Life Cycle Assessment of Biogas Production in Small-scale Household Digesters in Vietnam

A Critical Review of Data Science Applications in Resource Recovery and Carbon Capture from Organic Waste

Municipal and agricultural organic waste can be treated to recover energy, nutrients, and carbon through resource recovery and carbon capture (RRCC) technologies such as anaerobic digestion, struvite precipitation, and pyrolysis. Data science could benefit such technologies by improving their efficiency through data-driven process modeling along with reducing environmental and economic burdens via life cycle assessment (LCA) and techno-economic analysis (TEA), respectively. We critically reviewed 616 peer-reviewed articles on the use of data science in RRCC published during 2002-2022. Although applications of machine learning (ML) methods have drastically increased over time for modeling RRCC technologies, the reviewed studies exhibited significant knowledge gaps at various model development stages. In terms of sustainability, an increasing number of studies included LCA with TEA to quantify both environmental and economic impacts of RRCC. Integration of ML methods with LCA and TEA has the potential to cost-effectively investigate the trade-off between efficiency and sustainability of RRCC, although the literature lacked such integration of techniques. Therefore, we propose an integrated data science framework to inform efficient and sustainable RRCC from organic waste based on the review. Overall, the findings from this review can inform practitioners about the effective utilization of various data science methods for real-world implementation of RRCC technologies.

Possibility of using tannins to control greenhouse gas production during digestate storage

The presented paper deals with the testing of a possibility to reduce emissions of undesirable greenhouse gases (CH₄, CO_2; NO_x) and their mixture (biogas) during the storage of digestate using applications of secondary plant metabolites (tannins). The experiment was conducted in laboratory conditions in which the digestate was placed in fermentation chambers. Prior to the fermentation process, preparations were applied to the digestate, which contained tannins: Tanenol Antibotrytis (TA), Tanenol Clar (TC) and Tanenol Rouge (TR) in three concentrations (0.5, 1.0 and 2.0% w/w). The application of these preparations demonstrably affected the production of biogas and the contents of CH₄, CO₂ and N therein. The application of TR preparation in the concentration of 1.0% and 2.0% significantly reduced the production of biogas as compared with all variants. The preparation further inhibited the process of CH₄ development. In contrast, the other preparations with the content of different kinds of TA and TC increased the production of biogas (on average by 15%), CH₄ (on average by 7%) and CO₂ (on average by 12%) as compared with the control variant and TR variant. These two variants reduced the concentration of N in biogas on average by 38%. Thus, the tested Tanenol tannin preparations can be used in different concentrations either to control emissions of greenhouse gases during the storage of digestate or, in case of increased production of CO₂ for its reuse in order to increase methane yields in the process of anaerobic fermentation.

Environmental impacts of a rice-beef-biogas integrated system in the Mekong Delta, Vietnam evaluated by life cycle assessment

It is essential to increase the production of foods to meet the increasing future food demand, but this should be done in an environmentally sustainable manner. Integrated crop-livestock systems have been suggested to balance the reduction of environmental impacts and the increase in food production. Here we assessed and compared the environmental impacts of specialized (SPC) and integrated (ITG) rice and beef production systems in the Mekong Delta, Vietnam, using a life-cycle assessment (LCA). The productions of rice and beef are separated in the SPC, whereas they are integrated in the ITG: cattle manure is treated by a biodigester for biogas production, its digestate is applied to rice paddy fields as fertilizer, and part of the rice straw is used as cattle feed. We developed an LCA model based on data collected by site investigations of rice and beef farms and the relevant literature and LCA databases. Our evaluation of the ITG and SPC rice-beef production systems using the LCA revealed that among the four environmental impact categories investigated herein, the ITG had less environmental impacts on climate change (22%), energy consumption (22%), and eutrophication (14%) compared to the SPC. With the ITG, the reduction of methane emissions from paddy fields, the avoided energy consumption by the biogas produced, and the lower ammonia, nitrate, and phosphorous emissions from cattle manure and no eutrophying pollutant emissions from grassland were the main contributors to the lower greenhouse gas emissions, energy consumption, and eutrophication potential of this system, respectively. A sensitivity analysis showed that the use of cover for digestate storage resulted in lower environmental impacts of the ITG system compared to SPC system in all of the impact categories investigated here. These results provide helpful information to develop a circular and resource-efficient rice and beef production system that balances increasing productivity with environmental sustainability in rice-producing countries, particularly in Asia.

Low-cost anaerobic digester to promote the circular bioeconomy in the non-centrifugal cane sugar sector: A life cycle assessment

This study aimed to assess the potential environmental benefits of implementing low-cost digesters to valorize agro-industrial waste in the non-centrifugal cane sugar (NCS) sector. Two scenarios were considered: i) the current scenario in which organic waste and wastewater were burned outdoor and discharged into a water body, respectively; ii) the anaerobic digestion (AD) scenario, in which low-cost biodigesters were used for organic waste and wastewater treatment on-site. Results showed that low-cost digesters were a sustainable alternative to mitigate environmental impacts, especially those associated with water source pollution. Indeed, in the AD scenario, the environmental impact categories of Freshwater Eutrophication and Marine Eutrophication showed a decrease of 87.6% and 99.4%, respectively, compared to the current scenario. Thus, by treating organic waste and wastewater on-site while producing bioproducts (i.e. biofuel and biofertilizer), low-cost digesters could contribute to boosting the circular bioeconomy in the NCS production sector.

Alternative Management Systems of Beef Cattle Manure for Reducing Nitrogen Loadings: A Case-Study Approach

Livestock manure is one of the main sources of agricultural nonpoint source pollution and poses a great threat to the environment and human health. Sustainable management of manure via recycling is an effective means to tackle the problem. Based on field interviews in China, multiple case studies were employed to investigate alternative manure management systems. Four conclusions arose. First, compost-based systems, product-based systems, substrate-based systems, and biogas-based systems were identified as four main types of manure management systems, with each possessing its success factors and risk factors. The adoption of a system was driven by various factors. Second, market-oriented operation was the dominant operation mechanism of all the manure management systems. Third, compared to direct application of manure to croplands, all the four manure management systems could reduce nitrogen loadings from livestock farms and lower their environmental effects. Among the systems, biogas-based systems could reduce nitrogen loadings to the greatest extent, followed by product-based systems and substrate-based systems, and then by compost-based systems. Lastly, integrated management of manure with mixed recycling systems is imperative for reducing its environmental effects, which can benefit from the increasing role of third-party entities in manure recycling. Policy implications were also discussed.

Development of sustainable approaches for converting the organic waste to bioenergy

Dependence on fossil fuels such as oil, coal and natural gas are on alarming increase, thereby causing such resources to be in a depletion mode and a novel sustainable approach for bioenergy production are in demand. Successful implementation of zero waste discharge policy is one such way to attain a sustainable development of bioenergy. Zero waste discharge can be induced only through the conversion of organic wastes into bioenergy. Waste management is pivotal and considering its importance of minimizing the issue and menace of wastes, conversion strategy of organic waste is effectively recommended. Present review is concentrated on providing a keen view on the potential organic waste sources and the way in which the bioenergy is produced through efficient conversion processes. Biogas, bioethanol, biocoal, biohydrogen and biodiesel are the principal renewable energy sources. Different types of organic wastes used for bioenergy generation and its sources, anaerobic digestion-biogas production and its related process affecting parameters including fermentation, photosynthetic process and novel nano-inspired techniques are discussed. Bioenergy production from organic waste is associated with mitigation of lump waste generation and its dumping into land, specifically reducing all hazards and negativities in all sectors during waste disposal. A sustainable bioenergy sector with upgraded security for fuels, tackles the challenging climatic change problem also. Thus, intensification of organic waste conversion strategies to bioenergy, specially, biogas and biohydrogen production is elaborated and analyzed in the present article. Predominantly, persistent drawbacks of the existing organic waste conversion methods have been noted, providing consideration to economic, environmental and social development.

Manure management and pollution levels of contract and non-contract livestock farming in Vietnam

In analyzing contract farming of livestock production, many studies have focused on the economic aspect. This paper offers the environmental issue by investigating manure management and pollution levels of contract farming (CF) and non-contract farming (NCF) livestock producers in Vietnam. By surveying 270 pig farms and applying logit model, we found that commercial pigpen type of CF reduces the probability of manure separation, while larger garden area and knowledge of composting increase it. By analyzing the wastewater samples collected from 59 farms and employing nearest neighbor matching technique, this paper indicated that CF reduces the pollutants' concentrations in effluents. Using OLS regression models, we found out that manure separation contributes to a reduction in nutrient matters, while biogas plant or combination of biogas plant and stabilization ponds helps to diminish organic matters. The study results suggest that the government should regulate the minimum required land area for installation of the combined manure treatment plants (MTPs). Additionally, to recycle manure and improve nutrient matters in effluent, advanced technologies for separating solid manure are extremely necessary for CF producers. Furthermore, we recommend the government to build mechanisms to compel agribusiness firms engaging in their liability for the environmental side effects caused by their CF producers.

Environmental assessment of energy production from anaerobic digestion of pig manure at medium-scale using life cycle assessment

This study assessed the potential environmental effects of energy production from pig manure treatment by anaerobic digestion at medium-scale based on the Life Cycle Assessment of a farm in Puebla, Mexico. It also compared the results from common practices of biogas flaring and conventional management. The analysis was based on one ton of pig manure in 4 systems: two with energy production, one with biogas flaring, and the last one conventional management. The use of biogas for electricity production combined with composting techniques generated the lowest net impacts on climate change of 272 kg CO₂eq and photochemical oxidation of 0.056 kg ethylene eq, while the biogas flaring registered impacts of 344 kg CO₂eq and 0.095 kg ethylene eq. The systems with energy production had environmental benefits on fossil resources depletion by avoiding the consumption of -863 MJ and -1608 MJ, but systems that burned biogas required fossil fuel consumption of 246 MJ from the grid. The conventional management generated the greatest environmental impacts, with eutrophication being the most important negative effect due to the manure discharge into water bodies (5.97 kg PO₄eq). Sensitivity analysis shown that energy production could generate greater impacts on global warming compared to the case in which manure was used directly in crop fields, if emissions from unintentional releases and a poor digestate management are not avoided. Results are relevant for developing countries in which processes are carried out in rural and semi-industrial areas with lack of technical knowledge and economic resources.

Assessment of a Cattle Manure Vermicomposting System Using Material Flow Analysis: A Case Study from Uganda

Growth in cattle population is associated with increased manure generation whose current management in low-income countries is associated with health and environmental problems as well as low utilization rates. This trend can be reversed by promoting better manure management technologies. This study assessed vermicomposting as one of the technologies to manage organic wastes, using the case study in Uganda. A vermicomposting system using cattle manure and earthworms (Eudrilus euginea) was monitored for one year with the harvesting of products (compost, earthworm biomass) after every three months. Vermicompost samples from the beginning of the experiment and after every harvest were analyzed for the following parameters: pH, ash content, volatile and total solids, nutrients N, P, K, and C. Emissions of CO2, CH4, NH3, and N2O were also measured. Material flow analysis was used to determine the flows and retention of nutrients within the system. Results showed that total solids, ash, N, P, and K content significantly increased, while contents of volatile solids and C, as well as the pH, significantly decreased over time. Of the materials that entered the vermicomposting system, 46% went to vermicompost, 2% into earthworms, and 52% was lost to the atmosphere. Substance flow analysis showed that 30% of C went to vermicompost, 69% was emitted to the atmosphere, and 2% ended up in earthworms while 75% of N was transferred to vermicompost, 7% went to earthworms, and 18% escaped into the atmosphere. The cumulative emissions were 102 g CO2 kg−1 waste, 7.6 g CH4 kg−1 waste, and 3.943 × 10−5 g N2O kg−1 waste on a dry basis, while NH3 was not detected throughout the measurement time. Compared to other manure management methods, vermicomposting demonstrated good potential in conserving nutrients as well as reducing greenhouse gas emissions.

Analysis of Greenhouse Gas Emissions in Centralized and Decentralized Water Reclamation with Resource Recovery Strategies in Leh Town, Ladakh, India, and Potential for Their Reduction in Context of the Water–Energy–Food Nexus

With the constant increase of population and urbanization worldwide, stress on water, energy, and food resources is growing. Climate change constitutes a source of vulnerability, raising the importance of implementing actions to mitigate it. Within this, the water and wastewater sector represents an important source of greenhouse gas (GHG) emissions, during both the construction and operation phase. The scope of this study is to analyze the GHG emissions from the current and future water supply scheme, as well as to draw a comparison between possible water reclamation with resource recovery scenarios in the town Leh in India: a centralized scheme, a partly centralized combined with a decentralized scheme, and a household level approach. Precise values of emission factors, based on the IPCC Guidelines for National Greenhouse Gas Inventories, previous studies, and Ecoinvent database, have been adopted to quantify the different emissions. Potential sources of reduction of GHG emissions through sludge and biogas utilization have been identified and quantified to seize their ability to mitigate the carbon footprint of the water and wastewater sector. The results show that the future water supply scheme will lead to a significant increase of the GHG emissions during its operation. Further, it is shown that decentralizing wastewater management in Leh town has the least carbon footprint during both construction and operation phases. These results have implications for cities worldwide.

Evaluating environmental benefits of low-cost biogas digesters in small-scale farms in Colombia: A life cycle assessment

The aim of this study was to assess the environmental benefits of implementing low-cost digesters in small-scale farms in Colombia by using the LCA methodology. Four scenarios were taken into account considering two small-scale farms located in different areas: two (previous) scenarios where manure was stored in a manure pit and liquefied petroleum gas (LPG) was used for cooking; and two (current) scenarios where manure is treated in low-cost digesters, the digestate replaces the synthetic fertiliser and the biogas is used for cooking replacing the LPG. Results showed that digesters implementation considerably reduced (by up to 80%) potential environmental impacts associated with manure handling, fuel and fertiliser use in the small-scale Colombian farms. This was mainly due to the reduction of LPG and synthetic fertiliser use which were replaced by biogas and digestate. An economic assessment showed that low-cost digesters reduced expenses associated with cooking fuel and fertiliser purchase by 80%.

An effective H2S sensor based on SnO2 nanowires decorated with NiO nanoparticles by electron beam evaporation

The highly toxic hydrogen sulphide (H₂S) present in air can cause negative effects on human health. Thus, monitoring of this gas is vital in gas leak alarms and security. Efforts have been devoted to the fabrication and enhancement of the H₂S-sensing performance of gas sensors. Herein, we used electron beam evaporation to decorate nickel oxide (NiO) nanoparticles on the surface of tin oxide (SnO₂) nanowires to enhance their H₂S gas-sensing performance. The synthesised NiO–SnO₂ materials were characterised by field-emission scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy analysis. H₂S gas-sensing characteristics were measured at various concentrations (1–10 ppm) at 200–350 °C. The results show that with effective decoration of NiO nanoparticles, the H₂S gas-sensing characteristics of SnO₂ nanowires are significantly enhanced by one or two orders compared with those of the bare material. The sensors showed an effective response to low-level concentrations of H₂S in the range of 1–10 ppm, suitable for application in monitoring of H₂S in biogas and in industrial controls. We also clarified the sensing mechanism of the sensor based on band structure and sulphurisation process.

NiO nanoparticles decorated on the surface of the on-chip grown SnO₂ nanowires exhibited excellent response to highly toxic hydrogen sulphide (H₂S) in air.

Anaerobic digestion for bioenergy production: Global status, environmental and techno-economic implications, and government policies

Anaerobic digestion (AD) is a mature technology that can transform organic matter into a bioenergy source - biogas (composed mainly of methane and carbon dioxide), while stabilizing waste. AD implementation around the world varies significantly, from small-scale household digesters in developing countries to large farm-scale or centralized digesters in developed countries. These differences in the implementation of AD technology are due to a complex set of conditions, including economic and environmental implications of the AD technology, and stimulus provided by a variety of polices and incentives related to agricultural systems, waste management, and renewable energy production. This review explores the current status of the AD technology worldwide and some of the environmental, economic and policy-related drivers that have shaped the implementation of this technology. The findings show that the regulations and incentives have been the primary factor influencing the steady growth of this technology, in both developing and developed countries.

Biochar for composting improvement and contaminants reduction. A review

Biochar is characterised by a large specific surface area, porosity, and a large amount of functional groups. All of those features cause that biochar can be a potentially good material in the optimisation of the process of composting and final compost quality. The objective of this study was to compile the current knowledge on the possibility of biochar application in the process of composting and on the effect of biochar on compost properties and on the content of contaminants in compost. The paper presents the effect of biochar on compost maturity indices, composting temperature and moisture, and also on the content and bioavailability of nutrients and of organic and inorganic contaminants. In the paper note is also taken of the effect of biochar added to composted material on plants, microorganisms and soil invertebrates.

Green-house gas mitigation capacity of a small scale rural biogas plant calculations for Bangladesh through a general life cycle assessment

Calculations towards determining the greenhouse gas mitigation capacity of a small-scale biogas plant (3.2 m³ plant) using cow dung in Bangladesh are presented. A general life cycle assessment was used, evaluating key parameters (biogas, methane, construction materials and feedstock demands) to determine the net environmental impact. The global warming potential saving through the use of biogas as a cooking fuel is reduced from 0.40 kg CO₂ equivalent to 0.064 kg CO₂ equivalent per kilogram of dung. Biomethane used for cooking can contribute towards mitigation of global warming. Prior to utilisation of the global warming potential of methane (from 3.2 m³ biogas plant), the global warming potential is 13 t of carbon dioxide equivalent. This reduced to 2 t as a result of complete combustion of methane. The global warming potential saving of a bioenergy plant across a 20-year life cycle is 217 t of carbon dioxide equivalent, which is 11 t per year. The global warming potential of the resultant digestate is zero and from construction materials is less than 1% of total global warming potential. When the biogas is used as a fuel for cooking, the global warming potential will reduce by 83% compare with the traditional wood biomass cooking system. The total 80 MJ of energy that can be produced from a 3.2 m³ anaerobic digestion plant would replace 1.9 t of fuel wood or 632 kg of kerosene currently used annually in Bangladesh. The digestate can also be used as a nutrient rich fertiliser substituting more costly inorganic fertilisers, with no global warming potential impact.

Developing zero-discharge pig-farming system: a feasibility study in Malaysia

Pig production in many rapidly developing Asian countries evolved from traditional small-family farms without parallel increase in land resource for waste treatment, thus further worsening the already fragile environment. The present paper reports results of a feasibility study on developing a zero-waste discharge pig-farming system in the hot-humid environment such as Malaysia. The approach included (1) reduction in the usage of water, (2) use of micro-algal culture (MAC) system to reduce pollutants in the wastewater and (3) use of constructed wetlands to further clean up wastewater and reduce its volume via evapo-transpiration. Results of the study showed that water usage could be reduced from the current 40–50 to 7.5 L/pig.day. The biological oxygen demand of the effluent was reduced to below 10 mg/L, while other pollutants, such as suspended solid, total nitrogen and total ammonium nitrogen were also reduced to levels that meet the standards required for affluent discharge in most countries in this region. Water-balance study based on a 180-pig experiment showed that 1.15 m3 of water were used daily and this was reduced to 0.38 m3 at the end of the system. Financial projection study based on a farm size of 2000 pigs (which represents a typical pig-farm size in many developing countries, including Malaysia) was conducted to gauge the economical viability of the system. The results showed that the primary challenge to the adoption of this system is its high initial investment costs, estimated to be 1.8 times those for a similar-sized traditional farm with open-sided house and lagoons for wastewater treatment. However, higher productivity is expected from the use of a ventilated close-house that provides a cooler environment for the pigs. This, together with the premium price of the pigs that could be fetched from this eco-friendly production system, would make it a technically and economically viable system in the long run.