Microalgae-based processes for the biodegradation of pretreated piggery wastewaters
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The potential and limitations of photosynthetic oxygenation on carbon and nitrogen removal from swine slurry were investigated in batch experiments using Chlorella sorokiniana and an acclimated activated sludge as model microorganisms. While algal–bacterial systems exhibited similar performance than aerated activated sludge in tests supplied with four and eight times diluted slurry, a severe inhibition of the biodegradation process was recorded in undiluted and two times diluted wastewater. Daily pH adjustment to 7 in enclosed algal–bacterial tests at several swine slurry dilutions allowed the treatment of up to two times diluted slurries (containing up to 1,180 mg N-NH4+ l−1). The combination of high pH levels and high NH4+ concentrations was thus identified as the main inhibitory factor governing the efficiency of photosynthetically oxygenated processes treating swine slurry. Measurements of soluble total organic carbon (TOC) and volatile fatty acids (VFA) present in the slurry suggested that VFA degradation (mainly acetic and propionic acid) accounted for most of the soluble TOC removal, especially during the initial stages of the biodegradation process. On the other hand, assimilation into biomass and nitrification to NO2− constituted the main NH4+ removal processes in enclosed algal–bacterial systems.
KeywordsAlgal–bacterial systems Ammonia inhibition Biodegradation Chlorella sorokiniana Photosynthetic oxygenation Swine slurry
This research was supported by the Spanish Ministry of Education and Science (RYC-2007-01667 contract and projects PPQ2006-08230, CONSOLIDER-CSD 2007-00055 and CTC2007-64324) and the Autonomous Government of “Castilla y Leon” through the Institute of Agriculture Technology (ITACYL project VA13-C3-1). Araceli Crespo is also gratefully acknowledged for her practical assistance.
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