Effects of new acidification methods on nitrogen conversion during agricultural waste composting
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摘要: 酸化是减少堆肥过程中氮素损失的有效手段, 而传统无机酸酸化具有成本高、二次污染严重等缺点, 探究新型酸化工艺对减少堆肥过程中的养分流失和环境污染具有重要意义。本研究以食品残渣(果渣、豆渣)为基质, 通过乳酸菌厌氧发酵制备了一种富含乳酸(70 mmol∙L−1)和乳酸菌(106 cfu∙mL−1)的酸性调理剂, 用于农业废弃物(猪粪、小麦秸秆)酸化堆肥试验,设置两种新型酸化方式处理: 添加30%酸性调理剂处理(MA)和添加3%酸性调理剂的厌氧自酸化处理(LA), 同时以不加酸处理(CK) 添加硫酸处理(SA)作为对照。通过分析堆肥过程中理化性质和氮素形态等变化发现, 3种酸化方式的堆肥产品均达到腐熟标准(发芽指数>80), 其中MA处理的腐熟程度最优(发芽指数=117.8%); MA、SA、LA处理的总氮损失较CK分别显著降低14.0%、25.6%、22.2% (P<0.05), 其中NH3挥发量较CK分别显著减少26.0%、36.5%、54.9% (P<0.05); 酸化处理提高了NH4+含量, 促进了硝化过程, 又间接增强了反硝化过程, MA、LA处理显著减少23.1%、69.4%的N2O排放(P<0.05), 而SA处理抑制了N2O的还原, 增加18.3%的N2O的排放; 同时MA、SA、LA处理总环境代价相较于CK分别显著降低34.5%、11.0%、55.9% (P<0.05), 且MA、LA每减少1 kg活性氮排放分别需要18.4元、0.9元, 远低于SA处理(91.26元)。综上所述, MA、LA处理可作为降低堆肥过程中氮损失的可行方法, 本研究为堆肥酸化保氮技术提供了理论依据。Abstract: Aerobic composting is a common way to treat agricultural waste. However, a large amount of nitrogen is lost during composting, which has become an important problem in agricultural waste composting. Material acidification is an effective method to reduce nitrogen loss during composting process, while conventional acidification using inorganic acids has disadvantages such as high cost and secondary pollution. Optimizing the acidification process is of great significance for reducingnutrient loss and environmental pollution during composting process. In this study, an acid conditioner was prepared by anaerobic fermentation of lactic acid bacteria with food residues (fruit dregs and soybean dregs) as substrate, which was rich in lactic acid (70 mmol·L −1) and lactic acid bacteria (106 cfu·mL −1). Two acidizing methods were designed by using the acid conditioner:1)a certain amount of acid conditioner (30%, w/w) was added directly to acidify the material (MA); 2) a small amount of acid conditioner (3%, w/w) was added and there was no forced ventilation for the first 3 days of composting to enable the lactic acid bacteria in acidic conditioners to function, lactic acid bacteria can produce lactic acid to achieve self-acidification of compost materials (LA). Meanwhile, we set up the experimental treatment of adding sulfuric acid (SA) and no acidification (CK) respectively. The changes of physicochemical properties (temperature, pH, EC, GI, OM) and nitrogen forms (NH3, N2O, Org-N, NH4+, NO2−, NO3−) during the composting process of agricultural waste were analyzed. The results showed that the compost products treated by three acidification methods all reached the standard of maturity (GI>80%), and the MA treatment was the best (GI=117.8%). The duration of the thermophilic phase (>50 ℃) of CK, MA, SA and LA was 10, 10, 9 and 7 days, respectively, all of which reached the harmless standard (>50 ℃ at least 7 days). The TN loss of MA, SA and LA decreased by 14.0%, 25.6% and 22.2%, and NH3 volatilization decreased by 26.0%, 36.5% and 54.9% compared with CK, respectively. Acidification treatment increased the NH4+ content, promoted nitrification, and indirectly enhanced denitrification. MA and LA treatments reduced N2O emission by 23.1% and 69.4%, while SA treatment inhibited N2O reduction and increased N2O emission by 18.3%. The ReCiPe evaluation method was also used to evaluate the total environmental burden of the different acidification treatments. The total environmental burden of MA, SA and LA decreased by 34.5%, 11.0% and 55.9% compared with CK, respectively, indicating that acidification is an effective way to reduce the environmental burden of composting. By comparing the economic benefits of the three acidizing methods, it is found that the costs of MA and LA treatments are 18.4 yuan and 0.87 yuan respectively for reducing the emission of 1 kg active N, which is far lower than that of SA treatment 91.3 yuan. These results indicate that the MA and LA acidification modes are economically feasible. In conclusion, MA and LA treatments can be a feasible method to reduce nitrogen loss during composting process. This study provides a new theoretical basis for composting acidification and nitrogen conservation technology, as well as a new scheme for the collaborative treatment of multi-source waste.
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Key words:
- Composting /
- Agricultural waste /
- Nitrogen transformation /
- Nitrogen loss /
- Acidification
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图 1 不同酸化方式下堆肥过程中的理化性质变化
CK: 对照; MA: 添加酸性调理剂处理; SA: 添加硫酸处理; LA:添加乳酸菌的自我酸化处理。CK: control; MA: treatment with acid conditioner; SA: treatment with sulphuric acid; LA: self-acidification treatment with lactic acid bacteria.
Figure 1. Variation of physicochemical properties during composting under different acidification methods
图 2 不同酸化方式下堆肥过程中的氮素形态的变化
CK: 对照; MA: 添加酸性调理剂处理; SA: 添加硫酸处理; LA:添加乳酸菌的自我酸化处理。CK: control; MA: treatment with acid conditioner; SA: treatment with sulphuric acid; LA: self-acidification treatment with lactic acid bacteria.
Figure 2. Variation of N forms during composting under different acidification methods
图 3 不同酸化方式下堆肥过程中的NH3与N2O的排放
CK: 对照; MA: 添加酸性调理剂处理; SA: 添加硫酸处理; LA:添加乳酸菌的自我酸化处理。CK: control; MA: treatment with acid conditioner; SA: treatment with sulphuric acid; LA: self-acidification treatment with lactic acid bacteria.
Figure 3. Emission of NH3 and N2O in composting process under different acidification methods
图 4 不同酸化处理方式堆肥过程不同氮素损失形式的占比变化
CK: 对照; MA: 添加酸性调理剂处理; SA: 添加硫酸处理; LA:添加乳酸菌的自我酸化处理。CK: control; MA: treatment with acid conditioner; SA: treatment with sulphuric acid; LA: self-acidification treatment with lactic acid bacteria.
Figure 4. Variation in the proportion of different forms of nitrogen loss during composting under different acidification treatments
图 5 不同酸化方式的环境代价与经济效益
CK: 对照; MA: 添加酸性调理剂处理; SA: 添加硫酸处理; LA:添加乳酸菌的自我酸化处理。CK: control; MA: treatment with acid conditioner; SA: treatment with sulphuric acid; LA: self-acidification treatment with lactic acid bacteria.
Figure 5. Environmental impact and economic benefits of different acidification methods
表 1 试验材料的理化性状
Table 1. Physical and chemical properties of experimental materials
试验材料
Materials含水率
Moisture content/%有机质a
Organic matter/%总氮a
Total nitrogen/%NH4+含量a
NH4+ content/( g·kg −1)pH值
pH value电导率
Electrical conductivity/
(mS·cm −1 )猪粪
Pig manure70.39±0.58 44.10±0.52 2.90±0.04 12.38±1.29 7.83±0.09 7.70±0.42 小麦秸秆
Chicken manure12.48±0.49 89.09±0.28 0.54±0.03 0.28±0.05 7.48±0.05 3.82±0.07 苹果渣
Apple pomace82.81±0.58 98.04±0.14 0.81±0.02 — 5.67±0.09 — 豆渣
Bean dregs79.95±4.14 95.73±0.07 2.64±0.01 — 7.07±0.04 — “a”: 基于物料干重; “—”: 表示未检测。“a”: based on dry weight of material; “—”: not measured; (n=3). 表 2 酸化剂及活性氮气体(NH3、N2O)的环境代价
Table 2. Environmental burden of acidifiers and reactive nitrogen gases (NH3, N2O)
影响类型
Impact categories酸性调理剂
Acid conditioner/kg硫酸
Sulfuric acid/kgNH3/kg N2O/kg 食品残渣处理
Food residue disposal/kg人类健康 Human health 622 174 676 920 15.8 生态系统 Ecological system 46.2 11 197 77.5 3.34 资源 Resources 2.71 0.434 0 2.37 0.06 总影响 Total impact 671 186 874 1000 19.2 环境代价单位为mPt, 表示单位排放因子。The unit of environmental burden is mPt, indicating unit emission factor. 表 3 酸性剂制备经济成本
Table 3. Acid preparation economic cost
yuan∙kg−1 酸试剂类型
Acid type材料费
Material cost电费
Electricity cost人工费
Labor cost总成本
Total cost酸性调理剂
Acid conditioner0.003 0.017 0.017 0.036 硫酸
Sulfuric acid— — — 48.9 硫酸为浓度98%的工业硫酸。Sulfuric acid is 98% industrial sulfuric acid. 表 4 酸性调理剂制备过程中酸度变化
Table 4. Experimental treatment and initial physicochemical properties
时间
Time (h)C(H+) (mol∙L−1) 乳酸含量
Lactic acid content
( mmol∙L−1)乳酸菌活菌数
Lactic acid bacteria
count (106 cfu∙mL−1)pH 0 0.01±0.00 2.30±0.41 0.34±0.06 4.53±0.03 12 0.04±0.00 55.39±0.82 24.00±5.89 3.56±0.04 24 0.05±0.01 62.39±1.23 17.00±0.41 3.44±0.03 48 0.08±0.01 64.45±4.12 4.63±3.68 3.33±0.02 72 0.09±0.01 70.21±16.13 3.67±6.02 3.30±0.05 -
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