Application of biogranules in the anaerobic treatment of distillery effluents

O'Kennedy, Onicha Deborah (2000-12)

Thesis (MSc Food Sc)--Stellenbosch University, 2000.

Thesis

ENGLISH ABSTRACT: The distillery industry produces large volumes of waste water with a high organic content throughout the year. These effluents must be treated in some manner before being discharged or recycled in the factory. Several treatment options are in use presently, but they all have disadvantages of some nature, such as long retention times, bad odours or the need for large areas of land. Considerable interest has been shown in the application of anaerobic digestion, especially the UASB design (upflow anaerobic sludge blanket), to treat this high strength waste water. Thus, the aim of this study was to investigate the efficiency of an upflow anaerobic sludge blanket (UASB) bioreactor using full-strength distillery effluent. The activity of the bacteria in the biogranules was also evaluated by developing an easy and reliable activity method to estimate the general biogas and methanogenic activity and to calibrate this method using different anaerobic granules from different sources. The influence of high strength distillery effluent on the anaerobic digestion process was investigated using a mesophilic lab-scale UASB bioreactor. During the experimental study, the organic loading rate (OLR) was gradually increased from 2.01 to 30.00 kgCOD.m-3.d-1, and simultaneously, the substrate pH was gradually lowered from 7.0 to 4.7. It was found that at an OLR of 30.00 kgCOD. m-3.d-1,the pH, alkalinity and biogas production stabilised to average values of 7.8, 6 000 mg.l-1 and 18.5 I.d-1 respectively. An average COD removal> 90% was found indicating excellent bioreactor stability. The low substrate pH holds considerable implications in terms of operational costs, as neutralisation of the biorector substrate is no longer necessary. The accumulation of fine solids present in the distillery substrate was found at the higher OLR's and resulted in the granular bed increasing with subsequent biomass washout and a lowering in efficiency parameters. However, a possible pre-treatment filtration of these fine solids would eliminate this problem. The success of the upflow anaerobic sludge bed (UASB) process is mainly due to the capability of retaining the active biomass in the reactor. Over the years, several methods have been developed to characterise and quantify sludge activity but each has advantages and disadvantages. There is thus an increasing need for a rapid method to evaluate the activity of the granular biomass. The activity method of Owen et al. (1979) as adapted by Lamb (1995), was thus evaluated in terms of efficiency and applicability in determining the activity of granular samples. The method was found to be inaccurate as well as time consuming and it was thus modified. Results obtained with the modified assay method were found to be more accurate and the impact of the different test substrates (glucose, lactate, acetate and formate) on activity, was more evident. The activity of seven different anaerobic granules, was subsequently evaluated. Biogas (Ss) and methanogenic (SM) activity was not measured in volume of gas produced per unit COD converted or volatile suspended solids (VSS), but as tempo of gas production (ml.h-1) in a standardised basic growth medium. The activity data obtained were also displayed as bar charts and "calibration scales". This illustrative depiction of activity data gave valuable information about population dynamics as well as possible substrate inhibition. The "calibration scales" can also be used to group the general biogas (Ss) and methanogenic activities (SM) of any new biogranule relative to active (O-type) and inactive (W-type) anaerobic granules, providing that the same method of activity testing is used. The "calibration scales" can thus be used to give a fast indication of how the activity value of one sample relates to the activity values of other granules, even when using different test substrates.

AFRIKAANSE OPSOMMING: Die stokery industrie produseer groot hoeveelhede afvalwater, wat hoë ladings van organiese materiaal gedurede die hele jaar bevat. Hierdie afvalwater moet op een of ander manier behandel word voordat dit gestort of vir hergebruik aangewend kan word. Daar is tans verskeie behandelingsmetodes wat gebruik kan word, maar elk het sy eie tekortkominge soos bv. lang retensie tye, onaangename reuke of die behoefte aan groot stukke oop grond. Groot belangstelling is getoon vir die gebruik van anaerobiese vertering, en meer spesifiek die "uflow anaerobic sludge blanket" UASB bioreaktor vir die behandeling van stokery uitvloeisels. Die doel van die studie was dus om die algehele effektiwiteit van 'n UASB bioreaktor, wat onverdunde stokery uitvloeisel behandel, te evalueer. Die methanogene- en algehele aktiwiteit van die bakterië in die biogranules was ook ge-evalueer deurdat 'n maklike en betroubare aktiwiteitsmetode omtwikkel is, waarna hierdie metode ook toegepas was op 'n reeks van verskillende tipe biogranules. Die invloed van volsterkte stokery uitvloeisel op die anaerobiese verteringsprosesse was ondersoek met die gebruik van 'n mesofiele laboratoriumskaal UASB bioreaktor. Gedurende die eksperimentele studie, was die organiese ladingstempo (OLT) verhoog van 2.01 na 30.00 kgCSB.m-3.d-1 (CSB = chemiese suurstof behoefte) met die gelyktydige verlaging in die pH van die bioreaktorsubstraat van 7.0 na 4.7. Dit was vasgestel dat met 'n OLT van 30.00 kgCSB.m-3.d-1, die pH, alkaliniteit en biogas geproduseer, gestabiliseer het na gemiddelde waardes van 7.8, 6000 mg.-1 en 18.5l.d-1 , respektiewelik, sowel as 'n gemiddelde CSB verwydering van> 90%. Al hierdie waardes dui uitstekende bioreaktor stabiliteit aan. Die lae bioreaktorsubstraat pH kan van groot waarde wees vir die industrie, aangesien neutralisering van die uitvloeisel nie meer nodig is nie en kan sodoende die operasionele koste van die proses verlaag. Die konsentrering van fyn opgeloste soliedes in die bioreaktor by hoë OLT's, kan egter problematies raak, aangesien dit die granule-bed kan vergroot en veroorsaak dat van die biomassa uitspoel en kan verlore gaan. Die verlies van aktiewe biomassa kan die effektiwiteitsparameters negatief beinvloed, maar die plasing van 'n filterings stap voor die verterings stap, behoort hierdie probleem op te los. The sukses van die UASB-stelsel rus op die versekering dat die aktiewe biomassa in die reaktor behoue bly. Oor die jare was daar 'n verskeidenheid van aktiwiteitstoetsings-metodes ontwikkel, elk met sy eie nadele. Daar bestaan dus nog steeds 'n groot behoefte vir die daarstelling van 'n aktiwiteitstoetsings-metode wat vinnig en maklik is om uittevoer. Die aktiwiteitstoetsings-metode van Owen et al. (1979) wat deur Lamb (1995) aangepas is, was in terme van sy effektiwiteit en toepaslikheid ten opsigte van die gebruik daarvan vir aktiwiteitstoetsing vir biogranules, ge-evalueer. Dit is bevind dat die metode onakkuraat sowel as tydsrowend was en gevolglik dus aangepas. Die aangepaste metode het meer akkurate resultate gelewer en die impak van die verskillende toetssubstrate (glukose, laktaat, asetaat en formaat) op die granules het ook meer duidelik na vore gekom. Gevolglik was die aktiwiteit van sewe verskillende anaerobiese biogranules ondersoek. Die eenheid waarin atiwiteitsresultate aangegee is, was nie in volume gas geproduseer per eenheid CSB verwyder of per hoeveelheid gesuspendeerde vlugtige vetsure in die biomassa nie, maar as tempo van biogas (S8)- of metaan (SM)produksie (ml.h-1). Die data wat op hierdie wyse bekom was, is gebruik om staafdiagramme sowel as "kalibrasie skale" daar te stel. Hierdie illustrerende wyse om aktiwiteitsdata uit te beeld verskaf waardevolle informasie ten opsigte van die interaksies tussen die verskillende populasies in die granule en kan ook die aanwesigheid van moontlike substraat inhibisie aandui. Die "Kalibrasie skale" kan ook gebruik word om die algehele (SB) en methanogene (SM)aktiwiteite van einge nuwe biogranule vinnig te klassifiseer ten op sigte van 'n aktiewe (O-tipe) en 'n minder aktiewe (W-tipe) anaerobiese granules, mits dieselfde metode gebruik word om die aktiwiteits data te bekom.

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