Roberto Passino

Anaerobic digestion of olive oil mill wastewaters

Abstract Anaerobic treatment of olive oil mill wastewaters (COD up to 220 kg/m3) is feasible, and the most promising results were obtained on UASB reactors, both at laboratory and pilot scale (tank capacity 15 litres and 5 m3), fed on diluted waste (COD = 13−18 kg/m3). Volumetric loading rates ranging from 16–21·5 kgCOD/mR3day and 70% removal efficiencies were obtained with these digesters. Start-up of UASB reactors fed on olive oil mill waste is a delicate step which still has to be fully controlled and optimized. The best results were obtained by starting with very diluted waste (COD = 5 kg/m3). Granulation of the sludge, as achieved in Dutch UASB digesters fed on sugar beet wastewaters, was not obtained, but, even so, the settleability of the sludge was very good.

Nutrient removal and recovery from wastewater by ion exchange

Abstract After about 500 cycles have been continuously performed on a laboratory pilot plant, ion exchange resins have proved to be an effective means to treat municipal secondary effluents to prevent eutrophication in the receiving water bodies. Clinoptilolite, a natural zeolite, and Kastel A 510, a strong base anion resin with adsoptive properties, act selectively to remove ammonium and phosphate ions, at the same time affording filtration and adsorption of the wastewater. NaCl at sea-water concentration is used as resin regenerant. After the recovery of products of fertilizing value, as MgNH 4 PO 4 and NH 4 NO 3 , from the eluates, the latter can be recycled.

Exchange equilibria on anion resins

Abstract Selectivity coefficients, free exchange energies and enthalpies between 5°C and 45°C of different anion resins with functional groups of the amino type were determined for the SO−4/Cl− system in a range of bulk salinities lying between 6 x 10−3 and 2.4 N The experimental results showed that the selectivity for the bivalent ion depends strongly on the basicity of the resin, the affinities of the various amino functional groups following the order primary > secondary > tertiary > quaternary. Furthermore, the affinity of every resin for the sulphate ion increases with the dilution of the aqueous phase and with the equilibrium temperature. These results are in full agreement with the theoretical forecasts, and show that in heterovalent exchange processes a fundamental role is played by the phenomena connected with the electrostatic interactions.

The 10 m3 h−1 rim-nut demonstration plant at West Bari for removing and recovering N and P from wastewater

The RIM-NUT, a new ion exchange-precipitation process for removing and recovering ammonium and phosphate ions from wastewater, has been tested on a 10 m3 h−1 demonstration plant for tertiary treatment of West Bari domestic effluent. Natural zeolite clinoptilolite and a porous strong base resin, regenerated in a “closed-loop” fashion with 0.6 M neutral NaCl, ensure ≥90% removal of both nutrient species. Nutrients are precipitated from resin eluates as MgNH4PO4, a premium quality slow-release fertilizer.

Low and non waste technologies for metals recovery by reactive polymers

Conservative technologies have been investigated in order to utilize natural and synthetic reactive polymers for selective metal removal, recovery and reuse. Examples refer to the treatment of industrial wastes containing silver, cadmium, mercury, chromium, iron and aluminum by different innovative processes. A precipitation process is described, namely Metals Extraction by Xanthate Insolubilization and Chemical Oxidation (MEXICO), using agricultural raw materials to prepare starch or cellulose xanthates as precipitating agents for metals. The process reliability has been proven at pilot scale level (15 m3/d) by a demonstrative campaign treating continuously real chlor-alkali wastewaters for mercury removal and recovery. Results demonstrated Hg concentrations in the filtered effluent in the range of 5–20ppb, with an average removal efficiency of 99.8%. The metal-xanthate sludge was then detoxified by treating with NaCIO solution at acidic pHs. Concentrated (> 10 g/l) chlorocomplex Hg(II) solutions were obtained, to be directly recycled to the electrolytic cell. Other applications deal with the treatment of segregated chromium in exhausted spent baths. The patented Ion Exchange REcovery of CHROMium (IERECHROM) process utilizes a weak cation (carboxylic) ion exchange resin and allows for recovery and reuse of 90% of high purity (> 99%) chromium from other interfering metals such as Fe and Al present in the spent tanning baths. A process for the treatment of tannery sludges has also been studied, particularly for possible restoration of contaminated landfilling sites. The process is based on the acid leaching of the sludges and on treating the leachate by a weak base anion resin, selective to ferrie species, coupled with a strong cation resin (sulphonic) for the separation and recovery of chromium and aluminum. The economical evaluation of the conservative processes described is favorable, without taking into account the economic revenues from the recycling operation of the metals recovered and from the minimized environmental impact related to these technologies.

Degradation of sulphur containing s-triazines during water chlorination

Abstract The reactions of four sulphur containing s-triazines (prometryne, terbutryne, ametryne and desmetryne) with hypochlorous acid (HClO) and chlorine dioxide (ClO 2 ) have been investigated using an 11 ppm/3 ppm oxidant/herbicide ratio. The main objective of the study was the identification of by-products. Additionally, to study the effect of oxidant concentration on the reaction rate, two more oxidant/herbicide ratios (3 ppm/3 ppb and 11 ppb/3 ppb) have been investigated only for prometryne. Oxidation reactions were monitored by high performance liquid chromatography (HPLC), while, the identification of by-products was initially carried out by low resolution HPLC-mass spectrometry (HPLC-MS) and confirmed by accurate mass measurement. Under the experimental conditions ( T = 20°C, pH = 8, reaction time = 48 h), the results indicate that all the investigated triazines react in the same way with each oxidant. The reactions with HClO occur much faster than those with ClO 2 and give rise to three identified oxidation by-products: the sulfoxide, the sulfone and the sulfones hydrolysis product. The reactions with ClO 2 , instead, give rise to a sole oxidation by-product: the sulfoxide. With both oxidants, as expected, the lower the oxidant concentration the slower the oxidation rate. Based on the obtained results, a general pathway for the oxidation of sulphur containing s-triazines is proposed.

Phosphates and ammonia recovery from secondary effluents by selective ion exchange with production of a slow-release fertilizer

A process for the reduction of eutrophic potential in urban secondary effluents. which comprises the selective exchange of phosphates on a weak anion resin and of ammonia on clinoptilolite, is described. Sodium chloride is used to regenerate both resins, with some Ca(OH)2 added for clinoptilolite. By adding Mg(OH)2, eventually precipitated with lime from sea water, the premium quality, slow-release fertilizer MgNH4PO4-6H2O is recovered from the concentrated regeneration streams, which can then be recycled. Laboratory evaluations of the hydrolysis extent of the weak anion resin in the presence of bicarbonates showed that a steady-state is attained with resin exchange capacity reproducibly averaging about 80 mmol phosphates 1,−. The preliminary runs on a pilot plant for the tertiary treatment of urban sewage are also presented.

Prometryne oxidation by sodium hypochlorite in aqueous solution: kinetics and mechanism.

The reaction of the herbicide prometryne (C 9 H 16 N 5 -S-CH 3 ) with sodium hypochlorite has been investigated from the kinetic and mechanistic stand point. Under the fixed experimental conditions : pH = 7, T = 25 °C, [NaClO]/[substrate] = (10 -3 M)/(10 -5 M), prometryne oxidation takes place according to the following pathway : R-S-CH 3 (P) → R-SO-CH 3 (a) → R-SO 2 -CH 3 (b) → R-O.SO 2 -CH 3 (x) → R-OH (c), where R stands for C 9 H 16 N 5 , i.e., the substituted triazine ring of prometryne and (x) is an unexpected intermediate never previously detected nor identified. After having synthesized the pure intermediates (a), (b), and (x), the values of the pseudo-first-order kinetic constants of the first three steps were experimentally obtained : [k 1 = (0.64 ± 0.03) s -1 , k 2 = (1.81 ± 0.05) x 10 -3 s -1 , k 3 = (1.50 ± 0.03) x 10 -4 s -1 ]. As for k 4 , its value [(2.5 ± 0.2) x 10 -5 s -1 ] has been calculated indirectly on the basis of the kinetic theory concerning consecutive reactions. All the steps were pseudo-first-order reactions with respect to their specific substrate. The effect of pH on the hydrolysis of (b) [(b)→(c)], in the absence of NaClO, has been also assessed to better elucidate the mechanism of the overall pathway.

Exhaustion-regeneration behaviour of carboxylic resins. The Cr(III)/Al(III)/Fe(III) system

Abstract It is not an easy task to regenerate chromium(III) ions from weak electrolyte carboxylate resins using conventional chemicals (e.g., mineral acids, saline solutions, alone or in combination). In areas of environmental control, referring to some specific cases of industrial effluents (e.g., tanneries), where metal complexing agents are present, additional difficulties in separation and recovery of the metals may arise by use of carboxylate form resins. Referring to the Cr(III)/Al(III)/Fe(III) ionic system in a solution simulating a typical spent chrome tanning bath, the exhaustion-regeneration behaviour of a commercial acrylic-based macroporous carboxylic resin (i.e., Purolite C106) is reported. The exhaustion behaviour of the resin is straightforward, whereas regeneration by using chemicals, such as sulphuric acid, sodium hydroxide, sodium sulphate, is difficult. The adoption of hydrogen peroxide in alkaline media, during the regeneration step, seems very promising. The general behaviour is interpreted in terms of ionic speciation and complex formation. A mechanistic explanation is provided in support of the experimental findings.

Chloride/sulfate exchange on anion resins. Kinetic investigations. II. Particle diffusion rates

Abstract The exchange rates for the chloride to sulfate conversion on several anion resins, when particle diffusion is the rate determining step, have been measured, using the stirrer-reactor technique and infinite solution volume conditions. The interdiffusion coefficients resulted to be variable, depending mainly on the conversion degree of the resin. Two approaches have been used to calculate the exchange rates. The first one, based on the simpler rate laws for isotopic exchanges, allowed the exchange kinetics to be anticipated by the aid of a semiempirical equation for the interdiffusion coefficient. According to the second procedure, the single ion diffusion coefficients, calculated as limiting values of the (apparent) interdiffusion coefficients, and the more rigorous Nernst-Planck model for ion exchange processes were applied. Both approaches showed a satisfactory agreement between calculated and experimental kinetics.