**2. Bioremediation and ecological engineering**

Ecological engineering has been proposed as a theoretical framework to design *"sustainable ecosystems that integrate human society with its natural environment for the benefit of both"* [4]. Bioremediation is generally considered an ecological engineering practice but even if it addresses one of the core goals of ecological engineering, i.e. *restoration of damaged ecosystems* [5], bioremediation can be energy-intensive and have a serious impact on the remediated ecosystems particularly if excavation and ex situ methods are employed.

Mitsch and Jørgensen [5] identify 5 basic concepts that have been developed to distinguish ecological engineering from other approaches such as industrial ecology, biotechnology or environmental engineering. Ecological engineering:


If used collectively, these 5 concepts can provide guidelines for design of sustainable biore‐ mediation projects. In a sustainable society the ultimate goal is to limit the rate of pollution to what ecosystems can assimilate and break down without long term negative effects on ecosystem functions or human health. Meanwhile that goal is attained we will have to give the ecosystems a hand to boost their intrinsic biodegradation capacity.

#### **2.1. Self design**

Self-design is the property of a system to reorganise in an unstable non-homogeneous environment [5]. The inclusion of self design in a project can facilitate the implementation of flexible strategies that adapt to new conditions. The powerful capacity of ecosystems to reorganise after change can be used in bioremediation projects as a means to reduce costs and energy use. Consortiums of soil microorganisms naturally restructure to adapt to new conditions including contamination and are therefore good candidates for self-design strat‐ egies. A typical microbial community in soil consist of less than 1 % hydrocarbon degraders but that fraction can increase to 10% after exposure to oil pollutants [6]. An example of how engineers can accelerate the ecosystems self-designing capacity is the introduction of a microbial strain with capacity to initiate degradation of high molecular-weight pollutants that later provide food (energy) for other microorganisms that take care of the metabolic byproducts as the introduced strain dies off. In conventional engineering, items are often designed to behave in an as predictable way as possible since reliability and robustness are desired criteria of safety and quality. The outcomes of a technology that depend on self-design, on the contrary, are often a lot more difficult to predict. Bioremediation projects that include self-designing strategies thus require thorough monitoring to make sure that the degradation of the pollutants is satisfactory.

## **2.2. The acid test**

or immobilize toxic compounds [3]. Bioremediation have been gaining terrain recently [1] and some authors predict a further increase as technological advances surmount the limitations

In this chapter we briefly discuss how principles of ecological engineering in concurrence with the application of basic thermodynamic principles and kinetic modelling can provide useful tools for the development of energy conserving and economically feasible bioremediation projects. We further discuss the potential of organic waste materials and by-products in locally adapted soil bioremediation. Finally we present some illustrative cases of novel research on sustainable bioremediation for tropical developing countries and remote locations and discuss

Ecological engineering has been proposed as a theoretical framework to design *"sustainable ecosystems that integrate human society with its natural environment for the benefit of both"* [4]. Bioremediation is generally considered an ecological engineering practice but even if it addresses one of the core goals of ecological engineering, i.e. *restoration of damaged ecosystems* [5], bioremediation can be energy-intensive and have a serious impact on the remediated

Mitsch and Jørgensen [5] identify 5 basic concepts that have been developed to distinguish ecological engineering from other approaches such as industrial ecology, biotechnology or

If used collectively, these 5 concepts can provide guidelines for design of sustainable biore‐ mediation projects. In a sustainable society the ultimate goal is to limit the rate of pollution to what ecosystems can assimilate and break down without long term negative effects on ecosystem functions or human health. Meanwhile that goal is attained we will have to give

Self-design is the property of a system to reorganise in an unstable non-homogeneous environment [5]. The inclusion of self design in a project can facilitate the implementation of flexible strategies that adapt to new conditions. The powerful capacity of ecosystems to reorganise after change can be used in bioremediation projects as a means to reduce costs and

some promising fields of future research and possible future applications.

ecosystems particularly if excavation and ex situ methods are employed.

the ecosystems a hand to boost their intrinsic biodegradation capacity.

**2. Bioremediation and ecological engineering**

environmental engineering. Ecological engineering:

**2.** can be the acid test of ecological theories

**4.** conserves non-renewable energy sources

**3.** relies on systems approaches

**2.1. Self design**

**5.** supports ecosystem conservation

**1.** is based on the self-designing capacity of ecosystems

that exist today.

58 Environmental Risk Assessment of Soil Contamination

Just as strong acids were traditionally used to distinguish gold from base metals, a full scale bioremediation project can be used to confirm or reject ecological theories. Ecological theories provide a useful framework that establishes restrictions and opportunities for bioremediation strategies. The complex nature of full scale in-situ bioremediation however might lead to outcomes somewhat different from what was expected. Since intense use of monitoring is required for full scale implementations of unproven technologies, the result from these can be used to refine the theories on which the project was based.

#### **2.3. A systems approach**

Reductionist analysis of the parts of a system in isolation from each other can provide important data and basic understanding of significant mechanisms but should be combined with a holistic view of the entire system in order to achieve a sustainable bioremediation project. The site specific conditions of the ecosystem that is subject to remediation must be quantified and analysed with appropriate models. That particular ecosystem however is part of a greater context whose characteristics must also be born in mind. When bioremediation strategies are chosen, socioeconomic and even cultural aspects must be taken into account. Questions like "what is the economic impact of the project?", "can polluted land be reclaimed for food production or construction?", "what resources are available in the human environ‐ ment around the site?" might supply useful information. The use of locally available agricul‐ tural waste products, that are potential polluters by themselves, as amendments (see section about waste recycling) is an example of advantageous design that requires a systems approach. The source of the pollution must also be addressed to make sure that the remediation project isn't an encouragement to further pollution.

#### **2.4. Non-renewable resources conservation**

Energy use is one of the major sustainability issues for conventional remediation projects. Exsitu remediation is typically too energy-intensive to be considered ecological engineering. Furthermore it resembles what Jørgensen & Mitsch [5] call a *shell game*, in which pollutants are moved from one location to another. In sustainable bioremediation external energy input is ideally used only in the initiation phase to start a process that is subsequently powered by solar energy and the embodied chemical energy of the pollutant itself. The engineer's role is to facilitate the proper conditions in which such a process can take place.

#### **2.5. Ecosystem conservation**

The ability to cycle nutrients is a fundamental function of all ecosystems. Within the mattercycling function lies the catabolic capacity to degrade and mineralise molecules of varying complexity, including pollutants. This function alone gives a nonmarket value to ecosystems, not always recognised by society. The role of ecological engineers is to identify ecosystem functions that are adoptable to human needs and apply them in ways that doesn't create any further degradation of nature. Since bioremediation projects aims at eliminating pollution that exerts stress on the ecosystem, it is by definition an ecosystem conservation approach. However, if large amounts of soil are physically removed from the site in ex-situ operations the remediation itself might be a threat to the ecosystem. Bioremediation projects are typically involved in the restoration of disturbed ecosystems but measures to prevent toxic compounds from entering sound ecosystems are likewise part of the bioremediation agenda.
