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Respirometric techniques were applied to estimate the toxic effect of several heavy metals (chromium(III), lead, nickel, mercury and zinc) on the activity of the heterotrophic bacteria present in activated sludge and to ascertain how the presence of these pollutants can affect biological treatment. For the assays, activated sludge was collected from the biological reactor (oxidation ditch) of a sewage treatment plant that also receives industrial wastewater. The tests were performed in a batch respirometer operating in dynamic mode, and the corresponding respirograms were obtained. The values obtained (between 0.47 and 0.71) for the specific growth yield coefficient in the different activated sludge samples pointed to the adequate performance of the biological treatment applied. The experimental data obtained showed that inhibition percentage is a logarithmic function of metal concentration, the toxicity of the heavy metals following the order: Hg ≫ Zn > Cr > Pb > Ni.

In this work, an innovative arrangement of a vertical subsurface flow wastewater infiltration system (SWIS) was studied. The principal objective of this study was to evaluate the oxygen transfer rate (OTR) in two different pilot-scale arrangements of an SWIS. The two pilot plants were composed of four filter beds in series, one with a vertical arrangement of the beds (one over the other) and the other with a horizontal arrangement of the beds (one next to the other). Furthermore, two kinetic models were applied for correlating the COD and NH4+-N concentrations at the inlet and outlet of each treatment step in both pilot plants. The fitting of experimental data to the models allowed the calculation of the areal rate constants. The OTR values obtained were 54.69 g m&minus, 2 h&minus, 1 and 28.84 g m&minus, 1 for horizontal and vertical arrangement, respectively. These values were considerably higher than those obtained by other authors. The plug flow model describes the behaviour of these SWISs better, and the best fits were achieved for the vertical arrangement. The areal rate constant values obtained in this study were higher than those reported in the bibliography, which indicates a great removal efficiency and therefore lower surface area needed for the treatment.

Natural, HCl-treated, and formaldehyde-treated non-living leaves of Posidonia oceanica, a marine plant, were investigated as potential biosorbents to remove Cd2+ from aqueous solutions. The studied biosorbents were characterized by elemental analysis and Fourier transform infrared spectroscopy (FTIR) and it was observed that the adsorption capacity of the biosorbents strongly depended on the pH, increasing as the pH rises. The adsorption process was fast. The adsorption kinetic was analyzed using five kinetic models: pseudo-first order, pseudo-second order, Elovich, intraparticle diffusion, and Bangham models. The adsorption isotherms were analyzed by the Langmuir, Freundlich, Dubinin-Radushkevich, Sips, Redlich-Peterson, and Toth models. The maximum biosorption capacity was attained by the biosorbent treated with HCl (1.11 mmol g-1). The distribution equilibrium constant and the Gibbs free energy change were calculated. The effects of the presence of Na+, K+, Mg2+, and Ca2+ ions in the solution on Cd2+ uptake were studied. Results indicate that non-living leaves of P. oceanica, natural or treated, can be considered as effective and low-cost biosorbents for the removal of cadmium from aqueous solutions.

The overall aim of this research was to apply a hybrid constructed soil filter for sewage treatment. A hybrid constructed soil filter is an ecological process used for decentralized sewage treatment in villages, small towns or scattered residential areas. Sewage is firstly treated by conventional physicochemical or biological treatment and then allowed to infiltrate through aerated unsaturated zone wherein it gets purified through processes such as filtration, adsorption, chemical reaction and biodegradation. This system has demonstrated a consistent capacity to remove organic matter and nitrogen. Experimental results have shown that under hydraulic load rates of 0.22 m3/m2 · h and organic load rates ranging from 47 to 156 g COD/m2 · h, mean removal efficiencies of 89% for COD, 99% for BOD5, 86% for suspended solids and 52% for total nitrogen can be achieved using an hybrid constructed soil filter. Compared to the conventional activated sludge process, this technology has many advantages, such as simple construction, low operation and maintenance costs, as well as a simple operation.

This study focuses on the roles played by three major functional groups (amine, carboxyl and hydroxyl) in the orange waste biomass for sorption of three heavy metals (Cd2+, Zn2+ and Cr3+). The biosorbent was chemically modified to block the mentioned functional groups in order to determine their contribution to the adsorption of metals. Fourier transform infrared (FTIR) and solid state carbon-13 nuclear magnetic resonance (13C NMR) spectroscopy were used to investigate the chemical modification. Additionally, batch biosorption tests were carried out with the different biosorbents in order to determine the possible reduction in metal uptake with the chemically modified biosorbent. Blocking of the COOH groups by chemical esterification resulted in an important reduction in metal binding. Nevertheless, no significant modification in metal removal was observed with acetylated and methylated orange waste.

BACKGROUND: This research provides new insights into the biosorption of zinc on a waste product from the orange juice industry. Optimal operating conditions maximizing percentage zinc removal were determined in batch and fixed-bed systems. Biomass was characterized by FTIR spectroscopy and by major cation content in order to better understand the biosorpion mechanism. Zn-loaded orange waste was proposed to be used as an alternative fuel in cement kilns. RESULTS: Sorption capacity was strongly affected by biosorbent dose and solution pH, and was not strongly sensitive to particle size under the experimental conditions studied. Equilibrium data were successfully described by a Langmuir model and sorption kinetic data were adequately modelled with the pseudo-second-order and Elovich rate equation. The biomass was found to possess high sorption capacity (qmax = 0.664 mmol g−1) and biosorption equilibrium was established in less than 3 h. Experimental breakthrough curves were adequately fitted to the Thomas model and the dose–response model, obtaining sorption capacities in continuous assays higher than those found in batch mode. Characterization of the biomass suggested the possible contribution of carboxyl and hydroxyl groups of biomass in Zn2+ biosorption and it also highlighted the important role of light metal ions in a possible ion-exchange mechanism. CONCLUSIONS: Orange waste could be used as an effective and low-cost alternative biosorbent material for zinc removal from aqueous solution. Copyright © 2010 Society of Chemical Industry

The use of orange wastes, generated in the orange juice industry, for removing cadmium from aqueous solutions has been investigated. The material was characterized by Fourier transform infrared spectroscopy and batch experiments were conducted to determine the adsorption capacity of the biomass. A strong dependence of the adsorption capacity on pH was observed, the capacity increasing as pH value rose. Kinetics and adsorption equilibrium were studied at different pH values (4–6). The adsorption process was quick and the equilibrium was attained within 3 h. The maximum adsorption capacity of orange waste was found to be 0.40, 0.41 and 0.43 mmol/g at pH 4–6, respectively. The kinetic data were analysed using various kinetic models – pseudo-first order equation, pseudo-second order equation, Elovich equation and intraparticle diffusion equation – and the equilibrium data were tested using four isotherm models – Langmuir, Freundlich, Sips and Redlich–Peterson. The data were fitted by non-linear regression and five error analysis methods were used to evaluate the goodness of the fit. The Elovich equation provides the greatest accuracy for the kinetic data and the Sips model the closest fit for the equilibrium data.

The presence of heavy metals in the sludges produced in wastewater treatment restricts plants growth and hence their use for agricultural purposes. This study looks at different types of sludges (aerobic, anaerobic, unstabilised and sludge from a waste stabilisation pond) and compares the distribution of the heavy metals that they contain according to the treatment that they have undergone. The sewage sludges were subjected to chemical characterisation and phytotoxicity testing (in absence of substrate) to provide a preliminary assessment of their suitability for land application. In addition, the total quantity of metals (Cd, Cr, Cu, Ca, K, Fe, Mg, Ni, Na, Pb and Zn) was determined. The Community Bureau of Reference (BCR) method for heavy metal speciation was followed. It was confirmed that the total concentration of heavy metals did not exceed the limits set out by European legislation and that the stabilisation treatment undergone by the sludges strongly influenced the heavy metal distribution and the phases to which they were associated. The sludge extracts did not exert any significant adverse effect on the relative seed germination (RSG) of barley (Hordeum vulgare L.) or cress (Lepidium sativum L.), although the reduction in germination index (GI) indicates that some characteristics existed did have an adverse effect on root growth.

Solid particles were removed from a slaughterhouse liquid effluent by physicochemical treatment (coagulation-flocculation process) using aluminium sulfate as the coagulant, and activated silica, powdered activated carbon, precipitated calcium carbonate, polyacrylic acid, or anionic polyacrylamide as coagulant aids to improve the settling time. Once the optimal conditions of the coagulation-flocculation process had been established (speed and time of stirring during flocculation, pH, coagulant and coagulant aid doses), the particle number and size distribution were measured before and after the addition of aluminium sulfate as the coagulant and the different coagulant aids, to determine the efficiency of the coagulation-flocculation process. When aluminium sulfate was used without the coagulant aids, overall efficiency of particle removal was 87%. Use of powdered activated carbon, polyacrylic acid, or anionic polyacrylamide improved removal to values between 92 and 98%.

The use of sulphorhodamine B, a known red fluorescent dye as a quantitative tracer in hydrological studies related to wastewaters has been proved experimentally. The interference in the accuracy of fluorescence readings owing to dissolved or suspended contaminants in wastewaters, especially at low concentrations of dye, was solved by successive filtering and eluting of the sample through a sep-pack C-18. The sulphorhodamine B, which is concentrated by displacement with small volumes of methanol, was thus retained. Volumes were then read with an fluorescence spectrophotometer. The procedure was demonstrated to be valid for use with sewers, stabilization ponds and wastewaters for concentrations as low as 5 × 10−7 g litre−1.

The hydraulic performance of a deep wastewater stabilization pond located in the Espinardo Campus of the University of Murcia was studied. The pond has a maximum capacity of 15,000 m3, with a maximum depth of 8 m. Sulforhodamine B dye is used as a tracer in the experimental study, which was carried out in two different climatic periods, winter and summer, so that the influence of temperature on the internal hydrodynamic of the lagoon could be ascertained. Two types of sample were obtained. One was taken from the mass of water within the pond and the other at the outlet. The mean real residence time ( t ) was calculated and it was below the spatial time (τ) both in summer and winter. Sampling carried out in the outlet flow along the time allowed the application of population balance models and to analyze the existence of short circuits and dead spaces. The pond active volume was calculated, being 70 and 22% of total volume in winter and summer, respectively. In both seasons, the active zone showed a hydrodynamic behaviour similar to the completely mixed continuous tank reactor (observed in the curves C and in the fitting of the experimental data at outlet and the use of the combined model of Cholette and Cloutier). From the experimental data of the remaining BOD5 it was possible to calculate the global kinetic constants for organic matter degradation and, from this, the constants at 20°C obtained at the most unfavourable (higher) water temperature observed. Both in winter and summer constants values (k20 = 0.46 and 0.32 d−1) seemed to point to the active zone of the system, showing a fundamentally aerobic behaviour.

Nitrogen removal and transformations were studied in two pilot-scale combinations of a special configuration of a subsurface wastewater infiltration system with vertical flow named symbiotic treatment®. Both pilot-scale combinations operated in parallel and each one consists of four stages in series, one of them with a vertical distribution of stages and the other one with a horizontal distribution. The main differences between them were the separation between stages (presence (the horizontal distribution)/absence (the vertical distribution) of filtration between steps), the hydraulic load (0.113 m3/m2 h and 0.082 m3/m2 h for the horizontal and the vertical distribution, respectively) and the depth of the soil filters (1 m each stage in the horizontal distribution whereas the depths in the vertical distribution ranges from 20 cm to 40 cm). Results of both configurations showed elevated dissolved oxygen concentration, and high removal of organic matter and total suspended solids (with mean removal values of 96% for COD for both plants and 90% and 98% for TSS for the vertical and the horizontal distribution, respectively). High total Kjeldahl nitrogen removals were obtained in both configurations (mean removals of 70% and 90% for the vertical and the horizontal distribution, respectively). Whereas the nitrification potential was higher in the configuration with horizontal distribution which includes pumping and filtering between stages and higher depth of the soil filters, both tested configurations showed promise for nitrification of wastewater, ammonia nitrogen was efficiently transformed to nitrate.

The presence of heavy metals in the sludges produced in wastewater treatment plants restricts their use for agricultural purposes. This study looks at different types of sludge (aerobic, anaerobic, unstabilised, sludge from a waste stabilisation pond, sludge from an extended aeration plant and heat treated sludge) and compares the distribution of heavy metals with the treatment that they have undergone. In addition, the total quantity of metals (Cd, Cr, Cu, Ca, K, Fe, Mg, Ni, Na, Pb and Zn) and some agronomic parameters necessary for characterising a sludge as suitable for use as amendment were determined. The BCR method for heavy metal speciation was followed. Principal component analysis (PCA) was applied in order to obtain more information about metal speciation in the sewage sludges. It was confirmed that the concentration of heavy metals did not exceed the limits set out by European legislation and that the stabilisation treatment undergone by the sludges strongly influenced the heavy metal distribution and the phases to which they were associated. The waste stabilisation pond sludge, which has undergone a higher degree of mineralisation than the others, shows a lower metal bioavailability index since practically all the heavy metals in it are associated to the oxidisable and residual fraction. On the other hand the unstabilised sludge, which, along with that exposed to extended aeration, contains the highest accumulations of heavy metals in the most easily assimilable fractions.

The presence of heavy metals in the sludges produced in wastewater treatment plants restricts their use for agricultural purposes. This study compares different types of sludges (aerobic, anaerobic, unstabilised and sludge from a waste stabilisation pond) in order to assess the extractability of heavy metals using simple extraction, water and DTPA. The stabilisation treatment undergone by the sludges influenced the heavy metals extractability. The least mineralised sludges (unstabilised and aerobic) showed higher metal extractability. The sewage sludges were subjected to chemical characterisation and toxicity testing (ecotoxicity and phytotoxicity assays) in absence of substrate, to provide a preliminary assessment of their suitability for land application. The ecotoxicity assays confirmed that no sludge constituted a hazardous waste. The sludge extracts had significant adverse effect on the germination index (GI) of barley (Hordeum vulgare L.) and cress (Lepidium sativum L.), a fact which indicates that some characteristics affected root growth.

The presence of heavy metals in the sludges produced in waste-water treatment plants restricts their use for agricultural purposes. This study looks at different types of sludges (aerobic, anaerobic, unstabilised and sludge from a waste stabilisation pond) and compares the distribution of the heavy metals they contain according to the treatment that they have undergone. Some agronomic parameters necessary for characterising a sludge as suitable for use as amendment were determined. The aim of this study is to compare the availability and the localisation of heavy metals in different sewage sludges using simple (water and DTPA) extraction and the BCR (Community Bureau of Reference) sequential extraction procedure. It was confirmed that the total concentration of heavy metals did not exceed the limits set out by European legislation and that the stabilisation treatment undergone by the sludges strongly influenced the heavy metal distribution and the phases to which they were associated and their bioavailability level. The DTPA extraction procedure is cheap and easy to perform and the obtained results are similar to those obtained with the sequential procedure.

A physicochemical treatment (coagulation-flocculation) was applied to a slaughterhouse wastewater, using anionic polyacrylamide as coagulant aid to improve the settling velocity of the flocs formed with the coagulants used: ferric sulphate, aluminium sulphate and polyaluminium chloride. The optimum speed and stirring time for the flocculation stage were ascertained along with the optimum pH and coagulant and coagulant aid doses. The speed and coagulation time were initially set according to recommendations in the literature concerning the treatment of this type of water. Chemical Oxygen Demand (COD), Biochemical Oxygen Demand at five days (BOD5) and Total Suspended Solids (TSS) were recorded at the beginning and end of each experiment in order to monitor the process. Once the optimal conditions had been established, several parameters were measured in order to assess the coagulation-flocculation process: particle number and size, sludge volume, nutrients (ammonia nitrogen, total Kjeldahl nitrogen, albuminoid nitrogen, orthophosphate, total phosphorus) and the residual concentration of iron and aluminium in clarified water. Anionic polyacrylamide, when added with ferric sulphate or polyaluminium chloride led to a significant increase in the settling speed.

A coagulation–flocculation treatment has been applied to a slaughterhouse liquid effluent, using ferric sulphate as coagulant and activated silica, powdered activated carbon, cationic polyacrylamide, polyvinyl alcohol, polyacrylic acid and anionic polyacrylamide as coagulant aids in order to improve the settling time. Once the optimal conditions had been established (speed and time of stirring during flocculation step, pH, coagulant and coagulant aid doses), the efficiency of the coagulation–flocculation process was studied by comparing the particle size distribution before and after the addition of the coagulant. When ferric sulphate was used without the coagulant aids, particle removal efficiency varied with size, although overall efficiency was quite substantial (87%). The use of coagulant aids improved the removal efficiency, except in the case of activated silica, when it fell to 78%. In all other cases removal efficiency values between 93% (for polyvinyl alcohol) and 99% (for anionic polyacrylamide) were reached.

Nutrient removal and sludge production in the coagulation-flocculation process, applied to a slaughterhouse effluent, have been studied. Fe2(SO4)3, Al2(SO4)3 and polyaluminium chloride were used as coagulants. Inorganic products were used as coagulant aids: activated silica, powdered activated carbon and precipitated calcium carbonate and synthetic polyelectrolytes: cationic polyacrylamide, polyacrilic acid, anionic polyacrylamide and polyvinyl alcohol. Performances were measured under optimum conditions for the products used. They were found after studying the different variables which influence the process. Phosphorus removal is very high (approximately 100% for the orthophosphate and between 98.93% and 99.90% for the total phosphorus). Ammonia nitrogen removal is very low although appreciable performances are observed for albuminoid nitrogen (73.9-88.77%). The use of coagulant aids reduces the volume of the sludge produced up to 41.6%.

A wastewater treatment plant of an innovative technology, designed by Golftrat S.L., was constructed to evaluate its success in treating the wastewater generated from various installations in the Campus of Espinardo (University of Murcia). The cited technology, named "symbiotic plant ®" , combines a natural and subterranean treatment with the generation of green areas over the surface of the plant. It is a promising technology, when comparing with conventional system, due to the low energy cost and the simple operational and maintenance procedures. In spite of the variation in the characteristics of the wastewater generated at the University, a great homogeneity in the quality of the effluent is obtained. The removal efficiency is up to 95% for COD, 97% for BOD, up to 87% for suspended solids, up to 80% for nitrogen and at least 40% for phosphorus. Besides, an increasing in dissolved oxygen is obtained along the treatment with the consequent increase in nitrates concentration. With the final treatment in the wetland an important level of denitrification is achieved. The overall treatment plant provides an effluent with enough quality to be used for irrigation of the green areas in the Campus of Espinardo.

The fractional composition and potential mobility of particulate phosphorus was investigated in sediment from a deep wastewater stabilization pond. The predominant phosphorus fractions were Fe- and Al-bound P (NaOH-RP) and Residual-P (consisting mainly of organic P), which amounted to 35 and 34% of total phosphorus, respectively. A laboratory study was conducted to determine the influence of various environmental parameters (pH, redox conditions, biological activity and temperature) on phosphorus release from lagoon sediment. Phosphorus release was observed under both anaerobic and aerobic conditions. Anaerobic release was about 1.4-5 times greater than aerobic release. Phosphorus release was redox-sensitive and favoured by high pH values, up to 17.4% of total phosphorus being liberated anaerobically and at high pH. Biological activity favoured phosphorus release, since the amount released under non-sterile conditions exceeded that observed under sterile conditions. Sediment phosphorus was fractionated before and after the release experiments. The NaOH-RP fraction was sensitive to pH and redox environmental changes, and was readily released under reduced conditions and at high pH. The mobility of the Residual-P fraction was enhanced in incubations involving biological activity due to the decomposition of the organic matter in the sediments, and NaOH–nRP (organic phosphorus) decreased by up to 45% during the incubation of non-sterile suspensions.