Environmental Technology

Mapfumo, E.; Chanasyk, D. S.

doi: 10.1080/09593331908616711pmid: N/A

Fly ash is a by-product of coal combustion that requires disposal worldwide. Few studies have been conducted on the potential utilization of fly ash to improve soil physical properties and workability. The objective of this study was to investigate the impact of fly ash amendments on the plasticity, water retention and penetration resistance-density-moisture relationships of three soils of sandy loam, loam and clay loam textures in order to determine the potential compaction of these soil/fly ash mixtures if they were worked at different moisture ranges. For all three soils the addition of fly ash decreased the plasticity index, but slightly increased the Proctor maximum density. This implies that fly ash amendments reduce the range of moisture within which soils are most susceptible to compaction. However, for the sandy loam and loam textured soils amended with fly ash, cultivation must be avoided at moisture contents close to field capacity since maximum densification occurs at these moisture contents. In all three soils the addition of fly ash increased water retention, especially in the sandy loam. Correlation analysis indicated significant (p≤0.05) positive correlation between critical moisture content and field capacity, critical moisture content and plastic limit, and plastic limit and field capacity. Fly ash amendments increased penetration resistance of the clay loam, but decreased penetration resistance of the sandy loam. For the loam there was an inconsistent response of penetration resistance to fly ash additions. Regression analysis indicated that penetration resistance of sandy loam/fly ash mixtures and loam/fly ash mixtures was significantly (p≤0.05) dependent on bulk density. For the clay loam/fly ash mixtures penetration resistance was significantly (p≤0.05) dependent on both bulk density and volumetric moisture content.

Le Bihan, Y.; Lessard, P.

doi: 10.1080/09593330.1998.9618670pmid: N/A

Many methods exist to monitor the microbial activity of a biological treatment process. These methods have been used mostly for suspended biomass rather than for fixed film processes: the sampling of the biomass in the latter case is more difficult, especially for a full scale plant. For the biofiltration processes, this difficulty can be avoided by the use of the washwaters which however have to be proven to be representative of the biofilter's biomass. The objective of this paper is to assess the microbiological representativity of the washwaters when compared to the fixed biomass of a full scale biofiltration process, Biodrof®. The organisms selected to compare washwaters and fixed biomass are: heterotrophic aerobic bacteria (HAB), Pseudomonas, Flavobacterium, Aeromonas, moulds and yeasts. The vertical distribution of HAB has also been evaluated across the biofilter in order to verify if a vertical stratification occurred in this kind of process. The results showed no significant differences between mean counts (t-Test) of microorganisms in washwaters and fixed on the media suggesting the representativenness of the washwaters with the fixed biomass. No vertical distribution of HAB was observed from the different depths (0–25cm, 45–70cm, 90–115cm) across the biofilter: the same mean counts (statistic Anova) are observed at each depth suggesting an homogeneous vertical distribution of microorganisms in the Biodrof® process studied.

Esnaola, M. V.; Millán, E.

doi: 10.1080/09593331908616713pmid: N/A

A leaching experiment with reconstructed soil columns was conducted in order to assess the effect of irrigation with water at different pH values on three soils affected by different sources of heavy metals (mining works, industry and vehicle emissions). The leachates obtained were characterised by their pH, conductivity, alkalinity, oxidizable matter and heavy metal concentrations. The relationship among these parameters was studied by factor analysis. Metal concentrations were low and decreased quickly in successive leachates. Therefore, not very hazardous leachates are expected from these soils, unless continuous metal input causes greater concentrations in the leachates produced in the field compared with the laboratory experiment. No significant differences were observed in the leachates produced by the different treatments. The experiment caused a drop in the pH of one of the soils and a decrease in the base saturation and an increase in the contents of CaCl2-extractable Cd, Mn and Zn in the three soils. These changes observed in the soils were not related with the pH of the irrigation water, but must be linked to an internal acidity source in the soils.

Clark, T.; Stephenson, T.

doi: 10.1080/09593331908616714pmid: N/A

Chemical wastewater treatment is a commonly used and highly effective process. Chemicals can be dosed at a series of different points during the full treatment process. As addition directly to the biological system, or ‘co-precipitation’, becomes increasingly popular, the direct effect of the chemicals on the biomass becomes of interest. The two major reasons for dosing chemicals in this manner are for phosphorus removal and the prevention of sludge bulking/foaming. Another possible use for chemicals at this point is for enhancement of biological treatment via micronutrient addition. This paper demonstrates the effectiveness of the use of chemicals for these three functions as well as exploring their effect on the biomass. The possibility of chemical dosing to achieve good phosphorus removal, sludge bulking control and biological treatment enhancement is also considered. Certain vitamins and trace metals were found to benefit aerobic biological treatment and other advantages of their use were improved sludge bulking control and alternative sludge disposal routes. However, some toxic effects have been reported if overdosed and the required concentration is difficult to determine. Chemicals used for phosphorus removal during co-precipitation have been found to control sludge bulking problems, increase BOD and suspended solids removal and enhance the removal of trace metals amongst other benefits. Drawbacks included nitrification/denitrification inhibition and increased sludge volume. Beneficial effects of chemicals used primarily for sludge bulking control included phosphorus removal, increased BOD and suspended solids removal and biological treatment enhancement. Detrimental effects included increased sludge production and increased costs.

Welander, U.; Henrysson, T.

doi: 10.1080/09593331908616715pmid: N/A

Leachate from a Swedish municipal landfill in the methanogenic phase was nitrified and then treated by various physical and chemical methods: oxidation with Fenton's reagent and with ozone, precipitation with ferric chloride and with aluminum sulphate and adsorption onto activated carbon. The leachate was analyzed by measuring the COD (chemical oxygen demand), the BOD7 (biochemical oxygen demand) and the TOC (total organic carbon). Specific organic compounds were analyzed by GC/MS (gas chromatography and mass spectrometry) while the molecular weight of the organic matter was determined by ultrafiltration. The nitrification process resulted in 20–30% of the COD being removed. The maximum COD removed after nitrification and oxidation was 80% using Fenton's reagent and 54% using ozone. The combination of nitrification and precipitation gave a maximum COD removal of 68% using ferric chloride and 54% using aluminum sulphate, while nitrification and adsorption onto activated carbon gave a maximum COD removal of 76%. A combination of nitrification, precipitation with ferric chloride and adsorption on activated carbon gave a TOC removal of 96%. The ultrafiltrations showed that nitrification and adsorption onto activated carbon were the most efficient processes for the removal of low molecular weight compounds. The GC/MS analyses showed that, for instance, C3-substituted benzenes and C2-C4 substituted phenol isomers were degraded during the nitrification process, while phthalates were unaffected even after treatment with Fenton's reagent or by adsorption onto activated carbon.

Trouve, C.; Chazal, P. M.; Gueroux, B.; Sauvaitre, N.

doi: 10.1080/09593331908616716pmid: N/A

Nitrates removal from waters can be achieved by physicochemical or by biological means. The use of ion exchange processes can be applied in both superficial and ground waters. The biological technologies are restricted nowadays to groundwater, because the heterotrophic microorganisms implied in such processes in the case of superficial waters generally have a weak efficiency during winter time leading to troubles such as the release of nitrites, which are intermediary products of the reduction procedure. Biological autotrophic processes using Thiobacillus denitrificans have been elaborated at least at a pilot scale, and with a good efficiency. Until now no work had been done upon the ability of this bacterium to denitrify under non standard conditions, including low temperatures. The purpose of this work was to isolate environmental Thiobacillus denitrificans strains able to remove nitrates under unusual temperature and pH conditions. We isolated several psychrophilic strains, some of them removing nitrates at 5°C in fixed cultures, and at pH ranging from 6 to 8, in batch conditions. The sulphur sources influenced nitrates removal and were classified as S2O3 2− > FeS > FeS2 > S°, according to the affinity of Thiobacillus denitrificans for the source.

Ohkubo, N.; Yagi, O.; Okada, M.

doi: 10.1080/09593331908616717pmid: N/A

The effects of chelate substances on the growth of Microcystis aeruginosa K-5 in Lake Kasumigaura water were investigated. A chelate compound, EDTA (Ethylenediaminetetraacetic acid disodium salt) and natural chelate substances, such as humic and fulvic acids isolated from Lake Kasumigaura sediment, stimulated the growth of the K-5 strain. We investigated the mechanism of this stimulation by chelate compounds. The toxicity of heavy metals such as copper, nickel, and zinc, and the alleviation of heavy metal toxicity by chelate compounds were determined. The 50% growth inhibition (EC50) values of copper and zinc for the K-5 strain were 8.4 and 11.4µg l−1, respectively, close to levels measured in Lake Kasumigaura. Humic and fulvic acids mitigated copper and zinc toxicity. Humic and fulvic acids may significantly affect the occurrence of water blooms of Microcystis in Lake Kasumigaura.

Young, E.; Banks, C. J.

doi: 10.1080/09593331908616718pmid: N/A

A heat treated non viable cell suspension of the fungus Rhizopus oryzae was used for the removal of low concentrations of lindane from aqueous solution in a series of shake flask experiments. Experimental design was such as to allow the data to be tested against the Freundlich adsorption isotherm model thus quantifying the effect of experimental variables on both the adsorption capacity and intensity of adsorption exhibited by the fungus. The effects of temperature (5–45°C), pH (2.0–10), biomass density (1–12 g l−1) and biomass age (1–7 days) were studied. The results indicated that the mechanism of adsorption was by physical bonding of the negatively charged lindane molecule to the negatively charged fungal cell wall with hydrogen ions acting as the bridging ligand. Adsorption was most effective at low temperature and pH and was shown to be influenced, to a lesser extent, by cell density and biomass age. Data are presented in the form of adsorption isotherms and the Freundlich parameters associated with each of the experimental variables tabulated.

Wibulswas, R.; White, D. A.; Rautiu, R.

doi: 10.1080/09593331908616719pmid: N/A

This paper deals with the synthesis and use of alumina-pillared clays, Al-PILCs, for water treatment in removing humic substances. Al-PILCs represent a new class of adsorbents with an increased potential for the removal of colour generating compounds such as ‘humic’ and ‘fulvic acids’. High content Al-PILCs were synthesised. Various thermal treatment conditions, 453K and 673K, and the effect of ultrasonic treatment during the preparation of Al-PILCs were also explored. Comparative adsorption experiments were conducted with Montmorillonite, as the starting clay as a reference material, and several different batches of Al-PILCs. Adsorption of ‘humic acid’ from both distilled and tap water were studied. A maximum adsorption capacity of 23.4 mg g−1 of ‘humic acid’ on Al-PILCs was obtained with PILC-O-453 which represents Al-PILCs treated at 453K. Al-PILCs are more effective at removing ‘humic acid’ from tap water especially at high ‘humic acid’ concentrations. The adsorption process is described by Langmuir-type isotherms. It is shown by these experiments that Al-PILCs represents a valuable adsorbent for the removal of colour-generating compounds such as ‘humic acid’.

Muhammad, N.; Parr, J.; Smith, M. D.; Wheatley, A. D.

doi: 10.1080/09593331908616720pmid: N/A

This paper is concerned with the microbiological uptake of heavy metals in slow sand filtration (SSF) and the determination of active biomass by organic nitrogen analysis described herein. The heavy metal accumulation and the total biomass in the schmutzdecke scrapings were determined and compared. The heavy metals were extracted from the sand scrapings by means of HNO3-HCl digestion. The percentage nitrogen content of volatile solids (VS) for the same sand scrapings were determined, and this measure was taken as being directly equivalent to the biomass in the schmutzdecke scrapings. The results show that the more the biomass, the greater the metal accumulation, which indicates microbiological accumulation/uptake rather than simple adsorption of heavy metals in SSF.