Wastewaters from different sources undergo a series of treatment processes and the byproduct of the treatment results in sludge. Sludge is generally a mixture of organic matter such as food waste particles, human wastes, trace chemicals, microorganisms and inorganic solids from medicines and products that we use.
The treatment of sludge is important which is why there are several types of sludge treatment solutions available. Post any type of treatment, the sludge is referred to as “biosolids”. Hence, it can be said that sludge when treated gets converted into biosolids. These biosolids are either incinerated, landfilled or applied on land. While it is obtained from municipal wastes, they also come from industrial facilities.
Sludge that results from industrial facilities is a byproduct of particular factory processes and varies extensively in their composition for each industry sector. There are some specific types of industrial sludge that are allowed to enter into a municipal sewer network for their treatment with the municipal sludge.
In this post, we discuss all about essential aspects of sludge treatment and their disposal. Keep reading till the end to find out all.
Sewage Sludge Treatment (SST)
Sewage sludge and its treatment is one of the critical components of municipal wastewater treatment. With sewage sludge treatment, the following purposes are served.
- • Reduces detrimental microorganisms (eg. pathogens) present in sludge and in process lowers the health risks for the masses and environments that are exposed or come in contact with the material.
• Helps in lessening the final volume of the sludge that contributes towards bringing down the attached handling costs.
• Stabilises some of the organic matter present in the sludge that would otherwise convert into harmful gases naturally and contaminate the atmosphere.
• Collects by-products and products coming from the treatment process, which may otherwise be sold or used to offset the sludge treatment costs.
In wastewater treatment plants, the activities that offset sludge treatment costs and volume reduction plays significant roles. Although sludge makes up only 0.2-0.4% of the wastewater flow, its treatment accounts for up to 50% of the operational expenditures of the facility.
Why Is Treatment of Sludge Needed To Be Done?
Wastewater is untreatable and clean water cannot be restored unless the solids from wastewater (sludge) are separated appropriately. Once the separation is done successfully, the disposal procedure is carried out. However, the sludge cannot be disposed of in its raw form as its composition can be harmful for the environment, food systems and also affect the health of communities directly.
From the late 1800s and early 1900s only the treatment of sludge was practised. Developed nations supported as well as actively adopted the measures to treat raw sludge prior to their safe disposal. However, over the years the treatment of sludge has evolved drastically with new technologies and innovations involved.
There are many advanced sewage treatment methods and in fact, companies these days consider sludge as a resource. Through the process of anaerobic digestion the water companies are able to recover biogas from the sludge materials and transform the biosolids into a nutrient-rich product for soils.
Some of the companies even go beyond these measures and retrieve from the sludge certain minerals such as phosphorus and non-renewable resources. This is why in several places the value of sludge treatment reaches above hazard management and priorities on resource recovery.
Steps Of Sewage Sludge Treatment
There is not a single sludge treatment method involved. A successful sewage sludge treatment is only possible through a series of steps. Some of these are –
Sludge Thickening
One of the first steps in a sewage sludge treatment plan is commonly the sludge thickening method. As the name suggests, here sludge is thickened in a gravity thickening device for the purpose of reducing the overall sludge volume.
When the sludge goes through the thickening process successfully, the sludge gets easy to handle. Alternatively, there is a dissolved air flotation method that can be effectively used for thickening of sludge.
Sludge Digestion
After collecting all the solids from the sludge, the process of sludge digestion begins. This is a biological procedure in which the organic solids present in the sludge are decomposed and converted into stable substances.
This step further reduces the total mass of sludge solids and destroys any active pathogens for seamless dewatering. The sludge digestion process is completed in two phases.
Dewatering
In this step, the remaining sludge is dewatered prior to the final step of disposal. In most circumstances, dewatered sludge includes a significant amount of water, as much as 70% even though it is in solidified state. This is why it becomes critical to dry and dewater the sludge beforehand.
Disposal
After the dewatering step is completed, finally disposal of the sludge happens. The above steps of treatment makes the sludge safe for disposal into the landfill or for reuse as a resource.
If it is still toxic then the sludge is incinerated.
