What are the routine monitoring items of sludge anaerobic digesters?

The items that should be regularly monitored and recorded in each shift of the sludge anaerobic system are: (1) sludge intake, sludge discharge, supernatant discharge, hot water or steam consumption; (2) VFA and ALK of sludge feeding, sludge discharge, digestive juice and supernatant; (3) The pH value of the sludge, digestion and supernatant; (4) The temperature of the digestive juice, and it is necessary to detect and observe the temperature difference between each point at multiple points; (5) Biogas production. In addition to VFA and ALK, the rest of the projects can be monitored at any time with ** instruments and displayed in the control room.

The items that should be tested daily in the sludge anaerobic digestion system are: (1) total suspended solids SS, organic components, ammonia nitrogen and total nitrogen in sludge inlet, sludge discharge, digestion solution and supernatant; (2) Burn weight reduction and ash content of sludge feeding, sludge discharge and digestion solution, that is, measuring the change of organic matter content in sludge; (3) BOD5, CODCR and TP in the supernatant; (4) The content of CH4, CO2, H2S and other components in biogas.

The items that should be tested weekly in the sludge anaerobic digestion system are: coliform bacteria and the number of roundworm eggs in the sludge and sludge discharge.

Through the above monitoring data, the indicators that should be calculated regularly are: VFA ALK value, digestion time (or hydraulic retention time),

Hydraulic load and organic matter dosing load, gas production per unit volume of sludge or organic matter per unit weight of sludge input, organic matter decomposition rate (digestibility, i.e., the proportion of organic components put into sludge for gasification and inorganicization).

The initiation of the sludge anaerobic digestion system is the complete anaerobic digestion of sludge, that is, anaerobic activated sludge.

or the culture process of methanobacteria. There are two cultivation methods for anaerobic digestion sludge:

1) Step-by-step cultivation method: that is, the method of gradually putting raw sludge into the anaerobic digester, so that the raw sludge is gradually transformed into anaerobic digested sludge by itself. This method makes the activated sludge undergo a transition process from aerobic to anaerobic, and the growth rate of anaerobic microorganisms is much lower than that of aerobic microorganisms, so the gradual cultivation process takes a long time, generally taking about 6 months to 10 months to complete.

2) Inoculation culture method: that is, the method of injecting 10% and 30% of the total volume of anaerobic inoculation sludge into the sludge anaerobic digester. Inoculated sludge is generally taken from the sludge anaerobic digester of a running municipal sewage treatment plant, and when the liquid digested sludge is not easy to transport, the dry sludge that has undergone mechanical dewatering can be used.

In the absence of anaerobic digestion sludge, the decaying organic sediment can be taken from the dusty pit pond, and the human manure, pig manure, cow manure, distiller's grains or primary sedimentation tank sludge can be used as the strain. The sludge is first dissolved with water, then filtered with a 2mm 2mm filter to remove large impurities, and then static precipitation is carried out to remove part of the supernatant, and the sludge with a solid concentration of 3% and 5% is thrown into the digester as inoculated sludge.

In addition to collecting biogas, the normal operation of the sludge anaerobic digester consists of five main operation links: sludge feeding, sludge discharge, supernatant discharge, heating and stirring.

It is impossible to carry out the five operations of sludge feeding, sludge discharge, supernatant discharge, heating and stirring at the same time, and the different operation sequences will have a certain impact on the digestion effect. How to ensure the best operation effect and determine the reasonable operation sequence needs to learn from practical experiments. Generally, the single-stage sludge digester with overflow sludge discharge and internal steam heating is adopted, and its reasonable operation sequence is sludge inlet, sludge discharge, supernatant discharge, heating and stirring.

When non-overflow sludge discharge and heat exchanger heating outside the pool are used, the reasonable operation sequence is to discharge the supernatant, discharge the sludge, feed the sludge, heat and stir. In addition, the shorter the cycle time of the five operation links, the closer to continuous operation, the better the digestion effect. When manual operation is adopted, the operation cycle is generally 8h, and when the operation can be fully controlled, the operation cycle can be 2 4h.

Anaerobic digestion can be divided into artificial digestion and natural digestion. According to the operation mode, it can be divided into first-level digestion and second-level digestion.

1 Level 1 digestion.

Primary digestion refers to the completion of the whole process of digestion in a digestion device, and there is generally no stirring equipment in this digester, so the sludge in the tank has a stratification phenomenon, only a part of the pool volume plays a role in the decomposition of organic matter, and the bottom volume of the tank is mainly used to store and thicken cooked sludge. Because the microorganisms cannot fully contact with the organic compounds, the digestion rate is very low, and the digestion time is very long, generally 30 to 60 days. Therefore, the primary digestion process is only suitable for small units and is rarely used in recent years.

2 Secondary digestion.

Secondary digestion refers to the division of the digester into two, the sludge is first digested in the first digester (equipped with a heating and stirring device, and a gas collection hood to collect biogas), and after 7 12 days of vigorous digestion reaction, the discharged sludge is sent to the second stage of the pruning stove or chemical tank.

When using two-stage digestion, the ratio of residence time between the primary digester and the second-stage digester can be used: 1 or 3:2, where 2:

1 is the most. The liquid level height of the primary digester must be able to meet the needs of the sludge flowing to the secondary digester, when the groundwater level is high, the anti-floating of the tank body must be considered, and it is best to choose when the groundwater level is low when the digester is cleaned.

The sludge oxygen digester generally uses a reinforced concrete structure with good water tightness, air tightness and corrosion resistance, with a diameter of 6 35m, the ratio of total height to diameter, and the ratio of inner diameter to cylindrical height is 2:1. The slope of the bottom of the tank is 8%, the height of the top of the tank from the mud surface is greater than that, the diameter of the top gas collection hood is generally 2m, the height is 1 2m, and the diameter and height of the gas collection hood of the large digester are better than 4m and 2m respectively.

The sludge anaerobic digester is generally equipped with a sludge inlet pipe, a sludge outlet pipe, a supernatant discharge pipe, an overflow pipe, a circulating stirring pipe, a biogas outlet pipe, an emptying pipe, a sampling pipe, a manhole, a pressure measuring pipe, a temperature measuring pipe, etc. Generally, the mud inlet pipe is arranged above the mud level in the pool, and its position, quantity and form should be conducive to mixing evenly and crushing the scum. The minimum diameter of the sludge pipeline is 150mm, and the pipe should be corrosion-resistant or anti-corrosion, and equipped with pipeline cleaning equipment.

The supernatant discharge tube can be set at different heights 3 4 pcs, with a minimum diameter of 75 mm, and there are measures to isolate it from the atmosphere; The overflow pipe should be one level larger than the mud inlet pipe, and the diameter should not be less than 200mm, and the overflow height should be able to ensure that the pool is in a positive pressure state; The drain pipe can share the same pipe as the sludge pipe; The minimum diameter of the sampling tube is 100mm, at least one in the pool and one at the edge of the pool, and extends below the mud level; There should be two manholes, and the location should be reasonable.

The walls and roof of the pool must be insulated.

1) Management of microorganisms.

The anaerobic digestion process is carried out under closed anaerobic conditions, and microorganisms cannot survive under such conditions as various organisms that are indicators in aerobic treatment, and rely on microscopic examination to judge the activity of sludge. Compared with the activated sludge aerobic treatment system, the anaerobic digestion system of sludge and hall is more sensitive to the changes of process conditions and environmental factors per mu. In order to grasp the normal operation of the digester, the daily instantaneous monitoring and laboratory indicators required above should be monitored and tested in a timely manner, such as temperature, pH, biogas yield, mud level, pressure, moisture content, components in the biogas, etc.

Make quick adjustments as needed to avoid major losses.

2) For the daily operation status, treatment measures, and equipment operation status, it is required to make written records, provide operation data for the next shift, and make reports to the management at the next level, and provide process adjustment data.

3) Frequently inspect and inspect sludge pipelines, biogas pipelines and various valves to prevent them from clogging, leaking or failing. Wash the movable cleaning port that may be blocked on the pipeline on a daily basis with high-pressure water. In addition to lubricating grease on time, the normally closed gate and normally open gate should be regularly activated to test whether it can work normally.

If there is a serious problem, it will also need to be discontinued or replaced.

4) Regularly inspect the pressure, safety valve, instrument, alarm device, and send it to the technical supervision department of the city's special anti-hidden door, and obtain the national authority to approve it before it can be installed and used.

5) Regularly inspect and maintain the mixing system. The main pipe of biogas mixing is often blocked by sludge and other dirt, so the rest of the main pipe can be shut down and the blocked pipeline can be flushed with atmospheric volume. For the mechanical stirring paddle to be wound by cotton yarn and other long strips of debris, the failure can be reversed, and the mechanical agitator can be reversed to get rid of the winding debris.

In addition, the airtightness of the junction between the mixing shaft and the floor slab should be checked regularly.