Sludge is a semi-solid waste by-product that is most commonly associated with sewage. It can also be a component of waste water treatment process. Most commonly, sludge settles out of the liquid itself while it can occasionally remain suspended if this fluid is agitated. There are many different types of sludge and these are primarily results from man-made processes. Some of the most common are organic (such as sewage), oil sludge, industrial chemicals and post-processing waste.
Governmental Agencies Which Treat Sludge
Within the United Kingdom, the primary authoritative body which deals with sludge treatment (and usage) is the Environment Agency. Not only does this agency oversee the various regulations in regards to how sludge is dealt with, but it also sets up very specific guidelines in terms of addressing the potential presence of heavy metals within this substance. Furthermore, it sets forth stipulations on how to process both treated and untreated sludge. The latter is strictly prohibited from being used within farms and similar agricultural areas.
Of course, there are local services which will deal with sludge as well. These still must adhere to the guidelines put forth by the Environmental Agency. For example, this role is relegated to Thames Water within the London city limits. Other organisations such as Ofwat (Water Services Regulation Authority) and Severn Trent Water (Birmingham) are further examples of local bodies that are subject to regulation by the Environmental Agency. Any private firms must likewise abide by the rules put forth.
Applying Modern Technologies to Mitigate the Impact of Sludge
1. Farming Applications
One of the most interesting advancements in recent years involves the secondary use of treated sludge within the agricultural community. Also known as "biosolids", treated sludge is considered safe for some uses if 99 per cent of the pathogens are shown to have been removed (1). There are nonetheless some regulations that have been put in place by the Environmental Agency. For instance, conventionally treated sludge must be deeply injected into the ground as opposed to spread across the surface. One must additionally wait to harvest any vegetables for a period of twelve months after the initial application.
There is a final type of sludge which can be used within the farming community. This for is known as enhanced sludge. To qualify for this category, it must be shown that virtually all of the pathogens have been removed. In this case, the farmer will wait for three weeks before allowing animals to graze. No less than ten months must elapse between the initial time of treatment and the harvesting of any crops destined for human consumption.
2. Phosphorus Recovery
Another interesting and environmentally friendly method is known as phosphorous recovery. As the name suggests, chemical processes are utilised to separate the phosphorous held in suspension. These are then formed into pellets and marketed to the fertiliser industry.
3. Digestion Treatments
One common method utilised to decrease the toxicity of sludge is to employ tiny organisms that actually feed upon the particulate matter. Both aerobic and anaerobic bacteria will often be used. In fact, one interesting result of anaerobic digestion is the production of large quantities of methane. This gas can then be burned to create a green source of electricity.
4. Emerging Technologies
One concept which is being examined is known as thermal depolymerisation. This essentially retrieves light hydrocarbons from untreated sludge. Hydrocarbons can then be used in a variety of industries. Finally, a drying process is said to be able to produce excess quantities of electricity while clean drinking water is another extremely beneficial result..