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

[摘要] ENGLISH ABSTRACT:The South African apple juice processing industry is growing rapidly and during theharvesting season the wastewater volumes and organic loads increase significantly with aconsiderable environmental impact. These larger apple juice processing wastewater(AJPWW) volumes and chemical oxygen demand (COD) loads subsequently lead to fasterincreases 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 canhandle such drastic increases over short periods. The objective of the study were toevaluate the efficiency of the UASB process in the treatment of an AJPWW; to determinewhat effect a substrate viscosity increase, based on a pectin calcium gel has on theperformance of an UASB system, and to determine what impact ozonation has on thepectin content, gelformation ability and biodegradability of the AJPWW.The ability of the UASB to maintain stability during the apple-processing seasonwas 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 alkalinityremained at levels indicative of good reactor stability. It was thus concluded that theUASB reactor could operate successfully during the apple-harvesting season whenwastewater volumes and organic loads increase significantly.In the study it was found that the viscosity of the AJPWW, containing 750 mq.L-1pectin, increased from 8.5 to 47.0 cps after a 312 rnq.L-1 Ca2+ addition. This increasedviscosity 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 decreasedfrom 94 to 11%, while the reactor pH decreased from 7.5 to 4.9. During this period, pectinaccumulated in the UASB and led to biomass washout and rapid UASB failure. Thepossible elimination of pectin by ozonation was thus investigated, and a 77% decrease inpectin 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 wassubsequently investigated. It was found that a 10 min pre-ozonation decreased theAJPWW COD by 19% and the total suspended content by 36%, while the soluble portionof the total COD was increased from 81.7 to 92.4%. This increase in soluble COD contentshould lead to increased wastewater biodegradability. The ozonated AJPWW was thenused to replaced the raw non-ozonated AJPWW as reactor feed. Results showed that theCOD removal increased from 78 to 90% within 24 h of starting with the ozonated feed. Itwas also found that the reactor stability improved after AJPWW pre-ozonation as an OLRincrease 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-ozonatedwhich resulted in 64.8% COD and 79.0% colour reductions. The final effluent had a CODof 180 rnq.L-1 (98% reduction).The ability of the ozonation/digestion system as described in this study to degradeAJPWW at a higher OLR is of value to the apple industry, as it may lead to larger organicpollutant removals and thus a more effiecient treatment system. Increased reactorperformance will directly improve the quality of the final wastewater produced, which inturn will have a significant impact on the treatment ability of the South African appleprocessing industry currently limited by the production of large wastewater volumes.

[发布机构] Stellenbosch University