Water quality standards are higher in Sweden than in many other countries.

People living in countries like Sweden often take abundant, high-quality water for granted. But elsewhere in the world it can be hard to find enough water for food production, sanitation and economic development. Population growth, water pollution and climate change all add to pressure on available freshwater resources, and humankind’s global “water footprint” is expanding at an alarming rate.

Water is a fragile resource, and many activities of our modern society threaten its quality. Current methods for the purification of wastewater containing persistent chemical substances, drug residues, arsenic or other toxic substances are not effective enough, as shown by the many studies that find drug residues in streams and groundwater. Because they are both persistent and water soluble, some active pharmaceuticals can potentially pass through traditional wastewater treatment plants and enter natural cycles. Knowledge is limited on the effect of drug residues on human health, but biological effects have been confirmed in fish and other aquatic organisms.

Pharmaceutical residues in the environment

In Sweden, approximately 1,200 pharmaceutical substances are in widespread use, and the number is steadily increasing. Hundreds of tons of drugs are used each year, many of which do not entirely break down in the body, leaving active ingredients and degradation products to be secreted in urine and feces.

Researchers, pharmaceutical companies and health care providers are showing an increasing interest in investigating what happens to drug residues in aquatic ecosystems. In parallel with traditional pharmaceutical research, manufacturers are looking at practical efforts to develop treatment methods to deal with these difficult-to-treat chemical products.

The Stockholm-based company Xzero has developed the world’s first full-scale water purification system based on membrane distillation.

Only water molecules pass through.

Along with IVL Swedish Environmental Research Institute, KTH Royal Institute of Technology and the Hammarby Sjöstadsverk municipal water treatment facility in the Swedish capital, Xzero has joined a project aimed at developing advanced control technologies for handling drug residues in sewage. Membrane distillation technology may well prove to be a key process for the effort, and Xzero is the first company in the world to develop a full-scale system based on this promising approach.

Membrane distillation for ultra-pure water

Manufacturing microprocessors and memory chips for the computer industry requires absolutely pure process water. With current technology, rinse water is purified in 15 to 20 different steps before it becomes clean enough, and a large fabrication factory may consume between 2 and 4.8 million liters per day.

Xzero’s membrane distillation system first removes volatile contaminants by degassing. Next, the water is vaporized through a waterproof membrane and non-volatile impurities are removed in a concentrate. The membrane is hydrophobic (water repellent) creating a barrier for the liquid that only vapor can penetrate.

Membrane distillation differs from other separation techniques because the temperature differential between the cold and warm sides of the membrane drives the separation. Xzero claims that membrane distillation is simpler and more effective than other treatment methods for producing ultra-pure water.

Demonstration plant

Membrane distillation is also suitable for concentration and separation of drug residues in municipal wastewater, and a full-scale demonstration plant with a capacity of 10,000 gallons of water per day will soon be tested at Stockholm’s Hammarby Sjöstadsverk treatment facility. The study not only involves testing the technology and treatment efficiency, but also looking at membrane distillation from a system perspective, for example measuring energy consumption. At Hammarby Sjöstadsverk, waste heat can be used as an energy source for the separation process, which is advantageous from an economic standpoint. Although power consumption is low, membrane distillation produces ultra-pure water, and the feed water requires no extensive pretreatment.

The Swedish Environmental Research Institute is also evaluating other techniques for removal of pharmaceutical residues from water, such as filtration through activated carbon and ozonation.

Article published in December 2010