Nowadays, many steps are taken to monitor, sample, treat and purify contaminants from the environment and from domestic and industrial wastewater in particular. In Israel, there are over 40 wastewater purification facilities, designed to treat the wastewater in order to reduce the environmental and health damage. The existing contaminants are varied and diverse: there are organic contaminants (TPH, PAH), heavy metals (Hg, Fe, As), acids, fuels and different oils. Wastewater purification is carried out by different methods, such as: physical processes (filtration, vaporization), biological processes (microbial activity, which enhances biodegradation of organic matter) and chemical processes (redox, chelation, neutralization and adsorption).
The main product of the wastewater treatment is the water used for agricultural purposes and river restorations, however it is unsuitable for drinking. The secondary product of the treatment is the sludge, which is i.e. the wet sediment of the organic matter, contaminants and a rich microorganism’s environment. The resulting sludge is turbid, greasy, viscous, can contain pathogens, heavy metals, organic and synthetic materials and more, and that’s why it is an environmental and economic nuisance. Thus, in recent years efforts are being made to convert the sludge into a product, which can be used as a fertilizer. The sludge itself is reduced progressively by the existing microorganisms, which consume the organic matter in it, until finally the sludge is burned or concealed at an authorized landfill.
The sludge undergoes various processes before concealing: at first the sludge is collected post-treatment and is stabilized to reduce or neutralize the contaminants. Then, the sludge undergoes dewatering (and sometimes thickening) processes. The next step is consolidation in the presence of consolidation factors like cement, which results in a stable, solid sludge that can be easily transported and concealed.
Industrial sludge treatments:
Activated sludge- one of the most common methods of treatment. The sludge is ejected from the wastewater purification facility with a primary concentration of microorganisms. The sludge is returned to the facility to raise the concentration. The activated sludge is more efficient for wastewater treatment. With every return the organic matter-consuming microorganisms’ concentration grows and they become more dominant (natural selection). In the end, there is a big dominant colony in the sludge, while the reclaimed water contains a small concentration of microorganisms.
Thermal desorption system- this treatment is done by instilling tubes inside the sludge and sparging air at high temperatures (over 400 degrees Celsius) in a closed system, so that the thermal conduction is indirect to prevent sludge drying. Above the sludge there is a gas receptor, which collects the gas and contaminants mixture and transports them to a separate treatment (biological, strip, etc.).
Geotubes- the geotubes are fabric tubes, through which liquids are filtrated back to the surroundings, while the solids are trapped inside. The sludge is pressed inside the geotubes to reduce the water content and solidify the sludge.