definition
it refers to the operation process of sewage treatment system during off-season production period (usually october to march of next year, winter or holidays etc.). off-season sewage operation has the characteristics of large fluctuation of water quality and quantity, low temperature of raw water, which brings certain difficulties to sewage operation control and normal operation.
purpose
according to the characteristics of sewage in some industries, corresponding preventive measures are taken to ensure the stable operation of sewage in off-season and discharge up to the standard.
3. off-season operation control
this is the first performance of off-season production. the plant did not stop production, but when the output was high or low, the water uniformity was poor. sometimes only packing line drainage, sometimes only brewing drainage, sometimes drainage at the same time. water quantity and quality change from high to low. the system impact trap. how to control the fluctuation of influent quality and quantity without impacting the biological treatment process and ensure the stable discharge rate is the key point.
1. key control points for off-season operation of anaerobic systems:
reactor requirement: the fluctuation range of water quantity per reactor in normal operation is not more than 20% of that in the last one. the influence of water quantity on anaerobic treatment system usually occurs within 3-4 days after shutdown and returns to normal soon.
response measures: temporary storage of incoming water in workshop of sewage station, pre-acidification in catchment tank and regulating tank can remove part of cod. at the same time, according to the production plan, the discharge of wastewater is estimated and the water inflow plan is formulated. intermittent water intake, but the inflow must be guaranteed to be constant.
1.1 influent cod load control:
reactor requirements: cod fluctuates greatly, but the normal operation of the reactor has a constant sludge load requirement according to the design requirements. the influent cod concentration should be as constant as possible.
responding measures: make full use of regulating pool or accident pool to dilute high cod wastewater. give full play to the homogeneity of the regulating pool. meanwhile, the influent time is reduced, the influent time interval is increased, and the ph is increased appropriately. if necessary, open the circulating pump to dilute the water intake.
1.2 intake temperature control:
reactor requirement: the optimum temperature for medium temperature anaerobic reactor is 30 ~ 35 c. in the above range, the microwave fluctuation at 1 ~ 3 c has no obvious effect on anaerobic reaction. however, the sudden change of temperature will just decrease the sludge activity and cause acid accumulation.
response measures: anaerobic system water temperature can be increased by steam heating in regulating pool in factories with lower inlet water temperature and lower ambient temperature. ensure that the temperature of anaerobic influent is at least above 20 c.
1.3 influent ph control:
out-of-season status: due to low production and long shutdown time, washing (acid or alkali washing) should be carried out before each production. if there is no other sewage mixing during washing, the influent ph value of sewage station will rise or fall suddenly.
reactor requirements: acidogenic bacteria and methanogenic bacteria live in an acid-base buffer system in a normally operating reactor, so the ph of complete anaerobic reaction should be strictly controlled, that is, the optimum ph range of methanogenic bacteria is 6.8-7.2.
response measures: the influent ph of anaerobic pond can be controlled by adjusting the pond and adding acid and alkali. the lower the water volume in off-season, the more the ph value should be controlled to meet the technological requirements. the accuracy of ph control of anaerobic pond can be improved by increasing the detection frequency of ph in the influent of regulating pond and anaerobic pond.
2. key control points for off-season operation of aerobic system
2.1 suitable dissolved oxygen
off-season status: in off-season production, because only the packaging workshop drainage (cod is lower), sometimes only the brewing drainage (cod is higher), the fluctuation of cod in water is larger.
aerobic system requirements: aerobic aeration system also needs to be adjusted for different cod concentration of incoming water. different cod concentration corresponds to different aeration volume. the dissolved oxygen concentration in the normal operating aerobic system should be controlled at 2-4 mg/l.
response measures: timely monitoring of cod concentration in source water and anaerobic mountain water show. when the concentration of cod is high, the aeration rate will be increased, and when the concentration of cod is low, the aeration rate will be reduced.
2.2 sludge settling ratio:
off-season status: off-season production is generally in winter, and the activity of aerobic sludge is not as active as in summer. therefore, a slightly higher sludge settling ratio can be properly controlled. in summer, because of the high temperature, it is easy to cause aerobic sludge bulking, sludge sedimentation ratio can control the lower limit.
aerobic system requirement: sludge sedimentation ratio should be controlled between 20 and 40 in winter and 10 to 30 in summer.
response measures: according to the amount of aerobic activated sludge, the sludge reflux ratio should be adjusted in time. the activated sludge reflux in the aerobic tank should be properly increased and the sludge sedimentation ratio should be controlled between 20 and 40.
3. operation control during shutdown period
this is the second situation of off-season production: when the factory has no production plan, brewing will not be produced for a period of time, the sewage station can only stop operation, how to ensure the activity of sludge after shutdown, how to quickly recover after shutdown and start-up, and how to ensure discharge up to standard is the key point of control during shutdown.
3.1 key points of operation control for short term outage (3-5 days)
3.1.1 understand the situation of short-term shutdown. before shutdown, the catchment pool and regulating pool should be filled in advance. ph must be controlled between 6 and 8.5.
3.1.2 before shutdown, the cod of the wastewater from the regulating pond was increased to ensure that anaerobic bacteria could obtain certain nutrition under the condition of low flow of influent during shutdown. or, during the shutdown period, waste yeast dilution (supernatant after precipitation of waste yeast) and high cod waste liquor such as saccharified scrubbing water or sub-liquor are discharged to sweat water treatment closedly.
3.1.3 intermittent water intake, daily anaerobic tank intermittent small flow water intake. processing according to normal procedure.
3.1.4 aerobic tank intermittent aeration, at least 2 hours a day after each treatment cycle stops feeding water or adding drugs, the first treatment cycle can stop aeration once, each time does not exceed 2 hours.
3.2 operational control points of 5-15 days outage
3.2.1 anaerobic tank in front
