Anaerobic commissioning
1. Selection and treatment of inoculated sludge
Sludge with similar characteristics of wastewater can be introduced for inoculation. Sludge with more methanogens should be selected as much as possible, such as anaerobic digestion sludge from urban wastewater treatment plants, dehydrated anaerobic and aerobic sludge, and sewer and pond sludge for long-term storage and discharge of wastewater. For over-thick inoculated sludge, water can be used for dilution, filtration and sedimentation to remove large solid particles and floating debris entrained in the sludge.
2. Factors affecting commissioning
In addition to inoculated sludge, factors affecting commissioning include wastewater water quality characteristics, organic matter load and toxic pollutant load, environmental conditions, filler types, etc. Anaerobic commissioning takes a long time, generally ranging from 16 to 24 weeks.
(1) pH value: pH changes will directly affect the survival and activity of methanogens. The pH value of the anaerobic tank should be maintained between 6.5 and 7.8, and the optimal range is around 6.8 to 7.5. The anaerobic tank has a certain buffering capacity. When operating normally, the pH value of the inlet water can be slightly lower than the above value.
(2) Temperature: Use medium temperature adjustment. The suitable temperature for most methanogens is between 35 and 40°C. Under medium temperature conditions, there are many types of methanogens, which are easy to cultivate and domesticate and have high activity. The temperature fluctuation range of the anaerobic tank should be controlled. Generally, it should not exceed ±2°C per day, and the temperature should not exceed 42°C.
(3) Alkalinity: The reasonable alkalinity range of anaerobic tanks (measured in CaCO3) is 2000-4000 mg/L.
(4) The ratio of carbon, nitrogen, phosphorus and trace elements in the matrix: For anaerobic treatment to maintain normal operation, the wastewater must contain enough bacteria to synthesize their own cell substances. The main nutrients of methanogens are nitrogen, phosphorus, potassium and sulfur and other necessary trace elements. The ratio of nutrients in the anaerobic tank is generally BOD5:N:P=(200-300):5:1, while the ratio of main nutrients in the biological contact oxidation tank and the biological iron micro-electrolysis tank is generally BOD5:N:P=100:5:1. The trace elements required by bacteria are very few, but the lack of trace elements can lead to a decrease in bacterial activity. Appropriate amounts of trace elements should be added during the commissioning phase.
3. Anaerobic tank commissioning operation
(1) Put the inoculated sludge into the anaerobic tank and soak it in diluted wastewater for 2 days. Adjust the pH value in the anaerobic tank to about 7.0-7.5.
(2) Inject about 1/3 of the tank volume of production wastewater into the anaerobic tank, and then add domestic wastewater to the designed capacity. A lower load should be used at the beginning of the commissioning, generally about 1/6-1/4 of the normal operating load.
(3) Continuously infuse water at about 1/4 of the designed treatment capacity.
The anaerobic tank in the wastewater treatment design has no return pump. During the commissioning phase, a temporary return pump should be installed to return the effluent from the anaerobic tank to increase the number of biological bacteria in the tank to prevent a large amount of sludge from being lost. The return ratio is about 1:4.
The biological contact oxidation tank is commissioned at the same time. In order to prevent the high-concentration wastewater from the anaerobic tank from impacting the biological contact oxidation tank during the commissioning phase, the amount of wastewater flowing from the anaerobic tank into the biological contact oxidation tank should be controlled.
(4) Attention should be paid to the temperature changes in the tank, and the temperature should not rise too fast. When the pH of the effluent from the anaerobic tank is less than 6.5, the amount of alkali in the influent should be increased, and the pH should be tested in time.
(5) Under the above conditions, the anaerobic tank can be operated stably for 2 to 3 weeks, and the volume load of the anaerobic tank can be gradually increased. Each increase is about 0.3kgCOD/(m³.d), and the stable operation time is about 2 weeks.
During this period, the effluent from the anaerobic tank should be observed. If the pH value is reduced, the amount of alkali should be increased. If an abnormality occurs after adjusting the load, measures such as reducing the load or temporarily stopping the water inlet should be taken, and the load should be increased after stabilization.
(6) If the effluent quality is good and stable, the amount of water from the anaerobic tank to the biological iron micro-electrolysis tank can be gradually increased, and finally all the effluent from the anaerobic tank will flow into the biological contact oxidation tank.
(7) When the influent concentration of the anaerobic tank is increased to the raw water concentration, the water is directly inlet. It should be observed for 10 days for stable operation. The reflux pump can be gradually cancelled.
Normal mature sludge is dark gray to black, with tar gas, no hydrogen sulfide odor, pH value between 7.0 and 7.5, and the sludge is easy to dehydrate and dry. When the influent volume reaches the design requirements and a high treatment efficiency is achieved, the gas production is large, and the methane content is high, the anaerobic commissioning can be considered to be basically completed.
Aerobic biochemical treatment commissioning operation
(1) Put the activated sludge transported from outside into the biological contact oxidation tank, and the sludge volume is 0.01-0.05 of the tank volume.
(2) Pump the wastewater from the pre-aeration regulating tank into 1/5-1/3 of the tank volume of the biological contact oxidation tank, and then fill it with tap water. Control the pH value of the biochemical tank water at this time to 7 or slightly greater than 7. Since the pollutant concentration in the tank is high at this time, it is not necessary to add nutrients and carbon sources.
(3) Start the Roots blower, and after 8 hours of aeration (continuous aeration without water), stop aeration and let it settle for 0.5 hours, then continue aeration. After that, stop aeration every 8 hours and let it settle for 0.5 hours before continuing aeration.
(4) After 1 day of aeration, a small amount of wastewater can be added from the regulating tank.
(5) During the aeration process, the dissolved oxygen content in the biochemical pool should be controlled between 2 and 4 mg/l, and the sludge settling ratio should be tested. If the value gradually decreases, it means that the sludge has adhered to the filler.
(6) Add an appropriate amount of trace elements every day and replace about 1/3 of the pool volume of wastewater. After several days of aeration, static sedimentation, and wastewater replenishment, water can be continuously added at 1/3 to 1/2 of the designed flow rate.
In order to prevent the life of the submersible wastewater pump from being affected by too small a water inflow, a return branch pipe with a gate valve should be installed behind the pump when the wastewater pump is installed, so that part of it can flow back to the regulating tank through the branch pipe.
(7) Domestication and bacterial cultivation are carried out simultaneously, and the biofilm growth speed is very fast. Generally, a thin layer of film can be seen on the surface of the filler after one week.
(8) If the microbial film proliferation is normal, after about 7 days, part of the effluent from the biological contact oxidation pool can flow into the sedimentation tank, and part of it still flows back to the regulating tank, so that continuous water inflow and return can be achieved.
(9) After about 20 days, a layer of orange-black biofilm will be formed on the filler, and water can be added according to the designed water volume.
(10) Under this condition, it can run stably for about one month. At this time, the biofilm is basically completed and microorganisms begin to multiply in large numbers. At this time, close attention should be paid to monitoring the changes in water quality to avoid the impact of sudden load changes on the biochemical pool.
If a large amount of foam is generated on the liquid surface and the amount continues to increase, covering the biochemical pool, it means that the aeration volume is too large or a large amount of synthetic detergents and other substances have entered. The aeration volume should be reduced and defoaming agents should be added. Tap water showers can also be installed around the biochemical pool to spray and remove foam.
As time goes on, the biofilm begins to metabolize, the old film begins to peel off, and suspended matter appears in the effluent, indicating that the biofilm stage is over and normal operation can be entered.
Judging the operation status of the biochemical pool
The operation status of the biochemical pool can be judged according to the following conditions:
(1) Color: When the operation is good, the mixed liquid is brown and bright in color; when the operation is deteriorating, it is dark brown or black.
(2) Odor: When the operation is good, no unpleasant odor is produced, it should be a slightly musty earthy odor; when the operation is deteriorating, the wastewater has a foul odor similar to rotten eggs.
(3) Foam: A small amount of foam appears in the biochemical pool, which is a normal phenomenon; the appearance of white foam rolling in the effluent indicates that the concentration of suspended solids is too high.
(4) pH value: When the operation is normal, the pH value should be between 6.5 and 8.5; if it drops, it may be due to excessive aeration and toxic substances entering. Quicklime (or industrial Na2CO3) can be added for adjustment.
When the anaerobic pool is debugged, the aerobic biochemical pool operates normally, and the entire debugging work is basically completed.
Determine process control parameters
The designed process control parameters are determined under the expected water volume and water quality conditions, but the water volume and water quality of the sewage treatment plant actually put into operation are often quite different from the design. Therefore, it is necessary to determine the appropriate process control parameters based on the actual water volume and water quality to ensure normal operation and reduce energy consumption as much as possible while ensuring that the effluent quality meets the standard.
1. Process control parameters
The important process control parameters to be determined include: the control water level of the water inlet pump room, the sand discharge cycle of the slurry sand settling tank, the pool redox potential ORP, the sludge concentration MLSS, the sludge return ratio R, the sludge settling ratio SV, the sludge index SVI, the sludge age SRT, the residual sludge discharge cycle and the daily discharge volume. Among them, the main factors affecting energy consumption are the height of the water inlet level and the size of the sludge concentration MLSS, and the main factor affecting the nitrogen and phosphorus removal effect is the pool sludge age SRT.
2. Determination method
(1) The water level of the water inlet pump room should be controlled at a high water level as much as possible while ensuring that the water inlet system does not overflow.
(2) Determine the sand discharge cycle based on the comparison between the treatment capacity of the sand-water separator and the volume of the slurry sedimentation tank.
(3) The ORP of the biochemical pool is mainly determined by the phosphorus release in the anaerobic pool and the phosphorus absorption and nitrification in the aerobic pool. In general, the DO of the anaerobic pool is less than 0.2 mg/L, and the DO of the aerobic pool is about 2.0 mg/L; the ORP of the anaerobic pool is less than -250 mV, and the ORP of the aerobic pool is greater than 40 mV.
(4) By monitoring the anaerobic pool and the aerobic pool, when there is obvious release and absorption of phosphorus, the nitrate in the anaerobic pool is below 0.5 mg/L.
(5) When the ammonia nitrogen in the effluent decreases, the TP value increases. There is a contradiction between denitrification and phosphorus removal. Both indicators should be taken into account during operation, that is, efforts should be made to control and reduce the impact of NO3--N in the return sludge on biological phosphorus removal.
(6) In order to obtain a good phosphorus removal effect, the sludge age should be less than 12 days (lower than the design value), otherwise the phosphorus removal effect will be unstable.
(7) The sludge concentration MLSS is determined according to the sludge load. The designed sludge load is 0.08kgBOD5/kgMLSS·d, so the sludge concentration MLSS should be maintained at about 3.0g/L.
(8) If BOD5 is low, phosphorus removal should be the main focus, and the residual sludge discharge should be adjusted to adjust the sludge age so that the sludge age is between 5 and 12 days.
(9) The sludge settling ratio SV can directly reflect the condition of the activated sludge. The aerobic sludge is generally controlled at 15%~30%, and the return sludge is generally controlled at 20%~40%.
(10) The residual sludge discharge cycle, daily discharge volume, and mud surface height are determined based on the sludge age SRT.
(11) According to the size of the influent, adjust the operating conditions of the structure (single tank or double tank) to ensure the best phosphorus removal effect.