Each time regulatory agencies initiate more stringent environmental controls, treatment technologies are refined to meet the updated standards. Centrifuges and hydrocyclones are, by and large, producing satisfactory effluents for meeting current quality requirements for the offshore petroleum industries. The European standard for effluent from onshore petroleum activities, however, requires less than 5 mg/l total hydrocarbons (HC) and less than 10 mg/l suspended solids. Such low concentrations are out of reach for the above classical separation processes. The amount of produced water in the North Sea is projected to increase by a factor of 6 from 1990 to the year 2000; from 16 to 90 million cubic meters each year. Produced water is the predominant source for oil discharges. The synergistic effects of chemicals, oil and dissolved components in the produced water effluent are given increased attention, with expectations of tougher effluent criteria. Microfiltration (MF) and ultrafiltration (UF) pilot trials with produced water from the Snorre field in the North Sea showed that UF, but not MF, could meet more stringent effluent standards for total HC, suspended solids and dissolved constituents. Total HC in the produced water was typically 50 mg/l and was reduced to 2 mg/l in the UF permeate (96% removal). The aromatics benzene, toluene and xylene (BTX) were similarly reduced by 54% and the heavy metals copper (Cu) and zinc (Zn) by 95%. UF trials were performed with organic tubular membranes with typical transmembrane pressures between 6 and 10 bars. The feed velocities through the tubes were between 2 and 4 m/s. Flux varied from 140 to 550 l/m2/h (lmh) at a produced water temperature of 60°C and membrane molecular weight cut-off between 100,000 and 200,000 daltons. By recirculating UF retentate as membrane feed, a volume reduction (VR) of 24 was obtained in the trials; i.e., 96% permeate recovery. The limited volume of produced water available in the feed tank negated further volume reduction. Full-scale design is based on permeate recovery of 99%. No irreversible fouling of the membrane surface was experienced. The cleanwater flux was restored after chemical cleaning. The alkaline detergent Ultrasil 11 was chosen as the optimal cleaning agent.
Naphthalene, the smallest polycyclic aromatic hydrocarbon (PAH), is found in abundance in crude oil, its major source in marine environments. PAH removal occurs via biodegradation, a key process determining their fate in the sea. Adequate estimation of PAH biodegradation rates is essential for environmental risk assessment and response planning using numerical models such as the oil spill contingency and response (OSCAR) model. Using naphthalene as a model compound, biodegradation rate, temperature response and bacterial community composition of seawaters from two climatically different areas (North Sea and Arctic Ocean) were studied and compared. Naphthalene degradation was followed by measuring oxygen consumption in closed bottles using the OxiTop(®) system. Microbial communities of untreated and naphthalene exposed samples were analysed by polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) and pyrosequencing. Three times higher naphthalene degradation rate coefficients were observed in arctic seawater samples compared to temperate, at all incubation temperatures. Rate coefficients at in situ temperatures were however, similar (0.048 day(-1) for temperate and 0.068 day(-1) for arctic). Naphthalene biodegradation rates decreased with similar Q10 ratios (3.3 and 3.5) in both seawaters. Using the temperature compensation method implemented in the OSCAR model, Q10 = 2, biodegradation in arctic seawater was underestimated when calculated from the measured temperate k1 value, showing that temperature difference alone could not predict biodegradation rates adequately. Temperate and arctic untreated seawater communities were different as revealed by pyrosequencing. Geographic origin of seawater affected the community composition of exposed samples.
Manure ought to be controlled and handled environmentally soundly. Volume reduction of surplus manure by reverse osmosis (RO) is a viable and economic option in certain areas where another alternative is to reduce the number of animals. This membrane separation project arose out of an urgent need to re-establish an ecological balance between farming and the natural environment without necessarily having to decrease the number of livestock. The suggested technical solutions should not significantly reduce the standard of living of the farmers. Dewatering of manure makes it easier to store and transport the nutrients. RO coupled to anaerobic digestion as pretreatment with inherent production of biogas energy leads to on-site production and use of biological fertilizer and humus. Such treatment will improve the hygienic conditions and general health of the farming communities compared to purchase and sole use of chemical fertilizers. Mechanical dewatering of raw as well as anaerobically digested pig manure yields a cake of 25 % solids and a liquid fraction containing 1 % solids. The solid cake contained virtually all the phosphorous, whereas nitrogen was dissolved equally in water in both fractions. A tubular RO membrane plant separated 95 % of the total nitrogen in the liquid fraction. The particle free permeate met the effluent criteria for direct discharge to the neighbouring fjord. The concentrate approached one tenth of the original manure volume and is considered a liquid fertilizer. Cleaning of the membranes was performed with nitric acid and the alkaline detergent Ultrasil 11. The membrane flux was fully recovered after each chemical cleaning.
A predictive model correlating the parameters in the mass transfer-based model Spiegler–Kedem to the pure water permeability is presented in this research, which helps to select porous polyamide membranes for enhanced oil recovery (EOR) applications. Using the experimentally obtained values of flux and rejection, the reflection coefficient σ and solute permeability Ps have been estimated as the mass transfer-based model parameters for individual ions in seawater. The reflection coefficient and solute permeability determined were correlated with the pure water permeability of a membrane, which is related to the structural parameters of a membrane. The novelty of this research is the development of a model that consolidates the various complex mechanisms in the mass transfer of ions through the membrane to an empirical correlation for a given feed concentration and membrane type. These correlations were later used to predict ion rejections of any polyamide membrane with a known pure water permeability and flux with seawater as a feed that aids in the selection of suitable nanofiltration (NF) for smart water production.
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