CN108905965A - The method that sludge bioleaching-pyrolysis Combined Treatment prepares heavy metal absorbent - Google Patents

Abstract

The invention discloses a method for preparing a heavy metal adsorbent through sludge bioleaching-pyrolysis combined treatment. (1) Using the concentrated sludge as the bacterial source, FeSO ₄ 7H ₂ O was added as the energy substrate, cultivated until the pH was 2.0-3.0, and then the bacterial liquid was added to the concentrated sludge for 3-5 times as the inoculum. As a bioleach inoculum; (2) Adjust the concentrated sludge to a solid content of 2%~6%, add the above inoculum, add FeSO ₄ 7H ₂ O, treat for 3~7 days, separate the solid and liquid and dry to If the moisture content is below 10%, it is leaching and drying sludge; (3) Crush the obtained sludge to 0.3 mm, add the crushed organic waste, raise the temperature to 300~700 ^o C, and pyrolyze at a constant temperature for 0.5~3 hours . The invention has low cost and wide material sources, and the obtained composite sludge-based biochar has low heavy metal residue, high iodine adsorption value and high heavy metal ion adsorption capacity.

Description

Method for preparation of heavy metal adsorbent by sludge bioleaching-pyrolysis combined treatment

technical field

The invention relates to the technical field of resource utilization of solid waste, in particular to a preparation method of a heavy metal adsorbent obtained by using urban sludge as a main raw material and utilizing a bioleaching-pyrolysis combined treatment technology.

Background technique

With the rapid development of my country's social economy, the amount of excess sludge produced in the process of urban sewage treatment has increased dramatically year by year. According to the National Bureau of Statistics, by the end of 2016, more than 3,500 sewage treatment plants had been built in cities and counties across the country, with a daily sewage treatment capacity of 150 million cubic meters. According to the estimation of 5 tons of dewatered sludge (water content 80%) for every 10,000 tons of sewage treated, about 30 million tons of sludge will be generated in 2016. According to the requirements of the national "Water Ten Measures", the amount of urban sewage in my country will further increase. It is estimated that by the end of 2020, the amount of dewatered sludge in my country will increase to 50-60 million tons. At present, a large amount of sludge is discarded without harmless treatment, causing huge environmental risks to the surrounding soil and water environment, and it is urgent to carry out harmless and resourceful treatment and disposal.

The current mainstream sludge treatment and disposal technology routes mainly include: deep sludge dehydration + drying + sanitary landfill, aerobic fermentation + land use, anaerobic digestion + land use, dry incineration + ash landfill (or building material utilization )Wait. Since a certain proportion of industrial wastewater is often mixed into urban sewage in our country, the concentration of heavy metals in some sewage plant sludge is relatively high, and there are potential environmental risks whether it is land utilization, building material utilization or landfill. Bioleaching uses sulfide or ferrous salt as the energy substrate, and utilizes the acidic environment produced by acidophilus thiobacillus in the process of oxidizing the substrate in the above process, so that the heavy metals adsorbed or precipitated on the surface of the sludge bacteria micelles are dissolved, and the pollution is eliminated. Environmental risks of heavy metals in sludge subsequent disposal. In addition, during the above treatment process, the dewatering performance of sludge has been significantly improved, therefore, bioleaching pretreatment is becoming one of the important process options in the process of sludge treatment and disposal.

Pyrolysis is one of the common treatment methods for organic solid waste. Under certain temperature conditions, organic solid waste such as animal manure, wood, straw, activated sludge, etc. are placed in an anoxic or anaerobic environment for high-temperature pyrolysis treatment, and biochar, pyrolysis oil and pyrolysis gas can be obtained Wait. Among them, biochar obtained by pyrolysis has the advantages of low preparation cost and large adsorption capacity, and can be widely used for the removal of heavy metal ions in sewage and polluted soil. Municipal sludge can also be dried to prepare biochar directly, but the resulting product has the disadvantages of high heavy metal residues, low specific surface area and high ash content. Therefore, it is necessary to pretreat municipal sludge to reduce its environmental risk and improve the pore structure of biochar, thus making it an environmentally friendly adsorption material.

For municipal sludge, the main pretreatment method currently used is to add other substances to degrade heavy metals in sludge through dilution or immobilization. For example, in the report with patent number 201310445872.4, organic and inorganic antidotes were used to reduce the activity of heavy metals in sludge charcoal, and in the report with patent application number 201610363037.X, palygorskite was used as an additive to reduce the activity of heavy metals in the prepared biochar. In contrast, the removal of heavy metals from sludge directly through bioleaching pretreatment can completely eliminate the hidden dangers of heavy metals in sludge-based biochar. At present, there is no patent report on the preparation of biochar by bioleaching-pyrolysis. In other documents, there are reports similar to the process of the present invention, such as bioleaching modification of sludge by pure bacteria and further preparation of biochar. However, there are significant differences between the present invention and its specific implementation process, which are specifically manifested in: (1) the present invention uses the mixed flora obtained from domestication to carry out bioleaching treatment, which can improve the scope of technical application and reduce the cultivation cost of strains; (2) The present invention uses agricultural waste as an auxiliary material to increase the specific surface area and heavy metal adsorption capacity of the prepared sludge biochar.

Contents of the invention

The purpose of the present invention is to provide a method for preparing composite sludge-based biochar by adopting mixed bacteria as leaching inoculum and organic waste as auxiliary material, bioleaching-pyrolysis combined treatment of urban sludge.

The specific steps are:

(1) Add 4-10g of energy substrate FeSO ₄ 7H ₂ O to 1000mL of gravity-concentrated municipal fresh sludge, and shake and cultivate at 180r/min at a constant temperature of 25-28°C until the pH value of the sludge drops to the set value. The fixed value is 2.0-3.0, and the sludge bacterial liquid is obtained.

(2) Take 50-200mL of the sludge bacterial liquid obtained in step (1) and add it to 1000mL of fresh sludge, add 4-10g of FeSO ₄ 7H ₂ O, and vibrate at 180r/min at a constant temperature of 25-28°C. Until the pH value of the sludge drops to the set value of 2.0 to 3.0, repeat the above steps 3 to 5 times to inoculate the sludge bacterial solution.

(3) Adjust the water content of municipal fresh sludge after gravity concentration to 2% to 6%.

(4) Add 50-300mL of inoculated sludge bacterial solution obtained in step (2) to 1000mL of sludge obtained in step (3), then add 4-10g of energy substrate FeSO ₄ 7H ₂ O, and treat at 25-28°C After 3 to 7 days, centrifuge, discard the supernatant, and dry in a freeze dryer until the moisture content of the sludge is lower than 10%, which is the leached dried sludge.

(5) The leached and dried sludge obtained in step (4) is crushed until the particle size is less than 0.3mm, and 100-500mL of pulverized organic waste with a particle size of less than 0.5mm is added and mixed into the porcelain boat. Put the porcelain boat into the sampling tube of the vacuum furnace with _N2 flow rate of 300mL/min for pyrolysis. After 0.5 to 3 hours, the solid product obtained after pyrolysis is the composite sludge-based biochar.

The organic waste is one of rice straw, sawdust and wheat straw.

The prepared composite sludge-based biochar can be used as a heavy metal adsorbent to treat heavy metal-containing sewage and heavy metal-contaminated soil.

The present invention has remarkable beneficial effect:

1. Use leached sludge and agricultural waste as the principle to prepare biochar, solve the two problems of agricultural waste and sludge disposal at the same time, and explore new ways for the resource utilization of municipal sludge.

2. The acidification effect of the mixed bacteria bioleaching treatment sludge is better, and the sludge leaching system can be reduced to pH below 3.5 within 3 to 5 days.

3. The bioleaching treatment effectively removes the heavy metals remaining in the sludge. The removal rate of Pb, Zn, Cu, Ni, Cd and Cr reaches 61%-90%. The pollutant control standard in sludge GB4284-2018 is below the limit value of A-grade sludge products.

4. The bioleaching treatment and the addition of auxiliary materials can effectively improve the adsorption performance of sludge-based biochar. Its iodine adsorption value is 116%-239% higher than that of biochar without leaching treatment, and 15%-80% higher than that of biochar without auxiliary materials.

5. Composite sludge-based biochar has a high adsorption capacity for heavy metal ions. The adsorption capacity for Pb ²⁺ and Cd ²⁺ at 25°C is 30.68 and 19.82 mg/g, and it is suitable for heavy metal-containing sewage treatment and heavy metal Potential for contaminated soil remediation.

Description of drawings

Fig. 1 is a technical roadmap of the present invention.

Fig. 2 is a time-state change diagram of pH and ORP in the sludge bioleaching process of the embodiment of the present invention; wherein: a-pH; b-ORP.

Fig. 3 is the temporal change figure of 6 kinds of heavy metal removal rates in the sludge in the embodiment bioleaching process of the present invention, wherein: a-Cd; b-Cr; c-Cu; d-Ni; e-Pb; f- Zn.

Fig. 4 is a scanning electron microscope photograph of the sludge-based biochar of the embodiment of the present invention: a, sludge-based biochar without leaching treatment; b, sludge-based biochar obtained from leaching treatment.

Fig. 5 is the iodine adsorption value and the productive rate of the composite sludge-based biochar of the present invention.

Fig. 6 is the adsorption isotherm of sludge-based biochar to heavy metal ions after bioleaching according to the embodiment of the present invention, wherein: a-Pb ²⁺ ; b-Cd ²⁺ .

Detailed ways

Example:

(1) Take fresh sludge from the sludge concentration tank of a sewage treatment plant in Guangxi, add 500mL of fresh sludge to a 1000mL serum bottle, add 5g of FeSO ₄ 7H ₂ O as a substrate, and add 5g of FeSO 4 7H 2 O as a substrate. Shake the culture until the pH value of the sludge drops and stabilizes to 2.0 to obtain the sludge bacterial liquid.

(2) Take 50mL of the sludge bacterial solution obtained in step (1) and add it to 500mL of fresh sludge, add 5g of FeSO ₄ ·7H ₂ O, and shake at 25°C and 180r/min until the pH value is stable to 2.0. Repeat the above steps 5 times to inoculate the sludge bacterial solution; with the increase of the number of inoculations, the time for each culture of the bacterial solution to the stable growth period is gradually shortened to 5 days.

(3) Take the fresh sludge from the sludge thickening tank of a certain sewage treatment plant in Guangxi, adjust the sludge solid content to 2.2%; put 300mL of the above fresh sludge into a 1000mL Erlenmeyer flask, add 30mL of the obtained product from step (2) Inoculate the sludge bacteria solution, add 4, 6, 8, 10g of FeSO ₄ 7H ₂ O respectively, take the treatment without FeSO ₄ 7H ₂ O as the control, do 3 repetitions for each group of experiments, and take the average value as an experimental result. The Erlenmeyer flask used was sealed with two layers of gauze, placed in a 160r/min, 26°C constant temperature shaker for shaking culture, and the pH (written test pH meter, model CT-6123) and oxidation-reduction potential ORP ( The written test ORP meter, model SX630) changes until the pH value stabilizes to 2.0, and the ORP value stabilizes at around 500mV as the reaction is over. During the cultivation period, the weighing method was used to replenish the water lost due to evaporation every day.

(4) Take the sludge after the above-mentioned bioleaching treatment by adding 6g of FeSO ₄ 7H ₂ O, dry and dehydrate, crush and sieve, add the crushed and sieved rice straw as an auxiliary material, and carry out pyrolysis treatment, Put the bioleached sludge in a centrifuge tube, centrifuge at 4000r/min for 10 minutes, discard the supernatant, put the remaining sludge in a freeze dryer to dry until the moisture content is lower than 10%, take it out, grind and dry Pass through a 100-mesh sieve; take the rice straw and dry it until the moisture content is below 10%, crush it and pass through a 100-mesh sieve. Take the sieved sludge and rice straw, wherein the volume percentage of rice straw is 10%, 20%, 30%, 40%, 50%, take 6.0g of fully mixed materials and put them into a porcelain boat, put the porcelain boat into into the injection tube of a GWL-1200°C tube vacuum furnace for pyrolysis. Before heating, a N ₂ protective atmosphere (N ₂ flow rate 300mL/min) was passed into a closed tube vacuum furnace, and the temperature was raised to 500°C at a heating rate of 15°C/min, and then calcined at a constant temperature for 2 hours. After the product is cooled, it is ground, mixed with 1mol/L HCl and shaken for 10 minutes, and then the adsorbent is washed repeatedly with distilled water until the pH of the washed aqueous solution is close to neutral. The product obtained is the composite sludge-based biochar product. The treatment without straw was used as the control.

(5) Characterization and heavy metal adsorption of composite sludge-based biochar: the experiment was carried out under the condition that rice straw was added with a volume percentage of 20%, and the surface morphology of the scanning electron microscope was used respectively; the adsorption capacity of biochar to organic matter was characterized by the iodine adsorption value , the adsorption capacity of biochar was used to characterize the adsorption capacity of biochar to heavy metal ions. The determination of the iodine adsorption value of activated carbon adopts the "Determination of Iodine Adsorption Value of Wood Activated Carbon Test Method (GB/T12496.8-1999)" stipulated in the national standard. Weigh 0.1g of sludge-based biochar after bioleaching and put it in a 100mL plastic centrifuge tube. At 25°C, 35°C, and 45°C, add 50mL of 50, 60, 80, 100, 120, 150, 200, 300, 400, 500mg/L containing Pb ²⁺ , Cd ^{2 +} solution, adjust the pH of the solution to 5, and carry out the adsorption test in a 200r/min water bath constant temperature shaker , set the reaction time to 24 hours. After the adsorption reaction is completed, place the centrifuge tube in a centrifuge with a speed of 4000r/min and centrifuge at high speed for 5 minutes, draw the supernatant with a syringe and pass it through a 0.45μm filter membrane, and measure the remaining Pb ²⁺ and Cd by ICP-AES ²⁺ content, the adsorption capacity was calculated and the adsorption capacity was obtained by fitting the Langmuir equation, see Table 1.

Table 1: Adsorption capacity of composite sludge-based biochar for heavy metal ions Pb ²⁺ and Cd ²⁺

Claims (2)

1. a kind of preparation method of composite sludge base charcoal, it is characterised in that the specific steps are：

（1）4 ~ 10 g energy substrate FeSO47H2O are added into the municipal fresh sludge after 1000mL gravity concentration, 25 ~ 28 ^o180 r/min shaken cultivation under C constant temperature obtains sludge bacterium solution until sludge pH is down to setting value 2.0 ~ 3.0；

(2) 50 ~ 200 mL steps are taken（1）Gained sludge bacterium solution is added in 1000 mL fresh sludges, 4 ~ 10 g's of addition FeSO₄·7H₂O, 25 ~ 28^o180 r/min shaken cultivation under C constant temperature, until sludge pH be down to setting value 2.0 ~ 3.0, it repeats the above steps 3 ~ 5 times, obtains seed sludge bacterium solution；

（3）Municipal fresh sludge moisture content after adjusting gravity concentration is 2% ~ 6%；

（4）In 1000mL step（3）50 ~ 300 mL steps are added in gained sludge（2）Gained seed sludge bacterium solution, add 4 ~ 10 g energy substrate FeSO47H2O, temperature are 25 ~ 28^oC is handled 3 ~ 7 days, is then centrifuged for handling, is discarded supernatant liquid, is put into Dry in freeze drier, until moisture percentage in sewage sludge is lower than 10%, dewatered sludge is soaked in as drip；

（5）By step（4）Gained drip leaching dewatered sludge is crushed to partial size lower than 0.3 mm, 100 ~ 500mL partial size is added and is lower than The organic waste mixing that the pulverization process of 0.5 mm is crossed is put into porcelain boat, and porcelain boat is put into and is passed through N₂Flow is 300 mL/min Vacuum drying oven sample feeding pipe in be pyrolyzed, pyrolysis temperature program be with 10 ~ 20^oThe rate of C/min is warming up to 300 ~ 700^oC, Duration is 0.5 ~ 3 hour, and the solid product that pyrolysis terminates to obtain is composite sludge base charcoal；

The organic waste is one of rice straw, sawdust and wheat straw.

2. the application of the composite sludge base charcoal of preparation method preparation according to claim 1, it is characterised in that described multiple Closing sludge base charcoal can apply to handle as heavy metal absorbent containing heavy metal containing sewage and heavy-metal contaminated soil.