Performance of a hybrid reverse osmosis-constructed wetland treatment system for brackish oil field produced water

Using constructed wetlands, produced waters from oil fields (i.e., waters that have been in contact with oil in situ) can be treated to enhance water quality for irrigation purposes, or subsequent discharge to receiving aquatic systems. In produced water containing elevated levels of salt (i.e., brackish-produced waters), the ability to decrease the conductivity of the produced water may influence potential reuse of the water for irrigation purposes. The objectives of this research were (1) to determine the efficacy of a pilot-scale hybrid reverse osmosis (RO)-constructed wetland system for treatment and reuse of produced waters from an oil field, and (2) to assess the quality of treated water in terms of physicochemical characteristics and toxicity influencing reuse of the water for irrigation or other designated uses. Specifically, the performance of the hybrid treatment system was examined in terms of outflow water conductivity, total dissolved solids (TDS), and toxicity using Ceriodaphnia dubia and Pimephales promelas in 7-day static/renewal exposure tests. Prior to treatment, significant mortality was observed for C. dubia and P. promelas exposed for 7 days to 6.25% untreated produced water. Following treatment through the hybrid system, no significant mortality was observed in C. dubia or P. promelas exposed to 100% treated produced water when compared to the control organisms. The pilot-scale RO-constructed wetland system effectively decreased conductivity by 95% and TDS by 94% in the brackish produced water tested in this study. Following treatment, the produced water was suitable for irrigation or discharge to surface waters. Therefore, hybrid RO-constructed wetland treatment systems present a viable alternative for treatment and reuse of produced waters from oil fields.     

Pathways and metabolites of microbial degradation of selected acidic pharmaceutical and their occurrence in municipal wastewater treated by a membrane bioreactor

Laboratory degradation tests with five acidic pharmaceuticals using activated sludge as inocculum under aerobic conditions were performed and microbial metabolites were analysed by liquid chromatography-mass spectrometry (LC-MS). Ketoprofen was partly mineralized as a sole source of carbon and energy and the metabolites determined by LC-MS suggest microbial ketoprofen degradation to proceed along the pathway known for biphenyls and related compounds. Bezafibrate, naproxen and ibuprofen were degraded only cometabolically whereas no transformation was obtained for diclofenac. Some biodegradation intermediates in these batch tests could be tentatively identified by means of LC-MS. The first step in microbial bezafibrate degradation appears to be the hydrolytic cleavage of the amide bond, generating well degradable 4-chlorobenzoic acid as one of the hydrolysis products. As previously found for mammals, ether cleavage and formation of desmethylnaproxen was the initial step in microbial degradation of naproxen. Two isomers of hydroxy-ibuprofen were detected as intermediates in the mineralization of ibuprofen. Laboratory studies suggest that naproxen and ibuprofen can be fully mineralized whereas more stable metabolites occur in microbial ketoprofen and bezafibrate transformation, that may deserve further attention. A LC-MS method for the trace analysis of these metabolites in water was developed and applied to municipal wastewater. Municipal wastewater treatment by a membrane bioreactor may gradually improve the removal of these pharmaceuticals.     

Kinetics and mechanism for degradation of dichlorvos by permanganate in drinking water treatment

The degradation kinetics and mechanism of dichlorvos by permanganate during drinking water treatment were investigated. The reaction of dichlorvos with permanganate was of second-order overall with negligible pH dependence and an activation energy of 29.5 kJ·mol⁻¹. At pH 7.0 and 25 °C, the rate constant was 25.2 ± 0.4 M⁻¹ s⁻¹. Dichlorvos was first degraded to trimethyl phosphate (TMP) and dimethyl phosphate (DMP) simultaneously which approximately accounted for <5% and ≥95% with respect to phosphorus mass, respectively. Further oxidation of DMP generated a final byproduct, monomethyl phosphate (MMP). MMP was for the first time identified as a major byproduct in chemical oxidation of dichlorvos. The kinetic model based on degradation mechanism and determined reaction rate constants allowed us to predict the evolution of dichlorvos and its byproduct concentrations during permanganate pre-oxidation process at water treatment plants. These results suggest that even though the dichlorvos concentration in surface water complies with the surface water quality standards of China (50 μg L⁻¹), its concentration after conventional water treatment will most probably exceed the drinking water quality standards (1 μg L⁻¹). Moreover, luminescent bacteria test shows that the acute toxicity of dichlorvos solution evidently increased after permanganate oxidation.     

Bacterial response to a shock load of nanosilver in an activated sludge treatment system

The growing release of nanosilver into sewage systems has increased the concerns on the potential adverse impacts of silver nanoparticles (AgNPs) in wastewater treatment plants. The inhibitory effects of nanosilver on wastewater treatment and the response of activated sludge bacteria to the shock loading of AgNPs were evaluated in a Modified Ludzack-Ettinger (MLE) activated sludge treatment system. Before shock-loading experiments, batch extant respirometric assays determined that at 1 mg/L of total Ag, nitrification inhibitions by AgNPs (average size = 1-29 nm) and Ag⁺ ions were 41.4% and 13.5%, respectively, indicating that nanosilver was more toxic to nitrifying bacteria in activated sludge than silver ions. After a 12-h period of nanosilver shock loading to reach a final peak silver concentration of 0.75 mg/L in the MLE system, the total silver concentration in the mixed liquor decreased exponentially. A continuous flow-through model predicted that the silver in the activated sludge system would be washed out 25 days after the shock loading. Meanwhile, a prolonged period of nitrification inhibition (>1 month, the highest degree of inhibition = 46.5%) and increase of ammonia/nitrite concentration in wastewater effluent were observed. However, nanosilver exposure did not affect the growth of heterotrophs responsible for organic matter removal. Microbial community structure analysis indicated that the ammonium-oxidizing bacteria and nitrite-oxidizing bacteria, Nitrospira, had experienced population decrease while Nitrobacter was washed out after the shock loading.     

天津市某污水处理及再生水利用工程设计探讨

结合GB 18918-2002城镇污水处理厂污染物排放标准,对天津市某污水处理及再生水利用工程设计进行了探讨,分别阐述了具体处理工艺及相关设计参数,并归纳了该设计方案中的节能措施,以指导今后同类工程项目。     

Occurrence and removal of pharmaceuticals in a municipal sewage treatment system in the south of Sweden

The occurrence and removal rate of seven pharmaceuticals (ibuprofen, naproxen, diclofenac, fluoxetine, ofloxacin, norfloxacin, ciprofloxacin), two metabolites (norfluoxetine, clofibric acid), one degradation product (4-isobutylacetophenone) and 3 estrogens (17α-ethinylestradiol, 17β-estradiol, estrone) were studied in the inlet and outlet of a tertiary sewage treatment plant (STP) in Sweden as well as between different treatment steps in the STP which includes a conventional activated sludge step. Pharmaceuticals in raw household and raw hospital sewage streams leading to the STP were as well investigated. Hydraulic retention times (HRT) of each treatment step was considered for sampling and for the calculation of the removal rates. These rates were above 90%, except for diclofenac, clofibric acid, estrone and ofloxacin. However, only diclofenac and naproxen showed significant effluent loads (> 145 mg/d/1000 inh). Diclofenac was not eliminated during the treatment and in fact even higher concentrations were found at the effluent than in the inlet of the STP. 17α-Ethinylestradiol was not detected in any of the samples. Results indicate that a STP such as the one in Kristianstad, Sweden, with a tertiary treatment is sufficient to remove significantly most of the investigated pharmaceuticals. The chemical treatment improved the removal of several pharmaceuticals especially the antibiotics, which showed step removal rates between 55 and 70%. The expected concentration levels of the pharmaceuticals in the surface water (dilution 1 to 10) close to the outlet of the STP are below the no-observed effect-concentration (NOEC). However, despite that this would imply no important effects in the aquatic environment one cannot rule out negative consequences nearby the STP because most of the NOEC values are derived from acute toxicity data. This may underestimate the real impact of pharmaceuticals in the aquatic ecosystem.     

Development of solar-driven electrochemical and photocatalytic water treatment system using a boron-doped diamond electrode and TiO2 photocatalyst

A high-performance, environmentally friendly water treatment system was developed. The system consists mainly of an electrochemical and a photocatalytic oxidation unit, with a boron-doped diamond (BDD) electrode and TiO₂ photocatalyst, respectively. All electric power for the mechanical systems and the electrolysis was able to be provided by photovoltaic cells. Thus, this system is totally driven by solar energy. The treatment ability of the electrolysis and photocatalysis units was investigated by phenol degradation kinetics. An observed rate constant of 5.1 × 10⁻³ dm³ cm⁻² h⁻¹ was calculated by pseudo-first-order kinetic analysis for the electrolysis, and a Langmuir-Hinshelwood rate constant of 5.6 μM⁻¹ min⁻¹ was calculated by kinetic analysis of the photocatalysis. According to previous reports, these values are sufficient for the mineralization of phenol. In a treatment test of river water samples, large amounts of chemical and biological contaminants were totally wet-incinerated by the system. This system could provide 12 L/day of drinking water from the Tama River using only solar energy. Therefore, this system may be useful for supplying drinking water during a disaster.     

Measurement of the initial phase of ozone decomposition in water and wastewater by means of a continuous quench-flow system: application to disinfection and pharmaceutical oxidation

Due to a lack of adequate experimental techniques, the kinetics of the first 20s of ozone decomposition in natural water and wastewater is still poorly understood. Introducing a continuous quench-flow system (CQFS), measurements starting 350 ms after ozone addition are presented for the first time. Very high HO. to O3 exposures ratios (Rct=integralHO.dt/integralO3dt) reveal that the first 20s of ozonation present oxidation conditions that are similar to ozone-based advanced oxidation processes (AOP). The oxidation of carbamazepine could be accurately modeled using O3 and HO. exposures measured with CQFS during wastewater ozonation. These results demonstrate the applicability of bench scale determined second-order rate constants for wastewater ozonation. Important degrees of pharmaceutical oxidation and microbial inactivation are predicted, indicating that a significant oxidation potential is available during wastewater ozonation, even when ozone is entirely decomposed in the first 20s.     

Occurrence of aromatic amines and N-nitrosamines in the different steps of a drinking water treatment plant

The occurrence of 24 amines within a full scale drinking water treatment plant that used chlorinated agents as disinfectants was evaluated for the first time in this research. Prior to any treatment (raw water), aniline, 3-chloroaniline, 3,4-dichloroaniline and N-nitrosodimethylamine were detected at low levels (up to 18 ng/L) but their concentration increased ∼10 times after chloramination while 9 new amines were produced (4 aromatic amines and 5 N-nitrosamines). Within subsequent treatments, there were no significant changes in the amine levels, although the concentrations of 2-nitroaniline, N-nitrosodimethylamine and N-nitrosodiethylamine increased slightly within the distribution system. Eleven of the 24 amines studied were undetected either in the raw and in the treatment plant samples analysed. There is an important difference in the behaviour of the aromatic amines and N-nitrosamines with respect to water temperature and rainfall events. Amine concentrations were higher in winter due to low water temperatures, this effect being more noticeable for N-nitrosamines. Aromatic amines were detected at their highest concentrations (especially 3,4-dichloroaniline and 2-nitroaniline) in treated water after rainfall events. These results may be explained by the increase in the levels of amine precursors (pesticides and their degradation products) in raw water since the rainfall facilitated the transport of these compounds from soil which was previously contaminated as a result of intensive agricultural practices.     

Measurement of dissolved organic nitrogen in a drinking water treatment plant: size fraction, fate, and relation to water quality parameters

This paper investigates the characteristics of dissolved organic nitrogen (DON) in raw water from the Huangpu River and also in water undergoing treatment in the full-scale Yangshupu drinking water treatment plant (YDWTP) in Shanghai, China. The average DON concentration of the raw water was 0.34 mg/L, which comprised a relatively small portion (~ 5%) of the mass of total dissolved nitrogen (TDN). The molecular weight (MW) distribution of dissolved organic matter (DOM) was divided into five groups: > 30, 10-30, 3-10, 1-3 and < 1 kDa using a series of ultrafiltration membranes. Dissolved organic carbon (DOC), UV absorbance at wavelength of 254 nm (UV254) and DON of each MW fraction were analyzed. DON showed a similar fraction distribution as DOC and UV254. The < 1 kDa fraction dominated the composition of DON, DOC and UV254 as well as the major N-nitrosodimethylamine formation potential (NDMAFP) in the raw water. However, this DON fraction cannot be effectively removed in the treatment line at the YDWTP including pre-ozonation, clarification and sand filtration processes. The results from linear regression analysis showed that DON is moderately correlated to DOC, UV254 and trihalomethane formation potential (FP), and strongly correlated to haloacetic acids FP and NDMAFP. Therefore, DON could serve as a surrogate parameter to evaluate the reactivity of DOM and disinfection by-products FP.     

The impact of pH on floc structure characteristic of polyferric chloride in a low DOC and high alkalinity surface water treatment

The adjustment of pH is an important way to enhance removal efficiency in coagulation units, and in this process, the floc size, strength and structure can be changed, influencing the subsequent solid/liquid separation effect. In this study, an inorganic polymer coagulant, polyferric chloride (PFC) was used in a low dissolved organic carbon (DOC) and high alkalinity surface water treatment. The influence of coagulation pH on removal efficiency, floc growth, strength, re-growth capability and fractal dimension was examined. The optimum dosage was predetermined as 0.150 mmol/L, and excellent particle and organic matter removal appeared in the pH range of 5.50-5.75. The structure characteristics of flocs formed under four pH conditions were investigated through the analysis of floc size, effect of shear and particle scattering properties by a laser scattering instrument. The results indicated that flocs formed at neutral pH condition gave the largest floc size and the highest growth rate. During the coagulation period, the fractal dimension of floc aggregates increased in the first minutes and then decreased and larger flocs generally had smaller fractal dimensions. The floc strength, which was assessed by the relationship of floc diameter and velocity gradient, decreased with the increase of coagulation pH. Flocs formed at pH 4.00 had better recovery capability when exposed to lower shear forces, while flocs formed at neutral and alkaline conditions had better performance under higher shear forces.     

A hybridized photocatalysis-microfiltration system with iron oxide-coated membranes for the removal of natural organic matter in water treatment: Effects of iron oxide layers and colloids

A photocatalysis/microfiltration (MF) hybrid system, with the coating of a membrane using iron oxide particles (IOPs), was investigated with respect to natural organic matter (NOM) removal and membrane permeability during the treatment of various surface waters. A comparison of the performance between bare (uncoated) and IOP-coated membranes employed for the photocatalytic hybrid system was made. Due to the additional adsorption of NOM onto IOPs on the membrane surface, the IOP-coated membrane system always achieved greater DOC removal efficiencies during photocatalysis/MF. Particularly, the influence of colloidal particles that were present in different water sources with respect to membrane fouling was explored. Colloidal fouling occurred to both bare and IOP-coated membranes, but the interaction of colloids with IOP coating layers was in close association with the characteristics of colloids, such as size distribution, resulting in opposing fouling behaviors with varying water sources. The IOP-coated membrane was able to control fouling properly when a relatively large size of colloidal particles existed in raw water, but not for the case of small colloids. The IOP coat layer may become denser as small colloids penetrate into it, therefore leading to further fouling. The analysis of the hydraulic filtration resistances revealed that such fouling was virtually reversible in being removed by backwashing processes. Scanning electron microscopic observations, however, visualized the existence of several foulants remaining at the membrane surface after backwashing when feed water, containing a relatively large portion of small-sized colloids, was supplied.     

Inhibition and recovery in a fixed microbial film leachate treatment system subject to shock loading of copper and zinc

The impacts of shock loadings of copper and zinc (up to 50 mg l(-1)) on the treatment efficiency of a mesoscale-fixed microbial film landfill leachate treatment system were investigated. Treatment inhibition and recovery were monitored in sequence over two 36 h experimental runs. The fate of added metals was also investigated. Copper, and to a lesser extent zinc, added to the treatment systems accumulated on the biofilm media. Increasing copper inputs (>10 mg l(-1)) progressively inhibited biological treatment of ammoniacal-nitrogen and carbon; this inhibition persisted into the recovery phase for nitrogen but not for carbon. Only the highest input of zinc affected media metal contents and carbon treatment rates; the latter inhibitory effect did not persist into the recovery phase. A small proportion of the metals accumulated on the biofilm media during the inhibition phase was released into the bulk leachate during the recovery experiment. These findings suggest a need to manage metal inputs into leachate treatment systems in order to ensure their continued efficacy.     

Sustainable reduction in the flux of microbial compliance parameters from urban and arable land use to coastal bathing waters by a wetland ecosystem produced by a marine flood defence structure

'Natural' treatment systems such as wetlands and reed beds have been proposed as sustainable means of reducing fluxes of faecal indicator organisms (FIOs) to recreational and shellfish harvesting waters. This is because FIO fluxes to coastal waters from both point (effluent) and diffuse (catchment) sources can cause non-compliance with microbiological standards for bathing and shellfish harvesting waters. The Water Framework Directive requires competent authorities in the member states to manage both point and diffuse sources of FIOs in an integrated manner to achieve compliance with 'good' water quality as defined in a series of daughter Directives. This study was undertaken to investigate the relative sources of FIOs to the popular bathing waters around Clacton, UK. In this predominantly arable (mainly cereal cropping) farming area, the principal land use predictor, explaining 76% of the variance in geometric mean presumptive Escherichia coli concentration at sub-catchment outlets during the bathing season, was the proportion of built-up (i.e. urbanised) land in each sub-catchment. This new finding contrasts with earlier studies in livestock farming regions where the proportion of improved grassland has proven to be the strongest predictor of microbial concentration. Also novel in this investigation, a flood defence wall has been built creating a wetland area which discharges every tidal cycle. The wetland produces over 97% reduction in the flux and concentrations of FIOs to the marine recreational waters. Also, FIO concentrations in water draining through the wetland to the sea were similar to concentrations measured in six UK sewage treatment plant effluents subject to secondary (biological) treatment followed by UV disinfection.