Bacteria in jelly purifies water
Åse Dragland
By adding bacteria embedded in jelly to waste water from Norwegian dairies, researchers at SINTEF have managed both to purify the water and to precipitate out proteins that can serve as animal feed.
Nils Dyrset uses bacteria embedded in jelly to purify waste water from dairies.
An average sized dairy generates up to 240 cubic meters of waste water per day, or about 200 litres per minute. This waste water, mainly originating from the cleaning processes, contains fat, proteins and lactose as the dominant contaminants. If discharged to the public sewage system, the lactose in the waste water will lead to a rapid depletion of the oxygen in the water, leaving no or little oxygen for the microbial degradation of other compounds.
Beneficial circle
"When our selected bacteria, embedded in a jelly, are added, they will convert the lactose into organic acids, and the waste water becomes acidic. The process does not consume oxygen, and in the acidic water the proteins precipitate out as small lumps. By adding small amounts of gas to the water, bubbles are formed around the lumps, and the cheese-like material floats to the surface where it is easily collected . In this way, we combine biological and chemical purification processes to set up a beneficial circle: waste milk is returned to the farm as feed," says Nils Dyrset, project manager at SINTEF Applied Chemistry.A similar process has already been tested by some dairies. But in this process commercial inorganic acids are added to make the waste water acidic. Disadvantages of this process are the cost of the added acid, and that the lactose leaves the purification plant untreated.
Scientists at SINTEF have worked on this project since 1992. The project is financed by the Norwegian Dairies and the Research Council of Norway, each contributing 2 million NOK the project.
"The financial benefits to the dairies are small," Dyrset points out. "The primary incentive for the project is the environmental aspect."