In industrial wastewater treatment, municipal wastewater and industrial sludge treatment, the amount of sludge produced is about 0.3% to 0.5% of the total treatment (97% water content). The composition of the sludge is complex, containing parasitic eggs, heavy metals and pathogenic microorganisms, which must be treated to prevent secondary pollution to the environment.
At present, a large number of unsettled sludge has become a heavy burden for sewage treatment plants. How to treat the sludge with large output and complex composition properly and safely to make it harmless, resource-resourced and reduced, has been widely used. attention.
At present, the commonly used sludge treatment schemes include: concentration, sludge conditioning, anaerobic digestion, dehydration, composting and other treatment technologies. As for aerobic digestion, wet oxidation, disinfection, thermal drying, incineration, low temperature pyrolysis, etc. stage.
Industrial sludge type and characteristics
First, urban sludge
The amount of sludge produced by urban sludge is moderate, generally accounting for about 0.1% of the total volume of domestic sewage treatment, but the total amount is large, the organic matter content is high, and the water content is high, generally reaching 95% to 99%, even after dehydration. Still 60%~80%, there are a lot of pathogens and parasites, which are easy to rot and stink, very unstable.
Second, petrochemical sludge
The composition of petrochemical sludge is complex and contains different kinds of heavy metals. Generally, petroleum sludge contains oil, has high viscosity and high water content, generally up to 96%~99%, and still 70%~85% after mechanical dehydration. The volume and mass are still large, the organic matter content is small, and the calorific value is low.
Third, printing and dyeing sludge
The printing and dyeing mud production is large, the total sludge volume accounts for 0.3%~1.0% of the total volume of the sewage, and the water content is high, generally up to 96%~99%. After mechanical dehydration, there are still 55%~85%, and the volume and quality are still relatively good. Large, printing and dyeing sludge generally has a higher inert content, while organic matter, pathogenic bacteria and other content are less, the calorific value is also lower, and the general heavy metal content is high.
Fourth, paper sludge
Papermaking sludge ash is relatively large, generally can reach 50%~70%, so the calorific value is relatively low and the water content is high, generally reaching 95%~99%. Even after dehydration, the water content is still 60%~80%. And it contains a lot of fiber.
Five, tannery sludge
The tanning industry produces a large amount of mud. Generally, it can produce 40-80 tons of sludge per ton of wastewater per day. The organic matter content is high. Due to the large amount of fur and blood pollution generated during the leather treatment process, the organic matter content is very high and there are many toxic substances. The content of S2- and trivalent chromium is high, and the conversion of trivalent chromium to hexavalent chromium has carcinogenic effects.
Sixth, electroplating sludge
The electroplating sludge contains cyanide and heavy metals such as hexavalent chromium, copper, zinc, cadmium and nickel. The chemical treatment of electroplating wastewater is the main source of sludge. The electroplating sludge has low organic content and low calorific value.
Industrial sludge conventional treatment method
(1) Sludge concentration method: concentrated by gravity, concentrated by centrifugation and concentrated. The gravity concentration method has the advantages of high sludge storage capacity and simple operation, and is one of the most commonly used methods for sludge volume reduction.
(2) Sludge adjustment method: sludge adjustment treatment can reduce the hydrophilicity of sludge and improve the dehydration efficiency. Commonly used adjustment methods include chemical adjustment method and thermal regulation method. The thermal regulation method, the water-freezing-melting method, and the addition of an inert substance are in the experimental research stage.
(3) Anaerobic digestion: Sludge anaerobic digestion is currently the most commonly used sludge stabilization treatment process, with medium temperature digestion (32~C~35~c) and high temperature digestion. With the advancement of technology.
(4) Sludge dewatering method: The water content after sludge dewatering can generally be reduced to 70%~80% to reduce the volume of sludge. Commonly used dehydration methods include natural drying and mechanical dehydration. Currently, the commonly used mechanical dewatering machines include vacuum filters, plate and frame filter presses, belt filter presses and centrifuges.
(5) Composting method: Composting is a comprehensive treatment technology of harmless, volume reduction and stabilization. The mixed microbial community decomposes organic matter in a humid environment, and the high temperature generated during the composting process can effectively kill Dead pathogenic microorganisms and various parasitic eggs are a comprehensive treatment technology that is harmless, volume-reducing and stable.
Research progress in industrial sludge treatment
1. Sludge reduction technology: The sludge reduction mechanism has become a research hotspot. The principle is to make the sludge as far as possible in the sewage treatment system. The main methods of research are:
(1) Study sludge biological volume reduction technology, using thermophilic bacteria or micro-animals to reduce excess sludge.
(2) The excess sludge is treated by a membrane bioreactor.
2. Sludge volume reduction technology: sludge volume reduction is studied from sludge concentration and dewatering. After sludge concentration and dewatering, its volume is greatly reduced, reducing transportation costs and subsequent disposal costs.
In terms of sludge concentration:
(1) Bioflocculation The remaining sludge from the secondary settling tank is mixed with the raw water and returned to the primary sedimentation tank. The flocculation performance of the activated sludge is used to improve the sedimentation effect of the primary sedimentation tank, and at the same time, the activated sludge is concentrated;
(2) Concentrating the sludge by air flotation and bio-floating method, such as using the gas generated by the reverse digestion of the sludge to make the sludge float and concentrate;
(3) Improve the structure of the concentration equipment and increase the concentration efficiency.
In terms of sludge dewatering:
(1) Pretreatment of sludge before chemical pretreatment (chemical conditioning, heat treatment, freezing method, panning method, etc.)
(2) Using biological engineering methods to improve the properties of the sludge, such as using lysing rain to destroy the micelles to improve the dewatering performance of the sludge;
(3) Exploring new agents for improving sludge dewatering performance, such as adding surfactants;
(4) Improve the working efficiency of the traditional sludge dewatering machine and study the new sludge dewatering equipment.
3, the stability of the sludge: the purpose of stability is to degrade the perishable organic matter in the sludge, reduce the amount of liquids and solids, reduce pathogenic bacteria, eliminate odor. The main methods of sludge stabilization include anaerobic digestion, aerobic digestion, wet oxidation, low temperature pyrolysis, and composting.