Seaweed biomass as a source of energy

Production of biogas from seaweed is a novel idea for coastal people. Present research work deals with anaerobic digestion of marine algae (Sargassum) at room temperature. Comparisons are made between biogas from seaweed, water hyacinth and cowdung; the NPK ratios are also compared. Bioconversion of seaweed to methane has the potential of supplying a significant portion of the current demand for natural gas, especially in coastal areas. The present investigation deals with the yield of biogas in anaerobic digestion of marine algae.     

皇竹草厌氧发酵特性及稀土元素溶出研究

为探讨稀土尾矿区修复用皇竹草的厌氧发酵特性和发酵过程稀土元素溶出情况,开展不同发酵浓度（总固体浓度分别为2%、4%、6%、8%、10%）的中温（37±1℃）批式厌氧发酵实验。结果表明,总固体（TS）浓度为4%条件下皇竹草产甲烷性能最佳,日产甲烷率和累积产甲烷率分别为25.56 mL/g和197.33 mL/g。采用修正Gompertz方程能较好地模拟不同TS下皇竹草发酵累积产甲烷率的变化。分析发酵液中稀土元素浓度变化,结果表明,皇竹草内的稀土元素在厌氧发酵过程中只发生小部分溶出,主要包括La、Ce、Nd、Sc、Y等,各处理发酵液中稀土元素浓度并未超出文献报道的抑制浓度。相关性分析结果表明,稀土元素溶出率与发酵体系的TS浓度、化学需氧量（COD）呈负相关,与pH呈正相关。研究可为稀土矿区皇竹草沼气工程应用和发酵剩余物的肥料化利用提供指导。     

Hydrogen production from (cane-molasses) stillage by citrobacter freundii and its use in improving methanogenesis

Citrobacter freundii is a facultatively anaerobic fermentative organism capable of H₂ production from sugars and lactate. A locally isolated strain of C. freundii was shown to be capable of H₂ production on an equimolar basis (i.e. 1:1.2 mol/mol) from glucose. It was also found capable of H₂ production from cane-molasses stillage (having BOD₅ of 54 kg m⁻³) at a rate of 1.2 m³ (m³waste) ¹ day⁻¹. This was tested on various scales, ranging from 0.06 to 100 1 and was found to be consistent over these variations in scale. Simultaneously, the BOD₅ value was reduced at a rate of 5.4 kg (m³waste)⁻¹ day⁻¹.

One of the uses of the evolved H₂ was as feed for an anaerobic digestor containing (untreated) cane-molasses stillage as substrate. With this arrangement, the methanogenesis was enhanced by way of increased production of methane (i.e. rise in volumetric methane content of the evolved gas), while added H₂ vanished totally from the digestor. The question of whether microbially produced H₂ can be used more profitably in microbial utilization of H₂ for energy production is considered in detail.     

Monitoring of methanogen density using near-infrared spectroscopy

In order to improve anaerobic digester productivity, raising the microbial mass in the reactor and the prediction of changes in the biomass is required. In this study the possibilities for using near-infrared spectroscopy (NIR) to monitor methanogen density in a biogas process was examined. Methane production from H₂ and CO₂ was carried out with acclimated-methanogens with fed-batch substrate gas (H₂/CO₂, 80:20 v/v) at pH 7 and 37°C. The cells of the methanogens were washed and dried, and then original NIR spectra for predicting methanogen density were recorded. The specified absorption spectra were collected and examined. As a result, absorption spectrum peaks were found to be predominantly based on alpha proteins and lipids mainly from the cytoplasm and cell membranes of the methanogens. Furthermore, NIR was used to monitor the methane fermentation system using acetic acid as substrate. The responses from NIR analysis were correlated to methanogen density of fermentation broth by partial least-squares regressions. The correlation coefficient (R), model standard error of calibration (SEC) and standard error of prediction (SEP) of the test calibration for methanogen density were 0.99, 0.14 gl⁻¹ and 0.55 gl⁻¹, respectively. For volatile fatty acids (acetic acid) R, SEC and SEP were 0.99, 0.36 gl⁻¹ and 0.63 gl⁻¹, respectively. The results indicated that within the range of the density of methanogens and the concentration of acetic acid used in this study, it was possible to monitor the important variables of methanogen density and acetate concentration simultaneously in pure substrate-fed anaerobic digesters.     

Two-stage anaerobic dry digestion of blue mussel and reed

Blue mussels and reeds were explored as a new biomass type in the Kalmar County of Sweden to improve renewable transport fuel production in the form of biogas. Anaerobic digestion of blue mussels and reeds was performed at a laboratory-scale to evaluate biogas production in a two-stage dry digestion system. The two-stage system consisted of a leach bed reactor and an upflow anaerobic sludge blanket (UASB) reactor. The two-stage system was efficient for the digestion of blue mussels, including shells, and a methane yield of 0.33 m³/kg volatile solids (VS) was obtained. The meat fraction of blue mussels was easily solubilised in the leach bed reactor and the soluble organic materials were rapidly converted in the UASB reactor from which 68% of the methane was produced. However, the digestion of mussels including shells gave low production capacity, which may result in a less economically viable biogas process. A low methane potential, 0.22 m³/kg VS, was obtained in the anaerobic two-stage digestion of reeds after 107 days; however, it was comparable to similar types of biomass, such as straw. About 80% of the methane was produced in the leach bed reactor. Hence, only a leach bed reactor (dry digestion) may be needed to digest reed. The two-stage anaerobic digestion of blue mussels and reeds resulted in an energy potential of 16.6 and 10.7 GWh/year, respectively, from the estimated harvest amounts. Two-stage anaerobic digestion of new organic materials such as blue mussels and reeds can be a promising biomass resource as land-based biomass start to be limited and conflict with food resources can be avoided.     

Evaluation of biogas production from different biomass wastes with/without hydrothermal pretreatment

Municipal biomass waste is regarded as new available energy source, although it could cause serious environmental pollution. Generally, biogas recovery by anaerobic digestion was seen as an ideal way to treat biomass waste. Different types of biomass waste have different biogas production potential. In this paper, cow manure, pig manure, municipal sewage sludge, fruit/vegetable waste, and food waste were chosen as typical municipal biomass waste. In addition, hydrothermal pretreatment was used to accelerate digestion and increase biogas production. Biochemical methane potential (BMP) test was used to evaluate biogas production for raw biomass and hydrothermal treated waste. Raw materials of fruit/vegetable and food waste show higher methane production than that of cow manure, pig manure, and municipal sewage sludge. After hydrothermal pretreatment at typical condition (170 °C at 1 h), the biogas production of pig manure, cow manure, fruit/vegetable waste, and municipal sewage sludge increased by 7.8, 13.3, 18.5, and 67.8% respectively. While, for treated food waste, the biogas decrease by 3.4%. The methane yield of pig manure, fruit/vegetable waste, and municipal sewage sludge increased by 14.6, 16.1, and 65.8%, respectively. While, for treated cow manure and food waste, the methane decrease by 6.9% and 7.5%.     

Overview analysis of bioenergy from livestock manure management in Taiwan

The emissions of greenhouse gases (GHGs) from the livestock manure are becoming significant energy and environmental issues in Taiwan. However, the waste management (i.e., anaerobic digestion) can produce the biogas associated with its composition mostly consisting of methane (CH₄), which is now considered as a renewable energy with emphasis on electricity generation and other energy uses. The objective of this paper was to present an overview analysis of biogas-to-bioenergy in Taiwan, which included five elements: current status of biogas sources and their energy utilizations, potential of biogas (methane) generation from livestock manure management, governmental regulations and policies for promoting biogas, benefits of GHGs (i.e., methane) emission reduction, and research and development status of utilizing livestock manure for biofuel production. In the study, using the livestock population data surveyed by the Council of Agriculture (Taiwan) and the emission factors recommended by the Intergovernmental Panel on Climate Change (IPCC), the potential of methane generation from livestock manure management in Taiwan during the period of 1995–2007 has been estimated to range from 36 to 56 Gg year⁻¹, indicating that the biogas (methane) from swine and dairy cattle is abundant. Based on the characteristics of swine manure, the maximum potential of methane generation could reach to around 400 Gg year⁻¹. With a practical basis of the total swine population (around 4300 thousand heads) from the farm scale of over 1000 heads, a preliminary analysis showed the following benefits: methane reduction of 21.5 Gg year⁻¹, electricity generation of 7.2 × 10⁷ kW-h year⁻¹, equivalent electricity charge saving of 7.2 × 10⁶ US$ year⁻¹, and equivalent carbon dioxide mitigation of 500 Gg year⁻¹.     

Semi-continuous co-digestion of solid slaughterhouse waste, manure, and fruit and vegetable waste

The potential of semi-continuous mesophilic anaerobic digestion (AD) for the treatment of solid slaughterhouse waste, fruit-vegetable wastes, and manure in a co-digestion process has been experimentally evaluated. A study was made at laboratory scale using four 2 L reactors working semi-continuously at 35 °C. The effect of the organic loading rate (OLR) was initially examined (using equal proportion of the three components on a volatile solids, VS, basis). Anaerobic co-digestion with OLRs in the range 0.3–1.3 kg VS m⁻³ d⁻¹ resulted in methane yields of 0.3 m³ kg⁻¹ VS added, with a methane content in the biogas of 54–56%. However, at a further increased loading, the biogas production decreased and there was a reduction in the methane yield indicating organic overload or insufficient buffering capacity in the digester.In the second part of the investigation, co-digestion was studied in a mixture experiment using 10 different feed compositions. The digestion of mixed substrates was in all cases better than that of the pure substrates, with the exception of the mixture of equal amounts of (VS/VS) solid cattle–swine slaughterhouse waste (SCSSW) with fruit and vegetable waste (FVW). For all other mixtures, the steady-state biogas production for the mixture was in the range 1.1–1.6 L d⁻¹, with a methane content of 50–57% after 60 days of operation. The methane yields were in the range 0.27–0.35 m³ kg⁻¹ VS added and VS reductions of more than 50% and up to 67% were obtained.     

二价铁离子对糖蜜酒精废水厌氧发酵的影响

提高糖蜜酒精废水的厌氧发酵效率,实现其资源化再利用,本文研究了添加一定量Fe²⁺ 对糖蜜酒精废水厌氧发酵处理过程的影响。结果表明：添加Fe²⁺后发酵液中SO₄²⁻ 的去除率由77.12%提高至90.79%;COD去除率由57.34%提高至81.14%;累积沼气产量由386 mL•g⁻¹ VS提高至475 mL•g⁻¹ VS;产气周期由29天缩短为26天;其氧化还原电位（ORP）升高,pH值降低。     

Energy optimisation from co-digested waste using a two-phase process to generate hydrogen and methane

The total energy produced from co-digested food waste and sewage sludge was compared for single phase mesophilic anaerobic digestion producing methane and two-phase hydrogen production followed by methane production. Both single and two-phase reactors were operated at close to optimum conditions. The single phase methaniser had a methane yield of 0.48 m³ methane/kg VS destroyed. The two-phase system had a hydrogen yield of 0.13 m³ hydrogen/kg VS destroyed, and a methane yield of 0.67 m³ methane/kg VS destroyed. Introduction of a hydrogen producing, pre-treatment phase increased the overall VS destruction 69-89%, however the total energy yield decreased by 13.4% due to the low hydrogen yield obtained in the first stage. The release of ammonia in the hydrogeniser was low and so with less alkalinity available, pH control was necessary. It was much higher in the methaniser and adequate to buffer any pH change. This also ensures more nitrogen in the digestate to enhance its value for recycling. The two-stage process is an attractive option where solids destruction is an important consideration but further optimisation of the hydrogen production stage is still required.     

Degradation and transformation of extracellular polymeric substances (EPS) and dissolved organic matters (DOM) during two-stage anaerobic digestion with waste sludge

Two-stage anaerobic digestion of heating pretreated waste sludge was conducted to evaluate the ability of biogas production and the changing of soluble chemical oxygen demand (SCOD), carbohydrate and protein in extracellular polymeric substances (EPS) and dissolved organic matters (DOM). The changes of volatile fatty acids (VFAs) and NH₄⁺-N were analyzed. The duration of hydrogen production was 1 day and that of the methane production was 10 days. The highest hydrogen yield of 5.5 ml H₂/g VSS and methane yield of 62.1 ml CH₄/g VSS were obtained. The VSS removal of two-stage anaerobic digestion was 40%. Carbohydrate was the main substrate for hydrogen production and protein in DOM was the main sources for methane production. The structural and functional properties of organics in DOM were evaluated by using three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy with fluorescence regional integration (FRI) analysis. Moreover, the humification index (HIX) and the fluorescence index (FI) were used to evaluate the humification and DOM source.     

Investigation of anaerobic digestion of Chlorella sp. and Micractinium sp. grown in high-nitrogen wastewater and their co-digestion with waste activated sludge

This study investigated two wildtype green algae, Micractinium sp. and Chlorella sp., for their growth in high nitrogen wastewater (mixture of sludge centrate and primary effluent wastewater) and subsequent anaerobic digestion under mesophilic conditions. Extraction and analysis of extracellular polymeric substances (EPS) in both algal species during cultivation showed that Micractinium generated larger quantity of EPS-proteins than Chlorella. Anaerobic digestion of harvested algae showed the opposite trend that Chlorella allowed a higher CH₄ yield on the volatile solids fed the digester (VS_fed) of 230 dm³ kg⁻¹ than Micractinium (209 dm³ kg⁻¹). These results suggested that different growth patterns of two types of algae, with different quantity of EPS expressed, affected anaerobic digestibility and biogas yield. Co-digestion of algae with waste activated sludge (WAS) improved the volatile solids reduction, hydrolysis efficiency as well as the biogas yields of algae.     

Agronomic characteristics of US 72-1153 energycane for biomass

Biomass production and plant quality vary between plant species and morphological components of a plant. The purpose of this two-part experiment was (1) to study the influence of energycane [Saccharum sp. (L.) ‘US 72-1153’] harvest treatments (6) on dry biomass yield and (2) monitor changes in quantity and quality of plant components with increased plant height. Treatments for Part 1 determined the influence of plant height when harvested at 1.2, 2.5, and 3.7 m, mature stage in October (4.9 m, in flower), mature stage in December (4.9 m, in flower), and additional treatment harvested in October, which received half the total N (168 kg ha⁻¹) on dry biomass yield from 1986 to 1989. Part 2 treatments were to monitor changes in quantity and quality (crude protein and in vitro organic matter digestion) of plant components (green leaf, dead leaf, and stem) at 0.6 m plant height increments to a final height of 4.3 m during 1986 and 1987. Treatments from both parts of the study received 25 kg P ha⁻¹ and 93 kg K ha⁻¹ in one application and 336 kg N ha⁻¹ yr⁻¹ in single or split applications applied prior to growth of each harvest. Plants repeatedly harvested at the 1.2 m height (Part 1) and mature stage produced a 4-year average yield of 10 and 48 Mg ha⁻¹ yr⁻¹ dry biomass, respectively and decreased in dry biomass yield 89% (1.2 m harvest) and 53% (mature harvest) between years 1 and 4. The stem (1986 and 1987) and dead leaf (1986) plant components increased quadratically as plant height increased, and green leaf decreased from 70% (0.6 m) to 17% (4.3 m height). The crude protein concentration decreased 51% (green leaf) and 81% (stem) and in-vitro organic matter digestion decreased 54, 32, and 34% for dead leaf, green leaf, and stem, respectively as plant height increased from 0.6 to 4.3 m. These data indicate that harvest management is an important factor for energycane biomass yield, ratoon-crop success and plant quality if biomass is used as a methane source.     

Economic analysis of renewable heat and electricity production by sewage sludge digestion—a case study

In this paper, we assess the total cost of energy recovery from sewage sludge through anaerobic digestion with biogas utilization in combined heat and power (CHP) system. The important advantage of anaerobic digestion process is the production of biogas, which can be used to generate electricity and heat as a source of renewable energy. From this study, it can be retained that the generated thermal energy from the anaerobic digestion process meets the needs of the wastewater treatment plant (WWTP) and guarantees its self‐sufficiency in heat. The surplus of renewable heat produced by CHP is not a primary factor to improve the economic viability of the process. Moreover, the sales of electricity output represent about 76% of the operating costs of anaerobic digestion process. Renewable energy production is not economically viable by its own, without considering the wastewater treatment function and the associated incomes. Nevertheless, sludge digestion helps to reduce the wastewater treatment costs mainly by giving a good source of revenue via electricity production. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of Spartina alterniflora as feedstock for anaerobic digestion

Smooth cordgrass (Spartina alterniflora), a saltmarsh plant with high production, was characterized for its potential for use as feedstock for anaerobic digestion processes. The anaerobic digestibility and biogas yield of S. alterniflora were evaluated by anaerobic batch digestion experiments performed at 35 ± 1 °C at initial volatile solids (VS) of 6%. The nutrient content analysis indicated that S. alterniflora contained the required nutrition for anaerobic microorganisms, but its high C/N of 58.8, high K and Na contents of 8.1, 22.7 g kg^?1, respectively, may be disadvantageous to its anaerobic digestion. The cumulative biogas yield was determined to be 358 L kg^?1 VS and the biodegradation efficiency was 45% after 60 days of digestion. The methane content of biogas increased from 53% on day 3 to around 62% after 13 days of digestion. The changes of volatile fatty acids (VFAs) indicated that the acidification of S. alterniflora was propionate-type fermentation with proportion of acetate and propionate ranging from 54.8% to 98.4%, and the hydrolysis of lignocellulose was the rate-limiting step for its anaerobic digestion. The analysis of cations suggested that K⁺ and Mg²⁺, with the maximum concentration of 1.35 and 0.43 g L^?1 in fermentation liquor, respectively, could be inhibitory to the anaerobic digestion of S. alterniflora. It is concluded that S. alterniflora can be transformed into clean energy by anaerobic digestion and the high contents of K, Na, Ca and Mg may be the inhibitory factors when S. alterniflora is digested by continuous or semi-continuous anaerobic process.     

大型海藻发酵生产甲烷技术研究

大型海藻发酵生产甲烷属生物质能,是一种碳中性的清洁能源,是重要的海洋生物碳汇。不同种类的藻类发酵产甲烷的潜力是不一样的,其中巨藻含有丰富的甲烷成分,但其自然资源量有限,而人工养殖依然是一个难题,如何持续不断地提供原材料是巨藻生物质能源开发中亟待解决的问题。海藻发酵产甲烷是多种微生物联合作用的结果,从整体上可划分为产甲烷菌群和不产甲烷菌群,它们相互依赖又相互制约,产甲烷菌利用不产甲烷菌的代谢产物H2、CO2等最终合成甲烷。海藻发酵过程的微生物要求具有一定的耐盐性,大体可以利用沼气发酵微生物经过定向培养和筛选而获得。多数人支持将沼气发酵过程分为水解液化、酸化和甲烷化三个阶段的理论,而甲烷形成途径包括菌种间H2的转移和由乙酸产生甲烷。甲烷发酵的影响因素包括原料的预处理、原料的成分和颗粒大小以及接种物、发酵温度、发酵料液pH值、接种率及接种物中对发酵菌活性有影响的物质等,甲烷产率最大化的最主要前提是反应条件要达到最优化。我国在海藻大规模养殖方面具有先天的自然条件及技术和人力优势,为海藻生物质能源开发提供了巨大的潜力,但在技术上还有待突破,特别是在接种物培养、甲烷产率控制等一些特定环节上还需加强研究。     

System optimization for effective hydrogen production via anaerobic digestion and biogas steam reforming

To construct a system for the effective hydrogen production from food waste, the conditions of anaerobic digestion and biogas reforming have been investigated and optimized. The type of agitator and reactor shape affect the performance of anaerobic digestion reactors. Reactors with a cubical shape and hydrofoil agitator exhibit high performance due to the enhanced axial flow and turbulence as confirmed by simulation of computational fluid dynamics. The stability of an optimized anaerobic digestion reactor has been tested for 60 days. As a result, 84 L of biogas is produced from 1 kg of food waste. Reaction conditions, such as reaction temperature and steam/methane ratio, affect the biogas steam reforming reaction. The reactant conversions, product yields, and hydrogen production are influenced by reaction conditions. The optimized reaction conditions include a reaction temperature of 700 °C and H₂O/CH₄ ratio of 1.0. Under these conditions, hydrogen can be produced via steam reforming of biogas generated from a two-stage anaerobic digestion reactor for 25 h without significant deactivation and fluctuation.     

Optimal and cost-effective industrial biomethanation of tobacco

Extremadura is a Spanish south western region located by the Portuguese border. For decades, tobacco has been traditionally cultivated in Cáceres, the north province of such region. As a result, farmers in the area have extensive experience with this crop, and a fresh tobacco annual production is therefore guaranteed. This way, tobacco plant appears as an excellent candidate as energy crop.The present work reports on the economic viability of the anaerobic digestion of tobacco plant under the two following scenarios: 1) biogas generated in the biological process to be used as fuel to produce heat, thus avoiding the consumption of any other fossil fuel; 2) electric and thermal power generated by the anaerobic digestion plant to be self-consumed or sold to nearby industries.The mesophilic anaerobic digestion experiments carried out in semicontinuous mode yielded the highest methane production (53.84 ± 15.48 Nm³CH₄/t fresh tobacco) for substrate composition 15% fresh tobacco/85% water and 16 days degradation period.However, such methane yield by anaerobic digestion was seen not to meet economic feasibility requirements. Instead, methane production rates should be increased up to 90 and 110 Nm³ methane/t fresh tobacco (1500 €/ha production costs) in order to achieve 8.91 and 9.08 years for investment return according to scenarios 1 and 2, respectively.     

尿素预处理对玉米秸秆厌氧发酵产沼气特性影响及动力学分析

针对玉米秸秆厌氧发酵产沼气过程中难降解问题,选用尿素对玉米秸秆进行预处理,并进行批次厌氧发酵产沼气试验研究。结果表明:经过45 d厌氧发酵,累积产气量最高为757.83 mL/g VS,最低为588.64 mL/g VS,厌氧发酵进行到25 d时达到45 d累积产气量的85%。分析联合预处理对累积沼气产气量影响得出,尿素质量浓度、预处理时间和玉米秸秆粒径3个因素对累积沼气产气量的影响程度是:玉米秸秆粒径>尿素质量浓度>预处理时间。通过2种动力学模型分析产气规律,对比模型的检验参数,得出Cone模型拟合预处理玉米秸秆厌氧发酵产气规律的适合度较高。     

Impact of acetic acid in methane production from glycerol/acetic acid co-fermentation

Co-fermentation of glycerol and acetic acid in anaerobic digestion was set up to generate biogas in batch reactors under mesophilic condition, pH 7. The experiments were varied COD ratios of glycerol and acetic acid were varied with the total combined COD of 5,20 0 mg/L. The maximum methane yield was obtained from glycerol/acetic acid ratio of 6:4. The cumulative methane, production rate and lag phase were 240 mL, 14 mL hr⁻¹, and 11 hr. The research indicated acetic acid boosted methane production when it was co-fermented with glycerol.