Bioaugmentation an effective strategy to improve the performance of biobeds: a review.

Abstract

Climate change, one of the planet’s main current environmental problems, requires urgent attention and is accelerating the need for developing low-cost technologies for wastewater depuration, which are able to promote the conservation of water natural resources worldwide.

In order to protect natural resources, the European Union has been creating ever more restrictive directives with the aim of preserving the quality of surface and groundwater resources by reducing their pollution and promoting their sustainable use. Given the goal of recycling and safe reuse of wastewaters set by European countries to be achieved by 2030 (UN Sustainable Development Goal on Water, SDG 6), strategies to clean up wastewaters from agricultural activities are therefore required.

The use of pesticides in agricultural and nonagricultural contexts since the 1950s has brought considerable progress to the management of food resources as well as to human and animal life. Nevertheless, as it is widely recognized and due to extensive applications of crop treatments, an undesirable fraction of some active ingredients of pesticides can be frequently detected in freshwater systems, as a result of their physicochemical properties and biochemical behavior. In fact, their ubiquitous presence in water resources has an important role in the global loss of freshwater biodiversity and ecosystem functioning.

Factors controlling the fate of a pesticide include a variety of chemical and environmental properties [e.g., (bio)degradation rate, sorption to organic carbon, and water solubility], climatic factors (e.g., temperature and precipitation), soil characteristics (e.g., topography), and agricultural practices.

Following field application, pesticides may reach water bodies through a series of different pathways with surface runoff and tile drains being widely accepted as the most important nonpoint sources. On the other hand, inadequate handling of pesticides during filling and cleaning of spraying equipment, spillages during tank filling or improper disposal of application residues have been identified as the major point-source contamination. Accordingly, disposal of pesticide-containing wastewaters must be undertaken properly to avoid the decline of water quality.

Several physicochemical or biological systems for mitigating the effect of pesticide pollution have been applied. Nevertheless, many of them are costly or require complex technology to be carried out, restricting their use in farms. Due to these limitations, simpler systems, called pesticide biopurification systems (BPS), have been developed and implemented.

BPS make use of and improve the ability of microbial degradation (mainly by bacteria and fungi), and also of the sorption ability of its components, in order to minimize the extent of the impact that pesticides could have in the environment. BPS were first implemented in Sweden in the 1990s as simple and cheap constructions, built to contain and (bio)degrade pesticide residues in agricultural farms. BPS consist of excavations or containers filled with a biologically active matrix called biomixture, composed by soil, a lignocellulosic substrate, and a component with a high humic content mixed in different proportions. The effectiveness of a BPS is based on the capacity of the biomixture to (bio)degrade and sorb high loads of pesticides being discharged on the system. Therefore sorption and microbial degradation abilities of the biomixture play a fundamental role in achieving an adequate efficiency, which could be improved by bioaugmentation with specific microorganisms.