Abstract
Biological treatment of table olive processing wastewater (TOPW) may be problematic due to its high organic and polyphenolic compound content. Biomass acclimatization is a necessary, yet sensitive, stage for efficient TOPW biological treatment. Next-generation sequencing technologies can provide valuable insights into this critical process step. An aerobic membrane bioreactor (MBR) system, initially inoculated with municipal activated sludge, was acclimatized to treat TOPW. Operational stability and bioremediation efficiency were monitored for approx. three months, whereas microbial community dynamics and metabolic adaptation were assessed through metagenomic and metatranscriptomic analysis. A swift change was identified in both the prokaryotic and eukaryotic bio-community after introduction of TOPW in the MBR, and a new diverse bio-community was established. Thauera and Paracoccus spp. are dominant contributors to the metabolic activity of the stable bio-community, which resulted in over 90% and 85% removal efficiency of total organic carbon and total polyphenols, respectively. This is the first study assessing the microbial community dynamics in a well-defined MBR process treating TOPW, offering guidance in the start-up of large-scale applications.
Highlights
Table olives are an important agro-industrial product, especially in Mediterranean countries
The present study addresses the acclimatization period of an aerobic pilot scale membrane bioreactor (MBR) treating table olive processing wastewater (TOPW), under well-defined operating conditions
The overall biomass concentration was estimated based on the mixed liquor volatile suspended solids (MLVSS) fraction, a safe indicator of the active biomass in wastewater treatment plants [5]
Summary
Table olives are an important agro-industrial product, especially in Mediterranean countries. Table olive processing aims to eliminate the natural bitterness of the fruit, due to polyphenolic substances, and render it edible and marketable, through several process steps, namely: debittering, washing, fermentation, and packaging. Large quantities of freshwater are used, and 3–4 m3 of table olive processing wastewater (TOPW) per ton of olives may be produced [1]. TOPW is a turbid effluent with a characteristic odor and high organic content, comprising sugars, acids, phenols, polyphenols, tannins, pectins, and oil residues [2,3]. TOPW possesses antimicrobial and phytotoxic properties [4], mainly due to its polyphenolic compounds content, wide pH variation (3.5–13.0), and high concentrations of sodium hydroxide (lye) and/or sodium chloride (brine) [2,3].
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