Contaminated wastewater is the cause of any number of serious environmental problems. Biological methods for wastewater treatment were developed during the middle of the 20th century, as attention focussed on the effects of oxygen-consuming organisms on lakes, rivers and seas. In many parts of the world, these new technologies brought back to health waterways that had once been biologically out of balance.

But wastewater problems are highly complex, and municipal engineers soon had to find ways to reduce excess nitrogen and phosphorus in municipal wastewater. At the same time, new environmental legislation required many industries to remove specific pollutants from industrial and agricultural effluents.

With significant progress having been made in reducing the load of waterborne fertilisers from human activity, the current challenge in wastewater treatment is developing purification methods to take care of the myriad complex chemicals occurring in small amounts in many common products and medicines. These may be endocrine disrupters, pharmaceutical residues, food additives, persistent chemicals and much more.

A global market for wastewater treatment

Many countries have introduced increasingly stringent demands for effective wastewater treatment. For example, directives from the European Union will require expenditures of up to €30 billion for upgrading sewage plants in the new Member States. Among EU candidate countries, the need is even greater; for example, only 1 percent of all municipal wastewater in Croatia is currently treated.

The global market for biological wastewater treatment is large and growing, and AnoxKaldnes, based in the southern Swedish university town of Lund, is well positioned to exploit these market opportunities. The company offers a variety of wastewater treatment technologies, ranging from specialty training courses to water quality analysis and process testing — even the design, development and delivery of full-scale treatment processes.

Micro-organisms form a biofilm

When micro-organisms grow on a surface, the resulting layer is known as a biofilm. Organisms in a biofilm acquire energy by breaking down organic substances in the surrounding water. This process was identified as early as the end of the 19th century, when wastewater was treated by allowing it to seep slowly over wooden walls. The method was reliable, although it was easily thrown out of balance under heavy loads.

The AnoxKaldnes™ MBBR technology is based on specially designed plastic biofilm carriers — or biocarriers — that are suspended in wastewater and in continuous movement. With their large surface areas, these biocarriers can handle extremely heavy loads of highly polluted wastewater. The container tank, called a reactor, holds numerous biocarriers, creating large amounts of active area upon which the biofilm can grow and allowing micro-organisms to effectively break down the pollutants.

To function properly, the system requires that both oxygen and polluted water continuously contact the biofilm, making the form of the biocarrier an essential consideration. Air pumped into the bottom of the reactor keeps the biocarriers in motion and mixes the wastewater. Clean water leaves the reactor through sieves.

Hybrid processes for multiple pollutants

Research and development is an important part of AnoxKaldnes’ activities. In biofilm technology, for example, the company is focussed on the design of biocarriers, new applications and hybrid processes such as the Hybas™ technology, where activated sludge is used together with mobile carriers in a single reactor. This process is particularly suitable for nitrogen separation and decomposition of organic material. Reduction of the organic material and denitrification takes place in the suspension phase while nitrification occurs on the biofilm.

Wastewater as a raw material

More than 80 years ago, researchers discovered that certain bacteria can form polymers known as polyhydroxyalkanoates, or PHAs. Polymers provide nutrients to bacteria, but also exhibit properties typical of plastics. This has resulted in a great interest in PHA as a biodegradable and renewable raw material for production of plastic.

AnoxKaldnes is working to develop a new process using bacteria in wastewater to produce PHA. Testing conducted in 2008 showed considerable promise for the aim of turning wastewater treatment plants into profitable factories producing “green plastics”.

Article published in April 2009