System and method for controling amount of liquid carbon source released to constructed wetland

A method for controlling an amount of a liquid carbon source released to a constructed wetland for treatment of polluted water using a system, the system comprising:

• a carbon source pool, a carbon source pipe, a peristaltic pump, a programmable logic controller (PLC), a computer, a first flow meter, a first chemical oxygen demand (COD) sensor, a first total nitrogen (TN) sensor, a second TN sensor, a second COD sensor, an inlet pipe, and an outlet pipe;
• wherein:
• the first flow meter, the first COD sensor, and the TN sensor are disposed on the inlet pipe;
• the second COD sensor and the second TN sensor are disposed on the outlet pipe;
• the inlet pipe and the outlet pipe are connected to the constructed wetland;
• the carbon source pipe is connected to the carbon source pool via the peristaltic pump;
• the computer, the peristaltic pump, the first flow meter, and all sensors are connected to the PLC;
• and
• the first flow meter is configured to measure a flow of an influent to the constructed wetland;
• the first COD sensor is configured to monitor a concentration of COD in the influent (CODin);
• the first TN sensor is configured to monitor a concentration of TN in the influent (TNin);
• the second TN sensor is configured to monitor a concentration of TN in an effluent from the constructed wetland (TNout);
• and the second COD sensor is configured to monitor a concentration of COD in the effluent (CODout);
• the method comprising:
• S1. disposing the carbon source pipe in a water distribution channel in the constructed wetland;
• S2. gathering aquatic plant straws from the constructed wetland;
• grinding the aquatic plant straws into powders;
• and soaking the powders in the carbon source pool;
• passing a resulting mixture through a filter so that the liquid carbon source is separated from carbon residues;
• S3. receiving, by the PLC, data from the first flow meter, the first COD sensor, the first TN sensor, the second TN sensor, and the second COD sensor;
• and sending the data to the computer to calculate a preset volume (V) of the liquid carbon source to be released to the constructed wetland;
• S4. calculating the preset volume (V) of the liquid carbon source released to the constructed wetland according to following formula:
• V=(Q*(5*(TNin−TNout)−(CODin−CODout))/COD equivalent of carbon source from plant)/ρ;
• wherein:
• V is a volume of the liquid carbon source;
• Q is a volume flow rate of the influent flowing into the constructed wetland (unit:
• m3/d);
• ρ is a density of the liquid carbon source (unit:
• 1.0 g/mL);
• when the influent has a ratio of CODin to TNin of greater than 6, the carbon source is not an impact factor hindering denitrification in the constructed wetland, and thus the liquid carbon source is not released;
• and
• S5. sending the preset volume to the PLC;
• and controlling, by the PLC, operations of the peristaltic pump and a regulating valve connected to the peristaltic pump, so that the preset volume (V) of the liquid carbon source is added to the constructed wetland via the carbon source pipe;
• and monitoring, by a second flow meter disposed on the carbon source pipe and connected to the PLC, the flow of the liquid carbon source released to the constructed wetland.