D.C. Baruah

Phosphorus recovery as struvite from farm, municipal and industrial waste: feedstock suitability, methods and pre-treatments

Global population growth requires intensification of agriculture, for which a sustainable supply of phosphorus (P) is essential. Since natural P reserves are diminishing, recovering P from wastes and residues is an increasingly attractive prospect, particularly as technical and economic potential in the area is growing. In addition to providing phosphorus for agricultural use, precipitation of P from waste residues and effluents lessens their nutrient loading prior to disposal. This paper critically reviews published methods for P recovery from waste streams (municipal, farm and industrial) with emphasis on struvite (MgNH4PO4·6H2O) crystallisation, including pre-treatments to maximise recovery. Based on compositional parameters of a range of wastes, a Feedstock Suitability Index (FSI) was developed as a guide to inform researchers and operators of the relative potential for struvite production from each waste.

Emerging role of Geographical Information System (GIS), Life Cycle Assessment (LCA) and spatial LCA (GIS-LCA) in sustainable bioenergy planning.

Sustainability of a bioenergy project depends on precise assessment of biomass resource, planning of cost-effective logistics and evaluation of possible environmental implications. In this context, this paper reviews the role and applications of geo-spatial tool such as Geographical Information System (GIS) for precise agro-residue resource assessment, biomass logistic and power plant design. Further, application of Life Cycle Assessment (LCA) in understanding the potential impact of agro-residue bioenergy generation on different ecosystem services has also been reviewed and limitations associated with LCA variability and uncertainty were discussed. Usefulness of integration of GIS into LCA (i.e. spatial LCA) to overcome the limitations of conventional LCA and to produce a holistic evaluation of the environmental benefits and concerns of bioenergy is also reviewed. Application of GIS, LCA and spatial LCA can help alleviate the challenges faced by ambitious bioenergy projects by addressing both economics and environmental goals.

Assessment of by-products of bioenergy systems (anaerobic digestion and gasification) as potential crop nutrient.

Alternative fertilizer resources have drawn attention in recent times in order to cope up with ever increasing demand for fertilizer. By-products of bioenergy system are considered favourable as organic fertilizer due to their ability to recycle plant nutrients. Present study evaluates fertilizer suitability of by-products of two bioenergy systems viz. 3 types of anaerobic digestion by-products (digestate) from local surplus biomass such as cowdung, Ipomoea carnea:cowdung (60:40) and ricestraw:green gram stover:cowdung (30:30:40) and one gasification by-product (biochar) from rice husk. Digestates were assessed considering 4 different application options of each viz. whole, solid, liquid and ash from solid digestates. Digestate characteristics (organic matter, macronutrients, micronutrients and heavy metal content) were found to be a function of feedstock and processing (solid liquid separation and ashing). Ipomoea carnea based digestates in all application options showed comparatively higher N, P, K, NH4+-N, Ca, Mg, S and micro nutrient content than other digestates. Separation concentrated plant nutrients and organic matter in solid digestates, making these suitable both as organic amendments and fertilizer. Separated liquid digestate shared larger fraction of ammonium nitrogen (61-91% of total content), indicating their suitability as readily available N source. However, fertilizer application of liquid digestate may not match crop requirements due to lower total nutrient concentration. Higher electrical conductivity of the liquid digestates (3.4-9.3mScm-1) than solid digestates (1.5-2mScm-1) may impart phyto-toxic effect upon fertilization due to salinity. In case of by-products with unstable organic fraction i.e. whole and solid digestates of rice straw:green gram stover:cowdung digestates (Humification index 0.7), further processing (stabilization, composting) may be required to maximize their fertilizer benefit. Heavy metal contents of the by-products were found to be within the permitted range specified for organic fertilizer (vermicompost) in India. However, higher Al content of the digestates in whole, solid and ash phase (0.06-16.97gkg-1 fresh matter) can be a concern in acid soil which may cause Al toxicity. Understanding on agrochemical characteristics of bioenergy by-products with varying feedstock and application option is expected to promote their valorization opportunities considering user specific requirements. In the context of agriculturally dominant but energy deficient rural Indian scenario, integrated production of bioenergy and by-product based fertilizer could be very significant to meet the critical additional requirement of both energy and fertilizer.

Investigation on by-products of bioenergy systems (anaerobic digestion and gasification) as potential crop nutrient using FTIR, XRD, SEM analysis and phyto-toxicity test

Success and acceptability of the bio energy conversion technology to a large extent depend upon management of the inevitable by-products generated during the conversion process. By-products can be considered favourable as organic fertilizer as they retain nutrients with varying composition depending upon input biomass. However, characteristics of these heterogeneous resources with respect to feedstock and processing conditions have to be assessed to state on their agricultural and environmental benefits. Therefore, 3 types of anaerobic digestion by-products (digestate) from surplus biomass viz. cow dung, Ipomoea carnea:cow dung (60:40 dry weight basis) and rice straw:green gram stover:cow dung (30:30:40 dry weight basis) and one gasification by-product (biochar) from rice husk are considered to understand the fertilizer prospects. Considering 3 potential application options, digestate from each feedstock option was further processed as separated solid, separated liquid and ash from solid digestates. Thus, a total of 10 by-products were investigated for understanding their prospects as fertilizer using Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X ray Spectroscopy (EDX) and phyto-toxicity test to have a broad insight in terms of their organic, mineral, elemental composition, morphological feature and potential phyto-toxicity. In general, irrespective of origin of feedstock, solid digestate, ash digestate and char showed similarity in terms of composition of functional groups with some degree of variation in relative content as reflected by FTIR analysis. Dominance of organic functional groups in separated solid digestates compared to liquid fraction indicated the former as favourable organic amendments. Quartz was the prevalent mineral phase in all separated solid, ash digestate and rice husk char. Digestates in ash phase represent more concentrated plant nutrient source with higher content of K, Ca, P, Na and Mg than their respective solid phase. Application of ash digestates and char is likely to improve adsorptive capacity of soil for water and nutrient due to presence of relatively uniformly distributed porous particles. Liquid fraction of Ipomoea digestates exhibited inhibitory effect on seed germination of greengram (Vigna radiate) with significant reduction of germination index. Inhibitory effects of by-products were found to correlate negatively with their electrical conductivity and ammonia-nitrogen content. Understanding on spectroscopic, morphological and phytotoxic properties of different application options of bioenergy by-products would be useful for assessment of their appropriate use in agriculture.

Performance and energy analyses of a diesel engine fuelled with Koroch seed oil methyl ester and its diesel fuel blends

Performance of a single cylinder four-stroke diesel engine is analysed in the light of first law of thermodynamics in this study considering 10% (B10) to 40% (B40) (by volume) blending of Koroch seed oil methyl ester (KSOME) with diesel as fuels. An energy balance study is carried out to quantify the various losses associated with diesel engine processes on the basis of experimental data. Performance parameters such as brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), indicated power (IP), indicated thermal efficiency (ITE), indicated specific fuel consumption (ISFC), exhaust gas temperature (EGT) are determined for each fuel operation at various loads. It was found that KSOME and its diesel blends show slightly higher BSFC, lower BTE, and higher EGT. IP was more for the blends up to B30 compared to diesel fuel operation, but it significantly reduced in case of the blend B40 indicating more energy losses with this fuel blend. ITE was also lower and ISFC was more for B40 at all loads. The energy analysis indicates higher unaccounted heat losses for the blend B40 which mainly accounts for the losses resulting from incomplete fuel combustion.

Prospects of Utilization of Liquid Fraction of Biogas Digestate as Substrate Supplement for Mushroom Cultivation

Biogas digestate is the by-product of ‘anaerobic digestion’ process that produces biogas as the primary form of energy. Since digestates are the inevitable commodities of the conversion process, means of their appropriate management is essentially required for sustainability of bioenergy system. In developing countries, with faster adoption of biogas technology, a simultaneous increase in biogas residue is also expected drawing attention for their immediate and effective utilization. Since biogas digestate retains nutrients from input feedstock with enhanced bioavailability and minimum variation, these could be potentially used as growth supplement for mushroom. Present study discusses the prospects of utilization of the liquid fraction of biogas digestate as a substrate along with rice straw for enhancing the production of white oyster mushroom (Pleurotus florida) under laboratory conditions. The study investigates the effect of liquid fraction of biogas digestate on yield and growth parameters (stem height, cap diameter, mean weight) of mushroom. An enhancement of yield by 38% was observed under liquid digestate application compared to control using only rice straw as substrate. In addition, cost dynamics analysis also showed feasibility of production of mushroom at commercial scale. Integrated development of biogas technology with subsequent valorization of digestate through mushroom cultivation may help in increasing overall profitability of biogas system.

By-Products of Bioenergy Systems (Anaerobic Digestion and Gasification): Generation and Prospects of Utilization

The producer gas and biogas are biomass-based renewable energy sources drawing increased attention worldwide. Substantial quantities of by-products are also generated during the production of these fuels from biomass. While primary emphasis is on main energy form, management and utilization of by-products are also of concern, both from economic and environmental points of view, as these are the inevitable commodities. There have been some reports on utilization of these by-products, mostly traditionally, to supplement soil nutrients. However, lack of proper management could lead to their nonoptimal use through loss of nutrients. The present investigation considers the by-products of two bioenergy systems, viz. digested slurry from anaerobic digestion unit and tar from bio-gasification unit, available in food industry through case studies to understand the rate of by-product generation, characterization and prospective utilization. From the total slurry generated using cow dung as feedstock, an estimated amount of 3.68 kg of dry mass (solid digestate) and 36.28 l of liquid (liquid digestate) per cubic metre of biogas were obtained. While analysing the digested slurry in terms of thermal and nutritional characteristics, it is known that recovery of second-stage thermal energy without losing essential nutrients could be possible if appropriate management strategy is taken. It has been estimated that 54.56 MJ energy could be made available per cubic metre of biogas, considering second-stage energy recovery route through briquetting technology using solid fraction of digestate. While estimating gasification tar, for generating 1 m3 of producer gas using bamboo, an average of 0.041 g tar could be obtained. The prospects of utilization of gasification tar could be possible from the presence of a number of useful chemicals as indicated by characterization study.

Feasibility Study on Implementing Kitchen Waste-Based Biogas Plant at Tezpur University, Assam

The growing demand for cooking fuel and non-reliable supply of commercial cooking fuel has become a major concern in recent years. In this context, biogas, a clean and renewable energy source, can be a supplement to non-renewable conventional cooking fuel. In India, small-sized biogas plants have been prevalent in domestic sectors with mixed degree of success. However, the application of community-sized biogas plants is very limited. In case of residential institute like Tezpur University, Assam, India, considering the huge amount of food waste generated, conversion of kitchen waste into useful cooking gas (biogas) through anaerobic digestion can be a better option to supplement the elevated requirement of LPG. In this work, feasibility study of renewable energy-based cooking system (biogas plant, size 50 m3), implemented in one of the hostels of Tezpur University, is thoroughly examined from commissioning to operational stage, in order to assess the barriers and carriers of such renewable energy technology. A study investigated the performance of the installed plant, feedstock characteristics, composition and economic assessment of biogas-fuelled cooking at Tezpur University campus. Performance analysis and economic assessment of the 50 m3 biomethanation plant showed that it can be a viable option for utilization of the food waste generated in educational institutions through production of clean cooking fuel. However, proper monitoring of feeding rate and quality is critical for smooth performance of the biogas system.

Farm/Industrial/Municipal Waste: Prospects of Nutrient (Phosphorus) Recovery

External supply of plant nutrients is a must to achieve intensification of agricultural sector, thereby meeting food demand of growing global population. However, non-substitutable nutrient like phosphorus (P) with finite natural reserve makes recovery of it a progressively attractive option from alternative waste sources. P recovery method identifies production of P-enriched mineral as mainstream option through technically and economically viable recovery processes. In this context, recovery of struvite (MgNH4PO4.6H2O), an alternative P fertiliser from waste streams of farm, municipal and industrial origin, remains a research focus, as considerable fraction of P ends up in these P sinks. The recovery process creates added benefits of quality control of nutrient-laden waste before environmental disposal and reduction of waste volume. In this study, we evaluate some potential P wastes for struvite recovery, in terms of some compositional parameters (orthophosphate, ammonium, calcium). Among these sources, anaerobically digested waste represents suitable considerations for struvite recovery because of retention of nutrient with increased plant availability. Study assessed the potential of anaerobic digestate of different climatic zones (India and the UK) as prospective P source by determining their chemical composition. Through a range of treatments (acidification and chelating agent), P availability was shown to be elevated, indicating its further enhanced potential recovery.

Possibility of biomass gasification in tea manufacturing industries in Assam, India

Tea manufacturing industries in India use natural gas, tea drying oil, wood, and coal for process heat. India is the second largest producer of tea [(1,137.07, China 1,761.00) million kilogram] in 2012. About 0.6–1.2 kg of coal is required to produce one kilogram of dried tea with average moisture of 2.5–3 percentage (w.b.). Biomass gasification is an established renewable energy technology for heat and power applications. Biomass gasifier based tea drying using five biomasses namely shisham (Delbergia sissoo), gulmohar (Delonix regia), bamboo (Banbusea Tulda), dimaru (Ficus lepidosa wall), and neem (Melia Azedarach L) were considered as feedstock for an experimental 10 kW thermal downdraft gasifier cum tea dryer. It was observed that bamboo chips producer gas gave the best calorific value (4.85 MJ Nm–3). Shisham gave average calorific value of producer gas 4.83 MJ Nm–3. Therefore, biomass gasification may be recommended for partial conventional energy substitution in tea manufacturing industries in India.