Yee Van Fan

The Update of Anaerobic Digestion and the Environment Impact Assessments Research

An increasing number of studies on biogas as a renewable energy including the industrial implementation have been published. The important issues dealing with anaerobic digestion (AD) includes integration of the evidence into patterns, capable of illustrating the current research trend and gaps. Although AD is widely perceived as a clean technology, the assessing and reporting of its environmental impacts remain an important research scope. This work attempts to highlight the recent AD development through a systematic reviewing approach. The criteria for searching are year, type of search engine, keywords and for the selection according to the relevance of the available sources. The presented review covers a case study, mixed mode, by experiment and review. The environmental impact analysis in AD life cycle assessment is also discussed. This facilitates the future studies in improving the environmental impact of AD system. The digestate management and application were suggested as the hotspot of AD system that needs to be improved as the first priority. The AD overview that has been presented statistically proposes the other potential research direction through the interpretation of the type, amount and characteristics of available research. The key future research area is a feasibility study of AD with the consideration to optimise the energy efficiency, economic and environmental aspects which would attract the investors as well as convince the policy makers.

Anaerobic digestion of lignocellulosic waste: Environmental impact and economic assessment

Lignocellulosic waste (LW) is abundant in availability and is one of the suitable substrates for anaerobic digestion (AD). However, it is a complex solid substrate matrix that hinders the hydrolysis stage of anaerobic digestion. This study assessed various pre-treatment and post-treatments of lignocellulosic waste for anaerobic digestion benefiting from advanced P-graph and GaBi software (Thinkstep, Germany) from the perspective of cost and environmental performances (global warming potential, human toxicity, ozone depletion potential, particulate matter, photochemical oxidant creation, acidification and eutrophication potential). CaO pre-treatment (P4), H2S removal with membrane separation post-treatment (HSR MS) and without the composting of digestate is identified as the cost-optimal pathway. The biological (P7- Enzyme, P8- Microbial Consortium) and physical (P1- Grinding, P2- Steam Explosion, P3- Water Vapour) pre-treatments alternatives have lower environmental impacts than chemical pre-treatments (P4- CaO, P5- NaOH, P6- H2SO4) however they are not part of the near cost optimal solutions. For post-treatment, the near cost optimal alternatives are H2S removal with organic physical scrubbing (HSR OPS) and H2S removal with amine scrubbing (HSR AS). HSR AS has a better performance in the overall environmental impacts followed by HSR MS and HSR OPS. In general, the suggested cost-optimal solution is still having relatively lower environmental impacts and feasible for implementation (cost effective). There is very complicated to find a universal AD solution. Different scenarios (the type of substrate, the scale, product demand, policies) have different constraints and consequently solutions. The trade-offs between cost and environment performances should be a future extension of this work.

Anaerobic digestion of municipal solid waste: Energy and carbon emission footprint

Anaerobic digestion (AD) serves as a promising alternative for waste treatment and a potential solution to improve the energy supply security. The feasibility of AD has been proven in some of the technologically and agriculturally advanced countries. However, development is still needed for worldwide implementation, especially for AD process dealing with municipal solid waste (MSW). This paper reviews various approaches and stages in the AD of MSW, which used to optimise the biogas production and quality. The assessed stages include pre-treatment, digestion process, post-treatment as well as the waste collection and transportation. The latest approaches and integrated system to improve the AD process are also presented. The stages were assessed in a relatively quantitative manner. The range of energy requirement, carbon emission footprint and the percentage of enhancement are summarised. Thermal hydrolysis pre-treatment is identified to be less suitable for MSW (-5% to +15.4% enhancement), unless conducted in the two-phase AD system. Microwave pre-treatment shows consistent performance in elevating the biogas production of MSW, but the energy consumption (114.24-8,040 kWeh t-1) and carbon emission footprint (59.93-4,217.78 kg CO2 t-1 waste) are relatively high. Chemical (∼0.43 kWeh m-3) and membrane-based (∼0.45 kWeh m-3) post-treatments are suggested to be a lower energy consumption approach for upgrading the biogas. The feasibility in terms of cost (scale up) and other environmental impacts (non-CO2 footprint) needs to be further assessed. This study provides an overview to facilitate further development and extended implementation of AD.

Efficiency of microbial inoculation for a cleaner composting technology

AbstractThere are contrasting opinions on the utilisation of microbial inoculant (MI) as a bioremediation technology for composting. The effectiveness can be affected by a diversity of factors, and the reproducibility of results can be a great challenge. This study aims to review the effectiveness of MI, specified as isolated or cultured single and consortium micro-organisms, for composting, with the main component of lignocellulosic waste (LW) and the organic portion of municipal solid waste (OPMSW). The potential for the enhancing effect of each parameter, i.e. compost quality parameters: pH, germination index, nitrogen content, phosphorus content, potassium content, C/N ratio; composting parameters: temperature, odour, enzymatic activities, organic matter content, microbial population, volume reduction, humification, is discussed and evaluated. Based on 13 analysed parameters, the use of MI tends to exert a significant positive effect on the composting of LW compared to that of OPMSW. There has not been a full consensus on the efficiency of MI for composting as it varies on a case-by-case basis. A decision framework is required for the application of MI for different composting scenarios. This overview proposes MI technology, which has been generally less practical than optimising the physicochemical parameters of the composting due to the higher variation in the composting efficiency. Comprehensive comparison studies between the two approaches are needed for further verification which can contribute to the support of composting as a clean technology. The unnecessary uses of resources (e.g. MI, electric, fuel) can consequently be avoided for environmental footprint minimisation.

Evaluation of Microbial Inoculation Technology for Composting

Utilisation of microbial inoculant (MI) in composting is a bioremediation technology aiming to enhance the degradation rate and the compost quality. There is a diverse opinion about the effectiveness of MI in composting. The reproducibility of the results is a great challenge notably for an open composting system compared to a closed in-vessel system. Its efficiency is expected to be affected by the starting materials and the operating conditions. Optimising the physicochemical parameters during composting, i.e. the initial C:N, pH values, moisture content and aeration during composting was reported to be more crucial than the role of MI. This study aims to review the effectiveness of MI for the composting of two types of starting materials, i.e. the organic portion of municipal solid waste (OP-MSW) and lignocellulosic waste (LW). The potential effects of MI to enhance the composting parameters are presented. It is found that the effectiveness of MI to facilitate the composting process is depending on the type of wastes to be managed and the aims to improve the targeted quality of composting. The use of MI tends to exert a more significant positive effect on the composting of LW than the OP-MSW. There is no absolute consensus on the efficiency of MI for composting as it varies on a case-by-case basis. A decision framework is needed for the application of MI for different composting scenarios.

Challenges for energy efficiency improvement Anaerobic Digestion (AD)

One of the major environmental issues and research challenges have been to reduce emissions and effluents without compromising the production performance. The renewable energy recovery from waste to energy is less emitting than using fossil fuels. It can compete with the other renewables if properly generated, transferred, transmitted and used. Anaerobic digestion (AD) is a potential production process to improve the security of energy supply. It also serves as a promising alternative to waste disposal. The feasibility of AD technologies for power generation has been proven in some of the technologically and agriculturally advanced countries however world-wide implementation still needs some development. Presented work focuses to overview the challenges and practices for energy efficiency improvement of AD that have been reported recently, mainly between the years of 2015-2016. The assessment suggests the consideration and/or attentions for substrate, pre-treatment and operation mode of digesters for a better risk minimisation and feasibility maximisation. The characteristics and supply of the substrate were suggested as the initial susceptible factor for the energy efficiency of AD. The systematic review serves as an overview of the AD development and an establishment of technically feasible technologies for further study and extended implementation.

Growth of bacillus coagulans using molasses as a nutrient source

Bacillus coagulans (B. coagulans) can be utilized as microbial inoculant to speed up the bioremediation of wastewater. The effectiveness of the microbial inoculant for treatment is highly selective and relying on the characteristics of the wastewater. A feasible carbon source must be first chosen to pre-culture the microbe prior to the bioremediation. Commercial nutrient broths are efficient to grow the microbial; they are costly for the treatment of large volume of wastewater treatment. This study aims to evaluate the growth rate of B. coagulans using a cheaper nutrient source, i.e. molasses. The commercial Man, Rogosa and Sharpe (MRS) media was used as a benchmark. The growth rate of B. coagulans was conducted at different concentrations of molasses (1 %, 3 % and 5 % (w/v)) and in the MRS broth as benchmark. B. coagulans grown in the MRS has shown a much higher maximum specific growth rate (0.69 h-1) compared to that grown in 1 % (w/v) molasses (0.14 h-1). No growth was observed in the higher concentrations of molasses (3 and 5 % (w/v)). Measuring the colonyforming units of B. coagulans in both the MRS and molasses mediums validated the results. Molasses is a desirable carbon source as it is relatively cheaper and easily available. More studies are needed to improve the maximum specific growth rate of B. coagulans in 1 % (w/v) of molasses.