Catalytic-Iron Filters for Effective and Low-Cost Treatment of Odorous Air

Several methods are available to remove hydrogen sulphide and volatile organic sulphides from ventilated air at sewage-treatment works. Some methods use alkaline and oxidative chemical scrubbers which may have high capital and operational costs. Other methods, such as bio-scrubbers and bio-filters, are used to biochemically oxidize sulphides. Biological scrubbers have the advantage of low operating costs, but their performance may be adversely affected by a high concentration of sulphide (> 100 ml/m³).
This paper describes the development of a novel, compact and low-cost 'rusty-iron' chemical filter which catalyzes the oxidation of hydrogen sulphide and organic sulphides to colloidal sulphur and water. Operating costs are relatively low, with no need for routine maintenance. Full-scale demonstration of the effectiveness of such filters was carried out over two years at several treatment works, the results of which are described and discussed together with details of capital costs. The overall percentage removal of hydrogen sulphide by compact multistage filters was found to exceed 95%, irrespective of inlet sulphide concentrations which varied from 34 to 500 ml/m³ (ppm).     

Studies on marine biological filters: Model filters

Model systems of 401. capacity were used to study chemical changes which affected buffering in continuously recycled sea water and which restricted nitrification in percolating biological filters at 28°C.

Sustained hydrogen ion production during the microbial oxidation of ammonia to nitrite caused continuous carbon dioxide formation from carbonate and bicarbonate. The carbon dioxide was steadily lost to the air through vigorous aeration, leaving < 2 mg inorganic carbon 1⁻¹ in the sea water. Oxidation of nitrate to nitrate did not significantly reduce pH nor deplete buffer capacity.

Ammonia oxidation was severely inhibited by the combination of low pH and dissolved inorganic carbon levels, but similar low levels of pH produced when carbon dioxide was bubbled through the water had only a moderate effect. Inhibition could be rapidly overcome or prevented by additions of inorganic carbon, sodium hydroxide or sodium dihydrogen phosphate.

Values recorded for the maximum specific growth rate of Nitrosomonas and Nitrobacter were 0.53 and 0.81 d⁻¹ respectively. The corresponding generation or doubling times were calculated to be 31.4 and 20.5 h.

Some evidence was found for the uptake of phosphate and the formation of hydroxylamine during nitrification.     

Micro-organisms and manganese cycling in a seasonally stratified freshwater dam

This work describes investigations into the role that biotic and abiotic mechanisms play in the manganese redox cycle in a freshwater dam over a twelve month period. Enzymatic control of manganese oxidation was taking place with a temperature optimum of approx. 30°C. Manganese oxidation was only significant above about 19°C. The temperature and season play vital roles in determining the extent to which abiotic and microbial mechanisms contribute to manganese oxidation. Results showed that microbial catalysis is overwhelmingly responsible for manganese oxidation in the lower epilimnion from November to May. Significant abiotic catalysis (up to 25%) can occur in late summer/autumn when the water temperature is greatest. Mn(II) oxidation, pseudo-first order rate constants to 1.12 × 10²² M⁻⁴ · d⁻¹ were measured while poisoned sample experiments confirmed the role of biological mediation. In winter, biological control could not occur because of the lower temperature of the water column. The measurement of “x” in MnO_x showed that higher manganese oxidation states were expected when the manganese oxidation rate was at a maximum and therefore when microbial activity was greatest. Direct microbial reduction of MnO_x in the water column was of much less significance. However, indirect reduction may have taken place through the reaction of MnO_x with sulfide. The results of this work have important implications for the design and operation of artificial destratification units for the control of manganese speciation.     

Influence of method and duration of curing and of mix proportions on strength of concrete containing laterite fine aggregate

In this paper, the influence of six curing methods (water, air, moist soil, jute bag, air/water and water/air) on the compressive strength of concrete cube specimens that contain laterite fine aggregate is investigated. Three different mixes of cement, laterite and gravel were used: ; 1:2:4 and 1:3:6 with water/cement ratios of 0.62, 0.75 and 1.02 by weight respectively. Four curing ages of 7, 14, 21 and 28 days were adopted. The results showed that the strength that a particular mix can attain is affected by the curing method used. The water/air curing technique gave the highest strength values of 28.2 Nmm⁻² for Nmm⁻² and 17.4 Nmm⁻² for 1:2:4 and 1:3:6 mixes respectively, while the air-cured specimens gave the lowest strength values of 17.2 Nmm⁻² for Nmm⁻² and 8.0 Nmm⁻² for 1:2:4 and 1:3:6 mixes. The higher the cement/aggregate ratio the higher the strength. Generally, there was increase in strength with age irrespective of the mix and the curing technique.     

Removal of cadmium and manganese by a non-toxic strain of the freshwater cyanobacterium Gloeothece magna.

The ability of both living and dry cells of Gloeothece magna, a non-toxic freshwater cyanobacterium, to adsorb cadmium and manganese is demonstrated in this study. Chlorophyll a content of living cells was not influenced by either cadmium or manganese concentrations, indicating that adsorption of both Cd²⁺ and Mn²⁺ by living cells of G. magna, was independent of the metabolic state of the organism. Moreover, the adsorption of both Cd²⁺ and Mn²⁺ to living cells and dry cells, was dependent on the metal concentrations, and fitted the Freundlich adsorption isotherm. However, dry cells had larger binding capacity for both Cd²⁺ (K_f=912.6) and Mn²⁺ (K_f=2398) than living cells (K_f=151.4 & 63, respectively). The role of the capsular polysaccharides, the main constituents of the cyanobacterial envelope, in binding these two metals was also studied. Polysaccharide extracts of this organism adsorbed high amounts of both Cd²⁺ (115–425 μg mg⁻¹) and Mn²⁺ (473–906 μg mg⁻¹). This study suggests that G. magna would probably be cultured in water bodies contaminated by heavy metals to ameliorate their toxicity. Also dry material of this cyanobacterium being a non-toxic species, could be used as a safe biofilter to remove toxic metals from drinking water.     

Removal of As(III) and As(V) from water using a natural Fe and Mn enriched sample

The arsenic removal capacity of a natural oxide sample consisting basically of Mn-minerals (birnessite, cryptomelane, todorokite), and Fe-oxides (goethite, hematite), collected in the Iron Quadrangle mineral province in Minas Gerais, Brazil, has been investigated. As-spiked tap water and an As-rich mining effluent with As-concentrations from 100 μg L⁻¹ to 100 mg L⁻¹ were used for the experiments. Sorbent fractions of different particle sizes (<38 μm to 0.5 mm), including spherical material (diameter 2 mm), have been used. Batch and column experiments (pH values of 3.0, 5.5, and 8.5 for batch, and about pH 7.0 for column) demonstrated the high adsorption capacity of the material, with the sorption of As(III) being higher than that of As(V). At pH 3.0, the maximum uptake for As(V) and for As(III)-treated materials were 8.5 and 14.7 mg g⁻¹, respectively. The Mn-minerals promoted the oxidation of As(III) to As(V), for both sorbed and dissolved As-species. Column experiments with the cFeMn-c sample for an initial As-concentration of 100 μg L⁻¹ demonstrated a very efficient elimination of As(III), since the drinking water limit of 10 μg L⁻¹ was exceeded only after 7400 BV total throughput. The As-release from the loaded samples was below the limit established by the toxicity characteristic leaching procedure, thus making the spent material suitable for discharge in landfill deposits.     

Removal of metal ions by modified Pinus radiata bark and tannins from water solutions

Pinus radiata bark and tannins, chemically modified with an acidified formaldehyde solution were used for removing metal ions from aqueous solutions and copper mine acidic residual waters. The adsorption ability to different metal ions [V(V), Re(VII), Mo(VI), Ge(IV), As(V), Cd(II), Hg(II), Al(III), Pb(II), Fe(II), Fe(III), Cu(II)] and the factors affecting their removal from solutions were investigated. Effect of pH on the adsorption, desorption, maximum adsorption capacity of the adsorbents, and selectivity experiments with metal ion solutions and waste waters from copper mine were carried out. The adsorbents considerably varied in the adsorption ability to each metal ion. The adsorption depends largely upon the pH of the solution. Modified tannins showed lower adsorption values than the modified bark. For the same adsorbent, the maximum capacity at pH 3 for the different ions were very different, ranging for modified bark from 6.8 meqg⁻¹ for V to 0.93 meqg⁻¹ for Hg. Waste waters were extracted with modified bark as adsorbent and at pH 2. The ions Cu(II) (35.2 mgL⁻¹), Fe(III) (198 mgL⁻¹), Al(III) (83.5 mgL⁻¹) and Cd(II) (0.15 mgL⁻¹) were removed in 15.6%, 46.9%, 83.7% and 3.3%, respectively, by using 1 g of adsorbent/10 mL of waste water. In general, a continuous adsorption on a packed column gave higher adsorbed values than those observed in the batchwise experiment.     

Estimation of film accumulation in percolating filters: Comparison of methods

Estimation of film accumulation is necessary for the successful operational management of percolating filters. Prevention of ponding and loss of performance due to excessive film accumulation, and the optimization of the recirculation and alternating double filtration processes can only be achieved by regular monitoring of film growth. Five methods of determining film accumulation are compared; total film weight, total dry solids, volatile solids, percentage settlement of solids and the neutron scattering technique. The methods were used to monitor the film growth in pilot filters containing a mineral and a random plastics medium, over two twelve-month loading periods at 1.68 m³ m⁻³ day⁻¹ (0.28 kg BOD m⁻³ day⁻¹) and 3.37 m³ m⁻³ day⁻¹ (0.63 kg BOD m⁻³ day⁻¹).

Good correlations (P < 0.001) are found between all methods at the lower loading although the neutron scattering results are not significantly correlated (P > 0.10) with any of the gravimetric methods at the higher loading. Although the neutron scattering technique does provide a rapid and sensitive measure of hydrogen atoms in the filter, the results, expressed as percentage saturation of the voids, are not directly transferable to film weights and should be treated separately and not as a true measure of film accumulation.     

反硝化滤池反冲洗效能综合影响因素及微生物种群

采用正交实验考察了水冲洗强度、水单独漂洗时间、气水联合冲洗时间、气冲洗强度、滤料粒径对反硝化滤池反冲洗效能及微生物种群的综合影响。结果表明,当以反硝化滤池运行周期、耗水量、系统恢复时间作为反冲洗效能的综合评价指标时,各因素对综合评价指标影响的显著性次序为:水冲洗强度>气水联合冲洗时间>气冲洗强度>滤料粒径>水单独漂洗时间;得出气水联合反冲洗最优工况参数如下:滤料粒径为2~4 mm、气冲洗强度为15 L/(m²·s)、水冲洗强度为10 L/(m²·s)、气水联合冲洗时间为8 min。PCR-DGGE分析结果表明,反冲洗对滤料层生物量、生物种群多样性有显著影响,对滤料层生物活性、微生物种群丰度影响不显著。     

Phytoplankton biomass and production in the river meuse (Belgium)

The biomass and production of the phytoplankton in a relatively unpolluted reach of the River Meuse (Belgium) were followed through two years (1983 and 1984). Chlorophyll a varied from 0.2 to about 120 mg m⁻³, and production ranged between 0.05 and 5.78 gC m⁻² d⁻¹. The mean photosynthetic quotient (PQ) was 1.25.

The parameters of the light-photosynthesis relationship (P_opt and l_k) were calculated and related to the variations of temperature and light in the water column. A simple model allowed calculations of the annual production, which was estimated to be 494 gC m⁻² yr⁻¹ in 1983 and 547 gC m⁻² yr⁻¹ in 1984.

Finally, a simple model is developed, which explains the relationship between phytoplankton development and discharge; this model shows how the effect of discharge can be described by a “dilution rate” of the plankton growing in the river water.     

Interstitial inorganic phosphorus concentrations in lakes Mendota and Wingra

Interstitial P levels in Lake Mendota and Lake Wingra were evaluated as a function of season and water column and sediment depth. Interstitial water was obtained by the centrifugation-filtration method. Temporal variations were observed over the entire 15 cm sediment depth interval examined in all four locations evaluated. Interstitial reactive P (IRP) levels in Lake Mendota ranged from 0.014–1.67 mg l⁻¹ at the 5–6 m water column depth and from 1.20–5.75 mg l⁻¹ at the 18–19.5 m depth. IRP levels in Lake Wingra ranged from 0.029–2.15 mg l⁻¹ at 3.5 m and from 0.191–3.96 mg l⁻¹ at 2 m. Variations in interstitial P were attributed to variations in oxidation state of Fe as influenced by oxygen transport and reduction rates.     

Lagooned, secondary effluents as water source for extended agricultural purposes

Chlorination of trickling filter effluents at 40 mg l⁻¹ chlorine for 4 h and 20 mg l⁻¹ for 4 and 6 h showed very limited coliform survival. The number of viruses decreased from a few hundred in 100 ml before chlorination to 0 after chlorination. A 70,000 m³ pond (4 m deep) was used for holding non-chlorinated secondary effluents for 73 days. Bacterial and viral counts were performed every few days. In addition BOD, TC, pH and solar radiation were monitored. After this, the water was pumped out and chlorinated in a pipeline with 8 or 20 mg l⁻¹ chlorine. After chlorination the coliform count was reduced by from 3 to 5 orders of magnitude. After storage for 43 days the non-chlorinated secondary effluents viral count was nil. After chlorination these effluents were also virus-free.

In the second experiment, secondary effluents chlorinated with 20 mg l⁻¹ chlorine with a contact period of 2 h. They were then introduced to the pond. No viruses were found in the incoming water, neither during holding nor after the second chlorination, Coliform regrowth was very slow because of the temperature of the water was only 18–20°C. Identification of the M. Endo membrane filter grown isolated colonies proved that E. coli I disappeared, and all the coliforms were of non-fecal origin or that other growths were non-coliform organisms growing on the MF.

The third experiment was a repetition of the first, in spring, after the temperatures rose. The results confirmed the findings in the first experiment. Therefore, it is thought that 70 days holding of wastewater would permit its extensive agricultural use. For safety, the addition of 20 mg l⁻¹ chlorine to effluents and a short storage could be adequate from a public health point of view.     

The effect of biofilter loading rate on the removal of organic ozonation by-products

The effect of biofilter loading rate on the removal of organic ozonation by-products (OBPs) was studied in three biofilters used for the pretreatment of drinking water. One of the biofilters contained plastic biofilm media (KMT) and the two others contained expanded clay aggregates (Filtralite). Tests were carried out with ozonated humic water at several OBP concentration levels using empty bed contact times (EBCTs) from 6.2 to 48 min. The sum of aldehyde (formaldehyde, acetaldehyde, glyoxal and methyl glyoxal) and acetone concentrations ranged from 21 to 77 μg l⁻¹ in the ozonated water. The total ketoacid (glyoxylic, pyruvic, and ketomalonic acids) concentrations varied from 92 to 521 μg l⁻¹. The results were modelled using a first-order model including parameter for minimum substrate concentration (S_min). The OBPs showed different sensitivities to decreasing EBCT. Formaldehyde and pyruvic acid had the highest specific removal rates and their removal was little affected by increased loading rate. Ketomalonic acid had the lowest specific removal rate and its removal efficiency was reduced most with decreasing EBCT. The other studied OBPs had specific removal rates close to each other. The ketoacids had higher S_min concentrations than aldehydes and the S_min concentrations were influenced by the influent OBP concentrations. The biofilter media did not have a significant effect on OBP removal efficiency. Generally, over 80% removal efficiency was obtained for OBPs at EBCTs over 20 min. The significance of OBP concentrations close to S_min for the biological stability of drinking water needs to be determined.     

Development of an advanced biological treatment system applied to the removal of nitrogen and phosphorus using the sludge ceramics

To develop a method of forming lake sediment into sludge ceramics with porosity and good biological adhesion for use as a medium for microorganisms in wastewater treatment, a study of the effects of forming conditions was conducted by adjusting the water content of sludge and compounding some additives. By adjusting the water content of the raw material at the kneading/pelletizing step to 40–42% and adding 3% waste glass to the raw materials to make up for the lack of flux, a sludge ceramic with a density in terms of specific gravity of saturated surface dry aggregate of about 1400 kg m⁻³ was formed. In addition, to develop a small-scale wastewater treatment system capable of removing nitrogen and phosphorus, a sludge ceramic was applied as a medium for biological filtration. The results indicated that the BOD removal nitrification rate were superior to those of conventional ceramic media, reached at 95.3% and 87.4%, respectively. The introduction of iron electrolysis resulted in high treatment performance achieving BOD levels of 10 mg L⁻¹ or less, T-N of 10 mg L⁻¹ or less and T-P of 1 mg L⁻¹ or less.     

Impacts of impregnation with Imersol-Aqua on the compression strength of some solid wood materials

The aim of this study was to investigate the effects of impregnation with Imersol-Aqua on the compression strength of some solid wood materials. For this aim, Oriental beech (Fagus orientalis Lipsky), European oak (Quercus petrea Liebl.), Scotch pine (Pinus sylvestris Lipsky), Uludag fir (Abies Bornmülleriana Mattf.), Oriental spruce (Picea orientalis Lipsky) and Lombardy poplar (Populus nigra Lipsky) wood samples were prepared according to TS 2595 and impregnated with Imersol-Aqua, commonly being used in construction wood materials by the method of short, medium and long-term of dipping according to ASTM D 1413 and producers’ definition. After the impregnation process, compression strength was measured according to TS 2595. Consequently, among the non-impregnated wood materials, the highest compression strength was obtained in beech and pine samples. Compression strength at this situation from the highest to lowest can be enumerated beech, pine, oak, spruce, fir and poplar. With regard to the impregnation period, the sequence form the highest to lowest was as long-term, medium-term and short-term dipping. In the interaction of wood material and impregnation period, the highest compression strength values were obtained in Scotch pine (71.220 N mm⁻²) impregnated with long-term dipping method whereas the lowest in Lombardy poplar (35.710 N mm⁻²) impregnated with short-term dipping method.

In consequence, in the massive constructions and furniture elements that the compression strength after the impregnation is of great concern, long-term impregnation of solid wood material could be recommended.     

Modelling of volatile organic compounds emission from dry building materials

A numerical and an analytical model were developed to predict the volatile organic compound (VOC) emission rate from dry building materials. Both models consider the mass diffusion process within the material and the mass convection and diffusion processes in the boundary layer. All the parameters, the mass diffusion coefficient of the material, the material/air partition coefficient, and the mass transfer coefficient of the air can be either found in the literature or calculated using known principles.

The predictions of the models were validated at two levels: with experimental results from the specially designed test and with predictions made by a CFD model. The results indicated that there was generally good agreement between the model predictions, the experimental results, and the CFD results. The analytical and numerical models then were used to investigate the impact of air velocity on emission rates from dry building materials. Results showed that the impact of air velocity on the VOC emission rate increased as the VOC diffusion coefficient of the material increased. For the material with a diffusion coefficient >10⁻¹⁰ m²/s, the VOC emission rate increased as the velocity increased; air velocity had significant effect on the VOC emission. For the material with a VOC diffusion coefficient <10⁻¹⁰ m²/s, the VOC emission rate increased as the velocity increased only in the short-term; <24 h. In the medium to long-term time range, the VOC emission rate decreased slightly as the air velocity increased; velocity did not have much impact on these materials. Furthermore, the study also found that the VOC concentration distribution within the material; the VOC emission rate and the VOC concentration in the air were linearly proportional to the initial concentration. However, the normalized emitted mass was not a function of the initial concentration: it was a function of the properties of the VOC and the material.     

Bioscrubbing: An Effective and Economic Solution to Odour Control at Sewage-Treatment Plants

As a result of odour nuisances from Damhusaaen sewage-treatment works in Copenhagen, it was decided that critical sections of the inlet plant should be covered and enclosed. Ventilated air (6000 m³/h) is cleaned in a bioscrubber, and this installation has reduced the odour around the plant to the extent that it is no longer detectable. A cleaning efficiency (for hydrogen sulphide) of more than 99% and low residual emissions (less than 0.1 mg/m³ of organic sulphur compounds) are achieved by the bioscrubber. Space requirements and operational costs are relatively low, and the bioscrubber has proved to be reliable, requiring minimal maintenance.     

Accumulation of nitrous oxide in aerobic groundwaters

N₂O concentrations in the groundwaters collected in the Kanto District and Nagano Prefecture in Japan and five counties in New York State were determined. These N₂O data were obtained from the water samples from wells, springs and seepages from soils in forests and cropping fields. The N₂O concentrations in all samples greatly exceeded those of atmospheric equilibration. The average concentration of 690 nM N₂O is one order of magnitude larger than that in deep ocean. All groundwaters of the present study were aerobic with a high level of NO₃⁻, but with the absence of NO₂⁻ and NH₄⁺, and with a very low level of dissolved organic carbon. These characteristics suggest that the nitrate respiration in the aquifers is of little significance for the production of N₂O.

ΔN₂O/NO₃⁻ molar ratios in the groundwaters were between 10⁻⁴ and 10⁻² (Δ indicates the excess gas over that which would be in equilibrium). This supports the above view since the observed N₂O yield agrees with that reported for the production during an ammonia oxidation. If nitrification was indeed a major mechanism for the production of groundwater N₂O, subsequent release of N₂O from the aquifers that are polluted with nitrogen may deserve more close attention as a potential source of atmospheric N₂O via diffusion and discharge.     

Electrochemical Treatment of Acidic Aqueous Ferrous Sulfate and Copper Sulfate as Models for Acid Mine Drainage

Acid mine drainage (AMD) is a serious environmental problem in the mining industry. The present work describes electrolytic reduction of solutions of synthetic AMD, comprising FeSO₄/H₂SO₄ and CuSO₄/H₂SO₄, in flow-through cells whose anode and cathode compartments were separated using ion exchange membranes. In the case of FeSO₄/H₂SO₄ at constant flow rate, the pH of the effluent from the catholyte increased progressively with current at a variety of cathodes, due to electrolytic reduction of H⁺ ions to elemental hydrogen. Near-quantitative removal of iron was achieved by sparging air into the catholyte effluent, thereby precipitating iron outside the electrochemical cell, and avoiding fouling of the electrodes. The anode reaction was the oxidation of water to O₂, a proton-releasing process. Using cation exchange membranes and sodium sulfate as the supporting electrolyte in the anode compartment, the efficiency of the process was compromised at high currents by transport of H⁺ competitively with Na⁺ from the anode to the cathode compartments. Higher efficiencies were obtained when anion exchange membranes were used, and in this case no additional supporting electrolyte other than dilute H₂SO₄ was needed, the net reaction being the electrochemically driven transfer of the elements of H₂SO₄ from the cathode to the anode compartments. Current efficiencies 50% were achieved, the loss of efficiency being accounted for by ohmic heating of the solutions. In the case of CuSO₄/H₂SO₄ and anion exchange membranes at high currents, reduction of Cu²⁺ and H⁺ ions and transport of SO₄²⁻ ions out of the catholyte caused unacceptably high potentials to be generated.     

A computer-based system for the acquisition and display of continuous vertical profiles of temperature, salinity, fluorescence and nutrients

A vertical profiling system was developed to continuously measure and simultaneously log temperature, salinity, depth, fluorescence and selected nutrient concentrations (NO₃⁻, NH₄⁺, SiO₄⁴⁻ and PO₄³⁻) in the euphotic zone in coastal waters. A hose was attached to a CTD sensor and lowered through the water at 1 m min⁻¹. Water was pumped to the ship's deck with a diaphragm pump, and passed through a fluorometer and Technicon AutoAnalyzer^® to measure fluorescence and selected nutrients, respectively. A 25 m vertical profile takes about 30 min to complete. These instruments were connected to an analog-to-digital converter, and the data were stored and plotted using an IBM personal computer to simultaneously display real-time vertical profiles of temperature, salinity, fluorescence and several nutrient concentrations. This instrument package is invaluable because it provides real-time data that are essential for choosing discrete sampling depths, and for obtaining a time series of the vertical structure of the euphotic zone of dynamic coastal waters or lakes.