At present, the situation of pneumonia caused by novel coronavirus (hereinafter referred to as the epidemic) is grim. In order to promote effective response to the epidemic in various projects, strengthen production regulation and occupational health protection during the epidemic period, we have formulated guidance on production operation during the epidemic period for reference by various projects.
Since the Ministry of Environmental Protection issued the Notice on Doing a Good Job in the Supervision of Medical Sewage and Urban Sewage from the Pneumonia Epidemic Caused by novel coronavirus, how sewage plants respond to the epidemic has become the focus of attention of the industry, and it is urgent to form a set of effective, easy to implement, and personal safety of employees. Today we are forwarding a summary and analysis of operational guidance from frontline operators, which provides detailed explanations on sampling, monitoring, and operations for readers to refer to and learn from.
At present, the situation of pneumonia caused by novel coronavirus (hereinafter referred to as the epidemic) is grim. In order to promote effective response to the epidemic in various projects, strengthen production regulation and occupational health protection during the epidemic period, we have formulated guidance on production operation during the epidemic period for reference by various projects.
1. Precautions for Sampling and Laboratory Testing
During the epidemic, for projects with stable water quality and quantity, the inflow indicators can be automatically detected by online monitoring equipment, while the outflow indicators are manually detected.
When manually sampling and testing, attention should be paid to:
(1) Before sampling, protective equipment should be worn correctly, including masks, goggles, work clothes (medical protective clothing is recommended if possible), waterproof gloves (or medical rubber gloves);
(2) The pre-treatment unit should maintain good ventilation and deodorization, and the sewage channels and related equipment should be kept sealed to prevent odors and bacteria from spreading into the limited space;
(3) When sampling, avoid direct contact between body parts and sewage;
(4) During the testing period, the ventilation system should be turned on and personnel who have not taken protective measures are prohibited from entering;
(5) After the testing is completed, the sampling equipment and laboratory should be disinfected;
If conditions permit, a peristaltic pump can be used for sampling, as shown in the following figure.
2 Disinfection precautions
It is recommended to use chlorine disinfectants (sodium hypochlorite, liquid chlorine) to disinfect the effluent. It is recommended to add effective chlorine with a concentration of 3-5mg/L and maintain the residual chlorine in the effluent at 0.1-0.2mg/L.
For projects that use ultraviolet disinfection, it is recommended to add temporary pipelines to add chlorine disinfectant with a concentration of 1-2mg/L effective chlorine.
3. Strengthen the monitoring of biochemical systems
If there is excessive residual chlorine in the influent, it will reduce or inhibit the activity of the activated sludge, affecting the normal operation of the biological treatment unit. Therefore, it is necessary to closely observe the shape of the activated sludge.
(1) For large-scale projects with a relatively small proportion of hospital sewage, the specific oxygen consumption rate (SOUR) of activated sludge, sludge settling, and mixed liquid filtration can be monitored. The relevant judgment indicators are detailed in the attachment.
(2) For projects with low water volume and high proportion of hospital sewage, residual chlorine in the influent should be monitored (residual chlorine meter or residual chlorine test paper can be used). When the residual chlorine is high, measures such as refluxing excess sludge and adding reducing agents in severe cases can be taken to reduce the residual chlorine entering the biochemical system.
(3) When the sludge activity decreases, it is necessary to reduce the remaining sludge discharge, increase the sludge concentration, appropriately increase the aeration rate, and supplement fresh sludge if necessary to ensure the effectiveness of sewage treatment.
(4) During the epidemic, it is necessary to closely observe changes in the quality and quantity of incoming and outgoing water, predict in advance, and adjust process parameters in a timely manner to ensure system stability.
4 Countermeasures for abnormal water quality
At present, the northern region is in winter, with low inlet water temperature and low sludge activity, which can easily lead to TN, ammonia nitrogen, and TP exceeding the standard. The following measures are recommended for treatment.
(1) Excessive ammonia nitrogen
(2) TN exceeds the standard
(3) TP exceeds the standard
5 Solutions for Membrane Pollution
For projects with sufficient drug procurement, it is necessary to strictly follow the standard of washing the membrane with sodium at a concentration of 500-1000mg/L per week, maintain appropriate sludge concentration (6-10g/L) and good filtration (25ml/50ml. 5min), and ensure sufficient strength and uniform aeration, which are the basic conditions for maintaining the sustainability of the membrane system.
For projects with insufficient supply of sodium hypochlorite due to the epidemic, in order to delay membrane fouling, the following measures can be taken:
(1) Appropriately increase the aeration intensity (aeration amount);
(2) In addition to washing the membrane with sodium hypochlorite for 7-10 days, consider backwashing with clean water every 2-3 days (i.e. online membrane washing without medication).
(3) When the transmembrane pressure difference is greater than 25kPa, attention (intervention) should be paid to prevent rapid membrane fouling from causing insufficient water production.
(4) If the water production meets the requirements, it is recommended to conduct 1-2 hours of air aeration in each corridor every day.
When the sludge filtration performance deteriorates due to water quality impact, appropriate chemicals can be added for regulation, mainly PAC or multi-core flocculants, with a dosage of 20-50mg/L.
6 Key points for personnel safety protection
Always wear protective equipment during work, wash hands frequently, pay attention to personal hygiene, wear masks when traveling, and avoid close contact with patients with symptoms such as cough and fever;
From the production area to the office area, it is necessary to wash hands and disinfect before entering the office area to avoid carrying bacteria and viruses into the office area;
Equipment such as grilles, sand water separators, and dehydrators that are prone to wastewater splashing must wear masks, waterproof gloves, goggles, and safety helmets;
Increase the power of the deodorization fan to create negative pressure;
The office area should be ventilated at least 3 times a day for 20-30 minutes each time. In the office area, avoid gatherings of people, maintain distance during communication, wear masks, avoid physical contact, and do not shake hands;
Forced ventilation should be turned on 24 hours a day in underground areas or between various process equipment rooms;
Disinfect the lobby, corridor, meeting room, staircase, toilet and other public parts every day, and try to use spray disinfection. The cleaning tools used in each area should be separated to avoid mixing;
The restaurant is disinfected daily, and tables and chairs are disinfected after use. Tableware must be disinfected at high temperatures. Keep the operating room clean and dry, strictly prohibit the mixing of raw and cooked food products, and avoid consuming raw meat.
After the work is completed, it should be thoroughly cleaned before leaving the factory. Do not bring pathogenic microorganisms from the sewage treatment plant out of the factory, block the diffusion pathway, and avoid the widespread spread of biological damage.
Meeting precautions: During the epidemic, except for special circumstances, only video conferencing will be used. If a symposium is necessary, attendees must wear masks, wash their hands and disinfect before entering the conference room, and maintain a distance of at least 1 meter between people. Control the meeting time. If the meeting time is too long, open the window for ventilation once. After the meeting, the venue and furniture must be disinfected. Tea utensils are recommended to be soaked in boiling water for disinfection
(2) Frontline operators and testing personnel
In addition to the conventional protective measures mentioned above, frontline operators and testing personnel should also achieve the following four points.
When entering the workplace, it is necessary to wear protective equipment such as disposable gloves, masks, goggles, helmets, disposable foot covers, etc., and try to achieve effective zero contact with sewage. In workplaces where conditions permit, protective masks, protective clothing, etc. can also be worn.
When leaving the workplace, it is necessary to fold the back of disposable gloves, foot covers, etc., and wrap the parts that come into direct contact with sewage or sludge on the outside inside for centralized treatment at designated locations.
Before leaving the workplace that comes into direct contact with sewage, it is necessary to use cleaning products such as soap, soap, and hand sanitizer, and rinse with running water for no less than 20 seconds.
Then, before leaving the workplace, wash your hands again using the above methods and remove masks, protective goggles, and other items for centralized disinfection or treatment.
Attachment 1: Simple Measurement Method and Judgment of Activated Sludge (SOUR)
1. Device preparation:
DO analyzer, thermometer, 300mL capacity BOD culture bottle, magnetic stirrer, timer.
2. Measurement procedure:
(1) Take an appropriate amount of mixed liquid solid (MLSS) from the aeration tank, continuously aerate in the laboratory for 5-10 minutes, measure the temperature T (℃) of the mixed liquid, then inject it into a 300mL capacity BOD culture bottle, insert a DO probe and seal the bottle mouth;
(2) Place the BOD culture bottle on a magnetic stirrer and start stirring;
(3) Record the changes in dissolved oxygen (DO) in the bottle over time, every 30 seconds for approximately 10-15 minutes, until the DO decreases by more than 1 mg/L. Otherwise, continue to extend the recording time;
(4) Measure the volatile suspended solids (MLVSS, g/L) in the mixed solution.
3. Calculation method:
Plot the measured DO over time as a curve, and take the linear part of the curve to calculate its slope. This slope is the oxygen consumption rate (OUR), measured in (mgO2/L)/min. The SOUR calculation formula is:
When T ≥ 20 ℃, θ=1.05; When T<20 ℃, θ=1.07
4. Determination of sludge activity
Sampling from different locations in the aeration tank results in different measured SOURs. The sample taken from the first end of the aerobic section of the aeration tank is represented by SOURfed, and the sample taken from the end of the aeration tank is represented by SOURend. SOURfed is usually higher than SOURend. SOUR is influenced by many specific factors, and each sewage treatment plant should focus on self comparison. When SOUR decreases compared to previous data, it indicates that activated sludge is affected by certain factors leading to a decrease in activity. When there is a lack of historical data from our factory, the following table can be used to determine whether the sludge activity is normal. When the measured SOURend is lower than the corresponding reference value, it indicates that the sludge activity has been inhibited due to some factor:
The inhibition of sludge activity can be determined based on the ratio of SOURfed to SOURend, as shown in the table below:
Attachment 2: Key points for observing sludge settling ratio
The settlement ratio detection is convenient, providing the possibility for early detection of biochemical system problems. The observation points when conducting sedimentation ratio experiments include the liquid level of the supernatant, sedimentation process, supernatant, sediment, etc.
1. Carefully observe whether there are oily substances, floating slag, and bubbles on the liquid surface of the supernatant, and gently fan the mouth of the measuring cylinder with your hand to smell the odor.
① Oil like substances usually do not appear clearly, pay attention to carefully observing the hazy oil like substance covering the liquid surface; The reason for the presence of oily substances is that the incoming water contains mineral oil or emulsified oil, detergents, and defoamers.
② Scum usually appears as brownish yellow or black flocculent masses floating on the liquid surface, due to excessive aeration; Aging of activated sludge; Caused by oily substances on the liquid surface; Sludge poisoning; Filamentous bacterial expansion; Activated sludge lacks oxygen.
③ Bubbles usually manifest as rows of larger bubbles between the liquid surface and the measuring cylinder, or smaller bubbles attached to the floating slag on the liquid surface. Reason for formation: excessive aeration; Aging of activated sludge; Caused by oily substances on the liquid surface; Caused by denitrification; Filamentous bacteria expand.
④ The odor is detected during the initial settling stage, and a strong earthy smell indicates high activity; If the acidity and alkalinity are strong, the pH of the mixed solution will be abnormal; If the odor is severe, there may be oxygen deficiency; Other odors may be considered as special industrial wastewater inflow.
2. Carefully observe the settling properties, velocity, interstitial water, floc state, and other aspects during the settlement process.
① At the stage of free sedimentation to group sedimentation, the settling performance shows clear mud water interface and overall sedimentation. Reason: Excessive aeration leads to poor performance; Poor settling ability of poisoned sludge; Filamentous bacteria have good swelling and settling properties but slow settling speed.
② Speed is divided into initial flocculation speed; The speed of free sedimentation and group commitment; The speed at which the mud water interface forms. Reason: The more the sludge ages, the faster it ages; The higher the activated sludge load, the slower; Filamentous bacteria expand slowly; The higher the content of inert substances, the faster.
③ After the formation of flocs, the water conditions, clarity, and particulate matter between flocs. Reason: Excessive aeration does not flocculate fine particles; Active aging and disintegration of activated sludge; The sludge load is too high and the mixed solution is turbid; Filamentous bacteria expand with high clarity.
④ The floc state refers to the particle size, floc movement direction, and floc color after flocculation. Reason: Excessive aeration leads to loose flocs; The aged flocs of activated sludge are coarse and solid, with a dark color; Excessive activated sludge load leads to the formation of small flocs; Filamentous bacteria expand and form fine flocs.
3. Carefully observe the clarity, particles, interstitial water, wall hanging, and other phenomena of the supernatant.
① Clarity refers to the overall color and turbidity of the supernatant. Performance and reasons: The higher the sludge load, the worse; Excessive aeration results in poor performance; Sludge poisoning and poor sedimentation; The swelling supernatant of filamentous bacteria is clear.
② The number of suspended particles in the supernatant. Reason: The more aged the sludge is, the more particles it contains; The supernatant of sludge poisoning is turbid and accompanied by small loose particles; The higher the activated sludge load, the more turbid it becomes; The higher the content of inert substances, the more turbid it becomes.
③ The clarity of water dispersed between particles. Reason: Excessive aeration leads to the presence of small particles in the interstitial water; The aged activated sludge has clear interstitial water; The sludge load is too high and the interstitial water is turbid; Sludge poisoning leads to turbid interstitial water.
④ The measuring cylinder wall is covered with activated sludge floc particles. Reason: Aging of activated sludge; Excessive aeration.
4. Carefully observe the compaction and bubbles of the sediment.
① The compactness is the final sediment density. Reason: The more inert material content, the denser it becomes; The lower the sludge load, the denser it becomes; Excessive aeration results in poor performance; Sludge poisoning leads to fine and dense particles; The expansion of filamentous bacteria varies with the degree of expansion.
② There are bubbles trapped inside the sediment floc. Reason: Small bubbles can be seen immediately after excessive aeration and sedimentation; Filamentous bacterial expansion; The viscosity of activated sludge increases after aging; Activated sludge will be released after denitrification mixing; Due to the expansion of small bubbles at high temperatures after sampling.
