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Process integrated closed cycle water management system for dry docks (PI-WAMAS)


The occurring wastewater shows high values of suspended solids and COD. The suspended solid concentrations range from 40 to 1000mg/l and COD from 20 to 545mg/l. According to the German regulations these values are very high. The quantity of oxygen used in biological and non-biological oxidation of materials in water is the COD, it is therefore a measure of water quality. In shipyards the high COD demand results from the use of paints, glues and detergents. A large number of organic halogens, which are of environmental concern, were found in the examined wastewater. Instead of analysing the concentration of each compound separately, the sum parameter of the absorbable organic halogens AOX is determined. The load of AOX at the shipyard results from the cleaning and washing of the ships. Regarding the German restrictions AOX concentrations have to be below 0,5 mg/l. Three of the samples, which were analysed, exceed this limit. Due to the discharge of ballast water and dry docking activities a lot of mineral oil hydrocarbons can be found in the wastewater of shipyards which are very difficult to reduce. According to the analysis the hydrocarbons seem not to be a big problem in comparison to the suspended solids and COD. Except one sample all the other values were under the limit. The heavy metal concentrations of copper, nickel and chromium in the filtrate, sediments and suspended solids pass the limit values.
With the samples for the analysis of the occurring wastewater (Task A) also a size distribution of the particles was carried out. With the help of this analysis the range of the distribution of the particles occurring in the wastewater could be determined. The size distribution is very important for the simulation procedure. All results were sent to the project partnersA CAD design of the polyphase separator with a flow rate about 5m{3}/h was drawn up. The fluid to be purified enters a specially sized inlet chamber between via a supply pipeline. The fluid travels down and enters the second chamber where the lamella is installed. Through the lamellas it flows up and exits the separator via the drain pipeline. Sedimentation occurs during the upward flow of the fluid to be purified. The solids sediment on the plates and slide down into the sludge funnel. The sludge is thickened in the sludge funnel and exits the separator via the sludge extractor. A barrier between the two chamber prevents turbulence. The solids sedimented on the lamella cannot be carried away when the fluid enters. Two inlets will give us the opportunity to make a optimisation. For the separation of the oil two outlets are installed in the first and second chamber (above the outlet of the effluent). A funnel is installed for the sludge above the lamella. This CAD design is transferred into the process simulation system CFD. With this CFD program the first simulations were executed. With the main parameters as specified under Task A simulations were carried out with taking into consideration of flow, gravity and density of the particles and the particle size distribution for the simultaneous separation of particulates over wide operational conditions. Due to the CFD optimisation ttz contacted together GEI-2A and ProSys companies in order to choose the most suitable separator. The purchased separator has these specifications: - Material: HD-PE; - Height x length x depth: 3250 x 2340 x 1330mm; - Lamella package: 1196 x 1320 x 1000mm; - Distance between the lamella: 44mm; - Angle: 60°.
Instituto de soldadura e qualidade (ISQ) was responsible for the design of a compact high efficient low-energy electrolsys cell for removing low salt concentrations from the pre-treated water. It was found that this type of technology is not suitable for desalination /removal of salts and it was necessary to find another desalination solution. He project decided to change the system for a Reverse Osmosis technology for shipyard wastewater at a flow rate of 1m{3}/h for demonstration. This technology has the following advantages: - Plant specially designed to treat high salt contents water; - Does not require the use of any chemical regenerants; - Excellent efficiency (90 - 95 %); - Low energy consumption.
Further optimisation is still needed regarding the flow in the lamella separator. The simulation has shown that the velocity in the second chamber is only routed to another direction but an equal distribution of the flow could not be reached. The angle of the lamella has not been changed as we had the highest angle. If the angle would be smaller, the slipping of the particles, settled down on the lamellas, could be prevented. For the further optimisation of the separator, different lamella types and the modification of the distance between the lamellas could be performed. Due to time limitations, this could not be done during the project. The activated carbon prototype was built to test the efficiency of absorption of TBT, PCB and heavy metals from shipyard wastewater. The prototype consisted of three columns, two of which were packed with KAC in different configurations (1 rolled KAC, 1 stacked KAC). The third column was packed with GAC. Wastewater was pumped through the 3 columns at similar flow rates. Outlet samples were collected for analysis and results were compared. The GAC column and the stacked KAC configuration gave the most favourable results under real conditions at the shipyard. Some problems were experienced with the stacked KAC configuration: the wastewater did not flow through through the KAC layers with ease, a fact supported by the high back pressure observed at the base of this column. Some design changes, which improved performance for a short period, were made The Reverse Osmosis was supplied to remove the salt concentrations of the waste water that will be re-utilized in cleaning operations of the shipyards. Samples were collected in the inlet and outlet water in order to determine the efficiency of the system. The outlet streams from the three separate AC columns were combined to form one single wastewater stream, which was pumped to the desalination system. The pump (P6) feeding the desalination system requires continuous operation, while the pumps (P3, P4, P5) feeding the activated carbon columns operates on a discontinuous basis. Therefore, the flow-rate to the desalination unit was not as effective as had been hoped. In addition, the hydraulic pressure is higher than 0.5 bar and the system is now mere operation to protect the reverse osmosis membranes rejecting water directly through a bypass system. Regarding the wastewater quality a continuous monitoring at the outlet of each individual treatment step must be installed. A PLC (SIMATIC S7-300) was used to program the control system. With appropriate sensors such as conductivity, pH value and turbidity the individual treatment steps (lamella separator, activated carbon unit and desalination) are switched on or off in dependence of the measured degree of water quality. The treated water from a certain treatment step is recycled via a valve into a storage basin if a parameter is above a certain limit value. If the water quality at the end of a treatment step requires further treatment, the next treatment unit is activated and the water treatment is hence improved. For the process control and visualization application the WinCC (Windows Control Centre) system software was used. WinCC is a Human Machine Interface means controlling the process, keeping machines and plant operating on standard PCs running Windows NT and Windows 2000. It enables individually configured user interfaces to be created for every application - for more reliable process control and optimisation of production in general.
Laboratory investigations have indicated that a new knitted activated carbon (KAC) material is an effective adsorbent of heavy metals and tri-butyl tin (TBT) from water. Adsorption of TBT by this material proceeds at a particularly high rate, and the KAC has a considerable capacity for the organic compound. Two KAC prototype designs have been built for testing in real conditions. A spiral design aims to treat wastewater running along and between lengths of rolled KAC, compressed and held in position by expandable foam. The second design was based on a similar principle to granular activated carbon (GAC) treatment beds - effluent will be treated as it percolates between pieces of folded KAC. A GAC column was installed alongside the KAC prototypes so that results could be easily compared with conventional adsorption techniques. Dissemination of results from the trial will be of interest to naval communities worldwide, as well as those interested in environmental affairs.