Torleiv Bilstad

Nitrogen separation from domestic wastewater by reverse osmosis

Abstract Norway is committed by the North Sea Convention to reduce nitrogen in liquid effluents in general by 50% by 1995. The base year is 1985. Communities treating more than 10 000 p.e. are ordered to remove a minimum of 70% total nitrogen from domestic effluents in specified sensitive areas. The Norwegian Enviromental Protection Agency has completed a three-year study on alternative nitrogen removal processes suitable for Norwegian conditions. Existing secondary-treatment plants are by and large based on chemical precipitation which therefore could be considered pretreatment for future nitrogen removal plants. Nitrogen separation trials by reverse osmosis (RO) was performed between October 1990 and August 1991 on domestic wastewater as well as on combined domestic-industrial wastewater. Separate RO trials were performed with both tubular and spiral-wound membrane elements. For domestic wastewater the separation efficiency was 95% for total nitrogen. No pretreatment was necessary for tubular RO membranes in addition to the existing chemical precipitation performed in the main treatment plant. Chemical precipitated effluent from the main treatment plant was the feed to the RO units. The spiral RO elements, however, did receive additional 25–200 μm cartridge filters as pretreatment. This was essential as solid separation in the chemical precipitation pretreatment plant was unpredictable, and carry-over solids easily clogged the spiral-wound flow channels. This was especially a problem for treatment of combined domestic-industrial wastewater and not during treatment of domestic wastewater only. Chemical cleaning of the spiral-wound membranes was performed every other day for treatment of domestic wastewater. This ensured a permeate flux of 201/m2/h at 25°C and an inlet feedwater pressure of 35 kg/cm2. No optimization of recovery rate was attempted during the trials. A full-scale design, however, for treating 40 and 200 m3/h is included in the paper. Also, steam stripping of NH3 from the retentate is suggested, with nitrogen recovered as (NH4)2SO4, NH4NO3 or (NH4)3PO4.

Effect of selective organic fractions on denitrification rates using Salsnes Filter as primary treatment

The purpose of this project was to investigate the effect of selective particle removal during primary treatment on downstream biological nutrient removal processes. Bench-scale Salsnes Filter fine mesh sieves were used as a primary treatment to obtain different organic fractions to test the effect on denitrification. Activated sludge and moving bed biofilm reactor anoxic tests were performed on municipal wastewater collected from two full-scale wastewater treatment plants located around the Oslo region (Norway). About 43% of the suspended solids in the wastewater was less than 18 μm, and 14% was between 18 and 150 μm. The effect of particulate chemical oxygen demand (COD) removal on denitrification rates was very minor.

Impact of fine mesh sieve primary treatment on nitrogen removal in moving bed biofilm reactors

The purpose of this project was to investigate the effect of selective particle removal during primary treatment on nitrogen removal in moving bed biofilm reactors (MBBRs). Two small MBBR pilot plants were operated in parallel, where one train treated 2 mm screened municipal wastewater and the other train treated wastewater that had passed through a Salsnes Filter SF1000 rotating belt sieve (RBS) with a 33 µs sieve cloth. The SF1000 was operated without a filter mat on the belt. The tests confirmed that, for the wastewater characteristics at the test plant, Salsnes Filter primary treatment with a 33 µs RBS and no filter mat produced a primary effluent that was close to optimum. Removal of organic matter with the 33 µs sieve had no negative effect on the denitrification process. Nitrification rates improved by 10-15% in the train with 33 µs RBS primary treatment. Mass balance calculations showed that without RBS primary treatment, the oxygen demand in the biological system was 36% higher. Other studies have shown that the sludge produced by RBS primary treatment is beneficial for biogas production and will also significantly improve sludge dewatering of the combined primary and biological sludge.

Wind-powered RO desalination

AbstractTwo pilot projects were dedicated to wind-powered RO desalination. Project #1 had a wind turbine connected to a battery bank, while Project #2 had a wind turbine connected directly to a crank mechanism, a compressor, and a water pump. The target of both projects was to produce potable water from sea water with satisfactory pressure and flow rate of RO permeate. Both projects showed that a combination of RO desalination and wind power is technological feasible when the RO system is operated with fluctuating and intermittent loads following the energy supply characteristic of the wind turbine. Depending on the technical design, the systems provide 1.4 and 7.5 m3/24 h potable water, which satisfy basic needs for small populations in coastal regions.

Produced Water Treatment with Membranes for Enhanced Oil Recovery in Carbonate and Sandstone Reservoirs

The research is focused on determining the technical performance of membranes for treating and reinjecting produced water (PW). Ionic composition of pre-treated PW containing 90,000 ppm total dissolved solids (TDS) is manipulated by membrane separation and reinjected as smart water in carbonate and sandstone reservoirs. Nanofiltration (NF) membranes coupled with reverse osmosis (RO) membranes are tested in this research. TDS of less than 5,000 ppm with negligible divalent ions is defined as Smart Water for sandstone reservoirs. High divalent ion concentrations with TDS typically above 10,000 ppm compose Smart Water for carbonate reservoirs. The performance of NF membranes at different pH of PW is evaluated at various pressures. An economic analysis is performed for different combinations of membranes with TDS of 90,000 ppm as reference. A combination of two NF membranes are used to produce Smart Water for carbonate reservoirs. The power consumption is calculated at 0.37 kWh/m3. PW reinjection in sandstones with TDS of 5,000 ppm require either the use of permeate from RO or supplying fresh water by other means for diluting permeate from NF. A power consumption of 14.8 kWh/m3 is calculated for the combination of two NF membranes and RO for Smart Water production for sandstones.

Smart Water for Enhanced Oil Recovery by Nano-Filtration

Chemistry of injected water can modify the wettability behaviour of carbonate reservoirs. Wettability modification towards more water-wet reservoir rocks results in increased oil production. Smart water production by selective ionic water content is a major developing area in current enhanced oil recovery (EOR). Technical limitations for smart water production for EOR using seawater as feed for membranes are described in this paper. Desired characteristics of smart water for injection into carbonate reservoirs are low Na+ and Cl- and high divalent ion concentrations. Wettability alteration by smart water occurs due to symbiotic behaviour of Ca2+, SO4 2- and Mg2+ ions and the carboxylic material of the reservoir rock surface. Nano-filtration (NF) and Reverse Osmosis (RO) membranes were used for ion separation experiments. Retentate from NF contains the main constituents of smart water. Membrane performance was evaluated in terms of rejection under varying feed compositions and pressures. An analysis of general approaches for water injection processes from seawater is discussed. This paper delivers an economic framework for evaluation of the water injection process by including major technical and economical elements. Main criteria considered in this research were how to decrease monovalent ion rejection. This was achieved by increasing divalent ion concentration by spiking feed water with selected chemicals. Results showed that a decrease in retention of monovalent ions was achieved by increasing multivalent ion concentration in the feed. A challenge of smart water production is the high dissolved solids content (TDS) in retentate from NF. Three options to dilute the retentate were evaluated; i.e., combinations of NF and RO, MSFD and fresh water. The most feasible process is a combination of NF and RO, with an energy consumption of 3.8 kWh/m3.

Implementation of Spiegler–Kedem and Steric Hindrance Pore Models for Analyzing Nanofiltration Membrane Performance for Smart Water Production

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.

Petroleum production in symbiosis with fisheries? The Norwegian experience

francaisLes peches et les industries Petrolieres et Gazieres (P&G) offshore ont une longue histoire de coexistence. Les deux industries laissent un impact sur le milieu marin et sont soumises a des reglements afin de garantir une utilisation durable des ressources. Les activites d’exploration offshore, forage et production de P&G peuvent affecter les peches a travers des activites sismiques, le deversement de dechets dangereux et la presence de structures physiques. Historiquement, les deblais provenant de puits de forage sous la surface ont ete deposes directement a partir de la plateforme au fond marin. Cependant, les lois et reglements environnementaux pour le secteur offshore norvegien interdisent une telle pratique lorsque l’huile de la coupe depasse 1% en poids. La reinjection de deblais sous forme de boue dans des formations souterraines est encore pratiquee. A cause de la migration, les fuites, la boue rentrant sur le fond marin et l’effondrement des formations, cette methode d’elimination est sur le declin. Le transport des deblais huileux a terre pour le traitement final c’est la pratique que privilegient les norvegiens. Toutefois, le traitement des deblais sur les plateformes est egalement evalue en permanence. Pour des raisons de logistique et de cout, ainsi que pour des raisons de sante, de securite et d’environnement (HSE) et de milieu de travail, l’accent est mis sur la reduction des dechets en mer, la reutilisation et le recyclage. EnglishFisheries and offshore Oil and Gas (O&G) industries have a long history of co-existence. Both industries leave an impact on the marine environment, and are subject to regulations in order to ensure sustainable use of resources. Offshore O&G exploration, drilling and production activities may impact fisheries through seismic activities, discharge of hazardous waste and presence of physical structures. Historically, cuttings from drilling sub-surface wells have been deposited directly from the platform to the seabed. However, environmental laws and regulations for the Norwegian offshore sector prohibit such practice when the oil on cutting exceeds 1% by weight. Re-injection of cuttings as a slurry into subsurface formations is still practiced. Due to migration, leaks, re-entering of slurry onto the seabed, and collapsing formations this disposal method is on a decline. Transport of oily cuttings to shore for final treatment is the preferred Norwegian practice. However, cutting treatment on platforms is also continuously evaluated. For logistics and cost reasons, as well as health, safety and environmental (HSE) and working environment reasons, emphasis is put on offshore waste minimization, reuse and recycle.

Full-scale experience with enhanced biological phosphorus removal (EBPR) in cold climates

Abstract This investigation includes three years of full‐scale experiences at the first EBPR plant in Norway, Groos WWTP in Grimstad. The main focus was on low temperature performance (below 7 °C) and the effect of wastewater characteristics (COD). The treatment efficiency was not affected by low temperature; 0.35 mg/1 phosphorus in the effluent during 1998 (94 % removal). COD‐levels, however, did affect the process. The results from the study are used as a basis for retrofitting plants that removes phosphorus by chemical precipitation. Results from experiments at a partly retrofitted plant are also presented.