sewage sludge disposal
- a global dilemma
Millions of tons of toxic human sewage sludge – the end product of the wastewater treatment process – are dumped in landfills, spread on agricultural land, or composted each year. Millions more tons are incinerated and on some parts of the planet raw sewage is poured straight into rivers and oceans. For a world so technically advanced, it would appear no real solution has yet been found for the complete elimination of such a highly toxic waste, a waste that is slowly poisoning our planet.
The safe, efficient treatment and disposal of wastewater is fundamental to every community and society in the world. The methods and processes chosen to handle and dispose of waste and effluent are important because of the impact those processes have on the health of the community and the quality of the environment we live in.
Wastewater treatment in developed countries deals with inflows of highly variable volumes and quality. The quality of inflows depends on the industries, housing and infrastructure within the catchment area of the particular treatment facility. Also, the quality of output from treatment facilities varies widely depending on the quality of the inflows and the treatment technologies employed by the facility.
Facilities typically have very little control over material received. Often treatment facilities were established well before many of the industries operating in their areas were built.
Many wastewater treatment plants are ill-equipped to deal with the complex inflows, including prescription-drug residue, heavy metals and toxins generated by industry, with the result that the quality of the outputs – water and sludge (bio-solids) – are detrimentally affected. Concurrently, many governments are legislating to tighten the standards that have to be met in the disposal and use of treated water and bio-solids.
The combination of these factors and the presence of increasingly vigilant environmental groups are creating pressure on wastewater treatment operators to upgrade facilities and improve output quality.
Most waste treatment plants dispose of their bio-solids in one of four ways:
• Dumping in landfill sites
• Spreading on land to grow crops (land application)
Increasingly, these disposal methods are becoming questionable for environmental, health, regulatory and political reasons.