J.M. Quiroga

The effect of temperature on the biodegradation of a nonylphenol polyethoxylate in river water

Abstract In this paper a study is made of the biodegradability of a non-ionic surfactant, a nonylphenol polyethoxylate, in river water by means of monitoring the residual surfactant matter and the metabolites that may be generated. The influence of temperature on the extent of primary and ultimate biodegradation, and the kinetics of degradation are also determined. The method used was the river die-away test, and the biodegradation process was monitored by normal and reversed phase high-performance liquid chromatography (HPLC). These results are supported by other indirect measurements and indicators of the existence of microbial degradation process, as well as the parameters for the control of the process. The results obtained indicate that temperature has a strong influence on the period of acclimation of the microorganisms and on the rate of biodegradation. The percentages of primary biodegradation vary from 68% at 7°C to 96% at 25°C, and at all the temperatures studied, metabolites are generated during the biodegradation process which do not totally disappear at the end of the assay. The percentages of mineralization reached in the various assays, ranging from 30% at 7°C to 70% at 25°C, also show the great influence of temperature. Finally, a kinetic study of the biodegradation process has been carried out, with excellent fit of the experimental data to the kinetic model of Quiroga and Sales.

Ozonation of ibuprofen: a degradation and toxicity study.

This paper presents the results obtained in the degradation of ibuprofen by ozonation. This study aims to evaluate the degradation of ibuprofen by ozonation once the operating variables have been optimized, investigating the degradation and degradation efficiency of the compound and assessing the toxic effect of ibuprofen and of the intermediate compounds generated during oxidative treatment. Work was carried out to optimize the four operating variables: pH, conductivity, hydraulic retention time and the use of a maze of pipes to enhance contact between the ozone and the drug. All the trials were conducted in a purpose-built pilot-scale reactor. Analyses of the compound were carried out after solid-liquid phase extraction on high resolution liquid chromatography (HPLC). Working under optimal operating conditions (pH=9, HRT=20 min and 12 ± 2 gN/m(3)), a degradation value of 99% was obtained, although degradation efficiency or mineralization of the compound was not achieved. The toxicity of ibuprofen and its intermediate compounds formed during the oxidative process was likewise studied. This toxicity was found to increase with increasing initial concentrations of the compound, with the intermediate compounds thus formed being more toxic than the starting compound.

Levels of linear alkylbenzenesulfonate (LAS) in waters and sediments of the coastal ecosystems of the Gulf of Cadiz

The observed concentration of linear alkylbenzenesulfonate (LAS) in some coastal ecosystems of the Gulf of Cadiz are a function of the lack of sewage treatment plants, the water depth and the rate of renewal of the receiving water course. Concentration ranging from 2 to 510 μg.L‐1 were found in the waters of the Bay of Cadiz. Concentrations of LAS in sediments ranged from 0.4 to 49 μg g‐1. A procedure based on solid phase extraction has been developed for the isolation and concentration of LAS in environmental samples; this enables the subsequent determination of the concentrations of both total LAS and its individual homologues in marine samples with a complex organic matrix by liquid chromatography. It is a simple, sensitive and specific method.

Pre-treatment optimisation studies for secondary effluent reclamation with reverse osmosis.

Physical-chemical pre-treatment was used for the reverse osmosis unit for reclamation of secondary effluents. The pilot plant was equipped with a variety of tertiary treatment units to prevent fouling and biofouling of the cellulose-acetate reverse osmosis membranes used. The optimisation of pre-treatment involved application of various concentrations of lime to raise the pH to 10.3-12.1, and to stabilise the sludge generated, as well as different dosages of ferric chloride (15, 20, and 25 mg/L) for the coagulation and solid-liquid separation. Sodium hypochlorite (8 mg/L) and UV disinfection are used for microbiological control. The water quality obtained, under the optimum conditions (pH=10.5; FeCl(3): 25 mg/L; anionic flocculant: 0.5 mg/L; sodium hypochlorite: 8 mg/L) was high, showing an average conductivity of 66 microS/cm and low COD values 4 mg O(2)/L. The product water is suitable for injection into a groundwater aquifer to counteract seawater intrusion.

Comparison of four chemical uncouplers for excess sludge reduction

A substantial part of the operating costs of wastewater treatment plants (WWTP) is associated with the management and treatment of the excess sludge generated during the treatment process. Different strategies have been applied for excess sludge reduction, such as the oxic‐settling‐anaerobic process, the high dissolved oxygen process, the uncoupler‐containing activated sludge process, the ozonation‐combined activated sludge process, control of sludge retention time and biodegradation of sludge in a membrane‐assisted reactor. Chemical uncouplers have been shown to reduce excess sludge production, disassociating the energy coupling between catabolism and anabolism. These metabolic uncouplers may be organic compounds, such as 2,4‐dinitrophenol (2,4‐DNP) or 3,3′,4′,5‐tetrachlorosalicylanilide (TCS), or heavy metals. In this paper, four different chemicals (2,4‐DNP, TCS, copper (Cu) and zinc (Zn)) were chosen for short‐term tests for studying their ability to reduce sludge yield (Yx/s ) and, consequently, their potential for reducing excess sludge production. According to the results obtained, only TCS seems to be very effective in reducing sludge production from the activated sludge process. Compared with the control test, Yx/s can be reduced by over 30% at 0.8 mg/l TCS. It was also found that the substrate removal capability was not adversely affected by the presence of TCS. Furthermore, an increase in the microbial activity of the system was observed.

Experimental evaluation of pollution potential of anionic surfactants in the marine environment

Abstract A study of the influence of temperature and salinity on the biodegradation of a commercial anionic surfactant (LAS) in waters and sediments of the Bay of Cadiz (SW Spain) is reported. The assays were carried out using batch reactors, and the surfactant concentrations used were similar to those found in the urban effluents which discharge into the bay. Temperature was found to have a decisive effect on the degradation rate. At temperatures of 20–25°C, degradation exceeded 90% within less than 10 days of assay whereas at temperatures under 10°C, degradation scarcely took place (the percentage of degradation did not exceed 5% after 21 days of assay). Variation in salinity, particularly marked during wet seasons, disturbs the activity of bacterial flora and slows down biodegradation of surfactant. All this means that the pollution potential of urban waste containing detergents undergoes significant seasonal variation. The rate of surfactant degradation was remarkably accelerated in the presence of sediments, except in those tests where anoxic conditions were established. This occurs where there is high benthic oxygen demand from sediments containing high percentage of easily-biodegradable organic matter.

Catalyzed Hydrogen Peroxide Treatment of Polychlorinated Biphenyl Contaminated Sandy Soils

This paper reports the results of the treatment of polychlorinatedbiphenyl (PCB) contaminated sandy soils (100 mg kg-1 Aroclor 1242) with the Fenton advanced oxidation process (AOP). The results obtained in the various assays permitted the optimization of conditions as follows: 5% H2O2; 100 ppm of Fe3+; and a ratio of sandy soil mass/volume of oxidizing solution (m/V) of 1/3 g mL-1. In addition, these tests established the need for agitation and dispensed with the need for heat. The results obtained confirm that the oxidation process occurs in solid phase (on the PCBs adsorbed to soil particles), producing 98% elimination of the original PCB structure and 82% dechlorination, all within a reaction time of 72 hr. The degree of elimination was found to be dependent on the level of congener chlorination and the process displays a pseudo first order kinetics. In addition, the Fenton chemical oxidation process may be complemented by subsequent aerobic biological degradation which, after 15 days, produces 72% mineralization of the products generated during the chemical oxidation process.

Qualitative Estimation of Heavy Metals in Marine Sediment Using Thermal Analysis

This article proposes a method for the thermogravimetric analysis (TGA) of marine sediment suspected of pollution by heavy metals, which may be appropriate for a selected region where the regression equations relating W2 weight loss as the independent variable and estimated metal abundance as the dependent variable have already been derived. Automated TGA may then be employed as a reconnaissance tool, to give a rapid and inexpensive predictive index of quality. The method has been applied to actual samples of known heavy metal content and the results have been compared with the quality criteria for dredged sediment proposed by the USEPA and other standards. These criteria have been translated into the corresponding classification categories provided by the TGA method. The sediment samples, on which thermal analysis from 50 to 900°C was performed, are from the southwest of Spain and several showed high levels of pollution. The first derivative of TG curves (DTG) and the chemical parameters analyzed were compared and those that provide better Pearsons coefficients were fitted by linear regression. From these fits several linear regression equations were proposed and taken as the basis for transforming the metal content values proposed in the USEPA and other international regulations in the form of TG data; finally, the method were validated by a certified material (MESS-3).

Overview of sewage sludge minimisation: techniques based on cell lysis-cryptic growth

Abstract Sewage sludge production is currently considered as one of the most important problems in wastewater treatment due to the high costs of management and treatment, as well as limitations in its final use. In accordance with the order of priority in waste management options, based on the 3Rs’ (reduce, reuse and recycle), numerous studies are addressing this need to minimize the sewage sludge production. This paper presents a review of recent studies in the field of sewage sludge minimisation, focusing on the techniques based on the cell lysis and cryptic growth mechanism. In addition to reducing sludge, the cell lysis-cryptic growth technologies applied in the sludge return line provide, biodegradable carbonaceous matter that aids denitrification. The promising results obtained in the full-scale application of some of the cell lysis-cryptic growth technologies constitute yet another advantage of this strategy.

Thermal analysis in the evaluation of sediment pollution.

Characterization of organic matter in four sediments in the influence area of wastewater discharges was carried out by both chemical and thermal analysis in order to assess their pollution level. Oxidisable organic carbon and organic matter were calculated by the standard methodology in laboratory. Thermogravimetry (TG), between 50 and 900° C, was simultaneously performed in oxidizing conditions on ground sediments samples after three different pretreatments. Linear regression adjust of thermal analysis results versus chemical parameters provides the better Pearsons coefficients, leading to the best coefficients for weight loss in 250-400° C temperature range versus oxidisable organic carbon and organic matter at 360°C, respectively. These results demonstrated the utility of thermoanalysis technique for the evaluation of the organic matter content of fresh sediments.