Letters to the editor

Malathion exposure at a concentration above 50 ppm elicited some alteration in the respiratory, swelling and contraction characteristics of mitochondria in the roots of 72 hr germinating seeds of Vigna sinensis (L). Change in these parameters is reflected by seedling growth characteristics of V. sinensis (L). The alteration of mitochondria by malathion (above 50 ppm) is also supported by the experiments which showed a marked leakage of NAD from the intra‐mitochondrial pool and a change in the activities of mitochondrial membrane bound ATPase and acid pyrophosphatase activities. Some change of sterol and phospholipid patterns in the associated mitochondrial membrane are also observed in the roots of the 72 hr germinating seeds of V. sinensis (IS) under malathion exposure (above 50 ppm).     

Comparative studies of the effect of moderate and high altitude stress on human subjects: studies on erythrocyte ghost ATPases

Studies have been carried out on erythrocyte membrane‐bound ATPases of ten female subjects at a moderate altitude (2200 m) and at a high altitude (5100 m). Mg²⁺‐ATPase activity of the subjects was found to be significantly stimulated under conditions at a high altitude in comparison to that at a moderate altitude. The changes in total lipids and cholesterol contents of erythrocyte ghosts and plasma Na⁺/K⁺ levels at high altitude in comparison to the moderate altitude indicates an alteration in the membrane permeability under high altitude stress. On acclimatization of the subjects from a high to a moderate altitude, the studied parameters reverted to the values as observed at a moderate altitude.     

The pH influence on the index properties of clays

Three clay sediments, concerning Pliocenic clay, Chaotic Complex clay and commercial kaolinic clay, have been studied in order to verify the pH influence on the index properties. The analysed clays have been mineralogically characterized in natural, conditions, and in modified pH conditions. This last procedure, obtained respectively by adding NH₄OH or CH₃COOH 1 mol., in a pH range between 4.5–11.3 has been carried out. To verify the different experimental conditions the C.E.C. of exchangeable cations as K⁺, Na⁺, Ca⁺⁺ and Mg⁺⁺, has been measured. The index properties obtained show a different behaviour of the three clays. The kaolin is not much affected only a limited W_L% increase is recognizable when the pH decreases. The Chaotic complex clay evidence a considerable rise of the W_L with the pH uncrease. In the Pliocenic clay the W_L value increased with the pH. The described process can be related to the natural environment, connected also with various pollution phenomena.     

Extracellular polymeric substances (EPS) in upflow anaerobic sludge blanket (UASB) reactors operated under high salinity conditions

Considering the importance of stable and well-functioning granular sludge in anaerobic high-rate reactors, a series of experiments were conducted to determine the production and composition of EPS in high sodium concentration wastewaters pertaining to anaerobic granule properties. The UASB reactors were fed with either fully acidified substrate (FAS) consisting of an acetate medium (reactor R1) or partly acidified substrate (PAS) consisting of acetate, gelatine and starch medium (reactors R2, R3, and R4). For EPS extraction, the cation exchange resin (CER) method was used. Strength and particle size distribution were determined by assessing the formation of fines sludge under conditions of high shear rate and by laser diffraction, respectively. Batch tests were performed in 0.25 L bottles to study Ca²⁺ leaching from anaerobic granular sludge when incubated in 20 g Na⁺/L in the absence of feeding for 30 days. Results show a steady increase in the bulk liquid Ca²⁺ concentration during the incubation period. UASB reactor results show that the amounts of extracted proteins were higher from reactors R2 and R3, fed with PAS compared to the sludge samples from reactor R1, fed with FAS. Strikingly, the amount of extracted proteins also increased for all reactor sludges, irrespective of the Na⁺ concentration applied in the feed, i.e. 10 or 20 gNa⁺/L. PAS grown granular sludges showed an important increase in particle size during the operation of the UASB reactors. Results also show that, addition of 1 gCa²⁺/L to the high salinity wastewater increases the granules' strength.     

Simultaneous nitrification and denitrification in a CEM (cation exchange membrane)-bounded two chamber system

A novel process was developed to induce a simultaneous oxidation of ammonia and denitrification in a single system consisting of two chambers separated by a cation exchange membrane. One was an anoxic chamber and the other was an aerobic chamber. The maximum mass flux via the membrane was calculated as 0.83 mg NH₄⁺-N/m² s in a batch test when the initial concentration of NH₄⁺ was 700 mg N/L. And it was observed that NO₃⁻ and NO₂⁻ moved via the membrane in a reverse direction when NH₄⁺ was transported. When the system was operated in a continuous mode by feeding a wastewater containing glucose and NH₄⁺, it was observed that soluble chemical oxygen demand and NH₄⁺ were simultaneously removed showing 99% and 71  86% of efficiency, respectively. Denitrification occurred in the anoxic chamber and nitrification was carried out in the aerobic chamber.     

The effect of natural water conditions on the anti-bacterial performance and stability of silver nanoparticles capped with different polymers

This study evaluated the effect of natural water composition onto the bactericidal and physicochemical properties of silver nanoparticles (AgNPs) stabilized with three different polymeric compounds.All the nanoparticles behaved similarly in the water conditions tested. Compared to solutions with low organic matter content and monovalent ions, lower disinfection performances of AgNPs suspensions were obtained in the following order seawater ≤ high organic matter content water ≤ high divalent cations content synthetic water. Suspension of AgNPs in seawater and water with divalent cations (Ca²⁺ and Mg²⁺) formed larger AgNPs aggregates (less than 1400 nm) compared to other solutions tested (up to approximately 38 nm). The critical coagulation concentration (CCC) of AgNPs was determined to quantitatively evaluate the stability of the nanoparticle suspension in different water conditions. When the concentration of dissolved organic matter was increased from 0 mg/L to 5 mg/L, the CCC increased by a factor in the range of 2.19 ± 0.25 for all AgNPs in divalent solutions, but a smaller increase occurred, in the range of 1.54 ± 0.21 fold, when monovalent solutions were used.The concentration of ionic silver released indicated that the dissolved Ag⁺ (3.6-48.2 ppb) was less than 0.5% of the total mass of Ag⁰ added. At all the conditions tested, the concentration of silver ions in solution had a negligible contribution to the overall anti-bacterial performance of AgNPs.This study demonstrated that the anti-bacterial performance of AgNPs at selected natural water conditions decreases in the presence of dissolved natural organic matter or divalent ions, such as humic acid and calcium carbonate. These results may be helpful in understanding the toxicity of AgNP in various natural water conditions and in explaining the risk associated with discharging AgNP in natural aquatic systems.     

Phosphate adsorption onto hydrous manganese(IV) oxide in the presence of divalent cations

Alkaline earth cations, Ba²⁺, Sr²⁺, Ca²⁺, Mg²⁺ and transition metal ions, Mn²⁺, Co²⁺, Ni²⁺, cause hydrous manganese(IV) oxide (HMO) to strongly adsorb phosphate between pH 6 and 9 depending on the cation. The effectiveness of the alkaline earth cations to cause P adsorption was Ba²⁺ > Sr²⁺ > Ca²⁺ > Mg²⁺, which is the same order as their affinities for the oxide. Changes with time were found in the abilities of the transition metals to cause P adsorption onto HMO and this may be due to conversion of the adsorbed cation to its oxide. A new potential role for HMO as an adsorbent of phosphate in natural waters was indicated.     

Kinetic constants of nitrification

A modified respirometric method for measuring the kinetic constants r_x,m and K_s, of the first stage of nitrification was developed and verified. The method has the following advantages; the duration of measurement is significantly decreased compared with the original method and r_x can be determined at relatively high concentrations of substrate. The effect of substrate and activated sludge composition (COD:NH₄⁺-N ratio, fraction of nitrifiers) on respirometric methods application is discussed.     

Evaluating the influence of process parameters on soluble microbial products formation using response surface methodology coupled with grey relational analysis

Soluble microbial products (SMPs) present a major part of residual chemical oxygen demand (COD) in the effluents from biological wastewater treatment systems, and the SMP formation is greatly influenced by a variety of process parameters. In this study, response surface methodology (RSM) coupled with grey relational analysis (GRA) method was used to evaluate the effects of substrate concentration, temperature, NH₄⁺-N concentration and aeration rate on the SMP production in batch activated sludge reactors. Carbohydrates were found to be the major component of SMP, and the influential priorities of these factors were: temperature > substrate concentration > aeration rate > NH₄⁺-N concentration. On the basis of the RSM results, the interactive effects of these factors on the SMP formation were evaluated, and the optimal operating conditions for a minimum SMP production in such a batch activated sludge system also were identified. These results provide useful information about how to control the SMP formation of activated sludge and ensure the bioreactor high-quality effluent.     

Biodegradation of chlorpyrifos and 3, 5, 6‐trichloro‐2‐pyridinol by a novel rhizobial strain Mesorhizobium sp. HN3

A chlorpyrifos (CP) and 3,5,6‐trichloro‐2‐pyridinol (TCP) degrading bacterial strain, Mesorhizobium sp. HN3, was isolated and characterized. Mesorhizobium sp. HN3 degraded CP efficiently up to 400 mg/L initial concentration at wide range of temperatures (30–40°C) and pH (6.0–8.0). However, optimal degradation of CP was achieved at 37°C and neutral pH (7.0) at an initial inoculum density 2 × 10⁷ colony forming unit/mL of culture medium. Kinetic parameters for CP degradation by Mesorhizobium sp. HN3 were estimated at different initial concentrations. Cultures exhibited significant variation (P ≤ 0.05) in the specific growth rate (μ), cell mass formation rate (Q_X) and the substrate uptake rate (Q_S) during degradation of CP. The values of kinetic parameters increased up to 100 mg/L CP and decreased at higher concentration. Investigation of degradation metabolites indicated that CP is converted to diethylthiophosphate and TCP that leads to the formation of 3,5,6‐trichloro‐2‐methoxypyridine.     

The synthesis of the dissimilatory nitrate reductase under aerobic conditions in a number of denitrifying bacteria, isolated from activated sludge and drinking water

A number of denitrifying bacteria were isolated from activated sludge and drinking water. These bacteria were tested for the synthesis of the dissimilatory nitrate reductase under aerobic conditions (dissolved oxygen concentration above 4 mg · l⁻¹). The synthesis of this enzyme varied from total repression by oxygen in some bacteria, especially those isolated from drinking water, until a nearly non oxygen-repressed synthesis in other bacteria (strains 15 and N4). The effect of the dissolved oxygen concentration during growth of the bacteria on the synthesis of the dissimilatory nitrate reductase in cells of strain 15 was studied more extensively. A considerable repression of the enzyme synthesis was obtained when the dissolved oxygen concentration was relatively high (approx 15 mg·l⁻¹). Addition of chlorate to the growth medium of strain 15 (using NH⁺₄-N as nitrogen source) also resulted in a serious repression of the nitrate reductase synthesis during aerobic growth (dissolved oxygen above 4 mg·l⁻¹). The dissimilatory nitrate reductase of aerobically grown cells of strains 15 and N4 was found to be mainly localized in the membrane fraction.     

Copper toxicity to fishes and an extremely sensitive shrimp in relation to a potential Australian tropical mining‐waste seep

Ephemeral or seasonal streams tributaries to Magela Creek (Alligator Rivers Uranium province, Northern Territory), containing perennial pools, lie adjacent to a 1 km² tailings storage dam, still being filled, whose partial seepage collecting system contains an increasing concentration of copper. Acute copper toxicity to local fauna was determined in a flow‐through apparatus at 27°C and pH 6. The 4‐day LC50 values (μg L^‐1) for total copper were: rainbowfish Melanotaenia splendida inornata 170–190, pennyfish Denariusa bandata 75, and atyid shrimp Caridina sp. 3–4, and the 3‐day LC50 of the catfish Porochilus rendahli 85. Free ionic copper approximated the total copper. Test water quality was as predicted for seepage‐affected streams during a brief critical period in some years: of low hardness and alkalinity but enriched in Mg²⁺ and SO₄ ^2‐. The relative LC50 values correspond to the relative occurrence of similar species among zones of the metals‐affected Finniss River. Magela Creek system waters often had naturally low pH and ion‐concentrations (pH < 6, conductivity < 20 μS cm^‐1); the total copper concentration has repeatedly been similar to the free ionic copper LC50 of Caridina sp. The abundance and distribution of Caridina sp. are likely already influenced by local natural copper concentrations. Seepage total copper has increased to the fishes’ free ionic copper LC50.The hydraulic head of the wet tailings will increase further from 15 to 20 m.     

Assessment of phosphogypsum use in a nursery for plant propagation

Phosphogypsum (PG) was used as substrate for the multiplication of eight ornamental species; six by cuttings and two by sowing. The results obtained showed a high rooting or percent germination for the six plants: Ficus benjamina, Pelargonium × Hortorum, Washingtonia filifera, Eucalyptus camaldulensis, Hibiscus rosa sinensis and Acalypha wilkesiana. For a percentage of 50% PG, only F. benjamina, H. rosa sinensis and W. filifera showed high percentage rooting. Plant vigour (height and biomass) depends on both species and treatment. Two species showed high sensitivity to PG during the propagation by cuttings, Nerium oleander and Myoporum laetum. We observed high variation in substrate characteristics; with 50% PG, pH was increased from 2.84 to 6.22, and electrical conductivity (EC) and gypsum concentration were reduced from 15.56 to 4.23 mS/cm from 36.23 to 11.82%, respectively. The results showed the possibility of using PG in nurseries for the multiplication and fertilization of several forest and ornamental plant species by cuttings and sowing.     

Concentration of viruses from water on bituminous coal

The potential of bituminous coal for adsorption of viruses, using poliovirus as a model, was investigated. Influence of pH of water on the adsorption of viruses on a coal bed with and without addition of cation (Al³⁺) indicated that poliovirus could be adsorbed efficiently at pH 5 in presence of AlCl₃ at a concentration of 0.0005 M. Studies on the effect of different concentrations of monovalent, divalent and trivalent cations showed that the trivalent cation was more effective and was required at a lower concentration than other cations tested. A coal bed of 1.5 g could adsorb as high as 204,000 PFU from water based on the absence of virus in the filtrate. Total organic carbon content (TOC, 21–51 mg 1⁻¹) of the water did not interfere in virus adsorption to coal. The results obtained indicated that a bituminous coal bed could be used as one of the methods for efficient concentration of viruses from water.     

Fabrication of polymer-supported nanosized hydrous manganese dioxide (HMO) for enhanced lead removal from waters

In the current study, a new hybrid adsorbent HMO-001 was fabricated by impregnating nanosized hydrous manganese dioxide (HMO) onto a porous polystyrene cation exchanger resin (D-001) for enhanced lead removal from aqueous media. D-001 was selected as a support material mainly because of the potential Donnan membrane effect exerted by the immobilized negatively charged sulfonic acid groups bound to the polymeric matrix, which would result in preconcentration and permeation enhancement of lead ions prior to their effective sequestration by the impregnated HMO. HMO-001 was characterized by scanning electron micrograph (SEM), transmission electron micrograph (TEM), and X-ray diffraction (XRD). Lead adsorption onto HMO-001 was dependent upon solution pH due to the ion-exchange nature, and it can be represented by the Freundlich isotherm model and pseudo-first order kinetic model well. The maximum capacity of HMO-001 toward lead ion was about 395 mg/g. As compared to D-001, HMO-001 exhibited highly selective lead retention from waters in the presence of competing Ca²⁺, Mg²⁺, and Na⁺ at much greater levels than the target toxic metal. Fixed-bed column adsorption of a simulated water indicated that lead retention on HMO-001 resulted in a conspicuous decrease of this toxic metal from 1 mg/L to below 0.01 mg/L (the drinking water standard recommended by WHO). The exhausted adsorbent particles are amenable to efficient regeneration by the binary NaAc-HAc solution for repeated use without any significant capacity loss. All the results validated the feasibility of HMO-001 for highly effective removal of lead from contaminated waters.     

Analyses and assessment of the spatial and temporal distribution of nitrogen compounds in surface waters

The temporal concentration variations and spatial distribution of nitrogen compounds (nitrate, nitrite, ammonium) in the natural surface waters of Stara Zagora Region, Bulgaria, over a period of 1 year were assessed in the present study. Nitrate‐nitrogen concentrations in all surface water samples, except for the December value – 21.8 mg/L in Zetyovo Reservoir, were within the permissible national quality standards. NO₂ ^–‐N could be classified as a priority pollutant of Chirpan and Zetyovo Reservoirs waters. The greatest extent of NH ₄ ⁺‐N pollution was registered in Chirpan Reservoir surface waters. The correlation study revealed appreciable mutual relationship only between NH₄ ⁺‐N and NO ₂ ^–‐N in the surface waters. The hierarchical cluster analysis (HCA) exhibited divergent apportionment of nitrogen compounds in the surface water bodies.     

Adsorption of ammonium to activated sludge

The adsorption of ammonium (NH₄⁺) to the sludge floc matrix has been investigated in two activated sludge treatment plants. When activated sludge was extracted in 1 N KCl the extractable amounts were between 0.5 and 1.3 mg NH₄⁺-N/l higher than the dissolved ammonium concentration at dissolved ammonium concentrations between 1 and 6 mg NH₄⁺-N/l. The difference between the extractable and the dissolved ammonium, the exchangeable ammonium, thus represented 18–30% of the dissolved ammonium concentration. A part of this, around 0.5–0.6 mg NH₄⁺-N/l was not exchangeable under the actual operational conditions in the treatment plants due to a slow desorption kinetics, but seemed to be accessible for nitrification under prolonged aeration. The highest observed amount of adsorbed ammonium corresponded to 0.4–0.5 mg NH₄⁺-N/gSS. Adsorption of ammonium should be investigated in more details and included in models for nitrogen mass balances for activated sludge.     

Biochemical studies of some hydrolytic enzymes in malathion treated germinating seeds of Vigna sinensis (l): effect of growth hormone supplementation

Studies have been carried out on the different hydrolytic enzymes of the germinating seeds of V. sinensis (L) by exposing them to various concentrations of malathion (O, O dimethyl phosphorodithioate of diethyl mercaptosuccinate), an organophosphorus insecticide. At 50 ppm the insecticide induces the seedling growth and at 400 ppm caused a significant inhibition. On simultaneous application of either of the plant hormones, i.e., IAA, GA₃ and kinetin with different concentrations of malathion, it was found that there was a trend to overcome of malathion inhibition of seedling growth. It was also found that treatment of seeds with growth hormones, at 400 ppm malathion exposure, helps to restore the normal activities of certain hydrolytic enzymes, which showed otherwise, significant altered activities. Kinetic studies show that the stimulation of acid phosphatase activity due to malathion exposure was non‐competitive in nature.     

The development of a novel hybrid aerating membrane-anaerobic baffled reactor for the simultaneous nitrogen and organic carbon removal from wastewater

A novel hybrid aerating membrane-anaerobic baffled reactor (HMABR), based on the installation of aerating membrane into an anaerobic baffled reactor (ABR), to achieve simultaneous removal of nitrogenous and carbonaceous organic pollutants was developed in this study. The results demonstrated that after the installation of membrane module, total VFA and COD concentration in the HMABR effluent were decreased by 68.1 and 59.5% respectively, with increased nitrogenous pollutant remove efficiency by 83.5%, at influent COD concentration of 1600 mg/L and NH₄⁺-N concentration of 80 mg/L. Fluorescence in situ hybridization (FISH) results of the aerating membrane biofilm showed that the biofilm stratification for the spatial profiles of ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, aerobic heterotrophic bacteria, and denitrifying bacteria. The potential usage of HMABR widens the usage of aerobic-anaerobic combination technology for industrial wastewater treatment.     

Concentration-dependent response of estrone-degrading bacterial community in activated sludge analyzed by microautoradiography-fluorescence in situ hybridization

Inefficient removal of estrone (E1) in wastewater treatment plants (WWTPs) causes feminizing effects in male aquatic creatures. As E1 is mainly removed by biodegradation, investigation of E1 degradation is important to determine better removal strategies. Using microautoradiography-fluorescence in situ hybridization (MAR-FISH), we demonstrated that the structures of [³H]E1-incorporating bacterial communities were different at different E1 concentrations applied to activated sludge. At 200 μg/L E1, almost all [³H]E1-incorporating cells were associated with either Betaproteobacteria or Gammaproteobacteria (60% and 40% of MAR (+) cells, respectively). The proportion of Betaproteobacteria and Gammaproteobacteria in the total number of [³H]E1-incorporating cells decreased as the concentration of E1 decreased. In contrast, the proportion of Alphaproteobacteria in the total number of [³H]E1-incorporating cells increased as the concentrations of E1 decreased. At the lowest applied concentration (540 ng/L), almost all the [³H]E1-incorporating cells were Alphaproteobacteria (96%). The results of MAR-FISH applied to sludge samples collected from various plant locations and activated sludge processes, and during different seasons also demonstrated the high contribution of Alphaproteobacteria to the entire E1-degrading bacterial community (50.4 ± 11% of the total number of [³H]E1-incorporating cells) at 1 μg/L E1. Since the E1 concentration in domestic wastewater is at sub-μg/L levels, the key E1 degraders in activated sludge of domestic WWTPs are probably be Alphaproteobacteria. All [³H]E1-incorporating Alphaproteobacteria were hybridized with probe ALF968. Few MAR (+) cells were Sphingomonadales. An E1-degrading bacterial community at low E1 concentration appeared to consist of diverse bacterial groups of Alphaproteobacteria. This study suggested that substrate concentration is an essential factor for revealing E1-degrading bacteria in complex communities.