[Hongjie Water Service] Detailed explanation of 18 professional terms for sewage treatment

1. What is the biological wastewater treatment method?

Biological treatment is the use of microorganisms to adsorb, decompose, and oxidize organic matter in wastewater, degrading unstable organic matter into stable and harmless substances, thereby purifying wastewater.Modern biological treatment methods can be divided into two categories based on the different microorganisms involved, aerobic oxidation and anaerobic reduction.The former is widely used for treating urban sewage and organic industrial wastewater. Aerobic oxidation has a wide range of applications, including many techniques and structures.There are various processes and structures such as biofilm method (including biological filtration tank, biological turntable), biological contact oxidation, etc. Activated sludge method and biofilm method are both artificial biological treatment methods. In addition, there are natural biological treatment methods for farmland and ponds, namely irrigated fields and biological ponds. Biological treatment is currently the most widely used sewage treatment method due to its low cost.

2. What is the total amount of wastewater treatment or BOD5 removal and treatment quality?

◆ Sewage treatment capacity or total BOD5 removal amount: The total daily sewage flow rate (in m3/d) entering the sewage treatment plant can be used as an indicator of the sewage treatment capacity.The total amount of BOD5 removed daily can also be used as an indicator of the treatment capacity of the sewage plant. The total amount of BOD5 removed is equal to the product of the difference between the treated flow rate and the inlet and outlet water BOD5, in kg/d or t/d.

◆ Treatment quality: The secondary sewage treatment plant uses the factory's BOD5 and SS values as the treatment quality indicators.According to the newly formulated effluent discharge standards for sewage treatment plants, the BOD5 and SS of the effluent from secondary sewage treatment plants are both less than 30mg/L. The quality of treatment can also be measured by removal rate. The removal rate is determined by subtracting the inlet concentration from the outlet concentration and dividing it by the inlet concentration. Ammonia nitrogen, TP effluent value or removal rate should also be used as treatment quality indicators.

3. What is pH value and its indicative significance?

PH represents the acidity and alkalinity of wastewater.It is the logarithm of the reciprocal of hydrogen ion concentration in water, ranging from 0 to 14. If the pH value is 7, the water is neutral. If it is less than 7, it is acidic. The smaller the value, the stronger its acidity. If it is greater than 7, it is alkaline. The larger the value, the stronger its alkalinity. The pH value in sewage has a certain impact on pipelines, water pumps, gate valves, and sewage treatment structures.The pH value of sewage treatment plants, mainly composed of domestic sewage, is usually between 7.2 and 7.8. Excessive or insufficient pH values can indicate the entry of industrial wastewater. A low value can corrode the pipeline and pump body, and may cause harm. For example, sulfides in wastewater can 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, identify sources of pollution, and take countermeasures to detect a decrease in pH.Meanwhile, the allowable pH range for biochemical treatment is 6-10, and either too high or too low can affect or disrupt the biological treatment.

4. What is Total Solid (TS)?

◆ refers to the total amount of solid left after the water sample evaporates to dryness on a water bath at a temperature of 100 ℃.It is the sum of dissolved solids and insoluble solids in wastewater. It can reflect the total concentration of solids in wastewater. The analysis of inflow and outflow solids can reflect the effectiveness of sewage treatment structures in removing total solids.

5. What is suspended solids (SS)?

◆ refers to the amount of solid substances that can be intercepted by filters in wastewater. A portion of suspended solids can precipitate under certain conditions. The determination of suspended solids is usually carried out using the asbestos filter filtration method. The main equipment is the Gucci crucible.When the conditions of the laboratory equipment are not available, filter paper can also be used as a filter to obtain the suspended solid amount from the difference between total solids and dissolved solids.When measuring suspended solids, significant differences often occur due to different filters.

This indicator is one of the most basic data for sewage. The determination of suspended solids in influent and effluent can be used to reflect the reduction of suspended solids in wastewater after treatment in the primary and secondary sedimentation tanks. It is the main basis for reflecting the efficiency of sedimentation construction.

6. What is Chemical Oxygen Demand (COD)?

Chemical Oxygen Demand (COD) refers to the amount of oxygen required by oxidants to oxidize organic matter in wastewater using chemical methods.The result obtained by using potassium permanganate as an oxidant is commonly referred to as oxygen consumption, expressed as OC. The result obtained by using potassium dichromate as an oxidant is called chemical oxygen demand (COD), and the difference between the two lies in the choice of oxidant.Using potassium permanganate as an oxidant can only oxidize linear organic compounds in wastewater, while using potassium dichromate as an oxidant has a stronger and more complete effect than the former. Apart from linear organic compounds, it can oxidize many structurally complex organic compounds that potassium permanganate cannot oxidize.Therefore, the COD value of the same wastewater is much larger than the OC value. Especially when a large amount of industrial wastewater enters the sewage treatment plant, the chemical oxygen demand of the potassium dichromate method should generally be measured.The COD value of urban sewage treatment plants is generally about 400-800mg/L.

The consumption value of potassium permanganate method is often used as a reference data for determining the dilution factor of five-day biochemical oxygen demand in sewage treatment plants.

7. What is Biochemical Oxygen Demand (BOD)?

Biochemical Oxygen Demand (BOD) refers to the amount of oxygen required by microorganisms in water to decompose organic matter under aerobic conditions.It is an indirect indicator of the degree of organic pollution, and the biochemical oxidation and decomposition of organic matter usually have two stages. The first stage is mainly the oxidation of carbon containing organic matter, called the carbonization stage, which takes about 20 days to complete. The second stage mainly involves the oxidation of nitrogen-containing organic matter, known as the nitrification stage, which takes about 100 days to complete. Under recognized circumstances, the general standard practice is to cultivate at a temperature of 20 ℃ for 5 days for measurement, and the measured data is called the five day biochemical oxygen demand. Abbreviated as BOD5, BOD5 represents the oxygen demand for partial decomposition of organic matter containing carbon. The BOD5 of domestic sewage should be around 70%.

The determination of five-day biochemical oxygen demand is to take raw water samples or water samples that have been appropriately diluted to contain enough dissolved oxygen to meet the requirements of five-day biochemical oxygen demand. The water sample is divided into two parts, one part measuring the dissolved oxygen content of the day, and the other part is placed in a 20 ℃ incubator. After 5 days of cultivation, its dissolved content is measured. The difference between the two is multiplied by the dilution factor to obtain BOD5.

It is crucial to choose the correct dilution factor during the BOD5 determination process.It is generally believed that the chosen dilution ratio should be such that the dissolved oxygen of the diluted water sample decreases by 20% to 80% after being cultured in a constant temperature incubator at 20 ℃ for 5 days. However, sometimes numerical errors are caused by improper control of the dilution ratio of BOD5, and even the dilution ratio is too small to obtain data on BOD5.

8. What is the purpose of measuring BOD?

BOD can reflect the degree of organic pollution in wastewater. The more organic matter in wastewater, the more oxygen is consumed, and the higher the BOD value, and vice versa.Therefore, it is the most important indicator of sewage quality. Although measuring BOD takes a long time and the data is not timely, the BOD indicators have comprehensiveness - reflecting the total amount of organic matter comprehensively, and simulation - imitating the self purification of water bodies. Therefore, it is difficult to replace it with other indicators.

For sewage treatment plants, the purpose of this indicator is:

a. Reflect the concentration of organic matter in wastewater. The concentration of organic matter in the incoming wastewater and the concentration of organic matter in the outgoing wastewater. The influent BOD5 of urban sewage treatment plants can generally reach 150-350mg/L.

b. Used to indicate the treatment efficiency of a sewage treatment plant. The difference in BOD5 between the inlet and outlet is divided by the inlet BOD5, which is an important indicator for the removal rate of BOD5 in the plant.

c. The total removal amount and effluent BOD5 of a sewage treatment plant represent the total treatment capacity of the plant and its impact on the water environment.

d. Used to calculate the operating parameters of the treatment structure, such as the sludge load BOD5kg (MISS) or volumetric load BOD5kg/(m3/d) of the aeration tank.

e. Reflect the technical and economic data of the operation of the sewage treatment plant, such as the amount of air required to remove electricity consumption per kg of BOD (in degrees) and 5 per kg of BOD.

f. To measure the biodegradability of wastewater, when BOD5/COD is greater than 0.3, it indicates that the wastewater can undergo biochemical treatment. When it is less than 0.3, it is difficult to perform biochemical treatment. When the ratio is between 0.5 and 0.6, the biochemical process is easily carried out.

From this, it can be seen that the determination of BOD5 is very useful, as it is the most important measurement item in sewage treatment plants.But the measurement takes a long time and cannot provide data in a timely manner. The COD assay reflects the oxygen demand for organic matter in wastewater to be oxidized by oxidants, and its data value is close to the oxygen demand of all organic matter. Therefore, it is also of great use, and COD determination is brief. Generally, COD in urban sewage plants is greater than BOD. If there is less change in the types of organic matter in the sewage, there is a certain correlation between COD and BOD. Therefore, the COD of the day can be used to predict the BOD5 value.

According to the operational data of sewage treatment plants in various cities, SS and BOD5 are generally similar or slightly higher in value.The SS of various sewage treatment plants in Shanghai is on average about 50mg/L higher than BOD5.

If BOD5 and SS increase exponentially in the incoming wastewater, there may be high concentration organic wastewater flowing in or a large amount of feces entering the plant.This will increase the processing load. To reduce processing efficiency and even block pipelines, it is necessary to investigate the cause and take measures.

9. What are the indicative meanings of total nitrogen, ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen (N, NH4+, NO2-NO-3)?

There are a large amount of carbon containing organic matter and nitrogen containing organic matter in sewage, with carbon, hydrogen, and oxygen as the basic elements. The latter consists of nitrogen, sulfur, and phosphorus as basic elements. During the aerobic decomposition process, nitrogen-containing organic matter will ultimately be converted into inorganic substances such as ammonia nitrogen fertilizer, nitrite nitrogen fertilizer, nitrate nitrogen, water, and carbon dioxide. Therefore, measuring the above three indicators can reflect the process of wastewater decomposition and the degree of inorganic treatment. When only a small amount of nitrite nitrogen appears in the secondary sewage treatment plant, the treated effluent is not yet stable. When the oxygen content is insufficient, most of the organic nitrogen in the sewage is converted into inorganic substances, and the effluent is relatively stable when it flows into the water body.The ammonia nitrogen value of general incoming wastewater is about 30-70mg/L.The incoming water generally does not contain nitrite and nitrate.Secondary sewage treatment plants generally cannot remove a large amount of nitrogen fertilizer. When the treatment level is high, they can convert some ammonia nitrogen into nitrate nitrogen.

10. What is the significance of phosphorus and nitrogen (P, N) indicators?

The content of phosphorus and potassium in sewage affects the growth of microorganisms. Activated sludge wastewater treatment requires maintaining a BOD5: N: P ratio of 100:5:1 or above, which is generally achievable in urban sewage plants.Some industrial wastewater cannot reach this ratio, so it is necessary to add nutrients to the wastewater.

11. What is dissolved oxygen and what is the purpose of measurement?

Dissolved oxygen refers to the amount of oxygen dissolved in water, which is closely related to temperature, pressure, and the biochemical effects of microorganisms. At a certain temperature, water can only dissolve a certain amount of oxygen at most. For example, at 20 ℃, the saturation value of dissolved oxygen in distilled water is 9.17 mg/L.

In sewage treatment, the dissolution values in the effluent and aeration tank are often measured, and the air supply is adjusted based on their size to understand the oxygen consumption in the aeration tank and determine the oxygen consumption rate under various water temperature conditions. During operation, it is required that the dissolved oxygen in the aeration tank be above 1 mg/L. Low dissolved oxygen values indicate oxygen deficiency in the aeration tank, while high dissolved oxygen not only wastes energy consumption but may also cause sludge to become loose and aged.

The presence of dissolved oxygen in the effluent of sewage treatment plants is beneficial to the water environment. If possible, some dissolved oxygen should be allowed in the effluent.

Dissolved oxygen is an important parameter in the self purification process of water, which can reflect the balance between oxygen consumption and dissolved oxygen in the water.

12. What is the relationship between water temperature and operation?

The water temperature has a significant impact on the operation of the aeration tank. The water temperature of a sewage treatment plant gradually changes slowly with the season, with almost no significant change throughout the day. If significant changes are found within a day, an inspection should be conducted to see if industrial cooling has entered. Throughout the year, within the range of 8-30 ℃, when the aeration tank operates at a water temperature below 8 ℃, the treatment efficiency decreases, and the BOD5 removal rate is often below 80%.

13. What is the sludge load? How to adjust it?

a. Sludge load=quantity of BOD5 entering the aeration tank (flow rate) × Concentration/Total MLSS in aeration tank (MLSS × Pond accumulation.

b. Due to the fact that the amount of BOD5 in the effluent of the initial sedimentation tank is determined by the incoming water quality, it is generally difficult to regulate. To adjust the sludge load and reduce MLSS, the sludge load should be increased. Increasing or reducing MLSS is generally achieved by increasing or decreasing the discharge of sludge.

The sludge load has a significant impact on the treatment efficiency, sludge growth, and oxygen demand, and must be carefully controlled.Generally speaking, the sludge load is between 0.2~0.5kg (BOD5)/(kg. d), and is controlled around 0.3kg (BOD5)/"kg (MLSS). d".

14. Volume load of aeration tank?

The daily burden of BOD5 per unit volume of the aeration tank is called the volumetric load kg (BOD5)/(m3. d).The volumetric load represents the economic feasibility of constructing the aeration tank. The relationship between volumetric load, mixed liquid concentration, and sludge load is as follows:

BV=x B5, in the formula (x is MLSS).

15. What is the meaning of sludge age?

◆ Sludge age=number of MLSS in the aeration tank (MLSS)× Pond volume/Solid content in residual sludge (discharge volume) × Sediment discharge concentration).

The sludge age is the ratio of the total amount of activated sludge working in the aeration tank to the remaining sludge discharged every day, in units of d.When running smoothly, it can be understood as the average residence time of activated sludge in aeration.

The sludge age of a general aeration tank system is about 5-6 days.When reaching the nitrification stage, the sludge age needs to reach 8-12 days or higher.

There is an opposite relationship between sludge age and sludge load, with longer sludge age and lower load, and vice versa, but it does not form an absolute inverse proportional function relationship.

16. Mixed liquid suspended solid concentration (MLSS)?

The concentration of suspended solids in the mixed solution is the amount of suspended solids in the mixed solution of sewage and activated sludge in the aeration tank, measured in mg/L. It is an indicator for measuring the amount of activated sludge in the aeration tank. Due to its simplicity, it is often used as a rough measure of the microbial biomass of activated sludge.In the process of promoting flow aeration, the MLSS is generally 1000-4000mg/L. In a fully mixed aeration tank built together, the MLSS in air aeration rarely exceeds 8000mg/L.This is because MLSS is too high. Obstructing oxygenation also makes it difficult for it to settle in the secondary sedimentation tank.

17. What is the concentration of volatile suspended solids in the mixed liquid (MLVSS)?

The concentration of volatile suspended solids in a mixed solution refers to the weight of organic matter in the suspended solids (usually measured by the reduction in burning at 600 ℃), so some people believe that it can more accurately represent the number of microorganisms in activated sludge than MLSS.However, MLVSS also includes non active and non degradable organic matter, which is not the most ideal indicator for measuring MLSS. For domestic wastewater, it is often around 0.75.

18. Sludge Index (SVI)?

The sludge index refers to the volume (in ml) of 1g dry sludge after 30 minutes of settling of the mixed liquid in the aeration tank, which is:

SVI=Sedimentation of sludge after 30 minutes of settling of the mixed solution (ml)/Dry weight of sludge (g)

The SVI value can better reflect the degree of looseness and coagulation settling performance of activated sludge. A good activated sludge SVI is often between 50 and 300. Only when the SVI concentration is too high can the SVI value measured at the same concentration be valuable. Additionally, the size of the measuring container has a certain impact on the quantity of measurements, and it is necessary to uniformly measure the containers.

More information can be found on the official website of Shenzhen Hongjie Water Technology Co., Ltd. www.czhengwei.net. If you need it, you can call the company's hotline for free at 180 3800 0078, and we will be happy to serve you.