Mass transfer resistance in ASFF reactors for waste water treatment

Analysis of mass transfer resistances was performed for an aerated submerged fixed-film reactor (ASFF) for the treatment of waste water containing a mixture of sucrose and ammonia. Both external and internal mass transfer resistances were considered in the analysis, and characterized as a function of feed flow-rate and concentration. Results show that, over a certain operating regime, external mass transfer resistance in the system was greater for sucrose removal than ammonia. This is because the reaction rates for carbon removal were much larger than those of nitrogen. As a result, existence of any form of mass transfer resistance caused by inadequate mixing or diffusion limitations, strongly affects the overall removal rates of carbon more than nitrogen. Effects of the internal m?ss transfer resistance were virtually non-existent for ammonia removal. This behaviour was found over two orders of magnitude range for the effective diffusivity for ammonia, and one order of magnitude for the film specific surface area. However, over the same parameters' range, it is found that sucrose removal was strongly affected upon lowering its effective diffusivity and increasing the film specific surface area.     

Influence of reduced dietary calcium on the accumulation and effects of lead, cadmium, and aluminum in birds

The influence of low dietary calcium on the accumulation and effects of dietary lead, cadmium and aluminum was examined in zebra finches and ring doves. In zebra finches fed a diet containing 0.3% Ca, the hepatic and renal accumulation of lead was enhanced approximately 400% and of cadmium about 150-200%, compared to birds fed a 3.0% Ca diet. Low dietary Ca also caused bones of female finches to lose an average of about 60% of their normal Ca content. Loss of bone-Ca was also observed in male finches, but was less than in females. In reproductively active ring doves, low (0.4%) dietary Ca enhanced the accumulation of lead and cadmium, but not of aluminum, compared with accumulation in doves consuming a 2.0% Ca diet. Enhanced accumulation of lead and cadmium was accompanied by increased synthesis of the metal-binding protein metallothionein and by greater inhibition of delta-aminolevulinic acid dehydratase activity. These results indicate that, under conditions of reduced dietary Ca availability, such as can occur in acid-impacted environments, wild birds risk increased uptake of certain toxic metals and may accumulate toxic concentrations of these metals more rapidly. Researchers should take account of dietary Ca levels when interpreting results of dosing studies in which metals such as lead and cadmium are administered to birds.     

Long-term trends and sources of organochlorine contamination in Canadian tundra Peregrine Falcons, Falco peregrinus tundrius

Levels of eggshell thinning, and organochlorine residues in egg contents, blood plasma of adults and juveniles, tissue samples, and prey species were determined for a population of migratory Peregrine Falcons (Falco peregrinus tundrius) breeding in the Canadian Arctic. Temporal trends were assessed by comparing data collected during 1991-1994, with data from 1982-1986, for the same population. Shells (n=54) from 1991-1994 averaged 15% thinner than eggs produced prior to the introduction of DDT. No improvement in shell thickness was detected between decades. Mean DDE residue levels in eggs showed a decline from 7.6 mg kg (1982-1986) to 4.5 mg kg (1991-1994), but there was no significant change in SigmaPCB residues. Moreover, the proportion of clutches with eggs exceeding critical SigmaPCB, DDE, and dieldrin residue levels (10%) did not change between decades. Relative to Greenland and Alaskan populations, F. p. tundrius at Rankin Inlet show high levels of organochlorine contamination and little reduction in residues over the last decade. These Tundra Peregrines continue to be exposed to organochlorines in Latin America; however, results also link relatively high levels in the study population with waterfowl species that do not leave Canada in winter.     

Environmental management auditing: When credentials count!

We all know that the process of driving a car is not as simple as turning a key in the ignition and moving. When you want to drive a car, you take a written test to show your knowledge of the rules of the road. You learn to operate a vehicle (remember the operating difference between a standard shift and an automatic?) and then how to operate that vehicle in moving traffic. After you have gained competence in vehicle operation, you take a “hands-on” driving test to prove to an independent third party (the State) that you know what you are doing. Then, if you do know, you are issued a license, subject to renewal and perhaps retesting at some later point in time. Your license has become your credential to operate. It implies a certain minimum level of knowledge and experience. Should environmental auditing be any different? This article considers the application of a uniform standard for environmental auditor qualification. With an emphasis on ISO 14001¹ and auditing of environmental management systems, it discusses:

• the evolution of environmental auditing;
• established environmental auditor qualification processes;
• limitations of compliance auditing; and
• characteristics of a good auditor.

     

Control of ammonia toxicity to Hyalella azteca by sodium, potassium and pH

The toxicity of ammonia to Hyalella azteca at constant pH in artificial media was controlled by sodium and potassium, and not by calcium, magnesium, or anions. Small increases in the LC50 for total ammonia (from 0.15 to 0.5 mM) occurred as sodium was increased from 0.1 to 1 mM and above, but major increases in the LC50 (to over 10 mM total ammonia) required the addition of potassium. Potassium was, however, more effective at reducing ammonia toxicity at high (1 mM) sodium than at low (0.1 mM) sodium. Ammonia toxicity was independent of pH at low sodium and potassium concentrations, when ammonia toxicity appeared to be associated primarily with aqueous ammonium ion concentrations. At high sodium and potassium concentrations, the toxicity of ammonia was reduced to the point where un-ionized ammonia concentrations also affected toxicity, and the LC50 became pH dependent. A mathematical model was produced for predicting ammonia toxicity from sodium and potassium concentrations and pH.     

The uptake of particulates by an urban woodland: site description and particulate composition

Woodlands may improve local air quality by increasing the uptake rates of gaseous, particulate and aerosol pollutants from the atmosphere and can also act as relatively permanent sinks for some pollutants. Rough Wood, Walsall was selected for a study of the material which accumulates on tree foliage because of its location in a densely populated urban area, and its proximity to a motorway with high traffic flow (the M6) and to other pollutant sources. Methods were developed for leaf washing to allow determination of the quantity of dust and the identification of the dust particles present on oak leaves. Elemental analysis of particles was also undertaken using scanning electron microscopy coupled with electron probe microanalysis. A large proportion of particles were organic in origin. Of the inorganic particles, the majority contained silicon and aluminium in varying proportions suggesting that they were soil derived. Some particles were clearly identified as the products of combustion, and sea or road salt was present on leaf surfaces. Some particles contained copper, tin and titanium which may reflect the proximity of Rough Wood to local metal workings. The number of particles counted on leaf surfaces decreased as distance from the motorway increased.     

Biomonitoring environmental contaminants near a municipal solid-waste combustor

Tetrachlorodibenzo-p-dioxin (TCDD), tetrachlorodibenzofuran (TCDF) and selected metal concentrations were measured in eggs and nestlings of anhingas (Anhinga anhinga) and white ibises (Eudocimus albus) collected from a colony next to a municipal solid-waste (MSW) combustor and ash landfill. Most of the measured residues, including TCDD, TCDF, arsenic, beryllium, cadmium and nickel, remained at pre-operational levels during the first five years of facility operation. Selenium (in anhingas) and mercury (in both anhingas and ibises) occurred at their lowest concentrations in samples collected during the fifth year of facility operation (Year-5). Alternatively, concentrations of lead in ibis nestlings were highest in Year-1 and Year-5 compared to Year-0. The MSW combustor could neither be ruled out nor confirmed as the source of this lead.     

The influence of particle surface characteristics on pollutant metal uptake by cells

The phosphatic mineral, hydroxyapatite, and two ion exchange resins have been used as artificial sediment particles. The surface properties of these materials have been studied using the Langmuir adsorption isotherm to calculate the binding capacity (B(max)) and the adsorption constant (K(L)) for zinc and cadmium ions. Mussels (Mytilus edulis) were fed on the particles and their digestive glands were subsequently removed and subjected to cell fractionation. The supernatant fraction was used to determine cytosol metal levels as a measure of the materials absorbed from the ingested particles. The level of cytosol zinc and cadmium was correlated with the K(L) values of the artificial sediments. It is suggested that phagocytosis of sediment particles plays an important part in transferring pollutants into benthic organisms and that the efficiency of this process is related to the adsorption coefficient of the particle surfaces.     

The fate of endosulfan in aquatic ecosystems

Endosulfan, one of the major pesticides used in cotton-growing, is of environmental concern because of its toxicity to fish and its apparent persistence in the environment. This study examines the distribution and degradation pathways for endosulfan in an aquatic system and the processes by which it is removed. In the alkaline waters of the cotton region, hydrolysis is the dominant degradation process. By this mechanism alone, the expected half-lives for the alpha- and beta-endosulfan isomers were found to be 3.6 days and 1.7 days, respectively. Partitioning studies showed, however, that the major proportion of endosulfan would associate with the sediments (log Koc(alpha) 3.6 and log Koc(beta) 4.3). Field studies confirmed the presence of high concentrations in sediments. Microcosm experiments showed that loss of endosulfan was slower than predicted from hydrolysis rates. Models are presented to explain how desorption from sediment limits the loss of endosulfan from a system.     

Reproduction of mallards following overwinter exposure to selenium

Forty pairs of mallards (Anas platyrhynchos) were fed 15 ppm selenium as selenomethionine for about 21 weeks during winter. Twenty pairs served as controls. At the end of 21 weeks, which coincided with the onset of the reproductive season, selenium treatment was ended. Four birds died while on selenium treatment. Treated females lost weight, and their egg-laying was delayed. Hatching success of some of the first eggs laid by selenium-treated females was lower than that of controls, and a few of these early eggs contained deformed embryos, but, after a period of about two weeks off the selenium-treated diet, reproductive success returned to a level comparable with that of controls. The return to normal reproductive success was the result of a corresponding decrease in selenium concentrations in eggs once selenium treatment ended.