Sharing of operation and maintenance experience for zero wastewater discharge
Published Time:
2025-03-21
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Regulation Driven
Due to high equipment investment and operating costs, the market application of ZLD technology is entirely driven by regulations;
① "Regulations on Taihu Lake Basin Management", State Council Order No. 604 (2011/11/1)
② Various local environmental protection assessment requirements adopt zero-discharge processes
③ Enterprises expand production capacity but lack wastewater discharge quotas, thus adopting zero-discharge processes
Zero liquid discharge (ZLD) technology is the strictest mode of industrial water treatment, characterized by high operating costs and complex systems
1. Challenges of Material Circulation
Challenges:
Mainstream ZLD systems use biochemical methods to remove COD, ammonia nitrogen, etc. At the same time, ZLD technology requires the infinite recycling of water. This leads to a contradiction between the nutrient requirements of the biochemical system and the recycled water. This constitutes the challenge of material circulation in ZLD systems.
Experience Sharing in Addressing Challenges:
By monitoring the dynamic changes of COD, ammonia nitrogen, and total phosphorus in the biochemical system, and conducting biological microscopic examinations for assessment. Based on the detection data and microscopic examination results, necessary nutrient additions are made.
Results:
After a year and a half of operation, the COD removal rate remains above 80%,
Meeting production requirements
2. Challenges in the Physicochemical Stage
Challenges:
Since ZLD technology uses membrane processes, evaporation processes, and drying processes. Meeting the operational requirements of these processes requires achieving predetermined quantitative indicators. In the cases operated by our company, there are the following indicator requirements:
MBR membrane pool requires oil content less than 10mg/L
NF membrane requires fluoride ions less than 10mg/L
Evaporator requires inlet water hardness less than 100
The above quantitative parameters all depend on the control of the physicochemical stage. Considering the fluctuation of influent wastewater, achieving the above control indicators is particularly challenging.
Countermeasures:
Identify the above key requirements, monitor the influent, effluent, and biochemical system for physicochemical processes; ensure water quality meets requirements; develop contingency plans for exceeding process control indicators.
Results:
A parameterized control scheme has been established; normal production can be guaranteed,
The lifespan of each group of membranes needs to be continuously observed.
Challenges:
The treatment capacity of the membrane process is related to the degree of membrane fouling, while the evaporation capacity of the evaporation system is basically stable. To ensure the system's treatment capacity, membrane process maintenance is challenging;
Countermeasures:
Identify and monitor sensitive pollutants. In this case, fluoride ions are the key pollutants affecting the system's treatment capacity. Data monitoring from physicochemical treatment to membrane treatment has been established for fluoride ions.
At the same time, closely monitor the water production rate and pressure difference to ensure timely cleaning and maintain the membrane system in good condition
Challenges:
Scaling in the evaporator is an unavoidable problem in ZLD technology, and scaling is directly related to the hardness of the influent water. How to ensure that the hardness of the influent water meets the requirements constitutes a challenge;
Countermeasures:
Monitor the parameters of the dehardening process before the evaporator, establish data records of three key variables: influent water hardness, dehardening agent dosage, and effluent water hardness, and continuously optimize the process to ensure that the influent water meets the requirements.
Closely monitor the scaling situation of the evaporator and clean the evaporator and pipelines in time
Results:
Meeting production requirements; parameters have been gradually optimized
Challenges:
This case uses imported evaporation equipment, with a high degree of automation integration; however, the operation of the evaporation equipment is closely related to the influent water quality, influent water quantity, and various sensors of the equipment. The on-site operators' ability to analyze equipment failures cannot meet the requirements.
Countermeasures:
Together with the client and manufacturer, we compiled equipment operation manuals; established fault handling archives for various types of failures; and established an instant communication group with the equipment manufacturer's technical personnel to seek timely assistance from the manufacturer.
Results:
Production can be met; however, an accident occurred due to excessively long equipment startup time.
1. Summary of Experience
Water quality testing is performed from the influent wastewater, achieving quantitative control of water quality;
Water quality testing is performed for each process in the physicochemical stage to ensure stable water quality
Water quality testing is performed for each segment of the biochemical stage to ensure stable water quality.
Based on the characteristics of the ZLD system, such as long process flow, high water quality requirements, and high system value, the following experience is summarized:
① Quantitative water quality control is a prerequisite for the stable operation of the ZLD system
② Each wastewater treatment process needs necessary buffering to cope with actual water quality fluctuations
③ The maintenance of the biochemical system is more difficult and requires professional biochemical maintenance engineers/technicians
④ The maintenance requirements of various membrane systems are higher, and timely responses to anomalies are required
⑤ Timely cleaning of the evaporation system is crucial to prevent system scaling and blockage
The above experience only ensures the normal operation of the ZLD system,
More data needs to be accumulated to optimize system maintenance!
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