The water quality online monitoring system (WQMS) is a comprehensive online automatic monitoring system that takes online automatic analysis instruments as the core, and uses modern sensor technology, automatic measurement technology, automatic control technology, computer application technology, and related special analysis software and communication networks. WQMS can detect abnormal changes in water quality as early as possible, quickly make early warnings to prevent downstream water pollution, and track pollution sources in a timely manner, thereby serving management decisions.
Main features
The online water quality monitoring system is a system that takes online analytical instruments and laboratory research needs as its service target, takes providing representative, timely and reliable sample information as its core task, and uses automatic control technology, computer technology and professional software to form a complete system from sampling, pretreatment, analysis to data processing and storage, thereby realizing online automatic monitoring of samples. The automatic monitoring system generally includes a sampling system, a pretreatment system, a data acquisition and control system, an online monitoring and analysis instrument, a data processing and transmission system and a remote data management center. These subsystems are both self-contained and mutually cooperative to complete the continuous and reliable operation of the entire online automatic monitoring system.
Main Types
The multi-parameter water quality online automatic monitoring system, also known as the multi-parameter water quality online analysis instrument integrated system, is suitable for: water source monitoring, environmental monitoring stations, municipal water treatment processes, municipal pipe network water quality supervision, rural tap water monitoring; circulating cooling water, swimming pool water operation management, industrial water recycling, factory aquaculture and other fields.
Analytical Instruments
Water quality online analyzers are usually divided into two types according to the measurement method: electrode method and photometry method. The corresponding selection should be made according to the different use environments.
Currently, common manufacturers of water quality online analyzers include: HACH in the United States, SERES in France, WTW in Germany, E+H in Germany, KUNTZE in Germany, Shimadzu in Japan, Horiba in Japan, SCAN in Austria, etc.
According to the measured parameters, there are the following types of water quality online analyzers:
Water intake system
The design of the water intake system is mainly aimed at meeting the representativeness, reliability and continuity of water samples. The main components of the system are: water intake head, water intake pump, water sample delivery pipeline and flow rate and flow regulation. According to the water intake method, it is mainly divided into direct intake type and float type. The direct intake type is mainly used in environments with small water level changes, such as sewage treatment plants, pollution sources, tap water culvert water intake, etc., while the float type is mainly used in environments with large water level changes, such as surface water.
Pretreatment system
The design of water sample pretreatment is mainly to eliminate factors that interfere with instrument analysis and affect instrument use, while maintaining the representativeness of the water sample. Pretreatment methods usually include natural sedimentation, physical filtration and infiltration. The level of pretreatment is usually determined by the purity of the water sample. Some analytical instruments have already considered the pretreatment of injection during design, and it is necessary to consider using it in conjunction with the system integration.
Data acquisition control
The data acquisition control system is mainly composed of PLC, on-site industrial control computer, central station computer, transmitter, actuator, etc. Its main functions are:
(1) Control the automatic operation of the entire online monitoring system, which is mainly completed by writing the program into the PLC;
(2) Collect, store and transmit the data analyzed by the instrument, which is mainly completed by the collaboration between the on-site industrial control computer and the data acquisition and transmission module.
Integrated assistance systems
The design of the auxiliary system is mainly to ensure the continuous and stable operation of the online monitoring system. It needs to be adjusted accordingly according to the changes in the on-site conditions. In general, the following aspects need to be paid attention to:
(1) Pipeline cleaning: Since the dirt remaining in the pipeline and the algae that grow therefrom will pollute the water sample, the pipeline needs to be cleaned regularly and quantitatively. The cleaning methods and contents are varied, and the goal is to ensure the authenticity and representativeness of the water sample.
(2) Power guarantee: The stability of power is directly related to the accuracy and continuity of instrument analysis. Therefore, first of all, a stable AC power grid should be selected as much as possible for access; secondly, before the AC power enters the automatic monitoring system, the current needs to be rectified again to cope with the occurrence of sudden current instability; finally, if necessary, a backup power supply can be equipped to ensure the normal operation of the online monitoring system during power outages.
(3) Lightning prevention: Lightning protection is mainly divided into station building lightning protection, power supply lightning protection and communication lightning protection. When a lightning strike occurs, the current first breaks through the lightning arrester to achieve the purpose of protecting the instrument and system equipment. This is especially important in areas prone to thunderstorms. After a thunderstorm, the staff should check the status of the lightning arrester as soon as possible. If it is damaged, it should be replaced in time.
(4) Adjusting temperature and humidity: Appropriate temperature and humidity are also important for the stable operation of the instrument. This function is mainly achieved by air conditioning and dehumidification equipment.
Research significance
The online water quality monitoring system can realize automated monitoring and early warning of water pollution, which plays a vital role in preventing the further development of pollution incidents. The online water quality monitoring system can also realize online query and sharing of water quality information, which can quickly provide a scientific basis for leadership decision-making.
