As for water resources quality, the critical situations recorded in many countries represent a great opportunity for developing innovative wastewater treatments and/or processes more efficient from the technological point of view, and more sustainable from the economic, social and environmental stand point. The attention is focused on technologies and/or processes characterized by: low production of green-house gases, sludge or byproducts to be disposed of; reduced energy consumptions; high compactness and flexibility; recovery of energy and raw materials. Currently, and presumably even during the coming years, pollutants removal from municipal as well as industrial wastewater is mainly carried out by “end of pipe” processes. The continuous introduction in the global market of new toxic and environmentally persistent chemicals and the need to guarantee “zero emissions” (European directives WF2000/60/CE e 2008/105/CE) by 2020 for those most hazardous classified as “priority pollutants”, require continuous improvements as for removing and recovering technologies. Moreover, the negative effects of climatic changes on water resources availability call for alternative or non-conventional resources and, then, for technologies for reusing municipal and industrial wastewater
Integration of chemical and biological oxidation processes
Recalcitrant pollutants, potentially toxic and/or inhibitor for the biomass occurring in the treatment plants, are usually removed using a polishing step downstream biological treatment featured by large quantity of sludge and high treatment costs. In this context, IRSA has developed, during recent years, a process for treating wastewater containing refractory compounds characterized by low excess sludge production and operative costs. In this process the biological degradation, carried out in a SBBGR system (Sequencing Batch Biofilter Granular Reactor), is integrated with chemical oxidation (based on ozone), used only with the aim of making recalcitrant compounds biodegradable. SBBGR is a periodic submerged biofilter in which the biomass grows as granules characterised by very high density. These granules are entrapped in the pores produced by packing the reactor with a filling material (a secondary settler is therefore no longer necessary) allowing a very high biomass concentration to be achieved with interesting repercussions on treatment capability and sludge production (up to one magnitude order lower than that recorded in conventional biological systems). Due to certain features of the SBBGR (i.e., discontinuous operation conditions and separation between biomass and wastewater), ozone can easily be used in a specific (i.e., soon after a biological degradation phase to avoid consuming the oxidant for degrading biodegradable pollutants) and controlled (i.e., with the aim of rendering recalcitrant compounds biodegradable so they can be removed biologically) way.
This process was successfully applied for treating tannery wastewater, textile effluents and municipal landfill leachates.
Biotechnological processes and membrane applications
Biotechnological processes for removal of the main pollutants in municipal and industrial wastewater are studied with the aim of contributing to design, set-up, and optimization of novel technologies based on aerobic and anaerobic biological processes. Examples of recent activities in this field are the development of a new system for odour removal at activated sludge plants (AS Diffusion), and the investigation of various applications of the last generation of filtration membranes. In particular, in view of developing new treatment processes with higher efficiency and lower sludge production, the current research activity aims to the development and optimization of aerobic and anaerobic membrane bioreactors (MBR), both as stand-alone technologies and within integrated chemical-physical-biological processes. After a well-established experience on biomass characterization based on engineering tools (chemical-physical parameters and respirometric activity), new approaches towards quantitative evaluation of microbial consortia are currently under investigation, with particular focus on functional aspects such as enzymatic expression (metaproteomics). Knowledge on biomass characterization and process modelling is also exploited in definition of guidelines for optimized management of wastewater treatment processes, and in cost/benefit evaluations related to the investigated technologies, also taking into account the opportunities for effluent reuse.
Biological removal of xenobiotic compounds from wastewater
Biological processes are attractive as “green” remediation strategies for xenobiotic removal in that are able in principle to attain complete mineralization of many persistent compounds and at the same time are characterised by low capital and operating costs. Notwithstanding these advantages, biological processes possess a major limitation due to substrate toxicity that can significantly reduce process efficiency and the applicable substrate load. In order to overcome this limitation the development of alternative technologies is a focus in the research demand. An extremely promising technology is based on the use of two phase partitioning bioreactors (TPPBs) able to optimize the “substrate delivery” and, at the same time, reduce the toxic concentration to which the microorganisms are exposed. The strategy utilized in TPPBs is to insert an immiscible second phase (liquid solvent or polymer) within the bioreactor, whose function is to selectively partition toxic substrates and gradually deliver them to the microorganisms in biodegradative reactions. In this way the microenvironment of cells is favourably influenced by the selective partitioning of toxic substrates resulting in significantly enhanced performance. Discontinuous TPPBs reactors, both in the liquid-liquid and solid-liquid configurations, have been successfully investigated at IRSA for the removal of phenolic compounds from aqueous matrices. At present the biodegradation of mixtures of xenobiotic compounds (more similar to the real wastewater) and the utilization of used tires as partitioning phase are under investigation.
Advanced oxidation processes
The advanced oxidation processes (AOPs) are successfully employed for the treatment of wastewaters contaminated by non-biodegradable and toxic organic pollutants (pesticides, dyes, industrial solvents, pharmaceutical intermediates, endocrine disruptor compounds, etc.). AOPs use different combinations of chemical oxidants (ozone, hydrogen peroxide), ultraviolet radiation and catalysts (Fe, Mn, TiO2), in homogeneous or heterogeneous phase, for producing hydroxyl radicals, i.e. a very reactive and non-selective oxidant specie. This allows the degradation of most of organic pollutants that, depending on the reaction time, could proceed up to their complete mineralization. In case the mineralization is not complete, the identification of degradation by-products is of great relevance in order to assess whether they are more or less toxic than the parent compounds. Accordingly, once equipped its laboratories with very advanced analytical instrumentation, IRSA has achieved a significant expertise in the field reaction by-products identification. From the technological side, IRSA is currently testing the effectiveness of nanosized catalysts for the degradation of organic pollutants by photocatalysis. Nanosized TiO2 is supported onto a material (glass of glass-fiber) with the aim to overcome the limitation for practical application of the conventional TiO2 powder due to the difficult removal of the catalyst at the end of the treatment. Research activities are presently focused on the optimization of catalyst efficiency and its robustness, in terms of prolonged use without loss of performance, and on the minimization of catalyst leaching.
Composition and role of mixed biomass involved in wastewater treatment
The effectiveness of each biological process is determined by the action of selected microbial communities operating the municipal and industrial wastewater treatment. The definition of the microbial composition and function of such mixed biomass is therefore crucial for a successful application of treatment technologies. Traditional microbiological as well as advanced biomolecular (FISH, qPCR, RT-PCR, genomic libraries) methodologies are valuable tools widely utilized at IRSA for the characterization of mixed biomass. These approaches allow to monitor the main component of the microbial communities and to define their role and the mechanisms related to water treatment. Furthermore, in complex aggregated biomass (i.e. activated sludge flocs, biofilms and granular biomass) also the structure and the spatial distribution of the identified microbial populations can be revealed by combining in situ hybridization techniques and confocal laser microscopy. Bacterial populations involved in carbon and nutrient removal, such as nitrifiers, denitrifiers, sulphate reducers, methanigens, phosphate and polyhydroxyalkanoates accumulating microorganisms, or detrimental to the treatment process, such as filamentous bacteria responsible of bulking and foaming phenomena, are investigated in municipal and industrial WWTP. Focus of the research activity is also the identification of new unknown microbial populations whose metabolic activities can be exploited in advanced wastewater treatment system for energy and material recovery.