Present Solutions for Sewage Sludge Disposal

Conventional methods of sewage sludge disposal – land filling, ocean dumping, compost and incineration – are causing irrevocable environmental damage. This is seen in the contamination of underground water reservoirs and fertile land, the pollution of oceans and the emission of hazardous gases into the air. Sludge fertilizer is already banned in several European countries. The move is in response to growing concern about residues in the sludge, particularly synthetic hormones and some pharmaceutical compounds. Today, an average of 40% sludge is used in agriculture with the rest being incinerated.

Changing regulations are the catalyst driving the wastewater and sludge treatment market. These regulations are driving the end-users to search for final treatment methods other than incineration, agricultural use, landfills and ocean dumping. Due to a decrease in the disposal sites for industrial and municipal sludge, and due to national and international regulations, it will soon be more common to reuse primary and secondary sludge as a sustainable energy source, such as fuel for industrial plants.

Pyrolysis and gasification, like incineration, are options for recovering value from sewage sludge by thermal treatment. Both pyrolysis and gasification turn sewage sludge into energy-rich fuels by heating the sludge under controlled conditions. Whereas incineration fully converts the input sewage sludge into energy and ash, these processes deliberately limit the conversion so that combustion does not take place directly. Instead, they convert the sewage sludge into valuable intermediates that can be further processed for materials recycling or energy recovery.

Pyrolysis and gasification offer more scope for recovering products from sewage sludge than incineration. When sludge is burnt in a modern incineration the only practical product is energy, whereas the gases, oils and solid char from pyrolysis and gasification can not only be used as fuel, but also purified and used as a feedstock for petrochemicals and other applications. Obviously, there is a growing demand for sludge management technologies capable of: 1). Meeting increasingly stringent regulatory requirements. 2.) Effectively utilizing potential for material and/or energy recovery.