Environmental Anaerobic Technology

The following sections are included:

• Contents

• Preface

Although the feasibility of anaerobic wastewater treatment (AnWT) has been successfully demonstrated over 100 years ago, its development and implementation had been hampered for decades until the re-introduction of the anaerobic filter process in the 1960s and the technological breakthrough in the 1970s of the upflow anaerobic sludge blanket (UASB) pprocess. This has led to the further developments of a number of modern high-rate AnWT systems, such as expanded granular sludge bed (EGSB) reactor, and anaerobic baffled reactor (ABR), for numerous types of industrial wastewaters. Furthermore, UASB reactor systems have been successfully applied for the treatment of raw domestic sewage, followed by an aerobic polishing post-treatment, if needed; the enormous potentials of the innovative micro-aerobic post-treatment will soon be demonstrated at full scale. Moreover, based on improved understanding of these processes, e.g., in the microbiology, biochemistry, the immobilization of required organisms and consortia, and reactor and process technology, and in control and steering, undoubtedly substantial further progress in the applicability of these anaerobic systems will be achieved in near future. These treatment systems, greatly based on the Natural Biological Mineralization route (NBM), are going to act as a crowbar to force Environmental Protection toward a significantly more sustainable tackle. They enable closing of water and substance loops, viz. valorization of pollutants, reuse of treated water, and will stimulate minimization of wasting of clean water in wastewater collection and transport. Along with the implementation of these systems a major step will be made toward more sustainability in society.

In France, treatment of industrial effluents by anaerobic treatment has been well established especially in the agricultural and food industries. With the increasing cost of green electricity, we see an increase of anaerobic reactors constructions for farm and municipal solid wastes. Here we report five developments currently underway. The first is a modified moving bed process,called “anaerobic moving bed biofilm reactor” (AMBBR), in which a carrier is moving inside the reactor. It is easy to manage, and we can reach an organic load of 24 kg-COD·m⁻³·d⁻¹. The second technology, called “PROVEO”, is for wastewater treatment. The process uses support media for trapping microbial flocs and for biofilm growth. The third technology is combining an anaerobic filter with ultrafiltration (UF) membranes that have been applied to the treatment of dairy wastewater. The treated wastewater is free of suspended solids and the organic load reaches 10 kg-COD·m⁻³·d⁻¹. The fourth technology, named ERGENIUM, is about the treatment of solid wastes in a two-stage process, i.e., acidogenesis followed by methanogenesis. The leachate from the first reactor is separated from the solid fraction and further treated in an anaerobic filter. The fifth technology development is on the pH control of the anaerobic reactor so that the biogas may have a steady methane concentration.

This chapter is to summarize the history and applications of anaerobic technology in Japan for decades to industrial wastewater treatment, sewage sludge digestion and methane fermentation of food/agricultural wastes, based on literature available only in Japanese. Over 300 upflow anaerobic sludge bed (UASB) and expanded granular sludge bed (EGSB) full-scale plants are now in operation for the treatment of beer, soft drink, distillery, food and chemical wastewaters. Anaerobic sludge digestion began in 1932, and is now used in over 300 sewage treatment plants with a total digester volume of 2.1 × 10⁶m³, producing enough methane to heat the digester or to generate biofuel or electricity. Since the enactment of the Basic Act for the Promotion of the Recycle-Oriented Society, a national program called Biomass Nippon Strategy started in 2002 has attracted much public attention to the concept of converting the annual 89 × 10⁶ tons of livestock wastes to resources. The estimated potentials of methane recovery are 1.6×10⁹m³·y⁻¹ from the livestock wastes and 1.7 × 10⁹m³·y⁻¹ from the municipal solid wastes (MSW). Since 2006, over seventy methane fermentation plants have been in operation treating livestock wastes, and another fifty plants for the treatment of food wastes and the organic fraction of MSW. Recent developments of biogas technology include the application of anaerobic membrane bioreactor and bio-desulfurization of biogas.

Anaerobic pre-treatment of domestic sewage using UASB reactor systems offers a number of advantages, e.g., system compactness, negligible or no energy consumption, stabilised excess sludge production, potential for energy recovery, low-cost accessibility of sewage for agricultural reuse purposes, etc. Research on high-rate anaerobic sewage treatment started in the early 1980s with the 64m³ UASB pilot plant in Cali, Colombia and various other initiatives in Brazil. Hereafter, the technology was adapted to full-scale conditions and slowly introduced in the market. This chapter describes the anaerobic treatment process for domestic sewage and evaluates the performance of current large-scale reactor systems located in (sub-)tropical areas. Although the perspectives from the early 1980s were confirmed in bench-scale studies, a considerable number of the recently constructed treatment plants deliver disappointing performance results. In many cases, inadequate designs, improper reactor operation and insufficient control are responsible for these poor performances. A brief survey is made on the preconditions that must be met prior to starting and operating sewage treatment plants based on the UASB concept. Adequate maintenance and basic system knowledge at the level of plant manager seem to be indispensable for full-scale success.

The upflow anaerobic sludge blanket (UASB) process has been shown to be effective for removal of organic substances from sewage, especially under warm climate conditions. However, treatment of sewage by UASB alone is not sufficient to meet the effluent discharge standards set by many developing countries, meaning that UASB effluent needs post-treatment process. In combination with properly selected processes, a sustainable and appropriate wastewater treatment system can be established. In this chapter, the down-flow hanging sponge (DHS) process is introduced as an appropriate post-treatment process for UASB-treated sewage, with emphasis on its basic concept, mechanism of treatment, history of development, and recent successful results of a demonstration study at a full-scale DHS plant in India.

Advanced anaerobic processes integrating granular sludge are emerging technologies for efficient wastewater treatment. As a result of increasing acceptance toward the anaerobic granular processes, a growing interest in the technology has resulted in a remarkable increase of full-scale plants installed worldwide over the last three decades. While the technology is well accepted and much research work had been conducted on granule formation, insight unfolding the granulation remains unclear. This chapter presents a review of literature documenting theoretical elucidations on anaerobic granulation and recent advances in granulation research with hydrogen production. Applications of anaerobic granulation in various reactor systems and the future trend are also outlined.

In the last decade anaerobic membrane reactors (AnMBRs) have evolved from aerobic MBRs, with the membrane either external or submerged within the reactor. These reactors can achieve high chemical oxygen demand (COD) removals (∼98%) at low hydraulic retention times (HRTs) of 3 hours. In addition, since the membrane stops biomass being washed out of the reactor, they are capable of enhancing performance with inhibitory substrates, and at psychrophilic and thermophilic temperatures, and enable nitrogen removal via Anammox. As with MBRs, fouling is an issue, but addition of activated carbon or resins/precipitants can remove soluble organic products (SMPs) and enhance flux. Due to their low energy use and solids production, and a solids-free effluent, they also have considerable potential to enhance nutrient and water recycling. Nevertheless, more work is needed to compare fouling in aerobic and anaerobic systems, to determine how much knowledge in aerobic systems can be transferred, to determine how reactor operation influences fouling, to evaluate the effect of different additives to the reactor on membrane fouling, to determine whether nitrogen removal can be incorporated into AnMBRs, to determine methane solubility at low temperatures and recover it from the effluent, and to establish sound mass and energy balances on pilot scale plants to evaluate the economics of AnMBRs.

The anaerobic baffled reactor (ABR) was developed in the early 1980s, and consists of a series of compartments (up to 8) in one reactor which are baffled to force the incoming wastewater up through a series of sludge blankets, thereby reducing the loss of biomass. It can also be operated with granules or internal media which enhance its stability. Hence the sludge retention time (SRT) can be separated from the hydraulic retention time (HRT), leading to good chemical oxygen demand (COD) and solids removal, low sludge production, and a small footprint. Tracer studies have shown that the reactor approximates to a series of completely stirred tank reactors (CSTRs), and this promotes the separation of bacterial trophic groups down the length of the ABR enhancing performance and stability. Due to its design, the reactor can tolerate both severe hydraulic and organic shock loads without failing, and is now starting to be used at full scale in many developing countries as a cheap and efficient method of low cost sanitation, and industrial wastewater treatment, often with the added benefit of energy production. This chapter reviews the current state of knowledge with ABRs focussing on: reactor development, hydrodynamics, performance, biomass characteristics and retention, soluble microbial products (SMPs), modelling, and full-scale operation.

Phenolic pollutants are commonly found in wastewaters from synthetic chemicals, pesticides, coal conversion, pulp-paper, oil-refining, plastics, and pharmaceuticals industries. They are of significant environmental concerns because of their toxicity and potential carcinogenic property. The upflowanaerobic sludge blanket (UASB) process has been found effective for the degradation of many recalcitrant pollutants, including phenols. However, phenolic pollutants at high concentrations in wastewater may also inhibit the bioactivities of the granular sludge and consequently lower the treatment efficiency. This paper is to review literature on the anaerobic treatment of phenolic pollutants with emphasis on the following aspects: (1) phenolic inhibitory effect to the anaerobes, and the tolerance levels; (2) treatment of phenolic wastewater in anaerobic reactor of various designs; (3) effects of operating factors, including hydraulic retention time, effluent recirculation, temperature, loading shock and co-substrate on the biodegradation of phenols; and (4) the anaerobes and the degradation pathway involved in anaerobic degradation of phenols. Overall, phenolic pollutants in wastewater, when operated below the inhibitory concentrations and avoiding the loading shocks, can be effectively degraded under anaerobic processes with proper sludge acclimation, effluent recirculation and, if necessary, co-substrates.

Anaerobic technology has been applied to sludge digestion for over 50 years and to wastewater treatment for nearly 30 years. This chapter reviews the nucleic acids-based molecular methods for the analysis of microbial communities, and their applications for the microbial communities in anaerobic reactors. At first, nucleic acid extraction and selection of nucleic acid biomarkers are discussed with emphasis on special aspects related to anaerobic sludge samples. Second, the common nucleic acids-based methods are introduced, including cloning and sequencing for characterization, quantitative real-time polymerase chain (qRT-PCR) for quantification, fluorescence in situ hybridization (FISH) for visualization, denaturing gradient gel electrophoresis (DGGE) and terminal restriction fragment length polymorphism (T-RFLP) for screening/typing/monitoring, and stable isotope probing (SIP) and microautoradiography–FISH to link the microbial identity with the specific functions. Finally, applications of the aforementioned molecular methods in anaerobic technology are summarized, focusing on identification of new species in the anaerobic process, characterization of microbial compositions in the anaerobic reactors, visualization of layered structure of anaerobic granular sludge, etc.

The application of mathematical models has become a standard practice in wastewater treatment plant design, optimization, and operational control. There are many state-of-the-art models currently available for different unit processes applied forwastewater treatment plants. These models have been implemented in various commercial process simulators and are readily available for uses by researchers, engineers, and consultants. Although, the commercial process simulators are easy to use, the magnitude and complexity of biochemical, and physico-chemical reactions involved in wastewater treatment make it challenging for the first time practitioner to adequately grasp the intricate details of the model. As the benefits of modeling in wastewater treatment are well accepted, the intention of this chapter is first to familiarize the first-time user to important basic fundamentals and terminologies used in present day wastewater treatment models. This is followed by detailed discussions on a few important issues which shall be helpful in practical application of Anaerobic Digestion Model No. 1 (ADM1).

A huge volume of lignocellulosic wastes is currently produced worldwide. Anaerobic digestion is an effective disposal method for these wastes because of its low cost and environmental benefits. The utilization of the produced methane-rich biogas can reduce the dependence of energy on fossil fuels and reduce the emission of greenhouse gas. However, the recalcitrant structure of lignocelluloses in these wastes is the barrier for the hydrolysis of lignocelluloses by microorganisms. Many microbial resources have been used for improving the hydrolysis, among which, rumen microorganisms have shown some advantages because of their high cellulolytic activities. The characteristics and structure changes of lignocelluloses in biological conversion have been investigated with chemical and imaging analysis to determine which characteristics are responsible for limiting the microbial hydrolysis and which changes benefit for the bioconversion. This chapter describes the recent results of chemical analysis using atomic force microscopy (AFM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), GC/MS, and X-ray diffraction (XRD) on the biological conversion of lignocellulosic wastes, and especially on the anaerobic digestion of lignocellulosic wastes by rumen microorganisms, and kinetic analysis of such a bioconversion.

Active research has been conducted on the production of biofuels from the abundant and inexpensive lignocellulosic wastes of forestry, agriculture, and municipal solid wastes. However, degradation of lignocellulose is hindered by the recalcitrant nature of lignocellulose. Hence, hydrolysis/saccharification of lignocellulose becomes the rate-limiting step for the fermentative production of cellulosic biofuels (such as H₂ and ethanol). Hydrolysis of cellulosic materials by biological means is environmentally benign and could be achieved either by using cellulolytic microorganisms or cellulolytic enzymes collected from those microorganisms. Biofuels production could be achieved by direct fermentation of raw lignocellulosic wastes or by a twostage process, in which the hydrolysis step and the anaerobic fermentation step are operated separately. In this chapter, we review the state-of-the-art of the following aspects related to the enzymatic hydrolysis of lignocellulosic wastes for anaerobic fermentation and bioenergy production: (1) structure of plant cell walls and their cellulose, hemicellulose, and lignin components; (2) lignocellulose-degrading microorganisms and their characterisitics; (3) production of enzymes degrading lignocellulose; (4) treatment of wastes using lignocellulose-degrading enzymes; and (5) anaerobic fermentation process for bioenergy production from enzymatically pretreated lignocellusic wastes.

This chapter is to review recent research progress on the three technologies for biohydrogen production from wastes and wastewater, i.e., dark fermentation, photo-fermentation, and microbial electrolysis cells (MEC). Among the three technologies, the development of dark fermentation is the most advanced, as evidenced by the installation of a full-scale demonstration plant, whereas the development of the other two still remains at infancy stage. For dark- and photo-fermentation, discussions are mainly focused on the development in China. Discussion of dark fermentation includes reactor types, startup strategies, and factors affecting the hydrogen production process, such as pH, partial pressure of hydrogen, hydraulic retention time, organic loading rates, sludge pretreatment, and metal toxicity, as well as pilot and full-scale production experiences. Discussion of photo-fermentation includes inoculums, light intensity, carbon and nitrogen sources, pH, metal ions, and the process of coupling with dark fermentation. Discussion of MEC includes its architecture, startup, membrane and electrode materials, anode potential, methane production, etc. Examples of producing hydrogen from MEC using fermentation effluent of molasses, lignocellulose, and cellobiose are also reviewed. Lastly, a conceptual flow diagram for a proposed biohydrogen production system treating wastes and wastewater is discussed.

We have studied biohydrogen production in three kinds of continuous reactors: continuous stirred anaerobic bioreactor (CSABR), carrier-induced granular sludge bed reactor (CIGSBR), and agitated granular sludge bed reactor (AGSBR). Among the three, the CSABR was the most efficient one with a hydrogen production rate (HPR) of 362 1·1⁻¹·d⁻¹ (i.e., 14.7 mol·1⁻¹·d⁻¹), using sucrose as substrate, and an optimal yield of ca. 3.5 mol-H₂·mol-sucrose⁻¹ with a feeding sucrose concentration of 30–40 g-COD·1⁻¹ and a short hydraulic retention time (HRT) of 0.5 h. En route toward the commercialization of this high-rate biohydrogen production process, a pilot-scale system with a 4001 fermentor was constructed and operated to identify the scale-up operating parameters. The pilot fermentor was operated at 35°C and fed with sucrose (20 g-COD·1⁻¹). After two days of startup operating in batch mode, the fermentor was operated in continuous feeding mode with 12 h of HRT. The H₂ production rate increased from 2.5 to 15.6 1·1⁻¹·d⁻¹ with the increase of organic loading rate from 40 to 240 g-COD·1⁻¹·d⁻¹. Results of DGGE analysis indicate that a stable hydrogen production was obtained as Clostridium pasteurianum was being predominant in the fermentor.

Although various means of biological H₂ production have been introduced, fermentative H₂ production has superior aspects such as fastest H₂ production rate and waste treatment. This chapter describes the principle and performance of various processes producing H₂ from wastewater, livestock wastes, and solid wastes. Of all the possible feedstock, food-processing wastes have been studied the most for H₂ production since they are rich in easily biodegradable carbohydrates. More recently, there is an increasing interest in using lignocellulosic biomass due to their abundance on earth. The existence of indigenous non H₂-producing bacteria in the waste biomass and the low carbohydrate content in the substrate are the key obstacles for enhancing H₂ yield. In order to maximize bioenergy recovery and waste reduction, a two-stage process, consisting of a fermentative H₂ production stage followed by a second fermentation stage of CH₄ production from the organic residues, was proposed. It was found that 80–90% of the energy content in the wastes could be recovered by this two-stage process with less than 10% in the first-stage. At the end of chapter, the feasibility of the two-stage process as well as further research areas needed to improve the process efficiency and applicability are discussed.

The technologies for hydrogen and ethanol productions from sugarcane juice were described based on information from laboratory-scale experiments. Bioconversions of sugarcane bagasse to hydrogen and ethanol were also discussed in terms of bagasse pretreatment and detoxification of the inhibitors in the hydrolysate. Two process configurations used in the ethanol fermentation process, i.e., separate hydrolysis/fermentation and simultaneous saccharification/fermentation, were also presented.

Using unsustainable fossil fuels for energy is a critical issue in today's society, and seeking a reliable and economical alternative energy source has raised a lot of attention recently. One of the potential solutions is to convert biomass, which is available in many forms, into fuels and commercial chemicals. The gasification of biomass followed by synthesis gas (syngas) fermentation is one of the novel methods for the potential commercialization necessary to the answer of fossil fuels replacement. An overview of fermentation from biomass-generated syngas is summarized in this chapter.

The following sections are included:

• Index