Investigating the treatment optimisation of a pilot-scale Anaerobic Sequencing Batch Reactor (AnSBR) and partial characterisation of the winery wastewater using Near-infrared (NIR) spectroscopy

Thesis (MScFoodSc)--Stellenbosch University, 2020.

ENGLISH ABSTRACT: Water is arguably the most vital natural resource on Earth. It is of critical importance to humans, plants, animals, environments as well as ecosystems. Agriculture is estimated to be responsible for the abstraction of approximately 66 – 70 % of the freshwater supply globally, with that number rising to 90 % in some countries. The wine industry in South Africa is responsible for producing large amounts of wastewater with 1.24 billion litres of wastewater generated in 2018. Winery wastewater is challenging to treat due to variable strength and seasonal compositional variation. Biological treatments are very effective for the removal of organic pollutants in winery wastewater. Anaerobic digestion is an example of a biological treatment that has been widely used for the treatment of winery wastewater. Anaerobic sequencing batch reactor (AnSBR) is a viable option for the treatment of winery wastewater. The technology is still under development and has not been used extensively in the wine industry. The advantages of the AnSBR include ease of changing operational parameters, can operate in batch or fed-batch mode; it efficiently removes chemical oxygen demand (COD) and generates biogas with a high methane percentage, that can potentially be reclaimed as a source of heat generation. Knowledge of the optimal conditions for pH, mixing intervals and feeding time of the AnSBR is limited and needs to be investigated. Two important parameters for the overall stability and performance of an AnSBR are COD and total suspended solids (TSS) concentrations. Determination of these parameters are however time-consuming and laborious. Near-infrared (NIR) spectroscopy is a rapid, non-destructive technique which makes use of the wavelength range of 780 – 2 500 nm. The first aim of this study was to investigate potential for the use of NIR to quantify and classify winery wastewater based on the COD and TSS concentration. Near-infrared spectroscopy was used in combination with multivariate data analysis (MDA) for the classification and quantification of COD and TSS in winery wastewater. Spectra were acquired using a benchtop FT-NIR (Büchi NIR-Flex N500) spectrophotometer with a wavelength range of 1 000 – 2 500 nm and a portable spectrophotometer with a wavelength range of 900 – 1 700 nm. The concentration of COD could be predicted with a RMSEP value of 893 mg.L-1, an error of 9.9 % compared to the range of the reference values, using PCR along with orthogonal signal correction (OSC). This was achieved using the wavelength range 2 060 – 2 340 nm on the benchtop instrument. The PCR model performed to a satisfactory degree to be used as a screening method to rapidly determine COD concentration of winery wastewater. The concentration of TSS could be predicted with a RMSEP of 136.94 mg.L-1 , an error of 5.72 %, using the benchtop instrument. The prediction model for TSS achieved a prediction performance that was almost comparable to the reference method, meaning it is suitable for screening purposes at the very least. Classification accuracies of 90.4 % (COD) & 100 % (TSS), 80.1 % (COD) & 95 % (TSS) could be achieved with the benchtop and handheld instruments respectively. Both the benchtop and the handheld instruments could classify winery wastewater based on their COD or TSS concentrations to a satisfactory degree. The above classification accuracies for the handheld instrument indicates that classification of winery wastewater, into low or high strength categories, may be possible for in-line monitoring of winery wastewater and screening via class, instead of quantification. The second aim of this study was to evaluate whether the AnSBR technology could successfully treat winery wastewater of varying quality and determine the optimal operational parameters for the reactor A pilot-scale AnSBR with a volume of 165 L was operated for 16 cycles treating winery wastewater. The cycle length was 24 h and the hydraulic retention time (HRT) was approximately 1.85 days. The reactor was initially seeded with 22 kg anaerobic granules. A central composite design (CCD) was performed to determine the optimal operational parameters. A mean COD reduction of 68.32 % (mean influent 5 852 mg.L-1 ) was achieved along with a mean polyphenol reduction of 53.35 % (mean influent 215 mg.L1 )(SAWIS, 2018) and a stable VFA:Alkalinity of 0.23 on average. The AnSBR technology could therefore feasibly be used to treat winery wastewater. The pH, feeding time and mixing interval were selected to determine the optimal operational parameters. The optimal values achieved were determined to be: pH 7.30; feed time 180.91 minutes and a mixing interval of 84.17 minutes. This study confirmed the optimal operational parameters previously obtained for treatment of synthetic winery wastewater with an AnSBR.

AFRIKAANSE OPSOMMING: Water is waarskynlik die belangrikste natuurlike hulpbron op aarde. Dit is van kardinale belang vir mense, plante, diere, die omgewing sowel as ekosisteme. Landbou sal na raming verantwoordelik wees vir die onttrekking van ongeveer 66 – 70 % van die varswatertoevoer wêreldwyd, en styg tot 90 % in sommige lande. Die wynbedryf in Suid-Afrika is verantwoordelik vir die vervaardiging van groot hoeveelhede afvalwater, met 1,24 miljard liter afvalwater wat in 2018 gegenereer was. Die afvalwater van die wynmakery is uitdagend om te behandel weens die wisselvallige sterkte en seisoenale samestelling. Biologiese behandelings is baie effektief vir die verwydering van organiese besoedelende stowwe in wynkelderafvalwater. Anaërobiese vertering is 'n voorbeeld van 'n biologiese behandeling wat wyd gebruik word vir die behandeling van afvalwater van die wynmakery. Anaerobiese Opeenvolgende Lot Reaktor (AOLR) is 'n lewensvatbare opsie vir die behandeling van wynkelderafvalwater. Die tegnologie is nog in die ontwikkelings-fase en word nog nie breedvoerig in die wynbedryf gebruik nie. Die voordele van die AOLR sluit in: die gemak om bedryfsparameters moeiteloos te verander, dit kan in 'n lot proses of semi-lot proses werk; dit verwyder chemiese suurstof vereiste (CSV) doeltreffend en genereer biogas met 'n hoë metaanpersentasie, wat moontlik as 'n bron van hitte-generasie herwin kan word. Kennis van die optimale toestande vir pH, mengintervalle en voedingstyd van die AOLR is beperk en moet ondersoek word. Twee belangrike parameters vir die algehele stabiliteit en werkverrigting van 'n AOLR is, CSV en totale gesuspendeerde vastestowwe (TGV). Die bepaling van hierdie parameters is egter tydrowend en moeisaam. Naby-infrarooi (NIR) spektroskopie is 'n vinnige, nie-vernietigende tegniek wat gebruik maak van die golflengte reeks van 780 - 2 500 nm. Die eerste doel van hierdie studie was om die potensiaal vir die gebruik van NIR om wynafvalwater te kwantifiseer en te klassifiseer op grond van die CSV- en TGV-konsentrasie te ondersoek. Naby-infrarooi (NIR) spektroskopie is gebruik in kombinasie met meerveranderlike data analise (MDA) tegnieke vir die klassifikasie en kwantifisering van CSV en TGV in wynkelderafvalwater. Spektra is verkry met behulp van 'n tafelmodel FT-NIR (Büchi NIR-Flex N500) spektrofotometer met 'n golflengte reeks van 1 000 - 2 500 nm en 'n draagbare spektrofotometer met 'n golflengte reeks van 900 - 1 700 nm. Die CSV-konsentrasie kon voorspel word met 'n RMSEP-waarde van 893 mg.L-1, 'n fout van 9,9 % in vergelyking met die reeks verwysingswaardes, met behulp van PCR saam met ortogonale seinkorreksie (OSK). Dit is bereik met behulp van die 2 060 - 2 340 nm golflengte reeks op die tafelmodel instrument. Die PCRmodel is bevredigend uitgevoer, om as 'n siftingsmetode gebruik te word, om die CSV-konsentrasie van die wynkelderafvalwater vinnig te bepaal. Die konsentrasie van TGV kon voorspel word met 'n RMSEP van 136,94 mg.L-1, 'n fout van 5,72 %, met behulp van die tafelmodel instrument. Die voorspellingsmodel vir TGV het 'n voorspellingsprestasie behaal wat amper vergelykbaar was met die verwysingsmetode, wat beteken dat dit ten minste geskik is vir siftingsdoeleindes. Klassifikasie akkuraatheid van 90.4 % (CSV) en 100 % (TGV), 80.1 % (CSV) en 95 % (TGV) kon onderskeidelik met die tafelmodel en die draagbare instrument verkry word. Beide die tafelmodel en die draagbare instrument kon die wynkelderafvalwater volgens hul CSV- of TGVkonsentrasies in ‘n bevredigende wyse klassifiseer. Die bogenoemde klassifikasie-akkuraatheid vir die draagbare instrument dui aan dat die klassifikasie van wynkelderafvalwater, in lae of hoë sterkte kategorieë, moontlik is vir in-lyn monitering en sifting van wynkelderafvalwater in plaas van kwantifisering. Die tweede doel van hierdie studie was om te evalueer of die AOLR-tegnologie suksesvol wynkelderafvalwater van verskillende gehalte kan behandel en die optimale bedryfsparameters vir die reaktor bepaal. ‘n Kleinskaal AOLR met 'n volume van 165 L het vir 16 siklusse gehardloop om die wynkelderafvalwater te behandel. Die sikluslengte was 24 uur en die hidrouliese retensietyd (HRT) was ongeveer 1,85 dae. Die reaktor is aanvanklik met 22 kg anaërobiese korrels gesaai. ‘n Sentrale saamgestelde ontwerp (SSO) is uitgevoer om die optimale bedryfsparameters te bepaal. 'n Gemiddelde CSV-vermindering van 68,32 % is behaal, tesame met 'n gemiddelde polifenolvermindering van 53,35 % en 'n stabiele VFA:alkaliniteit van gemiddeld 0.23. Die AOLR-tegnologie kan dus gebruik word vir die behandeling van wynkelderafvalwater. Die pH, voedingstyd en meng-interval is gekies om die optimale bedryfsparameters te bepaal. Daar is bepaal dat die volgende optimale waardes bereik is: pH 7,30; voer-tyd 180,91 minute en 'n meng-interval van 84,17 minute. Hierdie studie het die optimale bedryfsparameters wat voorheen verkry is vir die behandeling van sintetiese wynkelderafvalwater met 'n AOLR bevestig.

Masters