Introduction of some indicators in water treatment

1.PH

◆pH indicates the acidity and alkalinity of sewage. It is the logarithmic value of the reciprocal of the hydrogen ion concentration in the water. Its range is 0~14. The pH value is equal to 7, the water is neutral, and less than 7 is acidic. The smaller the value, the stronger the acidity, and the value greater than 7 is alkaline. The larger the value, the stronger the alkalinity. The pH value of sewage has a certain impact on pipelines, pumps, gate valves and sewage treatment structures. The pH value of sewage treatment plants with domestic sewage as the mainstay is usually 7.2 to 7.8. A pH value that is too high or too low can indicate the ingress of industrial wastewater. A value that is too low will corrode the pipeline and pump body and may cause harm. For example, sulfide in sewage will generate H2S gas under acidic conditions. High concentrations can cause headaches, runny nose, suffocation and even death during operation. Therefore, it is necessary to strengthen monitoring to find the source of pollution and take countermeasures if the pH is lowered. At the same time, the allowable range of pH for biochemical treatment is 6~10, too high or too low can affect or destroy the biological treatment.

2.Total solids (TS)

◆It refers to the total amount of solids left after the water sample evaporates to dryness on the water bath at a temperature of 100°C. It is the sum of dissolved solids and non-dissolved solids in sewage. It can reflect the total concentration of solids in sewage. The analysis of solids in and out of the water can reflect the effect of sewage treatment structures on the removal of total solids.

3.suspended solids (SS)

◆It refers to the amount of solid matter in the sewage that can be intercepted by the filter. Part of the suspended solids can settle under certain conditions. The determination of suspended solids is usually carried out by the asbestos filter layer filtration method. The main equipment is Gu's crucible. When the laboratory equipment conditions are not available, filter paper can also be used as a filter to obtain the amount of suspended solids from the difference between the total solids and the dissolved solids. When measuring suspended solids, there are often big differences due to different filters.

◆This indicator is one of the most basic data of sewage. The measurement of suspended solids in influent and factory water can be used to reflect the reduction of suspended solids after the sewage passes through the primary sedimentation tank and the secondary sedimentation tank. It is the main basis for reflecting the construction of sedimentation efficiency.

4.chemical oxygen demand (COD)

◆Chemical oxygen demand (COD for short) refers to the amount of oxygen in the oxidant required to oxidize organic matter in sewage by chemical methods. Using potassium permanganate as an oxidant, the measured result is customarily called oxygen consumption, expressed by OC. Using potassium dichromate as the oxidant, the measured result is called the chemical oxygen demand and expressed in COD. The difference between the two lies in the choice of the oxidant. Using potassium permanganate as an oxidizing agent can only oxidize linear organic compounds in sewage, while potassium dichromate as an oxidizing agent has a stronger and complete effect than the former. In addition to linear organic compounds, it can oxidize permanganic acid. Many complex organic compounds that potassium cannot oxidize. Therefore, the COD value of the same sewage is much larger than the OC value. Especially when a large amount of industrial wastewater enters the sewage plant, the chemical oxygen demand of the potassium recomplex method should generally be measured. The COD value of urban sewage plants is generally about 400~800mg/L.

◆The consumption value of the potassium permanganate method is often used as a reference data for determining the five-day BOD dilution factor in the sewage plant.

5.Biochemical oxygen demand (BOD)

◆Biochemical oxygen demand: (BOD for short) refers to the amount of oxygen required by microorganisms in water to decompose organic matter under aerobic conditions. It is an indicator that indirectly indicates the degree of pollution of organic matter. The biochemical oxidation and decomposition of organic matter usually has two stages. The first stage is mainly the oxidation of carbon-containing organic matter, which is called the carbonization stage, which takes about 20 days to complete. The second stage is mainly the oxidation of nitrogen-containing organic matter, called the nitrification stage, which takes about 100 days to complete. Under recognized circumstances, the general standard practice is to incubate for 5 days at 20°C for measurement, and the measured data is called the five-day biochemical oxygen demand. Abbreviated as BOD5, BOD5 represents the oxygen demand for the decomposition of some carbon-containing organic matter, and the BOD5 of domestic sewage should be about 70%.

◆The five-day biochemical oxygen demand determination is to take the original water sample or the water sample that has been properly diluted to make it contain enough dissolved oxygen to meet the five-day biochemical aerobic demand. This water sample is divided into two parts, one The dissolved oxygen content of one part is measured on the day, and the other part is placed in a 20°C incubator, and the dissolved content is measured after 5 days of cultivation. The difference between the two and the dilution factor is BOD5.

◆During the determination of BOD5, the correct selection of the dilution factor is very important. It is generally believed that the dilution factor should be selected so that after the diluted water sample is cultured in a 20 ℃ thermostat for 5 days, its dissolved oxygen will be reduced by 20% to 80%. However, sometimes due to improper control of the BOD5 dilution factor, numerical errors are often caused, and even the dilution factor is too small to obtain BOD5 data.