Method for promoting degradation and humification of sludge compost organic matters

Abstract

The invention discloses a method for promoting degradation and humification of sludge compost organic matters, and belongs to the technical field of sludge treatment. The method comprises the following steps: mixing sludge and straws to obtain a compost raw material, adjusting the carbon nitrogen ratio by utilizing the straws and improving the bulkiness of the compost raw material, adding phosphate and steel slag into the compost raw material, and uniformly mixing to obtain compost; and fermenting the compost until the compost is thoroughly decomposed to obtain the organic fertilizer. The phosphate and the steel slag are selected as a combined additive, the phosphate is used for reducing compost nitrogen loss and improving compost nutrients, meanwhile, the steel slag is further used for regulating and controlling pH and NH4 < + > conversion in the composting process, degradation and humification of compost organic matter are synergistically promoted, and the quality of a final compost product is improved. The cost is low, the operation method is simple, the effects of improving the composting efficiency and quality and degrading and converting organic matters are obvious, the decomposition degree of a compost product is improved, and the humic acid and humification degree in the compost after fermentation are increased.

Description

Technical Field

[0001] The invention relates to a composting method, in particular to a method for promoting degradation and humification of organic matter in sludge composting. Background Art

[0002] Sludge is a solid sediment produced by the water and sewage treatment process. With the increasing amount of sludge produced, if it is not handled properly, it will have a serious impact on the environment and human health. Therefore, how to effectively and safely treat these sludges has become an urgent problem to be solved. Compared with the unsustainable disposal mode of traditional landfill and incineration, aerobic composting is a green method that can achieve the stabilization, harmlessness and resource utilization of organic solid waste. It can convert organic matter (OM) into stable humic acid substances (i.e. humus) and promote the recycling of resources. However, the traditional sludge composting process mainly aims at reduction, but ignores the quality of the compost product, that is, it faces problems such as severe nitrogen loss and low degree of humification. This not only affects the agronomic value of the compost product organic fertilizer, but also limits the engineering application of aerobic composting technology.

[0003] It is worth noting that phosphates are high-quality fertilizers for agronomic soil improvement. Adding an appropriate amount of phosphates to compost materials can not only effectively reduce the nitrogen loss caused by the volatilization of ammonia (NH3), but also help improve the quality of compost products. For example, Chinese invention patent CN116283393A discloses a method for nitrogen preservation and quality improvement of pig manure composting. The use of potassium dihydrogen phosphate (KH2PO4) as an acidic additive in the compost matrix can not only improve the retention of nitrogen, but also the phosphorus and potassium contained in it can make up for the low content of nutrient elements in organic fertilizers; Chinese invention patent CN112479758B discloses a method for nitrogen preservation and quality improvement of pig manure composting. An in-situ efficient deodorization method for livestock and poultry manure and sludge composting. Further adding KH2PO4 to the fermented compost material can promote the stabilization of ammonium ions, effectively reduce ammonia emissions and promote the in-situ stable storage of nitrogen and phosphorus nutrients; Chinese invention patent CN109776138A discloses a method for producing compost by fermenting organic waste. By adding dipotassium hydrogen phosphate and / or potassium dihydrogen phosphate buffer substances to sludge and crop fermentation raw materials for aerobic fermentation, this method can not only significantly reduce the loss of ammonia produced by composting fermentation, but also better supplement the content of potassium and phosphorus in the resulting compost, thereby improving fertilizer efficiency. However, these methods are limited to the use of phosphates to regulate unilateral effects such as nitrogen conversion and nitrogen retention during composting. However, phosphates as acidic chemical additives may cause a decrease in pH and NH4 +Excessive accumulation is not conducive to microbial activity and OM biodegradation, which in turn limits compost maturity and the polymerization of precursor substances to form humic acid, affecting the quality of the final product. Therefore, how to utilize the superior nitrogen fixation performance and agronomic value of phosphates and take appropriate measures to further promote OM degradation and humification is of great significance to the optimization of traditional composting processes and the resource utilization of sludge.

[0004] Steel slag, as an industrial waste residue from steel smelting, contains high concentrations of electron acceptors, such as free alkaline oxides such as active iron, calcium, magnesium and silicon. The high porosity, high specific surface area and rich chemical composition determine the availability of steel slag, especially its ability to play a non-biological humification role. Its rich transition metals such as iron and manganese can act as Lewis acids, and promote the nucleophilic addition and condensation of humus precursors to form humus by obtaining electrons from small molecular precursors. In addition, steel slag, as a bulk solid waste in the metallurgical industry, is highly accessible and low-cost. However, existing reports have not explored the effects of adding steel slag as an additive during the composting process on the degradation and humification of compost organic matter, especially the reports on its combined addition with acidic chemical additives such as phosphates to improve the limitations of acidic chemical additives alone. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a method for promoting the degradation and humification of organic matter in sludge composting, and to solve the problem of how to promote the degradation and humification of organic matter in the composting process. Another purpose of the present invention is to provide an organic fertilizer that can fully degrade organic matter.

[0006] Technical solution: The method for promoting the degradation and humification of organic matter in sludge composting according to the present invention is characterized in that it comprises the following steps:

[0007] (1) mixing sludge and straw to obtain a compost raw material, using the straw to adjust the carbon-nitrogen ratio and improve the fluffiness of the compost raw material, adding phosphate and steel slag to the compost raw material, and mixing them uniformly to obtain compost;

[0008] (2) Fermenting the compost until it is fully decomposed to obtain organic fertilizer.

[0009] The combined addition of steel slag in the present invention can effectively buffer the H generated by the addition of KH2PO4 alone and the composting organic acid. +and acidity, and significantly promotes the degradation of organic matter; unlike the addition of KH2PO4 alone, which leads to the accumulation of ammonium nitrogen and inhibits the production of nitrate nitrogen, the joint addition of steel slag helps to promote the conversion of ammonium nitrogen and enhance the nitrification of compost; in addition, the joint addition of steel slag can improve the humification of compost in an acidic environment, can synergistically promote the formation of compost humic acid and effectively improve the polymerization degree of compost products. The present invention mixes sludge and straw to obtain compost raw materials, and the addition of straw can increase the C content and adjust the C / N ratio; make the compost raw materials fluffy, and improve the air flow and transmission during aerobic composting; add phosphate and steel slag to the compost raw materials, mix them evenly to obtain compost; steel slag can produce an adsorption effect on phosphate, which is beneficial to the slow release of phosphate and enhances the continuous fertilizer effect of the finished compost product.

[0010] When steel slag and phosphate are added during sludge composting, the alkaline oxides in the steel slag can effectively buffer the H generated by the addition of KH2PO4 alone and the composting organic acids. + The pore structure and high surface area of ​​steel slag provide a suitable microenvironment for the growth and metabolism of microorganisms, significantly promoting the degradation of organic matter. Unlike the addition of KH2PO4 alone, which leads to the accumulation of ammonium nitrogen and inhibits the production of nitrate nitrogen, the abundant alkaline oxides in steel slag can absorb CO2 to form a bicarbonate buffer system, providing the required carbon source and alkalinity for the growth of autotrophic nitrifying bacteria. In addition, the rich Fe 2+ and Fe 3+ It can enhance the activity of ammonia monooxygenase and hydroxylamine oxidoreductase and promote the nitrification reaction. Therefore, the combined addition of steel slag helps to promote the conversion of ammonium nitrogen and enhance the nitrification of compost; the combined addition of phosphate and steel slag has a synergistic effect on the formation of HA. This is because under the action of steel slag, the degradation of complex OM is effectively promoted, which leads to an increase in the skeleton precursors required for HA formation. In addition, the rich Fe 3+ Oxides, such as hematite and magnetite, can act as catalytic sites, helping to promote the transformation of precursor substances into dark polymers such as HA. Therefore, the combined addition of steel slag can help improve the compost humification efficiency and product quality. The combined addition of steel slag and phosphate can provide a stable composting microenvironment, which can promote unstable low-molecular-weight FA to participate in biological metabolism and gradually transform into more stable HA. The combined addition of steel slag can provide a stable composting microenvironment, which can promote unstable low-molecular-weight FA to participate in biological metabolism and gradually transform into more stable HA. Therefore, the combined addition of phosphate and steel slag can improve the compost humification in an acidic environment, synergistically promote the formation of compost humic acid and effectively increase the degree of polymerization of compost products.

[0011] Preferably, in step (1), the fresh weight mass ratio of sludge to straw is 4-6: 1. For example, the fresh weight mass ratio of sludge to straw is 4: 1, 4.5: 1, 5: 1, 5.5: 1, 6: 1.

[0012] Preferably, in step (1), the amount of steel slag added is 5% to 10% of the dry weight of the compost raw material. For example, the amount of steel slag added is 5%, 6%, 7%, 8%, 9%, 10%, etc. of the mass of the compost raw material.

[0013] Preferably, in step (1), the ratio of phosphate to compost raw material is 0.25-0.3 mol:1 kg based on the dry weight of the compost raw material. For example, the ratio of phosphate to compost raw material is 0.25 mol:1 kg, 0.26 mol:1 kg, 0.27 mol:1 kg, 0.28 mol:1 kg, 0.29 mol:1 kg, 0.30 mol:1 kg, etc.

[0014] In a preferred embodiment of the present invention, based on the dry mass of the compost raw material, the added amount of steel slag is 5% of the mass of the compost raw material, and the ratio of phosphate to the compost raw material is 0.3 mol:1 kg.

[0015] Preferably, in step (2), the fermentation method is aerobic fermentation with ventilation, and the fermentation time is 28-42 days. During the fermentation process, when the temperature is ≥45°C, the compost is turned once every 3-4 days; when the temperature is <45°C, the compost is turned once every 7 days. For example, the fermentation time is 28 days, 30 days, 32 days, 34 days, 36 days, 38 days, 40 days, 42 days, etc.

[0016] Preferably, in step (2), the moisture content of the compost before fermentation is 55-65%. For example, the moisture content of the compost is 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, etc. When adding slag and phosphate, the slag and phosphate need to be added to water to prepare a suspension for addition. The present invention does not need to limit the amount of water added, but only needs to maintain the moisture content of the compost at 55% to 65% before fermentation; and when adding water, the present invention does not limit the source of water, such as ultrapure water, tap water, and deionized water.

[0017] Preferably, in step (2), during fermentation, the aeration intensity is based on the dry mass of the compost raw material, and the gas flow rate is 0.35-0.60 L·kg -1 ·min -1 For example, the gas flow rate is 0.35L·kg -1 ·min -1 , 0.40L·kg -1 ·min -1 , 0.45L·kg -1 ·min -1 , 0.50L·kg -1 ·min -1 , 0.55L·kg -1 ·min-1 , 0.60L·kg -1 ·min -1 wait.

[0018] Preferably, in step (1), the straw is derived from at least one of wheat, corn and rice, and the straw particle size is 0.5-1.0 cm.

[0019] Preferably, the steel slag contains CaO, Fe2O3, SiO2, MgO, Al2O3 and MnO, and the phosphate contains hydrogen phosphate ions, such as disodium hydrogen phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate and the like.

[0020] Another aspect of the present invention discloses an organic fertilizer prepared by the method for promoting the degradation and humification of organic matter in sludge composting.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0022] (1) The present invention uses phosphate and steel slag as a combined additive. While using phosphate to reduce nitrogen loss in compost and increase compost nutrients, steel slag is further used to regulate pH and NH4 in the composting process. + conversion, synergistically promoting the degradation and humification of compost organic matter and improving the quality of the final compost product.

[0023] (2) The additives selected by the present invention are low in cost, simple in operation method, and easy to implement. They have obvious effects on improving composting efficiency and quality as well as degradation and conversion of organic matter, and improve the maturity of compost products. After fermentation, the humic acid and humification degree in the compost increase.

[0024] (3) The present invention uses steel slag as an additive. Steel slag is a major metallurgical solid waste with an easy source and low cost. It can be added to compost and is easy to operate. It can treat waste with waste, thus providing a new waste resource recovery method. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Graphs showing changes in pH of each treatment group during the composting process; wherein (a) is a graph showing changes in pH of Example 1 and Comparative Examples 1 and 2 after composting for 42 days, and (b) is a graph showing changes in pH of Examples 2, 3, 4 and Comparative Example 3 after composting for 28 days;

[0026] Figure 2Graphs showing changes in organic matter content and degradation rates during composting of the present invention; wherein (a) is a graph showing changes in OM after composting for 42 days in Example 1 and Comparative Examples 1 and 2, (b) is a graph showing changes in OM after composting for 28 days in Example 2, 3, 4 and Comparative Example 3, (c) is a graph showing degradation rates of OM after composting for 42 days in Example 1 and Comparative Examples 1 and 2, and (d) is a graph showing degradation rates of OM after composting for 28 days in Example 2, 3, 4 and Comparative Example 3;

[0027] Figure 3 is a graph showing the change in ammonium nitrogen content in each treatment group during the composting process; wherein (a) is a graph showing the NH4 + -N change diagram, (b) shows the NH4 in Examples 2, 3, 4 and Comparative Example 3 after 28 days of composting + -N change graph;

[0028] Figure 4 The graphs are the changes of nitrate nitrogen content in each treatment group during the composting process; wherein (a) is the NO3 content of Example 1 and Comparative Examples 1 and 2 after 42 days of composting. - -N change diagram, (b) shows the NO3 of Examples 2, 3, 4 and Comparative Example 3 after 28 days of composting - -N change graph;

[0029] Figure 5 2 are graphs showing changes in humic acid content in each treatment group during the composting process; wherein (a) is a graph showing changes in HA in Example 1 and Comparative Examples 1 and 2 after 42 days of composting, and (b) is a graph showing changes in HA in Examples 2, 3, 4 and Comparative Example 3 after 28 days of composting;

[0030] Figure 6 1 and 2. The graphs are of the change in HA / FA of Example 1 and Comparative Examples 1 and 2 after 42 days of composting, and the graphs are of the change in HA / FA of Example 2, 3, 4 and Comparative Example 3 after 28 days of composting. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0032] The sludge used in the embodiment of the present invention comes from the dehydration workshop of a sewage treatment plant in Ma'anshan City, Anhui Province, and the water content of the sludge is 70% to 80%; the wheat straw used is purchased from a farm in Ma'anshan City, Anhui Province; the steel slag is taken from a steel company in Ma'anshan City, Anhui Province; the steel slag is alkaline converter slag, as shown in Table 1, the main chemical composition of the steel slag of the present invention obtained by X-ray diffraction analysis, the steel slag is ground by a ball mill and passed through a 100-mesh sieve for drying; potassium dihydrogen phosphate is purchased from Sinopharm Chemical Reagent Co., Ltd.

[0033] Table 1 Main chemical composition of steel slag of the present invention

[0034] Element CaO <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> MgO <![CDATA[Al2O3]]> MnO other wt.% 37.78 19.98 17.97 10.26 5.95 3.26 4.80

[0035] Example 1: A method for promoting the degradation and humification of organic matter in sludge composting, comprising the following steps:

[0036] (1) Fresh sludge taken out from a dewatering workshop of a sewage treatment plant and wheat straw cut into 0.5-1.0 cm are used as compost raw materials, and are evenly stirred at a fresh weight ratio of 5:1, and the total weight of the sludge and wheat straw is controlled to be 12 kg to obtain compost raw materials; then, based on the dry weight of the compost raw materials, steel slag is weighed according to 10 wt% of the dry weight of the compost raw materials; KH2PO4 is weighed according to 0.25 mol / kg of the dry weight of the compost raw materials, 10% of the steel slag and 0.25 mol / kg of KH2PO4 are respectively poured into ultrapure water, stirred to prepare a suspension, and evenly sprinkled in the compost raw materials, and water is added to control the moisture content of the compost to 65%. After being evenly stirred, compost is obtained.

[0037] (2) The compost obtained in step (1) is placed in a closed fermentation tank, and an air pump is used to force ventilation and aerobic fermentation of the compost reactor for 42 days. Based on the dry weight of the compost raw materials, the gas flow rate is controlled by a gas flow meter to be 0.35 L kg in the first 3 weeks after the start of composting. -1 ·min -1 , and the gas flow rate was controlled at 0.60 L·kg for the last 3 weeks -1 ·min -1 The interval for turning the compost is every 3-4 days when the temperature exceeds 45℃ in the early stage, and once a week when the temperature is below 45℃ in the later stage. After each turning of the compost, sampling is carried out using the five-point method to determine pH, ammonium nitrogen, nitrate nitrogen, organic matter and humus data.

[0038] Example 2: A method for promoting the degradation and humification of organic matter in sludge composting, comprising the following steps:

[0039] (1) Fresh sludge taken out from a dewatering workshop of a sewage treatment plant and wheat straw cut into 0.5-1.0 cm are used as compost raw materials, and are evenly stirred at a fresh weight ratio of 5:1, and the total weight of the sludge and wheat straw is controlled to be 12 kg to obtain compost raw materials; then, based on the dry weight of the compost raw materials, steel slag is weighed according to 5wt% of the dry weight of the compost raw materials; KH2PO4 is weighed according to 0.30mol / kg of the dry weight of the compost raw materials, 5% steel slag and 0.30mol / kg KH2PO4 are respectively poured into ultrapure water, stirred to prepare a suspension, and evenly sprinkled in the compost raw materials, and water is added to control the moisture content of the compost to 65%. After being evenly stirred, compost is obtained.

[0040] (2) The compost obtained in step (1) is placed in a closed fermentation tank, and an air pump is used to force ventilation and aerobic fermentation of the compost reactor for 28 days. The gas flow rate during the entire composting cycle is controlled by a gas flow meter to be 0.35 L kg based on the dry weight of the compost raw material. -1 ·min -1 The interval for turning the compost is every 3-4 days when the temperature exceeds 45℃ in the early stage, and once a week when the temperature is below 45℃ in the later stage. After each turning of the compost, sampling is carried out using the five-point method to determine pH, ammonium nitrogen, nitrate nitrogen, organic matter and humus data.

[0041] Example 3: A method for promoting the degradation and humification of organic matter in sludge composting, comprising the following steps:

[0042] (1) Fresh sludge taken out from a dewatering workshop of a sewage treatment plant and wheat straw cut into 0.5-1.0 cm are used as compost raw materials, and are evenly stirred at a fresh weight ratio of 5:1, and the total weight of the sludge and wheat straw is controlled to be 12 kg to obtain compost raw materials; then, based on the dry weight of the compost raw materials, steel slag is weighed according to 7.5 wt% of the dry weight of the compost raw materials; KH2PO4 is weighed according to 0.30 mol / kg of the dry weight of the compost raw materials, and 7.5% of the steel slag and 0.30 mol / kg of KH2PO4 are respectively poured into ultrapure water, stirred to prepare a suspension, and evenly sprinkled in the compost raw materials, and water is added to control the moisture content of the compost to 65%. After being evenly stirred, compost is obtained.

[0043] (2) The compost obtained in step (1) is placed in a closed fermentation tank, and an air pump is used to force ventilation and aerobic fermentation of the compost reactor for 28 days. The gas flow rate during the entire composting cycle is controlled by a gas flow meter to be 0.35 L kg based on the dry weight of the compost raw material. -1 ·min -1 The interval for turning the compost is every 3-4 days when the temperature exceeds 45℃ in the early stage, and once a week when the temperature is below 45℃ in the later stage. After each turning of the compost, sampling is carried out using the five-point method to determine pH, ammonium nitrogen, nitrate nitrogen, organic matter and humus data.

[0044] Example 4: A method for promoting the degradation and humification of organic matter in sludge composting, comprising the following steps:

[0045] (1) Fresh sludge taken out from a dewatering workshop of a sewage treatment plant and wheat straw cut into 0.5-1.0 cm are used as compost raw materials, and are evenly stirred at a fresh weight ratio of 5:1, and the total weight of the sludge and wheat straw is controlled to be 12 kg to obtain compost raw materials; then, based on the dry weight of the compost raw materials, steel slag is weighed according to 10 wt% of the dry weight of the compost raw materials; KH2PO4 is weighed according to 0.30 mol / kg of the dry weight of the compost raw materials, and 10% of the steel slag and 0.30 mol / kg of KH2PO4 are respectively poured into ultrapure water, stirred to prepare a suspension, and evenly sprinkled in the compost raw materials, and water is added to control the moisture content of the compost to 65%. After being evenly stirred, compost is obtained.

[0046] (2) The compost obtained in step (1) is placed in a closed fermentation tank, and an air pump is used to force ventilation and aerobic fermentation of the compost reactor for 28 days. The gas flow rate during the entire composting cycle is controlled by a gas flow meter to be 0.35 L kg based on the dry weight of the compost raw material. -1 ·min -1 The interval for turning the compost is every 3-4 days when the temperature exceeds 45℃ in the early stage, and once a week when the temperature is below 45℃ in the later stage. After each turning of the compost, sampling is carried out using the five-point method to determine pH, ammonium nitrogen, nitrate nitrogen, organic matter and humus data.

[0047] Example 5: A method for promoting the degradation and humification of organic matter in sludge composting, comprising the following steps:

[0048] (1) Fresh sludge taken out from a dewatering workshop of a sewage treatment plant and corn stalks cut into 0.5-1.0 cm are used as compost raw materials, and are evenly stirred at a fresh weight ratio of 4:1, and the total weight of the sludge and corn stalks is controlled to be 12 kg to obtain compost raw materials; then, based on the dry weight of the compost raw materials, steel slag is weighed according to 10 wt% of the dry weight of the compost raw materials; KH2PO4 is weighed according to 0.28 mol / kg of the dry weight of the compost raw materials, and 10% of the steel slag and 0.28 mol / kg of KH2PO4 are respectively poured into ultrapure water, stirred to prepare a suspension, and evenly sprinkled on the compost raw materials, and water is added to control the moisture content of the compost to 60%. After being evenly stirred, compost is obtained.

[0049] (2) The compost obtained in step (1) is placed in a closed fermentation tank, and an air pump is used to force ventilation and aerobic fermentation of the compost reactor for 35 days. Based on the dry weight of the compost raw materials, the gas flow rate is controlled by a gas flow meter to be 0.35 L kg in the first 3 weeks after the start of composting. -1 ·min -1 , after 2 weeks, the gas flow rate was controlled at 0.55 L·kg -1 ·min -1The interval for turning the compost is once every 3 to 4 days when the temperature exceeds 45°C in the early stage, and once a week when the temperature is below 45°C in the later stage. After fermentation is completed, organic fertilizer is obtained.

[0050] Example 6: A method for promoting the degradation and humification of organic matter in sludge composting, comprising the following steps:

[0051] (1) Fresh sludge taken out from a dewatering workshop of a sewage treatment plant and rice straw cut into pieces of 0.5 to 1.0 cm are used as compost raw materials, and are evenly stirred at a fresh weight ratio of 6:1, and the total weight of the sludge and rice straw is controlled to be 12 kg to obtain compost raw materials; then, based on the dry weight of the compost raw materials, steel slag is weighed according to 8 wt% of the dry weight of the compost raw materials; KH2PO4 is weighed according to 0.28 mol / kg of the dry weight of the compost raw materials, and 8% of the steel slag and 0.28 mol / kg of KH2PO4 are respectively poured into ultrapure water, stirred to prepare a suspension, and evenly sprinkled in the compost raw materials, and water is added to control the moisture content of the compost to be 55%. After being evenly stirred, compost is obtained.

[0052] (2) The compost obtained in step (1) is placed in a closed fermentation tank, and an air pump is used to force ventilation and aerobic fermentation of the compost reactor for 35 days. Based on the dry weight of the compost raw materials, the gas flow rate is controlled by a gas flow meter to be 0.35 L kg in the first 3 weeks after the start of composting. -1 ·min -1 , after 2 weeks, the gas flow rate was controlled at 0.60 L·kg - ·min -1 The interval for turning the compost is once every 3 to 4 days when the temperature exceeds 45°C in the early stage, and once a week when the temperature is below 45°C in the later stage. After fermentation is completed, organic fertilizer is obtained.

[0053] Comparative Example 1: A sludge composting method, the steps are as follows:

[0054] (1) Fresh sludge taken out from a dewatering workshop of a sewage treatment plant and wheat straw cut into 0.5-1.0 cm thick are used as compost raw materials, and are evenly mixed at a fresh weight ratio of 5:1, and the total weight of the sludge and wheat straw is controlled to be 12 kg to obtain compost raw materials; water is added to control the moisture content of the compost to 65%, and the compost is obtained after being evenly mixed.

[0055] (2) The compost obtained in step (1) is placed in a closed fermentation tank, and an air pump is used to force ventilation and aerobic fermentation of the compost reactor for 42 days. Based on the dry weight of the compost raw materials, the gas flow rate is controlled by a gas flow meter to be 0.35 L kg in the first 3 weeks after the start of composting. -1 ·min -1 , and the gas flow rate was controlled at 0.60 L·kg for the last 3 weeks -1 ·min -1The interval for turning the compost is every 3-4 days when the temperature exceeds 45℃ in the early stage, and once a week when the temperature is below 45℃ in the later stage. After each turning of the compost, sampling is carried out using the five-point method to determine pH, ammonium nitrogen, nitrate nitrogen, organic matter and humus data.

[0056] Comparative Example 2: A sludge composting method, the steps are as follows:

[0057] (1) Fresh sludge taken out from a dewatering workshop of a sewage treatment plant and wheat straw cut into 0.5-1.0 cm are used as compost raw materials, and are evenly stirred at a fresh weight ratio of 5:1, and the total weight of the sludge and wheat straw is controlled to be 12 kg to obtain compost raw materials; then, based on the dry weight of the compost raw materials, KH2PO4 is weighed according to a ratio of KH2PO4 to 0.25 mol / kg of the dry weight of the compost raw materials, 0.25 mol / kg of KH2PO4 is poured into ultrapure water, stirred to prepare a suspension, and evenly sprinkled in the compost raw materials, and water is added to control the moisture content of the compost to 65%. After being evenly stirred, compost is obtained.

[0058] (2) The compost obtained in step (1) is placed in a closed fermentation tank, and an air pump is used to force ventilation and aerobic fermentation of the compost reactor for 42 days. Based on the dry weight of the compost raw materials, the gas flow rate is controlled by a gas flow meter to be 0.35 L kg in the first 3 weeks after the start of composting. -1 ·min -1 , and the gas flow rate was controlled at 0.60 L·kg for the last 3 weeks -1 ·min -1 The interval for turning the compost is every 3-4 days when the temperature exceeds 45℃ in the early stage, and once a week when the temperature is below 45℃ in the later stage. After each turning of the compost, sampling is carried out using the five-point method to determine pH, ammonium nitrogen, nitrate nitrogen, organic matter and humus data.

[0059] Comparative Example 3: A sludge composting method, the steps are as follows:

[0060] (1) Fresh sludge taken out from a dewatering workshop of a sewage treatment plant and wheat straw cut into 0.5-1.0 cm are used as compost raw materials, and are evenly stirred at a fresh weight ratio of 5:1, and the total weight of the sludge and wheat straw is controlled to be 12 kg to obtain compost raw materials; then, based on the dry weight of the compost raw materials, KH2PO4 is weighed according to a ratio of KH2PO4 to 0.30 mol / kg of the dry weight of the compost raw materials, 0.30 mol / kg of KH2PO4 is poured into ultrapure water, stirred to prepare a suspension, and evenly sprinkled in the compost raw materials, and water is added to control the moisture content of the compost to 65%. After being evenly stirred, compost is obtained.

[0061] (2) The compost obtained in step (1) is placed in a closed fermentation tank, and an air pump is used to force ventilation and aerobic fermentation of the compost reactor for 28 days. The gas flow rate during the entire composting cycle is controlled by a gas flow meter to be 0.35 L kg based on the dry weight of the compost raw material. -1 ·min -1 The interval for turning the compost is every 3-4 days when the temperature exceeds 45℃ in the early stage, and once a week when the temperature is below 45℃ in the later stage. After each turning of the compost, sampling is carried out using the five-point method to determine pH, ammonium nitrogen, nitrate nitrogen, organic matter and humus data.

[0062] Figure 1 The pH changes of each group during the composting process are shown in Figure 2. Figure 1 As shown in (a), compared with the comparative example 1 without any addition treatment, the pH of the comparative example 2 treated with only 0.25 mol / kg KH2PO4 decreased rapidly after the 4th day of composting, and was significantly lower than that of the comparative example 1 on the 19th day, while the pH of the example 1 treated with the combined addition of 10% steel slag was higher than that of the comparative examples 1 and 2 on the 28th to 42nd day of composting, which indicates that the combined addition of steel slag effectively buffered the H generated by the addition of KH2PO4 and the composting organic acid. + and acidity, which is beneficial to promote the composting process and improve the microenvironment. Figure 1 (b) in the figure also shows that the addition of steel slag in different proportions of 5%, 7.5% and 10% and 0.3 mol / kg KH2PO4 effectively increased the pH during the composting process. From the 11th day of composting to the end of the 28th day of composting, the pH of Examples 2, 3, and 4 was significantly higher than that of Comparative Example 3, which was treated with only 0.30 mol / kg KH2PO4 (p<0.05). This can be attributed to the alkaline neutralization effect of the abundant alkaline oxides (such as CaO) in the steel slag (see Table 1), which can be balanced with the acidic phosphates to provide a buffer environment for composting.

[0063] Figure 2 The graphs of OM content changes and degradation rates of each group during composting are shown in Figure 2. Figure 2 As shown in (a) and (c) in Figure 1, at the end of 42 days of composting, the OM degradation rate of Comparative Example 2 treated with only 0.25 mol / kg KH2PO4 was lower than that of Comparative Example 1 without any addition, while the final OM degradation rate of Example 1 treated with 10% steel slag was higher than that of Comparative Example 1 and Comparative Example 2; compared with Comparative Example 1, the OM degradation rate of Example 1 increased by 10.3%. This can be attributed to the fact that the OM degradation rate of H + PO4 - and NH4 +The accumulation of slag inhibits the activity of microorganisms and prolongs the degradation duration of complex organic matter such as lignocellulose in compost. The special pore structure and high surface area of ​​steel slag in the combined addition treatment can provide a suitable microenvironment for microbial growth and metabolism, thereby promoting the degradation of organic matter. Figure 2 It can also be observed from (b) and (d) that at the end of 28 days of composting, the OM degradation rates of Examples 2, 3, and 4 were all higher than those of Comparative Example 3. Compared with Comparative Example 3 treated with only 0.30 mol / kg KH2PO4, the OM degradation rates of Examples 2, 3, and 4 were increased by 43.1%, 36.2%, and 39.7%, respectively.

[0064] Figure 3 NH4 in each group during composting + -N content change chart. Figure 3 As shown in (a), at the end of 42 days of composting, the NH4 + -N content is lower than that of Comparative Example 1 and Comparative Example 2, while only 0.25 mol / kg KH2PO4 is added to treat NH4 + -N content was the highest, which may be due to the fact that the addition of KH2PO4 made the pH value lower in the later stage of composting, inhibiting the NH4 + -N is converted to NH3; in addition, KH2PO4 can chemically adsorb NH4 + , which will lead to NH4 + -N fixation and accumulation during composting. Figure 3 (b) It was observed that from the 11th day of composting, only 0.30 mol / kg KH2PO4 was added to the NH4 + -N content gradually increased, all higher than that of Examples 2, 3, and 4. Based on the above analysis, it is found that the combined addition of steel slag helps to reduce NH4 + -N accumulation and promotion of its conversion, this is because the activity of nitrifying bacteria is enhanced, so that the accumulated NH4+-N is nitrified into nitrate nitrogen in time.

[0065] Figure 4 The NO3 of each group in the composting process - -N content change chart. Figure 4 As shown in (a), as the compost temperature decreases, the activity of nitrifying bacteria increases and they proliferate, promoting the production of NH4 + -N to NO3 - -N conversion, NO3 - -N content increased immediately. During the 28th to 35th day of composting, only 0.25 mol / kg KH2PO4 was added to treat NO3 in Comparative Example 2. - -N content was significantly lower than that of the comparative example 1 without any addition treatment (p < 0.05), which may be due to the accumulation of NH4+ -N inhibits the nitrification reaction to produce NO3 - -N; In addition, the low pH environment will inhibit the activity of ammonia oxidizing bacteria, limit the nitrification reaction and lead to the production of N2O. The final NO3 in Example 1 treated with 10% steel slag was - The -N content of the steel slag is significantly higher than that of the comparative examples 1 and 2, which can be attributed to the fact that the abundant alkaline oxides in the steel slag can absorb CO2 to form a bicarbonate buffer system, providing the required carbon source and alkalinity for the growth of autotrophic nitrifying bacteria; in addition, the rich Fe 2+ and Fe 3+ It can enhance the activity of ammonia monooxygenase and hydroxylamine oxidoreductase and promote the nitrification reaction. Figure 4 It can also be observed in (b) that compared with the comparative example 3 treated with only 0.30 mol / kg KH2PO4, the NO3 - The peak and final contents of -N were increased. Therefore, the combined addition of steel slag was helpful to promote the nitrification and nitrogen transformation of compost.

[0066] Figure 5 The HA content of each group changes during the composting process. Figure 5 As shown in (a), the HA content of each treatment increases continuously as the composting progresses until it stabilizes. This can be attributed to the continuous condensation of intermediate products to form complex and stable humic acid after the microorganisms decompose and utilize fulvic acid (FA) and non-humus components for growth and metabolism. At the end of composting, the HA contents of Comparative Examples 1, 2 and Example 1 were 31.79 g / kg, 27.47 g / kg and 35.18 g / kg, respectively. Unlike the inhibition of HA formation by adding only 0.25 mol / kg KH2PO4 to Comparative Example 2, the combined addition of steel slag has a synergistic effect on HA formation. In addition, Figure 5 It is also observed in (b) that compared with the comparative example 3 treated with only 0.30 mol / kg KH2PO4, the HA content at the end of the composting in Example 2, Example 3, and Example 4 increased by 20.3%, 13.4%, and 3.9%, respectively. This can be attributed to the fact that under the action of steel slag, the degradation of complex OM was effectively promoted, which led to an increase in the skeleton precursors required for HA formation. In addition, the abundant Fe 3+ Oxides, such as hematite and magnetite, can act as catalytic sites, helping to promote the transformation of precursor substances into dark polymers such as HA. Therefore, the combined addition of steel slag can help improve the compost humification efficiency and product quality.

[0067] Figure 6The following is a graph showing the changes in HA / FA in each group during the composting process. HA / FA is the ratio of humic acid to fulvic acid (FA). The higher the value, the higher the degree of humus polymerization and the maturity of the final product. Figure 6 As shown in (a) in the figure, with the degradation of FA and the condensation and aggregation of HA during the composting process, the HA / FA of all treatments showed an increasing trend. At the end of composting, the HA / FA of Example 1 was higher than that of Comparative Examples 1 and 2; however, the HA / FA of Comparative Example 2, which was treated with only 0.25 mol / kg KH2PO4, was the lowest, which may be due to the low pH of KH2PO4 and the easy release of high salt ions (such as PO4) by hydrolysis. 3- 、HPO4 2- or H2PO4 - ) inhibit the activity of bacteria or microbial communities, thereby limiting the condensation reaction of humus precursors (such as protein degradation products or glucosamines), making the humification efficiency of this treatment relatively low. The combined addition of steel slag can provide a stable composting microenvironment, which can promote unstable low-molecular-weight FA to participate in biological metabolism and gradually transform into more stable HA. In addition, Figure 6 The results of (b) show that, compared with the comparative example 3 treated with only 0.30 mol / kg KH2PO4, the HA / FA at the end of the composting in examples 2, 3, and 4 increased by 38.5%, 19.8%, and 17.5%, respectively. Therefore, the combined addition of steel slag can improve the humification of compost in an acidic environment and effectively increase the humus polymerization degree of the compost product.

Claims

1. A method for promoting the degradation and humification of organic matter in sludge composting, characterized in that: The steps include: (1) mixing sludge and straw to obtain a compost raw material, using the straw to adjust the carbon-nitrogen ratio and improve the fluffiness of the compost raw material, adding phosphate and steel slag to the compost raw material, and mixing them uniformly to obtain compost; (2) Fermenting the compost until it is fully decomposed to obtain organic fertilizer.

2. The method for promoting the degradation and humification of organic matter in sludge composting according to claim 1, characterized in that: In step (1), the fresh weight ratio of sludge to straw is 4-6:

1.

3. The method for promoting the degradation and humification of organic matter in sludge composting according to claim 1, characterized in that: In step (1), the amount of steel slag added is 5% to 10% of the dry mass of the composting raw material.

4. The method for promoting the degradation and humification of organic matter in sludge composting according to claim 1, characterized in that: In step (1), based on the dry weight of the compost raw material, the ratio of phosphate to compost raw material is 0.25-0.3 mol: 1 kg.

5. The method for promoting the degradation and humification of organic matter in sludge composting according to claim 1, characterized in that: In step (2), the fermentation method is aerobic fermentation with ventilation, and the fermentation time is 28-42 days. During the fermentation process, when the temperature is ≥45°C, the compost is turned over once every 3-4 days; when the temperature is <45°C, the compost is turned over once every 7 days.

6. The method for promoting the degradation and humification of organic matter in sludge composting according to claim 1, characterized in that: In step (2), the moisture content of the compost before fermentation is 55-65%.

7. The method for promoting the degradation and humification of organic matter in sludge composting according to claim 1, characterized in that: In step (2), during fermentation, the aeration intensity is based on the dry mass of the compost raw material, and the gas flow rate is 0.35-0.60 L kg -1 ·min -1 .

8. The method for promoting the degradation and humification of organic matter in sludge composting according to claim 1, characterized in that: In step (1), the straw is derived from at least one of wheat, corn and rice, and the straw particle size is 0.5-1.0 cm.

9. The method for promoting the degradation and humification of organic matter in sludge composting according to claim 1, characterized in that: The steel slag contains CaO, Fe2O3, SiO2, MgO, Al2O3 and MnO, and the phosphate contains hydrogen phosphate ions.

10. An organic fertilizer prepared by the method for promoting degradation and humification of organic matter in sludge composting according to any one of claims 1 to 9.

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