Environmental Technology

Behrens, M. L.; Dvorak, B. I.; Woldt, W. E.

doi: 10.1080/09593332108618111pmid: N/A

Traditional cost analyses used for process cost comparisons often ignore costs (e.g., waste disposal, regulatory compliance, long-term liabilities) that are lumped into general overhead but actually are incurred during the process. In this research, both a traditional cost analysis and a total cost assessment (which includes many often-neglected process costs) were performed on five potential methods of testing the bitumen composition of newly paved asphalt. In the past, the bitumen content of asphalt pavement was determined by tests using toxic solvents; alternative, less polluting methods have been developed that can replace the traditional solvent extraction method. In order to represent the uncertainties in the design and cost data (especially the liability costs) for this cost comparison, fuzzy set theory was used. A traditional economic analysis that included only the capital and operating and maintenance costs found that the most environmentally friendly process (ignition ovens) was only slightly less costly than two other options. The cost of the ignition ovens and two other options were similar enough to be considered within the range of uncertainty for the analysis. However, when the hidden costs related to the environmental, health, and safety aspects for a bitumen testing procedure were incorporated into the cost analysis, the cost comparison changed significantly; the most environmentally-friendly option, ignition ovens, was shown to be by far the least-cost option. Thus, incorporating hidden environmental costs into a cost analysis can have a significant impact.

Guibaud, G.; Ayele, J.

doi: 10.1080/09593330.2000.9618908pmid: N/A

The objective of this work was to study the effect of pH and ionic strength on the ability of a forest soil to release aluminium in order to give information on the risk of contamination of natural water neighbouring forests of conifers. The horizons A, B and C, of an acid brown soil, planted with three different forests (Chestnuts (Castanea sativa), young Douglas fir (Pseudotsuga menzesii) and old Douglas fir) were selected and characterised. The effect of the pH (pH 0.5 to 9.0) and of the ionic strength (setting by NaCl or CaCl2, 0 to 1.71 M) on the release of aluminium monomer ions was investigated using batch reactor experiments. For moderately acid pH the released aluminium concentrations are related to the buffer value of the horizon, at very acid pH in addition to the mobile form of aluminium a part of the aluminium of the soil crystal structure particles is released. With the weak ionic forces, the solutions of CaCl2 involve released aluminium concentration more significantly than do the solutions of NaCl in the majority of the studied concentrations. For the horizons B and C, starting from 0.2 M this difference attenuates and could be reversed for strong ionic strength (1.7 M). The aluminium concentrations released under the effect of the ionic strength are related to the speciation of aluminium in the soils: released aluminium comes from the fractions of exchangeable aluminium for the horizons A, B, and C. But for A horizons a part comes from the fraction bound to the organic matter. With the weak ionic strength (0.017 M), the released aluminium rates are a function of the content of exchangeable cations of the horizon. A model according to the results of the literature, based on a reaction of exchange between protons, Na+ ions or Ca2+ ions in solution and the aluminium ions of the soil was developed, in order to obtain a conditional constant of desorption and an apparent number of exchanged ions. The conditional constants of desorption represents the effect of the two physicochemical factors well, but for high values: pH acid (from 3) and strong ionic strength (starting from 0.2 M). This study shows the importance of the ionic composition of water, which is in contact with soil. Acid or mineral-bearing water can involve strong aluminium releases and thus pollute the rivers neighbouring conifers forest or not very deep underground water by aluminium.

Wani, A. H.; Lau, A. K.; Branion, R. M. R.

doi: 10.1080/09593332108618116pmid: N/A

The work reported here describes the aerobic biodegradation in biofilters of methyl mercaptan, which is a foul smelling compound found in the air emissions from Kraft pulp mills. Experiments were conducted in three bench-scale biofilters packed with the mixtures of compost/perlite (4:1), hog fuel/perlite (4:1), and compost/hog fuel/perlite (2:2:1), respectively. These biofilters were exposed to variations in methyl mercaptan concentration, fluctuating waste airflow rate, and periods of non-use to evaluate the effects of changes in contaminant mass loading and starvation on biofilter dynamics and performance. Inoculation of the biofilter materials with pulp mill wastewater sludge significantly reduced the initial start-up time. The initial acclimation period for the three biofilters was about 56 hours. During that time the outlet methyl mercaptan concentration declined from 2 to 1 ppmv and the elimination capacities remained constant at around 6 g m−3 h−1. Step changes in methyl mercaptan concentration and waste airflow rate demonstrated that the biofilters acclimatized rapidly to the new operating conditions. However, an inlet concentration of about 109 ppmv caused a measurable decrease in the % removal and elimination capacity of the biofilters, so did a waste airflow rate of 2.9 m3 h−1. A massive reduction in % removal and elimination capacity of all the three biofilters was observed when the inlet mercaptan concentration rose to 141 ppmv, moreover the biofilters could not recover to the % removal and elimination capacity levels they had before this increase. In most cases about 8 - 16 h were needed, after the step changes, by the biofilters to recover to initial removal capacity. All three biofilters exhibited diminished levels of performance immediately after the inlet mercaptan concentration was raised from 88 ppmv to 158 ppmv and held there for 30 minutes. After that the inlet concentration returned to 88 ppmv and the biofilters' original levels of performance were regained in 1 - 6 hours. The re-acclimation time was dependent on the duration of the non-use period, and was much shorter following a no-contaminant-loading phase than that after an idle phase. The re-acclimation time (≈ 1 day) for the biological activity after the longest starvation period of one-week was much shorter than the initial start-up time of 5 – 6 days.

Crouzet, C.; Kedziorek, M.A. M.; Altmann, R. S.; Bourg, A.C. M.

doi: 10.1080/09593332108618119pmid: N/A

A protocol for determining the distribution of sulphur forms in aquifer solids is proposed. A series of single parallel extractions and of two-step treatments, derived from a combination of previously described extractions are tested on simple Fe and/or S minerals (goethite, alkageneite, hematite, ferrous sulphide, pyrite, flower elemental sulphur and ferrous sulphate). Monosulphides are extracted with hot HCl. Iron disulphides are determined using a Cr(II) digestion after preliminary elimination of monosulphides, elemental sulphur and sulphates with HI. Sulphate is extracted by NaH2PO4 followed by HI treatment. Elemental sulphur is estimated from differences between total sulphur and the fractions quantified above. The method is applied to reduced and oxidised sediments from a well-characterised sandy aquifer system downgradient from the Danish Vejen landfill. Total inorganic sulphur decreases rapidly when moving away from the landfill. Sulphidic phases are dominant in the most reduced sediment. Iron disulphide is found in the moderately reduced sediments (iron reducing conditions). Oxygenated sulphur is significant in the most oxidised samples. Several discrepancies between water composition and sulphur forms in the solids are explained by non-equilibrium conditions.

Wasserman, J. C.; Freitas-Pinto, A. A. P.; Amouroux, D.

doi: 10.1080/09593332108618117pmid: N/A

The present and past degrees of contamination by mercury were evaluated in the Guanabara Bay by the study of five sediment cores. The cores were sampled from the deltaic mouth of the São João de Merití River (cores SJ1, SJ2, SJ3, and SJ4), adjacent to a large mangrove stand and in a mangrove stand in Guapimirim (opposite side of the bay). The study area receives most of the domestic and industrial wastes from the metropolitan region of Rio de Janeiro city and, in consequence it becomes increasingly degraded. Among the sources of pollutants, mercury-spilling industries are inventoried in the São João de Merití River basin. Total mercury concentrations were measured in the sediments by cold vapour atomic absorption spectrometry. The fraction smaller than 63 µm, organic carbon and total sulphur concentrations were also measured. The results show that concentrations of mercury can reach high values (up to 37 µg g−1 at a depth of 34 cm in the core SJ4). The base of core SJ1 shows mercury concentrations that probably represent background values, as established elsewhere for the Guanabara Bay (51 ng g−1 at the depth of 32 cm). Among the studied cores, only core SJ1 seems to reach background levels.

De Gregori, I.; Lobos, G.; Lobos, S.; Pinochet, H.; Potin-Gautier, M.; Astruc, M.

doi: 10.1080/09593332108618112pmid: N/A

Total copper and selenium concentrations were determined in rain waters, soils and alfalfa samples collected during April-May 1997 at various sites from different zones of Valparaiso region, in Chile: Puchuncavi and Catemu valleys, (both impacted by mining activities) and Casablanca valley (reference site). In rain waters, Cu and Se concentrations clearly decreased exponentially with distance from the sources and were significantly correlated. The results obtained demonstrate that the mining activities have contributed to increase the contamination by copper in the agricultural ecosystems, particularly those located near the smelters. In all matrices from Puchuncavi and Catemu valleys copper concentrations were higher than in the reference site. In Puchuncavi valley, Cu concentrations in soils and alfalfa show close correlation and were a function of the distance from the smelter. Selenium concentration in soils and alfalfa follows a different pattern, being relatively constant in these matrices and presenting no clear dependency on the distance from the sources. In alfalfa they ranged between 0.10 and 0.40 mg kg-1; these concentrations are not high and do not represent a problem to livestock grazing in these areas.

Vigneswaran, S.; Ngo, H. H.; Hashimoto, K.; Hasegawa, T.; Watanabe, Y.

doi: 10.1080/09593332108618113pmid: N/A

The performance of a high rate floating medium flocculation-filtration system with an in-line addition of a silica-polymer compound, namely polysilicato-iron (PSI) has been investigated for water treatment. This study is intended to investigate the applicability of PSI as a sole flocculant or as a combined flocculant with an organic polymer in the downflow floating medium filter. The filter system was operated at a high loading rate of up to 60 m3 m−2 h−1. Filter column experiments were conducted at different PSI doses, filtration rates, filter depths and buoyant medium types and sizes. Results showed the filter system was able to yield uniform and filterable flocs (15 - 20 µm), even at a very high filtration rate of 60 m−3 h−1, through out the filter run time of 4 hours. Better filter performance was obtained when: (i) polystyrene beads of 1.9 mm diameter or polypropylene beads of 3.8 mm diameter; (ii) an in-line single dosage of 2.5 mg l−1 PSI; (iii) in-line combined dosages of 1.5 mg l−1 PSI and 0.4–0.6 mg l−1 organic polymers (cationic polyacrylamides, cationic polystyrene or Pollyallylamine hydrochloride) were used. When PSI was introduced as a sole flocculant, more than 90% turbidity was removed from a 54 NTU artificial kaolin clay suspension at a filtration rate of 30 m−3 m−2h−1 with very low headloss development. Greater removals were achieved when SIF was used in combination with a polymer (e.g.greater than 95% turbidity removal). Frequent (once in every 90 minutes) but short duration backwash (less than 60 s) by air and water enables the system to maintain a superior effluent quality (e.g. turbidity less than 1 NTU) during the filter run. Backwash water requirement was very low (approximately 1%-2% of filtered water production). A lower amount of sludge was produced from the filter in case of combined PSI and organic polymer coagulant addition.

Vaxelaire, J.; Mousques, P.; Bongiovanni, J. M.; Puiggali, J. R.

doi: 10.1080/09593332108618114pmid: N/A

Most of the studies dealing with water repartition within activated sludge focus essentially on the transition between free water and bound water; a transition which is important for mechanical dewatering investigations. But nowadays the drying of sludge is increasing and a better characterisation of the bound water is necessary. In this study a simple technique for the evaluation of sorption isotherms is presented. The experimental data obtained from this method indicate that flocculation and dewatering by filtration-compression (up to 10 bar) do not affect the distribution of the bound water. Otherwise usual models such as BET or GAB equations give a good representation of the desorption isotherms of activated sludge and allow an estimation of the adsorption heat of the water. The comparison of the experimental results (in terms of transition moisture content and specific area) with some data obtained from differential scanning calorimetry and porometry experiments shows a relatively good agreement between the different methods of evaluation and then validates the presented technique.

Fajerwerg, K.; Castan, T.; Foussard, J.-N.; Perrard, A.; Debellefontaine, H.

doi: 10.1080/09593330.2000.9618915pmid: N/A

Wastewater originating in the chemical process industries contain high concentrations of organics that must be treated before discharge. Phenol is one of the most important of these pollutants because it is toxic, even at low concentrations. Recently, hydrogen peroxide treatment has emerged as a viable alternative oxidation technique for treatment. It does not form any harmful or intrusive by-products and it is an ecologically clean and non-toxic chemical. However, the methods for treatment of wastewater with hydrogen peroxide are based mostly on homogeneous catalysis by metal ions inducing additional pollution. From this, it was anticipated that the use of heterogeneous catalysis would be a good alternative, thus opening up a new field of investigation. Previous studies, based on screening tests, evidenced the catalytic activity of an MFI zeolite Fe-ZSM-5 for phenol elimination by H2O2. The oxidation tests are carried out in a batch mode, using a stirred glass reactor. The influence of pH, temperature and H2O2 stoichiometric ratio on the phenol oxidation rate with Fe-ZSM-5 is studied. The temperature is below 100°C in order to avoid pressurization of the treatment reactor. Using a H2O2 stoichiometric ratio equal to 1.5 avoids accumulation of any quinone-like by-products. Under these conditions, the catalytic system H2O2 / Fe-ZSM-5 allows a total elimination of phenol and a significant TOC removal (50%) without leaching-off more than 1 ppm of Fe (III) ions. At the end of the reaction period, only carboxylic acids (maleic, fumaric, oxalic, acetic, accumulate. These latter should not be considered as a drawback of this process. The chemical oxidation process would be used only as a detoxification step and such compounds could be treated with a biological process, in a second step.

Ramasamy, E. V.; Abbasi, S. A.

doi: 10.1080/09593332108618120pmid: N/A

Anaerobic digestion of municipal solid waste (MSW) was studied in ‘high solids digesters’ (HSDs) for generating energy (as methane). Three kinds of HSDs were employed in which the waste along with inoculum (consisting of pre-digested cow dung slurry) were subjected to anaerobic digestion. The first type (HSD-I) was provided with two chambers; the upper chamber served as a solid phase in which only the solid portions of vegetable waste were subjected to digestion, while the lower chamber served as liquid phase where the leachates were allowed to ferment. The second type (HSD-II) was similar to HSD-I but had no partition. The third type (HSD-III) had two distinct units, one for solid phase and the other for the liquid phase; the units were connected by a tap with a flow regulator valve. The reactor performance was assessed in terms of biogas yield. The results of the study indicate that the performance efficiency (in terms of biogas yield) of the HSDs increased with the increase in the degree of phase separation. The performance of the digesters was further enhanced by providing additional props to facilitate biodegradation, such as biofilm support systems (BSS) in the liquid phase unit/chamber of the HSDs.