“Microthrix parvicella” strain RN1, isolated by micromanipulation from an activated sludge treatment plant in Italy, is phylogenetically identical to two other isolates from Australia. Our Italian isolate of “M. parvicella” is a slow growing (μmax ranging from 0.3 to 0.5 d−1), aerobic organism that exhibits nutritional versatility, being able to utilize simple and complex compounds as carbon and nitrogen sources. In pure culture, the organism cannot grow anaerobically nor is it able to denitrify. Strain RN1 is able to grow both in aerobic and in microaerophilic conditions and this metabolic versatility could give it a metabolic advantage in the activated sludge milieu.

The aim of the research was to study the treatability of tannery wastewater by a sequencing batch reactor (SBR) compared with a continuous flow full scale reactor. The experimental work presented in this paper was carried out on a laboratory scale anoxic-aerobic SBR fed with tannery wastewater coming from a full scale continuous flow treatment plant located in S. Miniato (Pisa, Italy). After a long acclimation period, a complete and stable nitrification has been developed. The denitrification was always performed without any additional carbon source with good results when influent COD/TKN ratio was higher than 8 and with a higher rate compared to that obtained in the continuous plant. When high effluent nitrate occurred, it was due only to stoichiometric (not kinetic) limitations. The organic substrate removal occurred mainly during the anoxic period and a high effluent COD (refractory) was often present at the end of the process. This research has shown the suitability of the industrial wastewater (particularly tannery wastewater) treatment by SBR because of its several advantages compared to the continuous reactors: i.e. a higher versatility and the possibility to work with higher loads (smaller volumes), by selecting, through the cyclic concentration gradients, a biomass resistant to the presence of inhibiting substances (often encountered in industrial wastewaters).

Difficulties met in the anaerobic treatment of olive oil mill effluents (OME) suggest the use of a chemico-physical pretreatment for the removal of biorecalcitrant and/or inhibiting substances (essentially lipids and polyphenols) as selectively as possible before anaerobic digestion. Laboratory scale experiments were carried out in order to identify pretreatment type and conditions capable of optimizing OME anaerobic digestion in terms both of kinetics and methane yield. Ultrafiltration, even if it allowed very high removals of lipids and polyphenols, was affected by poor selectivity (indeed, large amounts of biodegradable COD were also removed). Centrifugation turned out to be preferable to sedimentation owing to smaller volumes of separated phase. Results of great significance were obtained by adding Ca(OH)2 (up to pH 6.5) and 15 g/l of bentonite, and then feeding the mixture to the biological treatment without providing an intermediate phase separation. Indeed, the biodegradable matter adsorbed on the surface of bentonite was gradually released during the biotreatability test, thus allowing the same methane yield (referred to the total COD contained in untreated OME) both in scarsely diluted (1 : 1.5) pretreated OME and in very diluted (1 : 12) untreated OME. Application of a continuous process combining pretreatment (with Ca(OH)2 and bentonite) and anaerobic digestion without intermediate phase separation is suggested.

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