In order to realize the sustainable development strategy, the intelligent dosage system for its sewage treatment system to carry out the transformation, can comply with the national discharge standards of industrial wastewater as well as to meet the requirements of their own production and development.　　

The original sewage treatment frequency feeding system consists of SBR reaction tank PLC and on-site display instrumentation, of which the PLC due to the use of a longer period of time, the failure rate increased significantly, so that the control is mainly completed manually by the process personnel, and because of the harsh environment, the site weighing instrumentation is corroded, unstable, has affected the stable operation of sewage treatment system. Finally, DCS was chosen to update the dosage and replace the on-site transmitter.　　

I. Process flow　　

The whole sewage treatment process consists of the following five processes:　　

(I) Pre-treatment process　　

Industrial wastewater from each production workshop is discharged into the conditioning pool, due to the high water temperature, which is not conducive to the growth of the bacteria that decompose the organic matter in the later process, and needs to be naturally cooled before discharge. There is a temperature node in the pool, when the water temperature drops to the set value, open the valve to make the sewage flow into the flocculation and sedimentation pool. Electromagnetic flow meter is installed in the waste water pipe to fulfill the function of measuring and settlement of sewage.　　Sedimentation tank regularly open lime pumps and valves, add in accordance with the ratio of control of the proportion of slaked lime solution to strengthen the dewatering capacity of sludge and improve the PH value of sewage, in a number of periods of time offline collection of wastewater in the pool, measuring its pH. The mud scraper at the bottom of the sedimentation tank works regularly to scrape the settled sludge into the flocculation sedimentation tank, and then regularly control the daily discharge of a fixed amount of thickened sludge into the sludge dewatering process. The supernatant liquid in the sedimentation tank is diluted with water and discharged into the homogenization tank, which is regularly discharged into the next process.　　

(ii) Hydrolysis and acidification process　　

Hydrolysis acidification of the main equipment is four anaerobic desulfurization tower, respectively, to accept four homogenization tank in the sewage raw liquid, each with an electromagnetic flowmeter to do the cost of settlement. The anaerobic bacteria cultivated in the desulfurization tower can remove part of the BOD and COD of the raw sewage to achieve the purpose of sewage desulfurization. According to the process requirements, the tower temperature is the most critical for the growth of anaerobic bacteria, the tower top and kettle temperature as a reference amount. Because of the opening of the steam valve to control the temperature constant, and the steam flow interference on the temperature of the greatest impact, so the design of the tower temperature as the main control point, steam flow control as a secondary circuit of the temperature - flow cascade dosage system, to ensure the stability of the temperature in the tower. After desulfurization of sewage discharged into the SBR tank.　　

(C) SBR process　　

SBR is the abbreviation of sequential batch activated sludge method, which is a kind of activated sludge wastewater treatment technology operated according to the intermittent aeration mode. the SBR reaction tank is the core of the whole wastewater treatment plant, where the large molecule organic matter in the wastewater is decomposed into small molecule organic matter, which in turn is decomposed into carbon dioxide and water. Therefore, the self-control of SBR reaction tank is crucial for the whole sewage treatment system.　　

There is a large amount of activated sludge at the bottom of the SBR tank, and its main component is aerobic bacteria. Aerobic bacteria for the organic pollutants in the sewage has a strong degradation effect, the number of its population and the SBR pool of sewage treatment capacity has a direct relationship. From the reaction pool has been carried out in the nitrification reaction equation: NH4 + + 2O2 → NO3 - + 2H + + H2O + energy only have enough oxygen molecules, the nitrification reaction can be carried out normally, degradation of organic matter aerobic bacteria can survive; but too much oxygen will lead to a large number of foam production, sludge settling performance decline, increased energy consumption, so the SBR pool of the control of the amount of aeration is the most critical. Aeration is timed control, when the online dissolved oxygen meter concentration deviation is too large, change the set value to adjust the length of air intake. Sewage feed valve and sludge discharge valve are also timed control, SBR tank with input level meter control valves to prevent overflow of sewage, installation of ultrasonic flowmeter to measure the sewage, set up a temperature node to heat the water to achieve a constant temperature in the reaction tank.　　

(D) Contact oxidation process　　

The primary and secondary contact oxidation tanks in this process can be regarded as the continuation of the aeration tank, and after sufficient oxidation, they are discharged into the corresponding sedimentation tanks at regular intervals to remove the sludge and other suspended matters through the principle of gravity sedimentation, and drive the sludge suction machine at regular intervals to scrape the sludge into the sludge thickening tank. The treated water in the second sedimentation tank is filtered and sterilized to meet the national emission standards, and can be discharged directly or reused in the water return system.　　

(E) Sludge dewatering process in the above process through the mud scraper will be discharged into the thickener by the dehydrator dewatering sludge cake with low water content, sent to the rotary kiln combustion, and finally discharged in the form of harmless carbon dioxide and water, and the ash will be landfilled.

Second, the proportion of batching

(I) Hardware configuration of automatic batching system consists of one engineer station, one operator station, one I/O station and process control network, and is connected to the management computer of workshop director through Ethernet to realize remote inquiry and remote control. The engineer station is equipped with a configuration software platform to accomplish the tasks of parameter modification and system maintenance; the operator station is a platform for the operators to accomplish the monitoring and management of the production process; the I/O station accomplishes the implementation of the monitoring of the whole industrial process, which consists of the master control card, the data forwarding card, the I/O card, and the power supply unit, etc. In order to ensure the reliability of the intelligent weighing and loading system, the master control card and the data forwarding card are redundantly configured. There are 2 SP243X main control cards, 30 SP313 4-channel analog signal input cards, 3 SP322 4-channel analog output cards, 8 SP363 7-channel contact-type switching input cards and 10 SP364 7-channel relay output cards. In total, there are 108 AI signals; 8 AO signals; 40 DI signals; 50 DO signals.

(ii) Network structure

(III) software configuration 1. man-machine interface shows the general appearance of the data, the historical curve of each test point, the process flow diagram of each process and the status of each valve on the scene, and set up different rights to ensure the safety of the automatic dosage system. 2. the report is issued at 8:30, 16:30, 0:30, in the form of a shift report, which is: displaying the current shift of temperature, flow of the whole point of the data, the flow of the cumulative flow of the moment record of the valve open, close, equipment operation status; monthly records; monthly records; the status of equipment operation. Moment record, equipment operation status; monthly report, in the form of: daily as a recording unit, showing the average daily value of flow (daily sum of the positive point record/24), monthly cumulative value, the average daily value of temperature (daily sum of the positive point record/24), and at the same time, can be input into other data for editing.

4. SBR reaction pool valve status alarm: If the valve in the aeration tank fails and is not detected in time, the sewage will be discharged into the next process without adequate degradation, and it will not be able to meet the national emission standards for sewage purification, resulting in greater losses, so with the help of the intelligent valve feedback signals to design a valve alarm program in order to deal with the malfunctions that occur in a timely manner, to reduce losses. Alarm definition: valve open/close action, no feedback signal within 12 seconds will be considered as a valve failure, with sound and light alarm to remind the maintenance personnel to go to troubleshooting to resume production.

Third, the concluding remarks in the measurement of the dosage system put into use since its stability and the human-machine interface friendly and rich control functions than the original variable-speed dosage system to improve a lot of the process personnel and automatic control maintenance personnel, for the realization of the stable operation of wastewater treatment systems and the improvement of the surrounding environment to provide a guarantee. But in this period also found some problems, with a view to in the funds and the later maintenance means to keep up with the time to carry out this further improvement.

First, the use of online analytical instruments is relatively small. Only in the SBR reaction pool has dissolved oxygen online monitoring, flocculation and sedimentation pool in the acid-base is offline analysis, time lag is large, and thus only as a reference data can not realize the self-control. If online analysis is realized, the control of lime pump can be turned on and off to realize the control of pH in the pool. In addition, where conditions permit, a sludge concentration meter can be set up in the SBR reactor to enable the technicians to understand more intuitively the growth of aerobic bacteria in the pool, but also to provide a basis for the determination of the amount of reflux sludge;

Secondly, the decanter controller in the SBR reaction tank is a stand-alone control mode, which can only run in accordance with a pre-set single working mode, if a fieldbus-based data link is established between it and the main control unit of the DCS to realize data exchange, the decanter can be realized in accordance with the different site environments and process requirements, and run more flexibly;

Third, due to the demand for dissolved oxygen in the SBR reaction tank and the sludge aerobic bacteria life cycle, in the treatment of the initial oxygen consumption is larger, and then gradually reduce the situation, for the control of dissolved oxygen to seek a suitable control algorithm and the constant frequency fan can be replaced with variable frequency not only better able to complete the task of wastewater treatment, but also reduce energy consumption, shorten the cycle of treatment, and realize the optimization of the control.