The Application of Polymer in Sludge Dewatering

Within the world of Wastewater treatment, in addition to producing clean water, many processes tend to generate a significant amount of waste solids. This material is often referred to as sludge. In raw form, typically a slurry solution, the disposal of sludge waste can be a significant cost to industrial facilities. To reduce these costs, many will implement some form of sludge dewatering as part of their overall waste treatment process. With the proper use of chemistry and equipment optimization, sludge dewatering can significantly reduce the volume of sludge that is discharged from the site. The drier the sludge, the more savings can be realized.

To effectively promote sludge dewatering within a process, waste solids must be conditioned using a polymer. When added to a waste slurry, the functional charge, structure, and molecular weight that is built into the polymer will interact with the solids and clump them together. When this takes place, water starts to withdraw from the solids and larger floc structures start to form. Once properly conditioned, these structured solids can be mechanically compressed to produce a drier and more friable solid mass.   In many cases, cationic polymers (positively charged flocculants) are preferred for sludge dewatering applications. Within a robust polymer product line, two different cationic polymer structures can be applied, linear chained polymers and cross-linked polymers. The one you choose will be dependent on the physical and chemical properties of the solids that are being dewatered.

In terms of wastewater treatment and the accumulation of solids, the following production locations and or industrial facilities are commonly known to produce higher volumes of waste sludge, and by default, often require some form of sludge dewatering; septic or primary clarification sludge tanks, sealed waste collection tanks, anaerobic/aerobic biological systems, and in general any food-based production facility.

For many sludge conditioning polymers and the dewatering equipment in which they are applied, the type of sludge being processed, its physical and chemical properties, and the way it is handled/stored, can have a significant effect on operational performance. Below are a few examples of processing locations and or operating environments where dewatering equipment and polymer performance can vary.

Slaughterhouses – Here higher levels of fats, oils and grease can significantly increase polymer demand and produce sludges that are not as dry as desired. In this case, structured polymers are a viable option, as they can readily tie up any excess fats, oils and greases that are present and help transform the sludge into something that is more friable in nature.

Sealed Tanks – The frequent withdrawal of water from these types of systems (typically by vacuum truck) can limit the formation and growth of a viable bacterial ecosystem. When this takes place, water and waste solids cannot be effectively degraded or broken down. As a result, the sludge that accumulates tends to be watery and lacks enough sufficient fibrous or biologically degraded material to allow for effective and efficient dewatering. Once again structured or high charge linear polymers may be a viable option to attract and tie up any charge stable solids that are present.

Standardized Waste Treatment Facilities – When a more formal waste treatment process is in place, sludge dewatering activities tend to be easier to manage. This is typically due to the presence of higher levels of fibrous or solid material and a lower concentration of potentially charge stable contaminants (example; oils and grease) that need to be biologically broken down. Under these conditions, a linear polymer is commonly found to offer impressive efficiency as it relates to dewatering activities. Furthermore, in these sludge conditions, the choice of mechanical dewatering equipment might influence the choice of dewatering polymer. While a low shear mechanical dewatering system, such as a belt press, might work best with a lower charge linear polymer, a high shear system, such as a centrifuge, might work best with a high charge cross-linked polymer.

Regardless of the operational challenges that are present, the Aquasan Product Line is diverse and more than capable of addressing your sludge dewatering needs. Whether it be a linear polymer or something from our structured (cross-linked) product line, our team of experts will be more than happy to come to site to screen polymer chemistries and identify a solution that is a best fit for your operational and budgetary needs.