Speciation and fate of copper in sewage treatment works with and without tertiary treatment: the effect of return flows.

The removal of metals from wastewaters is becoming an important issue, with new environmental quality standards putting increased regulatory pressure on operators of sewage treatment works. The use of additional processes (tertiary treatment) following two-stage biological treatment is frequently seen as a way of improving effluent quality for nutrients and suspended solids, and this study investigates the impact of how back washes from these tertiary processes may impact the removal of copper during primary sedimentation. Seven sites were studied, three conventional two-stage biological treatment, and four with tertiary processes. It was apparent that fluxes of copper in traditional return flows made a significant contribution to the load to the primary treatment tanks, and that <1% of this was in the dissolved phase. Where tertiary processes were used, back wash liquors were also returned to the primary tanks. These return flows had an impact on copper removal in the primary tanks, probably due to their aerobic nature. Returning such aerobic back wash flows to the main process stream after primary treatment may therefore be worth consideration. The opportunity to treat consolidated liquor and sludge.flows in side-stream processes to remove toxic elements, as they are relatively concentrated, low volume flow streams, should also be evaluated.

Resource dependent biodegradation of estrogens and the role of ammonia oxidising and heterotrophic bacteria.

The influence of ammonia oxidising bacteria and bulk organic competition was assessed during laboratory scale activated sludge treatment. Under short and long hydraulic retention time (HRT) and solid retention time (SRT) conditions, bioreactors were supplied with synthetic sewage spiked with 0.04-2.1 mg m(3) d(-1) of steroid estrogens with and without ammonia as a nitrogen source. Non acclimated biomass that had previously not been exposed to estrogens was capable of biodegrading estrogens (89% and 78%) within 24 h in the short HRT/SRT and long HRT/SRT conditions respectively. Changing the nitrogen source from ammonia to nitrate caused reductions in ammonia oxidising bacteria (AOB) numbers from 2.47×10(8) to 1.17×10(7)AOB mL(-1) and 5.15×10(9) to 4.27×10(7)AOB mL(-1) for the short and long HRT/SRT conditions respectively. Despite these reductions, biodegradation of estrogens was unaffected, which demonstrated that heterotrophic bacteria were able to biodegrade estrogens. Estrogen biodegradation was unrestricted and estrogen could be removed at higher than environmental concentrations following a pseudo-first order relationship. During this study, bulk organic loading appeared not to have any appreciable influence upon estrogen biodegradation. These results suggest heterotrophic bacteria, capable of scavenging a broad spectrum of organic material, carry out estrogen biodegradation.

The effectiveness of anaerobic digestion in removing estrogens and nonylphenol ethoxylates.

The fate and behaviour of two groups of endocrine disrupting chemicals, steroid estrogens and nonylphenol ethoxylates, have been evaluated during the anaerobic digestion of primary and mixed sewage sludge under mesophilic and thermophilic conditions. Digestion occurred over six retention times, in laboratory scale reactors, treating sludges collected from a sewage treatment works in the United Kingdom. It has been established that sludge concentrations of both groups of compounds demonstrated temporal variations and that concentrations in mixed sludge were influenced by the presence of waste activated sludge as a result of transformations during aerobic treatment. The biodegradation of total steroid estrogens was >50% during primary sludge digestion with lower removals observed for mixed sludge, which reflected bulk organic solids removal efficiencies. The removal of nonylphenol ethoxylates was greater in mixed sludge digestion (>58%) compared with primary sludge digestion and did not reflect bulk organic removal efficiencies. It is apparent that anaerobic digestion reduces the concentrations of these compounds, and would therefore be expected to confer a degree of protection against exposure and transfer of both groups of compounds to the receiving/re-use environment.

Integrating anaerobic processes into wastewater treatment.

Over the past decade, the concept of anaerobic processes for the treatment of low temperature domestic wastewater has been introduced. This paper uses a developed wastewater flowsheet model and experimental data from several pilot scale studies to establish the impact of integrating anaerobic process into the wastewater flowsheet. The results demonstrate that, by integrating an expanded granular sludge blanket reactor to treat settled wastewater upstream of the activated sludge process, an immediate reduction in imported electricity of 62.5% may be achieved for a treated flow of c. 10,000 m(3) d(-1). This proposed modification to the flowsheet offers potential synergies with novel unit processes including physico-chemical ammonia removal and dissolved methane recovery. Incorporating either of these unit operations can potentially further improve the flowsheet net energy balance to between +0.037 and +0.078 kWh m(-3) of produced water. The impact of these secondary unit operations is significant as it is this contribution to the net energy balance that facilitates the shift from energy negative to energy positive wastewater treatment.

The pharmaceutical use of permethrin: sources and behavior during municipal sewage treatment.

Permethrin entered use in the 1970s as an insecticide in a wide range of applications, including agriculture, horticultural, and forestry, and has since been restricted. In the 21st century, the presence of permethrin in the aquatic environment has been attributed to its use as a human and veterinary pharmaceutical, in particular as a pedeculicide, in addition to other uses, such as a moth-proofing agent. However, as a consequence of its toxicity to fish, sources of permethrin and its fate and behavior during wastewater treatment are topics of concern. This study has established that high overall removal of permethrin (approximately 90%) was achieved during wastewater treatment and that this was strongly dependent on the extent of biological degradation in secondary treatment, with more limited subsequent removal in tertiary treatment processes. Sources of permethrin in the catchment matched well with measured values in crude sewage and indicated that domestic use accounted for more than half of the load to the treatment works. However, removal may not be consistent enough to achieve the environmental quality standards now being derived in many countries even where tertiary treatment processes are applied.

Fate and behaviour of copper and zinc in secondary biological wastewater treatment processes: I. Evaluation of biomass adsorption capacity.

The current sources of copper and zinc in municipal wastewaters have been considered, and the changes in the concentrations and quantities of these two elements entering sewage treatment works over the last three decades have been calculated. The concentrations and quantities of the heavy metals cadmium, chromium, copper, mercury, nickel, lead and zinc, entering UK sewage treatment works, have been reduced by between 50% and 90% during this period. However, the reductions in copper and zinc appear to be at the lower end of these ranges and thus remain a cause for concern, particularly their concentrations in sewage effluents and their potential environmental impacts on receiving waters. Bench studies have been undertaken to predict removals by three types of biological wastewater treatment plants: trickling filters, conventional activated sludge and membrane bioreactors, to determine if any of these processes are more efficacious for the removal of these metals. These results suggest that, despite membrane bioreactor biomass achieving the lowest effluent suspended solids concentration and having the lowest effluent chemical oxygen demand, which is accepted as a surrogate measure of organic chemical chelating ability of the aqueous phase, they produce the highest effluent values for the two metals in this study (copper and zinc). Removals of zinc and copper in biological wastewater treatment processes are probably primarily determined by those factors influencing metal solubility in the biomass matrix.

Fate and behaviour of copper and zinc in secondary biological wastewater treatment processes: II. Removal at varying sludge age.

The mechanisms for the removal of heavy metals during secondary biological treatment of wastewater, with particular emphasis on the activated sludge process, are considered. It is concluded that the predominant mechanism is the entrapment and co-settlement of insoluble metal species in the mixed liquor (biomass). Secondary extracellular polymeric materials, particularly extracellular polysaccharides and other capsule-forming materials, may also play a role. In general, removal of both copper and zinc was superior at the higher sludge ages employed in this study, 4.3 and 8 days, and can in part be attributed to the superior removals of both biochemical oxygen demand and effluent suspended solids achieved at these sludge ages compared with the lowest sludge age studied, 3.6 days. For both copper and zinc there is an increase in soluble metal across the activated sludge process. However, significant removal of both metals occurs as a consequence of the removal of substantial amounts of insoluble metal. The presence of returned sludge liquors, high in settleable solids, to the mixed liquor appears to moderately enhance the percentage removal of copper and zinc. Membranes used in place of secondary sedimentation also enhance removal of both metals by reducing effluent suspended solids. It is concluded that there is potential for maximizing metal removal by optimization of secondary biological treatment in a sustainable manner, without recourse to energy-intensive or chemically-dependent tertiary treatment technologies.

A novel approach to the anaerobic treatment of municipal wastewater in temperate climates through primary sludge fortification.

It is proposed that anaerobic treatment of municipal wastewater in temperate climates is attainable through the fortification of wastewater with primary sewage sludge to enhance the chemical oxygen demand (COD). Three bench-scale up-flow anaerobic sludge blanket (UASB) bioreactors (0.5 L) were operated to provide a preliminary verification of this approach. Mass and energy balances were modelled using the GPS-X (COST model, population equivalent of 118,500) to determine the energy balance of the primary sludge wastewater fortification process flowsheet in comparison with conventional aerobic secondary treatment with activated sludge. The addition of 5% primary sludge by volume to crude wastewater pretreated with ultrasound resulted in an increase in total COD from 536 mg L(-1) to 2300 mg L(-1). A COD removal of 86% +/- 8% and methane production of 400 mL L(-1) d(-1) were achieved in the reactor that was supplied with this primary sludge fortified wastewater. In comparison a COD reduction of 77% +/- 8% and 40 mL L(-1) d(-1) of methane were observed in the reactor which was supplied with crude wastewater only, and a 79% +/- 8% COD removal and 156 mL L(-1) d(-1) of methane were observed in UASB2, which was supplied with crude wastewater pretreated with ultrasound. The modelled energy balance for the fortified wastewater treatment process flowsheet was -305 kWh d(-1) compared with -937 kWh d(-1) in the aerobic flowsheet, corresponding to an energy saving of 67%.

The significance of sample mass in the analysis of steroid estrogens in sewage sludges and the derivation of partition coefficients in wastewaters.

Optimization of an analytical method for determination of steroid estrogens, through minimizing sample size, resulted in recoveries >84%, with relative standard deviations <3% and demonstrated the significance of sample size on method performance. Limits of detection were 2.1-5.3 ng/g. Primary sludges had estrogen concentrations of up to one order of magnitude less than those found in biological sludges (up to 994 ng/g). However, partition coefficients were higher in primary sludges (except estriol), with the most hydrophobic compound (ethinylestradiol) exhibiting the highest Kp value, information which may be of value to those involved in modeling removal during wastewater treatment.

Fate and occurrence of alkylphenolic compounds in sewage sludges determined by liquid chromatography tandem mass spectrometry.

An analytical method has been developed and applied to determine the concentrations of the nonionic alkylphenol polyethoxylate surfactants and their metabolites, alkylphenoxy carboxylates and alkyphenols, in sewage sludges. The compounds were extracted with methanol/acetone (1:1 v/v) from sludge, and concentrated extracts were cleaned by silica solid-phase extraction prior to determination by liquid chromatography tandem mass spectrometry. The recoveries, determined by spiking sewage sludge at two concentrations, ranged from 51% to 89% with method detection limits from 6 microg kg(-1) to 60 microg kg(-1). The methodology was subsequently applied to sludge samples obtained from a carbonaceous activated sludge plant, a nitrifying/denitrifying activated sludge plant and a nitrifying/ denitrifying activated sludge plant with phosphorus removal. Concentrations of nonylphenolic compounds were two to three times higher than their octyl analogues. Long-chain nonylphenol polyethoxylates (NP3-12EO) ranged from 16 microg kg(-1) to 11754 microg kg(-1). The estrogenic metabolite nonylphenol was present at concentrations ranging from 33 microg kg(-1) to 6696 microg kg(-1).

Treatment and removal strategies for estrogens from wastewater.

Natural and synthetic steroidal estrogens (estrone, 17beta-estradiol and 17alpha-ethinylestradiol) are endocrine disrupters, that are discharged consistently from the sewage treatment works into surface waters, thereby causing endocrine disrupting effects to aquatic organisms at trace concentrations (nanogram per litre). Several years of research have been focused on their fate, behaviour and removal in the environment but primarily in the sewage treatment works which acts as a sink for these compounds. This review attempts to summarize the factors involved in the removal of these chemicals from the sewage treatment works. Biological processes, and to a limited extent physio-chemical properties, play a vital role in the endocrinal deactivation of these compounds. The efficiency of these processes is highly dependent on operating parameters (such as sludge retention time, redox potential, etc) that govern the secondary treatment process of a functional sewage treatment works. Although advanced treatment technologies are available, cost and operational considerations do not make them a sustainable solution.

Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters.

Nonylphenol is a toxic xenobiotic compound classified as an endocrine disrupter capable of interfering with the hormonal system of numerous organisms. It originates principally from the degradation of nonylphenol ethoxylates which are widely used as industrial surfactants. Nonylphenol ethoxylates reach sewage treatment works in substantial quantities where they biodegrade into several by-products including nonylphenol. Due to its physical-chemical characteristics, such as low solubility and high hydrophobicity, nonylphenol accumulates in environmental compartments that are characterised by high organic content, typically sewage sludge and river sediments, where it persists. The occurrence of nonylphenol in the environment is clearly correlated with anthropogenic activities such as wastewater treatment, landfilling and sewage sludge recycling. Nonylphenol is found often in matrices such as sewage sludge, effluents from sewage treatment works, river water and sediments, soil and groundwater. The impacts of nonylphenol in the environment include feminization of aquatic organisms, decrease in male fertility and the survival of juveniles at concentrations as low as 8.2 microg/l. Due to the harmful effects of the degradation products of nonylphenol ethoxylates in the environment, the use and production of such compounds have been banned in EU countries and strictly monitored in many other countries such as Canada and Japan. Although it has been shown that the concentration of nonylphenol in the environment is decreasing, it is still found at concentrations of 4.1 microg/l in river waters and 1 mg/kg in sediments. Nonylphenol has been referred to in the list of priority substances in the Water Frame Directive and in the 3rd draft Working Document on Sludge of the EU. Consequently there is currently a concern within some industries about the possibility of future regulations that may impose the removal of trace contaminants from contaminated effluents. The significance of upgrading sewage treatment works with advanced treatment technologies for removal of trace contaminants is discussed.

Determination of steroid estrogens in wastewater by high performance liquid chromatography-tandem mass spectrometry.

This paper discusses the requirement for, and presents an analytical procedure for, the determination of four steroid hormones and a conjugated steroid (estrone-3-sulfate) in wastewaters. The method utilizes LC/MS/MS following solid phase extraction and a two stage clean-up procedure, achieving limits of detection of 0.2 ng l(-1) for estriol, 17beta-estradiol and 17 alpha-ethinylestradiol, and 0.1 ng l(-1) for estrone and the conjugate. The approach demonstrates that using appropriate clean-up and deuterated internal standards, the impact of matrix effects on ionization can be overcome to reliably determine estrogens at environmentally relevant concentrations. The robustness of the method was demonstrated by achieving recoveries of >83% for all steroids in settled sewage and final effluent samples with relative standard deviations of 0.5-12%.

The occurrence and removal of selected pharmaceutical compounds in a sewage treatment works utilising activated sludge treatment.

Pharmaceutical substances have been detected in sewage effluents as well as receiving waters in many parts of the world. In this study, the occurrence and removal of a number of drug compounds were studied within a large sewage treatment plant in the south of England. Samples were processed using solid phase extraction and analysed using gas chromatography-mass spectrometry (GC-MS). The results demonstrate that ibuprofen, paracetamol, salbutamol and mefenamic acid were present in both the influent and effluent of the works while propranolol-HCl was not found above the limit of quantification in any sample. Elimination rates were circa 90% for each compound but several hundred nanograms per litre were still present in the final effluent.

Monitoring losses of copper based wood preservatives in the Thames estuary.

Field trials were conducted at two sites in the Thames estuary to monitor losses of copper, chromium and arsenic from wood preservative treated timbers of varying sizes and treatment regimes. Results indicated that leaching tests conducted under standard laboratory conditions might overestimate losses compared to losses resulting from real environmental exposures. Amine copper treated wood was noted to leach higher levels of copper compared to chromated copper arsenate treated wood, and was therefore considered an inappropriate replacement biocide for fresh and marine construction purposes on this basis. Increases in copper concentrations in the outer sections of amine copper treated posts may have represented re-distribution of this component in this timber. No accumulation of metals was found in sediments surrounding field trial posts.

Partitioning behavior of five pharmaceutical compounds to activated sludge and river sediment.

Pharmaceutical substances have been detected in sewage effluents as well as receiving waters in many parts of the world. To assess the fate and removal of these compounds within sewage treatment plants, an understanding of their partitioning behavior between the solid and aqueous phases is critical. Therefore, a preliminary study was conducted to ascertain an understanding of the binding behavior of five drug substances sorbing to the solid phase in a laboratory scale-activated sludge plant (Husmann unit). For comparison, uncontaminated river sediment was also used as a substrate. All of the compounds tested partitioned more readily to the sludge than the sediment, likely because of the former's higher organic carbon content. Partitioning to the solid phase correlated roughly with predicted log Kow values. A period of initial sorption was followed by a phase of desorption, and net absorption of the selected drugs (with the exception of mefenamic acid) after 5 hours of mixing was minimal.

Removal of an endocrine disrupting chemical (17alpha-ethinyloestradiol) from wastewater effluent by activated carbon adsorption: effects of activated carbon type and competitive adsorption.

Granular activated carbon has been extensively used for the adsorption of organic micropollutants for potable water production. In this study the removal of an endocrine disrupting chemical from wastewater final effluent by three types of granular activated carbon (wood, coconut and coal based) has been investigated in batch adsorption experiments and correlated with the removal of chemical oxygen demand (COD), total organic carbon (TOC) and ultraviolet absorbance (UV). The results obtained demonstrated 17alpha-ethinyloestradiol (EE2) removals of 98.6%, 99.3%, and 96.4% were achieved by the coal based (ACo), coconut based (ACn) and wood based (AWd) carbons respectively at the lowest dose of carbon (0.1gl(-1)). The other adsorbates investigated all exhibited good removal. At an equilibrium concentration of 7mgl(-1) the COD adsorption capacities were 3.16mg g(-1), 4.8 mg g(-1) and 7.1 mg g(-1) for the wood, coconut and coal based carbons respectively. Overall, the order of removal efficiency of EE2 and the other adsorbates for the three activated carbons was ACn > ACo > AWd. The adsorption capacities of the carbons were found to be reduced by the effects of other competing adsorbates in the wastewater effluent.

Butyltin compounds in a sediment core from the old Tilbury basin, London, UK.

Sections from a sediment core taken from the River Thames were analysed for butyltin species using gas chromatography with species-specific isotope dilution mass spectrometry. Results demonstrated that in most samples tributyltin concentrations of 20-60 ng/g accounted for <10% of the total butyltin species present, which is in agreement with data from other sediment samples which were historically contaminated with tributyltin. Vertical distribution of the organotin residues with depth throughout the core, with data on organochlorine compounds and heavy metals allowed for the construction of a consistent hypothesis on historical deposition of contaminated sediments. From this it was possible to infer that the concentrations of tributyltin in sediments deposited during the early 1960s were in the order of 400-600 microg/g by using degradation rate constants derived by other workers. Such values fall well within the range quoted for harbour sediments in the literature.

Evaluation of environmental burdens associated with sewage treatment processes using life cycle assessment techniques.

Life cycle assessments of a range of wastewater treatment processes have been undertaken. At lower consent standards rotating biological contactors and biological filters exhibit lower environmental burdens for the required functionality than other process options. However, at tighter consents this distinction becomes less clear. Attempts to reduce environmental burdens should focus on operational energy requirements (which dominate burden profiles and, where appropriate, on synthetic materials used for bio-mass growth). However, differences between dry and operational weight, and the consequent size of necessary foundation structures are likely to limit opportunities for reducing overall burden profiles through material substitution. Comparison of processes across population equivalents suggests economies of scale may favour adopting larger scale plant, although there are additional factors yet to be included in this analysis. Furthermore, adopting different waste disposal routes during the demolition phase is unlikely to have a distinct impact on burden profiles.