Sludge dewatering may seem as simple as “removing water,” but as the moisture content decreases, the remaining water becomes increasingly difficult to remove. Recently, a research team from Dalian University of Technology explored a new approach to this long-standing challenge by using the phase transition of carbon dioxide hydrates to selectively extract residual water from sludge. The study provides a new perspective on deep sludge dewatering and further sludge volume reduction.
The research is particularly interesting because conventional mechanical dewatering is not necessarily the end point of sludge dewatering. In practical wastewater treatment processes, sludge may still contain a significant amount of water after thickening, conditioning and mechanical dewatering. For facilities seeking to further reduce sludge volume, transportation requirements or downstream disposal pressure, removing this residual water remains a technical challenge.
Why Does Sludge Become More Difficult to Dewater?
Water in sludge does not exist in a single form. During the initial stages of treatment, relatively easy-to-remove free water is separated first. The remaining water may exist as capillary water, interstitial water, or water more closely associated with sludge particles. As dewatering progresses, these forms of water become increasingly difficult to separate from the solids.
This is why simply increasing mechanical pressure cannot solve every dewatering problem. Dewatering equipment must balance dewatering performance with processing capacity, energy consumption, equipment load and operating stability. The achievable final moisture content also depends on factors such as sludge characteristics, sludge source, particle properties, conditioning conditions and feed concentration.
Therefore, deep sludge dewatering is not simply a matter of applying more pressure. It is a more complex solid-liquid separation challenge involving the different forms in which water is retained within sludge.
A New Approach to Deep Sludge Dewatering
To address the difficulty of removing residual water after mechanical dewatering, the research team from Dalian University of Technology explored a deep dewatering method based on the phase transition of carbon dioxide hydrates.
In simple terms, the approach uses the formation and decomposition of carbon dioxide hydrates to selectively extract water from sludge, providing a potential route for further reducing sludge moisture content. Unlike conventional mechanical dewatering, which mainly relies on pressure to achieve solid-liquid separation, this approach focuses on separating water that remains in different states within the sludge.
The significance of this research is not that conventional mechanical dewatering has become outdated. Rather, it demonstrates that when sludge treatment requires further moisture reduction, mechanical separation may not be the only technological pathway worth exploring.
At the same time, it is important to distinguish laboratory research from full-scale engineering application. Before a new deep dewatering technology can be widely adopted, factors such as scale-up, continuous operation, energy consumption, cost, sludge adaptability and integration with existing treatment processes all require further evaluation. At this stage, the technology is better viewed as a new research direction in deep sludge dewatering rather than a mature solution capable of replacing conventional mechanical dewatering across the board.
Will Deep Dewatering Replace Mechanical Dewatering?
Based on current engineering practice, a more realistic direction may not be the replacement of mechanical dewatering, but the combination of different technologies according to specific treatment requirements.
Mechanical dewatering remains an important and established step in sludge volume reduction. Equipment such as belt filter presses and screw presses can provide continuous sludge treatment and reduce moisture through processes involving sludge conditioning, gravity drainage and mechanical compression. These technologies have been widely applied in conventional sludge treatment projects.
For applications that require further moisture reduction, deep dewatering or other downstream technologies may be considered after mechanical dewatering. In other words, a future treatment train could potentially involve:
Sludge Thickening → Conditioning → Mechanical Dewatering → Deep Dewatering or Further Treatment → Final Disposal or Resource Recovery
This approach also reflects a broader change in sludge management: dewatering equipment is becoming one part of an integrated sludge reduction and disposal process rather than an isolated solution to water removal.
Why Does Sludge Moisture Content Matter?
The practical value of further reducing sludge moisture ultimately comes down to sludge handling and downstream management.
A high water content increases the amount of material that needs to be stored, transported and treated. Reducing moisture content can help decrease the volume and mass of sludge requiring transportation, storage and downstream treatment, potentially reducing the operational burden associated with these steps. This is one of the main reasons why sludge dewatering remains an important part of wastewater and industrial wastewater treatment.
However, sludge treatment is not simply a matter of achieving the lowest possible moisture content. Further moisture reduction may require additional treatment, energy or equipment, while different disposal and resource recovery routes may have different requirements for sludge characteristics.
The practical objective should therefore be to select an appropriate dewatering target based on sludge properties, treatment capacity, final disposal requirements and overall operating costs, rather than pursuing the lowest possible moisture content in every case.
From Dewatering Equipment to an Integrated Sludge Treatment Process
As sludge management requirements become more demanding, wastewater and industrial facilities are increasingly looking beyond the performance of a single dewatering machine and considering the entire treatment process.
For example, sludge thickening can increase the solids concentration before dewatering. Appropriate polymer conditioning can improve sludge flocculation and dewatering performance, while stable sludge feeding can help maintain consistent equipment operation. Depending on the type of sludge, the interaction between thickening, conditioning, dewatering, conveying and final disposal can all influence overall system performance.
This means that the future development of sludge dewatering may not necessarily be about one technology replacing another. Instead, it may involve better pretreatment, more effective mechanical dewatering and advanced deep dewatering technologies working together to form an integrated sludge treatment process.
For equipment suppliers, this also means looking beyond the performance of individual machines and considering the complete sludge treatment process. By taking into account sludge characteristics, flow rate, feed concentration and final disposal requirements, engineers can develop a dewatering solution that is better suited to the actual needs of a project.
Looking Ahead
Deep sludge dewatering remains an active area of research and development. The recent study from Dalian University of Technology provides a new approach to extracting residual water from sludge and highlights the fact that further sludge reduction continues to present technical challenges.
For the foreseeable future, established mechanical dewatering technologies will continue to play an important role in practical sludge treatment, while emerging deep dewatering technologies may provide additional options for specific applications. As disposal costs, resource recovery requirements and environmental standards continue to evolve, the focus may gradually shift from simply asking “How can we remove more water?” to asking “How can different treatment technologies work together to achieve more efficient and reliable sludge reduction and downstream management?”
Haibar provides sludge thickening and dewatering equipment, including belt filter presses, screw presses, polymer dosing systems and related sludge handling equipment. If you are evaluating a sludge dewatering project or looking for an integrated sludge treatment solution, contact our team to discuss your process requirements. >> Please feel free to contact us
Post time: Oct-07-2026