Roberto Ramadori

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)).

Nitrogen recovery from a stabilized municipal landfill leachate

The present paper reports the results of an investigation aimed at evaluating the effectiveness of magnesium ammonium phosphate precipitation (MAP), commonly called struvite, for removing ammonia from a mature municipal landfill leachate. MAP precipitation was carried out at laboratory scale by adding phosphoric acid and magnesium oxide as external sources of phosphorus and magnesium, respectively, and regulating the pH at 9.0. The effect of Mg:NH(4):PO(3) ratio was studied. Due to the low solubility of MgO, a low ammonia removal efficiency (i.e. 67%), with a rather high residual concentration, was obtained when the stoichiometric molar ratio was applied. However, by doubling the amount of magnesium oxide (i.e. by using a molar ratio of 2:1:1), ammonia removal efficiency increased up to 95% with a residual concentration compatible with a successive biological treatment. The struvite produced in the present study showed a composition close to the theoretical one. Furthermore, the precipitate was characterized by a heavy metal content much lower than that of typical raw soil, excluding any concern about heavy metal contamination in the case of its use as a fertilizer. The economic analysis of the process showed that ammonia can be removed at a cost of 9.6 euro/kg NH(4)-N(removed). This value can be greatly reduced, however, if the value of the struvite produced is considered.

The effect of ozone on tannery wastewater biological treatment at demonstrative scale.

This paper reports the results obtained during an investigation aimed at transferring to the demonstrative scale an aerobic granular biomass system (SBBGR--Sequencing Batch Biofilter Granular Reactor) integrated with ozonation for the efficient treatment of tannery wastewater. The results show that the integrated process was able to achieve high removal efficiencies for COD, TSS, TKN, surfactants and colour with residual concentrations much lower than the current discharge limits. Furthermore, the process was characterised by a very low sludge production (i.e., 0.1 kg dry sludge/m(3) of treated wastewater) with interesting repercussions on treatment costs (about 1 euro per m(3) of wastewater).

The essential role of filling material in aerobic granular biomass generation in a periodic submerged biofilter

The paper reports the results of a laboratory-scale investigation aimed at evaluating the influence of the filling material of a Sequencing Submerged Biofilter Reactor (SSBR) on granular biomass generation. The results showed that aerobic granular biomass generation was obtained only in the reactor filled with kmt-k1 carrier, since the features of this filling media are such that they generate a bed characterised by rather uniform internal and external small-sized pore volumes able to retain the released biofilm particles. Finally, the aerobic granule formation improved the biomass retention efficiency and reduced the excess sludge production.

Technological transfer to demonstrative scale of sequencing batch biofilter granular reactor (SBBGR) technology for municipal and industrial wastewater treatment

The paper reports the results of an experimental investigation aimed at transferring to demonstrative scale an innovative technology (SBBGR-Sequencing Batch Biofilter Granular Reactor) for the treatment of municipal and industrial wastewater by financial support of the EU Life programme. When this technology was applied for treating municipal wastewater, the results showed that the system was able to remove 80-90% of COD, total suspended solids and ammonia independently of the hydraulic residence time investigated (i.e., from 12 to 4 h). In the case of tannery wastewater, chosen as representative of concentrated industrial wastewater, SBBGR technology was suitable for removing 80-90% of the COD, suspended solids and ammonia content up to organic loading values of 3.5 kg COD/m3.d. During both periods, the process was characterised by a very high sludge age value (theta(c) approximately 150 d) that led to a biomass concentration as high as 35 gTSS/L(bed) and a sludge production much lower (5-6 times lower) that than commonly reported for conventional treatment plants.

Municipal landfill leachate treatment by SBBGR technology.

The paper reports the results of a laboratory-scale investigation aimed at evaluating the performance of a periodic biofilter with granular biomass (SBBGR) for treating leachate coming from a mature municipal landfill. The results show that the SBBGR was able to remove roughly 80% of COD in leachate. The remaining 20% of COD were, therefore, presumably owing to the presence in the leachate of recalcitrant compounds. Ammonia removal efficiency was low because of the presence of high salinity and inhibitory compounds in the investigated leachate. The process was characterised by very low sludge production (lower than 0.02 kg TSS/kg CODremoved).

Low Lime Coagulation for the Enhancement of Primary Treatment of Urban Wastewater

Pollutants in municipal sewage include a complex mixture of soluble and insoluble constituents ranging in size from less than 0.001 μm up to over 100 μm [1]. Several studies have been addressed to the classification of contaminants in wastewater in terms of particle size. Balmat [2], Heukelekian and Balmat [3] and Rickert and Hunter [4], using a sequence of sedimentation, centrifugation and filtration, separated the contaminants into four size fractions: settleable (> 100 μm), supracolloidal (1–100 μm), colloidal (0.08–1 μm), and soluble ( 106 μm), supracolloidal (3-106 μm), colloidal (0.025–3 μm), and soluble (< 0.025 μm). Notwithstanding the differences in the operating definition of the size ranges, these studies do agree that only a quarter or less of the COD of the raw sewage may be considered truly soluble [6]. The majority of the pollutant load is actually in suspended form, and is not easily biodegradable. In addition, other contaminants, such as heavy metals, bacteria and viruses, and organic micro pollutants (PCB, PAH) are strongly associated with the suspended phase.

Wastewater Treatment by Periodic Biofilter Characterized by Aerobic Granular Biomass

The paper reports the results of an experimental investigation aimed at evaluating the role of hydrodynamic conditions on generation and main properties of granular biomass grown under aerobic conditions in a periodic packed bed reactor. During the start-up period, the trend of the hydrodynamic shear forces, calculated by a methodology previous developed by authors, provided a key for explaining the process of biomass granulation. The granular biomass was characterized by a high density (i.e., 70–120 gVSS/Lbiomass) that permitted to achieve a biomass concentration such high as 20–38 gVSS/Lbed. The biomass density increased with the increase of shear forces. The EPS (Extracellular Polymeric Substances) content of the biomass (5–7% of the total organic matter) was not affected by hydrodynamic shear forces as well as the biomass protein content. Periodic packed bed reactor applied to a municipal wastewater showed performances very satisfactory with high efficiencies removal (around 90%) for both COD and ammonia, up to an applied organic loading value of 5.7 kgCOD/m3·d, and negligible sludge production.

Improving STP Performance by Lime Addition

• COD in Roma-Nord sewage is predominantly associated with settleable and supracolloidal particles, each size class containing about 40% of total COD. • A large fraction of COD associated with supracolloidal particles is characterised by slow degradability, therefore suggesting that removal of these particles prior to biological treatment may greatly improve the overall treatment scheme. • Pilot plant coagulation tests with lime at pH 9 showed that the lime-enhanced primary treatment may increase COD removal efficiencies from typical 30-35% up to 65–70%, by inducing an almost complete removal of the supracolloidal COD fraction. • An additional benefit of lime-enhanced primary treatment may be a certain degree of disinfection (1–2 log reduction in E. coli), which is not typically obtained in conventional primary treatment. • The main drawback of sewage coagulation with lime is the consumption of a large amount of lime and the consequent production of excess sludge, most likely due to the incomplete dissolution of lime. This drawback may be overcome by using a semi-batch coagulation process in place of the continuous flow mode.