PROJECT DESCRIPTION
BACKGROUND
The Uentrop plant of DuPont de Nemours (Germany) GmbH and DuPont Sabanci Polyester GmbH produce high grade plastics and synthetic fibres (eg. Butacite, Zytel, Crastin, Dacron). In the past, this has required the consumption of 800,000m3 of drinking water per annum, of which about 600,000m3 is ultimately released into the Lippe river as waste water, following full biological purification. Different water purities are required for different applications and these were previously prepared from drinking water in a central unit and then fed into the different pipe systems. This project aimed to close the water cycles in the Uentrop plant. Treated water was to be used as a process water and as a soft water, thereby reducing the volume of waste water by 540,000m3 (90%) while saving the same amount of drinking water.
OBJECTIVES
The objective of the project was to recycle 90% of the waste water from a state-of-the-art chemical plant, in order to preserve drinking water and minimised the waste water load being released into a local river. Each year 800,000m³ of potable water are needed to produce 150,000t of fibers and plastics. In addition 600,000m³ of waste water are released into the river after having been clarified in an on-site biological waste water treatment plant. With an opimised environmental management system it was intended to spare this natural water ressource. This was to be achieved by recycling the clarified waste water and returning it for use in the factory. If this was successful there would also be a significant economic benefit. Specific objectives included: - Good care of the drinking water resources - Protection of the environment - Render the chemical factory virtually free of waste water (90% of the waste water to be reused; the emissions from the plant into public water to be reduced to a minimum) - Expected cost-decrease of 1.5 MM DM each year - Enhanced attractiveness of the Uentrop site for other companies (few sewage-dues, decreased energy costs and personnel costs, etc.) - A new innovative waste water recycling-concept for other companies with immense water consumption (breweries, paper-manufacturers, food-industry) The project was based around a 3-step combination of innovative treatment and water processing units. 1. Alternating Aerobic Anoxic Sludge Process (to eleminate nitrogen and phosphorous). 2. Submerged membrane system (to eleminate of suspended solids and numbers of germs). 3. CARIX-Process (to soften water and to reduce sulfate, nitrate and chloride). These measures would also decrease the amount of impurities entering the river (Chemical oxygen demand, nitrogen, phosphorous, soluable salts) and would save 0.75 Mio € in costs each year. If this innovative techniques was proven, companies all over Europe (especially in chemical industry and breweries) would benefit.
RESULTS
The pilot trials served both to demonstrate that the required water quality can be achieved with the process and to provide a better assessment of the operating costs of a large scale plant with an average volume flow of 70m3/h. During the course of the project, it was discovered that technical changes in two of the three water processing units would give better cleaning results and would result in the production of better quality water, and therefore improved environmental and economic effects. The Submerged Membrane System was replaced by an Ultra-filtration Membrane System, and the CARIX process was replaced with hyperfiltration, according to the principle of reverse osmosis, applied in combination with softening agents and an acive carbon filter in a dead-end system. In the pilot study, drinking water requirements were achieved and the quantity of waste water were reduced by 90% (540,000m3/a). The waste water recycling concept developed could therefore be used to recover up to 90% of the waste water for production. This resulted in a considerable saving in the cost of drinking water and waste water charges. The potential saving is ca. € 0.75 million per annum. Moreover, the Chemical Oxygen Demand was reduced by 15%, the Nitrogen content was reduced by 60%, the Phosphorus content was reduced by 67% and soluble salts were reduced by 28%. After the successful pilot tests, a full-scale waste water recycling system started to operate from June 2001 onwards. The pilot trials served both to demonstrate that the required water quality can be achieved with the process and to provide a better assessment of the operating costs of a large scale plant with an average volume flow of 70m3/h. During the course of the project, it was discovered that technical changes in two of the three water processing units would give better cleaning results and would result in the production of better quality water, and therefore improved environmental and economic effects. The Submerged Membrane System was replaced by an Ultra-filtration Membrane System, and the CARIX process was replaced with hyperfiltration, according to the principle of reverse osmosis, applied in combination with softening agents and an acive carbon filter in a dead-end system. In the pilot study, drinking water requirements were achieved and the quantity of waste water were reduced by 90% (540,000m3/a). The waste water recycling concept developed could therefore be used to recover up to 90% of the waste water for production. This resulted in a considerable saving in the cost of drinking water and waste water charges. The potential saving is ca. € 0.75 million per annum. Moreover, the Chemical Oxygen Demand was reduced by 15%, the Nitrogen content was reduced by 60%, the Phosphorus content was reduced by 67% and soluble salts were reduced by 28%. After the successful pilot tests, a full-scale waste water recycling system started to operate from June 2001 onwards.
