CN111408604B

CN111408604B - Method for improving saline-alkali soil by biological two-stage harmless treatment of domestic sludge

Info

Publication number: CN111408604B
Application number: CN202010142592.6A
Authority: CN
Inventors: 柏彦超; 张文杰; 汤泽辉; 吕铭; 左文刚; 单玉华
Original assignee: Yangzhou University
Current assignee: Yangzhou University
Priority date: 2020-03-03
Filing date: 2020-03-03
Publication date: 2022-03-25
Anticipated expiration: 2040-03-03
Also published as: CN111408604A

Abstract

The invention discloses a biological two-stage harmless treatment method of domestic sludge, which comprises the steps of firstly digesting the domestic sludge by earthworms in an odorless front stage to obtain a mixture of excess sludge and earthworm cast; inoculating EM bacteria compost, surplus sludge and wormcast mixture, and fermenting to obtain harmless products. The invention also discloses a method for improving the saline-alkali soil by the biological two-stage harmless treatment of the domestic sludge, which effectively solves the problems that the saline-alkali soil is improved by the harmless treatment of the domestic sludge: screening domestic sludge meeting heavy metal limit standards specified in agricultural sludge pollutant control standards (GB4284-2018) to ensure the safety of the heavy metal environment for sludge agriculture; the earthworm and the EM are treated in a two-stage mode, the high-efficiency action time of the earthworm and the EM is staggered, and the advantages of the earthworm and the EM are played; ensures that the domestic sludge harmless products can meet all standards specified in agricultural sludge pollutant control Standard (GB4284-2018), thereby realizing the resource utilization of the domestic sludge harmless products and improving the saline-alkali soil.

Description

Method for improving saline-alkali soil by biological two-stage harmless treatment of domestic sludge

Technical Field

The invention relates to a technology for harmless treatment and resource utilization of domestic sludge, in particular to a method for improving saline-alkali soil by biologically (earthworm and EM) two-stage harmless treatment of domestic sludge.

Background

The urban sewage treatment industry in China develops rapidly until 2018, nearly 7000 urban sewage treatment plants are built in China, and the sewage treatment capacity reaches 1.5 multiplied by 10⁹m³.d^-1The total amount of sewage treated all year round reaches 4.50 multiplied by 10¹¹m³. A large amount of domestic sludge with complex components is generated in the sewage treatment process, the generation amount of wet sludge (calculated by water content of 80%) of sewage treatment plants in the national sewage treatment plant in 2018 is nearly 5000 ten thousand tons, and the sludge yield is estimated to break through 6000 ten thousand tons in 2020.

The domestic sludge has both the attributes of 'resource' and 'pollution', is an important reason for the difficulty in treatment and disposal of the domestic sludge, and is becoming a research hotspot of domestic and foreign scholars. The domestic sludge is a byproduct in the sewage treatment process, the content of organic matters reaches 40-60%, and the domestic sludge also contains a large amount of resource substances such as nitrogen, phosphorus and the like, and also contains polluting substances such as heavy metals, refractory organic matters, persistent organic matters, micro-plastics and the like. With the gradual optimization of the urban sewage pipe network, the inorganic components of the domestic sludge are further reduced, and the organic components are further increased from 40% to 60% -70%. The domestic sewage pipe network and the industrial wastewater pipe network are separated step by step, and the content of pollutants such as heavy metal in the domestic sludge can be reduced step by step. After the domestic sludge is subjected to harmless treatment, the threat of organic matters and harmful viruses which are difficult to degrade can be reduced, the sludge is turned into harm and changed into valuable, and thus the resource utilization of the sludge is realized.

The technical principle of earthworm treatment of organic waste is that the earthworm is used for swallowing organic matters by virtue of the amazing phagocytic capacity (the daily swallowing capacity can be several times of the weight of the earthworm) and then digesting the organic matters through a body cavity (digestive tract), and meanwhile, the earthworm rich in high protein and the earthworm feces with good properties and structures are obtained. A great deal of research is carried out on obtaining sludge earthworm cast by using earthworms to digest domestic sludge. The digestive tract of the earthworm can secrete a plurality of enzymes such as protease, lipase, cellulase, chitinase and amylase, and has stronger decomposition effect on sludge organic matters. After being ingested by the earthworms, a small part of the domestic sludge is directly assimilated and utilized, and the majority of the domestic sludge is discharged in a granular form after being subjected to grinding and extrusion in the earthworms, so that the function similar to extrusion granulation is achieved, and the aim of physical modification is fulfilled. Meanwhile, the earthworms can promote the activity of microorganisms, the decomposition and transformation of organic matters are accelerated by the combined action of the earthworms, and the odor generated in the composting process can be effectively removed or inhibited. The earthworms have the enrichment effect on heavy metals such As As, Cd, Cr, Cu, Hg, Pb, Se, Zn and the like, and are effective measures for reducing the total amount of the heavy metals in the sludge. In addition, the stability of the sludge heavy metal after earthworm digestion can be improved, and the pollution risk of the heavy metal can be further reduced.

The technology for treating organic waste by EM (effective microorganisms) is quite mature, is a practical and advanced application technology, is successfully popularized in more than 90 countries in the world, and is also popularized in more than 10 provinces and urban areas in China, so that higher social and economic benefits are generated. The EM bacteria is a beneficial microbial flora with strong activity, mainly comprises various microorganisms such as photosynthetic bacteria, actinomycetes, saccharomycetes, lactic acid bacteria and the like, and has the functions of rapid propagation, fermentation, deodorization, disinsection, sterilization, drying and the like. EM microbial inoculum is added into organic materials such as domestic sludge for stacking fermentation, beneficial microorganisms are rapidly propagated, organic matters in the organic materials such as the sludge are rapidly decomposed to generate biological heat energy, the stacking temperature can be raised to 60-70 ℃, and harmful organisms such as germs and worm eggs are inhibited or killed; in the process of mineralization and humation, nutrients such as nitrogen, phosphorus, potassium, trace elements and the like are released; absorb and decompose malodorous and harmful substances.

The earthworm and EM bacteria act synergistically to treat organic waste, which is one of the technical approaches for effectively utilizing and treating organic solid waste, but the effect of the earthworm and EM bacteria is greatly different. The earlier stage research of a subject group shows that the mode of earthworm-EM bacteria synergistic treatment of the domestic sludge is to inoculate earthworms and EM bacteria to a sludge stack body at the same time, the stack body temperature is too high due to the effect of the EM bacteria to influence the growth of the earthworms, and meanwhile, the fresh organic matters are quickly decomposed by the EM bacteria to reduce earthworm baits, so that the effects of the earthworms and the EM bacteria cannot be fully exerted, the difficulty is increased for stack body management (such as temperature, EM bacteria inoculation dosage and the like), and meanwhile, the stack body cannot be fully decomposed due to the limitation of the EM bacteria dosage, and the subsequent utilization of fermented products is influenced.

Disclosure of Invention

The purpose of the invention is as follows: the invention provides a method for improving saline-alkali soil by biological two-stage harmless treatment of domestic sludge, aiming at a series of practical problems that the domestic sludge is high in yield, has the attributes of resources and pollution, is difficult to perform harmless treatment and resource utilization and the like.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: the invention provides a biological two-section harmless treatment method for domestic sludge, which comprises the following steps:

1) firstly, earthworms are adopted to digest domestic sludge at an odorless front section to obtain a mixture of excess sludge and earthworm cast;

2) inoculating EM bacteria compost, residual sludge and wormcast mixture, and fully fermenting to obtain harmless products.

Wherein the specific steps of the step 1) are as follows: stacking the domestic sludge into a plurality of long strip stacks with the height of 25-30 cm, the width of 40-50 cm and the length of 3.0-3.5 m, wherein each long strip stack is separated by 20-30 cm; the mixture of the working earthworms and the wormcast is inserted into the long strip stack interval to form an earthworm working bed; the thickness of the wormcast mixture is 3-5 cm, after the wormcast mixture is digested for 6-8 days, earthworms are collected by adopting an artificial light-shielding method, and then the residual sludge and the wormcast mixture are obtained.

Wherein, the specific steps of the step 2) are as follows: stacking the mixture of the excess sludge and the wormcast into a long strip stack with the width of 2.0-2.5 m, the height of 1.2-1.5 m and the length of 50-100 m, inoculating EM microbial inoculum, timely turning the stack when the temperature rises to above 60 ℃, continuously turning the stack for 2-3 times, and completing full fermentation after the temperature of the stack is maintained at room temperature and does not rise any more.

The mixture of the domestic sludge, the working earthworms and the earthworm cast has insufficient mineralization of organic matters and water content of about 60-70 percent, and the properties of the mixture still do not meet the agricultural sludge pollutant control standard (GB 4284-2018).

Wherein the inoculation amount of the EM microbial inoculum in the step 2) is 1.5-2%.

The EM microbial inoculum in the step 2) is obtained by diluting 5-10 kg of EM microbial inoculum stock solution with 100kg of 10% brown sugar water.

Wherein the water content of the harmless product in the step 2) is less than or equal to 60%, the pH is 5.5-8.5, the organic matter content is more than or equal to 20%, the ascarid egg death rate is more than or equal to 95%, and the fecal coliform bacteria value is more than or equal to 0.01, namely the harmless product meets the heavy metal limit standard specified in the agricultural sludge pollutant control standard (GB 4284-2018).

The invention also discloses a method for improving saline-alkali soil by using the biological two-stage harmless treatment of domestic sludge, which comprises the step 1) and the step 2), and further comprises the step of adding the harmless product obtained in the step 2) into saline-alkali soil for treatment.

Wherein the organic matter content of the harmless product is that the water content of the harmless product is less than or equal to 60 percent, the pH value is 5.5-8.5, the death rate of ascarid eggs is more than or equal to 95 percent, the bacterial value of faecal coliform is more than or equal to 0.01, and the organic matter content is 200-500 g kg^-1And other related pollutant control indexes all meet the agricultural sludge pollutant control standard (GB 4284-2018).

The saline-alkali soil is a mild saline-alkali soil with the salt content of less than 4g/kg, the using amount of the mild saline-alkali soil is 1-2.5 tons/mu, and the mild saline-alkali soil is uniformly mixed with 0-20 cm of saline-alkali soil by using a rotary cultivator after being directly applied as a base fertilizer.

Has the advantages that: compared with the prior art, the invention has the following advantages: the invention effectively solves the problems of harmless treatment of domestic sludge and improvement of saline-alkali soil: firstly, screening and digesting domestic sludge through an odorless earthworm front section to obtain a mixture of excess sludge and earthworm cast, so that the mixture meets the domestic sludge of heavy metal limit standard specified in agricultural sludge pollutant control standard (GB4284-2018), and the safety of the heavy metal environment for sludge agriculture is ensured; then, residual sludge and wormcast mixture are further fermented by using EM (effective microorganisms) to obtain harmless products, and the high-efficiency action time of the earthworms and the effective microorganisms can be staggered by virtue of two-section treatment of the earthworms and the EM, so that the advantages of the earthworms and the EM are fully exerted respectively; ensures that the domestic sludge harmless products can meet all standards specified in agricultural sludge pollutant control Standard (GB4284-2018), thereby further realizing the resource utilization of the domestic sludge harmless products to improve the saline-alkali soil.

Drawings

FIG. 1: a flow chart for biological two-stage harmless treatment of domestic sludge to improve saline-alkali soil is shown;

FIG. 2: the influence of the harmless treatment product of the domestic sludge on saline-alkali soil EC (A) and pH (B);

FIG. 3: the influence of the harmless treatment product of the domestic sludge on the soil organic matters of the saline-alkali soil is applied;

FIG. 4: the influence of the harmless treatment product of the domestic sludge on the contents of N (A) and P (B) in the saline-alkali soil;

FIG. 5: the influence of the application of the harmless treatment product of the domestic sludge on the biomass (A) and the yield (B) of the barley;

FIG. 6: the influence of the application of the harmless domestic sludge product on the plant height (A) and biomass (B) of the corn plant;

FIG. 7: the application of the harmless domestic sludge product has the influence on the total amount of Cd, Cu, Pb and Zn heavy metals in the soil of the beach saline-alkali land;

FIG. 8: the application of the harmless domestic sludge product has influence on the forms of Cd, Cu, Pb and Zn heavy metals in the soil of the beach saline-alkali land;

FIG. 9: the application of harmless products of domestic sludge has the influence on the content of Cd, Cu, Pb and Zn at the root, stem and leaf parts of the corn plants.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

The implementation uses the domestic sludge and the working earthworms, the earthworms are taken from the ecological agriculture development limited company of spring light in Thai, and the earthworm cast mixture is the mixture of the working earthworms after the domestic sludge is digested. The EM microbial inoculum is obtained by diluting 5-10 kg of EM (the EM stock solution is purchased from Henan Yita biotechnology limited) with 100kg of 10% brown sugar water.

Example 1

The method for obtaining the harmless domestic sludge product comprises the following steps: a biological two-stage harmless treatment method for domestic sludge is adopted, namely firstly, earthworms are adopted to digest domestic sludge at an odorless front stage to obtain a mixture of excess sludge and wormcast, and then EM (effective microorganisms) compost is inoculated to sufficiently ferment the mixture of excess sludge and wormcast to obtain a harmless product (F3).

Firstly, piling up domestic sludge into 50 long-strip stacks with the height of 25-30 cm, the width of 40-50 cm and the length of 3.0-3.5 m, wherein each stack is separated by 20-30 cm; the mixture of the working earthworms and the wormcast is inserted into the strip stacks according to the space pore volume; the whole earthworm working bed is covered with a working earthworm and earthworm cast mixture with the thickness of 3-5 cm, and after 6-8 days of digestion, residual sludge and the earthworm cast mixture are obtained after earthworms are collected by adopting an artificial light-shielding method.

And then, stacking the mixture of the excess sludge and the wormcast into 1 strip stack with the width of 2.0-2.5 m, the height of 1.2-1.5 m and the length of 50-100 m, inoculating an EM microbial inoculum according to the using amount of 1.5-2%, timely turning the stack when the temperature is raised to be above 60 ℃, continuously turning the stack for 2-3 times, and after 16 days, not raising the temperature of the stack any more, thus obtaining a harmless product (F3) after complete fermentation.

Comparative example 1

The method for obtaining the harmless domestic sludge product comprises the following steps: and (3) digesting the domestic sludge only by adopting the odorless earthworm front section to obtain the rest sludge and the earthworm cast mixture (F1). Piling up the domestic sludge into 50 long-strip stacks with the height of 25-30 cm, the width of 40-50 cm and the length of 3.0-3.5 m, wherein each stack is separated by 20-30 cm; the mixture of the working earthworms and the wormcast is inserted into the strip pile interval; covering the whole earthworm work bed with 3-5 cm-thick earthworm cast, and collecting earthworms by adopting an artificial light-shielding method after digesting for 6-8 days to obtain residual sludge and an earthworm cast mixture (F1).

Comparative example 2

The method for obtaining the harmless domestic sludge product comprises the following steps: and (3) fermenting the domestic sludge by only adopting EM (effective microorganisms) compost to obtain a harmless product (F2). Stacking the domestic sludge into a long strip stack with the width of 2.0-2.5 m, the height of 1.2-1.5 m and the length of 50-100 m, inoculating an EM microbial inoculum, timely turning the stack when the temperature rises to above 60 ℃, continuously turning the stack for 2-3 times, and after 27 days, not rising the temperature of the stack any more, thus obtaining a harmless product (F2) after fermentation.

Experimental example 1

The domestic sludge harmless products F3, F1 and F2 obtained in example 1, comparative example 1 and comparative example 2 were measured for their relevant indexes according to the indexes specified in the agricultural sludge contamination control Standard (GB 4284-2018). The water content is measured by a gravimetric method, the pH is measured by a glass electrode method, the organic matter content is measured by a potassium dichromate volumetric method, the ascarid egg death rate is measured by a microscope method, and the faecal coliform bacteria value is measured by a fermentation method.

TABLE 1 measurement of the properties of the harmless products of test sludge

Researches show that the harmless products of the domestic sludge F3 all meet the indexes specified in agricultural sludge pollutant control Standard (GB 4284-2018). However, the water content and the ascarid egg death rate of the harmless products F1 and F2 of the domestic sludge fail to meet the corresponding standards specified in the agricultural sludge pollutant control Standard (GB 4284-2018).

Experimental example 2

The harmless products of domestic sludge F3, F1 and F2 obtained in example 1, comparative example 1 and comparative example 2 were used for the study of improving saline-alkali soil and were carried out in the test field of the Berth reclamation area of the tea town of Nantong city, Jiangsu province in 2016. The test area was in a subtropical humid monsoon climate with a total rainfall of 100.9mm and an average temperature of 12.5 ℃ during the test.

The test adopts field random block test, and the area of each cell is 3.6m multiplied by 3.6 m. The test is carried out according to the unit area of 2.0 tons^-1The sludge detoxification products (F3, F1, F2) were applied in (dry basis) doses, and each treatment was repeated 3 times. Applying harmless domestic sludge products (F3, F1 and F2) to each test cell in 2016 and 6 months, uniformly mixing the materials with 0-20 cm plough layer soil by using a rotary cultivator, collecting a soil sample after 30 days, and determining the roundworm egg detection condition.

Researches show that live roundworm eggs are detected in the mudflat soil treated by the domestic sludge harmless products F1 and F2, so that the live roundworm eggs do not meet the corresponding standard specified in agricultural sludge pollutant control standard (GB4284-2018), and cannot be used for agricultural soil improvement, while the live roundworm eggs are not detected in the mudflat soil treated by F3.

Experimental example 3

The harmless domestic sludge product (F3) obtained in example 1 was used for the study of improving saline-alkali soil in a test field of the ben tea town reclamation area in Nantong city of Jiangsu province in 2016-2018. The test area was in a subtropical humid monsoon climate with a total rainfall of 100.9mm and an average temperature of 12.5 ℃ during the test.

The saline-alkali soil in the test area belongs to sandy loam and coastal saline soil types, and the specific physical and chemical properties of the saline-alkali soil are shown in the following table. The content of organic matters in the harmless products of the test domestic sludge is 246.0 kg^-1The total nitrogen and the total content are respectively 32.8g kg^-1、5.17g kg^-1。

TABLE 2 basic physicochemical Properties of the saline-alkali soil to be tested

The test adopts field random block test, and the area of each cell is 3.6m multiplied by 3.6 m. The test is carried out by setting 5 treatments according to different application rates of harmless products of the dry-based domestic sludge to 0, 1.0, 1.5, 2.0 and 2.5 tons per mu^-1Each treatment was repeated 3 times. Applying harmless domestic sludge products (F3) to each test cell in 2016, uniformly mixing the materials with 0-20 cm plough layer soil by using a rotary cultivator, sowing barley in 2017 in 10 and 25 months, not applying fertilizers, periodically weeding and spraying pesticides, harvesting the barley in 2018 in 5 and 25 months, and collecting soil and plant samples.

(1) Influence of the application of the domestic sludge harmless treatment product (F3) on EC and pH of the soil in the beach saline-alkali soil

The application of the domestic sludge harmless treatment product (F3) reduces the EC and pH of saline-alkali soil (figure 2). Control soil EC and pH without sludge product application were 265.3 μ s cm^-19.43. Applying harmless domestic sludge treatment product (F3) for each treatment (1.0, 1.5, 2.0, 2.5 ton/mu)^-1) The EC of the intertidal soil is respectively reduced by 4.8 percent, 8.2 percent, 17.1 percent and 16.5 percent compared with the contrast, and the difference between the EC and the contrast reaches a significant level. Applying harmless treatment product of domestic sludge (F3) for treatment (2.0 and 2.5 tons per mu)^-1) The pH of the mud flat soil is obviously lower than that of the control, and is respectively reduced by 0.31 and 0.42 pH units compared with that of the control.

(2) The influence of the application of the harmless treatment product of the domestic sludge (F3) on the contents of organic matters, alkaline hydrolysis nitrogen and quick-acting phosphorus in the soil of the beach saline-alkali soil

The application of the domestic sludge harmless treatment product (F3) increases the soil organic matter content (figure 3) and the alkaline hydrolysis nitrogen and quick-acting phosphorus content (figure 4). The contents of organic matter, alkaline hydrolysis nitrogen and available phosphorus in the control soil without sludge product are respectively 9.98g kg^-1、46.91mg kg^-1、30.96mg kg^-1. The organic matters of the mud flat soil treated by the harmless treatment product of the domestic sludge (F3) (1.0, 1.5, 2.0 and 2.5 tons/mu) are respectively increased by 8.9 percent, 22.9 percent, 70.0 percent and 108.7 percent compared with the control; the contents of alkaline hydrolysis nitrogen and quick-acting phosphorus of the mud flat soil treated by the sludge products are respectively increased by 16.9%, 65.2%, 94.5%, 146.8% and 83.1%, 173.1%, 207.3% and 336.1% compared with the control. Except 1.0 ton/mu, the contents of organic matters, alkaline hydrolysis nitrogen and quick-acting phosphorus in the soil treated by the sludge products are obviously higher than those of the control.

(3) Effect of application of harmless treatment product of domestic sludge (F3) on barley Biomass and yield

The application of the harmless treatment product of domestic sludge (F3) promoted the growth of barley crops and increased their biomass and yield (FIG. 5). Control barley biomass and yield without sludge product application, 3.53kg plot respectively^-1、1.68t ha^-1. Applying harmless treatment products of domestic sludge for each treatment (1.0, 1.5, 2.0 and 2.5 tons per mu)^-1) Barley biomass and yield increased by 13.0%, 42.6%, 60.2%, 101.8% and 20.3%, 28.8%, 63.9%, 112.7%, respectively, over the control. Except 1.0 ton mu^-1In addition, the biomass and yield of the barley treated by each of the other sludge products were significantly higher than those of the control.

Experimental example 4

And (3) obtaining a domestic sludge harmless product (F3), and improving the pot culture research of saline-alkali soil. The test pot is a cylindrical plastic pot with the height of 29.5cm and the inner diameter of 26 cm. The pH of the soil of the tested saline-alkali soil is 8.36, and the EC is 0.36Ms cm^-15.58g kg of organic matter^-1Total nitrogen and total phosphorus are respectively 0.41g kg^-1、0.65g kg^-1. The pH of the harmless product of the test domestic sludge (F3) is 6.40, and the EC is 1.06Ms cm^-1280.3g/kg of organic matter, 18.81g kg of total nitrogen and total phosphorus respectively^-1、24.20g kg^-1The total amount of Cd, Cu, Pb and Zn is 1.27mg kg^-1、136.6mg kg^-1、36.8mg kg^-1、371.1mg kg^-1。

The test is carried out in a test greenhouse of environmental science and engineering college of Yangzhou university in 2018 from 6 months to 11 months. After the soil is naturally dried, the soil is sieved by a 2mm sieve, and 10kg of soil is filled in each pot. The tests were carried out with 4 treatments, respectively 0, 30g kg of sludge product^-1、60g kg^-1、90g kg^-1The sludge product and the soil are fully mixed, and each treatment is repeated for 2 times. And 6, 15 days after 6 months, 3 holes are sown in each pot, and 2 corn seeds are sown in each hole. 7 months and 5 days, thinning the seedlings to 3 maize seedlings. Other measures were kept consistent during the test. And (4) harvesting corn plants and testing seedlings after 10 months and 25 days, and collecting soil samples.

(1) Effect of harmless products of domestic sludge (F3) on growth of corn plants

The plant height and biomass of corn plants increased with the increase of the application amount of sludge products (fig. 6-a, B). The plant height of the control maize plants without sludge product was 79.5cm, and the plants were treated with harmless domestic sludge product (F3) (30g kg)^-1、60g kg^-1、90g kg^-1) The plant heights of the corns are respectively increased to 90.3cm, 94.2cm and 103.0cm, and are respectively increased by 13.6 percent, 18.4 percent and 29.6 percent compared with the control. Each treatment (30g kg) was carried out by applying a domestic sludge harmless product (F3)^-1、60g kg^-1、90g kg^-1) The biomass of the corn plants, which is increased by 67.4%, 68.5% and 82.6% compared with the control respectively, is obviously higher than the control, but the difference between the application treatments of the sludge products does not reach a significant level.

(2) Influence of harmless domestic sludge product (F3) on heavy metal content and form of mud flat soil

The influence of the harmless product of the domestic sludge (F3) on the total amount of Cd, Cu, Pb and Zn heavy metals in the soil of the beach saline-alkali land is shown in figures 7-A, B, C, D. Along with the increase of the application amount of sludge products, the total amount of Cu and Zn in the saline-alkali soil is in a remarkable rising trend. The total Cu content of the control soil without applying the sludge product is 13.94mg kg^-1Application of domestic sludge for harmlessnessThe products (F3) were each treated (30g kg)^-1、60g kg^-1、90g kg^-1) The total amount of Cu in the soil is 20.35mg kg^-1、30.45mg kg^-1、39.30mg kg^-1The increase of the content of the protein is 46.0 percent, 118.5 percent and 181.9 percent compared with the control respectively, and the difference between the protein and the control reaches a significant level. The harmless products of the domestic sludge (F3) are applied for treatment (30, 60 and 90 gkg)^-1) The total Zn content of the soil is respectively increased by 16.5 percent, 39.5 percent and 73.1 percent compared with the control, which are all obviously higher than the control, but the difference between the application treatments of the harmless products (F3) of the domestic sludge also reaches a significant level. The total amount of Cd and Pb in the beach soil is increased slightly with the increase of the application amount of the domestic sludge harmless product (F3), but the difference between treatments does not reach a significant level.

The application of the domestic sludge harmless product (F3) has influence on the morphological characteristics of heavy metals Cd, Cu, Pb and Zn in the soil of the beach saline-alkali soil, as shown in the figure 8-A, B, C, D. Along with the increase of the application amount of the sludge product, the proportions of Cd, Cu, Pb and Zn in the residue state all show a descending trend. When the dosage of the sludge product reaches 90g kg^-1When the method is used, the proportions of Cd, Cu, Pb and Zn in the residue state are respectively reduced by 13.18 percent, 51.09 percent, 16.93 percent and 32.26 percent compared with the control, and the proportions all reach significant levels. The sludge product is applied, and the ratio of Cd, Cu, Pb and Zn in an acid soluble state (EX) to a reducible state (RG) is obviously increased. When the dosage of the sludge product reaches 90g kg^-1The sum of the proportions of Cd, Cu and Zn in the acid soluble (EX) and Reducible (RG) states is increased by 45.7%, 145.5% and 543.1% respectively over the control. The application of the domestic sludge harmless product (F3) increases the oxidizable states (OXI) Cu and Pb, reduces the oxidizable state (OXI) Zn, and has no significant change in the oxidizable state (OXI) Cd proportion. The present test condition, application of the sludge innocent product (F3), had no significant effect on acid soluble (EX) Pb.

(3) Influence of harmless domestic sludge product (F3) on heavy metal absorption of corn plants

The effect of the application of the harmless product of domestic sludge (F3) on the heavy metal content of various parts of the corn plants is shown in FIG. 9. With the increase of the using amount of the domestic sludge harmless product (F3), the Zn content of each part of the corn plant is in an increasing trend. The Zn contents of the roots, stems and leaves of the control corn plants without applying the sludge product are respectively 9.67mg kg^-1、3.65mg kg^-1、19.91 mg kg^-1When the dosage of the sludge product reaches 90g kg^-1In the process, the Zn content of the root, the stem and the leaf of the corn is obviously higher than that of the control, and the increase rates are respectively 100.2%, 33.5% and 51.9%. The application of the domestic sludge harmless product (F3) obviously increases the Cu content of stems and leaves of corn plants, 90g kg^-1The Cu content of the stem and the leaf of the corn treated by the amount of the domestic sludge harmless product (F3) is respectively increased by 158.8 percent and 51.8 percent compared with the control. The application of the domestic sludge harmless product (F3) has no significant influence on the Cd and Pb contents of each part of the corn plant.

Claims

1. A method for improving saline-alkali soil by biological two-stage harmless treatment of domestic sludge is characterized by comprising the following steps:

1) firstly, digesting domestic sludge by adopting an earthworm odorless front section to obtain a mixture of excess sludge and earthworm cast;

2) inoculating EM microbial inoculum to fully ferment the mixture of the excess sludge and the wormcast to obtain a harmless product;

3) adding the harmless product obtained in the step 2) into saline-alkali soil for treatment;

the specific steps of the step 1) are as follows: stacking the domestic sludge into a plurality of long strip stacks with the height of 25-30 cm, the width of 40-50 cm and the length of 3.0-3.5 m, wherein each long strip stack is separated by 20-30 cm; the mixture of the working earthworms and the wormcast is inserted into the long strip stack interval to form an earthworm working bed; the thickness of the wormcast mixture is 3-5 cm, after the wormcast mixture is digested for 6-8 days, earthworms are collected by adopting an artificial light-shielding method, and then residual sludge and the wormcast mixture are obtained;

the specific steps of the step 2) are as follows: stacking the mixture of the excess sludge and the wormcast into a long strip stack with the width of 2.0-2.5 m, the height of 1.2-1.5 m and the length of 50-100 m, inoculating EM microbial inoculum, turning the stack when the temperature is raised to above 60 ℃, continuously turning the stack for 2-3 times, and completing full fermentation after the temperature of the stack is maintained at room temperature and is not raised any more; the inoculation amount of the EM microbial inoculum in the step 2) is 1.5-2%; the EM microbial inoculum in the step 2) is obtained by diluting 5-10 kg of EM stock solution with 100kg of 10% brown sugar water; the water content of the harmless product in the step 2) is less than or equal to 60%, the pH value is 5.5-8.5, the organic matter content is more than or equal to 20%, the ascarid egg death rate is more than or equal to 95%, and the faecal coliform bacteria value is more than or equal to 0.01; the saline-alkali soil is a mild saline-alkali soil with the salt content of less than 4g/kg, the using amount of the mild saline-alkali soil is 1-2.5 tons/mu, and the mild saline-alkali soil is uniformly mixed with 0-20 cm of saline-alkali soil by using a rotary cultivator after being directly applied as a base fertilizer.