An innovative technology based on aerobic granular biomass for treating municipal and/or industrial wastewater with low environmental impact.

The paper reports the results of an investigation carried out at lab scale to assess the effectiveness of an innovative technology (SUPERBIO) for treating municipal and/or industrial wastewater. When this technology was applied for treating municipal wastewater, the results showed that even at maximum organic load (i.e. 7 kg COD m(-3) d(-1)), the COD in the treated effluent was lower than 50 mg L(-1). In addition, both ammonia and TKN removal efficiencies resulted in higher than 87% up to an organic load of 5.7 kg COD m(-3) d(-1) corresponding to a nitrogen load of 0.8 kg TKN m(-3) d(-1). Very satisfactory process performances also resulted during tannery wastewater treatment, when a chemical oxidation step (i.e. ozonation) was inserted in the treatment cycle of SUPERBIO. In such an instance, at organic and nitrogen loadings of 3 kgCOD m(-3) d(-1) and 0.20 kg N m(-3) d(-1), COD, NH4+ -N and TSS average removals were 96, 99 and 98%, respectively. Finally, during the whole experimentation, SUPERBIO was always characterised by a very low sludge production. Such a result was ascribed mainly to the characteristics of biomass that grew in the form of very dense granules (i.e. 130 gVSS L(Biomass)(-1) allowing a biomass concentration as high as 50-60 gTSS l(bed)(-1) to be achieved.

Hydraulic shear stress calculation in a sequencing Batch biofilm reactor with granular biomass.

This paper reports the results of an experimental study specifically aimed at developing a simple methodology for calculating hydrodynamic shear forces in a sequencing batch biofilm reactor (SBBR) system with granular biomass. Using such a methodology, the hydrodynamic shear forces are simply calculated by measuring bed porosity and pressure losses. In addition, by applying this methodology an explanation for the biomass evolution from biofilm to granules under aerobic conditions has been provided and the following mechanism has been proposed: (i) formation of a thin biofilm that fully covers the carrier; (ii) increase of biofilm thickness; (iii) break-up of the attached biofilm with release of biofilm particles; (iv) rearrangement of biofilm particles in smooth granules. The hydrodynamic shear forces trend during the start-up period provides an explanatory key for the generation process of granular biomass. In fact, during the first two steps, the SBBR is characterized by rather weak shear forces values (lower than 1 dyn/cm2). Under these weak shear forces, the biofilm grows by increasing its thickness through a porous structure and weak adhesion strengths. Such a continuous increase of biofilm thickness produces an increase of the shear forces with negative effect on biomass stability, causing the detachment of biofilm particles. In turn, such detachment causes a further sharp increase of shear forces (more than 10 times) that promotes the rearrangement of the detached biofilm particles in smooth granules. A correlation between biomass density and hydrodynamic shear forces was observed. In particular, the biomass density linearly increases with the increase of shear stress.

Rethinking sewage treatment by enhancing primary settling with low-dosage lime.

This work presents a thorough fractionation of COD in raw sewage, followed by pilot plant coagulation tests with low-dosage lime (pH 9). Through a physical separation (sieving and crossflow filtration) total COD in the raw sewage was partitioned among eight size fractions in the range of 150-0.02 microm. In addition, respirometric tests were performed to measure the biodegradability of the different size fractions. More than 60% of COD was associated with settleable and supracolloidal particles (size > 1 microm), which are characterised by slow biodegradability. Coagulation with lime increased COD removal efficiencies in the primary treatment from typical 30-35%, up to 65-70%, suggesting that lime may induce the almost complete removal of the slowly settling, slowly biodegradable supracolloidal particles in the primary treatment. On the basis of these results a non-conventional sewage treatment scheme is proposed, considering that there is plenty of space for improving primary treatment efficiency through sewage coagulation. Higher primary treatment efficiency may present several advantages, including lower aeration energy in the subsequent biological unit and higher energy recovery from sludge digestion.

Tannery wastewater treatment by sequencing batch biofilm reactor.

The paper reports the results of an investigation aimed to evaluate the performances of an innovative process for treating tannery wastewater. In such a process biological degradation, carried out in a sequencing batch biofilm reactor (SBBR), is combined with chemical oxidation by ozone. The treatment was carried out at laboratory scale on a real primary effluent coming from a centralized plant treating the wastewater of a large tannery district in Northern Italy. SBBR performances without and with ozonation were compared with very satisfactory results particularly in the latter instance when the recorded COD, TKN, and TSS average removals, (96%), (92%), and (98%), respectively, permitted to achieve the fixed limits enforced by Italian regulation without needing any additional polishing step. With or without ozonation, the process that resulted was characterized by a specific sludge production (0.1 kgVSS/kg CODremoved) significantly lower than the values featuring conventional biological systems (i.e., 0.3-0.5 VSS/kg CODremoved). Moreover, as in the reactor the biomass density results were very high, i.e., 98 gVSS/Lsludge, it was possible to achieve and maintain biomass concentration as high as 20 gVSS/L.

Combined chemical and biological degradation of tannery wastewater by a periodic submerged filter (SBBR).

The paper reports on the results of an investigation aimed to evaluate the performances of an innovative tannery wastewater process based on the combining biological degradation, carried out in a sequencing batch biofilm reactor, with chemical oxidation, performed by ozone. The combined treatment was carried out at the laboratory scale on real primary effluent coming from a centralised plant treating the wastewater from a large tanning district in Northern Italy. SBBR performances with and without ozonation were compared resulting to be very satisfactory only in the latter instance where recorded COD, NH4-N and TSS average removals were 97%, 98% and 99.9%, respectively. Such efficiencies correspond to specific concentrations in treated effluent well below the limit values fixed by the in-force Italian regulations. Furthermore, it was proved that the combined process is characterised by a very low sludge production. In fact, the measured specific sludge production (0.03 kg TSS/kg COD(removed)) resulted unexpectedly much more lower than the value reported for conventional biological systems (i.e., 0.3-0.5 kg TSS/kg COD(removed)).

Soluble and particulate metals in the Po River: factors affecting concentrations and partitioning.

Fourteen metals (Ca, Mg, Al, Fe, Mn, Ba, As, Cd, Co, Cr, Cu, Ni, Pb and Zn) were monitored over a 2-year period in the waters of the lower Po River. Concentrations in the dissolved and particulate phases were measured, thus constructing a large database on metal variability. The influence of flow and solid transport on dissolved, particulate and total metal concentrations is discussed. In addition to flow rate and solid content, biological processes seem to be one of the main factors affecting concentrations in the dissolved phase, while the inorganic components of solids seem to control metal concentration in suspended matter. Data on partitioning of metals between the dissolved and particulate phases are presented, together with related information on the affinity sequence of metals for the particulate phase, and the influence of solid load on the modes of metal transport.