It is a fact that most of us know sewage sludge is turned into biosolids that we then apply on lands, forestlands, agricultural soil, and even gardens as organic fertilizer. What we are not aware of is that not all sewage sludge are naturally converted to biosolids. Instead, there are three factors that determine whether the sludge can turn into biosolids.
To convert municipal sludge into biosolids, it needs to undergo a stabilization process. The stabilization process will accelerate the biodegradation of organic compounds, thereby reducing the levels of pathogens in the sludge material. Microbiologically, the residue is safe for agricultural use but to be sure, it will undergo further treatment that will eventually produce a material that we call biosolids.
There are two kinds of stabilization process—biological and chemical. Biological stabilization uses aerobic and anaerobic treatment to reduce the organic content of solids through controlled biodegradation while chemical stabilization creates process conditions that inhibit microorganism that slow the degradation of organic materials and reduce the odor of the residue.
Presence of potentially harmful industrial contaminants
This could be the deciding factor in the utilization or the disposal of the wastewater material. The problem is with industries that continue to use the sewage system to discharge hazardous wastes. The reason simply is because it is convenient and it costs them almost nothing. However, this also means that hazardous chemicals are present in the system and could therefore post a problem once the treatment process is being decided upon. The contaminants from industrial plants accumulate in the biomass and sludge, and can render the material unfit for beneficial use.
If the contaminated material cannot be transformed into biosolids, then it will be send to the landfill or it will be incinerated. The cost of these two processes is usually shouldered by the municipality rather than the hazardous waste generator or basically, the industrial plants that produce these hazardous materials.
Primary and secondary sludge usually contain no more than 4 percent solids. This is the reason why the transportation of such materials become problematic. To produce biosolids, water content must first be removed through various processes. The simplest method used to do this is gravity thickening. The process involves providing sufficient time for the solids to settle in tanks, which can increase suspended solids concentration to five or six percent. Other methods of thickening include flotation processes, gravity drainage belts, perforated rotating drums, and centrifuges.