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Resource Recovery and Reuse for Sustainable Future Introduction and Overview

Wenshan Guo1,2, Huu Hao Ngo1,2, Lijuan Deng1, Rao Y. Surampalli3, and Tian C. Zhang4

1Centre for Technology in Water and Wastewater, School of Civil and Environmental Engineering, University of Technology Sydney, Sydney, New South Wales, Australia

2Joint Research Centre for Protective Infrastructure Technology and Environmental Green Bioprocess, School of Civil and Environmental Engineering, University of Technology Sydney, Sydney, New South Wales Australia and Department of Environmental and Municipal Engineering, Tianjin Chengjian University, Tianjin, China

3Global Institute for Energy, Environment and Sustainability, Lenexa, KS, USA

4Department of Civil Engineering, University of Nebraska-Lincoln, Omaha, NE, USA

1.1 Introduction

In recent years, resource (i.e. water, raw materials, and nutrients) and energy have been subject to high pressure caused by climate change, demographic and land use changes, increase in world population, and high standards of living together with urbanization [1]. Moreover, traditional water management (i.e. take-make-waste approach) and waste management (i.e. waste dumping in landfill sites) techniques have aggravated resource scarcity and environmental, social, and economic problems [2]. Additionally, rare and precious resources (i.e. indium, silver) will be used up by traditional supplies of these elements [3]. It is predicted that the annual energy demand will reach around 23?TW worldwide by 2050 [4]. Therefore, resource and energy recovery and reuse should be realized to alleviate resource scarcity and environmental degradation, and enable economic benefits.

Resource recovery can be achieved from two sources: water and waste. Current studies have focused on the recovery of heat, organic carbon, and nutrients from various types of wastewaters. The heat is recovered from household water (i.e. shower water), sewer, or wastewater treatment plants by a heat recovery system, which mainly contains a heat exchanger and a heat pump [5]. Nutrient recovery from wastewater, especially phosphorus recovery, is commonly achieved by struvite formation. Moreover, energy, nutrients, and materials can also be recovered from different kinds of wastes; one such example is the recovery of renewable energy from waste in the form of value-added products (e.g. methane containing biogas and ethanol), phosphorus from animal manures, food waste and sewage sludge, and materials in terms of heavy metals and scarce and valuable metals from mining waste, municipal and industrial waste, and e-waste [3, 6, 7].

This chapter gives a brief introduction, key drivers, current status, and future perspectives of resource and energy recovery and reuse. The chapter is divided into four sections: background, the current status for waste generation and recovery, the research needs of resource and energy recovery and reuse, and a brief review on the core ideas and key researches for each book chapter.

1.2 Background

1.2.1 Hierarchy of Resource Use

For effective resource management, an alternative "hierarchy of resource use" (HRU) has been proposed by Gharfalkar et al. [8] to clarify "prevention, preparing for re-use, re-cycling, other recovery and disposal" in the latest version of European Commission's Waste Framework Directive 2008/98/EC and consider the "waste" as "resource." Figure 1.1 displays the proposed alternative HRU. HRU consists of five sections as follows:

1. (i) Replacement: rethinking, reinventing, or redesigning to remove or replace existing demand with demand for environmentally benign materials or objects and/or replace nonrenewable resources with renewable resources.
2. (ii) Reduction: reinventing or redesigning to "reduce" use of resources, including reduction in consumption of resources, waste generation and resultant environmental degradation.
3. (iii) Recovery involves preparing materials for reuse (a reusable material or an object can be reused by the preparing operation); reuse (reuse without any further operation, repair and reuse, refurbish and reuse, recondition on and reuse, remanufacture and reuse, any other operation and reuse); reprocessing (recycle, downcycle, and upcycle ["waste" is reprocessed into materials with the same, lower, and higher purpose/value than the original, respectively)]), and other recovery (energy recovery and/or recovery of materials to be used as fuels or for backfilling operations).
4. (iv) Rectification (a waste treatment operation before disposal).
5. (v) Return (disposal).

1.2.2 Analyzing the Needs for Resource and Energy Recovery and Reuse

The key drivers for resource and energy recovery and reuse mainly comprise population growth, environmental impacts, resource scarcity, and economic aspects. Figure 1.2 shows the interaction among the four key drivers for resource and energy recovery and reuse.

1.2.2.1 Population Growth

In 2019, the global world population reached 7.7 billion and it has been predicted that the global population will increase dramatically up to 9.7 billion in 2050 and 10.9 billion in 2100 [9]. Less developed countries play a key role in urban growth, which contributes greatly to population growth. The world energy demand mainly comes from urban demands, with more than 2/3 of the world's energy expected to be consumed by cities from 2006 to 2030 [10]. World energy consumption is estimated to increase by approximately 23% from 2020 to 2040, reaching 820 quadrillion Btu [11]. Rapid urbanization also induces other striking problems, including land degradation, desertification, deforestation, resource (e.g. water, materials) depletion and pollution, and loss of biodiversity [12].

Figure 1.1 Proposed alternative "hierarchy of resource use" (reverse triangle) (Source: Modified from Gharfalkar et al. [8]).

Figure 1.2 Interaction among the four key drivers for resource and energy recovery and reuse.

1.2.2.2 Resource Scarcity

Natural resources are commonly classified into two types, namely renewable (water, land, forest, fish, etc.) and depletable (minerals, metals, oil, etc.) resources [13]. Resource scarcity is caused by the increase in population growth, economic level, standard of living, and the limited supply of resources. Although it is possible to obtain more and more energy from renewable and nuclear energy sources, the amount of generated energy is still lower than the increasing energy demands. It has been pointed out that the higher energy demand in Asia significantly induces CO2 emissions by combusting carbon-based energy sources (gas, oil, and coal), which annually increase by 2.3, 2.1, and 1.9% in India, China, and rest of Asia, respectively. It is also estimated that a large fraction of energy (> 76%) will originate from carbon-based source in 2040, which increases the diminishing rate of primary energy resources [14-16].

1.2.2.3 Environmental Impacts

The excessive discharge of nutrients into water bodies causes algal bloom and overgrowth of plants and "dead zones" in coastal marine ecosystems [17]. Nutrients exported from urbanized river basin in 2050 are projected to be around five times the level in 2000; these mainly come from sewage, industries, and urban agriculture [18]. Drinking water, soil, fodder and food are contaminated by heavy metals from industrial waste. Furthermore, contaminated sites being important sources of pollution can lead to ecotoxicological effects on terrestrial and aquatic ecosystems (e.g. increased cell size, shortened life span, and decreased body weight) [19, 20]. Resource consumption (e.g. fossil fuel for energy) together with increased life quality and world population, as well as industrialization of developing nations, exerts adverse impacts on the environment.

1.2.2.4 Economical Aspect

Zaman [21] pointed out that per capita gross domestic product (GDP/capita/year) is positively correlated with per capita waste generation (Table 1.1). It was reported that average waste generation rates in high-income (HIC, GDP = more than $12275/cap), upper middle-income (UMIC, GDP = $3976-$12275/cap), lower middle-income (LMIC, GDP = $1006-$3975/cap), and low-income (LIC, GDP = less than $1005) countries were 2.1, 1.2, 0.79, and 0.6?kg/cap/day, respectively [23]. Although 84% of waste generated is collected in the world, only 15% is recycled. In the future, waste generation would increase because of constant economic growth, especially in the developing countries. Moreover, HIC could gain remarkable economic benefits from resource recovery and energy savings compared to other income groups. In the United States, Japan, and the European Union, the supply of raw materials influences the economy (e.g. jobs) [1].

Table 1.1 Total nitrogen (TN) and total phosphorus (TP) content of different waste streams.