The combination of UASB and ozone technology in the treatment of a pectin containing wastewater from the apple juice processing industry

Van Schalkwyk, Nico
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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: The South African apple juice processing industry is growing rapidly and during the harvesting season the wastewater volumes and organic loads increase significantly with a considerable environmental impact. These larger apple juice processing wastewater (AJPWW) volumes and chemical oxygen demand (COD) loads subsequently lead to faster increases in the organic loading rate (OLR) of an upflow anaerobic sludge bed (UASB) wastewater treatment system and it is necessary to know if the treatment system can handle such drastic increases over short periods. The objective of the study were to evaluate the efficiency of the UASB process in the treatment of an AJPWW; to determine what effect a substrate viscosity increase, based on a pectin calcium gel has on the performance of an UASB system, and to determine what impact ozonation has on the pectin content, gelformation ability and biodegradability of the AJPWW. The ability of the UASB to maintain stability during the apple-processing season was investigated by increasing the OLR from 2.9 to over 14.0 kg COD.m-3.d-1 in 131 days. During this time the COD removal remained constant at 85%, while the pH and alkalinity remained at levels indicative of good reactor stability. It was thus concluded that the UASB reactor could operate successfully during the apple-harvesting season when wastewater volumes and organic loads increase significantly. In the study it was found that the viscosity of the AJPWW, containing 750 mq.L-1 pectin, increased from 8.5 to 47.0 cps after a 312 rnq.L-1 Ca2 + addition. This increased viscosity substrate was then fed to an UASB reactor at an OLR of 15.0 kg COD.m-3.d-1. During a 12 day increased viscosity (47 cps) feeding stage the COD removal decreased from 94 to 11%, while the reactor pH decreased from 7.5 to 4.9. During this period, pectin accumulated in the UASB and led to biomass washout and rapid UASB failure. The possible elimination of pectin by ozonation was thus investigated, and a 77% decrease in pectin content and 76% decrease in gel formation ability occurred after ozonation. The effect of pre- and post-ozonation on the efficiency of the UASB system was subsequently investigated. It was found that a 10 min pre-ozonation decreased the AJPWW COD by 19% and the total suspended content by 36%, while the soluble portion of the total COD was increased from 81.7 to 92.4%. This increase in soluble COD content should lead to increased wastewater biodegradability. The ozonated AJPWW was then used to replaced the raw non-ozonated AJPWW as reactor feed. Results showed that the COD removal increased from 78 to 90% within 24 h of starting with the ozonated feed. It was also found that the reactor stability improved after AJPWW pre-ozonation as an OLR increase from 10.0 to 16.6 kg COD.m-3.d-1 in 23 days did not detrimentally influence the stability of the reactor. This reactor effluent (COD = 465 rnq.L-1) was then post-ozonated which resulted in 64.8% COD and 79.0% colour reductions. The final effluent had a COD of 180 rnq.L-1 (98% reduction). The ability of the ozonation/digestion system as described in this study to degrade AJPWW at a higher OLR is of value to the apple industry, as it may lead to larger organic pollutant removals and thus a more effiecient treatment system. Increased reactor performance will directly improve the quality of the final wastewater produced, which in turn will have a significant impact on the treatment ability of the South African apple processing industry currently limited by the production of large wastewater volumes.
AFRIKAANSE OPSOMMING: Gedurende die oesseisoen word groot volumes afvalwater met 'n hoe organiese lading in die vinnig groeiende Suid-Afrikaanse appelsapprosesseringsbedryf geproduseer. Dit het 'n groot impak op die omgewing. Die groter volumes appelsapprosesseringsafvalwater (ASPAW) met 'n hoë organiese lading het 'n vinniger verhoging in organiese ladingstempo's (OLT) van 'n UASB-waterbehandelingstelsel tot gevolg. Daarom is dit belangrik om te weet of die stelsel die drastiese verhoging oor kort tydperke kan hanteer. Die doel van hierdie studie was die evaluering van die effektiwiteit van die UASB-proses in die behandeling van ASPAW; om te bepaal watter effek 'n substraatviskositeitsverhoging, gebaseer op 'n pektien-kalsium-jel, op die doeltreffendheid van 'n UASB-stelsel het; en om te bepaal watter impak osonering op die pektieninhoud, jelvormingsvermoe en bioafbreekbaarheid van ASPAW het. Die vermoe van die UASB om stabiliteit te handhaaf gedurende die appelsapprosesseringseisoen is ondersoek deur die OLT van 2,9 tot bo 14,0 kg CSB.m-3.d-1 te verhoog oor 131 dae. Gedurende hierdie tyd het die chemiese suurstofbehoefte- (CSB-) verwydering konstant gebly by 85%, terwyl die pH en alkaliniteit ook op vlakke aanduidend van goeie reaktorstabiliteit gebly het. Daar is sodoende bewys dat die UASB-reaktor suksesvol kan presteer tydens die appelsapprosesseringseisoen, wanneer daar 'n beduidende verhoging in OLT plaasvind. In die studie is daar gevind dat die viskositeit van die ASPAW, wat 750 mq.L-1 pektien bevat, van 8,5 tot 47,0 cps toeneem na die byvoeging van 312 rnq.L-1 Ca2+. Hierdie verhoogde vikositeitsubstraat is tot die UASB-reaktor toegevoeg teen 'n OLT van 15,0 kg CSB.m-1.d-1. Gedurende 'n 12-dae toevoer van verhoogde viskositeit (47 cps), het die CSB-verwydering van die reaktor afgeneem van 94% na 11%, terwyl die pH gedaal het van 7,5 na 4,9. Gedurende hierdie tydperk het pektien in die UASB geakkumuleer, wat gelei het tot die uitspoel van biomassa en vinnige UASB-reaktormislukking. Die moontlike eliminasie van pektien, deur osonering, is daarom ondersoek. 'n Verlaging van 77% in pektieninhoud en 76% in jelvormingsvermoe het na osonering plaasgevind. Die effek van pre- en post-osonering op die effektiwiteit van 'n UASB-stelsel is gevolglik ondersoek. Daar is gevind dat 'n 10 minute pre-osonering die CSB van die ASPAW met 19% verlaag en die totale inhoud van gesuspendeerde vaste stowwe met 36% verlaag, terwyl die oplosbare gedeelte van die totale CSB van 81,7% tot 92,4% gestyg het. Die verhoging in oplosbare CSB-inhoud behoort tot verhoogde bioafbreekbaarheid van ASPAW te lei. Die geosoneerde ASPAW is gebruik om die rou, ongeosoneerde ASPAW as reaktorsubstraat te vervang. Die resultate het getoon dat die CSB-verwydering verhoog het van 78% na 90% na 'n 24-uur toevoer van geosoneerde substraat. Daar is ook gevind dat die reaktorstabiliteit toegeneem het na ASPAW osoneering, aangesien 'n OLT-verhoging van 10,0 na 16,6 kg.CSB.m-3.d-1 in 23 dae nie die stabiliteit van die reaktor nadelig beinvloed het nie. Hierdie reaktoruitvloeisel (CSB = 465 rnq.L-1) is hierna gepost-osoneer, wat 'n 64,8% CSB- en 79,0% kleurverlaging tot gevolg gehad. Die finale uitvloeisel het 'n CBS-inhoud van 180 rnq.L-1 gehad (98,1% verwydering). Die vermoe van die osonering-/verteringstelsel om ASPAW te degradeer teen 'n hoër OLT, soos beskryf in hierdie studie, is van waarde tot die appelsapprosesseringsbedryf, aangesien dit tot groter organiese afvalstofverwydering kan lei en dus 'n meer effektiewe behandelingstelsel tot gevolg kan hê. Verhoogde reaktordoeltreffendheid sal 'n direkte verbetering tot gevolg hê in die gehalte van die finale afvalwater wat geproduseer word, wat op sy beurt 'n beduidende impak sal hê op die behandelingsvermoe van die appelsapprosesseringsbedryf, wat tans beperk word deur die produksie van groot volumes afvalwater.
Thesis (MSc Food Sc )--Stellenbosch University, 2004.
Apple industry -- Waste disposal, Water -- Purification -- Ozonization, Sewage -- Purification -- Biological treatment, Sewage disposal plants -- Efficiency, Upflow anaerobic sludge bed (UASB), Dissertations -- Food science, Theses -- Food science