Recycling of Solid Waste for Biofuels and Bio-chemicals

Industrialization and urbanization together have a cumulative effect on generating significant amounts of urban solid waste which leads to increasing threats to the environment. India with a population of about 1.27 billion people alone generates about 0.2–0.5 kg of waste day⁻¹ capita⁻¹ of which around 40–50 % is organic in nature. According to published reports, if these organic fractions of the waste are not treated properly and reach the landfill site; they can become a major source of greenhouse gas (GHG) emissions and causes leaching of harmful pollutants. These GHG and newly generated pollutants have been found to have detrimental effects on ground water, and create imbalances in the ecosystem. Therefore, ‘need of the hour’ is to utilize the energy that is stored in the waste through different available technologies like composting, vermicomposting, fermentation and biomethanation etc. The process of biomethanation appears to be a more reliable and promising technology as it not only aims to solve the problem of organic solid waste, but also provides sustainable energy in the form of biogas. Moreover, when compared with other technologies, biomethanation is economic, eco-friendly and less labor intensive. Even though several research studies were conducted in the field of biomethanation, the process is still unpopular especially in developing countries due to lack of appropriate knowledge, treatment systems and due consideration by the government.

As the world’s largest developing country, China creates considerable quantities of municipal solid waste (MSW) every day, which is one of the most serious urban pollution sources. Waste to energy can not only reduce greenhouse gas emission from simple piling of solid waste, but also can generate energy to cope with the increasing demand on fossil fuel. So far, landfill gas-fired power generation, MSW incineration and anaerobic digestion are the primary waste to energy technologies successfully applied in China. In recent years, MSW incineration power generation technologies have undergone rapid development with the demand for a low carbon economy and the encouragement of national policies. The distribution and operation status of various waste to energy facilities built in China are assessed. Meanwhile, the limitations and potential development trend of landfill, incineration and anaerobic digestion are discussed. In addition, a series of preferential policies and regulations to encourage the expansion of MSW to energy is presented.

In the 21st century, global warming and climate change are among the greatest environmental challenges and humanitarian crisis. Globally, annual greenhouse gas (GHGs) emissions from solid waste disposal sites is estimated to be approximately a quarter of total anthropogenic methane emission. Integrated solid waste management, therefore, provides significant opportunities to control environmental pollution and minimize the negative impacts of global climate change. This chapter illustrates the current status of global GHGs emission in relationship with population growth and solid waste generation. Mathematic models used to quantify GHGs generated from the waste sector as the zero-order model (i.e., SWANA, German EPER and IPCC Default Method) and the first-order model (i.e., TNO, LandGEM, IPCC First-Order Decay; FOD) are explained including application to certain inventory in selected countries. Life Cycle Assessment (LCA), which involves the cradle-to-grave concept, environmental burden from global warming and selected case studies are described and applied to assess GHGs emissions from various solid waste management options such as recycling, composting, sanitary landfilling, anaerobic digestion, incineration, mechanical biological treatment (MBT), source reduction, and utilization and application of biochar. Existing solid waste management practices and innovative options to achieve GHGs mitigation and community adaptation including resiliency are presented. Lessons learned and best practices in solid waste management from Thailand (i.e., Bangkok Kamphaeng Sean West: Landfill Gas to Electricity Project) and from other countries (i.e., GHGs mitigation project: MBT plant in Gaobeidian, Hebei province, People’s Republic of China; municipal solid waste composting project in Ikorodu, Lagos State, Federal Republic of Nigeria; and gasification, landfill gas and anaerobic digestion in Bali, Indonesia) are further discussed.

With climate change looming and the unsustainable supply of fossil fuels, the development of renewable and clean energy is urgently required. An often neglected source of clean energy is the organic material contained in waste and wastewater. Millions of tons of solid organic waste and wastewater are generated everyday worldwide. Instead of consuming energy, anaerobic digestion can be applied to treat the generated waste, thus achieving the objective of waste treatment for public health protection and also recovery of renewable methane for heat and power purposes. In this chapter, the benefits of anaerobic digestion will be introduced followed by a discussion on the mechanism and the typical design principles of anaerobic digestion systems. Some of the recent advancement of anaerobic digestion systems such as membrane bioreactors, fluidized bed reactors and co-digestion systems will be presented in the subsequent sections. The state-of-the-art molecular biological tools to monitor and diagnose the microbiology of anaerobic digestion systems will also be discussed. Lastly, the future outlook of anaerobic digestions will be addressed.

Anaerobic digestion (AD) is one of the significant strategy for the management of solid organic waste. It is a biological process that degrade the organic matter in the absence of oxygen with ultimate products being CO₂ and CH₄. Solid waste has to be treated, mechanically or chemically or biologically prior to fed into the anaerobic digesters for an efficient treatment. Solid wastes with lignocellulosic and hemi cellulosic materials are difficult to degrade and need proper pre-treatment. The anaerobic digester should follow optimum parameters such as; temperature 37 °C for mesophilic and 55 °C for thermophilic digestion, pH 6.5–8.0, hydraulic retention time (HRT) of about 35–40 days for mesophilic and 15 days for thermophilic digestion, feed C/N ratio 30/1 for a successful degradation of waste material and biogas production. A balanced active bacterial and methanogenic Archaeal population in the AD is most important factor that influence the stable digestion of the waste material. Molecular techniques based on 16S rDNA gene and other functional gene markers such as McrA, Pct, nif are handy to monitor the treatment process. The most advanced next generation DNA sequencing platforms have been serving to identify the community structure and playing an important role in assigning the microbial communities involved to their function. These techniques further helps in rapid bioaugmentaion of AD for the stable operation of digestion process.

The total amount of manure production increased fast in response to rapidly increasing demand for livestock production, which poses a strong public health threat due to the greenhouse gases (GHG) emissions and leachates without appropriate treatment. Anaerobic digestion is available technology for livestock manure treatment with new business opportunities and benefits for the society, such as bioenergy of CH₄ and nutrients are extra income, odor and pathogens are reduced and GHG emission are limited. The productions of chicken manure, cattle manure and pig manure were introduced with evaluation of potential energy production. The toxicity of ammonia/ammonium in the anaerobic digestion process was evaluated with microbial community dynamics. Operation conditions effects on methane production were analyzed, such as pH, organic loading rate (OLR) effects and the ammonia stripping pretreatment effects on the CH₄ conversion. The dynamic of functional archaeal and bacterial community were also conducted. Methanosaeta dominated in the steady stage of chicken manure thermophilic digestion but Methanothermobacter dominated in the inhibition stage and Methanosarcina thrived in the recovered stage. In contrast, under mesophilic conditions, Methanosarcina dominated in the steady stage while in the inhibition stage Methanosaeta and Methanoculleus thrived and lastly recovered to Methanosaeta. Poultry manure can be easily inhibited by ammonia compared to cattle manure and pig manure digestion since it has a high nitrogen content, which was more suitable for mesophilic digestion with evidence of process resilience in mesophilic digestion. Pre-treatment of ammonia stripping or co-digestion are the effective ways to generate a stable process.

Malaysia is one of the world’s largest palm oil exporter (39 % of world palm oil production and 46 % of world exports). In the process of producing palm oil, a considerable amount of water is needed, leading to the generation of large volumes of wastewater also known as palm oil mill effluent (POME). Anaerobic digestion of palm oil mill effluents (POME) has started as early as the 1990s using the anaerobic lagoon system comprising a series of ponds in combination with aerobic and pre-treatment ponds to effectively meet the effluent discharge standards. This conventional open pond system requires long hydraulic retention times, large land area and at the same time release uncontrolled greenhouse gas and odour to the atmosphere. Of late, there has been an emergence of more advanced anaerobic digesters in palm oil mills replacing the conventional lagoon system. This chapter discusses anaerobic technology for POME moving from a purely effluent treatment focus using conventional lagoons to more advanced controlled systems for energy recovery purposes using closed tank digesters. The issues of palm oil mill residues for energy recovery will also be looked at taking into consideration POME co-digestion with other materials and possible environmental impacts.

The content of this chapter focuses on the anaerobic BioReactor Landfill (BRL), an alternative to the traditional “dry tomb” landfill, with the aim of a more rapid degradation of the organic fraction of Municipal Solid Waste (MSW) through leachate recirculation. This technology is mainly based on the moisture increase of waste through liquid injection into the landfill body, as waste degradation is strongly dependent on humidity. The main advantage of bioreactor landfills is the rapid stabilization of the organic fraction, which can be reached in 5–10 years compared to 30–50 years under traditional operation. Biogas production can be therefore increased to higher volumes in less time, improving the efficiency of energy recovery. The main factors regarding MSW biodegradation in BRLs will be presented. Focusing on the different and interconnected phenomena, which take place in such a complex and heterogeneous system, it will be possible to gain an overview of the whole process. A number of studies have shown the positive effects of leachate recirculation on MSW degradation, either at laboratory-scale or on-site. The state of art of both, lab- and full-scale experimentations, will be presented, with a focus on an Italian case study.

A new and promising trend in solid waste management is to operate landfills as bioreactors in which moisture addition (often leachate recirculation) is used to create a solid waste environment capable of actively degrading the readily biodegradable organic fraction of the waste and produce bioenergy. Although the organic strength of leachate is significantly reduced in bioreactor landfills, ammonia-nitrogen (NH₄ ⁺-N) remains an issue, because there is no degradation pathway for ammonia-nitrogen in anaerobic systems. Ammonia-nitrogen removal methods often include complex sequences of physical, chemical, and/or biological processes, including chemical precipitation, nanofiltration, air stripping, and biological nitrification/denitrification via various reactor configurations. This chapter will present the facts about the ammonia nitrogen profile and nitrogen transformation pathways in bioreactor landfills including promising novel removal mechanisms (SHARON (Single reactor system for high activity ammonia removal over nitrite), ANAMMOX (Anaerobic Ammonium Oxidation), CANON (Complete Autotrophic Nitrogen removal Over Nitrite), OLAND (Oxygen Limited Autotrophic Nitrification and Denitrification) etc.) with the support of laboratory-scale and field-scale case studies. In a study on ex situ strategy for NH₄ ⁺-N removal by ANAMMOX applied using AnMBR (Anaerobic Membrane Bioreactors), NH₄ ⁺-N removal efficacy of 85.13 ± 9.67 % was achieved with an average nitrogen removal rate (NRR) of 5.54 ± 0.63 kg NH₄ ⁺-N/m³/day (d) at a nitrogen loading rate (NLR) of 6.51 ± 0.20 kg NH₄ ⁺-N/m³/d at a 1.5 d HRT. An in situ strategy for NH₄ ⁺-N removal by SHARON in a bioreactor landfill gave 85 % NH₄ ⁺-N removal efficacy with 98.5 % nitrite accumulation, while the ANAMMOX process gave 73 % of NH₄ ⁺-N removal efficacy with a specific ANAMMOX activity of 0.96 mg NH₄ ⁺-N/mg MLVSS (Volatile Suspended Solids)/d with an NLR of 1.2 kg N/d. Bioreactor landfills integrated with a combined SHARON-ANAMMOX processes provides promising results for nitrogen management (Total nitrogen removal—84 % and ammonia-nitrogen removal efficacy—71 % at NLR of 1.2 kg N/m³/d in 147 days). Further activities need to focus on full-scale demonstration of in situ ammonia-nitrogen removal in bioreactor landfills and assessing the effect of different environmental conditions affecting important operational parameters of the processes.

Fast pyrolysis is a thermo-chemical conversion method to produce liquid fuel from biomass. This process involves the rapid thermal decomposition of organic compounds in the absence of oxygen. The vapors formed are rapidly condensed to yield a liquid product called bio-oil. Since the major product is liquid, it is easy to store, and handle. Moreover, bio-oil can be readily transported to facilities where it can be most effectively used. Unlike other conversion methods for bio-fuel production, fast pyrolysis utilizes different types of feedstocks, therefore this process can be considered as a tool for solid waste management. Different types of feedstocks ranging from agriculture and forest residues to MSW, plastic wastes and animal manures have been utilized for pyrolysis studies around the world. Liquid fuel production using fast pyrolysis has received much attention in recent years. Bio-oil, the liquid product of fast pyrolysis, can be considered as an intermediate for fuel and chemical production. Bio-char, the solid product of pyrolysis, has multiple applications like bio-char from other methods. The chapter reviews different types of reactors used for fast pyrolysis, bio-oil properties, challenges and opportunities, and the current status of fast pyrolysis applications. In addition, the chapter discusses applications of bio-char and energy and economics of fast pyrolysis.

Plastic usage in daily life has increased from 5 to 100 million tons per year since the 1950s due to their light-weight, non-corrosive nature, durability and cheap price. Plastic products consist mainly of polyethylene (PE), polystyrene (PS), polypropylene (PP) and polyvinyl chloride (PVC) type plastics. The disposal of plastic waste causes environmental and operational burden to landfills. Conventional mechanical recycling methods such as sorting, grinding, washing and extrusion can recycle only 15–20 % of all plastic waste. The use of open or uncontrolled incineration or combustion of plastic waste has resulted in air and waterborne pollutants. Recently, pyrolysis technology with catalytic reforming is being used to convert plastic waste into liquid oil and char as energy and value-added products. Pyrolysis is one of the tertiary recycling techniques in which plastic polymers are broken down into smaller organic molecules (monomers) in the absence of oxygen at elevated temperatures (>400 °C). Use of catalysts such as aluminum oxides, natural and synthetic zeolites, fly ash, calcium hydroxide, and red mud can improve the yield and quality of liquid oil. The pyrolysis yield depends on a number of parameters such as temperature, heating rate, moisture contents, retention time, type of plastic and particle size. A yield of up to 80 % of liquid oil by weight can be achieved from plastic waste. The produced liquid oil has similar characteristics to conventional diesel; density (0.8 kg/m³), viscosity (up to 2.96 mm²/s), cloud point (−18 °C), flash point (30.5 °C) and energy content (41.58 MJ/kg). Char produced from pyrolysis can be activated at standard conditions to be used in wastewater treatment, heavy metals removal, and smoke and odor removal. The produced gases from pyrolysis are hydrogen (H₂), carbon monoxide (CO) and carbon dioxide (CO₂) and can be used as energy carriers. This chapter reviews the challenges and, perspectives of pyrolysis technology for production of energy and value-added products from waste plastics.

Food waste (FW) causes economic and environmental problems worldwide. Currently, most food waste is landfilled or incinerated for possible energy recovery. However, these methods have serious adverse effects on the environment. FW is nutritionally rich and offers a unique microbial feedstock for the production of numerous valuable bioproducts. The aim of this review is to investigate the technologies used to convert FW to forms of renewable energy such as biodiesel, ethanol, hydrogen and methane. Life-cycle assessment is performed to examine and compare the environmental effects of various methods of FW conversion.

The tanning industry occupies a unique place in the industrial map of India. Nearly 2000 tanneries are in operation in India, with a total processing capacity of 700,000 tonnes of hides and skins per annum. During treatment of tannery wastewater, primary (chemical) and secondary (biological) sludge are generated. Safe disposal of sludge generated during treatment of tannery wastewater is a major concern from an environmental point of view. At present, the sludge is being disposed off in secured landfill facilities. Each tannery is spending about Rs. 750 to Rs. 1000 per tonne for disposal of sludge into secured landfill facilities, which includes transportation of sludge from the tannery to the secured landfill facility, loading and unloading. Solidification and Stabilization (S/S) is the Best Available Treatment Technology (BATT). Hence, in the present study, in order to utilize the sludge generated during treatment of tannery wastewater, S/S studies were carried out for encapsulation of chromium-bearing sludge. The solidification process was carried out using binding materials such as cement and lime in various combinations. Various performance tests were carried out on the S/S blocks to understand the leaching behavior of chromium by conducting leaching tests viz., Toxicity Characteristic Leaching Procedure (TCLP), EP ToX and ANS Leaching Tests and compressive strength of S/S blocks were determined.

The accumulation and treatment of waste in a centralised facility has the potential to generate and become a source of odour nuisance in a community. Positive engagement with the public and developing their understanding of odour pollution can help resolve conflicts between the facility siting and operation and vicinity to nearby residences. This chapter unravels the potential of odour generation and common odorous compounds from different waste to energy recovery facilities including anaerobic digestion, incineration and refuse-derived fuel (RDF) plants. The olfactometer and its principals of operation will be described to justify the applicability of the equipment in odour impact assessments. Finally, the chapter also present technologies of odour control and life cycle approach in determination of the suitable control technologies.