Turn sludge into a valuable resource?

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Sludge treatment and disposal are urgent – “turning wastewater into clean water”. Wastewater treatment has always been a key focus in environmental management. Especially in recent years, wastewater treatment plants have been built across the country, leading to continuous improvements in wastewater treatment standards. Meanwhile, the disposal of sludge, a by-product of wastewater treatment, has become an urgent problem that needs to be addressed. A relevant official from the Ministry of Housing and Urban-Rural Development stated recently that the ministry conducted an investigation into the treatment and disposal of sludge from urban sewage treatment plants at the beginning of this year. The results show that currently, urban sewage treatment plants in China treat approximately 48 billion cubic meters of sewage per year, generating over 30 million tons of sludge with a water content of 80%. The rate of harmless disposal of this sludge is 56%; one-third of the sludge is subject to temporary disposal methods, and more than 10% of the sludge has an unknown destination. In recent years, **clear requirements have also been set for the treatment and disposal of sludge. The 12th Five-Year Plan issued by the State Council calls for a harmless disposal rate of 70% for urban sludge, and 80% for sludge in large and medium-sized cities. However, the construction of sludge treatment and disposal facilities is not satisfactory at present. The \"Ten Measures on Water Management\" introduced in the first half of this year also lists sludge treatment and disposal as a key item. “The \"Ten Measures on Water\" stipulate that the sludge generated by wastewater treatment facilities must be stabilized, rendered harmless, and recycled; it is prohibited to allow sludge that has not met the required treatment standards to enter farmland. All illegal sludge dumping sites must be shut down. The existing sludge treatment and disposal facilities should be essentially upgraded to meet the required standards by the end of 2017, and the rate of harmless treatment and disposal of sludge in cities at the prefecture level and above should reach over 90% by the end of 2020. This initiative, led by the Ministry of Housing and Urban-Rural Development, is being actively implemented. Past debts and current demands have highlighted the importance of sludge treatment and disposal in environmental management, making it particularly urgent to develop more advanced technologies. The advantages of zero-additive and low-energy consumption are evident. High water content and difficulty in dewatering, high organic matter content, tendency to **, production of foul odors, as well as the presence of pathogenic microorganisms and heavy metals among other pollutants – all these factors make the treatment and disposal of sludge more challenging than that of wastewater. Dewatering and drying technologies are therefore key to overcoming the difficulties associated with sludge treatment and disposal. At the \"Evaluation Meeting on the Electroosmotic Sludge High-Dryness Dewatering Technology,\" the evaluation experts noted that this technology combines \"electroosmosis\" with \"plate and frame filtration,\" enabling the reduction of the moisture content in urban sludge from 80%~85% to 60%~40%. Without the need to use any chemical agents, it results in a significant reduction in total electricity consumption. Compared with existing technologies that achieve similar dewatering results, it offers advantages in terms of investment costs and energy savings; this technological combination is therefore innovative. Furthermore, this technology uses static copper busbars to draw cables for power distribution, effectively solving technical issues such as loose connections and arcing, thereby improving the stability of the system. By using a low-voltage switching power supply, the electrical energy conversion efficiency is effectively improved, while the safety of the system is also enhanced. As a secondary dewatering technology, it can be directly integrated with existing conventional dewatering equipment without the need for a complex chemical dosing system. It features a simple process layout, small footprint, and easy operation and management, while also providing suitable sludge properties for subsequent treatment, disposal, and utilization. Experts believe that this technology provides a new method and equipment for reducing the volume of sludge. The combination of electroporation and plate and frame filtration is a first in China and represents an advanced level on the international scale. \"The primary goal is reduction in volume; it enables the removal of interstitial water, capillary water, adsorbed water, and some bound water from the sludge. The moisture content of the resulting sludge cake is less than 40%, and its solubility upon re-exposure to water is less than 5%, resulting in a 70% reduction in volume.\" Secondly is harmlessness, which is achieved by destroying the microbial cell membranes in order to kill the ascaris eggs and pathogenic microorganisms present in the sludge; some heavy metals are removed by taking advantage of the phenomenon of cations migrating toward the cathode. Finally, there is energy utilization: the thorough removal of moisture from the sludge increases its lower calorific value, enabling not only self-sustained combustion but also the recovery of thermal energy. ”