Biodegradation of winery wastewater

[摘要] ENGLISH ABSTRACT: Large volumes of wastewater are generated annually during the grape harvest season fromvarious processing and cleaning operations at wineries, distilleries and other wine-relatedindustries. South African regulatory bodies dictate that wastewater should have a pH of 5.5to 7.5 and a chemical oxygen demand (COD) lower than 75 mg/L. However, winerywastewater has a typical pH of 4 to 5 and a COD varying between 2 000 and 12 000 mg/L.Urban wineries channel the wastewater to local sewage treatment facilities and are oftenheavily fined for exceeding governmental requirements. Rural wineries usually have littleor no treatment operations for their wastewater and it is often irrigated onto crops, whichmay result in environmental pollution and contamination of underground water resources.Various criteria are important in choosing a wastewater treatment system, such as an ecofriendlyprocess that is flexible to withstand various concentration loads and characteristics,requiring low capital and operating costs, minimal personal attention and do not require toomuch land. In this study, a large variation in COD, pH and chemical composition of thewinery wastewater was observed that could be related to varying factors such as the harvestload, operational procedures and grape variety. Wastewater from destemming and pressingoperations contained higher concentrations of glucose, fructose and malic acid, whichoriginated from the grape berries. The fermentable sugars (glucose and fructose)contributed to almost half of the COD with a smaller contribution from ethanol and aceticacid. The low pH can be ascribed to relative high concentrations of organic acids in thewastewater.The efficacy of biological treatment systems depends strongly on the ability ofmicroorganisms to form biofilm communities that are able to degrade the organiccompounds in the wastewater. Preliminary identification of microorganisms that naturallyoccur in winery wastewater indicated the presence of various bacterial and yeast species thatcould be effective in the biological treatment of the wastewater. When evaluated as purecultures under aerobic conditions, some of the yeast isolates effectively reduced the COD ofa synthetic wastewater, whereas the bacterial isolates were ineffective. The most effectiveyeast isolates were identified as Pichia rhodanensis, Kloeckera apiculata, Candida kruseiand Saccharomyces cerevisiae. Our search for cost-effective biological treatment systems led to the evaluation of a RotatingBiological Contactor (RBC) for the treatment of winery wastewater. The RBC wasevaluated on a laboratory scale with 10% (v/v) diluted grape juice and inoculated with amixed microbial community isolated from winery wastewater. The results showed areduction in the COD that improved with an extended retention time. Evaluation of theRBC on-site at a local winery during the harvest season resulted on average in a 41%decrease in COD and an increase of 0,75 pH units.RFLP analysis of the biofilm communities within the RBC confirmed a population shift inboth the bacterial and fungal species during the evaluation period. The most dominant yeastisolates were identified with 18S rDNA sequencing as Saccharomyces cerevisiae, Candidaintermedia, Hanseniaspora uvarum and Pichia membranifaciens. All these species arenaturally associated with grapes and/or water and with the exception of Hanseniasporauvarum, they are able to form either simple or elaborate pseudohyphae.

[发布机构] Stellenbosch University