Environmental Technology

Spérandio, M.; Moreau – Le Golvan, Y.; Poux, D.; Lefebvre, X.; Paul, E.

doi: 10.1080/09593332108618163pmid: N/A

The behaviour of sludge added to municipal solid wastes placed in a landfill has been investigated. Biochemical methane potential of different non-stabilised sludges was measured and ranged between 135 and 287 l kg−1 VS added. The kinetics of methane production of an activated sludge at different moisture levels from 55 to 99% were compared. An important influence on the stabilisation rate of activated sludge was shown between 75 to 90%. The leachate organics, nitrogenous and phophorus load released by the dewatered activated sludge were quantified. Then the long-term anaerobic storage of municipal solid wastes alone and mixed with two types of sludge was studied in five pilot scale reactors. The addition of 10% of sludge in municipal solid wastes was shown, during the following three months of incubation, to increase up to 13 times the leachate volume, depending on the moisture of the sludge. The concentrations of organic matter and ammonia were also largely increased. The degree of mixing, the moisture and also the lime content of the sludge were shown to be crucial parameters for predicting the behaviour of the sludge in a co-disposal landfill. Activated sludge with no lime treatment, anaerobically as well as aerobically developed, proved to be a potential inoculum for municipal solid wastes stabilisation, improving the start of methane production.

Aioueche, F.; Lounici, H.; Belhocine, D.; Grib, H.; Piron, D. L.; Mameri, N.

doi: 10.1080/09593332108618148pmid: N/A

A technique for activation of granular activated carbon (GAC) is presented based on the electrochemical method. In this study, we investigate the effectiveness of the electroactivated GAC in removing phenol from water and determine the optimum conditions for activation. Electro-activation of the GAC appears to be an interesting technique; it requires a short electro-activation time Ta = 30 min and an optimum potential ranging from +200 mV/SCE to 400 mV/SCE. Phenol adsorption isotherms gave a limiting adsorption capacity Qm dependent on the applied potential, which at potential E=+300 mV/SCE was improved by about 55%, giving Qm = 75 mgphenol g−1 GAC.

Stokes, A. J.; Forster, C. F.; West, J. R.; Davies, W. J.

doi: 10.1080/09593332108618154pmid: N/A

The various activated sludge models within STOAT, a whole works package, were used to predict the oxygen requirements of a hypothetical activated sludge plant. The predictions which were obtained were then compared with the values calculated from standard equations. The results showed that there were very definite differences both between the predictions made by the models and between the model predictions and those produced using standard equations. The results also showed that, for carbonaceous oxidation, the COD-based model in STOAT (IAWQ model) was applicable to a wider range of process conditions than the BOD-based model (ASAL model). The IAWQ model was also found to be a more useful tool in optimising a nitrogen removal system.

Wong, J.W. C.; Lai, K. M.; Fang, M.; Ma, K. K.

doi: 10.1080/09593332108618149pmid: N/A

The aim of the present study was to evaluate the feasibility of using sewage sludge for ameliorating landfill cover soils by assessing soil biology and nutrient cycling because of the poor physical property and nutrient contents. An acidic sandy loam of these low graded subsoil materials commonly used for landfill cover soil was amended with sewage sludge at 0, 2.5, 5, 15 and 35% w/w fresh weight. An increase in the sludge amendment rate caused a rise in both pH and electrical conductivity (EC). However, with incubation time, pH decreased while EC increased and then declined. Nevertheless, salinity and heavy metal contents of the sludge amended soil were all within the toxic limits. Soluble NH4 +-N, NO3 −-N and PO4 3−-P increased after amending the soil with sewage sludge. However, increasing the sludge application rate decreased the N mineralization efficiency and created an adverse effect on nitrification, while the P- mineralization efficiency was enhanced by sludge amendment. The sharp peaks of NH4 +-N at day 21 with a concentration of 280 and 520 mg kg−1 for 15% and 35% sludge amended soil would probably be a limitation to plant growth. Soil respiration, as an indicator of microbial activity, demonstrated the same pattern for all treatments that CO2 evolution increased initially and then decreased until the end of incubation. The peak soil respiration was at day 7 for all treatments, except for the soil amended with 35% of sludge which had a peak at day 2 and of much higher level than others. The present results indicated that a sludge amendment rate of 5 to 15% would have the optimal beneficial effects on the cover soil quality in terms of microbial activity and nutrient mineralization.

Low, K. S.; Lee, C. K.; Wong, S. Y.; Tang, P. L.

doi: 10.1080/09593332108618152pmid: N/A

Various chemical modifications were attempted on rice hull in order to improve its metal sorption capacity. Ethylenediamine tetraacetic acid (EDTA) was found to give the greatest enhancement. Parameters investigated include pH, initial concentration, sorbent dosage and competition with other cations and chelators. Sorption was pH dependent with greater uptake at higher pH value. Equilibrium was attained in less than 60 minutes implying the material could be suitable for continuous flow system. Maximum sorption capacities of EDTA-modified rice hull were 8.86, 9.59, 8.76 and 28.65 mg g−1 for Cu(II), Cr(III), Ni(II) and Pb(II) respectively. The presence of EDTA and nitrilotriacetic acid (NTA) suppressed the metal binding capacity of EDTA-RH. Column study on the removal of Cu(II) from wood preservative waste showed that the removal of Cu(II) was a function of bed-depth.

Lin, S. H.; Shyu, C. T.

doi: 10.1080/09593332108618158pmid: N/A

Carbon dioxide (CO2) absorption by alkanolamines in a packed column was investigated experimentally and theoretically. The alkanolamines used in the present study were the primary monoethanolamine (MEA) and tertiary N-methyldiethanolamine (MDEA), two popular amines widely used in the chemical and petrochemical industries for gas purification. The CO2 absorption characteristics by these two alkamolamines were examined experimentally under various operating conditions. A theoretical model was developed for describing the CO2 absorption behavior. Test data indicated that the predictions using the proposed model and the observed CO2 absorption breakthrough data agree very well. Preliminary studies of regeneration of exhausted alkanolamine solution were also conducted to determine the optimum regeneration conditions. The test results revealed that the tertiary amine is easier to regenerate with less loss of absorption capacity than the primary one.

Ozaki, T.; Ambe, S.; Takahashi, Y.; Yoshida, S.; Minai, Y.

doi: 10.1080/09593332108618150pmid: N/A

This paper presents a study on the pH dependence of the adsorption of various elements, especially of lanthanides on solid-phase hematite (α-Fe2O3), in the presence and absence of humic acid. For a precise evaluation of the adsorption behavior, simultaneous determination of the adsorption of Rb, Ba, Pt, Eu, Gd, Tb, Tm, Yb, and Lu was conducted by the multitracer technique. The adsorption behavior of Eu onto Fe3O4 and α-Al2O3 was also studied, using a single tracer so that the effect of texture of the solid phase could be understood. From the present investigation, the adsorption behavior of Rb and Ba was found to be slightly influenced by the existence of humic acid. The pH dependence of the adsorption of lanthanides in the presence of humic acid differed from that in the absence of humic acid and was similar to the adsorption of humic acid on hematite, suggesting the adsorption of lanthanide-humate complexes. The texture of the minerals showed a small effect on the distribution of humic acid and the humic acid-Eu complex.

Pignon, H.; Faur-Brasquet, C.; Le Cloirec, P.

doi: 10.1080/09593332108618153pmid: N/A

The aim of this work was to estimate the efficiency of coupling the processes of ultrafiltration and adsorption onto an activated carbon cloth, in order to treat complex aqueous solutions containing both organic micropollutants and macromolecules. First, the effectiveness of each treatment process was studied separately in batch reactors for microorganics, like phenol or atrazine, and macromolecules like humic substances. The activated carbon cloth displayed higher adsorption capacities for microorganics than granular activated carbon, from 45 mg g−1 for phenol up to 370 mg g−1 for atrazine, whereas they were not efficient at adsorbing humic substances. Conversely, as many as 80% of these macromolecules were removed by an ultrafiltration membrane with a 10 000 D molecular weight cut-off. Secondly, the coupling was tested directly using a surface water with an initial total organic carbon of 20 mg l−1 and around 30 mg l−1 of suspended solids. At first, batch experiments showed that the ultrafiltration step increased the activated carbon cloth performance, and the comparison of several activated carbon cloths of different properties showed that the total organic carbon removal was dependent on the adsorbent pore-size distribution. Then, continuous flow reactor experiments were carried out using the surface water loaded with atrazine. A coagulation-flocculation step was tested as a pre-treatment. The specific adsorption of micropollutants onto the activated carbon cloth was displayed: the pre-treatment improved the permeate quality (lower values of total organic carbon), whereas it had a negligible impact on atrazine adsorption.

Bodurtha, P.; Brassard, P.

doi: 10.1080/09593332108618151pmid: N/A

Steel-making slag residues are potentially useful in the neutralization of acidic liquors such as acid-mine drainage (AMD) because of their high content of basic minerals. This work examined the neutralization capacity of slags by batch titration with sulfuric acid. Measurements of pH and elemental solution composition over time provided input to a dissolution model based on saturation driven surface kinetics, a process dependent on the relative degree of saturation of the dissolving solid, and solution equilibrium. The heterogeneous composition of slag grains was simplified to three compositional groups based on their solubility. Group 1 included free lime, magnesium and silicon oxides, and dicalcium ferrite. Group 2 included weakly bound lime and magnesium oxides. Group 3 contained tightly bound lime and magnesium oxides, and wüstite. Neutralization profiles consistently revealed a two-phased kinetics. Group 1 oxides dissolved almost entirely in the first days according to saturation driven kinetics. Group 2 dissolved over the next 10 to 80 days, driven by a pH gradient in a quasi-first order reaction rate with respect to H+. Group 3 did not dissolve. Indirect evidence suggests that the transfer from saturation to pH driven dissolution would be caused by armoring of the grain surface by precipitating iron oxides. Although only 60% in volume of slag dissolves, it still possess the same neutralizing capacity as calcite and can neutralize acidic liquors like AMD. However, due to the slag having slow dissolution kinetics and the necessity to use fine powders, rapid neutralization is hindered because of the high cost of crushing.

White, C. J.; Stuckey, D. C.

doi: 10.1080/09593332108618157pmid: N/A

Anaerobic technology is well suited for biological wastewater treatment of industrial effluents due to its low biological sludge production and energy consumption. However, problems can occur with this technology when the final step of the process, methanogenesis, becomes unbalanced. Due to a combination of their relatively slow growth rates and more stringent growth requirements, the methanogenetic microorganisms are more sensitive to fluctuations/deficiencies in their environment than are the other bacteria involved. Therefore, the aim of this work was to gain a better understanding of the metal ion nutrient requirements of the methanogenic phase when treating very high strength soluble feeds. A synthetic feed based on sucrose was supplied to six continuously stirred tank (CSTR) anaerobic digesters operating at 35°C with an hydraulic retention time (HRT) of 20 days. This feed contained 30gCOD l−1, requiring the methanogenic biomass to achieve acetate utilisation rates (AURs) of between 0.25 and 0.5 g.gVSS−1 day−1. It was found that the growth of the methanogenic population was limited by a lack of available nutrients. Growth limitation was indicated by rapid accumulation of high concentrations of acetate, due to a fall in acetate utilisation rates (AUR). The cause of the growth limitation was investigated in experiments using both batch assays and continuous reactor systems. Limitations in methanogenic activity were prevented and/or restored by the addition of a solution of metal salts into the reactors.