The Dilemma of Sludge Treatment in Wastewater Treatment Plant

A considerable part of wastewater treatment plants face the operating pressure of sludge during the production process. The management of sludge production in wastewater treatment plants is a very complex and high-cost production link. Most wastewater treatment plants have always been inconsistent with the operation of sludge production. The management idea of paying attention and light investment leads to unmatched and untimely sludge production, which causes a large amount of sludge accumulation in the system. These large amounts of accumulated sludge will lead to the treatment of water quality and environmental management in the sewage treatment process. Especially with the improvement of the society's water quality indicators for the operation of wastewater treatment plants, the output of sludge has also increased, which has increased the operational difficulties for the wastewater treatment plants.

Sludge is a solid product produced in the process of sewage treatment. In the biological treatment process of activated sludge, the organic matter in the sewage is absorbed by microorganisms and converted into substances inside the microorganism itself. This part of the organic matter self-transformed by the microorganisms will Increase the amount of activated sludge. This part of the increase requires the discharge of excess sludge to maintain the F/M balance of the system. Due to the high water content in the remaining sludge, it needs to be dehydrated to a solid form before it can be transported and disposed of. The dehydration process of sludge with a moisture content of more than 99% requires complex dehydration devices and efficient flocculation agents. The management equipment of the dehydration process is centralized, and the process flow (mud, chemical, water process pipeline) is large, resulting in a sludge treatment section. The management is complicated and the cost is high, accounting for 20% or even higher of the overall sewage treatment cost. Since its proportion in the overall sewage treatment volume only accounts for 1-2% of the sewage, the management of this part of the sewage plant often does not make a major effort.

Sludge treatment that has not received enough attention will have a huge impact on the sewage production of the sewage treatment plant. The increased sludge that cannot be removed from the sewage treatment system in time will increase the concentration of the sludge, increase the age of the sludge, and increase the degree of aging of the sludge. The aging of sludge will cause many process problems, such as sludge foam, sludge expansion, increased suspended solids in the effluent, floating sludge on the surface of the secondary settling tank, and deterioration of effluent water quality will all appear as the sludge concentration increases. This is also a series of problems that are very troublesome for many sewage plants. Why is the problem of sludge production increasingly becoming one of the difficulties in the operation of sewage plants at this stage?

From the perspective of the design and construction of wastewater treatment plants, the production capacity of the sludge workshop of the wastewater treatment plant should be in line with the sludge output of the wastewater treatment plant. However, in the operation of many wastewater treatment plants, it is increasingly found that the production of the sludge workshop is difficult to meet the requirements of sewage treatment. The production process has severely restricted the production of sewage, and even caused the above-mentioned various process abnormalities. Based on the actual operation of the sewage plant at this stage, it is believed that this situation is due to the following reasons:

1. The design does not match the actual situation. The design of the sewage treatment plant is a predictive design. It is difficult to obtain comprehensive and detailed collection of sewage water quality data at the beginning of the design. Many designs can only rely on short-term test data, or historical data from other surrounding sewage plants, or even these two types. None can only use manuals and regulatory data. Such data is often far from the actual operating data, which makes the sludge produced by the sewage production of the sewage plant inconsistent with the design. The actual water quality is lower than the design will be beneficial to the sludge production, but the water quality higher than the design will definitely cause the system The accumulation of sludge.

2. Sewage collection pipe network factors. The construction of my country's sewage collection pipeline network is affected by the economic strength and construction conditions of various regions, and the development is extremely uneven. Confluence of rain and sewage, damage and leakage of the sewage pipe network, illegal connection of the pipe network along the way, etc., a large number of problems exist in the sewage pipe network, causing the sewage to be disturbed by many external factors during the sewage collection process, and a large amount of inorganic matter enters the sewage along the way. The pipe network flows into the sewage plant. The pretreatment of most sewage plants in my country is designed to be small, and the ability to estimate the abnormally introduced inorganic substances in the pipe network is too low. This part of the extra inorganic substances is generally difficult to effectively remove in the pretreatment section, and these inorganic substances enter the biochemical process. After this period, the MLVSS/MLSS ratio will be reduced, and a larger amount of sludge will be produced, which will put pressure on the sludge output of the system.

3. Extensive operation and management. Most sewage plants are affected by practical problems such as lack of technical personnel, incomplete infrastructure and equipment construction, unreasonable process selection, and large changes in influent water quality. The operation of sewage plants has always been in an extensive management mode in China. This extensive management The model makes the sludge production unable to be effectively controlled. Lack of detailed management of each link, such as inaccurate control of dissolved oxygen in the aeration tank, will cause excessive aeration in the process of sewage treatment, accelerate the growth of microorganisms, and produce a large amount of sludge, which will make the water treatment The generation of sludge cannot be controlled reasonably, and the amount of sludge is accumulated.

4. Excessive index requirements. The most direct impact of higher and higher effluent indicators on the operation of sewage plants is the increase in sludge production. The reduction of the index needs to be achieved by the adsorption and degradation of more organic matter by microorganisms. The absorption of more organic matter will make the microorganisms grow faster and more, which will inevitably produce sludge output that exceeds the original effluent standard. And more detailed control is required, but under the extensive control of the sewage plant, it is generally carried out in a relatively simple and rude way, that is, dosing. The addition of medicament generally requires excessive input to ensure the stability of the index. Excessive medicament will also cause an increase in the amount of sludge in the system, which is higher than the design prediction value, and finally an increase in system sludge.

5. Mass production of chemical sludge. In terms of sources, the sludge of sewage treatment plants includes primary sludge, activated sludge from biological treatment system, and advanced chemical sludge. At this stage, most sewage plants need to remove the carbon source for phosphorus and nitrogen removal. In the primary sedimentation tank, the main sources of sludge are activated sludge and chemical sludge. In the design of the sewage plant, the two types of sludge are usually not separately designed and treated, but the same sludge storage tank is used for storage, and they are jointly entered into the sludge dewatering equipment for dewatering. However, there is a difference between the two sludges. Activated sludge is negatively charged. Excessive chemicals in chemical sludge will make the sludge positively charged. The corresponding sludge dewatering agent PAM is also different. Sewage plants will ignore this problem, but simply mix and use the same type of agent for dewatering. This will inevitably cause difficulties in the production of the sludge workshop. The sludge has high water content, the supernatant has serious sludge, the phenomenon of sludge running is obvious, and overflows from the dewatering machine continue to appear, causing the sludge workshop to return to the system. Increase the organic load of the system, resulting in sludge increase.

6. External transportation issues. The sludge is generally dehydrated to a moisture content of 80% in the sewage plant, and the resulting sludge cake is sent to the designated sludge disposal site for subsequent disposal. Sludge disposal sites will be built in the wilderness away from the city, which will increase the transportation distance and complex transportation routes. In this case, the sludge transportation will become the main factor restricting the production of the wastewater treatment plant within a certain period of time, such as the following In severe weather with rain and snow, the sludge that cannot be transported out of the sewage plant will force the production of the sludge workshop to stop, and the suspended sludge workshop will in turn cause the accumulation of sludge in the sewage system.

7. Chaos in the pharmaceutical market. The chaos in the PAM pharmaceutical market has been the consensus in the industry. The uneven quality of the pharmaceuticals, the grabbing of the pharmaceutical market, and the improper gains of pharmaceutical profits have made it impossible for the pharmaceuticals used by the users of the sewage plant to effectively dehydrate the sludge, resulting in continuous sludge workshop The water content remains high, and the actual amount of dry sludge produced is small. Most of the sludge is returned to the system under the action of inferior chemicals, increasing the sludge volume of the system.

The production of sewage plants is a systematic work. Each sewage plant needs to manage and mobilize all aspects of sewage production reasonably to ensure the stable and up-to-standard effluent water quality. The sewage plant sludge disposal is facing a lot of difficulties. It is important to pay attention to the operation and management personnel of each wastewater treatment plant. The operation personnel should take stable effluent water quality as the management and control goal, determine a reasonable sludge concentration, and discharge sludge in a timely and effective manner, regardless of design parameters. In response to the sludge dilemma in the plant, rectification measures are actively taken, and the complex sludge dewatering system is operated and maintained through such process management ideas.