While physico chemical and biotechnological methods for remediation of wastes contaminated with heavy metal cations are now well established the treatment of wastes containing anionic species of high valence metals/metalloids has lagged behind these developments. Metal anions are problematic; they mimic, but do not substitute for biochemically important species such as (SO4)2- (CrO4)2- and (PO4)3-(AsO4)3- and are also highly toxic.
Metal anions are produced from (e.g.) leather/tanning industries ), (old or new) mining activities (AsO43), minerals processing and surface treatements (CrO4)2-, (SeO4)2- and wood preservation treatments (CrO4)2-. AsO43) and have, in some cases, contaminated groundwater. This proposal aims to develop new biologically based technologies for the efficient removal of metal anions from processing wastewaters (low volume, heavily contaminated solutions) and groundwaters (high volume, dilute solutions).
Existing physico chemical treatments are either expensive or may fail to meet discharge limits; furthermore the widely used chemical precipitation processes produce a poor quality sludge of high water content and poor settling qualities that make downstream processing, transportation, final disposal or metal recovery very difficult. The low metal content precludes economic metal recovery. On the other hand a dense sludge of low water and organic content and with high metal content is highly attractive and production of this using the unique properties of microorganisms forms the major objective.
These properties are conversion of recalcitrant metal anions to new, low valence or volatile metal species which are concentrated locally by the biomass and which can be readily removed using classical precipitation or biosorptive methods. Bioaccumulation of native (CrO4)2- , (AsO4)3- and (SEO4)2- by native biomass is neglegible but biosorption/volatilization and entrapment of produced nascent species is documented. Using immobilized biomass fashioned into a filter new metal transformation, concentration and removal will be achieved in a single step to give a final, compact sludge of high metal content. This study will evaluate the bioprocess potential of documented microbial strains with useful properties of metal bioreduction to low valence species (in conjunction with biosorptive and precipitation techniques). Biomethylation, to yield volatile species (e.g. of As and Se) which can be trapped chemically, will be evaluated as an alternative or side reaction. Microorganisms will be procured from commercial or private collections under licensing arrangements as necessary.
The underlying biochemical and bioprecipitation mechanisms will be studied, with particular attention to examples where 'resting' (growth decoupled) biomass can be used in order to minimize the organic component of the final sludge. At the same time 'effective' metal biocrystallization on the biomass will enhance the metal content of the sludge.
Alongside evaluation of the biomasses for metal(loid) removal attention will focus on immobilization techniques as appropriate to the envisaged final process for particular examples taken from European industries. Three immobilizing techniques were foreseen: Biofilm Membrane Reactors, Biofilm bearing Sand Filters and Rotating Biological Contactors. The proposed technique will be compared with classical physicochemical processes in order to define the Best Available Technique Not Entailing Excessive Costs. Large industries, as well as SME's and governments (leachates from old mines or groundwater) will benefit from the newly developed technology by a reduction of treatment costs or the solving of large environmental problems. In order to achieve these objectives the project brings together a partnership of microbiologists, biofilm specialists, engineers and end users. Especially for the biocrystallization process a specialized laboratory from Canada is added to the project under the auspices of the Agreement for Scientifc and Technological Co operation between Canada and the European Commission.
Funding SchemeCSC - Cost-sharing contracts
B15 2TT Birmingham
N1G 2W1 Guelph - Ontario