Wastewater is among the most important reservoirs of antibiotic resistance in urban environments. The abundance of carbon sources and other nutrients, a variety of possible electron acceptors such as oxygen or nitrate, the presence of particles onto which bacteria can adsorb, or a fairly stable pH and temperature are examples of conditions favouring the remarkable diversity of microorganisms in this peculiar habitat. The wastewater microbiome brings together bacteria of environmental, human and animal origins, many harbouring antibiotic resistance genes (ARGs). Although numerous factors contribute, mostly in a complex interplay, for shaping this microbiome, the effect of specific potential selective pressures such as antimicrobial residues or metals, is supposedly determinant to dictate the fate of antibiotic resistant bacteria (ARB) and ARGs during wastewater treatment. This paper aims to enrich the discussion on the ecology of ARB&ARGs in urban wastewater treatment plants (UWTPs), intending to serve as a guide for wastewater engineers or other professionals, who may be interested in studying or optimizing the wastewater treatment for the removal of ARB&ARGs. Fitting this aim, the paper overviews and discusses: i) aspects of the complexity of the wastewater system and/or treatment that may affect the fate of ARB&ARGs; ii) methods that can be used to explore the resistome, meaning the whole ARB&ARGs, in wastewater habitats; and iii) some frequently asked questions for which are proposed addressing modes. The paper aims at contributing to explore how ARB&ARGs behave in UWTPs having in mind that each plant is a unique system that will probably need a specific procedure to maximize ARB&ARGs removal.

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The semi-solid wastes (pomace or alperujo) produced in the two-phase olive oil extraction process contains extremely high organic load and phenolic substances. Efficient treatment of such kinds of wastes using membrane filtration, should be sought to reduce the hazardous effects to the environment. On the other hand, phenolic compounds can be isolated and purified up to a level of commercial exploitation using the membrane technology. Firstly, the extraction process with mixtures of water and ethanol was optimized by testing extraction parameters (e.g., solvent’s mixture, duration, and temperature) at laboratory scale. Next, extraction was conducted using larger volumes and the treatment was continued in a pilot membrane filtration system, consisted of ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes. The extracted solution from the olive oil pomace was fed to the pilot membrane filtration system, where all fat, lipids, and solids were removed while the phenolic compounds were concentrated in the retentate streams of NF and/or RO. Total phenolic content (TPC) at the RO’s concentrate stream was 225 mg/L and at the final effluent was lower than 10 mg/lt. The chemical oxygen demand (COD) value at the final effluent was much lower (~280 mg/L) than in the feed stream (>32,000 mg/L).

BACKGROUND Coagulation/flocculation is a physico‐chemical method for the treatment of olive mill wastewater (OMW). Coagulation/flocculation and precipitation of the agglomerates formed relies on the effective decrease of the electrical charge of the suspended solids which allows particles to approach each other and form large clusters. The present work focuses on the decrease of the electrical charge of the suspended particles by monitoring the changes in the zeta potential of the particles. This approach can also indicate with accuracy the exact concentration of the coagulant or flocculant that must be added in the wastewaters, to achieve the highest removal of the solids and organic load. RESULTS In the present paper, experiments of coagulation/flocculation with electrolytes [FeCl3, Ca(OH)2, CaO, CaCl2] and polyelectrolytes (PDADMAC, PAH, PAA, PEI, Floccan 22‐23) are presented, either separately or in combination and screened with respect to their removal efficiency in terms of chemical oxygen demand (COD), total suspended solids (TSS), Total solids (TS) and total phenols (TP) removal and by monitoring the zeta potential. A relevant literature review is presented also regarding the coagulants and flocculants which have been examined for the physico‐chemical treatment of OMW. The compounds used, their concentrations and their removal efficiency in terms of COD, TS, TSS and phenols are listed, where possible. CONCLUSIONS The coupling of calcium hydroxide at 20 g L−1, with PDADMAC in a range of 0.75–2.00 g L−1 led to reductions of COD, TSS, TS and phenols up to 56%, 27%, 43% and 76%, respectively. © 2014 Society of Chemical Industry