Pollutants, recalcitrant

The refractory nature of some pollutants, notably, persistent polyhalogenated compounds, has raised problems of bioremediation of contaminated sites (e.g., sediments and dumping sites). There has been interest in the identification, or the production by genetic manipulation, of strains of microorganisms that can metabolically degrade recalcitrant molecules. For example, there are bacterial strains that can reductively dechlorinate PCBs under anaerobic conditions. 

The capacity of WRF to transform and mineralize a wide range of pollutants without a preconditioning period via co-metabolic pathways makes them interesting for the degradation of recalcitrant xenobiotics. The use of WRF and their LMEs for the removal of xenobiotics has been reviewed elsewhere [1-7]. 

Sandhya S, Swaminathan K, Swaminathan T (2007) Decolorization and treatment of recalcitrant dye industry wastewater containing azo dyes. In Trivedi PC (ed) Industrial pollution and its management. Aavishkar, India, pp 148-171... 

The advanced oxidation processes offer the possibility for destruction of recalcitrant biodegradable and toxic organic pollutants. The field of applications regarding wastewater treatment varies. AOPs can be applied as ... 

Treatment process for partial oxidation of recalcitrantly biodegradable organic pollutants. Aim is to make this recalcitrantly biodegradable products biodegradable in conventional aerobic and anaerobic wastewater treatment systems... 

A biological step is always necessary to remove the carbonaceous fraction from the influent wastewater suspended biomass treatments are the most common. These entail long SRTs (>25-30 d), and compartmentalization of the biological reactor is necessary for the removal of recalcitrant compounds. Furthermore, as many micro-pollutants tend to adsorb/absorb to the biomass flocks, efficient solid/ liquid separation can greatly improve their removal from wastewater and, at the same time, guarantee consistently good effluent quality. MBRs have been suggested for this purpose by many authors [9, 58, 80, 93], some of whom found that ultrafiltration (UF) membranes are more efficient than MF membranes [9, 93]. 

Treatment of bleach mill effluents using the white-rot fungi is promising and offers the option to expand the range of pollutants that cannot be biodegraded by the prokaryotes (bacteria). White-rot fungal remediation may be particularly suited for those recalcitrant compounds for which bioavailability and toxicity are the key issues. 

Of the VOCs, the halogenated ones are among the most recalcitrant, and several of them can be harmful at low or very low concentrations. As a consequence, these have been designed as priority pollutants. Unfortunately, substitutes for halogenated compounds cannot always be found in industrial processes. 

Photocatalytic oxidation over illuminated titanium dioxide has been demonstrated to be effective at removing low concentrations of a variety of hazardous aromatic contaminants from air at ambient temperatures. At low contaminant concentration levels and modest humidity levels, complete or nearly complete oxidation of aromatic contaminants can be obtained in photocatalytic systems. Although aromatic contaminants are less reactive than many other potential air pollutants, and apparent catalyst deactivation may occur in simations where recalcitrant reaction intermediates build up on the catalyst surface, several approaches have already been developed to counter these potential problems. The introduction of a chlorine source, either in the form of a reactive chloro-olefin cofeed or an HCl-pretreated catalyst, has been demonstrated to promote the photocatalytic oxidation of... 

Although AOPs are economically unsuitable for wastewaters containing high concentrations of organic constituents, AOPs can be used to transform recalcitrant organic pollutants into biodegradable compounds rather than to... 

Trihalomethanes (THMs) are priority pollutants listed by the U.S. Environmental Protection Agency (EPA). They are recalcitrant in nature, thus their destruction is difficult. The most commonly encountered THMs in drinking water threatening human health are chloroform, bromodichloromethane, dibromochloromethane, and bromoform. Tang and Tassos (1997) studied the oxidation kinetics and mechanisms of these four THMs. 

---