Urban Plant Biomass Residues from the Neotropics and Their Potential for Thermal Energy Generation

The material associated with tree pruning in a city in the Colombian neotropics was characterized in order to determine its energy potential.The species studied for their relevance in the territory were Prosopis juliflora,Licania tomentosa,Terminalia catappa,Azadirachta indica,Pithecellobium dulce,Ficus benjamina and Leucaena leucocephala.Moisture content,bulk density,hygroscopic response,elemental chemical analysis,proximal analysis,calorific value,ease of ignition and combustion,thermogravimetric and heat flow analysis,steam generation capacity,and qualitative analysis of gases(mass spectrometry)were determined.The results that were obtained show high initial moisture contents that vary between 37%and 67%and a variable density(when dry)between 0.21 and 0.41 g/cm3.Chemically,it was shown that all residues have lower carbon and sulfur content compared to a reference mineral coal.However,the residues of some species have higher nitrogen contents compared to the same coal.All biomasses are characterized by their high content of volatile fractions and by having a lower content of inorganic matter compared to carbon.The lower calorific values of these residues are between 14170 and 16928 kJ/kg,which are not negligible compared to other biomasses.This characteristic would be related to the high presence of hemicellulose in the residues.Flue gas monitoring revealed that there are different airflow needs in order to ensure complete combustion.Steam generation tests showed that the calorific value should not be the most relevant criterion to establish the potential use of the waste,since leucaena leucocephala,despite having the highest calorific value,was the material with the lowest performance in steam generation.

Calorific values and ash contents of different parts of Masson pine trees in southern China

Calorific value of plants is an important parameter for evalu- ating and indexing material cycles and energy conversion in forest eco- systems. Based on mensuration data of 150 sample sets, we analyzed the calorific value （CV） and ash content （AC） of different parts of Masson pine （Pinus massoniana） trees in southern China using hypothesis testing and regression analysis. CV and AC of different tree parts were almost significantly different （P〈0.05）. In descending order, ash-free calorific value （AFCV） ranked as foliage 〉 branch 〉 stem bark 〉 root 〉 stem wood, and AC ranked as foliage 〉 stem bark 〉 root 〉 branch 〉 stem wood. CV and AC of stem wood from the top, middle and lower sections of trees differed significantly. CV increased from the top to the lower sections of the tnmk while AC decreased. Mean gross calorific value （GCV） and AFCV of aboveground parts were significantly higher than those of belowground parts （roots）. The mean GCV, AFCV and AC of a whole tree of Masson pine were 21.54 kJ/g, 21.74 kJ/g and 0.90%, re- spectively. CV and AC of different tree parts were, to some extent, cor- related with tree diameter, height and origin.

Exploring relationships of gross calorific value and valuable elements with conventional coal properties for North Korean coals

Coal in North Korean(NKC)is one of the most important products;however,based on various strategic policies its detail properties remain opaque even for general researchers.Since there are some signs for opening of the North Korea economy,this investigation as a modest effort is going to explore principle relationships among some essential parameters of NKCs such as gross calorific value(GCV),valuable elements and conventional properties by different statistical methods.Correlations indicated that ultimate parameters(carbon,nitrogen,and hydrogen)are the best GCV predictors for NKCs in comparison with proximate parameters(ash,moisture and volatile matter).Multivariable regression demonstrated that predicted GCV based on ultimate properties has a quite accuracy when correlation of determination was 0.99.Descriptive statistics processes showed that on average,the contents of valuable elements such as Ga and V for NKCs are higher than the world coal ranges and they can be considered as byproducts of combustion of NKCs.Pearson correlations indicated that Y may have a mixed organic-inorganic affinity while Ga and V mainly occur in the inorganic part(mineral matter)of NKCs.High inter-correlations between Ga-V and Al showed that aluminosilicates can be considered as their main bring minerals.

Fuel properties and combustion characteristics of some promising bamboo species in India

We investigated the fuel characteristics of five important bamboo species viz., Dendrocalamus strictus, D. brandisii, D. stocksii, Bambusa bambos and B. balcooa. The selected species cover more than 85% of the total growing stock of bamboo in India. Basic density varied from 0.48 to 0.78 g.cm-3 among the bamboo species studied. Ash content, volatile matter content and fixed carbon content ranged between 1.4%-3.0%, 77.2%-80.8% and 17.6%-21.1%, respectively. Variation in calorific value （18.7-19.6 MJ-kg-l） was marginal. Fuel value index var- ied widely （586-2120） among bamboo species. The highest calorific value （19.6 MJ.kg＂l） and fuel value index （2120） were found in B. bal- cooa. Ash elemental analysis revealed that silica and potassium are the major ash forming minerals in bamboo biomass. Silica content ranged from 8.7% to 49.0%, while potassium ranged from 20.6% to 69.8%. We studied combustion characteristics under oxidizing atmosphere. Burning profiles of the samples were derived by applying the derivative thermo- gravimetric technique which is discussed in detail. The five bamboo species were different in their combustion behaviour, mainly due to differences in physical and chemical properties. We compare fuel prop- erties, ash elemental analysis and combustion characteristics of bamboo biomass with wood biomass of Eucalyptus hybrid （Eucalyptus tereticor- his × Eucalyptus camaldulensis）.

Accuracy improvement of quantitative analysis of calorific value of coal by combining support vector machine and partial least square methods in laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy(LIBS) is a potential technology for online coal property analysis,but successful quantitative measurement of calorific value using LIBS suffers from relatively low accuracy caused by the matrix effect.To solve this problem,the support vector machine(SVM) and the partial least square(PLS) were combined to increase the measurement accuracy of calorific value in this study.The combination model utilized SVM to classify coal samples into two groups according to their volatile matter contents to reduce the matrix effect,and then applied PLS to establish calibration models for each sample group respectively.The proposed model was applied to the measurement of calorific values of 53 coal samples,showing that the proposed model could greatly increase accuracy of the measurement of calorific values.Compared with the traditional PLS method,the coefficient of determination(R2) was improved from 0.93 to 0.97,the root-mean-square error of prediction was reduced from 1.68 MJ kg-1 to1.08 MJ kg-1,and the average relative error was decreased from 6.7% to 3.93%,showing an overall improvement.

The use of the white poplar(Populus alba L.)biomass as fuel

We determined the calorific value of white poplar（Populus alba L.） woody biomass to use it as firewood. The value of 19.133 MJ kg-1obtained experimentally shows that the white poplar can be quite successfully used as firewood. Being of a lower quality in comparison with usual beech firewood, the white poplar has similar calorific value. The white poplar has a calorific density of 30.7 % lower than that of current firewood. That is why the price of this firewood from white poplar is lower accordingly. Also, the prognosis of calorific value on the basis of the main chemical elements, being very close to the experimental value（＋2.6 %）, indicates an appropriate value can be achieved to be used for investigation with the chemical element analysis.

Numerical simulation of UCG process with the aim of increasing calorific value of syngas

The determination of operational parameters in the underground coal gasification(UCG)process should be considered in two aspects:first,the total coal in each UCG panel must be gasified and second,the calorific value of the produced gas should be acceptable.The main aim of this study is to present a model that meets these aspects and increasing the calorific value of syngas during this process.In order to achieve those aims,eight different increasing scenarios were devised for total gasification of coal per panel.These scenarios included:increasing oxygen injection rate(scenario 1),the amount of steam injection(scenario 2),operation time(scenario 3),cavity pressure(scenario 4),increase operation time and cavity pressure simultaneously(scenario 5),increase steam injection speed and oxygen injection rate simultaneously(scenario 6),increase in cavity pressure,operating time,steam injection rate and oxygen injection rate simultaneously(scenario 7)and also simultaneous increase in the operating time and steam injection rate(scenario 8).The results showed that for producing syngas with a higher calorific value,the following parameters had the most positive effects respectively:operation time,cavity pressure,steam injection rate and oxygen injection rate.Finally,the model validation was performed for the Centralia LBK-1 UCG pilot and the results showed that this model is very close to reality.

Characterization and Potential Recovery of Household Solid Waste in the City of Ouagadougou (Burkina Faso)

This study on physical and physicochemical characteristics of household solid waste (HSW) in the city of Ouagadougou by using MODECOM, “Method of Characterization of Household waste” was done fifteen (15) years after the first study. Special attention has been paid to waste sampled and also to estimate energy content, namely the higher heating value (HHV) and the lower heating value (LHV). As a general tendency, the results showed a sensitive evolution in the physical parameters of waste (composition by size and composition by category) and also in the physicochemical parameters (moisture content and energy content). The results of HSW composition study showed that regardless the seasons, fermentable fraction is dominant (39% in the rainy season and 20% in the dry season) followed by plastics (18% in the rainy season and 20% in the dry season). The moisture content is measured to be 56.69% and 37.69% respectively in the rainy season and dry season. The results analysis of the potential of recovery showed that the organic recovery is more important (60% in the rainy season and 55% in the dry season) than the matter recovery (43% in the rainy season and 46% in the dry season). These results highlight the need for organic recovery and matter recovery of HSW in the city of Ouagadougou. The results from the analysis of the energy content showed that the HHV is estimated to be 17.94 MJ/kg in the rainy season and 17.96 MJ/kg in the dry season. The LHV is calculated to be 6.38 MJ/kg in the rainy season and 10.27 MJ/kg in the dry season. These results suggest that incineration as treatment of HSW in the city of Ouagadougou is not economically an appropriate option.

Evaluation of Fuel Properties of Six Tropical Hardwood Timber Species for Briquettes

The fuel potential of six tropical hardwood species namely: Triplochiton scleroxylon, Ceiba pentandra, Aningeria robusta, Terminalia superba, Celtis mildbreadii and Piptadenia africana were studied. Properties studied included species density, gross calorific value, volatile matter, ash content, organic carbon and elemental composition. Fuel properties were determined using standard laboratory methods. The result indicates that the gross calorific value (GCV) of the species ranged from 20.16 to 22.22 MJ/kg and they slightly varied from each other. Additionally, the GCV of the biomass materials were higher than that of other biomass materials like;wheat straw, rice straw, maize straw and sugar cane. The ash and volatile matter content varied from 0.6075 to 5.0407%, and 75.23% to 83.70% respectively. The overall rating of the properties of the six biomass materials suggested that Piptadenia africana has the best fuel property to be used as briquettes and Aningeria robusta the worse. This study therefore suggests that a holistic assessment of a biomass material needs to be done before selecting it for fuel purpose.

Upgraded Pellet Making by Torrefaction—Torrefaction of Japanese Wood Pellets

Upgraded wood pellets were produced and evaluated by torrefaction of wood pellets. In this study, conventional wood pellets were initially prepared and subsequently torrefied on a laboratory and then larger scale. During the laboratory scale production, pellets from wooden parts of Japanese cedar (sugi, Cryptomeria japonica) and Japanese oak (konara, Quercus serrata) trees were heat- treated in an inert gas oven under nitrogen atmosphere around 170°C - 320°C. For the Japanese cedar, the calorific values were improved by heat treatment up to 260°C. By heat treatment at 240°C, the upgrade ratio of higher heating value (HHV) was nearly 30% and the energy yield was 97%. For the Japanese oak, the calorific values were improved by heat treatment up to 320°C. By heat treatment at 280°C, the upgrade ratio of HHV exceeded 30% and the energy yield was 84%. On a larger scale, a conventional charcoal oven was modified for torrefied wood pellet production, meaning that torrefied wood pellet with 25 MJ/kg of calorific value was produced during heat treatment at 350°C. A mixture of conventional and torrefied pellets was applied to a commercial pellet stove, and torrefied wood pellets produced in this study might be usable as fuel for conventional pellet stoves.

Biomass Energy Resource of the Highland Bamboo (<i>Yushania alpina</i>) and Its Potential for Sustainable Exploitation in Southern Aberdares Forest

Yushania alpina is the only bamboo species native to Kenya and covers about 150,000 ha growing in pure or mixed stands in the montane forests. The Aberdare forest is one of the natural habitats for Y. alpine occupying an area of 6419 ha mainly in the water catchment areas. The growing human population and depletion of other forest resources have necessitated the exploration of Y. alpine as a source of energy. This paper assessed the quantity of Y. alpine available for biomass energy and its potential for sustainable exploitation. Plots were laid on area maps to cater for altitude and distance from farms. The study area was stratified into three altitudinal zones: A (2220 - 2330 m), B (2331 - 2440 m) and C (2441 - 2550 m). The initial sampling plot of 10 m × 10 m was located randomly 500 m from the edge of the forest while the subsequent plots were laid out systematically at intervals of 500 m. In each plot, a total enumeration and biomass estimation of bamboo clumps were done using Muchiri and Muga (2013) [1] method. Bamboo samples and those of commonly used biomass energy sources were analysed for calorific value using bomb calorimeter. In addition, data for quantities of biomass energy used by some local industries were used to estimate the amount of bamboo required. The mean stocking was 19,981 (20,000) culms ha-1, and varied significantly among altitude strata and distance from adjacent farms. The mean biomass density and energy content were 86 tons/ha and 380,893 Kca/ha respectively with the higher altitudinal stratum (zone C) having the highest means (114 tons/ha) while the lower stratum (zone A) had the lowest (65 tons/ha). The energy needed by sampled local industries was 416,276,266 Kcal per year against 2.4 billion Kcal available in the bamboo forest. This implies that the bamboo forest in its present stocking can provide biomass energy for these local industries for more than five years. With bamboo maturing with less than five years, the forest can sustainably provide the required energy while still providing its environmental services.

Heating Process of Thermosetting Insulation Materials for Buildings

Polyurethane （PU） and phenolic （PF） foams used for building isolation were analyzed by thermal gravity/differential thermal analysis to determine their pyrolysis behavior, including the decomposition point and the maximum reaction rate point. Besides, the shape deformations of PU and PF foams were observed, and their oxygen index and the calorific value in combustion were also studied. The results showed that the pyrolysis of both PU and PF can be divided into three stages from room temperature to 1 000 ℃ in the atmospheric air, with total mass loss of 94.345% for PF and 88.191% for PU, respectively. The oxygen index of PU and PF decreased with increasing the temperature and the duration of the heat treatment. With the temperature increasing, the calorific values of both materials were reduced remarkably. These results of the PU and PF could provide basic data of the thermal stability and fire safety design in the application of thermosetting insulation materials.

An Evaluation of the Calorific Values of the Branches and Stems of 11 Tropical Trees

This work investigated and quantified the calorific values of the main branches and trunks of eleven (11) tropical trees in correlation with their chemical composition in order to assess their suitability for use as credible sources of wood fuel. The determination of the carbon, hydrogen, nitrogen, oxygen and sulphur (CHNOS) content of the samples was done using an organic elemental analyser, while an oxygen bomb calorimeter was used to experimentally determine their corresponding gross heat values. The experimental gross heat values for the branches examined ranged from 18,703.37 kJ/kg in Lophira lanceolata to 21,350.35 kJ/kg in Afzelia africana while that of the trunks ranged from 19,747.74 kJ/kg in Tectonia grandis to 22,408.68 kJ/kg in Prosopis africana. These values were within and about the expected ranges observed for tropical trees and may be considered adequate for wood fuel. The general trend in both branches and trunks was that the higher the carbon content, the higher the gross heat value of sample. The absence of sulphur in almost all the samples except, Prosopis africana, (0.055%) was indicative of the fact that the negative environmental impact with respect to harmful emissions of oxides of sulphur is practically non-existent with respect to these species. In the light of the aforementioned variables, the main branches of Afzelia africana (21,350.35 kJ/kg), Nauclea diderrichii (21,157.30 kJ/kg) and Tectonia grandis (20,257.13 kJ/kg) could be used as credible sources of firewood and charcoal production. With respect to the trunks, the timbers in order of preference would ideally be Prosopis africana (22,408.68 kJ/kg), Nauclea diderichii (21,436.42 kJ/kg) and Brachstigia eurychoma (20,924.7 kJ/kg).

An Experimental Determination of Gross Calorific Value of Different Agroforestry Species and Bio-Based Industry Residues

Solid biomass fuels are useful and cost effective renewable energy source. The energy content of biomass is determined by its calorific value. The objective of this study was to determine experimentally the gross calorific value (GCV) of different agroforestry species and bio-based industry residues that could be used by: a) companies specialized in processing raw biomass solid biofuel production, b) small-scale consumers (households, medium-sized residential buildings, etc.). The fuel samples used were from agricultural residues and wastes (rice husks, apricot kernels, olive pits, sunflower husks, cotton stems, etc.), energy crops and wetland herbs (cardoon, switchgrass, common reed, narrow-leaf cattail), and forest residues (populus, fagus, pinus). The GCV of the bio-mass samples was experimentally determined based on CEN/TS 14918:2005, and an oxygen bomb calorimeter was used (Model C5000 Adiabatic Calorimeter, IKA?-Werke, Staufen, Germany). The GCV of different agroforestry species and residues ranges from 14.3 - 25.4 MJ?kg–1. The highest GCV was obtained by seeds and kernels due to higher unit mass and higher lipid content. Pinus sylvestris with moisture content 24.59% obtained the lowest GCV (13.973 MJ?kg–1).

Sorption properties of Mg-Ni-CrCl_3 hydrogen storage composite

Hydrogen absorption composite powder of Mg incorporated with Ni and CrCl3 （88∶10∶2 in mass ratio） was prepared by reactive milling in hydrogen atmosphere. Hydriding/dehydriding performances were measured by self-made apparatus. The results show that reactive milling and multi-component addition of Ni and CrCl3 reduce the stability of hydride and improve the sorption performance of Mg-based materials. With powder milled for 60h, hydriding basically completes within 300s （250℃, 2.0MPa） and phase transformation fraction reaches 0.78. The phase transformation rate of hydriding/dehydriding progress increases significantly with the reduced particles size of powder while good kinetics of dehydriding at a relatively low temperature is gained with small grain size of hydride. Rapid temperature variations in a short span of time resulted from remarkable calorific effects of rapid phase transformation are detected in hydriding/dehydriding progress. The results of thermogravimetric and differential scanning calorimetric（TG/DSC） indicate that the onset temperature of desorption of composite milled for 100h is 272℃.

Quality and Emission Analysis of Charcoal from Various Species of Wood Using Improved Carbonization Technologies in Kenya

Biomass energy provides over 70%of the national energy demand in Kenya.Increased demand has contributed to increased environmental degradation through deforestation,contributing significantly to the global emissions of greenhouse gases,loss of habitats,and biodiversity,and increased health risks.Efficient charcoal conversion technologies have been researched and developed.However,no studies have been undertaken to establish the influence of the improved technologies on the quality of charcoal produced and the emission levels of greenhouse gases from each kiln.The study was undertaken(in eastern Kenya)to determine the effect of carbonization technology and tree species on the quality of the charcoal,the emission levels of the kilns,and the energy properties of the charcoal from various selected species.A total of 14 species were sourced for the study and carbonized using the Adams retort,portable metal,improved earth and the traditional earth kilns.The results indicated that Balanites aegyptiaca,Terminalia spinosa,Acacia nilotica and A.tortilis were ranked best indigenous species in terms of calorific values with mean calorific values above 6.0 kcal/g while Prosopis juliflora,Casuarina equistifolia and Eucalyptus camadulensis were the best exotic species with mean kcal/g of 6.430 kcal/g,5.972 kcal/g and 5.633 kcal/g respectively.Analysis of variance on the energy values indicated there was no significant difference in the quality of charcoal produced using the different kilns.The improved earth kiln and the portable metal kiln produced charcoal that was more dense and intact.Charcoal from the preferred indigenous species had also the longest burning time with a mean of 124 minutes compared to 62.4 minutes for the exotics.The highest burning temperature was found in the indigenous species.Results on emission tests were conducted using a portable gas analyzer on the four kiln types.The carbon dioxide emissions were rather high.Methane production in all kilns showed an upward trend at the beginning of the carbonization process and towards the end,the levels declined.The study concluded that a number of species are overexploited for charcoal production with no conservation measures being undertaken thus being threatened with extinction.The types of kiln have significant effect on the energy values(calorific values)of charcoal.The quality of charcoal using improved kilns gave high calorific values.Emission levels for all kiln types were generally high.The study recommends further research on all improved charcoal conversion technologies for reduced emission of greenhouse gases especially retorts since they utilize the flue gases.

Thermochemical Assessment of Solid and Liquid Fuels Used for Domestic Space Heating in Jordan

The gross calorific values of crude and exhausted olive pomace, oak, almond, olive wood, olive oil, kerosene, and diesel are reported in this article. Conversion of crude olive pomace into exhausted olive pomace resulted in 10% reduction in calorific value. The net calorific value of crude olive pomace amounts to 92% of its gross calorific value. The ultimate and proximate analyses of crude olive pomace representing the 2006-2008 olive harvest seasons were determined and compared with analyses pertaining to the 2009-2011 olive harvest seasons in Jordan. Controlled charring of crude olive pomace reduced its mass down to about 20%. Pyrolysis thermogravimetric (TG) and differential thermogravimetric (DTG) curves were recorded under nitrogen atmosphere for crude olive pomace and wood samples. Quantitative data on three DTG major peaks are reported for wood samples and crude olive pomace. A comparison based on market price and calorific value of a fuel showed that olive pomace is the most rewarding fuel for domestic space heating in Jordan.

Characterization of Coal Spoil Recovered from Coal Mine Drainage Water

Barapukuria Coal Mine situated in the district Dinajpur. Bangladesh is playing an important role in the economy of this country by the mining of top quality coal. With coal mining, mine waste is also generated called coal spoil. Coal spoil can impose environmental threat if not treated carefully. In contrast, it can also be converted to value added product. In the present work, coal spoils collected from Barapukuria coal mine drainage water were investigated to determine the quality of the samples by physico-chemical analysis (proximate and ultimate analysis) as well as by heating value determination. 50% of carbon was detected in the samples after elemental analysis, with sulfur content less than 0.4%. Calorific value around 9300 btu/lb was obtained for the coal spoil. Moreover, moisture content, ash, volatile matter content and fixed carbon also provided fruitful information regarding the quality and economic prospect of the samples in comparison to the quality of Barapukuria coal.

Bamboo Biomass for Bioenergy Production in Mauritius

Bamboo, globally renowned as being one of the fastest-growing plants in the world with versatile applications, has gained increasing attention during the past decades. It is being used by millions of people around the globe as a biomass resource for energy production, as timber for furniture making, in the food industry and many more. So far, on the Island of Mauritius, little to no consideration has been given to this fascinating plant. This paper presents the physical and chemical properties of two species of bamboo—Bambusia vulgaris and Bambusia bambos, compared to sugarcane bagasse for bio-energy production. Ten samples of each species were tested for gross calorific value (GCV), moisture, ash and chloride content. The results show that both species have a very good potential for energy recovery with a GCV of 16.77 MJ/kg for Bambusia vulgaris and 17.44 MJ/kg for Bambusia bambos, and are valuable sources of biomass with an average energetic yield of 717.8 GJ/ha/yr and 1587.1 GJ/ha/yr respectively. In comparison, the GCV for sugarcane bagasse was found to be 18.33 MJ/kg with an energetic yield of 824.9 GJ/ha/yr. Simultaneously, a research survey on community acceptance and perception of the Mauritian citizens towards the utilisation of bamboo biomass as an alternative to fossil fuels for bio-energy production was conducted via semi-structured questionnaires. The questionnaires were administered to a total of 54 respondents. 3 women and 3 men were randomly interviewed in each of the 9 districts of the island. The results show that the participants are very much aware of the many issues related to the exploitation of fossil fuels and support the use and implementation of renewable sources of energy for bio-energy production. Eighty percent of the participants supported the implementation of bamboo biomass in the overall energy generation mix in a bold move to lessen their ecological footprint.

Assessment of Municipal Organic Solid Waste, as a Potential Feedstock for Briquette Production in Kampala, Uganda

The current shortage of energy resources coupled with environmental degradation problems resulting from deforestation in Uganda has contributed to increased demand for renewable energy resources including municipal organic solid waste and agricultural residues. However, organic waste from Municipal Solid Waste (MSW) may contain contaminants that are harmful to public health and the environment. This study determined the heavy metal concentration in MSW in Kampala City, Uganda. Also, the physicochemical properties of briquettes produced from the MSW were compared with charcoal. The waste samples were collected from residential, institutional and market areas over a period of two weeks. They were then analyzed for the presence of heavy metals. Briquettes were made from the bio-waste and were subjected to calorific and proximate analysis. Results indicated that the mean concentrations of Cd, Cr, Cu, Fe, and Pb were 1.25 mg/kg, 2.04 mg/kg, 38.2 mg/kg, 3.97 mg/kg and 1.99 mg/kg respectively while Hg was not detected. The calorific values of briquettes ranged from 8.9 to 15.3 MJ/kg and were lower than those of charcoal. Heavy metal concentrations in bio-waste collected were below the permissible acceptable limits. These findings indicate that the sampled MSW does not pose a health hazard arising from the presence of such heavy metals and therefore could be a safe source of renewable energy.