产酸沼渣再利用稻秸两级联合产酸工艺研究

秸秆厌氧产挥发性脂肪酸(Volatile fatty acids,VFAs)工艺可生产具有较高经济价值的混合短链脂肪酸,但存在发酵周期短、秸秆降解率低等不足。为了提高VFAs产率和秸秆利用率,对产酸沼渣开展了二次产酸利用试验。将秸秆在3种预处理、3种产酸温度得到的产酸沼渣,统一在35℃进行二次产酸发酵,以考察各预处理组的二次产酸效果。结果表明,各组在二次产酸时均能获得更为稳定和适宜的pH值,水热组和2%HCl组在二次产酸时均有更佳产酸表现,1%Ca(OH)_2组在两级均采用35℃温度时获最大产酸量。采用两级联合产酸工艺,可将1%Ca(OH)_2预处理组的0.07～0.20 g/g的一次产酸率提高至0.27～0.38 g/g的总固体产酸率。以初始100 g原秸秆计算,1%Ca(OH)_2、35℃发酵时一次产酸和二次产酸量分别为12.24 g和11.69 g,两级联合的总产酸量为23.93 g,采用两级联合产酸比一次产酸的产酸量提高了95.5%,二次产酸使得木质纤维素各组分降解利用更为充分。     

Use of digestate as an alternative to mineral fertilizer: effects on growth and crop quality

Nowadays, the recycling of organic wastes represents a key factor for improving soil and crop quality with socio-economic and environmental benefits. In recent years, the production of digestate significantly increased with a crescent need to be sustainable disposal. The use of digestate as soil amendment has been widely studied but few researches evaluated the digestate effects on crop quality. Since it has been proven that digestate increased soil fertility, we hypothesized that it could increase crop quality as organic fertilizers do. To verify this hypothesis, we analyzed the effects of two digestates on Cucumber quality. Cucumber was chosen because it is an important old crop used worldwide as fresh food, and in cosmetic and pharmaceutic industries. Results showed that digestates increased its content of phenols and flavonoids with antioxidant activity. Neohesperidine and hesperitin with well-known antioxidant, anti-inflammatory and anti-carcinogenic properties as well as naringin and narirutin with the power of reducing the risk of atherosclerosis and cardiovascular complications were manifested only in digestate amended cucumbers. These results highlighted the potentiality of digestates not only as crop growth promoter but also as phytochemical inducers representing a good option for the production of high-quality food with reduced chemical mineral fertilizer inputs.     

Reduction of N2O emissions by DMPP depends on the interactions of nitrogen sources (digestate vs. urea) with soil properties

The inhibition of nitrification by mixing nitrification inhibitors (NI) with fertilizers is emerging as an effective method to reduce fertilizer-induced nitrous oxide (N₂O) emissions.  The additive 3,4-dimethylpyrazole phosphate (DMPP) apparently inhibits ammonia oxidizing bacteria (AOB) more than ammonia oxidizing archaea (AOA), which dominate the nitrification in alkaline and acid soil, respectively.  However, the efficacy of DMPP in terms of nitrogen sources interacting with soil properties remains unclear.  We therefore conducted a microcosm experiment using three typical Chinese agricultural soils with contrasting pH values (fluvo-aquic soil, black soil and red soil), which were fertilized with either digestate or urea in conjunction with a range of DMPP concentrations.  In the alkaline fluvo-aquic soil, fertilization with either urea or digestate induced a peak in N₂O emission (60 μg N kg^–1 d^–1) coinciding with the rapid nitrification within 3 d following fertilization.  DMPP almost eliminated this peak in N₂O emission, reducing it by nearly 90%, despite the fact that the nitrification rate was only reduced by 50%.  In the acid black soil, only the digestate induced an N₂O emission that increased gradually, reaching its maximum (20 μg N kg^–1 d^–1) after 5–7 d.  The nitrification rate and N₂O emission were both marginally reduced by DMPP in the black soil, and the N₂O yield (N₂O-N per NO₂^–+NO₃^–-N produced) was exceptionally high at 3.5%, suggesting that the digestate induced heterotrophic denitrification.  In the acid red soil, the N₂O emission spiked in the digestate and urea treatments at 50 and 10 μg N kg^–1 d^–1, respectively, and DMPP reduced the rates substantially by nearly 70%.  Compared with 0.5% DMPP, the higher concentrations of DMPP (1.0 to 1.5%) did not exert a significantly (P<0.05) better inhibition effect on the N₂O emissions in these soils (either with digestate or urea).  This study highlights the importance of matching the nitrogen sources, soil properties and NIs to achieve a high efficiency of N₂O emission reduction.     

The survival of pathogenic bacteria and plant growth promoting bacteria during mesophilic anaerobic digestion in full‐scale biogas plants

The introduction of biogas plants is a promising way to recycle organic wastes with renewable energy production and reducing greenhouse gas. Application of anaerobic digestate as a fertilizer reduces the consumption of chemical fertilizers. In this study, the survival of pathogenic bacteria and plant growth promoting bacteria (PGPB) in two full‐scale biogas plants operated at mesophilic condition were investigated. Feedstock and anaerobic digestate samples were collected from biogas plants and bacteria load in samples were detected using standard dilution plate method. Pathogenic bacteria were reduced to not detected level through mesophilic digestion tank except for Campylobacter. However, it could be reduced by 98.7% through a sterilization tank. Bacillus was detected at 8.00 and 7.81 log₁₀ CFU/g dry matter in anaerobic digestates, and it was also resistant to sterilization tank. Bacillus spp. is considered to be the safe bacteria that hold remarkable abilities for promoting plant growth. The results showed that treatment at biogas plants is effective to reduce pathogenic bacteria in dairy manure, and sterilization could further reduce the sanitary risks of pathogenic bacteria relating to anaerobic digestate application. Anaerobic digestates could also be utilized as bio‐fertilizer as the high load of plant growth promoting bacteria.     

沼肥种类及不同施氮量对芹菜品质影响研究

沼渣沼液作为厌氧发酵后的产物,因其量大消纳难,已逐渐成为限制沼气工程发展的制约因素。因此研究沼渣沼液作为肥料施用于农田对作物生长发育的影响具有重要的意义。该研究分别以猪粪厌氧发酵剩余物和秸秆牛粪厌氧发酵剩余物作为肥料,设置不同氮浓度施用水平(0,8.5,17,34,68 gTN·m-2 y-1),具体以沼渣作为底肥、沼液作为追肥的施肥方式,实际施用量以总氮(TN)作为标定指标,沼渣沼液施用比例为1∶2。研究结果表明:不同来源厌氧发酵剩余物对芹菜品质的影响效果不同;中低浓度氮条件下的猪粪沼肥和高氮浓度条件下的秸秆牛粪沼肥更有利于芹菜的营养物质的积累。     

Composting of the Solid Phase of Digestate from Biogas Production: Optimization of the Moisture,C/N Ratio,and pH Conditions

The management of biodegradable wastes is increasing, including the use of waste as a source of energy. Anaerobic digestion involves organic-matter decomposition under anoxic conditions by a microbial consortium, obtaining a source of renewable energy (biogas), mainly constituted of a mixture of carbon dioxide (CO₂, 25–45 percent), methane (CH₄, 55–75 percent), and the digested substrate (digestate). The direct application of digestate into agricultural soils presents several problems. These include agronomic (low concentration of nutrients, high salinity, etc.), economic (cost of transport and handling), and environmental issues (gaseous emissions, nutrient leaching, and pathogen spread). However, it is possible to obtain quality compost from the solid fraction of digestate, and the compost obtained can have good properties for use as container growing medium or for crop production. In this work, an optimized procedure has been developed for composting the solid phase of a digestate obtained from a continuous, anaerobic codigestion of cattle slurry with 84 percent of cattle manure, 7.4 percent of a mixture of maize/silage, and 8.6 percent of peach-juice pulp (fresh-mass basis). The experiment was designed to optimize pH, carbon (C) / nitrogen (N) ratio, and moisture values in order to maximize self-heating activity, using Dewar self-heating tests. A factorial optimization of moisture and C/N ratio was carried out. In the best moisture-C/N ratio treatment, pH optimization was also developed. To predict the optimum conditions of the studied residue related to the increase of temperature per dry matter, a multiple correlation analysis based on moisture, C/N ratio, and pH was developed, which explained 80 percent of the variance in this experiment.     

吹脱与鸟粪石沉淀组合工艺处理中温厌氧发酵沼液研究

利用吹脱+鸟粪石沉淀(MAP)组合工艺处理中温厌氧发酵沼液。研究发现沼液吹脱的最佳工艺参数为:p H值为10,吹脱时间8 h,气液比2 400,并添加填料,此时沼液中氨氮去除率在90%左右。吹脱后的沼液p H值在9.2左右,在MAP沉淀法的适宜p H值附近,不需再进行p H值调节,可节约药剂成本。经MAP沉淀处理后的沼液出水氨氮和总磷去除率分别达到了95%和80%。COD和SS去除率分别在40%和32%左右。MAP沉淀出水的p H值在8.3左右,可满足生化处理的进水要求。同时,MAP沉淀处理后的出水C/N比大大提升,从0.7上升到了10,有利于后续生化系统的进一步处理。该工艺既可使沼液得到净化处理,又可回收其中的营养物质。     

Forage types and origin of manure in codigestion affect methane yield and microbial community structure

In farm‐scale biogas systems, different kinds of manure are the most important substrate for anaerobic digestion, but result in low biogas yields. Biogas production can be increased by complementing the manure with forage crops, in codigestion. The aim of this study was to evaluate grass‐clover (GCS) and whole‐crop barley silages (WCB) in codigestion with manure from organic and conventional dairy production systems on biogas production, microbial community, degree of degradation and gas quality at different organic loading rates by addition of soya bean meal and wheat grain, which are rich in protein and starch. Four continuous stirred anaerobic laboratory‐scale reactors were used, and the codigestion resulted in additive effects on biogas production, but no synergistic effects. The highest biogas yield was obtained in reactors receiving WCB independently of manure types, for both experiments (7,416 ml/day and 10,978 ml/day respectively). The degradation efficiency, measured as the reduction in volatile solids was, on average, six percentage units higher in the reactors receiving manure from conventional compared with organic dairy cows, probably because of a higher concentration of undigested fibre and proteins in conventional cow manure. Microbiological analysis by illumina sequencing illustrated low impact of both manure types on the reactor community and only small differences between the reactors receiving GCS and WCB. However, addition of soya bean meal and wheat grain changed the community in all reactors. The ratio between Firmicutes and Bacteroidetes was comparably higher in reactors having the highest gas production and methane yield.     

三种湿地植物厌氧发酵产甲烷特性及产物稳定性研究

为研究湿地植物能源化利用潜力,采用全自动甲烷潜力测试系统对不同温度下三种湿地植物厌氧发酵产甲烷特性进行评价,并对产甲烷过程及发酵产物稳定性进行模拟和分析。结果表明:在30 d发酵周期内,中温(37℃)下三种湿地植物巨菌草、狐尾藻和水葫芦累积甲烷产量分别达166.5、159.4、236.9 m L·g~(-1)VS,分别比常温(25℃)提高了29.6%、18.3%和39.9%(P0.01),且中温发酵产气速度更快,发酵周期更短,挥发性固体(VS)去除率更高;采用热重-示差扫描量热法(TG-DSC)对发酵产物稳定性进行分析,TG曲线呈现三个明显失重过程(100℃,250~350℃及400~600℃),全发酵周期总失重率逐渐降低,DSC曲线有两个明显的放热峰,低温区(300℃)放热强度逐渐降低,高温区(400~550℃)狐尾藻峰强度逐渐降低,巨菌草和水葫芦逐渐增加,且峰值右移,表明有机物逐步降解,发酵产物稳定性增加;采用Cheynoweth方程对巨菌草、狐尾藻和水葫芦中温发酵产气过程进行拟合,模型相关系数均大于0.95,产气预测值和实测值差异比分别为1.98%、0.82%和0.32%(P0.05)。研究表明厌氧发酵制甲烷是湿地植物资源化利用的有效途径,有利于解决人工湿地技术二次污染问题。     

沼液深度处理技术研究与应用现状

针对我国大中型沼气工程沼液产生量巨大,沼液还田无法广泛实施,而直接排放又会造成环境污染的问题,通过对大量的文献资料和研究结果进行分析,得出沼液处理的2种主要途径:①降解其中的污染物使其能够达标排放或安全回用,②浓缩并回收沼液中营养物,使沼液体积减量化。建议今后的研究应选择适合的工艺,克服技术难题,以沼液高效利用为目标,以防止环境污染为前提,探索低运行费用的沼液处理方法。