Anaerobic Reactors for Sewage Treatment: Design, construction and operation

Carlos Augusto de Lemos Chernicharo, Thiago Bressani-Ribeiro, Carlos Augusto Lemos Chernicharo, Thiago Bressani-Ribeiro

• Editorial: IWA Publishing
• Año: 2019
• ISBN:
  9781780409245
• Categoría: Ciencias biológicas
• Categoría: Ciencia medioambiental

Anaerobic sewage treatment using UASB reactors has significantly expanded in the last few decades and is now a consolidated technology in some warm climate regions. Several advantages of the anaerobic process make it a more sustainable option for sewage treatment. However, there are still important constraints related to design, construction, and operation of UASB reactors. Conversely, there is enough knowledge, experience, and proven technology that can be used to effectively tackle all the related drawbacks.This book delivers the most relevant techno-scientific developments from academia and water authorities, comprehensively addressing the main aspects of interest in design, construction, and operation of UASB reactors for sewage treatment. Special attention is given to the proper and integrated management of sludge, scum, gaseousemissions, energy recovery, and effluent quality. The main purpose is to provide information and share experiences not yet compiled in the specialized literature on anaerobic sewage treatment. Therefore, a sequence of 12 well-interconnected chapters consolidates the practical knowledge and experiences that important research groups and recognized professionals worldwide have acquired over the past 20 years in demo- and full-scale anaerobic-based sewage treatment plants.Anaerobic Reactors for Sewage Treatment: Design, Construction and Operation can significantly contribute towards a responsible expansion of the anaerobic technology in the world. The book is a valuable tool for engineers, constructors, operators, wastewater utility managers, as well as for students interested in anaerobic processes for sewage treatment.

© IWA Publishing 2019. Carlos Augusto de Lemos Chernicharo and Thiago Bressani-Ribeiro Anaerobic Reactors for Sewage Treatment: Design, Construction and Operation DOI: 10.2166/9781780409238_0001

Chapter 1

Introduction to anaerobic sewage treatment

Carlos A. L. Chernicharo*, Thiago Bressani-Ribeiro and Marcos von Sperling

Department of Sanitary and Environmental Engineering (DESA), School of Engineering, Universidade Federal de Minas Gerais (UFMG), Av. Antônio Carlos 6.627, Belo Horizonte/MG, 31270-901, Brazil

*Corresponding author: [email protected]

1.1 INTRODUCTION

From the experience with anaerobic filters reported in the classic publication of Young and McCarty (1969), a group of researchers from the University of Wageningen in the Netherlands, led by Professor Gatze Lettinga, suggested replacing the support medium by inserting a phase separator (liquid, solid, and gaseous) at the top of the reactor. This concept was considered the initial stage in the development of the UASB (Upflow Anaerobic Sludge Blanket) reactor (Lettinga, 2014). The first investigations with UASB reactors were related to the treatment of high-strength wastewater from potato processing for starch extraction and from beet processing to obtain sugar. In the mid-1970s, the first tests with UASB reactors treating more diluted wastewater, such as sewage, were carried out at laboratory scale (30–120 L) and pilot scale (6 m³) at the village of Bennekom (the Netherlands). The difficulties associated with the need to heat the sewage to simulate the temperature in tropical countries motivated the search for partnerships in the effort to establish UASB reactors in developing countries. A project between the Dutch and Colombian governments, with the participation of the University of Wageningen and the consulting company Royal Haskoning, enabled the implementation of a demonstration-scale UASB reactor (64 m³) in the city of Cali in Colombia (Lettinga, 2014). The satisfactory results obtained have led to the definition of the initial basis for the criteria and parameters for the design, operation, and maintenance of UASB reactors applied to sewage treatment. From this experience, the implementation of full-scale reactors (∼1,000 m³) was carried out in the city of Cali, and research projects were conducted in India, Ghana, the Middle East, and in Latin America in Brazil, Colombia, and Mexico.

In Brazil, specifically, the use of UASB reactors for sewage treatment was introduced in the 1980s, when projects were initiated by several national research groups and engineers working in the sector. The designers of the Companhia de Saneamento do Paraná (Sanepar) in the state of Paraná visited the Netherlands in the 1980s, interacting with Professor Gatze Lettinga. This led to the design of a variant of the UASB reactor, named RALF, widely used by Sanepar. During the initial stages, the still incipient design and operation of the UASB reactors led to difficulties in respect of the credibility of the system, culminating in the rejection of anaerobic technology by some sanitation companies and environmental agencies. However, confidence has been re-established in recent decades because of the intensification of studies and research in this field, as well as the experience gained from the operation of full-scale reactors. Undoubtedly, an important contribution to the consolidation and dissemination of anaerobic technology for the treatment of sewage in Brazil was made by the Basic Sanitation Research Program (PROSAB), developed between 1997 and 2007, involving several universities, research institutes and sanitation companies (Campos, 1999; Chernicharo, 2001).

Sewage treatment plants (STPs), comprising UASB reactors followed by aerobic post-treatment, generally enable a reduction of 20–50% in implementation costs (CAPEX) and more than 50% in operational costs (OPEX) compared with conventional activated sludge plants (Alem Sobrinho & Jordão, 2001; Chernicharo, 2006; Silva, 1993; von Sperling & Chernicharo, 2005). This cost reduction is one of the leading factors for the increase in the levels of sewage treatment in Latin America (Chernicharo et al., 2015).

In addition to the operational simplicity of the UASB reactors compared with that of conventional aerobic (e.g. activated sludge) or physicochemical processes, as well as the financial aspects previously mentioned, the concentration of biomass (2–6 g L⁻¹) and the sludge age (>30 days) in the reactor are typically high, which significantly reduces its volume compared with those of the other sewage treatment processes. Other advantages of UASB reactors are the absence of a support medium because of the dispersed biomass growth, the low production of sludge, and the reduced (or zero) energy expenditure, factors that are typical of anaerobic systems. Additionally, the excess sludge that must be withdrawn is thickened and digested already and can therefore be routed directly to the dewatering unit. Finally, an important factor is the generation of biogas that can be used for energy recovery. The results of the Brazil–Germany Project to Promote the Use of Biogas in Brazil (Probiogás) show that the average methane content in biogas from UASB reactors treating sewage varies between 70 and 81% (Cabral et al., 2016). This means that the biogas has high calorific value, which opens possibilities for different uses, as further addressed in Chapters 2, 8 and 12 of this book.

1.2 UASB REACTORS AND POST-TREATMENT SYSTEMS IN BRAZIL

Given the favourable climatic conditions in Brazil, the anaerobic treatment of sewage and post-treatment of anaerobic effluents have been implemented widely. After successful and unsuccessful experiences in the 1980s and early 1990s, a concentrated research effort that started in the late 1990s and continues today has created significant impetus. In this regard, the aforementioned PROSAB should be emphasized. This initiative facilitated the consolidation of knowledge on several aspects of anaerobic treatment and post-treatment, paving the way for the applied research to be converted into full-scale units.

A survey undertaken by the National Water Agency (ANA, 2017), listing all the urban STPs in Brazil, reinforces this statement. The survey collected data only from the urban seats of all the 8,570 municipalities in Brazil, excluding treatment plants from small settlements, rural communities, industries, institutions, condominiums, hotels, restaurants, and the like. The number of identified STPs totalled 2,768, treating the sewage produced by approximately 71.7 million inhabitants, using several treatment processes. Altogether, the 1,047 existing anaerobic-based STPs (38% of the total STPs) treat the wastewater from about 21.5 million inhabitants (30% of all wastewater presently being treated in Brazil).

Figure 1.1(a–c) concentrates only on the anaerobic-based STPs and shows the data related to UASB reactors (alone) and UASB reactors followed by different forms of post-treatment technologies. In terms of the number of treatment plants (Figure 1.1a) and the population equivalent (Figure 1.1b), there is a wide distribution of the main post-treatment options, but the prevailing ones involve ponds, trickling filters and activated sludge.

Figure 1.1(a–c) Data on UASB reactors and post-treatment technologies applied in sewage treatment in Brazil (Source: adapted from ANA, 2017).

Figure 1.1c shows the mean BOD removal efficiencies obtained from each process variant involving UASB reactor and post-treatment. These data need to be regarded with caution, as they do not reflect all the treatment plants surveyed and, moreover, are based on self-declared information; however, they do present an initial overview of the supposed actual performance under real conditions. In most instances, the mean BOD removal efficiencies are close to 70% without any post-treatment, and in the range of 80 to 90% when post-treatment is applied.

1.3 EXPECTED CONTRIBUTION OF THIS BOOK

Despite the recognised advantages, using UASB reactors for sewage treatment still presents challenges that prevent their maximum operational performance. Notably, the problems associated with these reactors originated from defects in the initial phases of the design. However, inadequate construction processes and operational problems have also been reported in the literature and by sanitation companies (Chernicharo et al...