Decontamination of water by combined solar advanced oxidation processes and biotreatment - Solar Energy Sciences and Engineering Applications - page 375

Decontamination of water by combined
solar advanced oxidation processes
and biotreatment
Sixto Malato, Isabel Oller, Pilar Fernández-Ibáñez &
Manuel Ignacio Maldonado
Plataforma Solar de Almería (CIEMAT), Carretera Senés,Tabernas (Almería), Spain
12.1 INTRODUCTION
One of the major threats to water quality is chemical pollution from heavy metals, sol-
vents, dyes, pesticides, etc. Such chemicals enter the aquatic medium in several different
ways, either by direct dumping, such as in industrial effluents, or from wastewater
treatment plants (WWTP) that are unable to eliminate them. Another indirect source
is plant health products, such as biocides and fertilizers, in agriculture. Discharge
resulting from lax enforcement of legislation, illegal usage and inappropriate applica-
tion of substances may also be considerable. In general, very water-soluble substances
are transported and distributed more easily in the water cycle.
The main methods for destroying such toxic compounds in natural water are
biodegradation and photodegradation. Photodegradation may be by direct or indirect
photolysis. In indirect photolysis, a photosensitizer (such as nitrate or humic acids)
absorbs the light and transfers the energy to the pollutants, which otherwise would
not react, since they do not absorb light in the wavelength interval of solar photons
on the Earth's surface (i.e. > 300 nm). Biological degradation of a chemical refers to
its elimination by the metabolic activity of living organisms, usually microorganisms,
particularly the bacteria and fungi living in natural water and soil. In this context, con-
ventional biological processes do not always provide satisfactory results, especially for
industrial wastewater treatment, since many of the organic substances produced by the
chemical industry are toxic or resistant to biological treatment (Muñoz and Guieysee,
2006; Lapertot and Pulgarin, 2006). Conventional methods of water decontamination
that can address many of these problems are often chemically, energetically and oper-
ationally intensive, and when used in large systems require a considerable infusion of
capital, engineering expertise and infrastructure. This practically precludes their use in
much of the world. Furthermore, intensive chemical treatments (such as those involving
ammonia, chlorine compounds, hydrochloric acid, sodium hydroxide, permanganate,
alum and ferric salts, coagulation and filtration aids, anti-scalants, corrosion control
chemicals, and ion exchange resins and regenerants) and residuals resulting from treat-
ment (sludge, brines, toxic waste) can add to the problems of contamination and salting
of freshwater sources. Air stripping and adsorption, which merely transfer toxic mate-
rials from one medium to another, are not long-term solutions. Incineration converts
toxics into carbon dioxide, water and inorganic acids, but negative public perception
has very often prevented its implementation. In view of all of the above, a feasible