MISCELLANEOUS, TEXTILES, PRINTING, CAR WASH, AEROSPACE, DEFENSE, SHIPBOARD
Due to the ability of modern high-rejection reverse osmosis membranes to retain both organic and inorganic contaminants dissolved in water at rejection rates of 98-99 percent, reverse osmosis is useful for purifying liquid waste such as landfill leachate.
The amount of components dissolved in leachate from different kinds of landfills covers the range from 2 to 15 g/l. From this the fraction of organic components is considered to cover a range between 0.1 and 3 g/l. That is much smaller than the inorganic part, indicated to have a range from 1.6 to 14.3 g/l, including ammonia with values between 0.3 to 2 g/l.
Since such contaminants are mostly not appropriate for treatment by conventional biological processes, new regulations tend to limit the discharge of such complex wastes to municipal sewers. Even by combining biological treatment with adsorption by active carbon or with the oxidation of part of the dissolved organic material using ozone or other oxidizing agents, only partial destruction of contaminants will be achieved.
Tubular modules were the first medium used in the early reverse osmosis systems for the purification of landfill leachate. An alternative was introduced to this market in 1988. The disc-tube-module (DT-module) has been installed since then with great success.
The successful operation of reverse osmosis in the plant of the municipal waste landfill of Ihlenberg (former VEB Deponie Schönberg) near the city of Lübeck in Germany, the most modern and largest multi-stage plant that has been realized up to this time for landfill leachate purification, demonstrates the possibilities of modern membrane technology.
This reverse osmosis system with a capacity of 36 m3/h has been in operation without any problem since December 1989 with one change of the membranes till now. With two reverse osmosis stages, the average rejection rates for salts and organic contaminants are about 99 percent. Depending on the salt content of the feed water and the operation time between the cleaning cycles, the operating pressure ranges between 36 and 60 bar at ambient temperature. The specific permeate flux was calculated to be approximately 15 l/m2h.
The results obtained during the operation of an increasing number of plants under very different conditions prove that reverse osmosis is a very effective instrument for the purification of landfill leachate if all design criteria and requirements specific for landfill leachate have been taken into consideration, and if an adapted module system as well as correlated technologies are used.
This includes high pressure reverse osmosis, with operating pressure up to 120 bar and nanofiltration in combination with a controlled crystallization process, that allows permeate recovery rates of more than 97 percent.