproeiing met verdunde kelderafvalwater is in ‘n potproef ondersoek. Besproeiings is onder ‘n reënskuiling oor vier gesimuleerde seisoene toegedien. Vier gronde met verskillende teksture is besproei met kelderafvalwater wat tot 3000 mg/L chemiese suurstof aanvraag (Eng. = chemical oxygen demand, of kortweg COD). As ‘n kontrole is die vier gronde met munisipale water besproei. Die K+ toename in die grond wat 20% klei bevat het, was hoër as in gronde wat 13% of minder klei bevat het. Dit het aangedui dat die risiko van K+ aansameling hoër is in swaarder gronde. Die risiko van Na+ toename het reglynig toegeneem met klei inhoud in die grond. Lae Ca2+ en Mg2+ konsentrasies in die verdunde afvalwater het geen effek in die gronde gehad nie, ongeag die klei-inhoud. Besproeiing met verdunde kelderafvalwater het die grond pH(KCl) in al die gronde oor die vier gesimuleerde seisoene betekenisvol laat toeneem. Die pH toename in die gronde kon aan die toediening van organiese en mineraal soute deur middel van die verdunde kelderwater toegeskryf word. Die effek van gesimuleerde winterreënval op gronde wat eers met verdunde kelderafvalwater besproei is, is ook met behulp van ‘n potproef ondersoek. Ses gronde met verskillende kleiinhoude is vir een gesimuleerde besproeingseisoen met kelderafvalwater wat tot 3000 mg/L COD verdun is, besproei. Daarna is gesimuleerde winterreënval in die vorm van hoe kwaliteit rivierwater op die gronde toegedien. Die reënval is volgens die langtermyn gemiddeldes van die streke waar die gronde voorgekom het, gesimuleer. Loging van katione, veral K+ en Na+ het slegs by vier van die ses gronde tydens die gesimuleerde winterreënval voorgekom. In die geval van een van die sanderige gronde, was die gesimuleerde reënval te min om loging te veroorsaak. In die geval van die ander grond waar geen loging voorgekom het nie, het die hoë-klei inhoud van 35%, in kombinasie met lae winterreënval, loging verhoed. Waar drie gronde dieselfde hoeveelheid reënval ontvang het, het meer katione uit die sanderige grond in vergelyking met die twee swaarder gronde geloog. Hierdie tendense het aangedui dat loging van katione ‘n funksie van grondtekstuur en reënval is.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100081
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